Linking deterministic and stochastic processes of succession to understand drivers of ecological resilience

Background/Question/Methods

Recognizing the important role of non-equilibrium dynamics in succession has been a complicated and non-linear process, and one in which Chapin has left important legacies. This presentation explores how building a mechanistic understanding of successional processes has helped develop successional models that incorporate factors such as feedbacks and path dependence in a dynamic system. We use three case studies of vegetation succession in high-latitude forests to highlight some of Chapin’s legacies in developing our current understanding of ecological succession.  These case studies ask questions about the ecological mechanisms that drive successional patterns, examine characteristics that improve our ability to predict ecosystem consequences of succession, evaluate the role of stochastic vs. deterministic processes, and further our understanding of the socio-ecological resilience of Earth systems.

Results/Conclusions

On Alaskan floodplains (Case Study 1), species interactions such as facilitation and competition played dominant roles in driving successional change, and were closely tied to life history traits such as arrival time, growth rate and longevity. The net result of these complex species interactions had important outcomes for successional pathways. Studies of coastal forests following glacial retreat in Glacier Bay, Alaska (Case Study 2) further demonstrated that the impacts of species interactions vary between individuals and populations and within individual life history stages. Interactions between species functional traits (N-fixation, litter) and successional pathways meant that late-successional communities differed dramatically in key ecosystem properties, such as soil fertility and plant productivity. Finally, research on initial community assembly in boreal forests after fire (Case Study 3) showed how disturbance characteristics can filter species traits to drive rapid reorganization of ecosystems under environmental change.  Together, these studies demonstrate the key role of species traits and species interactions in succession, while emphasizing that stochastic events may often overrule deterministic processes. Chapin’s contributions have encouraged a synthetic understanding of both mechanistic processes and cross-scale feedbacks that drive succession and are a key component in predicting ecological resilience in a changing environment.