Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091154

    Reassessment of arboreal lichen biomass at the Pinkerton Mountain Silvicultural Systems Site 10 years after partial cutting
Project lead: Coxson, Darwyn (University of Northern British Columbia)
Contributing Authors: Stevenson, Susan K.; Coxson, Darwyn S.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Engelmann spruce-subalpine fir (ESSF) forests of the Interior Wetbelt are the primary winter habitat of the red-listed mountain caribou, and the hair lichens Bryoria spp. and Alectoria sarmentosa are the caribou’s primary winter food. In some parts of the Interior Wetbelt, land use plans currently in effect have zoned some ESSF forests for low-volume partial cutting rather than clearcutting, in an effort to maintain both logging opportunities and habitat for mountain caribou. The Mountain Caribou Recovery Implementation Plan, released October 16, 2007, calls for increased protection of high-suitability mountain caribou habitat, which may result in the transfer of some areas from special management zones to fully protected zones. Currently, Habitat Teams are developing recommendations on the spatial distribution of incremental mountain caribou habitat zones, and associated management guidelines. We understand that some areas are likely to be retained as special management areas zoned for partial cutting and some areas are likely to be designated as corridors, in which partial cutting may also be appropriate. We anticipate that the effectiveness of partial cutting in maintaining habitat for mountain caribou while allowing some timber extraction will continue to be an important management question.

The Mountain Caribou Implementation Plan Terms of Reference: Habitat ( also includes as an objective supporting adaptive management and research to increase the probability of successful recovery. Starting in the late 1980s, an important set of adaptive management trials were established to learn about the potential of low-volume partial cutting to maintain habitat for mountain caribou (Stevenson et al. 1994; 2001). These were designed as long-term trials in which a variety of caribou habitat attributes, including abundance and availability of hair lichens, would be monitored. Although extensive, inventory-level assessments of hair lichen abundance in the lower canopy have been carried out in many partial cuts (reviewed by Stevenson and Coxson 2007), only one ESSF silvicultural systems trial has incorporated detailed studies of the effects of partial cutting on hair lichen dynamics, including biomass, growth rates, litterfall rates, and the microclimate variables that affect the lichens. This site, the Pinkerton Mountain Silvicultural Systems trial, was harvested in 1998. Treatments included a group selection area in which 30% of the volume was removed in openings ranging from 0.1 to 0.4 ha; a single-tree selection area, also with 30% volume removal; and an unlogged control area (Stevenson et al. 1999).

Hair lichens in unharvested stands at Pinkerton Mountain exhibit a distinct vertical zonation, with upper canopy exposures dominated by Bryoria spp. and the lower canopy dominated by Alectoria sarmentosa (Campbell and Coxson 2001). Studies of canopy microclimate and the physiological responses of the lichens indicate that Bryoria spp. in the lower canopy may be limited by intolerance to prolonged wetting, whereas Alectoria sarmentosa in the upper canopy may be limited by greater fragmentation rates (Coxson and Coyle 2003). These observations suggest that over time, the increased exposure that results from partial cutting would cause a relative increase in the proportion of Bryoria to Alectoria in the residual trees. Such a shift would not be an adverse impact, as caribou prefer Bryoria (Rominger et al. 1996). During the two years after harvesting, growth rates of both genera were as high in the single-tree selection area as in the unlogged control area, but were reduced along the edges of group selection openings (Stevenson and Coxson 2003). There appeared to be a small post-harvest pulse of litterfall in the single-tree selection area, but it was largely masked by natural variation (Stevenson and Coxson 2003). Canopy lichen biomass declined slightly in all three treatments during this period, but the only significant treatment-related effect on hair lichens was a decline in upper-canopy Bryoria in the single-tree selection area (Coxson et al. 20030.

Changes in lichen biomass and distribution immediately after harvesting reflected short-term changes in exposure, but the time period was too short to evaluate changes in lichen loading resulting from an altered growth environment. Now, ten years after logging, enough time has elapsed that the lichens will have adapted to the changed environment, and changes in their distribution in the canopy should be evident. Specifically, we anticipate that a) the Bryoria in the upper canopy, which declined in all treatments during the 1998-2000 period, will have recovered, b) there will be an overall increase in the abundance of Bryoria in relation to Alectoria, and c) increased Bryoria abundance will be related to degree of exposure. This detailed information about changes in hair lichen distribution and abundance throughout the canopy will help to explain trends in lower canopy lichen abundance that have been identified in extensive, inventory-level surveys in other partial cuts (Stevenson and Coxson 2007). It will identify relationships between residual basal area after partial cutting and changes in lichen distribution and abundance, and can be used to refine future prescriptions in the ESSF where retention of arboreal lichens is a management objective.

Campbell, J., and D.S. Coxson. 2001. Canopy microclimate and arboreal lichen loading in subalpine spruce-fir forest. Can. J. Bot. 79: 537-555.
Coxson, D.S. and M. Coyle. 2003. Niche partitioning and photosynthetic response of alectorioid lichens from subalpine spruce–fir forest in north-central British Columbia, Canada: the role of canopy microclimate gradients. The Lichenologist 35(2):157-175.
Coxson, D.S., S.K. Stevenson and J. Campbell. 2003. Short-term impacts of partial cutting on lichen retention and canopy microclimate in an Engelmann Spruce-Subalpine Fir forest in north-central British Columbia. Can. J. For. Res. 33:830-841.

Rominger, E.M., C.T. Robbins and M.A. Evans. 1996. Winter foraging ecology of woodland caribou in northeastern Washington. J. Wildl. Manage. 60:719-728.

Stevenson, S.K. and D.S. Coxson. 2003. Litterfall, growth, and turnover of arboreal lichens after partial cutting in an Engelmann spruce-subalpine fir forest in north-central British Columbia. Can. J. For. Res. 33:2306-2320.

Stevenson, S.K. and D.S. Coxson. 2007. Arboreal forage lichens in partial cuts – a synthesis of research results from British Columbia, Canada. Proc. 11th N. Am Caribou Workshop. Rangifer Special Issue No. 17:155-165.

Stevenson, S.K., H.M. Armleder, M.J. Jull, D.G. King, E.L. Terry, G.S. Watts, B.N. McLellan, and K.N Child. 1994. Mountain caribou in managed forests: preliminary recommendations for managers. B.C. Min. For. and B.C. Min. Environ., Lands and Parks. Victoria, B.C. 33 pp.

Stevenson, S.K., M. Jull and D.S. Coxson. 1999. Selection silvicultural systems in mountain caribou habitat: logging and learning at Pinkerton Mountain. Prince George Forest Region Research Note # PG-19. Prince George, B.C. 8 pp.

Stevenson, S.K., H.M. Armleder, M.J. Jull, D.G. King, B.N. McLellan, and D.S. Coxson. 2001. Mountain caribou in managed forests: recommendations for managers: Second Edition. B.C. Min. Environ., Lands, and Parks. Wildlife Rep. No. R-26. Victoria, B.C. 58 pp.


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Updated August 16, 2010 

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