PS 85-34
Forests on the move? An assessment of the global boreal – deciduous forest ecotone response to climate change
Global climate is warming most dramatically at high latitudes and the effects of this change on forests are expected to be complex and varied. The impact of warming climatic regimes on northern and alpine treeline dynamics has been, and continues to be, well studied. An ecotone that has received less attention, yet which is an economically, culturally, and ecologically important component of the global forest is the southern boreal forest-deciduous forest ecotone (BDE). Globally, the BDE exists in North America, Europe and Asia in varying states of intactness, often in densely populated areas. Although northern range expansion is broadly expected for most forest types, the state of geographic equilibrium of the BDE is unknown. Here, we conducted a systematic review of journal articles identified through the SCOPUS database to i) assess whether a modern shift is occurring in the global BDE; and ii) reveal commonly identified limiting and facilitating factors that are at play across this global ecological setting in hopes of finding universal links between globally occurring, broadly similar forest types. We focussed results on modern changes evident in the BDE, rather than historical shifts.
Results/Conclusions
An overwhelming finding of this study was the paucity of studies we detected that directly examined temperate forest shifts into boreal forests. Once our initial results pool of 1,095 articles from our search was culled down, a final collection of just 21 studies were deemed specific to modern BDE shifts. While this number was too low to initiate statistical analysis, data extracted from these studies revealed interesting commonalities. All but one study from our final collection reported changes in the BDE due to changing climate, and the majority of authors that reported on whether the BDE was shifting asserted a northern shift. Changing climate regimes were often found to have knock-on effects, such as larger and more prevalent canopy gaps due to increased storm severity and frequency. Most commonly, temperature facilitated a northward shift while negative biotic interactions (e.g., seed predation) moderated or even constrained species responses to climate. The body of research on this subject is growing, particularly in North America; however, we have identified that the scope of species being included and geographic diversity of study sites are areas requiring further research in order to better assess the response of this global ecotone to on going climate change.