Climate change is affecting global forests in multiple ways, often by altering the abiotic conditions forests experience. Direct (e.g. increasing drought-induced tree mortality) and indirect (e.g. altered fire regimes) effects are altering productivity and/or geographical ranges. Significant shifts in ecological relationships – such as establishment of novel functional relationships or formation of no-analogue communities– are widely anticipated.
The coastal temperate rainforests of South and North America are the two largest examples of the biome (27.3 and 12.5 million ha) and are part of the most biomass dense forest biome (568-794 and 326-571 tons C/ha). They are also subject to rapid climatic shifts and, subsequently, new disturbance processes – snow-loss driven mortality and the emergence of fire in historically non-fire exposed areas.
The objectives of this review are to (1) synthesize and describe the significance of crossing precipitation and fire thresholds to the ecology and functioning of this globally important forest biome both currently and in the future, (2) discuss the spatial pattern of potential change within the regions via new downscaling of a global fire model, and (3) use the new analysis of disturbance drivers in this ecosystem to anticipate new dynamics in other temperate rainforest systems.
Results/Conclusions
In terms of snow loss, a rapid decline in winter snow is leading to mass mortality (4,000 km2) of Alaska yellow cedar in the northern hemisphere rainforests. High elevation southern hemisphere forests, which are beginning to see similar declines in snow, may be vulnerable in the future, especially bogs and high-water content soils. Southern hemisphere forests are seeing the invasion of fire as an ecological force at mid-to-high latitudes (with rapid increase in human- and lightning-ignited fires), a shift not yet observed in the north but are widely anticipated with ongoing climate change.
We suggest research should focus on the flammability of seral vegetation and bogs under future climate scenarios in both regions. Both snow loss and fire-regime shifts are major concerns to forest managers, conservationists, researchers, and culture bearers in forests worldwide. By comparing these two drivers of change (proceeding in similar directions but at different rates in each region) across similar gradients in the coastal temperate rainforests of the Americas, this work points to the potential for emerging change in unexpected places in both regions.