UC Santa Barbara

Habitat degradation and conversion have become a ubiquitous problem globally and are expected to increase with climate change. In areas where degradation and conversion have already occurred, ecological restoration – defined by the Society for Ecological Restoration as the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed – provides a promising avenue to conserve biodiversity and ecosystem function. However, while projects have achieved restoration success, that is not a consistent outcome, even in the most well-studied ecosystems. The burgeoning field of plant functional trait ecology posits, however, that there are fundamental relationships between plant functional traits and how species respond to their environment. Therefore, classifying species by their plant traits, instead of taxonomic identity, offers a promising way to expand the findings of restoration ecology research to new settings and species.

Here, we investigate how to conduct successful ecological restoration in the mediterranean shrublands of southern California, an ecosystem with very little ecological restoration research. Specifically, the research presented herein took place in the Los Padres National Forest, just outside Piru, California. This area has experienced extensive shrubland conversion to non-native grasses over the last few decades and has been identified as a specific area of restoration interest by the United States Forest Service. We first conduct a regional spatial analysis to identify where and why shrublands are being lost to inform how we might conduct restoration. Second, we conducted a large-scale landscape restoration project with a physiologically diverse set of ten species, measured a variety of plant traits (i.e. wood density, integrated water use efficiency, and parts of the leaf economics spectrum) and measured daily microsite temperature (n = 115), humidity (n = 39) and soil moisture (n = 30). This then allowed us to map microsite environmental conditions across the whole landscape, assess how the microsite differences influenced survival, and test how plant traits related to these interspecific responses. Lastly, we conducted another restoration experiment with 13 shrubland species. This experiment evaluated how a spectrum of planting densities in a ‘restoration island’ approach influenced survival in the harshest parts of the landscape and how plant traits relate to those influences.

Our findings showed 1.) shrubland conversion is primarily happening in low elevation, southwest facing slopes (i.e. more arid slopes) and during periods of postfire drought. 2.) Low soil moisture and high vapor pressure deficit (VPD) are primary drivers of year one mortality. Additionally, species with higher water use efficiencies can survive high VPD if soil moisture remains moderate. Conversely, species on the more acquisitive side of the leaf economics spectrum can survive low soil moisture if VPD remains moderate. And 3.) in general plot level survival increases significantly with higher planting densities. Inclusion of plant traits revealed that more acquisitive species benefiting the most from this facilitation. Conversely, species with higher water use efficiencies were negatively impacted by higher planting densities. Overall, my dissertation details foundational knowledge for the restoration of southern California shrublands and more broadly shows the potential for plant functional traits to inform restoration planning and increase the consistency of restoration success.