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LANDSCAPEAND URBANPLANNING

Landscape and Urban Planning 72 (2005) 95-112 This article is also available online at: www.elsevier.com/Iocate/landurbplan

Potential management of young-growth stands for understory vegetation and wildlife habitat in southeastern Alaska Thomas A. Hanley* USDA Forest Service, Pacific Northwest Research Station, 2770 Sher~vood Lane, Suite 2-A, Juneau, AK 99801, USA

Abstract

I review the current state of knowledge about dynamics of understory vegetation in postlogging succession and responses to silviculture treatments in southeastern Alaska, and I derive implications for future research and development. The classic Alaback [Ecology 63 (1982) 1932] model of postlogging succession has dominated ecological thinking in the region for the past two decades. Understory vegetation is believed to increase dramatically immediately after logging but decrease to near-zero levels as the young stands attain conifer canopy closure. Depauperate understories are believed to persist for >100 years. Early studies indicated that understory response to thinning of even-aged stands is mainly by dominant shrubs and is short-lived; response by herbs, especially forbs, is slight. Western hemlock (Tsuga heterophylla) was identified as a potential long-lived, second layer, understory dominant in stands thinned to wide spacing. Recent studies, however, indicate three important deviations from conventional wisdom: (I) Red alder (Alnus rubra)-conifer, even-aged standsproduce species-rich and high-biomass understories comparable to those of old-growth forests and much greater than similar-aged pure conifer stands. (2) "Commercial thinning" of older, even-aged stands may result in much greater understory biomass, including forbs, than previously thought, but time requirements might be longer than previously thought. (3) Extrapolation of data from small scales of research plots to large scales of timber-management stands tends to greatly overestimate stand homogeneity and underestimate understory biomass of even-aged conifer stands. The new findings provide a basis for renewed research into even-aged stand management in southeastern Alaska. I suggest a iwo-pronged approach emphasizing autecological studies of light and soil requirements of major understory species coupled with an "engineering" approach to designing optimal understory environments through silviculture. New silviculture prescriptions can be designed for specific understory objectives. Testing and application of new prescriptions is recommended at the scale of timber-management stands through adaptive management studies in collaboration between the Pacific Northwest Research Station and the Tongass National Forest. © 2004 Elsevier B.V. All rights reserved. Keywords: Silviculture; Forest management; Even-aged forests; Clearcutting: Picea sitchensis; 7kuga heterophylla

1. I n t r o d u c t i o n

* Tel.: +I 907 586 881 Ix250; fax: +1 907 586 7848. E-mail address: [email protected]. 0169-2046/$20.00 © 2004 Elsevier B.V. All rights reserved. doi: 10.1016/j.landurbplan.2004.09.015

Clearcui logging has been the predominant timbermanagement practice in southeastern Alaska since the advent of large-scale logging in the 1950s. It is a

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T.A. Hanley / I-zmdscape and Urban Planning 72 (2005) 95-112

preferred harvest method for a number of silvicultural reasons (Ruth and Harris, 1979): (1) The old-growth western hemlock (Tsuga heterophylla) and Sitka spruce (Picea sitchensis) forests have much defective timber (dead or dying trunks) that is best removed from the new stand. (2) Maximum opening of the forest canopy provides maximum light and soil temperature for regenerating trees. (3) The more commercially valuable Sitka spruce is less shade tolerant than is western hemlock. (4) Physical damage of residual trees, eventually leading to disease, is minimized in the regenerating stand. (5) Logging costs per unit of timber harvested are least with the clearcut method. However, natural overstocking of the regenerating stand is a common silvicultural problem following clearcutting of the hemlock-spruce forests (Harris and Farr, 1974). Even-aged forests resulting from clearcutting are widespread in southeastern Alaska, and clearcutting is expected to continue as a harvest technique. At the close of year 2000, there were over 160,000ha of Tongass National Forest and about 85,000 ha of Alaska Native corporation forests in an even-aged condition (Eugene DeGayner et al., USDA Forest Service, Alaska Region, Juneau, AK, unpublished report based on data in Forest Service files). The record of decision on the 1997 Tongass Land and Resource Management Plan projected an additional 35,000 ha harvested per decade, with 80% of that harvest by clearcutting. About 100,000ha of Alaska Native Corporation forests not yet harvested will likely be harvested by clearcutting. Although clearcut logging is a highly preferred timber-management practice, it is recognized as having negative consequences for wildlife habitat in southeastern Alaska, primarily because of its effects on understory vegetation in the regenerating stand (Wallmo and Schoen, 1980; Schoen et al., 1981, 1988; Samson et al., 1989; Hanley, 1993). Dense conifer regeneration and canopy closure result in a very depauperate understory from about 25-150 years stand age (Alaback, 1982, 1984a, 1984b). Understory vegetation is very important as food for herbivores and as cover for ground-nesting and ground-foraging birds and small mammals. Silvicultural thinnings of young stands have shown few encouraging results for long-term maintenance of a diverse and productive understory (Alaback and Tappeiner in Hanley et al., 1989, pp. 5--6; Deal and Farr, 1994). Recent observations, however, indicate new potentials for young-growth management along

