. "

No. 9 Vic to r i a , B. C . , September 4, 1942 0129523

" , ,- ' 9 '

.,

- . * . ." . " - DOUGLAS FIR

" _ . .. : .. ... -.

i

"~ . -.. . - . : .::: , (Pseudotauga tax i fo l ia (Lamb.) Britt.) ... . . -.__ . . ..

.. . , . . . .

A Summary of I ts Life History

G. S . Allen

""""""

CONTENTS

1 95Q Preface

The Cone . __ ..... 1

The Seed 2

S e e d f a l l . 3 Seed D i s t r l t x t i o c "- 6 Seed Losses ................................................................................................................................................... 7 Seed Germination I ....................... 7

I .

The Seedl ing .............................................................................................................................................................................................................................................. 8

Seedl ing Mor ta l i ty ... -. 9 Heat I n j u r y ......... 9 Drought .............I .. . .. 10 Fros t ...... . 11 Biologica l Fac tors ... 11

Seedl ing Dormancy .............................................................................................................................................................................................................. ....... 12

Natui-a 1 Reproduction 1 2

S lash Disposal ................................... 13 Source o f Seed ................................................................................................... I.. . . . .......................................................... 15

The Young Tree . 16

Physiology ........... .................................................................................. .. 17

Seed Production .. 19 Thinning and P r unirlg .I ...................................................... ...................................... ......... " 18

The Adult Tree .................................. .................................................................................................................................................................................................... 19

Physiology of Seed Production -. . 19 Seed Product ion in Forest Management . 20 Seed- t ree Charac te r l s t lcs 2 1 . .

Summary o f S i l v i c u l t u r a l P r a c t i c e s Recommended by Various Agencies ...... 2 1

S-mary and Conclus ions ~ ................. -- ". -- 22

D_ouG-F_IR

(Pseudotsuga tax i fo l ia ( Llamb. ) Britt. )

For the bene f i t o f t hose whose ir,terest l i e s i n t h e management o r u t i l i z a t i o n o f Douglas f ir , b u t who a r e u n a b l e t o s s a r c h t h e many t echn ica l pub l i ca t ions fo r i n fo rma t ion , t h i s pape r will a t t e m p t t o d e s c r i b e i n summary t h e l i f e h i s t o r y o f t h e t r e e . It w i l l a l so sugges t , d i r ec t ly o r i n d i r e c t l y , s i l v i c u l t u r a l problems which s t i l l remain to be solved. Free use w i l l be made of a l l ava i lab le in format ion , publ i shed o r unpubl ished, and references w i l l be made t o t h e a u t h o r i t i e s c o n c e r n e d . It should be emphasized a t t h i s p o i n t t h a t Douglas f ir i s a b o t a n i c a l s p e c i e s , and as such i s cha rac t e r i zed by a g r e a t v a r i a t i o n i n b e h a v i o r , much of which can be ascr ibed to heredi ty and the remainder to environment. Likewise, Douglas f i r s o i l s v a r y a g r e a t d e a l in t h e i r p h y s i c a l c o n s t i t u t i o n , t h e i r d e p t h , t h e i r f e r t i l i t y , and t h e i r mois ture-hold ing qua l i t i es . Gene . ra l iza t ions cannot be accura te , bu t i f

and s tands. Some o f t he da t a ava i l ab le a r e accu ra t e bu t some are rough, and the problem of evaluating them i s not an easy one.

. based upon sound data, can be of .value i n f o r e t e l l i n g t h e b e h a v i o r o f t r e e s

The f r u i t of Douglas f i r i s a much l ike t he cones o f o the r con i f e r s , bu t ea s i ly r ecogn ized b;y i t s three-pointed bracts which protrude beyond t h e t i p s o f t h e s c a l e s . Each sca l e bea r s two seeds upon i t s upper su r face . The cone begins i t s l i f e e n c l o s e d i n bud scales and resembles a l a r g e leaf bud s i tua t ed bes ide t he t e rmina l bud of twigs and branches. In September, the young c o n e l e t i n t h e bud i s about one-tenth inch long and cons is t s o f a cen t r a l ax i s a round .which a r e a r r anged t he young b r a c t s ( 9 ) . By t h e e a r l y s p r i n g , s c a l e s have begun to deve lop , one i n t h e a x i l of each b r a c t . On the upper surface of each scale appear two ovules which will even tua l ly become seeds . About the end of March the cone le t fo rces i t s way through the bud scales and appears as the female "flower,! ' approximately one i n c h i n l e n g t h . Male buds follow a similar development from September onwards, and about the end of March b u r s t t h r o u g h t h e i r bud s c a l e s . Each male Ilflower" c o n s i s t s of a c e n t r a l axis a t t ached t o wh ich a r e a l a r g e num- be r o f po l l en s acs . About t he f irst of Apl-il the walls o f t he po l l en s acs s p l i t and the po l len i s l i be ra t ed . . Po l l ina t ion las ts about two weeks on an area, but most t rees are f in i shed . i n abou t one week i f the weather i s f a i r l y d r y . The female f lowers are open fo r abou t two weeks during which time the po l len can s i f t between .the s c a l e s and reach the ovules . Then growth of the cone forces the sca les toge ther and thz ovules and po l len a r e s e a l e d i n . The cone then t u rns down and t he p ro t ec t ive s ca l e s fo rm a waterproof cover much l i k e a sh ing led roo f . The cone cont inues to develop u n t i l it reaches i t s f u l l s i z e e a r l y i n J u n e , I n A p r i l , t h e p o l l e n g r a i n s send out tubes which penetrate the ovule , reach the egg cel ls produced in- s ide each ovule and discharge male c e l l s o r sperms i n t o t h e e g g . F . e r t i l i z a - t i o n usually occurs during the fi.rst week o f June on lower Vancouver I s l and ( 9 ) . The f e r t i l i z e d egg nucleus divides several times t o form the beginning of' an embryo which grows r a p i d l y t o r e a c h i t s f u l l s i z e a b o u t two months af ter f e r t i l i z a t i o n . About t h i s time, the food supply surround- ing the embryo i n t h e s e e d , o r "endosperm," hardens and t h e s e e d i s mature. Surrounding the endosperm i s the hardened w a l l o f the ovule which has be- come the s eed coa t . By the end of August the l iving channels into the cone a r e c u t o f f , t h e cone d i e s and d r i e s up, t h e s c a l z s b e g i n t o s t r a i g h t e n up, and the cone opens t o l i b e r a t e i t s seeds .

The fo l lowing da ta (30, 3 8 ) , which show the s ize of cones and r e l a t e d c h a r a c t e r i s t i c s d u r i n g t h e good seed years of 1938 and 1939, may be o f i n t e r e s t a t t h i s p o i n t . I n 1!338, over 4000 bushels of Douglas f ir cones were c o l l e c t e d b y t h e B r i t i s h Columbia Forest Service and yielded about one ton of c leaned seed.

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Item ___

" - Cones per bus he 1

Tota l seed per bus. of cones Pounds

Clean seed per bus. of cones Pounds

Total no. of seeds per c,oue

No. of ciear:ed seed per corle

No, o f v i ab le seed per cone

13.2

8 .6

No. of Lots Average Range

800- 9 870 1100

0.65- 6 0.72 0.83

0.25- 9 0 .53 0 .71

6 43 36-51

27.5- 6 33 42.9

13.7- I 6 19 26.2

THE SEED _~ ."

Each fuliy developed Douglas f ir seed weighs about f o u r ten- thousandths of an ounce, and i s about three- tenths inch long, or ie- tenth inch wide and one-t .went. leth inch thick. It has a wing about one-half in;-h long and one quarter inch wide, which slows up the seed ' s desrer i t and alds i n i t s disseminat lon. The seed coa t i s s t rong arid qui te hard , bu t has a weak spot. a t the end f a r t h e s t from the wing, through whlch t he r o o t of the seed l ing emerges a t germinatiorL. The embryo of the seed i s about two- t en ths i nch l ong and cons i s t s of elementary root, stem, and seed-leaves o r coAledg.ns. The fol lowing tab1.e indicates some of the charac 'e r i s t i r s o f Douglas fir s e e d c o l l e c t e d i n i.938 and 1939. (30, 38),

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Tota l seeds per pound

Cleaned seed per pound

V i a b i l i t y o f seed. Per cent . (c leaned seed)

Of Average Range Lots

- -

9 41,320

9 65

-

36,200- 46,200

50-76

N o * Of Average Range Lots

42,700- 6 48,800 51,700

37,400- 7 43,900 54,700

7 59 50-68

S e e d f a l l

The amount of seed which fa l l s on a given area de te rmines t o a g r e a t P x t e n t t h e amount of regeneration which can be obtained from natural seeding. The quant i ty o f seed per acre in tu rn depends upon the s eed pro- duction of each t ree and upon t h e number o f t r e e s on o r bordering the area. Furthermore, seed years and the behavior of the individual trees determine the seed per tree, but the fo l lowing da ta (25, 27) i n d i c a t e i n a gene ra l way t h e v a r i a t i o n i n s e e d f a l l p e r a c r e from sources of supply such as a r e e n c o u n t e r e d i n a c t u a l p r a c t i c e .

I. 1938 seed crop (good) . Old-growth Douglas f i r , f u l l y s t o c k e d . Cameron River , B. C .

Species

F i r

Hemlock

Cedar

Viable seed per

a c r e

500,000

200,000

300,000

Seedfa l l per acre by per iods as percentage o f t o t a l .

Sept . Oct. Nov -Mar. Apr . -July 32 38 13

0 1 57

0 3 1 58

17

42

11

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11. 1938 seed c rop . A 35-ysar-old second-growth Douglas f ir s t a n d , f u l l - s tocked. Lake Cowichan, B. C .

Species

F i r

Hemlock

Cedar

Viable seed per

ac re

34,000

3,300

5,500

S e e d f a l l p e r a c r e by per iods as percentage o f t o t a l .

