Legacy Tree Guide for the Boise National Forest

Version 1.5 December 2015

i

Table of Contents Introduction ............................................................................................................ 1

Tree Age and Diameter Data Collection on the Boise National Forest............... 3 Legacy Tree Rating Methods ..................................................................................... 9

Part 1—Identifying Legacy and Legacy-Like Trees ......................................... 9 Ponderosa Pine ....................................................................................... 9 Western Larch....................................................................................... 19 Douglas-fir ............................................................................................ 27 Grand Fir .............................................................................................. 32

Part 2—Developing Legacy Tree Characteristics ........................................................ 36 Literature Cited ..................................................................................................... 38 Table of Tables Table 1. Percent of All Trees and Trees with Reliable Ages by Species ......................... 3 Table 2. Percent of Ponderosa Pine, Douglas-fir and Grand Fir Trees in Diameter at Breast High (DBH) Ranges........................................................................................ 4 Table 3. Percent of Ponderosa Pine, Douglas-fir and Grand Fir Trees in Age Ranges ..... 4 Table 4. Percent of Trees that Meet or Do Not Meet Legacy/Legacy-like Characteristics by Species .............................................................................................................. 6 Table 5. Percent of Trees Less Than and Greater Than 150 Years Old and Percent that Meet or Do Not Meet Legacy/Legacy-like Characteristics by Species ............................. 6 Table 6. Percent of Trees with Reliable Ages Less Than or Greater Than 150 Years Old and Less Than or Greater Than 27.5” DBH in Different Breakout Groups ...................... 7 Table 7. Percent of Trees Characterized as Legacy/Legacy-like (N=101) based on Number of Trees with Reliable Ages (N=653) by Age and Diameter Groups. Number of Trees in Each Cell is Number of Legacy and Legacy-like / Number of Trees with Reliable Age ........................................................................................................................ 8 Table 8. Rating System for Determining Young, Mature and Legacy Developmental Stages for Ponderosa Pine Trees ............................................................................. 18 Table 9. Rating System for Determining Young, Mature and Legacy Developmental Stages for Western Larch Trees .............................................................................. 26 Table 10. Rating System for Determining Young, Mature and Legacy Developmental Stages for Douglas-fir Trees ................................................................................... 31 Table of Figures Figure 1. The trees that survived this recent high intensity wildfire are legacies that will create diversity as the stand regenerates ................................................................... 1 Figure 2. Correlation of tree age to tree diameter for grand fir (ABGR), ponderosa pine (PIPO) and Douglas-fir (PSME) ................................................................................. 5 Figure 3. Correlation of tree age to tree diameter for all trees (includes ponderosa pine, Douglas-fir and grand fir) with legacy/legacy-like trees denoted separately .................. 6 Figure 4. Bark patterns on 130+ year old ponderosa pine ........................................ 10 Figure 5. Bark patterns on 270+ year old ponderosa pine ........................................ 11 Figure 6. Whorl-based branch growth on a younger ponderosa pine ......................... 12 Figure 7. Whorl-based branch growth below receding ponderosa pine crown ............. 13 Figure 8. Ponderosa pine bole with knot indicators .................................................. 14 Figure 9. Ponderosa pine bole with obscured knot indicators .................................... 15

ii

Figure 10. Ponderosa pine bole without knot indicators ............................................ 16 Figure 11. Generalized ponderosa pine crown form and tree vigor ............................ 17 Figure 12. Bark of mature western larch ................................................................. 19 Figure 13. Bark of very old western larch ................................................................ 20 Figure 14. Epicormic branches in western larch ....................................................... 21 Figure 15. Epicormic branches below main crown of western larch............................ 22 Figure 16. Large limbs with mature bark in western larch ......................................... 23 Figure 17. Reiterated bole formation in western larch .............................................. 24 Figure 18. Generalized western larch crown form and tree vigor ............................... 25 Figure 19. Bark patterns of trees about 100 – 200 years old ..................................... 27 Figure 20. Hard, thick and furrowed bark on older Douglas-fir ................................... 28 Figure 21. Branch scars on mature trees (left) and epicormics branches at old branch scar (right) ............................................................................................................ 29 Figure 22. Generalized Douglas-fir crown form and tree vigor ................................... 30 Figure 23. Bark on two mature grand fir trees showing smooth, vertical plates typical of this age ................................................................................................................ 32 Figure 24. Mature bark pattern on grand fir ............................................................ 33 Figure 25. Epicormic branches on grand fir ............................................................. 34 Figure 26. Generalized upper crown of old grand firs showing recovery from damage. 35 Figure 27. Indian paint fungus on grand fir, conk circled in yellow ............................ 35 Figure 28. Comparison of stands with high density understory groups (top) to stands with low density understory groups (bottom) ........................................................... 37

