Relative influenceof temperature and disturbance on vegetation dynamics in the low arctic: An investigation at multiple scales
Lantz, Trevor Charles. 2008. University of British Columbia, PhD
Abstract
Climate change will affect Arctic plant communities directly, by altering growth and recruitment,
and indirectly, by increasing the frequency of natural disturbance. Since the structure of northern
vegetation influences global climate, understanding both temperature and disturbance effects on
vegetation is critical. Here, I investigate the influence of temperature and disturbance on Low
Arctic vegetation at several spatio-temporal scales in the Mackenzie Delta Region, N.W.T. To
disentangle the relative impact of temperature and disturbance on forest-tundra and tundra
ecosystems, I sampled micro environmental variability, plant community composition, and green
alder abundance, growth, and reproduction on disturbed (burns and thaw slumps) and
undisturbed sites across a region altemperature gradient. Disturbed areas showed increases in
alder productivity, catkin production, and seed viability, as well as differences in plant
community composition and micro environment. The magnitude of plot-level responses to
disturbance compared to variation across the temperature gradient suggests that in the short-term,
increasing the frequency of disturbance may exert a stronger influence on tundra ecosystems
than changes in temperature. At the plot level,increases in alder seed viability and recruitment
at warmer sites point to the fine-scale mechanisms by which shrub abundance will change. To
examine the relative influence of temperature and biophysical variables on landscape-level
patterns of shrub dominance, I mapped Low Arctic vegetation using aerial photos. At this
broader scale, correlations between temperature and the areal extent of shrub tundra suggest that
warming will increase the dominance of shrub tundra. To assess the magnitude of changes in
temperature and thaw slump activity, I analyzed climate records and mapped retrogressive thaw
slumps using aerial photographs. An increase in thaw slump activity in recent decades,
coincident with higher temperatures, suggests that continued warming will change the area
affected by thermokarst disturbances like slumps. Taken together, my research indicates that the
effects climate change will be magnified by shifts in the frequency of disturbance, initiating
changes to Arctic vegetation with significant implications for global climate. My work also
shows that to fully understand the influence of patch-landscape feedbacks on Arctic vegetation
dynamics, the effects of disturbance must be examined across longer temporal and broader
spatial scales.