Sept . oc t . Nov . -Mar. Apr .-July

65 29 6 0

0 61 39 0

45 55 0 0

111. 1938 seed crop. Seed t rees scat tered over a logged and burned area, Hiilbank, B . C . Small area surrounded by marginal t imber and scat tered s e e d t r e e s . Two f ir seed t rees per acre , averaging 1020 cones per tree i n 1938.':'

Species Viable

seed per a c r e

Seedfa l l pe r ac re by per iods as percentage of t o t a l .

Sept . Oct. Nov . -Mar. Apr . -July -

F i r

0 77 23 0 15,800 Cedar

0 0 100 0 200 Hemlock

21 46 29 4 127,600

I V . 1 9 3 8 s e e d c r o p . S e e d t r e e s scatteredoveraloggedandburnedarea, Parksv i l l e , B . C . 2,37 fir seedt reesper~acreaveraging300cones pe r tree i n I 9 3 8 ." 0 . 2 hemlock and 0 ceda r s eed t r ee s pe r ac re .

Species

F i r

Hemlock

Cedar

Viable

Sep t . Oct. Nov . -Mar. Apr .-July ac re

S e e d f a l l p e r a c r e by per iods as percentage seed per o f t o t a l .

11,500

13 74 .12 0 121,700

0 82 18 0 2,800

52 32 14 2

%- Ocular estimates of cone c ropsbyA. P.MacBean. Fromactua lcounts , these e s t ima tes a r e l owand f ac to r s up t o 2 . 5 a r e n e c e s s a r y t o c o n v e r t t h e e s t i m a t e s t o a b s o l u t e v a l u e s .

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V. 1938 seed c rop . Seed t r ees s ca t t e r ed ove r a logged and burned area, Qualicum Bay, B . C . 2.24 fir seed t rees per acre averaging 1000 cones per t ree i n 1938 .” O.Ct8 hemlock and 0.04 cedar seed trees per a c r e .

Species

Fir

Hemlock

Cedar

Viable seed per

a c r e

34,900

200

173,700

Seedfa l l per acre by per iods as percentage o f t o t a l .

Sept . Oct . Nov .-Mar. Apr . -July

44 40 15 2

0 100 0 0

a1 16 3 0

Although data have not been compiled for the seedfal‘l on these areas f o r years subsequent to 1938, the average Douglas fir cone productlon i s given below, and from these f igures some idea of the probable seed- ;all can be obtained by comparison (25) .” -x

Area

Hillbank

P a r k s v i l l e

Qualicum

Viable seed per

a c r e

1938

127,600

34,900

11,500

Cones per seed tree ”

19: 8 1939 1940 1941

1020 1030 14 2570

346 1023 65 2300

1006 45 211 823

*Ocular estimates of cone crops by A . P . MacBearl. From ac tua l counts , t h e s e e s t i m a t e s a r e low and factors up t o 2 .5 a re necessa ry t o conve r t the e s t i m a t e s t o a b s o l u t e v a l u e s .

4% An exact comparison i s n o t p o s s i b l e s i n c e t h e s e f i g y e s do n o t t a k e i n t o accoun t t he mor t a l i t y o f s eed trees dur ing these years . The va lues are based upon t r e e s s t i l l l i v i n g i n 1941 only.

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It i s ev ident f rom these da ta tha t a mature, ful ly-s tocked s t and i s a heavy producer of viable seed in a good yaar , d isseminat ing over t e n pounds of such seed per acre. A second-growth fully-stocked stand i s a l ight producer , d isseminat ing about one pound o f v i ab le s eed pe r ac re . Sca t t e red s eed t r ee s ; du r ing an exce l l en t s eed yea r (1941) could be ex- pec ted t o d i s semina te 25,000 t o 75,000 v iab le s eeds pe r t r ee pe r ac re o r up t o two pounds of viable seed. This approximate f igure i s similar t o t h a t g i v e n by Munger and Morris (34) f o r t h r i f t y t r e e s , 100 t o 200 years of age, growing on good s i tes . Marginal timber could be expec ted t o pro- duce quantit ies of seed, immediately adjacent to the uncut margins, com- p a r a b l e i n amounts to those p roduced in the uncut s tand , bu t the dm- t r ibut ion outwards i r i to the cut-over area w i l l dec rease g rea t ly w i th d i s t ance .

The data i n d i c a t e t h a t 70 t o 90 per cent of the Douglas f i r seed fa l l s during September and October, and the greater part of the remainder

' between November and March. The monthly disseminat ion probably var ies f rom year to year according to the weather , s ince most o f t h e s e e d f a l l occurs dur ing dry spe l l s .

Seed Dis t r ibu t ion

The d i s t r i b u t i o n of seed over a e lear -cu t area i s extremely v a r i z b l e . I s a a c (20) has summed it up i n t h i s way: "Air movement i s so v a r i a b l e t h a t no p o s i t i v e d i s t a n c e o f s e e d f l i g h t c a n be s e t up f o r a 'SpPcific area. Douglas f i r seed fa l l s a t the r a t e of approximately 2 m i l e s . p e r hour and the dis tance it may be c a r r i e d may b e g r e a t l y af- f e c t e d by local topography and by v e r t i c a l as w e l l as ho r i zon ta l a i r c u r r e n t s . ...... r i s i n g a i r currents from 1 t o 10 miles per hour occur over warm s lopes . Should fa l l ing seed encounter a r i s i n g a i r cu r ren t that exceeded i t s r a t e o f f a l l is might be ca r r i ed unbe l invab le d i s t ances . . . .I1 The d i s t ance and d i r ec t ion o f t he a r ea from seed trees i s obviously an important factor in seed d i s t r i b u t i o n (14).

A s tand of t rees 150 f e e t i n h e i g h t , b e a r i n g a heavy crop, dis- t r i b u t e d 5 pounds of s eed pe r ac re a t 100 f e e t from the timber margin, 1 pourid pe r ac re a t 200 fee t , and one-ha i f pound pe r ac re a t 300 f ee t . A l i g h t s e e d c r o p on t r e e s 210 fee t i n h e i g h t produced as good o r b e t t e r d i s t r i b u t i o n of seed than the heavy crop on t h e s h o r t e r t r e e s . Both s tands -d i s t r ibu ted about 10,000 seeds per acre , o r about one-quarter pound, a t 800 f e e t from timber (18).

Records taken over three successive years on s e v e r a l areas in- d i c a t e t h a t , d u r i n g l i g h t s e e d y e a r s , mos t o f t he s eed f a l l s w i th ln 1000 f e e t of timber; but some i s c a r r i e d as f a r as one mile, possibly by a combination of upward a i r currents and horizontal winds. Maximum d i s - t ance o f s eed d i spe r sa l occu r red i n November, February and March (36) .

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Losses of cones and seeds caused by rodents , b i rds and o ther an imals , reduce the seed per acre mater ia l ly , and in a poor o r even a f a i r seed year , may accoun t fo r a l l the seed which i s produced (20). It has been s t a t e d (20) t h a t e i g h t t o t e n pounds of Douglas f ir seed may be necessary to seed up a s i n g l e a c r e ; t h a t most of the good s t ands of r e - product ion spr ing f rom the surplus of seed that occurs during the years of heavy crops . However, it has been found i n B r i t i s h Columbia (25) that adequate res tocking i s t a k m g p l a c e on a reas suppl ied wi th about one pound p e r a c r e . I n 1941, be fo re cu r ren t s eed fa l l cou ld have any e f f ec t , t he re were 3600 Douglas .fir per acre a t Qua'licun and 2290 pe r a c r e a t P a r k s v i i l e , as a r e s u l t o f one good seed year and two poor years.

Comparison between a r t i f i c i a l ly - sewn s eed spo t s p ro t ec t ed from roden t s and t hose l e f t unpro tec t ed has l ed MacBean (32) to conc lude tha t losses o f seed over win ter account for as much as 85 per cen t o f the amounts sown. The percentage l o s t prohahi-y deper;ds t o a g r e a t e x t e n t upon the s ize o f the seed c rop in r,at,ural seeding, and i s l i k e l y t o be g r e a t e r as the seed r rop becomes smai ie r . It i s the op in ion of the same a u t h o r i t y (32) t h a t ~ e ~ d _ l o s ses r educe t he po ten t i a l s t and o f s eed l ings t o a g r e a t e r e x t e n t t h a n do sgd&cLLgg l o s s e s .

The White-footed mouse and the shrew are the most important consumers of fo re s t t r ee s eed i n t he Pac i f i c Nor thwes t (33 ) . whereas s q u i r r e l s , chipmunks and o the r mammais are of minor importance i n t o t a l seed consumption. On one burned-over a rea , as many as 6 chipmunks and 25-white -footed mir.e were found on a s i n g l e a c r e , enough t o d e s t r o y n o t l e s s t h a n 80 per cent of any seed sown before it could germinate . ( 3 3 ) . According to Hoffman (17), Wlliis s t a t e d t h a t one wh i t e - foo ted mouse w i l l e a t 300 and one chipmunk 6C'O Douglas f i r seeds a day when i n cap- t i v i t y .

Mice do a g r e a t d e a l o f damage 01-i Vancouver I s l a n d by e a t i n g l a r g e q u a n t i t i e s of Feed and by e a t i n g t h e tops of s eed i ings soon a f t e r they have germinated. It, has bee!n concluded ten ta t ive ly (28) t h a t a r t i f i c i a l s e e d i n g o f Douglas fi.r on cut-over areas i s out of the ques- t i on w i thou t f irst des t roying the mouse populat ion. Current experiments i n d i r ec t s eed ing o f t h i s spec ie s and o the r s a r e d i r ec t ed t owards f i nd - fng a p r a c t i c a l s o l u t i o n t o t h i s p r o b l e m .

ked Germination

During Apr i l or May the seed germinates . The embryo grows u n t i l i t i s a b l e t o f o r c e i t s root th rough the weak spot of the seed coat into t h e s o i l . The minute stem and cotyledons deveiop inside the seed coat, and a t the time when the roo t has pene t r a t ed su f ' f i c i en t ly i n to t he so i l ,

- 7 -

I

a r e pushed above ground, and the new seedl ing appears . The food contained wi th in t he s eed i s absorbed by the co ty ledons for use by the seedl ing , the seed coat i s discarded, and the seedl ing i s or1 i t s own.