1

Introduction Large and old trees are important features within forested ecosystems serving a variety of structural and functional roles. Large trees as well as other sized trees contribute to landscape diversity including vertical heterogeneity in groups, clumps and openings. Old trees display characteristics that distinguish them from younger trees and these characteristics make them unique. Older trees are generally those that have survived past disturbances. These survivors provide continuity between disturbance events by preserving biological diversity through seeds, maintain certain types of habitat and microclimates, and help preserve connectivity within and across landscapes. Franklin et al. (2007) and Perry and Amaranthus (1997) describe these old trees and other survivors of disturbance as “biological legacies”. Kaufmann et al. (2007) and Van Pelt (2008) labeled these types of trees “legacy trees”. In simplest terms legacy trees are those that survived either a previous stand initiating event in lethal fire regimes (Figure 1) or numerous low to moderate intensity disturbance events in the other fire regimes. Legacy trees tend to emerge above younger trees in homogenous stand conditions but can be variable within a stand depending on the topography and amount of time that has elapsed since the last disturbance event. Often legacy trees are open-grown or dominant/co-dominants through different stages of landscape development and as such have larger crowns. They occur as individuals or in clumps and groups. Legacy tree characteristics include deep bark fissures, wide bark plates, altered bark color, flattened or rounded crowns, distinguishing branching characteristics, dead tops, and diverse crown form that generally develop as trees age. These characteristics generally start to develop in trees older than 150 years (Van Pelt 2008). Figure 1. The trees that survived this recent high intensity wildfire are legacies that will create diversity as the stand regenerates

2

Older trees ultimately provide the foundation from which to build restoration actions (Van Pelt 2008) and therefore, it is imperative to be able to recognize them during project planning and implementation. Franklin et al. (2008) state that 8 to 12 legacy trees per acre is an ecologically appropriate target. However, by themselves these trees do not constitute functional old forest habitat. They must occur in combination with other old forest habitat components including snags and large coarse woody debris and in vegetative conditions with the requisite canopy cover, species composition, and vertical and horizontal structure. The bole of legacy trees, by the nature of the structural complexity of their bark surface, can provide numerous microhabitat sites supporting abundant and diverse insect communities which in turn support insectivorous vertebrates (i.e. birds, mammals). Forest stands with residual legacy trees present can exhibit increased wildlife diversity. Legacy trees in conditions that contribute to functional old forest habitat and a few dispersed trees with legacy characteristics can serve as ecological “stepping stones” for species across a landscape (D’amato and Catanzaro 2009). Legacy trees serve a different function than other trees not only when alive but also when dead. Because they are often the older and larger trees in stands they provide a different kind of snag habitat than younger dead trees (Mannan et al. 1980). They often have greater surface area of loose bark, more rot, and larger cavities because of their size. Trees with legacy characteristics often provide greater dead wood medium for arthropods, crevices or cavities for roosting bats, perching sites for raptors and other birds, excavation opportunities for cavity nest or den sites, and a growth substrate for fungi, moss, and lichens than dead trees with less surface area or less structurally complex bark and limbs. They also tend to remain upright longer than younger snags because they have more extensively developed root systems. As described in the 2010 Forest Plan, Appendix E, pages E-27 to E-28, trees with legacy characteristics are integral to the restoration and maintenance of old forest habitat. In addition to the discussion of legacy trees in Appendix E, the 2010 Forest Plan contains a guideline (VEGU08) to retain ponderosa pine and western larch. Though ponderosa pine and western larch legacy trees were specifically identified in VEGU08 due to the Forest Plan emphasis on restoring early seral species, other species that have or can develop legacy characteristics also contribute to old forest habitat. These other species often develop characteristics similar to legacy ponderosa pine and western larch including crown structure, bark thickness and color, heartwood content and evidence of decadence (Franklin et al. 2008). Part 1 of the discussions about ponderosa pine and western larch in this guidebook assist in the identification of legacy trees relative to VEGU08. However, older trees of other species including Douglas-fir and grand fir are also important components of old forest habitat. To differentiate older trees of these species from the species identified in the guideline they are referred to as legacy-like. Part 2 of this document describes some of the stand dynamics by which younger trees develop legacy characteristics. Management activities that take development of legacy tree characteristics into account are important for maintaining functional habitat conditions within landscapes over time.

3

Van Pelt (2008) noted that in eastern Washington there is little relationship between tree diameter and age particularly for species with wide environmental amplitudes. He found that not all old trees were large, and not all large trees were old and subsequently not all large trees were legacies. He concluded that the size trees attain as they age is more a function of environmental conditions than of time. This is an important concept since he found older trees with legacy characteristics were not de facto large. To determine whether this conclusion holds true in different locations, personnel from the Boise National Forest collected information about common tree species growing in the grand fir habitat types. These types represent the most moderate growing conditions on the Boise National Forest and consequently, they represent ideal environments where soil moisture and season length should not constrain plant growth.

