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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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METHODS


This proposed research will incorporate a broad suite of plant and bird data collected throughout the Bay-Delta. Much of these data have been collected as part of two regional, multi-disciplinary research efforts, partly overlapping in research objectives and spatial extent. The Integrated Regional Wetlands Monitoring Program (IRWM; www.irwm.org) is an interdisciplinary research effort examining wetland restoration in the North Bay and Delta, with primary goals of (1) understanding how ecosystem restoration efforts affect ecosystem processes at different scales and (2) identifying useful monitoring indicators and protocols. IRWM activities have involved the intensive collection of nutrient, elevation, salinity, vegetation, invertebrate, fish, and avian data at six sites over two years throughout the northern bay and into the Delta. The PIs and senior personnel involved in this proposal have collaborated together under the IRWM project, which will be completed in 2007, with several publications in progress. BREACH is another interdisciplinary research effort, seeking to gain a conceptual and empirical understanding of the important mechanisms and thresholds of restoration processes in Bay-Delta tidal marshes. Two BREACH phases focusing on the Delta (fresh) and North Bay (saline to brackish) marshes have been completed (Simenstad et al. 2000), and a third phase, focusing on intensive monitoring and modeling of a single Delta restoration site, will commence in 2007. One of the PIs (Nur) has been involved in all three phases, and two senior personnel (Stralberg, Herzog) will play a role in the avian and landscape ecology components of the upcoming third phase.

Data collected through BREACH and IRWM, supplemented by long-term avian monitoring data collected by PRBO Conservation Science (PRBO), provide the basis for a comprehensive investigation into the effects of climate change on tidal wetland vegetation and vertebrate distribution and diversity in the Bay-Delta. Additional field sampling will be conducted to fill in any gaps along the salinity gradient, and public databases will be used to improve sample sizes for rare and special status species.


Sampling Sites

Intensive Sampling Sites


We have selected six natural marsh systems as the focus of intensive research in this investigation (Figure 2). These six sites span the full salinity gradient of the estuary and represent some of best representatives of historic tidal wetland landscapes in the region. They also have a rich legacy of scientific investigation and baseline data. We chose relatively undisturbed remnants of the Bay-Delta’s historic wetland ecosystem, rather than restoration sites, because the former should provide greater insight into how different salinity regimes affect existing wetland conditions.

The first two sites represent the saline end of the spectrum (25-45 ppt summer salinity). China Camp State Park is part of the San Francisco Bay National Estuarine Research Reserve and consists of about 125 ha with an uncharacteristically intact upland transition and large expanse of tidal mudflats. Petaluma Marsh represents the largest intact salt marsh in California, covering over 800 ha.

Two sites have been chosen that represent brackish tidal wetlands (15 ppt average summer salinity). Coon Island is one of the last undiked, large tidal wetland landscapes in the upper San Pablo Bay area, covers about 175 ha, and has received intensive investigation as part of the IRWM project. Rush Ranch Open Space Preserve is also part of the SF Bay NERR and contains the largest remnant brackish tidal wetland in the Bay-Delta, covering over 400 ha; it has been studied by PRBO since 1996.

The last two sites represent freshwater or near freshwater tidal marshes. Browns Island is in the western end of the freshwater delta created by the confluence of the Sacramento and San Joaquin rivers. It covers about 200 ha and has also received intensive investigation as part of the IRWM project. Sand Mound Slough is farther up the estuary and is comprised of a number of small, intra-channel remnants of historic Delta wetlands, covering a total of approximately 25 ha.


Extensive Sampling Sites


PRBO (Nur, Stralberg, Herzog) has been conducting breeding season point count surveys according to standardized protocols (Ralph et al. 1993) in Bay-Delta marshes since 1996, and has accumulated an extensive long-term database of avian occurrence and abundance, as well as data on plant species composition, structure, and cover proportions collected at each point location using a modified relevé protocol (Figure 2; Spautz et al. 2006). Currently, we have bird and vegetation data from over 450 survey points at over 55 marshes, including BREACH and IRWM sites (Figure 2). We will also select additional freshwater sites throughout the Delta (i.e., Lindsey Slough marsh and Upper Mandeville Tip) to conduct plant and avian surveys for modeling purposes. These sites will be used to fill in the gaps in our existing dataset, which may not adequately represent the fresh end of the salinity spectrum for some organisms (Figure 2).