What a c t u a l l y happens during germination i s not known. The pro- cess i s favored by moisture, warmth and a i r , bu t there a re compl ica t ions which suggest that the process i s anything but s imple. For example, t o obtain quick and complete germination, a cold moist t reatment of the seed f o r s e v e r a l weeks followed by moderate temperature (70° F. ) gives good r e s u l t s (4) , but a lmost as good germination i s obtained by the use o f high temperatures (90 t o 110' I?. ) wi th no pre t rea tment ( 5 ) . Light seems t o have a b e n e f i c i a l e f f e c t upon germination (5) as i t does with some o ther seeds , bu t the mechanism i s not known. S o i l n u t r i e n t s o r the minera l nu t r i en t s con ta ined w i th in t he :seed i t s e l f may be factors which inf luence germination ( 4 1 ) . Removal of the seed coa ts may g i v e s l i g h t l y f a s t e r and more complete germination (1).

To t e s t Douglas fir seed, It has beer1 f o u n d t h a t b e s t r e s u l t s a r e obtained by s t o r i n g i t i n m o i s t sand. i n a r e f r i g e r a t o r , o r underground i n a sand-p i t , fo r a period of four to eight weeks, then removing i t t o a moist warmer place, such as moist sand o r b lo t t i ng pape r a t room temperature (65-800 F . ) ( 4 ) . Most of the v iab le seed w i l l germina te wi th in a week under this t reatment . In natural seeding, most of t h e s e e d l i e s on t h e ground a l l winter and i s ready t o g e r m i n a t e i n t h e e a r l y s p r i n g when temperature becomes s u f f i c i e n t l y h i g h . It has been shown (19 ) t ha t t he seed which overwinters on the ground e i ther germinates the fol lowing sp r ing or d i e s ; none i s held over until the fo l lowing yea r , a l t hough t h i s may happen with a r t i f i c i a l s e e d i n g when the seed has not overwintered ou t s ide o r has no t r ece ived an equ iva len t a r t i f i c i a l t r ea tmen t . Seed which i s h e l d i n t h e c o n e s u n t i l l a t e s p r i n g may behave as unt rea ted seed and ho ld over un t i l the next year . Natural regeneration of Douglas f i r depends, therefore , a lmost completely upor, th? seed crop of the prev ious year .

Douglas f i r in Idaho germina tes near ly as w e i l on duff as on any o the r common su r face ( 1 6 ) . I n B r i t i s h Columbia ( 2 ) i t has been found t h a t Douglas f i r seed, under control led condi t ions, germinates as w e l l on any common su r face - -du f f , bu rned du f f , m ine ra l so i l , bu rned mine ra l so i l , o r moss-covered soil--providing that moisture i s adequate. Moisture ap- p e a r s t o b e t h e l i m i t i n g f a c t o r on a duff. o r humus sur face under na tura l condi t ions .

THE SEEDLING

Unt i l the food supply o f the seed has been completely absorbed by the co ty ledons , the young seed l ing i s largely independent of i t s environ- ment f o r i t s n u t r i t i o n . A f t e r i t has dropped i t s seed coat , i t must, make

- a -

i t s own foods and absorb i t s own moisture and mineral elements from the s o i l . I t s r o o t must descend i n t o d e e p e r s o i l f a s t e r t h a n t h e s o i l d r i e s ou t o r i t w i l l suffer f rom drought . The cotyledons and new leaves must manufacture-.-.out of carbon dioxide and water, and mineral elements-- carbohydra tes , p ro te ins , fa ts and other complex s u b s t a n c e s , i n q u a n t i t i e s suf f ic ien t to enable the top and roo t to cont inue g rowth and the whole p l a n t t o r e s p i r e and l i v e . But t hese a r e on ly t he p r imary e s sen t i a l s , and the p l an t i s s t i l l n o t s a f e . The base of t he s eed l ing may be scorched by ho t so i l du r ing t he summer. It may be a t t acked by mice, b i r d s , i n - s e c t s o r fung i . The seedling which grows i n dense shade may surv ive f o r some t ime, but it may manufac ture on ly suf f ic ien t food to keep it a l ive and no t enough for g rowth . The f i r s t d r o u g h t p e r i o d may k l l l i t s ince i t s root system i s underdeveloped; competit ion from the roots of o l d e r t r e e s may have a n e f f e c t similar to d rought .

Seed l ing Mor ta l i t 1

Of the annual seedl ing crop, 66 ‘LO 95 pe r cen t i s l o s t from one cause o r another (20) . The p r inc ipa l causes arp h e a t i n j u r y t o the stem, drought, rodent damage, f r o s t , i n s e c t i n j u r y , and competition from o t h e r v e g e t a t i o n . I n B r i t i s h Columbia, t he loss of Dougias f i r seed l ings i s riot as g r e a t as t h i s on the average, but may reach such proport ions on the more adve r se a r eas . The average annual l o s s of f i r s t - y e a r s e e d l i n g s on severa l exper imenta l areas (25, 26) is about 30 per cent , and var ies from i 5 t o 33 per cen t on sca t t e red - se~d . - l ; r e~ a r eas t o ove r 50 per r.ent on a c l ea r - cu t a r ea . On one iogged--and-burned a r e a a r t i f i c i a l l y sown i r l January, 1941, an experiment was des igned to s tudy i r , t ens ive iy the mor t a l i t y f ac to r s (51 ) . Seed l lng mortality on t h i s area amounted t o 16-Y8 per cen t on t h e t h r e e s u b p l o t s . Drought, a rcounted for 20 to 45 p e r c e n t o f t h e t o t a l m o r t a l i t y , i n s o l a t i o n f o r 0 t o 13 per cen t , fungi a t t a c k f o r 30 t o 45 per cen t , and o ther b io t ic causes for 9 t o 2 1 p e r cen t . Unknown f a c t o r s a c c o u n t e d for 5 t o 9 per c e n t of the total mortality. It i s i n t e r e s t i n g t o n o t e t h a t 96.5 per cen t of t h e m o r t a l i t y from drought ovcurred from July to September, 86.5 pe r cen t o f t ha t f rom in so la t ion i n July, 96 pe r cen t of tha t f rom fungi a t tack in Apr i l and May, and 75.6 pe r cen t of khat f rom other biot , ic causes in May.

Heat In ju rx

Temperatures , par t iculzr ly surface-soi l temperatures are sometimes v e r y s i g n i f i c a n t i n Douglas f i r s eed l ing e s t ab l i shmen t . Immedia t e ly a f t e r germinat ion the young s e e d l i n g s a r e h i g h l y s u s c e p t i b l e t o i n j u r y by hea t a t the so i l su r f ace . Tempera tu res a t th i s po in t a r e cons ide rab ly h ighe r than those f o r t he a i r and where t h e l a t t e r may reach 112O F. t h e s o i l surface temperature has been known t o r e a c h 164O F.

Heat in ju ry causes more f i r s t -year losses in Washington than any o ther envi ronmenta l fac tor s tud ied (20) . It can r e s u l t from surface- so i l t empera tures o f 125O F . wten the seedling is young and succulen t ; as the s eed l ing becomes o lder it. may be ab le to wi ths tand tempera tures as high as 150° F. w i t h o u t i n j u r y ( 2 0 ) . I n one in s t ance , a m o r t a l i t y of 100 pe r cen t was recorded on a b l ack so i l , whereas , on an adjoining y e l l o w s o i l i t amounted t o o n l y 52 per cen t (21 ) . The average loss caused by heat in jury over four successive years on an open burn was 43 per c e n t ( 2 1 ) . I n B r i t i s h Coiumbia, loss from h e a t i n j u r y seems t o be re la t ive ly un impor tan t , and drought i s a f a r more common cause of mor ta l i ty (25 , 26, 3 1 ) . Shade on an open burn has a f a v o r a b l e e f f e c t upon so i l - sur face t empera tures : on one a r e a , 55 pe r cen t were k i l l ed by h e a t i n j u r y i n Itno shade, 'I 29 p e r c e n t i n "medium shade, I ' and none i n "heavy shade" ( 2 1 ) . S i m i l a r r e s u l t s have been obtained i n B r i t i s h Columbia (29 ) . Heat in ju ry gene ra l ly occu r s be fo re so i l mo i s tu re be- comes c r i t i c a l l y low, and th i s expla ins the p redominance of hea t in jury over drought as a m o r t a l i t y f a c t o r i n some cases (2.1). I n one ex- periment, MacBean (31) found t h a t h e a t i n j u r y w a s a t i t s h e i g h t i n 1941 about 70 t o 90 days af ter germinat ion, whereas drought losses were a t a maximum some 110-140 days a f te r germina t ion; a t t he same t ime , hea t l o s ses were g rea t e r t h i s yea r t han i n p rev ious yea r s on o ther exper imenta l a reas (25, 26) . When hea t losses a re low, as they u s u a l l y a r e i n B r i t i s h Coiumbia and i n some y e a r s i n Washington and Oregon, l o s s e s from drought tend to be p ropor t iona te ly g rea t e r , and t h e two f ac to r s t oge the r can be considered the important agents of mor ta l i ty on exposed s i tes .

The average mor ta l i ty from drought over four successive years on an open burn was 26 per cen t (21 ) . In Br i+ , i sh Columbia, on one clear-cut-and-burned area, drought was r e spons ib l e fo r abou t 50 per cerit of Lhe to t a l mor t a l i t y du r ing 1539 and 1940 ; t o t a l mor t a l i t y w a s about 50 per cent of the germinat ion ( 2 6 ) . On three sca t te red-sped- t r ee a r eas , t he fo l lowing pe rcen tages of t o t a l m o r t a l i t y were a t t r i b u t e d to drought during 1939 and 1940 : Hillbank"52, Qualicum--46, and Pa rksv i l l e - -42 . To ta l mor t a l i t y on these t h ree a r eas du r ing t he two years was 26, 15 and 33 p e r c e n t r e s p e c t i v e l y (25). I n a c a r e f u l i y cont ro l led exper iment wi th a r t i f ic ia l seeding , d rought accounted for 25 p e r c e n t o f t h e t o t a l m o r t a l i t y , w h i c h i n t u r n amounted t o about 30 pe r cen t o f the germinat ion (31) .