Tree Age and Diameter Data Collection on the Boise National Forest Data were collected from 1,538 large (≥20.0” DBH) tree species including ponderosa pine, western larch, Douglas-fir, Engelmann spruce, grand fir and subalpine fir in five areas. Grand fir represented 45 percent of the sample followed by Douglas-fir (31%) and ponderosa pine (20%) (Table 1). Other species contributed only a small amount to the sample. On all trees personnel recorded species, diameter at breast high, and whether or not the tree rated legacy/legacy-like. Ages were collected in four of the sample areas when possible. The ability to age all trees was constrained by the length of the increment borers and presence of rot. For the dataset as a whole, tree ages fell into three categories: 1) no age (data not collected, or too large or too rotten); 2) estimated age (tree sound but could not reach the center or partially rotten and estimated missing years); and 3) reliable age. There were 691 trees with reliable ages 41 percent of which were grand fir followed by Douglas-fir (32%) and ponderosa pine (21%) (Table 1). Grand fir trees tended to have the most rot and subsequently the proportion of grand fir trees with reliable ages was lower than the proportion of grand fir trees sampled. Table 1. Percent of All Trees and Trees with Reliable Ages by Species Species All Trees

N= 1,538 Trees with Reliable Ages

N = 691 Ponderosa Pine 300 20% 146 21% Western Larch 7 <1% 7 1% Douglas-fir 474 31% 222 32% Engelmann Spruce

67 4% 30 4%

Grand Fir 687 45% 285 41% Subalpine Fir 3 <1% 1 <1% Ponderosa pine trees display a greater range of diameters than Douglas-fir or grand fir (Table 2). More than half the Douglas-fir and grand fir fell into the 20.0-24.9” DBH range while only 36 percent of the ponderosa pine occurred in this range. This means that ponderosa pine had the highest frequency of larger trees in the sample areas.

4

Overall, Douglas-fir were the smallest of the three species. In absolute terms, the largest tree in the sample was a 58.8” DBH ponderosa pine though the largest grand fir was close at 58.1” DBH. The largest Douglas-fir was 52.0” DBH. Table 2. Percent of Ponderosa Pine, Douglas-fir and Grand Fir Trees in Diameter at Breast High (DBH) Ranges DBH Range Ponderosa Pine

N = 300 Douglas-fir

N = 474 Grand fir N = 687

20.0-24.9” DBH 36% 65% 51% 25.0-29.9” DBH 29% 25% 28% 30.0-34.9” DBH 19% 7% 12% 35.0-39.9” DBH 10% 2% 6% 40.0-44.9” DBH 4% <1% 2% 45.0-49.9” DBH 2% 0% 1% 50.0-54.9” DBH 0% <1% 0% 55.0-59.9” DBH <1% 0% <1% Grand fir were the youngest trees in the sample followed by Douglas-fir (Table 3). More than half the grand fir fell into the 50-99 year range and 93 percent were less than 150 years old. Slightly less than half the Douglas-fir were in the 50-99 year range and 87 percent were less than 150 years old. Only 19 percent of the ponderosa pine were in the youngest range and only about half (55%) were less than 150 years old. Therefore, both Douglas-fir and grand fir trees were younger than ponderosa pine. Of the trees with reliable ages, the oldest was a 383 year old ponderosa pine. The oldest Douglas-fir was 286 years and the oldest grand fir was 226 years. Table 3. Percent of Ponderosa Pine, Douglas-fir and Grand Fir Trees in Age Ranges Age Range Ponderosa Pine

N = 146 Douglas-fir

N = 222 Grand fir N = 285

50-99 years 21% 45% 57% 100-149 years 34% 42% 36% Total 55% 87% 93%

150-199 years 22% 10% 7% 200-299 years 20% 3% <1% 300-399 years 3% 0% 0% Total 45% 13% 7% The correlation of tree age with diameter was poor (R2=0.39) (Figure 2) which is similar to what Van Pelt (2008) found for trees in eastern Washington. About half the ponderosa pine and grand fir were above and below the age to diameter regression line. However, this was not the case for Douglas-fir since only one-third of the trees were over the line and two-thirds fell below. This means that Douglas-fir diameters tend to be smaller than ponderosa pine and grand fir for trees of similar ages.

5

Figure 2. Correlation of tree age to tree diameter for grand fir (ABGR), ponderosa pine (PIPO) and Douglas-fir (PSME)

Of the 1,461 ponderosa pine, Douglas-fir and grand fir sampled, field personnel rated 13 percent as legacy/legacy-like trees (Table 4). Of the 653 ponderosa pine, Douglas-fir and grand fir with reliable ages, 15 percent were rated as legacy/legacy-like trees ((Table 5). Eighty-five percent of the trees rated as legacy/legacy-like were 150 years or older; only 5 percent of the trees not rated as legacy/legacy-like were over 150 years. All trees over 200 years old but one (a Douglas-fir) rated as a legacy/legacy-like tree (Figure 3). In both the total sample and sample of trees with reliable ages, a greater proportion of ponderosa pine than Douglas-fir or grand fir rated as legacy/legacy-like trees (Table 4 and Table 5). Fewer Douglas-fir than grand fir were identified as legacy-like trees in the overall sample but fewer grand fir in the reliable age sample were identified as legacy-like trees. This difference is likely a reflection of the high rate of rot found in grand fir compared to Douglas-fir which affected the number of grand fir trees with reliable ages. This likely also accounts for the lower proportion of legacy-like grand fir greater than 150 years old since older trees have greater levels of rot.

