Research Note NO. 86 1979 ISSN 0384-2002

Growth of lodgepole pine seedlings in competition with grass

M.B. Clark and A. McLean

prcrpritnce of Brftirsh Columbia Ministry of Forests

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GROWTH OF LODGEPOLE P I N E SEEDLINGS

I N COMPETITION WITH GRASS

BY

M.B. CLARK AND A.MCLEAN’

E.P. 590.4

Research Note #86 Resea rch Branch M i n i s t r y of Forests P r o v i n c e of B r i t i s h C o l u m b i a 1 4 5 0 Government S t ree t V ic to r i a , B . C . vaw 3 ~ 7

M.B. C l a r k - Research Forester , Min is t ry o f Forests, Kamloops, B.C.

A. McLean - E c o l o g i s t , A g r i c u l t u r e Canada, Kamloops, B.C.

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C a n a d i a n C a t a l o g u i n g i n P u b l i c a t i o n Data

C l a r k , Murray Bruce , 1923- Growth of l o d g e p o l e p i n e s e e d l i n g s i n compet i t ion

w i t h grass.

( R e s e a r c h n o t e - M i n i s t r y of F o r e s t s ; no. 86) " E . P . 590 .4" B i b l i o g r a p h y : p . ISBN 0-7719-8182-1

1. L o d g e - p o l e p i n e . 2 . Grasses - B r i t i s h Columbia. 3 . R e f o r e s t a t i o n - B r i t i s h C o l u m b i a . I . McLean, Alastair , 1921- . 11. B r i t i s h C o l u m b i a . F o r e s t r y D i v i s i o n . R e s e a r c h B r a n c h . 111. T i t l e . I V . Ser ies : B r i t i s h Columbia. M i n i s t r y o f Fo res t s . R e s e a r c h no te - M i n i s t r y of F o r e s t s ; n o . 86.

SD397.P585C55 634.9'751'56 C79-092112-X

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TABLE OF CONENTS Page

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ABSTRACT

Between 1973 and 1978, lodgepole pine was grown, from seed, under normal forest site conditions alone and in competition with different densities of grass, different species of grass, grass subjected to simulated grazing, and with grass fertilized with N and S fertilizers applied at variable rates.

The survival of lodgepole pine was not affected by density of grass sowing or species of grass, but early height growth of pine and total seedling weight were significantly reduced by high rates of grass sowing.

Additions of fertilizers had no significant effect on grass productivity after the first year following application. Clover, on unfertilized areas, produced herbage yields equivalent to herbage yields of all grasses on areas with the highest rates of fertilizer application.

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LIST OF TABLES Page

TABLE 1. Lodgepole Pine Survival and Growth Response, and Herbage Yields, in Relation to Rate of Grass Seeding-- - - - - - - - - - - -_- - - - - - - - - - - - - - - - - - - - - - - - - 8

TABLE 2 . Lodgepole Pine Survival and Growth Response, and Herbage Yields, in Relation to Application of N and S _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - - - - - - - - - - - - - - - - - - - - 9

TABLE 3 . Lodgepole Pine Survival and Growth Response, and Herbage Yields, in Relation to Grass Species---- 1 0

INTRODUCTION

A study to determine whether different densi t ies of grass plants influence survival and early growth of lodgepole pine (pinus eontorta var. ZatifoZia Engelm), and whether level of water supply influences competition between pine and grass (Clark and McLean, 1975) was inconclusive. However, results indicated that competition for nutrients, particularly for nitrogen and su l fu r i n which the soi ls of Bri t ish Columbia's southern interior are often deficient (Freyman and .van Ryswyk, 1969), may be of some importance. A la ter s tudy (Clark and McLean, 1978) suggested that competition from grasses sown a t 4.5 kg/ha may r e s t r i c t lodgepole pine seedling growth, and that grazing to reduce grass competition may have been beneficial .

Published information on the effect of grass on the growth rate of lodgepole pine seedlings, with or without grazing, or with or without addition of nutr ients , i s meagre, although some work has been reported for other species. Ponderosa pine (Pinus ponderosa Laws) is able to compete with grasses i f planted before o r a t the same time as grass, but the degree of competition depends upon the species of grass (Baron, 1962). However, both root and top growth of ponderosa pine seedlings is s ignif icant ly greater when grown in the absence of grass (Larson and Schubert, 1969). To produce both grass and conifers with minimum competition, Clark and McLean (1978) recommended that, since most stands w i l l increase in density during the f irst three years, lighter seeding rates than the normal 4 . 5 kg/ha of grass should be used.