two lines of approach very different from earlier thinking: (I) inclusion of red alder (Alnus rubra) in the regenerating stand, leading to an alternative pathway of secondary succession (Hanley and Barnard, 1998); and (2) commercial thinning of older, even-aged conifer stands (Zaborske et al., 2002). The purpose of this paper is to review the evolution of knowledge about even-aged stand management for understory vegetation in southeastern Alaska, to examine potentials for new approaches based on the most recent findings, and to suggest implications for the future for both research and application.

2. Empirical evidence and theoretical considerations The 1982 Ecology paper by Paul Alaback (Alaback, 1982), based on his Ph.D. research of understory response to postlogging succession, became a classic in the ecological literature for southeastern Alaska. It described the pattern of understory biomass and production along a chronosequence of 60 stands ranging from 3 to >550 years of age, with greatest emphasis on stands 10 times the canopy coverage of the understory of an adjacent predominantly spruce stand. All stands were even-aged and riparian; the mixed alder-conifer stands were 45 years old, and the spruce stand was 26 years old. Wipfli (1997) found significantly greater abundance of terrestrial-derived invertebrates in stream water from even-aged 3 I-yearold alder forests than from old-growth hemlock-spruce forests. He attributed the greater invertebrate abun-

dance to the deciduous overstory and to an understory that was both more species-rich and more "dense" in the alder than in the old-growth forests. All three of those studies highlighted the fact that there exists more than one potential postclearcutting successional pathway in southeastern Alaska, at least within riparian forests. General observations of upland forests quickly lead to extending the alder successional pathway to uplands as well. When large-scale clearcutting began in the 1950s, most logging was done with bulldozers, tractors, and "A-frame" yarding systems (methods of dragging logs to a central site) and resulted in much soil disturbance. Red alder quickly became established on such heavily disturbed sites, and many even-aged stands from the 1950s are mixtures of alder and conifer (western hemlock and Sitka spruce) today. With the advent of high-lead yarding systems in the 1960s, however, soil disturbance was minimized, and red alder did not become a significant component of even-aged stands, except along roads and landings. Thus, there exists an extensive red alder component in upland, even-aged stands throughout the Tongass National Forest, but it is largely limited to a narrow range o f stand ages. Alaback (1.982) purposely excluded red alder when selecting his stands for study, because he was interested in future implications of postlogging succession, and logging practices by then had virtually excluded red alder from the successional pathway.

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Table 2 Understory species composition (production of current annual growth, kg/ha) of two major community associations within upland, old-growth forests of southeastern Alaskaa Blueberry/Goldthread associationb

Blueberry/Skunkcabbage associationc

Forbs Coptis asplenifolia Comus canadensis* Listera cordata Lysichiton amertcanum " * Lycopodium spp. Maianthemum dilatatum Moneses uniflora Rubus pedatus Streptopus amplex(folius Streptopus spp.* Tiarella trifoliata Viola glabella