6

Table 4. Percent of Trees that Meet or Do Not Meet Legacy/Legacy-like Characteristics by Species Species Meets Legacy/Legacy-

like Does Not Meet

Legacy/Legacy-like Ponderosa pine (N = 300) 32% 68% Douglas-fir (N = 474) 6% 94% Grand fir (N = 687) 10% 90% Total (N = 1,461) 13% 87% Table 5. Percent of Trees Less Than and Greater Than 150 Years Old and Percent that Meet or Do Not Meet Legacy/Legacy-like Characteristics by Species

Species

Meets Legacy/Legacy-like

Does Not Meet Legacy/Legacy-like

Total <150 Years

≥150 Years

Total <150 Years

≥150 Years

Ponderosa pine (N = 146) 42% 8% 92% 58% 88% 12% Douglas-fir (N = 222) 10% 17% 83% 90% 95% 15% Grand fir (N = 285) 6% 38% 63% 94% 96% 4% Total (N = 653) 15% 15% 85% 85% 95% 5% Figure 3. Correlation of tree age to tree diameter for all trees (includes ponderosa pine, Douglas-fir and grand fir) with legacy/legacy-like trees denoted separately

7

Based on the regression line, the 150 year age intersects at 27.5” DBH. Table 6 displays the percent of trees with reliable ages based on age groups (<150 and ≥150 years) in the top portion, by species and age groups for trees ≥27.5” DBH in the middle portion and by diameter groups (<27.5” DBH and ≥27.5” DBH) in the bottom portion. Based on age groups, trees less than 150 years old were predominately (80%) smaller than 27.5” DBH; trees greater than 150 years old were predominately (76%) larger than 27.5” DBH. About half (53%) of the trees over 27.5” DBH and less than 150 years old were grand fir and 63 percent of the trees over 27.5” DBH and older than 150 years were ponderosa pine. Based on diameter groups, almost all (94%) trees less than 150 years old are smaller than 27.5” DBH. However, for trees larger than 27.5” DBH the distribution of tree ages is much less straightforward. In the ≥27.5” DBH diameter group, 55 percent were younger than 150 years and 45 percent were older than 150 years. There appears to be no clear age relationship for larger trees. Table 6. Percent of Trees with Reliable Ages Less Than or Greater Than 150 Years Old and Less Than or Greater Than 27.5” DBH in Different Breakout Groups Diameter Percent by Age Groups

<150 Years (N = 538) ≥150 Years (N = 115) <27.5” DBH 80% 24% ≥27.5” DBH 20% 76% Overall 100% 100%

Species Percent by Age Groups for Trees >27.5” DBH

<150 Years (N = 106) ≥150 Years (N = 87) Ponderosa Pine 22% 63% Douglas-fir 25% 21% Grand Fir 53% 16% Overall 100% 100%

Perc

ent b

y D

iam

eter

G

roup

s

Age <150 Years ≥150 Years Overall

<27.5” DBH (N = 460) 94% 6% 100%

≥27.5” DBH (N = 193) 55% 45% 100%

As displayed in Table 5, 15 percent of the trees with reliable ages were characterized as legacy/legacy-like. Of these field personnel rated 15 out of 538 (3%) of the trees <150 years old as legacy/legacy-like (Table 7). Of the trees ≥150 years, field crews rated 86 out of 115 (75%) legacy/legacy-like. Twenty-two out of 460 (5%) of the trees <27.5” DBH and 79 out of 193 (41%) ≥27.5” DBH were rated as legacy/legacy-like. Field personnel were able to interpret the rating system and apply it in a manner that identified older trees. Though the Forest has also used DBH as a method to conserve older trees, diameters appear to have low correlation with age.

8

Table 7. Percent of Trees Characterized as Legacy/Legacy-like (N=101) based on Number of Trees with Reliable Ages (N=653) by Age and Diameter Groups. Number of Trees in Each Cell is Number of Legacy and Legacy-like / Number of Trees with Reliable Age

Diameter Groups Age Groups

<150 Years ≥150 Years Overall <27.5” DBH 2% (8 / 432) 50% (14 / 28) 5% (22 / 460) ≥27.5” DBH 7% (7 / 106) 83% (72 / 87) 41% (79 / 193) Overall 3% (15 / 538) 75% (86 / 115) 15% (101 / 653)

