Relative impacts of disturbance and temperature: persistent changes in microenvrionment and vegetation in retrogressive thaw slumps
Lantz, T.C., Kokelj, S.V., Gergel, S.E. and Henry, G.H.R. 2009. Global Change Biology 15: 1664-1675
Abstract
In the Low Arctic, a warming climate is increasing rates of permafrost degradation and
altering vegetation. Disturbance associated with warming permafrost can change microclimate
and expose areas of ion-rich mineral substrate for colonization by plants.
Consequently, the response of vegetation to warming air temperatures may differ
significantly from disturbed to undisturbed tundra. Across a latitudinal air temperature
gradient, we tested the hypothesis that the microenvironment in thaw slumps would be
warmer and more nutrient rich than undisturbed tundra, resulting in altered plant
community composition and increased green alder (Alnus viridis subsp. fruticosa)
growth and reproduction. Our results show increased nutrient availability, soil pH,
snow pack, ground temperatures, and active layer thickness in disturbed terrain and
suggest that these variables are important drivers of plant community structure. We also
found increased productivity, catkin production, and seed viability of green alder at
disturbed sites. Altered community composition and enhancement of alder growth and
reproduction show that disturbances exert a strong influence on deciduous shrubs that
make slumps potential seed sources for undisturbed tundra. Overall, these results
indicate that accelerated disturbance regimes have the potential to magnify the effects
of warming temperature on vegetation. Consequently, understanding the relative effects
of temperature and disturbance on Arctic plant communities is critical to predicting
feedbacks between northern ecosystems and global climate change.
Key Words
climate change, disturbance ecology, green alder, ground ice, Low Arctic, Mackenzie delta, permafrost, shrub encroachment, tall shrub, thermokarst
