Morphological and Physiological Compensation Promote Climate-Induced Invasions Above and below Treeline

Abstract:

Elucidating the mechanisms underlying invasive species success is a challenge in ecology. Treeline ecotones are eminently suited to address this challenge given their sensitivity to climate change and the different abiotic filters in place over short distances. The invasive dwarf bamboo Sasa kurilensis has had pronounced effects on Japanese alpine plant communities, including the loss of over 1/3 of native species in some areas. The drivers of S. kurilensis invasions remain unresolved. We evaluated S. kurilensis stands along elevation and moisture gradients in Daisetsuzan National Park (Hokkaido, Japan) to identify strategy shifts that might facilitate invasions. We anticipated morphological responses to be correlated with invasion above treeline, while physiological processes to be more coordinated below treeline, reflecting different ecological filters in place within each community. We compared growth patterns and plant water status in the native (i.e., montane forests) and invasive (i.e., subalpine and alpine meadows) ranges of S. kurilensis. Dwarf bamboo at native lower elevations were taller than those at newly-invaded upper limits, indicating light limitation and investment in culm elongation. Culms in the native range grew faster than those at higher elevations. In contrast, culm density increased and plants allocated more to photosynthetic structures in invaded areas without overstory. Plants tended to invade drier soils but showed increased water stress, likely compensating by producing more photosynthetic structures to promote carbon gain. Overall, our results reveal dwarf bamboo exhibits both morphological and physiological variation across treeline ecotones. This appears to enable it to successfully invade subalpine and alpine communities while responding to a new climate. This pattern of variation coupled with changing soil dynamics as a result of earlier snowmelt will likely continue to promote the invasion of S. kurilensis into these systems. Linking resource allocation strategies and physiological responses to environmental variation will produce a mechanistically-based predictive framework vital to helping federal agencies apply limited funds to optimally conserve and manage sensitive lands.