9

Legacy Tree Rating Methods Part 1 of this document outlines a process for identifying legacy ponderosa pine and western larch and legacy-like Douglas-fir and grand fir. The scientific basis for the methodology and rating system described herein was derived almost exclusively from Identifying Old Trees and Forests in Eastern Washington (Van Pelt 2008). Van Pelt’s system rates ponderosa pine, western larch and Douglas-fir (but not grand fir) trees into four categories: 1) Young; 2) Mature <150 years old; 3) Mature ≥150 years old; and 4) Old tree (≥250 years). We expect the majority of trees exhibiting legacy/legacy-like characteristics to be in excess of 150 years of age (as shown in Table 7) and would therefore fall into Van Pelt’s mature ≥150 or old tree categories. For purposes of this field guide all trees that exhibit characteristics of older trees (i.e. meet the rating for mature ≥ 150 years or old) are labeled as legacy or legacy-like. Additional modifications were made, based on professional judgment and tree data, to reflect differences between trees in eastern Washington and the Boise NF. For example, trees in eastern Washington are generally taller than on the Boise NF and tree heights relative to the rating system were adjusted to reflect this difference. Restoring vegetative conditions includes developing trees that will eventually achieve legacy tree characteristics. That is, the intent of the legacy tree concept is not to focus only on the trees we rate as legacies today but also to develop trees that will replace current legacies or create and perpetuate legacy trees where they are missing in the landscape. While the trees that we identify as legacies now are often a product of the pre-1900 historical landscapes, legacies are not intended to be only those trees that were present historically. Not all pre-1900 trees are legacies because not all older trees exhibit legacy tree characteristics. In turn, trees that had not developed legacy tree characteristics before 1900 may now, 100 years later, be achieving them. Therefore, it is important to understand how legacy tree characteristics develop and provide the types, conditions and processes that create individual tree as well as desired stand conditions.

Part 1—Identifying Legacy and Legacy-Like Trees

Ponderosa Pine Legacy ponderosa pine tend to have little terminal leader growth, the top of the crown is generally flattened or appears rounded as the lateral branches reach the same height as the terminal, branches throughout the bole become larger in diameter, and lower branches tend to droop. Huckaby et al. (2003) noted that the majority of trees with large fire scarred cat-faces are legacies since most trees established more recently have not been subjected to the same fire regimes as occurred historically. Like with many tree species that have a wide distribution and ecological amplitude, age and size of ponderosa pine are not closely correlated (Van Pelt 2008). Because ponderosa pine can grow in a wide variety of site conditions ranging from rocky cliffs to riparian zones, the size of the tree often reveals little about its age (Van Pelt 2008). However, the color and condition of the bark, knot indicators on the main trunk of the tree, and the overall form of the tree’s crown help distinguish older from younger trees. These characteristics are used to identify them as legacy trees.

10

Unlike bole diameter, maximum bark plate width is well correlated with tree age (Van Pelt 2008). As the tree ages, the outermost bark continues to flake off, causing the colorful plates of outer bark to get wider, while the width of the dark fissures in between those plates remain relatively constant (Figure 4). Bark plates substantially widen, often more than three times, creating a colorful bark plate in contrast to the darker fissures that separate them. This feature is an indication of older age (Figure 5). Figure 4. Bark patterns on 130+ year old ponderosa pine

From Van Pelt 2008

11

Figure 5. Bark patterns on 270+ year old ponderosa pine From Van Pelt 2008

Ponderosa pine growth is “whorl-based”, like many members of the pine family (Van Pelt 2008). This means that branches arise in a ring versus alternating pattern along the tree bole. This pattern repeats every year so that over time the tree will consist of a series of branch whorls separated by short sections of trunk (Figure 6). Over time, branches in the lower crown die due to shading and/or are pruned by low intensity fire and the lower crown lifts as the tree grows taller (Figure 7).

12

Figure 6. Whorl-based branch growth on a younger ponderosa pine From Van Pelt 2008

13

Figure 7. Whorl-based branch growth below receding ponderosa pine crown

From Van Pelt 2008

14

Dead branches are usually present in the lower crowns of approximately 100 year old trees, but eventually fall off leaving tell-tale signs of knot indicators where the whorled branches once were (Figure 8). As the tree grows, the bark begins to cover up the locations of these former branches – however, residual evidence may be visible on trees older than 200 years (Figure 9). Original branches locations may be completely covered on trees 300 years and older (Figure 10). Figure 8. Ponderosa pine bole with knot indicators

From Van Pelt 2008

15

Figure 9. Ponderosa pine bole with obscured knot indicators

From Van Pelt 2008

16

Figure 10. Ponderosa pine bole without knot indicators

From Van Pelt 2008

17

A number of factors including site productivity and overall tree vigor affect the appearance of a tree of a given age. In general, differences become accentuated with age (Van Pelt 2008). To aid in their identification, a series of crown profiles of trees has been prepared that represent trees of different ages and degrees of vigor (Figure 11) (Van Pelt 2008). Figure 11. Generalized ponderosa pine crown form and tree vigor Idealized forms represent three general age and four vigor classes (A: high vigor to D: low vigor). Vigor is a function of site productivity, response to disturbance and environmental stress. More than one individual is shown for vigor classes B through D to illustrate possible variations. Competition-based mortality usually ensures that most trees in vigor classes C and D do not survive to the next age class.