4.5 4- 1.4 23.9 4- 5.0 0.2 4- 0.1 0 4- 0 0.4 4- 0.4 5.4 4- 3.6 6. I 4- 1.6 14.7 4- 1.5 0.2 4- 0.1 0.5 -t- 0.1 4.0 4- 1.8 O. 1 -4- O. I

5.6 4- 2.6 41.6 + 6.3 1.3 4- 0.6 107.2 + 29.9 6.4 4- 5.5 4.14- 1.2 5.9 :k 1.2 13.9 4- 1.6 04-0 0.25:0.1 1.8 4- 0.8 0.5 5:0.3

Ferns Athyriumfilix-femina Blechnum spicant Dryopteris dilatata* Gymnoearpium dryopteris

4.3 4- 2.3 12.8 -t- 6.4 7.7 + 2.8 10.6 4- 3.6

2.6 4- 1.9 19.3 4- 10.9 0.1 :t: 0.1 3.9 4- 1.6

0 4- 0

0.9 4- 0.6

Shrubs Gaultheria shallon Menziesiaferruginea Oplopanax horridum Rubus spectabilis Vaccinium ovalifolium d Vaccinium parvifolium Vaccinium spp. e

0.3 4- 0.3 15.6 4- 7.5 6.2 4- 4.8 7.3 + 4.1 97.4 4- 13.3 0.4 4- 0.3 10.5 5:2.9

6.1 :t:3.5 73.9 4- 14.6 2.2 4- 1.3 6.6 4- 6.6 128.5 4- 21.3 0.8 4- 0.6 8.7 4- 3.4

Conifers (seedlings) Picea sitchensis Thuja pl&ata Tsuga heten)phylla

10.5 4- 9,9 2.3 4- 1.6 26.2 5:9.7

1.6 4- 1.6 0.1 4- 0.1 35.8 4- 22.5

Graminoids Carex spp.

Values are mean 4- S.E. * Species that differ statistically (P < 0.05) between the two associations. a Data from Hanley and Brady (1997). All values are oven-dry weight. Only species with >1.0 kg/ha in any stand are included. b N= 19 stands, Admiralty and Prince of Wales Islands. c N= 12 stands, Admiralty and Prince of Wales Islands. d Includes V. alaskensis. e Immature, decumbent, evergreen form of V. ovalifolium, V. alaskensis, and E parviJblium. H a n l e y a n d B a r n a r d ( 1 9 9 8 ) f o l l o w e d up the initial r i p a r i a n o b s e r v a t i o n s with a study o f u n d e r s t o r y c o m p o s i t i o n a n d b i o m a s s in 16 e v e n - a g e d , m i x e d a l d e r - c o n i f e r s t a n d s on u p l a n d sites. T h e s t a n d s w e r e 2 8 - 3 9 y e a r s old w h e n studied a n d r a n g e d in size f r o m l 0 to 1 0 0 h a . H a n l e y a n d B a r n a r d used w i t h i n stand, m i c r o s i t e (80 m 2) variation to c o m p a r e u n d e r story species c o m p o s i t i o n a n d b i o m a s s u n d e r pre-

d o m i n a n t l y alder, m i x e d , a n d c o n i f e r o v e r s t o r i e s (microsites). T h e y f o u n d that b i o m a s s o f f o r b s a n d ferns were s i g n i f i c a n t l y g r e a t e s t u n d e r a l d e r overstory, least u n d e r c o n i f e r overstory, a n d i n t e r m e d i a t e u n d e r m i x e d o v e r s t o r y (Table 4). S p e c i e s c o m p o s i t i o n o f a l d e r microsites, however, t e n d e d to be m o r e s i m i l a r to w e t or r i p a r i a n sites than to species m o r e c h a r a c t e r i s t i c o f u p l a n d sites. For e x a m p l e , R u b u s s p e c t a b i l i s , Cir-

