Woody encroachment of grasslands is a worldwide phenomenon with functional consequences for carbon storage, nutrient cycling and ecohydrology. Understanding the physiological responses of an encroaching woody species to site-level heterogeneity and temporal climate variability will refine future predictions of changes in grassland ecohydrology. In this study, we created an isoscape using δ13C from leaves of rough-leaf dogwood (Cornus drummondii) sampled across topoedaphic gradients in a tallgrass prairie. During the 2008-2011 growing seasons (May-Sept), emergent leaves were collected monthly from 76 individuals of rough-leaf dogwood distributed across varying management (burned at 1, 2, 4, and 20 years and grazed—bison, cattle, or none) and topoedaphic gradients at the Konza Prairie Biological Research Station in eastern Kansas. Samples were analyzed for their carbon stable isotope signature (δ13C). Data were analyzed using a mixed-effects model ANOVA to identify the varying effects of site conditions, seasonal, and inter-annual drivers of leaf isotopic signature.
Across the 4-years studied, grazing treatment, elevation and day of year were significant predictors of δ13C, but no differences were present by burn frequency or among years, despite considerable interannual climate variability. These data reinforce the emerging theory that shrub invaders of grassland ecosystems are comparatively decoupled from site-level environmental conditions, compared to coexisting herbaceous species. Despite sampling across years with above (+6.43%) and below-average (-55.8%) rainfall and during the heat wave of 2011, leaf δ13C values had a narrow range (~1.5‰) and largely reflected seasonal dynamics in vapor pressure deficit. These data show robust physiological functioning by this species irrespective of site-level heterogeneity and inter-annual climate variability, and illustrate how access to groundwater by this species has the potential to alter site ecohydrology.