Akhalkatsi, Maia , Abdaladze, Otar , Smith, William K. , Nakhutsrishvili, George .
Mechanisms of Treeline Stability in the Caucasus Mountains of Georgia: Low-temperature Photoinhibition and Interspecific Facilitation.
Detailed descriptions of species composition and abundance have shown that birch (Betula litwinowii Doluch.) forests form the timberline/treeline at elevations ranging from 2100 to 2500 m a.s.l. in the Kazbegi Region, Central Caucasus, Georgia. Dwarf and small trees occur at treeline, while larger trees formed an intact subalpine forest at lower elevations. Important differences in leaf morphology and physiology occurred between dense forest, timberline trees, and individuals at treeline. In addition, natural treeline ecotones at the highest altitude consist of an association with the evergreen shrub, Rhododendron caucasicum Pall., that may represent an example of strong ecological facilitation between two species. Microclimatic data at all sites showed a decrease in minimum air temperatures and increases in incident sunlight with greater altitude, accompanied by low temperature photoinhibition of photosynthesis. Leaf, air, and soil temperatures were at least several degrees warmer inside the canopy of R. caucasicum, while instantaneous and total daily sunlight was reduced by over 50%. Additionally, the microclimate at the highest sites showed amelioration of these same photoinhibitory factors by R. caucasicum. Field and laboratory experiments are underway and designed to evaluate relationships between birch seedling establishment patterns and microhabitat characters of both the higher sites with R. caucasicum and the lower sites without. Thus, timberline/treeline in the Caucasus Mountains appear to be dependent on new seedling establishment away from the forest edge, microsite facilitation by another associated species, and low temperature photoinhibition, which limits photosynthetic carbon gain. Evidence is also presented that points to the possibility that treeline is currently undergoing a shift toward higher altitude, jeopardizing the alpine component of species diversity in these mountains.
1 - Wake Forest University, Department of Biology, P.O. Box 7325, Winston-Salem, North Carolina, 27109-7325, U.S.A.
2 - Georgian Academy of Sciences, Institute of Botany, Plant Reproduction Research, Kojori Road 1, Tbilisi, 0105, Republic of Georgia
Presentation Type: Paper
Location: Wasatch (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 9:15 AM