T.A. Hanley / lz, ndscape a'nd Urban Planning 72 (2005) 95-112

101

Table 3 Biomass (kg/ha, oven-dry weight) of understory species in three forest typesa Class/species Forbs Actaea rubra Circaeaalpina Coptis asplenifolia Comus canadensis Galium kamtschaticum Heracleum lanatum Impatiens noli-tangere Lysichiton americanum Maianthemum dilatatum Moneses uniflora Osmorl, iza spp. Streptopus amplexifolius Streptopus streptopoides llarella trifoliata Viola glabella Total forbs Ferns Athyriumfilix-femina Dryopteris dilatata Gymnocarpium dryopteris Polystichum braunii Thelypteris phegopteris Total ferns Shrubs Menziesia ferruginea Oplopanax horridum Ribes bracteosum. Rubus spectabilis Vaccinium alaskensis Vaccinium ovalifolium Total shrubs Total vascular biomass

Red alder riparian

Old-growth riparian

Old-growih upland

2 4- I 194-2 b 0 4- 0 0 4- 0 t 4- t 4 5:4 3 4- 3 25 4- 25 13 4- 7 t 4- t a 4 4- 1 b 3 4- 1 0 4- 0 21 4- 7 5 4- 1

t 4- t 154- 1 b 0 4- 0 0 4- 0 2 4- 1 3 4- 3 0 4- 0 0 4- 0 5 4- 3 t 4- t a t 4- t a 6 4- 3 t 4- t 30 4- 6

0 4- 0 1 4- 1 a 6 4- 4 15 4- 6 0 4- 0 0 4- 0 0 4- 0 185 4- 135 9 4- 2 3 4- 1 b 0 4- 0 a 1 4- t 1 4- 1 3 4- 3

5 4- 3

1 q- 1

97 5:2

64 4- 12

224 5:136

196 4- 112 31 4- 11 37 4- 7 10 4- 10 4 4- 2

122 4- 41 11 4- 5 108 4- 28 21 4- 16 0 4- 0

3 4- 3 4 4- 3 8 4- 4 0 4- 0 0 4- 0

277 4- 97

261 4- 89

15 4- 4

t± t 920 4- 150 ab 1165 4- 275 83 4- 78 . 0 4- 0 a • 0 4- 0 a

0 -b 0 2365 4- 35 b 1445 4- 555 0 4- 0 0 4- 0 a - 0 4- 0 a

475 4- 345 t 4- t a 100 4- 100 50 -I- 0 965 4- 185 b 1125 q- 95 b

2225 4- 165

3845 4- 555

2715 4- 155

2599 4- 67

4170 4- 655

2953 4- 23

Values are mean + S.E. N= 2 stands of each forest type. Values with different alphabetic letters within a row differ at the alpha level of 0.05. t = trace = 20 kg/ha and herbs with >2 kg/ha within a stand are listed. See Hanley and Hoel {.1996) for other species. c a e a a l p i n a , G a l i u m t r i f l o r u m , Tiarella trifoliata, Viola

1999b) s t u d i e d f o o d r e s o u r c e s , d i e t c o m p o s i t i o n , a n d population dynamics of Keen's mouse (Peromyscus

g l a b e l l a , A t h y r i u m f i l i x - f e m i n a , G y m n o c a r p i u m dryo p t e r i s , a n d Thelyptel"is p h e g o p t e r i s all are s p e c i e s m o r e c h a r a c t e r i s t i c o f r i p a r i a n f o r e s t s than o f u p l a n d

keeni) in e v e n - a g e d r e d a l d e r r i p a r i a n , o l d - g r o w t h riparian, beaver-pond floodplain, and old-growth upland

f o r e s t s ( c o m p a r e w i t h T a b l e 3). The species-rich and productive understory of red alder and mixed alder-conifer stands has important

f o r e s t s a n d f o u n d o n l y m i n o r d i f f e r e n c e s in d i e t c o m p o s i t i o n a n d n o s i g n i f i c a n t d i f f e r e n c e s in p o p u l a t i o n d y n a m i c s b e t w e e n habitats. S p e c i e s o f f o o d r e s o u r c e s

i m p l i c a t i o n s for w i l d l i f e . H a n l e y a n d B a r n a r d ( 1 9 9 9 a ,

d i f f e r e d b e t w e e n h a b i t a t s , a n d a b u n d a n c e o f f o o d re-

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T.A. Hanley / Landscape and Urban Planning 72 (2005) 95-112

