Spartina 'team' in SF BaySpartina clones in Willapa Bay


The site is currently under construction. 


Invasions and range expansions of non-native plant species are among the gravest threats to natural ecosystems and the maintenance of ecosystem services (Drake et al., 1989;Vitousek and Walter, 1989; Walker and Vitousek, 1991; Musil, 1993; Vitousek et al. 1997).  Given the interplay (e.g., Vitousek and Walker, 1989) among physical, human, and biological aspects, the problem must be studied using an integrated approach.  The key to understanding this issue is a system simple enough to disentangle and one complex enough to reveal the intertwined biological, physical, chemical, and social phenomena.  The massive invasions of Spartina alterniflora, an Atlantic cordgrass, into Pacific estuaries provide an ideal system for delving into the complex ramifications of alien species in ecosystems.  S. alterniflora invasions involve important feedbacks with the physical environment driven by sediment accretion that changes tidal height of the substrate; its tall, dense, thick growth drives interactions with the biota and changes profoundly the ecosystem of invaded estuaries.  We hypothesize that S. alterniflora invasions of Pacific estuaries will result in important biological impacts upon both invertebrates and vertebrates, including mammals and birds, and will affect human commercial and non-commercial activities and esthetic valuations of these ecosystems. 

We will investigate these linkages through the development of a predictive model of the dynamics and selected impacts of S. alterniflora invasions.  Remote sensing data provides detailed spatial information of current site conditions and a means to accurately reconstruct past distributions of species.  Because wetlands are difficult to access and directly observe, these data records are essential to accurate modeling. We propose an analysis of historical and current remote sensing data, integrated with site data in a GIS database,  that includes on-the-ground observations and experimental manipulations to elucidate critical physical, chemical and biological interactions between the cordgrass and the invaded environments.

The core model of S. alterniflora spread will include key feedbacks with the environment. We will also investigate the influence of environmental El Nio-Southern Oscillation (ENSO) fluctuations that very likely affect the performance of the invasive species, its rate of spread, and thus its feedbacks and non-reciprocal effects upon the environment in Pacific coast marshes in Washington and central California.  In addition, we will use the spread model to explore the effect of different control strategies on the spread of S. alterniflora.  Results from the model will provide the basis for estimating impacts on key native species, ecosystem services, and commercial and non-commercial economic valuations.

Models of range expansion and species invasions have a long history, beginning with Fisher (1937) and Skellam (1951) and continuing today (see reviews in Andow et al., 1990; Higgins and Richardson, 1996; Shigesada and Kawasaki, 1997; Hastings, 2000).  Many of these models have focused on the case of a single species in a hypothetical, uniform environment (with some notable exceptions such as Murray et al., 1986; Okubo et al., 1989).  Our goal is to move farther into the realm of reality by investigations of biological, physical, and human feedbacks interacting with a potent invasive species that is transforming the physical and biotic environments of large Pacific estuaries.  We contend that understanding range expansion and associated impacts requires explicit attention to feedback between the invasive organism, the physical environment, and other species.  The interactions among these elements are nonlinear; the interacting system will behave differently than just a sum of linear effects.

We will study the process of invasion and its consequences as five interrelated questions, where the answers we obtain for the Spartina invasion should be applicable to a wide range of other invasions:


Question 1: How do physical feedbacks and density-dependent interactions determine the spread of S. alterniflora from local to regional scales?

Question 2: How do invasions of S. alterniflora affect other wetland vegetation?

Question 3: How do invasions of Spartina affect animal species?

Question 4: What are the community, food web, and ecosystem, level effects of Spartina invasions?

Question 5: What are the impacts of a Spartina invasion on non-commercial human values?