On areas exposed to the sun , the rap id roo t per le t ra t ion of Douglas fir and some o the r spec ie s p ro t ec t s them from drought losses d e s p i t e e a r l y d r y i r i g o f t h e s u r f a c e s o i l (16). But on heavi ly shaded, cool , and re la t ive ly mois t a reas , , d rought may become t h e most i m p o r t a n t f a c t o r . I n i t i a l r o o t p e n e t r a t i o n i s si.ower, and even shailow drying of t h e s u r f a c e s o i l may cause mor;ality.

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It has been found that r o o t pene-tration ranges from 3 t o 1 2 inches dur ing the f i r s t season , bu t t ha t most of the feeding roots occur i n t h e .2- t o 7-inch zone ( 2 1 ) . The mois ture conten t o f the so i l i s lower a t t he 3- inch depth (1 1 / 2 t o 4 1/1 inches) than a t lower l eve ls . Wi l t ing of seedl ings occurs a t moisture contents up t o 12 p e r c e n t i n t h e s o i l s s tud ied ( 2 1 ) . Nloisture content of the 6-inch zone r a re ly approaches t h i s c r i t i c a l l e v e l d u r i n g t h e y e a r , s u g g e s t i n g t h a t s e e d l i n g s w i t h f e e d i n g r o o t s i n t h i s zone might be s a f e from drought whereas seedlings with more sha l low feeding roo ts p robably d ie o f d rought .

On one denuded a r e a i n New Hampshire, it was f o u n d t h a t t h e s o i l remainded moister than that of a fo re s t ed a r ea ( 4 2 ) . Even the upper 4- inch zone contained as much ava i l ab le mo i s tu re as t h a t o f t h e f o r e s t e d a r e a . Drought may be an important factor even on a wei l - shaded area, a l though losses o f water f rom the p lan t i tFe l f may be l e s s t h a n on an open a r e a .

Late s p r i n g f r o s t s may k i l l t e n d e r s e e d i i r , g s a n d i a t e f a l l a n d w i n t e r f r o s t s may cause seedi ing l o s s through heaving of the soil. Freez- i ng may occur when a i r temperatures are about 360 F. i n t h e open, 300 F. i n medium shade, and 290 F. i n heavy shade ( 2 1 ) . Shade i s the re fo re a protect ive agency under both high and iow temperat-me condi t ions. Similar ccnclusions have been drawn from e x p e r i m e n t s i n B r i t i s h Columbia (29) *

Bioiogl ; ai Factors

Fungi which cause damping-off diseases are considered important i n Idaho (16 ) . The l o s ses a re irregular and may occur before t h e seed- l i n g s emerge f r o m t h e s o i l , mak.ing i t d i f f i c u i t t o e s t i m a t e t h e i r i m - por tance. In the State of Washington, no evidence o f fmgi-caused mortali ty could be found ( 2 1 ) . Some moTta i i ty has been a t t r ibu ted to f u n g i a t t a c k i n B r i t i s h Co1umbi.a but, i t :is not usual ly an important f a c t o r (25, 2 6 ) . I n a more in tens ive exper iment in 1941, however, MacBean (31) found that an average o f over 35 per cen t of t he mor t a l i t y was caused by or a t l e a s t a t t r i b u t e d t o f u n g u s a t t a c k .

Insects, rodents and birds sometimes causc serious losses (16, 2 4 ) . The white-footed mouse does considerable damage by r .utt ing off seedlings j u s t above ground (21), and is b e l i e v s d t o be r e spons ib l e fo r cons ide rab le m o r t a l i t y on a r t i f i c i a l Feed-spots i n B r i t i s h Coiumbia ( 2 8 ) . Blrds may do a c e r t a i n amount of damage (24), ( 3 3 ) , and have been observed cutting o f f s eed l ing t ops i n po t expe r imen t s ( 2 ) . Cut-worms and s t rawberry weev i l a r e r epor t ed a s mor t a l i t y agen t s (21).

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Seed l ing mor t a l i t y i s fa . r g rea te r dur ing the f i r s t y e a r t h a n i n subsequent years (13, 21, 25, 26, 29 ) . The p l a n t ' s a b i l i t y t o s u r v i v e depends upon i t s own v igor inher i ted f rom i t s parents, and upon the en- vironment t o which i t i s subjec ted . To sum up, h e a t i n j u r y and drought a re p robab ly t he two most impor tan t fac tors , bu t occas iona l ly o thers may assume considerable importance (24, 311). Light shade reduces the mortali ty considerably, and any steps which can be t a k e n t o i n c r e a s e the shade on an open area should r e su l t i n g r e a t e r s e e d l i n g s u r v i v a l .

Garman (13) has given evidence of a good correlat ion between the mor ta l i ty o f 2- and 3-year old seedl ings and the July precipi ta t ion. Seventy 'per cen t o f the var iance o f mor ta l i ty , exc luding b io t ic , win ter and f i r e l o s s e s , i s caused by p rec ip i ta t ion .

Seedl ing Dormancy

The seedling which survlves the extreme hazards o f i t s f i r s t summer goes i n to a dormant period during July and forms a te rmina l bud. Bud sca l e s , i n s t ead o f more new :Leaves, a r e formed by t h e growing p o i n t and these a c t as a p ro tec t ive shea th . The growing point then forms new l e a v e s i n m i n i a t u r e f o r t h e f o l l o w i n g y s a r . By the end o f t h e growing season the new bud i s complete and consists o f a miniature shoot en- c l o s e d i n p r o t e c t i v e bud s c a l e s . I n s i d e t h e bud, a t t h e t i p o f t h e t i n y shoot may be the beginning of a new bud i n the form of new scales--a bud wi th in a bud.

7- What i n i t i a t e s dormanrsy i s nok known, but i t has been observed

t h a t s e e d l i n g s grown i n p o t s wi1:L form buds prematurely i n A p r i l o r May i f t h e s o i l i s allowed t o d ry ou t . Converse ly , when po t t ed s eed l ings are wl l -wa te red , t hey do not cease growth urlt,il the end of August. In the nursery , i t i s f a i r l y common for growth t o c o n t i n u e f o r a month beyond i t s c e s s a t i o n i n n a t u r a l s e e d l i n g s . It i s p o s s i b l e , t h e r e f o r e , t h a t s o i l moisture i s one o f t he f ac to r s conce rned . F requen t ly , a f t e r dormancy of the top has apparent ly set in , the nswly formed buds b u r s t i n the Late summer and a secor,d vegetat ive growth per iod fol lows, but the cause of t h i s behav io r a r e no t known.

NATURAL REPRODUCTION

The f ac to r s i n f luenc ing s eed fa l l , g s rmina t ion , and su rv iva l of seedl ings a re reasonably wel l known, b u t t h e a p p l i c a t i o n o f t h i s knowledge to p roduce more abundant natural regenerat ion i s nei ther s imple nor easy. If s i l v i c u l t u r e were the only considerat ion, the problem could be readi iy so lved . But s i l v i c u l t u r a l recommendations must be f i t t e d i r i t o e x i s t i n g pro tec t ion and eror:omic p r a c t i c e s , a n d i n most cases , subord ina ted to

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I

them. The main problems today centre about slash disposal and the source ” of seed f o r r egene ra t ion , wh ich a r e c lo se ly a s soc ia t ed i n p rac t i ce . If the p roblems involved can be so lved sa t i s fac tor i ly , the appl ied s i lv icu l ture o f Douglas f ir w i l l then, and only then, become a p a r t o f f o r e s t management i n t h i s r e g i o n .

g a s h D i s p o s a l

It has long been a rgued tha t s lash burn ing i s or i s no t a good t h i n g i n t h e Douglas f i r reg ion . From t he s t andpo in t o f fo re s t p ro t ec t ion , the genera l op in ion i s t h a t s l a s h d i s p o s a l i s abso lu te ly necessa ry ove r a g r e a t e r p a r t o f t h e a r e a s i n v o l v e d . From t h e s i l v i c u l t u r a l s t a n d p o i n t , op in ions d i f f e r .

Burning of slash produces fundamental changes i n t h e s o i l ( 2 2 ) . The l a y e r of duff contains more nu t r i en t s t han do the upper layers of the minera l so i l , which may a c t u a l l y be de f i c i en t . Burn ing r e su l t s i n t he loss of much o f t he n i t rogen s to re of t he du f f , and t he l i be ra t ion , i n the form of ashes , of re la t ively large amounts of phosphates, potash and c a l c i u m t o t h e s o i l . The s o i l i s made l e s s a c i d by burning, and the net r e s u l t a p p e a r s t o be a s t imu la t ion of the growth of competing plants such as fireweed, groundsel, and bracken d.uring the few years following the f r re . Burning removes some of the organic matter f rom the so i l it- se l f , t he reby dec reas ing i t s water-holding capacity and tending t o i n - t ens i fy d rough t cond i t ions . The high concentrat ion of sol1 n u t r i e n t s tends to p roduce a seed l ing w i th a large top and a d i sp ropor t iona te ly small, sha l low roo t . When the annual drought per iod or‘rcurs, water l o s s from t h e t o p i s g rea t and t he i n t ake of water by the small r o o t i s i n - s u f f i c i e n t t o m a i n t a i n l i f e .

Blackening of the soi l surface causes excessive surface temperatures during hot weather and i s responsible f o r some m o r t a l i t y ( 2 2 ) . The au thors conciude t h a t t h e h a r m f u l e f f e c t s o f t h e o r d i n a r y s l a s h f i r e more than out- weigh any beneficial effe(- , ts i t may have on the productiviLy of Douglas fir f o r e s t s o i l , and t h a t t h e harm done i:; propor t iona l to the comple teness wi th which the f i re consumes the duff and the organic matter of the sur- f a c e s o i l .

