Recent increases in the frequency, intensity and unprecedented coupling of several types of ecological disturbance (e.g., fires, droughts, floods, cyclones) with both natural and anthropogenic causes have highlighted the urgency to understand how disturbances interact. We propose a universal classification of disturbance interactions that considers the roles of biological legacies, endogenous and exogenous triggers, thresholds, and lag effects. We distinguish among random co-occurrences, single, and multiple linkages among disturbances resulting in disturbance loops, or cascading chains and networks. Complex, exogenous linkages are less predictable than simple, endogenous ones. These distinctions are important aspects of regional disturbance regimes. Abrupt ecological change is challenging to predict, because regional disturbance regimes depend on adjacent or synchronous events and underlie supra-regional forcing.
Results/Conclusions
We discuss these concepts by presenting pattern analysis of forest dynamics in Northern British Columbia along with field data from experimental community ecology in temperate grasslands of central Europe. Experimental data include effects of severe drought and heavy rainfall, winter warming and late frost on multiple ecosystem functions. Our results indicate that heavy rain spells have stronger impacts on productivity, nutrient cycling and biotic interactions than severe drought. Recurrent, severe drought results in ecological stress memory and cross-stress tolerance in grasses. Winter warm spells enhance sensitivity to late frost events in key European tree and grass species. By considering the mechanisms and consequences of disturbance interactions, we can improve our understanding of system dynamics leading to abrupt ecological change, improve ecosystem and risk management, and avoid ecological surprises that might threaten ecological and human values.