Remotely sensed vegetation phenology and productivity along a climatic gradient: on the value of incorporating the dimension of woody plant cover

Aim Woody plants affect vegetation-environment interactions by modifying microclimate, soil moisture dynamics and carbon cycling. In examining broad-scale patterns in terrestrial vegetation dynamics, explicit consideration of variation in the amount of woody plant cover could provide additional explanatory power that might not be available when only considering landscape-scale climate patterns or specific vegetation assemblages. Here we evaluate the interactive influence of woody plant cover on remotely sensed vegetation dynamics across a climatic gradient along a sky island. Location The Santa Rita Mountains, Arizona, USA. Methods Using a satellite-measured normalized difference vegetation index (NDVI) from 2000 to 2008, we conducted time-series and regression analyses to explain the variation in functional attributes of vegetation (productivity, seasonality and phenology) related to: (1) vegetation community, (2) elevation as a proxy for climate, and (3) woody plant cover, given the effects of the other environmental variables, as an additional ecological dimension that reflects potential vegetation-environment feedbacks at the local scale. Results NDVI metrics were well explained by interactions among elevation, vegetation community and woody plant cover. After accounting for elevation and vegetation community, woody plant cover explained up to 67% of variation in NDVI metrics and, notably, clarified elevation- and community-specific patterns of vegetation dynamics across the gradient. Main conclusions In addition to the environmental factors usually considered - climate, reflecting resources and constraints, and vegetation community, reflecting species composition and relative dominance - woody plant cover, a broad-scale proxy of many vegetation-environment interactions, represents an ecological dimension that provides additional process-related understanding of landscape-scale patterns of vegetation function.