Munger and Matthews (35) s t a t e t h a t , on seve ra l w ide ly s epa ra t ed t r a c t s of logged-off land, experiments show t h a t a f t e r s e v e n y e a r s , t h e unburned a r e a s had 5 1/2 times the s eed l ings pe r ac re o f t he a r eas s l a sh - burned. Most of the unburned areas were well-stocked, whereas a l l t h e burned areas were understocked o r non-stocked. During the f i r s t 20 years a f t e r l o g g i n g , unburned a r e a s g e n e r a l l y a t t a i n a ce r t a in deg ree o f s tock ing 3 t o 5 years more quick ly than do the burned a reas .

I n Br-it ish Columbia, the evidence for o r aga ins t burn ing , as judged by the na tu ra l r egene ra t ion , i s no; conclusive. Areas have been

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examined where, 1 7 y e a r s a f t e r b u r n i n g , 5400 Douglas f ir per acre were present 600 f e e t f rom t imber , 1400 per acre .a t 2000 f ee t , and 500 pe r ac re a t 2600 f e e t . ( 1 3 ) . On a more favorable nor th s lope on the same area,, the reproduct ion was near ly twice as d e n s e i n r e l a t i o n t o t h i s t r e n d . Reproduc t ion o f o the r spec ie s b rough t t he t o t a l t o 11,500 a t 600 f e e t , 5400 a t 2000 feet , and 1500 a t 2600 f e e t from timber. The i n c r e a s e i n t he dens i ty o f r ep roduc t ion from 10 t o 1 7 y e a r s a f t e r l o g g i n g w a s q u i t e small, and it can be considered that such an area was res tocked satis- f a c t o r i l y up t o 2000 f e e t from timber i n a b o u t ' 1 0 y e a r s a f t e r b u r n i n g .

On the o the r hand, a h i s t o r y map fitudy (11) which sampled nine operat ions covering 130,000 a c r e s , i n d i c a t e s t h a t o n l y 28 pe r cen t o f t he areas logged and burned are res tocking adequately, whereas areas which were l ogged on ly a r e s tock ing s a t i s f ac to r i ly t o t he ex t en t of about 68 per c e n t . The logged-and-burned areas were several times as ex tens ive . a s t h e unburned areas and the comparison may n o t b e j u s t i f i e d . The logged-- and--burned areas averaged 1394 t rees per acre of a l l s p e c i e s i n 1934-35, whereas the unburned areas averaged 3837 t r e e s p e r a c r e . Both types averaged about 20 per cent Douglas f ir . Burning may be j u s t i f i e d s i l v i c u l t u r a l l y on areas where sl-ash concentration i s extreme s ince i t i s o f t e n a p p a r e n t t h a t i t grea t ly reduces the a rea on which seedlings can become e s t a b l i s h e d ( 2 6 ) .

Data summarized by Garman (14 ) i nd lca t e t ha t r eburn ing i s one of the most s e r ious p rob lems i n na tu ra l r egene ra t ion . An area which had been burned once res tocked progressively, unt i l 15 years a f te r the burn, 58 per cen t was s a t i s f a r , t o r i l y s t o c k e d . But 10 y e a r s a f t e r a sec.ond burn on another area, only 5 per cen t was res tocked adequate ly .

Averages f o r s e v e r a l sample p i o t s d i s t r i b u t e d o v e r a l a r g e a r e a show 2600 seedl ings o f a11 spec ie s pe r ac re 15 y e a r s a f t e r b u r n l n g , sugges t ing tha t , g iven a be t t e r c t l s t r i bu te@ seed supp ly , s a t i s f ac to ry restocking could be ob ta ined i n sp i t e o f bu rn ing . A comparable un- burned area averaged about the same s tand per a c r e b u t w i t h a g r e a t e r percentage of f i r (13 ) .

Data have been presented (13) which ind ica te tha t the to ta l survival of Douglas f i r on burned and on unburned areas i s similar a t the end of a decade. The pe rcen tage su rv iva l o f f i r seems t o be b e t t e r on unburned than on burned areas.

On one burn , 17 years o ld , the decrease in s tocking f rom t lmber t o one quar te r mi le averaged over 600 p e r a c r e f o r e a c h 66 f e e t d l s t a n c e . Eighty-f ive per cent of a l l s eed l ings were i n t h i s zone, and 3000 f i r and 2000 hemlock were p re sen t pe r ac re a t t h e o u t e r limit. The i n d i c a t i o n s a re t ha t adequa te su rv iva l can be expec ted wi thm reasonable d i s tance o f seed supply withln orie or two decades, even on burned areas. Garman (13) conc ludes t ha t s t ands o f 500 o r rnore seed l ings per a c r e s h o u l d r e s u l t on burned areas from one good seed year , judging by the average mor ta l i ty which occurs.

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Source of Seed

It has been s ta ted (13) t ha t s low r e s tock ing du r ing t he ea r ly years a f te r logging and burn ing may be caused by low to t a i ge rmina t ion r a the r t han by low s u r v i v a l . The s ign i f i cance o f t h i s conc lus ion i s obvious: i f t rue gene ra l ly , i t means t h a t i n many cases the inadequacy of the seed source has a g rea t e r i n f luence upon res tockmg than has burning. From t h e p r a c t i c a l p o i n t of view t h i s i s a good th ing , fo r i t i s much e a s i e r t o modify p r a c t i c e t o p r o v i d e a seed supp ly t han t o f i nd a s imple subs t i tu te for b roadcas t burn ing . The main problem cons i s t s o f deciding on the t ype o f s eed supp ly bes t su i t ed t o ave rage cond i t ions .

It has been s ta ted tha t the bes t assurance o f an adequate seed supply i s a nearby block of uncut timber (20 ) . On the other hand, s ca t t e r ed s eed t r ee s p rov ide s eed fo r s a t i s f ac to ry r ep roduc t ion on c e r t a i n t e s t a r e a s ( 2 5 ) . It has been repor ted tha t the percentage surv iva l o f seedl ings i s g r e a t e r on sca t te red-seed- t ree areas than on c lear - -cu t areas .

seeded from marginal timber (13) and t h i s i s borne out by other invest iga- t i o n s (25, 2 6 ) . General iz ing, i t can be s a i d t h a t i n t h e m a j o r i t y o f cases , a good seed supply w i l l produce good restocking no mat te r how the seed supply is obta ined . From -the s t andpo in t o f e f f i c i ency of seed d i s t r i b u t i o n , t h e r e c a n be no d o u b t t h a t s c a t t e r e d s e e d t r e e s are b e t t e r than margina l t imber . In o rder tha t the sca t te red-seed- t ree method may be success fu l , it i s n e c e s s a r y t h a t s u f f i c i e n t t r e e s o f t h e d e s i r e d species be l e f t a f te r logging and burn ing , tha t these t rees be chosen for the i r windfirmness ra ther than for t h s i r s i z e , t h a t t h e y be i n s u f f i c i e n t numbers to supp ly p l en ty of seed, and that they be p ro tec t ed from burning a t the time o f s l a s h d i s p o s a l .

I s aac (20) i s o f t he op in ion t ha t s eed t r ee s a t t h e r a t e o f approximately 2 per acre are not adequate to reseed cut-over areas and s t a t e s t h a t 75 p e r c e n t o f t h e s e e d t r e e s a r e l o s t from various causes w i t h i n 10 y e a r s a f t e r l o g g i n g . I n British Columbia, 70 per cent o f the fir s e e d t r e e s on a burned-over area were l o s t by the end o f 10 years (13 ) . Windfal l accounted for 20 p e r c e n t a n d f i r e damage f o r a b o u t 15 per cent; the remainder probably died from exposure.

On 3 sca t te red-seed- t ree areas logged and burned i n 1938, t h e fo l lowing da ta apply (25) :

I

- 15 --

Area

Hillbank

Q u a l i c um

P a r k s v i l l e

F i r seed t r e e s p e r

ac re

1938

2

2.24

2.37

To t a l m o r t a l i t y

1941 %

1 3

66

58.5

Mor ta l i t y 1938-41 as a percentage o f t o t a l M o r t a l i t y

Logging and Wind Burning damage

Other

0 100 0

42 52 6

56 24 20

A considerabie number of the trees which were lost from windthrow o r windbreak a l so suf fe red from logging o r bu;-ning damage. It i s poss ib le , t h e r e f o r e t h a t a considerable propori-ion of t he loss of seed t r ees i s pre- ven tab le . A l l t h r e e a r e a s r e s t o c k e d s a t i s f a c t o r i l y d u r i n g t h e f i r s t t h r e e years a f te r burn ing , main ly as a r e s u l t of t h e good seed year o f 1938. If no seed years had occurred soon af t .er logging and burning, the s tory might, have been q u i t e d i f f e r e n t and more in acco rd w i th t he op in ion o f Isaac (20) mentioned above.

The obvious conclusion to be drawn from the i n fo rma t ion ava i l ab le i s t h a t a good seed supply i s a p re requ i s i t e t o r e s tock ing and t ha t i t must be protect,ed from f i r e and from logging damage. If seed t r ees a r e wor th l eav ing t hey a r e wor th p ro t ec t ing . Th i s may mean the planning of each s e t t i n g i n more d e t a i l , and the removal of s l a s h a d j a c e n t t o uncut trees o r t h e c , o n s t r m t i o n o f l o c a l i z e d f i r e i i n e s , b u t t h e c o s t i n v o l v e d s h o u l d be small compared w i t h t h a t o f p lan t ing . Seed t rees need no t be l a rge , valuable t r e e s . Conky o r k n o t t y t r e e s a r e as va luable for seed as the b e t t e r q u a l i t y t r e e s , and small hemlocks and cedars are eff ic ient seeders w h i l e t h e y l i v e ( 2 5 ) . But wha-;ever type of seed t ree i s l e f t , it must be p r o t e c t e d o r t h e e f f o r t i s en t i r e ly was t ed , and more expensive methods of res tocking w i l l be necessary.