Vegetation surveys will be conducted on many remnant freshwater marshes throughout the Delta in order to supplement species distribution and abundance data collected at the intensive sampling sites. At extensive sampling sites, we will do field surveys of each location to develop presence/absence data for plant occurrences. These data will be used in conjunction with the existing and new bird data to further evaluate bird habitat relationships and to expand data for modeling on plant species distributions


Field sampling

Plant Distribution and Diversity


Through IRWM vegetation surveys, we collected vegetation presence and cover data in over 300 randomly located plots at Coon and Browns Islands. We plan to continue this sampling at the remaining four intensive sites to analyze within-marsh patterns of distribution, diversity, and productivity. At each site, we will visit 100 randomly-selected points, recording species presence and percent cover in a 3m-diameter circular plot. Points will be stratified by distance from channel, as previous work has shown that the majority of species diversity occurs within 40 m of a channel edge (Sanderson et al. 2000; Parker, Callaway and Schile, unpublished data).

For distribution modeling purposes, we will use all available distribution and abundance data, including PRBO relevé data and intensive plot samples, and also conduct new surveys at a variety of remnant freshwater wetlands in the Delta to increase data coverage (approximately 15 sites). In addition to the random plot sampling, we will document locations of threatened, endangered, and invasive species across all sites, including invasive smooth cordgrass (Spartina alterniflora) and its hybrid and pepperweed (Lepidium latifolium). These data will be used to develop spatial models of individual species’ distribution and abundance (percent cover), as well as plant species diversity. We will also make use of extensive existing data on invasive plant species distributions within the Bay-Delta (e.g., existing Spartina distributions are available from the Invasive Spartina Project, http:\\www.spartina.org).


Plant Productivity


Our productivity measurements will focus on six vascular plants that are widespread across the Bay-Delta: Spartina foliosa, Sarcocornia pacifica (formerly Salicornia virginica), Bolboschoenus maritimus (formerly Scirpus maritimus), Schoenoplectus americanus (formerly Scirpus americanus), Schoenoplectus acutus (formerly Scirpus acutus), and Typha angustifolia. The first two species are dominant in salt marshes, the second pair is dominant in brackish marshes, and the last pair is prevalent in freshwater systems, although there is broad overlap in species distributions.

Over the past two years, we have collected annual net primary productivity (ANPP) data from a suite of dominant species within the Bay-Delta. We will supplement these data with collections at more sites throughout the Bay-Delta (Table 2). In August 2007, all standing biomass in five 0.25m2 plots will be collected for each species at both high and low marsh locations at a subset of sites. In the lab, clipped vegetation will be rinsed with freshwater, sorted by species and live/dead material, dried to a constant weight, and scaled up to a 1m2 estimate of ANPP.



Using intensive plot data to analyze the relationship between primary productivity and variations in salinity and species composition within and across sites, we will attempt to extrapolate these relationships across the Bay-Delta system.

Seed dispersal


To estimate seed dispersal abilities of salt marsh plant species into the tidal freshwater zones of the Bay-Delta, we will establish 0.25m2 seed traps at two sites representing the transition from oligohaline to freshwater tidal, Browns Island and Sand Mound Slough, and two sites farther up the Sacramento River (Liberty Island) and San Joaquin River (Mandeville Tip). Seed traps made from multiple layers of burlap will be anchored to the marsh surface near channel edges. All existing vegetation will be clipped from around the traps and a 3-m diameter vegetation survey will be conducted to determine presence and abundance of local species. Depending on the size of the site, 10-20 traps will be deployed at each site in September 2007 and will be replaced every three months for an entire year. A shallow soil core will be removed near seed trap locations to document the local seed bank. In a lab, traps and soil cores will be placed in cold storage for 2 weeks and then germinated in a greenhouse with freshwater in flats filled with sand. All seedlings will be identified to species and counted. This method has been used successfully to document seed dispersal and seed bank characteristics at tidal marshes along the Napa River, San Pablo Bay, CA (Diggory and Parker, unpublished data). These results will be used to modify model predictions for species found to be dispersal-limited.

Avian Distribution and Abundance


At least 10 study sites have been annually surveyed since 1996; other sites vary in the number of years in which avian surveys were conducted, but points at all sites have at least one associated vegetation survey. We do not plan to conduct additional surveys beyond our current core sites, except if additional freshwater delta sites are needed. However, upcoming BREACH III surveys are scheduled for a cluster of delta sites, and we will utilize those data.
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