Duffy (1974) suggested that competition between seeded grasses and loblolly pine (Pinus taeda L . ) could be reduced through proper time of fe r t i l i zer appl ica t ion but Fober and Giertych (1971) reported that grass has an increasingly adverse effect on spruce (Picea abies (L) Karst.) seedling growth as nutrient supply increases. Similarly, survival of one-month old jack pine (Pinus banksiana Lamb. ) seedlings decreases directly with N appli.cation rate (Winston, 1974) . Mugo pine (Pinus mugo Turra.) seedlings were shown to survive best in a grass-legume cover with minimal applications of f e r t i l i z e r (Anonymous, 1974) .

The study reported herein was in i t i a t ed i n 1973, t o determine the effects of grass density, with and without fert i l izer application, on lodgepole pine establishment, survival and growth under f i e ld conditions. The 1975 study (Clark and McLean) had been carried out under a partially-controlled environment. Seeding of clearcuts with domestic grasses for forage production on summer ranges within the Kamloops region of Inter ior Bri t ish Columbia has been a common practice fo r a number of years. However, f e r t i l i za t ion of these areas has not been attempted, and the values to be gained relative to forage productivity or e f fec ts on lodgepole pine establishment and growth are unknown.

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The experiment comprised four separate studies to determine: (a) effect of different densit ies of grass plants on survival and growth of lodgepole pine; (b) e f f ec t of application of N and S a t various rates on grass productivity and on the survival and growth of lodgepole pine; (c) effect of individual grass species on the survival and growth of lodgepole pine; (d) e f fec t of simulated grazing on survival and growth of lodgepole pine seedlings.

3 METHODS AND MATERIALS

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The experimental area was located a t approximately 1340 m elevation on the Thompson Plateau approximately 32 lan northeast of Kamloops, Bri t ish Columbia. The area was within the Engelmann spruce - sub-Alpine f i r biogeoclimatic zone with average annual precipitation of roughly 600 nun, approximately one th i rd of which occurs between May and October. The s o i l is a medium textured glacial till. Prior to plot establishment the area supported a dense stand of immature lodgepole pine. The portion of the stand where the plot was located had been destroyed by an escaped f i r e during slash burning of an adjacent clearcut. Following burning, a l l stems were fe l led , windrowed, and burned. Immediately pr ior t o plot establishment, the plot area was levelled with a road grader, virtually removing the surface organic (Ao) horizon.

The four separate studies were established wi th in a completely fenced area as follows:

A. GRASS - DENSITY TRIAL

Four replications, each 3 m by 1 5 m, were divided into five grass density treatment plots 3 m by 3 .m. Plots were s p l i t for season of grass and lodgepole pine seeding. Density treatment and season of seeding were randomized within plots and sp l i t -p lo t s , respectively, for each repl icate . Orchardgrass (Dactylis glornerata L.) was sown at five density treatments : zero, 2 . 2 kg/ha, 4 . 5 kg/ha, 9 .0 kg/ha, and 17 .9 kg/ha.

B. FERTILIZER TRIAL

Four replications, each 3 m by 24 m, were divided into eight treatment p lo ts , 3 m by 3 m. P lo t s w e r e s p l i t t o evaluate season of sowing. Fe r t i l i ze r i n the form of ammonium n i t r a t e and ammonium ni t ra te plus sulfur (S) was applied in autumn 1975. Randomized treatments were: No grass or fert i l izer, grass with no fer t i l izer , n i t rogen (N) a t 16.4 kg/ha, N a t 32.9 kg/ha, N a t 65.7 kg/ha, N a t 16.4 kg/ha plus S a t 5.3 kg/ha, N a t 32.9 kg/ha plus S a t 10.6 kg/ha, and N a t 65.7 kg/ha plus S a t 21.3 kg/ha. Forestland Mix1 was sown at the ra te of 6.7 kg/ha.

Forestland Mix Species Timothy Orchardgrass Bromegrass Crested wheatgrass Alsike Clover

- % by Weight 25 25 20 20 1 0

No. Seeds /kg 557,000 296,000

62,000 79,000

317,000

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C. GRASS - SPECIES TRIAL

Four replications, each 3 m by 2 1 m, were divided into seven grass species plots 3 m by 3 m. Plots were s p l i t f o r season of sowing of grass and pine. Within each replication species treatments were randomized within plots and sowing dates were randomized within split-plots. l 'reatments were: orchardgrass sown a t 9.0 kg/ha, Timothy (PhZeurn pratense L.) sown a t 4 . 5 kg/ha, bromegrass (Bromus inerrnis Leyss.) sown a t 26.9 kg/ha, red fescue (Festuca rubra L.) sown a t 9 . 0 kg/ha, hard fescue (Festuca owina var. duriuscula (L) Koch) sown a t 9.0 kg/ha, crested wheatgrass (Agropyron c r i s ta twn (L) Gaertn.) sown a t 6.7 kg/ha, and no grass.

