Workshop Proposal: Biodiversity of Riparian Ecotones

As ecotones between aquatic and terrestrial ecosystems, riparian zones are templates for the dynamic exchange of energy, nutrients and biological interactions. Recent studies in headwater systems have suggested that these exchanges constitute reciprocal subsidies (sensu Polis et al. 1996) between streams and terrestrial riparian habitats (Nakano & Murakami 2000; Kawaguichi & Nakano 2001). In a simplistic model, allochthonous leafy inputs and insects that feed stream invertebrates and fish are reciprocated with emerging insects feeding terrestrial predators. Because timing and magnitude of these processes would be subject to differences in climate, geomorphology, and associated patterns of vegetation and land use, we expect that temporal and spatial dynamics of these subsidies could vary greatly among watersheds at different latitudes or in contrasting biomes. The range of conditions expressed among LTER sites provide an excellent opportunity for cross-site comparison of reciprocal subsidies of riparian ecotones. Moreover, the multi-trophic approach creates a mechanism for documenting biodiversity in both aquatic and terrestrial systems across participating LTER sites. We are requesting funding for a workshop to identify and synthesize available information, to develop strategies for filling gaps in our knowledge at LTER sites, and to create plans for expanding information to other LTER sites and non-LTER sites under a variety of land uses.

Historically, stream ecologists have developed a network that provides an organizational structure for collegial pursuit of continental-scale information. The River Continuum Concept developed during the IBP era, and more recently, two LINX research initiatives, are well-recognized cross-site collaborations among our colleagues. Our proposal would bring together a similar group of scientists whose specific interests and expertise in biota vary, but who know each other’s work, and who already interact professionally. Our workshop would involve scientists from the H. J. Andrews, Coweeta, Sevilleta, Konza Prairie and Luquillo, but we would encourage participation of other sites in the development of a national database. At the recent All Scientists Meeting, frustrations over linking widely disparate taxa and divergent ecosystems seemed to impede discussions about biodiversity across sites. Our workshop may overcome some of these difficulties by taking advantage of existing ties among scientists who recognize some commonalities in the riparian systems where they work. Moreover the focus on a common theoretical construct (dynamics of riparian subsidies) and similar environmental structure (riparian zones) optimizes communication.

A primary goal of the workshop will be to identify measures of biodiversity already available at participating sites. We anticipate that extensive databases of aquatic and terrestrial invertebrates, riparian vegetation, fish, amphibian and birds exist; this will be an opportunity to recognize the spatial and temporal extent of the information. Secondly we will identify where there are gaps in the data and develop a strategy to fill critical ones. Integral to this effort will be creation of common protocols for sampling and taxonomic identification. One product of our work will be a cross-site synthesis of riparian biodiversity at multi-trophic levels.

Among the sites represented at the workshop several approaches to studying riparian interactions have been used; we have excluded litter experimentally (Coweeta), examined flow and retention of detritus (Luquillo and H. J. Andrews), studied effects of exotic species (Luquillo), conducted controlled flood experiments (Sevilleta) and examined vertebrate diets (H. J. Andrews, Konza Prairie). The proposed workshop would also provide an opportunity to explore how experimental approaches might be coordinated across sites.

The lengthy experience of workshop participants and extensive databases from each of the participating sites suggest that the synthesis of biodiversity across sites will be an important outcome of the workshop. Nonetheless, time would also be scheduled for exploring where other information should be gathered and how approaches might be applied more broadly. For example, we will consider opportunities for integrating with LINX researchers and others conducting stable isoptope analyses as a way of understanding riparian foodwebs. Though the small core of participants represent diverse biomes and climate regimes, expanding our data search to urban, agricultural, arctic and other biomes would be a natural extension of the workshop’s efforts. We will be using available information for the proposed workshop, and will proactively explore ways in which riparian systems can be understood more fully by including other research groups and other biomes.