" THE YOUNG TREE

Once the seedl ing has become d e f i n i t e l y e s t a b l i s h e d , i n t e r e s t l i e s pr imar i ly in g rowth and mor ta l i ty . Growt'h depends upon t h e i n h e r i t e d cha rac t e r o f t he i nd iv idua l as w e l l as upon s i t e , which i n t u r n i s a con- venient measure o f the envi ronment . S i te i s commonly measured by the average height of dominant and co-dominant trees a t a given age, usual ly 100 years , s ince hzight growth i s b e l i e v e d t o be c l o s e l y c o r r e l a t e d w i t h

- 16 -

s i t e q u a l i t y (10 ) . Height growth i n t u r n i s o f t e n c o r r e l a t e d w i t h s o i l moisture (10) and inves t iga t ions are b e i n g c a r r i e d o u t t o d a t e r m i n e t h e r e l a t i o n s h i p i n t h i s r e g i o n . It i s p o s s i b l e t h a t low s o i l m o i s t u r e con- t e n t may be a f a c t o r i n b r i n g i n g on the dormant period and the cessation of height growth in midsummer.

Physiology

Dur ing the win ter the t ree i s apparently dormant, al though the r o o t s may be ac t ive (X), and some normal functions may be ca r r i ed on a t a low r a t e b y t h e crown. About February , the foods s tored in the roo ts are changed t o sugars which move up into the t runk, branches, and twigs, mainly into the bark ( 8 ) . About t h i s t i m e t h e buds begin t o resume a c t i v i t y . I n March, the sugars a.re t o a g rea t ex t en t changed i n to s t a r ch , an inso luble food which does no t in te r fe re wi th the movements of newly elaborated foods coming from the isaves, but which i s ava i l ab le fo r u se at, any t ime. About the middle of Apri l , the leaf buds, considerably developed, burst , through their bud sc\&les t ,o appear as young shoots . Growth of $hese shoots consists in the elongation of the stem between the leaves and growth o f t he l eaves . No new k a v e s a r e i n i t i a t e d beyond the number which were i n t h e b u d . By t h i s t ime the o ld l eaves o f the t ree a re xo rk ing e f f i c i en t ly t o p roduce suga r s and o the r e s sen t i a l subs t ances needed by the growing parts of the crown and r o o t s . Any d e f i c i t i s pre- sumably suppl ied by the s tarch reserve formed in March, which does de.- c rease g radual ly dur ing the growing season.

DLlring most of the growing season, the amount of food manufactured i s p r o b a b l y e s s e n t i a l l y e q u a l t o t h e amount used for height and diameter growth, development of new twigs and maintenance of l i f e . When vege ta t ive growth ceases in July, manufacture exceeds usage and foods accumulate. Some are probably used in the development of next year 's buds; the re- mainder are t r a n s l o c a t e d t o places of storage, mainly t h e roots, and r ema in t he re un t i l aga in r equ i r ed t he fo l lowing sp r ing . Qua l i t a t ive ly , t h i s i s probabiy the deve lopmenta l h i s tory o f any t ree , bu t quant i ta t ive ly , each t 8 ree d i f f e r s f rom the o the r s i n t he d i . spos i t i on o f t he e i abora t ed foods. The weak t r e e , p a r t i a l l y o r wholly suppressed, cannot manufar-ture as much food as a h a a l t h y t r e e i n f u l l s u n l i g h t . The excess of assimila- t i on ove r amounts r e q u i r e d f o r ma:intenance may be so low t h a t l i t t l e re- mains f o r growth o r s t o r a g e ; i t s r o o t s may cease development and as com- p e t i t i o n becomes more s e v e r e f o r l i g h t a n d t h e s o i l n u t r i e n t s , t h e balance becomes s t i l l more unfavorable and the t ree s t a r v e s . On t h e o the r hand, a t r ee f avored by a l a r g e r crown, b e t t e r l i g h t c o n d i t i o n s , and a well-developed root system, w i l l produce a grea te r excess of foods over the amount n e c e s s a r y t o m a i n t a i n l i f e , a n d more will be a v a i l a b l e f o r growth of t op and roo t , enab l ing t he t r ee t o ma in ta in or b e t t e r i t s favored p o s i t i o n i n t h e s t a n d . Once a t r e e p u l l s ahead of o r lags behind i t s neighbors, a t r e n d i s s t a r t e d which becomes exaggerated, ar:d r e s u l t s

- 1 7 -

i n t h e dominance or suppress ion , respec t ive iy , o f the t ree , and u l t imate ly , i n n a t u r a l t h i n n i n g .

_" Thinnin.g . and - Pruning "_ - - (39)

A r t i f i c i a l t h i n n i n g aims a t the removal of t rees which s low down the growth of t he c rop t r ee s by competing with them f o r l i m i t e d amounts of l i gh t , so i l mos tu re and mine ra l nu t r i en t s ; i t aims a t the concent ra t ion of g rowth in the t rees which w i l l form t h e f i n a l c r o p . It i s c a r r i e d o u t l o g i c a l l y a t times when competit ion begins znd before i t can slow down t h e growth of the crop trees o r prevent them from attaining more rapid growth. Experimental th innings are being carr ied out , in Bri t ish Columbia. I n 1YZ9 and 1930, experiments were started in th inning and pruning young strands o f Douglas f ir . A second thinning was found to be necessary and t h i s was accomplished fol lowing the or iginal methods which conformed t o the Swedish system. Four deqrees of cutting were used, namely, heavy_ and xg<yhegvx low thinnings, and two crown th innings of similar i n t e n s i t i e s . It i s e v i d e n t t h a t t h e o r i g i n a l t h i n n i n g had a b e n e f i c i a l e f f e c t on t h e s t and , bu t t he fu l l i n f luence o f these t rea tments on q u a l i t y and q u a n t i t y of the crop will not be e v i d e n t f o r some t ime. It i s t o be hoped t h a t s u i t a b l e methods w i l l be worked o u t i n d e t a i l by the t ime it i s p r a c t i c a b l e t o u s e them i n n a t u r a l r e p r o d u c t i o n o r i n p l a n t a t i o n s .

C l o s e l y r e l a t e d t o t h i n n i n g i s pruning. Whereas th inning aims t o inc rease t he g rowth i n volume of the crop t rees , pruning aims t o i n c r e a s e the g rowth in ?glue. Pruning removes branches, dead or living, from the lower t runk , wi th the ob jec t o f concent ra t ing as much o f the growth as p o s s i b l e i n t h e p r o d u c t i o n of c le .sr t runk wood, and r a i s ing t he g rade and v a l u e o f t h e f i n a l p r o d u c t s .

Douglas fir is a poor self-pruner, and, i f commercially important q u a n t i t i e s of c l e a r m a t e r i a l a r e t o be harves ted f rom s tands l ess than 120 years of age, then some form of a r t i f i c i a l p r u n i n g must be introduced. This treatment, under present economic c o n d i t i o n s , o f f e r s t h e g r e a t e s t p o s s i b i l i t i e s f o r y i e l d i n g a s a t i s f a c t o r y r e t u r n t o t h e f o r e s t , owner. The p resen t expe r imen t s i nd ica t e t ha t p r iming ope ra t ions shou ld be s t a r t ed e a r l y (10 t o 15 years -of age) and cont inued a t i n t e r v a l s u n t i l t h e d e s i r e d l eng th of c lear bole has been obtained. Observat ion of a 20-year-old s tand pruned in 1930 shows tha t occ lus ion of the p runed branch s tubs i s s t i l l incomple te t en years l a te r on a t l e a s t 45 per cen t of t he t r ee s and a l so t ha t t he p run ing of l i v e b r a n c h e s r e s u l t s i n much more r a p i d occ lus ion t han i n t he ca se o f dea.d branches.

Curren t exper iments in p lan ta t ions a re d i rec ted towards the de te rmina t ion of the e f fec t o f va . r ious fac tors upon t h e r a t e o f heal ing- over of the branch s tubs: l ive pruning versus dead pruning; removal o f

- 18 -

t he b ranch co l l a r ; t he t ype of t o o l used--saw, axe, o r pruner . Economic a spec t s o f p run ing a r e a l so pa r t of the s tu .dy and include invest igat ion of t h e c o s t s of var ious types o f p runing toge ther wi th the expec ted in - c r eased r e tu rns .

Thinning and pruning, i f proper ly car r ied ou t , can reduce the ro ta t ion necessary for the g rowth of h igh qua l i ty saw t imber andcan there- by increase the va lue o f the l and .

Seed Production

Young trees i n f a i r l y open stands may bear va luable c rops o f sead a t an ear ly age ( 6 ) . It has been shown tha t the seed f rom young trees can be o f h igh qua l i ty p rovid ing tha t adequate po l l ina t ion i s e f f e c t e d , t h a t i s , i f o l d e r t r e e s a r e s c . a t t e r e d arour?d t h e a r e a o r i f marginal t imber i s c lose a t hand. If t h e r e i s doubt. as to the poller1 supply, sample corns ?.an be '

examined i n August, and i f a good p r o p o r t i o n o f t h e s e e d s a r e f i l l e d , t h e seed r.an be co l l ec t ed s a fe ly , o r can be re:lied upcin as a s o u r c e f o r n a t u r a l regenerat ion. Discussion of seed.-bear ing in general w i l l be found under the next, hsading.

THE ADULT """_ TREE

What has been said with regard t o growth and survival. of the young t r e e a p p l i e s e q u a l l y w e l l t o t h e a d u l t t r e e . T h e r e i s a p o s s i b l e d i f f e r e n c e caused by age. As a s tand grows o lde r , i t s s i t e r equ i r emen t s may change; the dense young s t and may draw more heavi ly upon t h e s o i l t h a n a more open o lde r s t and . Deeper l a y e r s o f t h e s o i l may be tapped by the older s tand for mois ture and mineral elements, and decaylng l i t t e r may have enriched the su r f ace soil. The most d i rec t ev idence appears as an apparent change i n t h e s i t e i n d e x . It i s possib:Le that, t;he s i t e i n d e x might; decrease i r : the case of an open stand approaching normallty, o r where a f i r e h a s t e m p o r a r i l y i n c r e a s e d t h e s o i l n u t r i e n t s a n d i s followed by a gradual de- c r e a s e i n f e r t i l i t y ( 2 2 ) .

