COS 90-6 - Where the trait rubber hits the application road: Are plant traits 'functional' for predicting restoration outcomes?

Abstract: Habitat degradation and type conversion have become ubiquitous problems globally and are expected to increase with climate change. In degraded areas, ecological restoration provides a promising avenue to conserve biodiversity and ecosystem function. While many studies report restoration successes, the applicability of such findings to new areas, let alone new species, is generally limited. The burgeoning field of plant functional trait ecology posits that there are fundamental relationships between plant functional traits and how species respond to their environment that can transcend esoteric, species-by-species analyses. Classifying species by their plant traits, instead of taxonomic identity, offers a promising way to guide restoration outplantings in unexplored settings and with untested species. One such unexplored setting is degraded chaparral shrublands in California’s Mediterranean climate region. These fire responsive plant communities are being degraded by too much fire combined with drought. The few restoration efforts that have been attempted report limited success. Here we asked how well plant functional traits predict interspecific survival and responses to microsite conditions in a Mediterranean climate shrubland restoration experiment. In January 2020, we randomly planted approximately 1600 1-year old individuals of ten shrub species across a 6-acre, topographically heterogeneous degraded shrubland in Ventura County, California, USA. Fine-scale mapping and hourly temperature and soil moisture measurements from a subset of locations were used to model the probability of species survival as a function of microsite environmental differences. Additionally, a wide range of functional traits for our ten species were measured directly or compiled from the literature and then compressed into a principal component analysis (PCA). We found a significant relationship between species’ responses to temperature and the PCA axis most associated with the leaf economic spectrum (r² = 0.672, p = 0.013) with short-lived “cheap” leaved species having higher survival at hotter microsites and long-lived “expensive” leaved species having higher survival at cooler microsites. Additionally, overall survival, across the heterogenous topography, was significantly related to the PCA axis most associated with wood density and growth traits (r² = 0.482, p = 0.026), with less dense wood and faster growing species having higher overall survival. These results indicate that shorter-lived, faster growing species may be more able to rapidly establish and survive the initial dry season in a Meditteranean climate. More broadly, these findings show that relatively easy-to-measure plant traits can be used to predict species survival and response to different microsite environmental conditions across a landscape.