Anticipating Species Responses

We are in an era of unprecedented rates of global change, causing biodiversity loss and decline almost everywhere. However, these threats are not only to rare or restricted species. Long-lived species with complex life-histories may remain common over a large geographic area, yet still be threatened by the suite of intensive changes occurring. These threats may not be immediately visible in the current distribution of adults, due to reproductive bottlenecks at early or vulnerable non-adult life-stages. California valley oak (Quercus lobata), a keystone, endemic species of the California floristic province, provides an ideal case study of a long-lived, wide-spread species that, despite exceptional cultural and ecological significance, appears to be declining.

Recruitment Failure of Valley Oak

The phenomenon of missing or depleted young cohorts in tree populations has been observed in multiple genera across geographies, and is particularly common in Quercus species. Our study of recruitment failure in valley oak attempts to integrate knowledge of this species across scales and to inform conservation of valley oaks in a rapidly changing environment. We are conducting historic resurveys, interviews with land stewards, recruiting site field surveys, GIS analysis, dendroecology and meta-analysis of planting studies to assess the current conservation status and state of recruitment in CA valley oak woodlands. We specifically address the following questions (1) how has the status of sapling recruitment changed over time in populations surveyed over the past 30-40 years; (2) is recruitment generally synchronous, confined to particular years or related to specific regional-scale events; and (3) where are valley oaks recruiting saplings and what land-use and environmental factors may be related to successful recruitment.

How do species shift their ranges? Refining predictions of species’ responses to climate change

The ability to anticipate and prepare for climate change is a major focus in conservation ecology, and species bioclimate models are one of few available predictive tools. Most bioclimate models are parameterized with data from adult life-stages and focus on distribution-scale shifts, limiting their ability to project changes for long-lived species subject to strong local interactions. The default use of climate parameters associated with the adult life stage could limit reliability of model predictions for species with long life spans or complex life histories. Yes, models could be refined to more accurately represent likely species-level responses to climate change with field data on the distribution of the most vulnerable and/or early life history stages of the species.

Using California valley oaks, we are conducting a multi-scale observational study to assess the correspondence between bioclimate model projections and actual patterns of sapling recruitment across sites. Our goal is to understand (1) the potential implications of an adult- versus early-life stage focus in generating model predictions and (2) how local refugia and redistribution dynamics relate to patterns projected at larger landscape scales.

Project participants: Blair McLaughlin and Erika Zavaleta