Physiology of Seed Production

The adul t t ree , even in fu l ly-s tocked s tands , eventua l ly p roduces seed . Var ious theor ies have been advanced to expla in the per iodic i ty o f seed-bear ing , bu t to da te none has been sa,t isfactor-y. It i s l i k e l y t h a t the explana t ion i s not simple but complex. It i s poss ib le tha t g rowth r e g u l a t o r s o r hormones", whose presence i n plant and animal i s unquestioned,

- 1 Y -

are involved. Whatever the factors inf luencing seed product ion, i t i s t r u e t h a t two good s e e d y e a r s r a r e l y f o l l o w i n s u c c e s s i o n b u t a r e usually separa ted by one or more f a i l u r e o r poor years. 1938 and 1939 were, how- ever , two good seed yea r s , bu t fo r t he most. p a r t , t r e e s which bore heavy crops In 1938 bore l igh t or f a i l u r e c r o p s i n 1939, with some except ions ( 2 5 ) . 1940 was a f a i l u r e y e a r b u t a few t r e e s d i d b e a r f a i r t o good crops. 1941 was a good year a l though many i n d i v i d u a l t r e e s d i d n o t bear seed. 1942 i s a f a i l u r e y e a r w i t h v e r y few t r e e s b e a r i n g . The q u a l i t y o f t h e seed produced i n an off year i s g e n e r a l l y poor, mainly because of in- adequate c ross -pol l ina t ion ( 7 ) and because of excessive insect damage ( 3 7 ) -

Douglas f i r i s a p p a r e n t l y s e l f - s t e r i l e ( 7 ) , t h a t i s , the female f lowers canno t be f e r t i l i zed by po l l en from the same t r e e . I s o i a t e d s e e d t rees cannot be expec ted to bear quant i t ies o f good seed s ince c ross - p o l l i n a t i o n t e n d s t o be incomplete. Because o f t he f ac to r o f c ross - p o l l i n a t i o n , a poor s eed yea r , f rom the p rac t i ca l s t andpo in t , may be considered as and c. lassed with a f a i l u r e y e a r .

Seed Production i n F o r e s t Management.

Seed production i n Dougias f i r s tands i s of importance to manage- ment and w i l l assume s t i l l grea te r impor tance as second-growth stands be- come more and more predominant i n t h e r e g i o n . The planning of operat ions, under ir;tensive management, may depend somewhat upon the type of regenera- t i o n methods considered necessary. The frequency o f seed years w i l l govern na tura l regenera t ion and i t w i l l be wise to l earn someth ing of the fac tors concerned. It i s n o t l i k e l y t h a t e i t h e r n a t u r a l s e e d i n g or a r t i f i c i a l regenera t ion w i l l be employed e x c l u s i v e l y i n t h e f u t u r e . R a t h e r , it i s q u i t e p o s s i b l e t h a t f u l l a d v a n t a g e w i l l be t aken o f na tu ra l met,hods, and where these f a i l t o succeed, planting w i l l be ca r r i ed ou t , o r a combination of p l a n t i n g Dougias fir and fa l l -sowmg hemlock and cedar seed ( 2 7 ) .

It would be an advantage to be ab le to es t imate the amount of n a t u r a l r e g e n e r a t i o n l i k e l y t o be o b t a i n e d i n a g iven year for a s p e c i f i c a rea . This would e n t a i l a reasonable forecast , of the seed crop for the area toge the r w i th a knowledge o f ge rmina t ion and su rv iva l l i ke ly t o r e s u l t . I n v e s t i g a t i o n s a l o n g t h e s e i i n e s are being pursued a t t h e present t ime (25, 2 6 ) .

Seed crops can be forecast one year previous to seedfal l for a g lven a r ea and w i th in ce r t a in limits ( 3 ) . An e s t ima te i s made, i n September , of the re la t ive quant i ty of female buds present . The method i s slow and laborious, and w i l l probably not be p r a c t i c a b l e until manage- ment has reached an in tens ive s tage . Bet te r methods o f forecas t ing seed crops may be disr-:overed through study of t h e fundamenta l fac tors respons ib le for seed product ion .

- 20 -

Seed- t ree Charac te r i s t ics

A s a r e su l t o f an ex tens ive s tudy begun 30 years ago, i t has been r e p o r t e d ( 3 4 ) t h a t s e e d t r e e s o f d i f f e r e n t a g e s a r e e q u a l l y good pa ren t s as far as growth of the progeny i3 concerned. Equally vigorous progeny are produced by open-grown and by dense-grown t r e e s . Progeny from pa ren t s i n - fec ted wi th pocket ro t o r Trametes p in i a re as vigorous a t 20 years of age as those f rom heal thy t rees . It i s concluded, however, t h a t i t i s no t s a fe t o use seed from a warm coas t a l c l ima te fo r p l an t ing i n h igh moun ta in c l imates , and tha t some s tock der ived f rom h igh a l t i tudes grows ooorly a t low a l t i t u d e s . Some s t r a i n s a r e more adaptable and do w e l l i n a l t i t u d e s o the r t han t ha t where they or iginated.

SUMMARY OF SILVICULTURAL PRACTICE ". :j RECOWENDED ~ __ BY VARIOUS __ AGENCIES -

I n Washington and Oregon i:, has been concluded that broadcast burn- ing of spots where s lash i s excessively heavy, supplemented by some p i l i n g - and -burning along routes of t r a v e l o r o ther p laces o f high hazard, and on southern exposures where i t i s undes i r ab le t o bu rn b roadcas t , shou ld s a t i s fy b o t h s i l v i c u l t u r a i and protect ion requirements ( 2 1 ) . S t r i p s or blocks of t imber a r e f avored ove r s ca t t e r ed s eed t r ee s as a source of seed and as an a i d t c f i r e p r o t e c t i o n . C l e a r - c u t t i n g may be rep laced to advantage by she i t s rwood-cu t t ing ( a form of seed-tree cut t lng but with a heavier r e s i d u a l s t a n d ) where prac t icable , and the l a t te r shouid p rovide more i d e a l s i l v i c u l t u r a l c o n d i t i o n s .

S imi la r Lyonclusions have been reached wi th regard to the whi te pme type i n Idaho (16) where cer ta in problems are similar. Seed l ing e s t ab l i sh - ment of a l l p r i n c i p a l s p e c i e s on t h e more s e v e r e s i t e s i s b e s t u n d e r p a r t l a l shade, and shei terwood cut t ing offers def ini te advantages. On more s h e l t e r e d s i t e s , s e e d - t r e e or clear-c-utting methods are considered more s u i t a b l e .

I n B r i t i s h Columbia, i t has been suggested (13) t h a t c i e a r - c u t t i n g i n small areas of about 50 ac re s on she i t e red s lopes , t oge the r w i th she l t e r - wood-cutting on southern siopes, should result in prompt and adequate re- stocking of cut--over areas. Experiments under way at, the p resent t ime s u g g e s t t h a t s c a t t e r e d - s e e d - t r e e methods may be s a t i s f a c t o r y or; certjain areas and under cer ta in condi t ions. (25)

Support for shel terwood-cut t ing in Colorado 'has been expressed (40) . This method, o f t h e s e v e r a l t r i e d , r e s u l t e d i n t h e d e n s e s t s t a n d of Douglas f i r reproduct ion and produced the greatest growth. After ten years the s tand per acre was .near ly the same where slasp had been s c a t t e r e d as where i t had been p i l e d and burned.

In the Southwest , however, based upon s tudies car r ied on over a per iod of 1 2 years (24), l i gh t s e l ec t ion , she i t e rwood , d l ame te r - l imi t ,

21 -

and scattered-seed-tree methods produced similar r e s u l t s . D e s p i t e 3 good and seve ra l l i gh t s eed yea r s , t he r ep roduc t ion was not adequate and was be l ieved due to poor su rv iva l r a the r t han t o de f i c i en t ge rmina t ion .

The l i f e h i s t o r y o f Douglas f i r , as f a r as it i s known, i s de- s c r ibed , from the production of cones and seeds, the disseminat ion of seed, germination and s u r v i v a l of seedl ings , to the g rowth and surv iva l of young and of a d u i t t r e e s .

It i s b e l i e v e d t h a t t h e r e a r e two fundamental condi t ions to be satisfied before nat ,ural reproduc;ion of Douglas f i r can become r e a l l y e f f e c t i v e . An adeqgu&g seed source. i s t h e f irst e s s e n t i a l ; t h e r e i s no subs t i t u t e and i t m u s t be protected from logging arld from f i r e . Glven a supply of seed, near ly a l l a r e a s would r e S t , o r k s a t i s f a c t o r i l y w i t h i n a reasonable t ime. Modif ipat ion of t h e s e v e n t y of t h e more extreme s i t e s i s a second e s s e n t i a l ; it may be acccmpiished by the modificatior, o f cu t t ing methods or of s lash-burning metkods, and shouid resul t in a h ighe r su rv iva l of s eed l ings , and , consequen t ly , i n be t t e r r s s tock ing . P rac t i c , a l ly , it w i l l mean leaving numerous seed t r ee s o r a p a r t i a l s t a n d , or lea. , ing considerabie unburned slash on the severe southern s lopes .