D. FREQUENCY OF CLIPPING (SIMULATED-GRAZING) TRIAL

Four replications, each 3 m by 15 m, were divided into f ive main plots 3 m by 3 m. Plots were s p l i t f o r season of sowing of grass and pine. Treatments were randomly allocated t o plots and season of sowing to sp l i t -p lo t s . Treatments were: clipping of grass a t two-week intervals on three occasions commencing early July, clipping at two-week intervals on three occasions commencing mid- b' August, c l ipping a t two-week intervals on five occasions commencing early July, cl ipping at end of season only, and no grass sown. Forestland Mix was sown a t t he r a t e of 6 .7 kg/ha. Within a l l t r ia l s g rass was sown during mid-October 1973 and l a t e June 1974, and w i t h i n a l l t r i a l s lodgepole pine was sown a t approximately 0.56 kg/ha i n mid-October, 1973, and early June, 1974.

A measure of grass productivity was obtained by annual harvest ing a t 16 sample points within each treatment plot within each t r i a l from 1975 through 1977, inclusive. Samples were oven- dr ied pr ior to weighing. The number of lodgepole pine seedlings were recorded annually for each treatment plot within each t r i a l from 1974 through 1978, inclusive. Late in 1978, each treatment plot2 of 3 m by 3 m i n each t r i a l was theoretically divided into 900, 10 cm sampling points. Sixteen points were randomly selected to sample lodgepole pine seedlings. Lodgepole pine seedlings occurring a t a sample point were carefully excavated, shoots and roots were measured, separated and placed in label led bags for oven-drying pr ior to weighing.

Analysis of variance tests were applied t o seedling survival, length and weight s t a t i s t i c s , and grass productivity measures.

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RESULTS MD DISCUSSION

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Germination of fall-sown lodgepole pine seed was inhibited by very cool conditions during spring, 1974. Some losses of seed to small mammals probably occurred also. As a r e su l t , t o t a l germination from fall-sown seed was much poorer than from spring-sown seed. Some seed from both sowing dates did not germinate until 1975. Because of the few seedlings germinating from t h e f a l l sowing sp l i t -p lo t s were combined for f inal evaluations of lodgepole pine survival and growth within grass treatments.

A l l grass sown in both autumn of 1973 and late spring of 1974 produced even and adequate stands, although there were some var iat ions between season of sowing by species. For example, orchard- grass and crested wheatgrass ge-rminated best from spring sowing whereas Timothy germinated best from autumn sowing. The autumn sowings of Forestland Mix were s l ight ly bet ter than spr ing sowings. However, wi th in a l l t r ials, the season spli ts were ignored for final analyses and productivity comparisons so as t o conform with final evaluations f o r lodgepole pine.

A. GRASS - DENSITY TRIAL

The rate of grass seeding had no s ignif icant effect on actual numbers of lodgepole pine seedlings germinating and surviving. However, t o t a l biomass of pine seedlings was s ignif icant ly reduced by a l l densit ies of grass sowing as compared with areas not sown to g rass . Also, height: growth of seedlings was s ignif icant ly reduced by rates of grass sowing equal to or heavier than the normal r a t e on clearcuts o f 4.5 kg/ha.

There were minor s ignif icant var ia t ions in herbage yields from grass sowing. The s ignif icant ly lower yield from the highest r a t e o f sowing (Table 1) indicat.ed some intraspecific competition. Yields from low ra tes of sowing increased annually whereas yields from high rates of sowing decreased.

The inhibi tory effect on lodgepole pine height growth, produced by sowing rates of 4 .5 kg/ha and. greater, supports the recommendation (Clark and McLean, 1978) that l ighter seeding rates than the normal 4.5 kg/ha be used t o reduce early competition with tree seedlings.

B. FERTILIZER TRIAL

A s ignif icant ly greater nunber of lodgepole pine seedlings survived, per square metre, on areas with no grass or fer t i l izer as compared with grass and fer t i l izer treatments but there were no differences in seedling biomass or seedling growth between treatments. The germination of lodgepole pine was very poor throughout a l l p l o t s and repl icates of t h e f e r t i l i z e r t r i a l i n comparison with the other three t r ia ls in t he same area.

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For the f i r s t and second years following application of fer t i l izer , the highest herbage yields were produced on areas with the highest rates of fer t i l izer . Thereaf ter , however, the herbage yield on unfer t i l ized plots was not significantly different from herbage yields from what had been the best of the fe r t i l i zed p lo ts .

Measures on grass and alsike clover, separately, showed that unfertilized grass plots produced a greater percentage of clover (53% of total y ie ld) than did fer t i l ized plots (28% of to ta l y ie ld) . The clover population enabled forage production on the control plots t o equal that of treated plots two years following fertilizer treatment. Leaf colour suggested that the soil at t h i s s i t e is nitrogen-deficient and, since the lowest clover yields were observed on plots with the highest rate of N , there is a strong possibil i ty that supplementing with nitrogen has caused development of a fertilizer-dependent, largely grass, population. In unfertilized plots the clover has been able to compete successfully with grass.