Generally 80 – 120 years

Generally 150 – 200 years

Generally > 250 years

18

Table 8 contains the characteristics and scoring for rating ponderosa pine trees. As with all field guides, the scoring system provided in this document will not address every situation and application of both professional judgment and common sense will be necessary and is encouraged. Table 8. Rating System for Determining Young, Mature and Legacy Developmental Stages for Ponderosa Pine Trees Lower Bole Bark Condition* Score

Dark Bark with Small Fissures 0 Outmost Bark Ridge Flakes Reddish, Fissures Small 1 Colorful Plates, Plate Width About Equal to Fissure Widths 2 Maximum Plate Width Between Fissures >6 inches and <10 inches 3 Maximum Plate Width Between Fissures >10 inches 5

Knot Indicators on Main Bole Below Crown Score

Dead Branches Below Main Crown, Whorl Indicators Extending Nearly to Tree Base

0

Old Knot/Whorl Indicators Visible Below Main Crown 1 No Knot/Whorl Indicators Visible 3

Crown Vigor (Refer to Figure 11) Score

Similar to a Tree in Top Row 0 Similar to a Tree in Middle Row 3 Similar to a Tree in Bottom Row 5

Developmental Stage Scoring Key**

<2 Young Tree 2 - 5 Mature Tree >6 Legacy Tree

* Determine bark condition on uphill side of tree at d.b.h. ** Choose one score from each category and sum scores to determine developmental stage.

19

Western Larch In some areas, generally moister and cooler environments western larch fills the niche occupied by ponderosa pine (Van Pelt 2008). Like ponderosa pine, western larch is an early seral, shade-intolerant species that most often regenerates on mineral soil produced by disturbances such as fire. Both species evolved to be fire resistant though under different fire regimes. Old, but slender western larch trees can often be found rising above canopies of Engelmann spruce and subalpine fir at higher elevations. Elsewhere under more favorable conditions, western larch can dominate forest stands with subordinate mixes of grand fir, lodgepole pine, and Douglas-fir (Van Pelt 2008). Like ponderosa pine, western larch develops very thick bark with age. Mature trees often have the rugged, grayish-brown bark similar to Douglas-fir (Figure 12). Old trees, greater than 250 years, often develop the richly colored bark of a ponderosa pine (Figure 13). However, the bark transformation from young to mature to old is not as consistent, nor as predictable, as that of ponderosa pine (Van Pelt 2008). Ultimately, other characteristics in addition to bark must be used to approximate tree age (Van Pelt 2008). Figure 12. Bark of mature western larch

Western larch (left) -- Douglas-fir (right). From Van Pelt 2008

20

Figure 13. Bark of very old western larch

Western larch (left) -- ponderosa pine bark (right). From Van Pelt 2008

While western larch branches do not grow in a whorl like ponderosa pine, young trees still develop tiers of branches. As the stand develops, lower branches shed as they become shaded (Van Pelt 2008). Depending on stand density, the crown base will often recede at a rate comparable to the height growth of the stand (Van Pelt 2008). Similar to ponderosa pine, as the tree grows bark begins to cover up the knot indicators of former branches. As the maturing stand thins, light is able to penetrate below the live crown (Van Pelt 2008). Western larch often respond by producing epicormic branches below the base of the live crown (Van Pelt 2008). Epicormic branches, which start from the cambium and not from terminal buds often occur at the axils of branches and twigs, the sites of old branch wounds, or other locations where the bark is thin (Figure 14). The crowns of mature western larch are often a combination of original and epicormic branches, a pattern that becomes accentuated as a tree ages (Van Pelt 2008). Because epicormic branches form on the outside of the bole they can grow in any direction, even tangential to the trunk. Original branches, in contrast, always form perpendicular (radially oriented) to the trunk. If many epicormic branches start from a common locus, a fan-shaped system of branches will result (Figure 15).

21

Figure 14. Epicormic branches in western larch From Van Pelt 2008

22

Figure 15. Epicormic branches below main crown of western larch From Van Pelt 2008

Crown complexity resulting from damage due to prolonged mistletoe infections or physical events can help determine tree age (Figure 16). In a manner similar to the

23

production of epicormic branches, western larch trees have the ability to produce reiterated boles following crown damage (Figure 17). A series of profiles have been prepared to illustrate the crown structures that can occur in western larch during its lifetime, including the variations imposed by site productivity and elevation (Figure 18). Figure 16. Large limbs with mature bark in western larch

From Van Pelt 2008

24

Figure 17. Reiterated bole formation in western larch

From Van Pelt 2008

25

Figure 18. Generalized western larch crown form and tree vigor Idealized forms represent three general age and four vigor classes (A: high vigor to D: low vigor). Vigor is a function of site productivity and response to disturbance and environmental stress. More than one individual is shown for vigor classes B through D to illustrate possible variations. Competition-based mortality usually ensures that most trees in vigor classes C and D do not survive to the next age class.

