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Predicting the effects of sea level rise and salinity changes on west coast tidal marsh plant and avian communities

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Predicting the effects of sea level rise and salinity changes on west coast tidal marsh plant and avian communities
PI: V. Thomas Parker, San Francisco State University

Co-PI: Nadav Nur, PRBO Conservation Science

John C. Callaway, University of San Francisco

Mark Herzog, PRBO Conservation Science

Diana Stralberg, PRBO Conservation Science

Lisa Schile, San Francisco State University


We propose to use new and existing data to examine the influence of salinity and inundation on the distribution, productivity and diversity of tidal marsh plant and avian species. We will generate spatially explicit models that predict the responses of tidal marsh extent and community processes using a range of future climate change scenarios in a Mediterranean climate system.

We will address the following questions: (1) How do salinity and tidal inundation influence the distribution, growth, productivity, and diversity of tidal marsh plant species? (2) How do biotic and abiotic factors influence the distribution and abundance of tidal marsh bird species? (3) How will these plant and avian species shift respond to predicted climate change? Which species and what areas of their distributions are most likely to be affected by climate change?

Research will be conducted within the tidal wetlands of the San Francisco Bay-Delta and adjacent uplands. Survey data of plant and bird occurrences will be collected for modeling purposes from sites throughout the Bay-Delta, while more intensive data collection will be conducted at six locations across the Bay-Delta to quantify factors affecting these distributions.

At intensive study sites, primary productivity will be measured by total standing biomass, and seed traps will be deployed to assess dispersal potential, abundance, and distance. Greenhouse experiments will assess the effects of salinity and inundation treatments on relative growth rates, mortality, and biomass of dominant tidal marsh plant species. Using field-based abundance and GIS-based environmental data, we will develop distribution models for dominant, rare, and invasive plant species, as well as spatial models for primary productivity and plant species diversity. Based on relationships between habitat distributions and bird occurrences, we will model bird species distribution and abundance and validate models using additional data not included in model development. Once models have been validated for existing conditions, Bay-Delta-specific predictions of sea-level rise and salinity will be used to predict changes in species distribution and abundance, and community composition.

Models will predict shifts in tidal marsh species distribution patterns for the Bay-Delta and identify species and geographic areas of conservation concern, as well as potential issues for rare or invasive species. Experimental data will identify underlying mechanisms for shifts in plant distributions and community composition. Predictive models and empirical results will be synthesized and testable predictions will be developed to further refine these models.


Mediterranean-climate tidal wetlands are particularly susceptible to the effects of climate change. As with other tidal wetlands, they share the threat of submersion if accretion rates are not in equilibrium with sea-level rise (SLR) (Morris et al. 2002, Turner et al. 2004) and differential impacts of CO2 fertilization on C3 and C4 plants (Rasse et al. 2005). However, Mediterranean-climate tidal systems are additionally threatened by salt accumulation during the lengthy dry summers that will accelerate with warmer temperatures, and changes in patterns of precipitation and water management will exacerbate this impact, especially given the increased societal demands for water in a semi-arid climate. The composition, structure and dynamics of tidal wetland plant and bird communities will be significantly changed by these influences, but current predictions are merely speculative. Current understanding of how these tidal systems will respond and the resulting management or policy actions relies on a relatively limited history of basic research. In this study, we propose a focused research plan comprised of complementary observational studies, experimental analysis, and spatial modeling that will provide critical insight needed for management.

Effective ecosystem management and species conservation require a thorough understanding of direct and indirect responses to environmental change (Burkett et al. 2005). Climate change combined with other anthropogenic influences is causing rapid, often non-linear, shifts in species’ distributions and life history characteristics (Parmesan 1996; Inouye et al. 2000; Ostander et al. 2000; Scheffer et al. 2001; Scheffer and Carpenter 2003; Folke et al. 2004; Hughes et al. 2005), and modifications at lower trophic levels can rapidly affect entire ecosystems (Porter et al. 2000; Dunne et al. 2002a, 2002b; Root et al. 2002; Lawrence and Soame 2004). One approach to assessing ecosystem-wide changes over large areas is the use of species distribution models (SDM), which use spatially-explicit empirical data to derive linear and non-linear relationships between species’ occurrence and environmental conditions. Many studies have modeled changes in species distribution due to climate change (Iverson and Prasad 1998; Bakkenes et al. 2002; Pearson et al. 2002; Thuiller 2004), but most have been based on global circulation model (GCM) predictions of temperature and precipitation at broad continental scales. Very few have explicitly modeled distribution shifts within tidal wetland ecosystems (but see Rehfisch et al. 2004), which are narrowly distributed and highly sensitive to fine-scale changes in elevation and salinity.

Thus, we propose to apply the most recent developments in species distribution modeling to tidal marsh plants and vertebrates using fine-scale, California-specific spatial inputs representing future tidal inundation and salinity patterns across the San Francisco Bay-Delta. We will investigate and model the distribution, diversity, and productivity of selected plant species, as well as the distribution and abundance of key tidal marsh endemic birds, under various climate change scenarios using an extensive set of new and existing field survey data. Because SDM predictions are based on current species’ distributions and do not explicitly consider community-level species interactions or dispersal abilities, we propose to complement our modeling work with an experimental greenhouse study of plant tolerances of salinity and inundation and a field-based study of plant dispersal. This will provide further insight into the mechanisms for shifts in plant distributions, and the potential for future communities to remain intact.

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