Table 4 Understory biomass (kg/ha, oven-dry weight) of"alder", "conifer", and "mixed" microsite types across sixteen 28-3%year-old red alder-conifer stands in Tenakee Inlet, Alaskaa Class/species

-Alder

Conifer

Mixed

Forbs

Actaea rubra . Circaea alpina Coptis asplenifolia Comus cantutensis Galium triflorum Heracleum lanatum Lysichiton americanum Maianthemum dilatatum Mitella penmndra Prenantheses alata Rubus pedatus Streptopus amplexifolius Stellaria crispa Tiarella trifoliata Viola glabella Total forbs

0.4 4- 0.3 9.5 4- 2.6 b

O. I 4- O. I O. i 0.4 - 8.9 1.0 4. I

44444-

O. I 0.2 b 4.3 1.0 1.4 O. 1 -4- O. 1 0.2 4- 0.1 O. 1 4- O. 1 4.7 4- 1.9 0.2 4- 0.2 12.2 4- 2.8 b 0.8 4- 0.2 c

0 4- 0 1.0 4- 0.5 a

O. 1 4- O. 1 0.5 4t 4- t a 0+ 0 1.7 41.4 40 4- 0 0 4- 0 O. 1 44.3 40 4- 0 2.9 4t 4- t a

0.3

04-0 2.9 4- t .2 a 0.1 4-0.1 0.1 4-0.1

t 4- t ab 1.3 0.2

O. 1 1.5 0.6 a

42.9 4- 5.7 c

12.4 4- 2.5 a

0.4 4- 0.3 56.5 4- 9.0 b

0 4- 0 7.5 4- 5.6 a

4.8 0.1 2.5 0.1 0-4-0 0.1 11.0 04-0 5.2 0.1

4- 3.0 4-0.1 4- 0.6 4-0.1 4-0.1 4- 4.5 4- 1.4 a 4- 0.1 b

27.1 4- 5.3 b

Ferns

Adiantum pedatum Athyriumfilix-femina Blechnum spicant Dryopteris austriaca Gymnocarpium dryopteris Thelypterisphegopteris Total ferns

O. 1 4- O. 1

O. 1 4- O. 1

13.0'4- 1.9 40.7 5:5.5 c 8. I 4- 2.3 c

10.6 4- 2.0 7.5 :t: 1.1 a 0.9 5:0.5 a

118.8 4- 11.8 c

26.5 4- 7.9 a

0+0 24.8 40.3 418.5 421.9+ 1.0 4-

7.8 ab 0.3 3.5 3.8b 0.4 b

66.64- 11.1 b

Graminoids

Carex mertensii Luzula parviflora Trisetum cernuum

0. I 4- 0.1 0.5 4- 0.4

O. 1 :t: O. 1

0 4- 0 0.2 4- 0.2 t 4- t

0+0 04-0 0±0

Total graminoids

0.7 4- 0.4

0.2 4- 0.2

04-0

Shrubs

Menziesia ferrugbtea Oplopanax horridum Ribes bracteosum Rubus spectabilis Sambucus racemosa Vaccinium ovalifolium Total shrubs

t 4- t 236.9 22. I 86. I 7.7 14.8

44444-

94.7 11.5 36.5 b 6.7 t2.5

367.5 4- 105.7 b

6.8 212.7 2.4 62.7 0.5 70.8

444444-

6.8 133.1 2.3 24.5 b 0.5 44.7

0.5 33.7 0.2 8.8 29.0 8.6

355.9 4- 147.8 b

444444-

0.4 30.7 0.2 3.9 a 27.2 5.4

80.8 4- 44.5 a

Conifer seedlings

Picea sitchensis Tsuga heterophylla

20.3 4- 10.8 19.8 4- 19.8

0 4- 0 3.2 4- 3.1

04-0 0:k0

Total conifers

40.1 4- 21.2

3.2 4- 3. I

04-0

Total vascular biomass

570.0 4- 111.0 b

398.3 4- 147.7 ab

,

175.44-54.6a

Values are mean 4- S.E. Values with different alphabetic letters within a row differ at the alpha level of 0.05. t = trace =