Generally 80 – 120 years

Generally 150 – 200 years

Generally > 250 years

26

Table 9 contains the characteristics and scoring for rating western larch trees. As with all field guides, the scoring system provided in this document will not address every situation and application of both professional judgment and common sense will be necessary and is encouraged. Table 9. Rating System for Determining Young, Mature and Legacy Developmental Stages for Western Larch Trees Lower Bole Bark Condition* Score

Hard, Bony Bark with Small Fissure 0 Hard Bark with Moderately Deep Fissures (2 to 4 inches) 1 Deep Fissures Present (>4 inches) 3 Maximum Plate Width Between Fissures >6 inches 3

Knot Indicators on Lower One-third of Tree Score

Branch Stubs Present 0 Old Knot/Whorl Indicators Visible 1 No Knot/Whorl Indicators Visible 2

Lower Crown Indicators Score

No Epicormic Branches 0 Small Epicormic Branches Present 1 Large and/or Gnarly Epicormic Branches Present 2

Crown Vigor (Refer to Figure 18) Score

Similar to a Tree in Top Row 0 Similar to a Tree in Middle Row 3 Similar to a Tree in Bottom Row 5

Development Stage Scoring Key**

<3 Young Tree 3 - 6 Mature Tree >7 Legacy Tree

* Determine bark conditions on the uphill side of tree at d.b.h. ** Choose one score from each category and sum scores to determine developmental stage.

27

Douglas-fir Douglas-fir characteristics are similar to those of ponderosa pine and western larch. However, Douglas-fir is more shade tolerant than these two species and as such can persist in the understory longer than shade-intolerant species. For this reason and because it is the most wide-spread of all the conifers on the Boise NF, it occupies a wide variety of site conditions from low to high elevation and everything from warm, to cold, to dry and to mesic aspects age and size are even less well correlated than for other species (Van Pelt 2008). Though Douglas-fir is less fire tolerant than ponderosa pine and western larch when young, old Douglas-fir trees are very fire resistant. This is a function of the protective bark that develops as a tree ages. Bark thickens over time developing a hard and bony, brown to gray color between 100 to 200 years old (Figure 19). The bark on older trees is much thicker, coarser and rougher with deeper furrows (Figure 20). Figure 19. Bark patterns of trees about 100 – 200 years old

From Van Pelt 2008

28

Figure 20. Hard, thick and furrowed bark on older Douglas-fir From Van Pelt 2008

Like ponderosa pine, Douglas-fir growth is “whorl-based” (Van Pelt 2008). Over time, branches in the lower crown die from shading lifting the crown as the tree grows taller. Many branches, after they die, rot at the base and drop off the tree leaving a small scar (Figure 21). Eventually the scars disappear but occasionally epicormics branches may form at these sites (Figure 21).

29

Figure 21. Branch scars on mature trees (left) and epicormics branches at old branch scar (right)

From Van Pelt 2008

Over time trees transition from a conical, whorl-based crown form to a variety of shapes depending on past stand disturbances, shading, damage and etc. Idealized profiles of Douglas-fir crowns are shown in Figure 22.

30

Figure 22. Generalized Douglas-fir crown form and tree vigor Idealized forms represent three general age and four vigor classes (A: high vigor to D: low vigor). Vigor is a function of site productivity, response to disturbance and environmental stress. More than one individual is shown for vigor classes B through D to illustrate possible variations. Competition-based mortality usually ensures that most trees in vigor classes C and D do not survive to the next age class.

Generally 80 – 120 years

Generally 150 – 200 years

Generally > 250 years

31

Table 10 contains the characteristics and scoring for rating Douglas-fir trees. As with all field guides, the scoring system provided in this document will not address every situation and application of both professional judgment and common sense will be necessary and is encouraged. Table 10. Rating System for Determining Young, Mature and Legacy Developmental Stages for Douglas-fir Trees Bark Conditions, Lower one-third of Tree* Score

Hard, bony bark with small fissures 0 Hard bark with moderately deep fissures 1 Deep fissures present (> 4 inches) 3

Knot Indicators, Lower one-third of Tree Score

Branch stubs present 0 Old knot/whorl indicators visible 1 No Knot/Whorl Indicators Visible 3

Lower Crown Indicators Score

No epicormics branches 0 Small epicormics branches present 1 Large and/or gnarly epicormics branches present 3 Crown Form (refer to Figure 22) Score Similar to tree in top row 0 Similar to tree in middle row 3 Similar to tree in bottom row 5

Developmental Stage Scoring Key** <3 Young Tree

2 - 6 Mature Tree >7 Legacy Tree-like

* Determine bark condition on uphill side of tree at d.b.h. ** Choose one score from each category and sum scores to determine developmental stage.

