Seasonal dry-down rates and high stress tolerance promote bamboo invasion above and below treeline

Abstract

How species invasions impact ecosystem structure and function at important ecotones or boundaries is unknown, but may provide insight into the impacts of climate change and the mechanisms underlying community change. The dwarf bamboo, Sasa kurilensis, may be a good system to understand these issues, as the species impacts ecosystem features as it encroaches beyond treeline into alpine systems. We used remote sensing imagery spanning a 35 year period to quantify S. kurilensis expansion patterns across its range, measured growth and stress tolerances of S. kurilensis above and below treeline, and evaluated components of growth to reveal how shifts in light and water limitations influence the ontogeny of height, branching, and leaf production. We show that S. kurilensis more than doubled its abundance across its range, but more than tripled its abundance near and above treeline. Soil dry-down rates were a key driver of invasion above and below treeline, where growth rates decreased with more rapid rates of soil moisture dry-down. We found S. kurilensis responds to competition and climate stress by increasing allocation to belowground structures at high elevations. Further, it invests more carbon in fewer—yet taller and heavier—aboveground structures in low-light, low elevation environments. It appears this species’ success is driven by considerable morphological and physiological flexibility, coupled with changes in water balance associated with snowmelt that in each habitat results in sites increasingly hospitable to bamboo. Overall, this study links resource allocation strategies and physiological responses to climate change and provides a mechanistic explanation of invasion success.