Although there i s g rea t , - va r i ab i l i t y i n t he r e s tock ing ob ta ined from marginai timber, i t ('an usua l ly be depended upon o n l y t o a d l s t ance of about 500 f e e t from timber. Beyond t h a t d i s t a n c e , d e n s i t y of repro- duct ion decreases and only par t ia l s tocking can be expected, assuming t h a t no s e e d t r e e s are present, on t h e c u t - o v e r a r e a . Each s p e c i f i c a rea w i l l be d l f f e ren t , however, and t h e r e i a t i o n between d i s t ance from t imber and densi ty of res tocking w i l l depend upon topography, winds, and t h e type and slze o f uncut t imber. A s tand of t a i l t lmber bearing Large q u a n t i t i e s o f sePd, with favorable wmds arld topography, and with favorable seedbed conditiorls, may restock the cut-over area outwards to one -ha l f mi l e o r fu r the r , b u t optimum condl t ions such as t h e s e r a r e l y occur . With two o r more adjacent margirls of uncut timber to seed an a rea , over lapping of par t ia l - res tocking zones may increase the range of adequate regenerat ion and should be c o n s l d e r e d i n s i i v i c u i t u r a i p l a n n m g

Generally speaking, marginal t imber should reseed the area within 500 fee t o f t imber ; beyond tha t d i s tance , p rovis ion should be made to p ro- vide a seed supply to t ake care o f t h e a r e a s t o be p a r t i a l i y r e s t o c k e d b y the marginal t imber . From 500 f e e t t o 2000 f e e t from t m b e r , one seed t r e e p e r a c r e may be s u f f i c i e n t . Beyond 2000 f e e t , 2 or more t r e e s p e r ac re w i l l probably be necessary.

From the p rac t i ca i v i ewpo in t , t he re fo re , t he rz arp 3 s i i v i c u l t u r a l systems which can be used t o r e g e n e r a t e Douglas f l r :

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1. Clear-cut t ing of small a r e a s , SO t o 100 a c r e s i n s ize , depending upon the number of margins of uncut t imber and the shape of the cutt ing. Kith four margins a s t r i p c u t t : i n g of any length can be taken up t o about 1000 f e e t i n w i d t h . With three margins uncut, areas up t o 100 ac res shou ld r ep roduce s a t i s f ac to r i ly . But the. u sua l cu t t i ng w i l l depend upon seeding from one or two margins only and should not exceed 50 a c r e s i n s ize . Cu t t ings o f t h i s na tu re are more a p p l l c a b l e t o second-growth than t o old-growth stands.

2 . C lea r -cu t t i ng i n l a rge a r eas w i th t he p rov i s ion t ha t a l l areas beyond the adequate-restocking zone be provided with seed trees s u f f i c i e n t t o br ing the s tocking up to normal . Under ave rage cond i t ions , t h i s means t h a t a l l areas between 500 and 2000 feel; from timber must be provided wi th a t lsast one seed tree per acre , and those beyond 2000 fee t wi th two o r more p e r a c r e .

3. C l e a r - c u t t i n g i n l a r g e a r e a s w i t h t h e p r o v i s i o n t h a t a l l a r e a s beyond the adequatz-restocking zone be brought up t o normal stocking a r t i - f i c i a l l y . Between 500 feet arid 2000 feet from timber, about 500 trees p e r a c r e w i l l be necessary, and beyond 2000 fee t , from 600 t o 1000 trees per acre , depending upon t h e d i s t a n c e from t imber . Fa l l - seeding o f hemlock and cedar may be a cheap method of supplementing natural re- s tocking on c e r t a i n areas (28).

Shelterwood, or a type of pa r t i a l cu t t i ng , has no t been cons ide red as a choice for two reasons: f irst , i t i s n o t l i k e l y t o be p rac t icable e x c e p t i n t h e c a s e of second-grow%h stands under intensive management, and second, shelterwood cutt ing as i t i s u s u a l l y d i s c u s s e d i n t h i s c o u n t r y i s very similar in p r inc ipa l t o s eed - - t r ee me thods , but, w i th a g r e a t e r nun- ber o f trees l e f t p e r a c r e .

I n conriusion, i t m u s t aga in be emphas ized tha t a l tho lgh s lash b u r n i n g i n t h e Douglas fir reg ion is neceszary for p ro tec t ion , the regenera- t i o n of Douglas f ir w i l l usua i iy fo i low provid ing tha t a seed SUPPLY can be maintained. Slash burning must , therefore , be conducted i n such a way tha t t he sou rce o f s eed i s no t damaged or des t royed . Pro tec t ion of a l l po ten t i a l s eed -bea r ing t r ee s i s as e s s e n t i a l t o f o r e s t management as i s p ro tec t ion o f e s t ab l i shed young s t ands .

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I

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( 3 1 ......................................... " ......................... 1941. A bas is for forecas t ing seed c rops of some con i f e rous t r ee s . Jou r . Fo r . 39:1014-1016.

(4) ............................................................... 1941. A s t anda rd ge rmina t ion t e s t for Douglas f ir seed . For. C h o n . 17 : 75-78,

(5 ) ................................................................. 1941. Light and temperature as f a c t o r s i n t h e germina- t i o n of the seed of Douglas f i r . For . Chon. 17:99-109.

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( 8 ) ............................................................... 1942. A physiological s tudy of seed product ion by Douglas f ir . Unpublished r e p o r t . F i l e 0145717. B r i t i s h Columbia Fores t Serv ice .

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(10) h < % . t ; ....... F..:?.:..1934. Theory and p r a c t i c e of s i l v i c u l t u r e . McGraw- Hili Book Co. New York.

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(16) , K . P. Davis, and R . H . Weidman. 1941. Natural r egene ra t ion i n t he wes t e rn wh i t e pine type. Tech. Bul. 767. U.S.D.A.

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(18) I saac , L . A . 1930. Seed f l i g h t i n t h e Douglas fir r s g i o n . Jour. For. 28 :492,-499.

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(20) ..................................................................... 1937 . Highlights of Douglas f i r na tu ra l r egene ra t ion . Forest Research Note No. 21. Pacific, North- west Forest Experiment Station.

(21) . .......................................................... 1938. Fac to r s a f f ec t ing t he e s t ab l i shmen t o f Dougias fir seed l ings . Circxiar 486. U e S . D. A .

(22) .................................................................. and H . G. Hopkins. 1937. The f o r e s t s o i l o f t h e Douglas fir reg ion , and changes wrought upon it by logging and slash burning. Ecology 18: 264-279.

(23) ........................................................................ and G . S . Meagher . 1936 . Natural reproduction of the Tiliamook burn two y e a r s a f t e r t h e f i r ' e . P a z i f i c Nort,hwest Forest Experiment Stat ion. Portland, Oregon.

,

(24) Krauch, H . 1936. Some f a c t o r s i n f l u e n c i n g Douglas f ir reproduc- t i o n i n t h e S o u t h w e s t . Jour. Fcr . 34:601-608.

(25) MacBean, A . P. 1938 -. Sca t t e red s eed t r ee s : t he i r su rv iva l and ' s eed disseminat ion. Unpublished data . Fi le 0132353 B r i t i s h Columbia Fores t Serv ice .

(26) ........................................................................ 1938 - * Natural regenera t ion of c u t o v e r f o r e s t b n d . Unpublished data. File 0153205. Brit ish Columbia Fores t Serv ice .

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(27) ................................................... ”.. 1938 - . Group seed t ree s tudy . (S tudy of seed product ion in s tands) . Unpublished d a t a . F i l e 0131644. B r i t i s h Columbia Fores t Serv ice .

(28) .................................................................................. 1938-40. A r t i f i c i a l s e e d i n g . F i l e 0133208. B r i t i s h Columbia Fores t Serv ice .

(29) ................................................................................... 193’8. Survival and growth of natural seedl ings i n r e l 3 t i o n t o c o n d i t i o n of s i t e . P r e - l iminary compilations and comment on r e su l t s . Unpub l i shed . F i l e 090477. B r i t i s h Columbia Fores t Serv ice .

(30) ................................................................................. 1941 . Yield and v iab i l i ty . Seed Col lec t ion 1939. Douglas f i r . Unpublished data. F i l e 0125722. B r i t i s h Columbia Fores t Serv ice .

(31) ..................................................................................... 1941-42. Experiment t o determine the cause of Douglas fir seed and seedl ing losses . Unpublished inter im report . Fi le 0142557. B r i t i s h Columbia Fores t Serv ice .

. (32) ............................................. ~ ................................... 1942 . Private communication.

3

(33) Moore, A . W. 1940. Wild animal damage to s eed and s eed l ings on cut-over Douglas f i r l a n d s o f Oregon and Washington. Tech. Bul. 706. U.S.D.A.

(34) Munger, T. T . and W. G . Morris. 1936. Growth of Douglas f ir t r e e s of known seed source. Tech, Bul. 537. U.S.D.A.

(35) Munger, T . T . and D. N . Mat thews. 1941. Slash disposal and forest management a f t e r c lear c u t t i n g i n t h e Douglas f i r region. Circ . 586. U.S.D.A.

(36) Pickford, A . E. 1929 . S tud ie s o f s eed d i s semina t ion i n Br i t i sh Columbia. For. Chron, 5 .

(37) Prebble, M. L. and K . Graham. 1941. Notes on cone-inhabi t ing in- s e c t s . Unpublished report;. Dominion Entomological Laboratory. Victoria, B . C .

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.... ............,.... .1942. Report of the Forest Branch f o r t h e year ended December 31st, 1941. p. 55.

A study of Douglas f ir reproduction under var ious cut t ing methods. Jour . Agric. Res. 28 :1233-1242.

E f fec t s of seed-ash characterist ics and t reatment of seed and soi ls 'upon conifer- ous seed germinat ion. Universi ty of Washington, S e a t t l e . D i g e s t of t h e s i s .

The vege ta t ion o f t h e f o r e s t f l o o r : l i g h t v e r s u s s o i l m o i s t u r e . I n t e r n a t l . Cong. Plant.Sci. Prog. (1926) 1:575-599.

A s tudy o f r e fo res t a t ion on Vancouver I s l a n d w i t h p a r t i c u l a r r e f e r e n c e t o the operat ions of Bloedel , Stewart and Welch, Limited. Unpublished report.

'\

1 (40) Roeser, J . Jr. 1924.

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