Spring phenological variability promoted by topography and vegetation assembly processes in a temperate forest landscape

Plant phenological processes significantly impact ecosystem function and services across multiple ecological scales and are widely viewed to be among the most sensitive indicators of global environmental change. Remote sensing has crucially expanded our understanding of phenological variability. Yet, we continue to lack a complete mechanistic understanding of phenology and its variability and drivers, which is important to the development of predictive models, especially under continued environmental change. We combined field inventories and Land Surface Phenology (LSP) approaches, using 36 years of Landsat phenological observations, to characterize the degree to which long-term spring greenup patterns are shaped by topography, vegetation, and topographically structured vegetation assembly processes within a dissected forest landscape in southeastern Ohio. We found temporal and spatial variability among the field samples where greenup patterns displayed rapid change (18 total days) over relatively short distances (<1 km). Slope position explained the most variation (35%), where the bases of hills displayed the latest timing in spring greenup. However, we found that differences in terrain aspect and slope influenced canopy diversity, height, and composition of forest stands, influencing plant community processes that support heterogeneity in spring leaf-out timing. Understanding how forest phenology is shaped by direct and often complex interacting processes that influence the distribution of species assemblages supports new insight into phenological variability and, importantly, the management of forest ecosystems facing continued environmental change.