Climate change, disturbance regimes and feedbacks in an uncertain world
The palaeorecord shows that disturbance regimes have shifted across time and space in response to climatic changes and that such shifts have resulted in the assembly of novel (non-anolog) vegetaition communities. This begs the question: can we predict how future vegetation patterns and disturbance regimes will respond to global climate change? We suggest that precise prediction of these trajectories is not possible because of webs of feedbacks that drive non-linear ecosystem trajectories and may push ecosystems across critical transitions from which recovery is difficult and hysteresis effects likely.
In most landscapes disturbances - whether exogenous or endogenous, anthropogenic or natural - act synergistically with climate change. Further, climate change effects are both direct and indirect, sometime only manifesting themselves as extreme events or emerging after considerable lags. Because of these feedbacks, understanding changes in disturbance regimes and their effects on ecosystems requires a synthetic framework that integrates a range of data and methods and emphasises diagnosis of the capacity of ecosystems to change rather than attempting precise prediction of the the timing and geographic extent of possible state changes. This is illustrated in a case study that combines palaeoecological, neoecological and model-based data from north New Zealand forests. Here synergies between fire, disperser loss and invasive species inhibit forest recovery, and climate change is likely to amplify these effects driving the landscape to switch towards novel ‘ragamuffin’ ecosystems.