32

Grand Fir No rating system has been developed for grand fir. Legacy-like determination is based on the descriptions below. Grand fir is the climax species and as such is the most shade tolerant of the conifers where it occurs. A fire sensitive species, older trees are generally found in microsites that historically burned less often or on aspects that burned less frequently. The bark does not develop the same fire resistant characteristics as ponderosa pine and Douglas-fir which can both occur on the same sites as grand fir. Young trees have smooth bark which as the tree grows develop finely-dissected fissures that isolate the smooth outer bark plates into tidy, vertical ridges (Figure 23). Unlike other species, an even pattern of gray bark persists into maturity and older age (Figure 24). Figure 23. Bark on two mature grand fir trees showing smooth, vertical plates typical of this age

From Van Pelt 2008

33

Figure 24. Mature bark pattern on grand fir From Van Pelt 2008

Grand fir, like western larch and Douglas-fir, produce epicormic branches to fill in crowns. As conditions around a tree change, gaps in the canopy allow light to penetrate lower into the crown stimulating the development of branches where previously lost (Figure 25). Grand fir trees also have the capacity to re-build damaged portions of their crowns through reiterated trunks which results in forking and other types of crown form (Figure 26). Older grand fir are also often infected with Indian paint fungus which produces extensive rot and for this reason older trees are often too rotten to age (Figure 27).

34

Figure 25. Epicormic branches on grand fir From Van Pelt 2008

35

Figure 26. Generalized upper crown of old grand firs showing recovery from damage From Van Pelt 2008

Figure 27. Indian paint fungus on grand fir, conk circled in yellow From Van Pelt 2008

36

Part 2—Developing Legacy Tree Characteristics Huckaby et al. (2003) theorized that older trees had likely developed as open-grown early in stand development possibly because they lacked competition and therefore were less susceptible to competitive mortality or were less likely to be destroyed by fire. Legacy trees display many of the characteristics of open-grown trees: they generally grew fast when younger and therefore tend to have larger diameters relative to their age; they are often the taller trees in a stand; and they have relatively large crown widths and substantial branches. Franklin et al. (2008) point out that it is important to manage a proportion of younger age classes present in stands to replace trees with legacy characteristics over time. Accomplishing this requires understanding the processes and conditions under which trees currently defined as legacy likely developed. Franklin and Van Pelt (2004) described stand development following lethal disturbance noting that stands starting as an even-aged cohort differentiate over time from a variety of processes. Though tree mortality is the agent of change, processes, patterns and consequences of mortality evolve through stand development. For example, the effects of low intensity fire may be greater in younger trees compared to older trees while the effects of bark beetles may be greater in older trees than younger trees. For individual trees, many of the characteristics they develop as they age are a function of what happens to them in younger stages and in many cases opportunities to develop certain characteristics may be lost over time. In Figure 27 the understory setting of the stand in the top compared to the bottom photograph will result in different individual tree characteristics as the stands progress through time. Without some form of adjustment in the high density patches, many of these trees may not develop legacy tree characteristics. However, while promoting the characteristics of individual trees, it is important to also promote the complexity of groups and clumps that contribute to functional habitat. The top photo in Figure 27 displays a greater variety of overstory groups and clumps than the bottom photo. This greater complexity provides for a greater diversity of habitats for a variety of species.

37

Figure 28. Comparison of stands with high density understory groups (top) to stands with low density understory groups (bottom)

38

Literature Cited D’amato, A.; Catanzaro, P. 2009. A forest manager’s guide to restoring late-

successional forest structure. Amherst, MA: Mass Extension Publication, 8 pages. Huckaby, L.S.; Kaufmann, M.R.; Fornwalt, P.J.; Stoker, J.M.; Dennis, C. 2003.

Identification and ecology of old ponderosa pine trees in the Colorado Front Range. Gen. Tech. Rep. RMRS-GTR-110. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 47 pages.

Franklin, J.F.; Hemstrom, M.A.; Van Pelt, R.; Buchanan, J.B.; Hull, S. 2008. The case

for active management of dry forest types in eastern Washington: perpetuating and creating old forest structures and functions. Olympia, WA: Washington State Department of Natural Resources, 97 pages.

Franklin, J.F.; Van Pelt, R. 2004. Spatial aspects of structural complexity in old-growth

forests. Journal of Forestry, April/May: 22-28. Kaufmann, M. R.; Binkley, D.; Fulé, P. Z.; Johnson, M. S.; Stephens, L.; Swetnam, T.

W. 2007. Defining old growth for fire-adapted forests of the western United States. Ecology and Society 12(2): 15. [online] URL: http://www.ecologyandsociety.org/vol12/iss2/art15/

Mannan, R.W.; Meslow, E.C.; Wight, H.M. 1980. Use of snags by birds in Douglas-fir

forests, western Oregon. Journal of Wildlife Management, 44(4): 787-797. Perry, D.A.; Amaranthus, M.P. 1997. Disturbance, recovery, and stability. In: Kohm,

K.A.; Franklin, J.E (Eds.), Creating a Forestry for the 21st Century: The Science of Ecosystem Management. Island Press, Washington, DC, pp. 31-56.

Van Pelt, R. 2008. Identifying Old Trees and Forests in Eastern Washington. Olympia,

WA: Washington State Department of Natural Resources, 166 pages.