Shifts in alpine grassland trait structure following whole-community turf transplantation
Plant traits are hypothesized to be general and easily measured indicators of plant ecological strategies. Studies have shown that plant trait values correlate consistently with environmental gradients, suggesting that these trends reflect changes in the interactions between plants and their environments. However, few studies have tested whether plant traits can actually be used to predict demographic success under particular environmental conditions. Experimental approaches have relied on transplantation of a small number species. This is problematic because species can respond idiosyncratically, especially when examined apart from their original community context. To address this, we conducted an experiment involving whole-community transplantation along precipitation and temperature gradients in southern Norway. Specifically, we excavated and transplanted 226 intact sub-alpine grassland communities (0.25m x 0.25m turfs) to warmer and/or wetter climates. Using four years of annual vegetation survey data, site-specific plant trait data, and data from publicly available plant trait databases, we determined (1) if/how community trait structure varies along precipitation and temperature gradients, (2) the rate of change in community trait structure in transplanted turf communities, and (3) whether changes in community trait structure matched predictions based on our gradient analyses.
Community trait structure varied consistently across precipitation and temperature gradients. Of the five traits analyzed at the species level (maximum potential height, leaf size, specific leaf area, leaf nitrogen content, seed mass), maximum potential height had the strongest trend, increasing with temperature. Leaf size and specific leaf area, two traits hypothesized to form a functional strategy associated with low soil water content and/or nutrient availability, significantly decreased with precipitation. No trends were seen in seed mass or leaf nitrogen content. We predicted that shifts in the community trait structure of transplanted turfs would mirror those observed in our gradient analyses. We observed a strong shift towards taller species in turfs transplantated to warmer climates, and a shift towards larger leaved species in turfs transplanted to wetter climates, but did not observe any changes in specific leaf area, leaf nitrogen content, or seed mass. Our results show that (1) community trait structure varies consistently with climate, (2) significant changes in trait-based community structure can occur in under four years, and (3) the changes observed in transplanted turfs mirror trends observed in our gradient analysis. Our results provide clear predictions of how sub-alpine vegetation may change under various future climate scenarios.