The possible implications of the fert i l izer treatments w i t h respect lodgepole pine establishment are: 1) high rates of N produce high grass yields and the density of t h i s grass may inhibi t development of lodgepole pine, 2) to balance grass and lodgepole pine productivity, it is probably necessary to apply N and S at less than 50 kg/ha.

On nitrogen-deficient soils, clover competes with domestic grasses and forms the major portion of the herbage production. This may inhibit establishment and growth of lodgepole pine as much, or more than, application of f e r t i l i z e r s a t low ra tes .

C. GRASS - SPECIES TRIAL

There were no apparent effects of individual grass species on establishment, survival, or growth of lodgepole pine seedlings. In t h i s t r i a l lodgepole pine seedlings were equally as good, s t a t i s t i c a l l y , f o r al1,treatments. For example, lodgepole pine seedlings growing in competition with the highest producer of herbage (Timothy) were a s t a l l , heavy and abundant as pine seedlings with no grass competition.

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Herbage yields of all grass species, with the exception of orchardgrass and crested wheatgrass, increased annually over the four- year period of measurements. Timothy and red fescue produced significantly higher yields than all other species, and Timothy produced the greatest increase in herbage over the period of the study.

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D. FREQUENCY OF CLIPPING (SIMULATED-GRAZING) TRIAL

The simulation of grazing by harvesting of grass at varying periods throughout the growing season had no significant effect on lodgepole pine seedling survival or total seedling mass. However, seedlings growing with no grass competition were significantly taller than seedlings growing in competition with grass. Although not significant, the total biomass of seedlings on plots with no grass tended to be greater than that of seedlings on grass plots. Whether or not a longer term of competition may have produced significant differences or whether, over a longer term, height differences may have become non- significant, is open to question.

Clipping regime had no significant effect on total yield of herbage although clipping only at the end of the season produced lower yields than from a number of clippings.

The data from this trial indicate that, for management of clearcuts for both grass and tree productivity, grazing during the first half of the annual grazing season would provide medium to high herbage yield and moderate growth of lodgepole pine seedlings.

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SUMMARY AND CONCLUSIONS

Many resource managers advocate delays of one to two years for grazing of clearcuts seeded with grass so as to permit development of, and prevent damage to, newly planted o r regenerated conifer seedlings. Similarly, grazing is not normally recommended until one or two years following grass seeding to assure the establishment of an acceptable stand of grass. The experimental trials in this study suggest that early grazing in terms of both stand life and grawing period would be beneficial to conifer seedling development by reducing grass competition and seed production of grass plants. Maximum productivity of grass can only be obtained at the expense of conifer seedling development and, vice versa, maximum conifer development can only be obtained in the complete absence of grass.

Results of these trials confirm previous recommendations (Clark and McLean, 1978) respecting sowing of legumes to increase soil nitrogen levels, and sowing of grass at reduced rates to minimize early competition with tree seedlings.

The trials indicate further investigations are necessary concerning the effects of fertilizer on competition between grass and pine . VLI"

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LITERATURE CITED

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Baron, F.J. 1962. Effects of different grasses on ponderosa pine seedling establishment. U.S.D.A. Pac. Southwest Forest and Range Exp. Sta. Res. Note 199.

Clark, M.B. and A. McLean, 1975. Growth of Lodgepole pine seedlings in competition with different densities of grass. B.C. Forest Service Res. Note 70.

Clark, M.B. and A. McLean, 1978. Compatibility of grass seeding and coniferous regeneration of clearcuts in the south central Interior of British Columbia. B.C. Forest Service Res. Note 83.

Duffy, P.D. 1974. Planting grass and pine for erosion control. Tree Planters’ Notes 25: 10-13. -

Fober, H. and M. Giertych, 1971. Effect of grass competition on the growth and mineral nut.rition of spruce, Picea abies Karst. Arboretum Kornichie 16: 81-103.

Freyman, S. and A.L. van Ryswyk, 1969. Effect of fertilizer on pine- grass in southern Brit.ish Columiba. J. Range Manage. 22: 390- 395.

Larson, M.M. and G.H. Schubert, 1969. Root competition between ponderosa pine seedlings and grass. U.S.D.A. Rocky Mountain Forest and Range Exp. Sta. Res. Paper RM 54.

New Zealand Forest Service, 1974. Report on Forest Research Institute.

Winston, D.A. 1974. Urea fertilizer toxic to young jack pine seedlings- ””” special precautions needed. Tree Planters’ Notes 25 NO. 2:s-6.