Spatial and Temporal Examination of Bivalve Communities in Several Estuaries of Southern California and Northern Baja California, MX.

A combination of historical bivalve surveys spanning 30-50 years and contemporary sampling were used to document the changes in bivalve community structure over time at four southern California and one northern Baja California estuaries. While there are limitations to the interpretation of historic data, we observed generally similar trends of reduced total bivalve species richness, losses of relatively large and/or deeper-dwelling natives, and gains of relatively small, surface dwelling introduced species across the southern California estuaries, despite fairly distinct bivalve communities. A nearly 50-year absence of bivalves from two wetlands surveyed in a Baja California estuary continued. A combination of site history and current characteristics (e.g., location, depth) likely contributes to maintenance of distinct communities, and both episodic and gradual environmental changes likely contribute to within-estuary temporal shifts (or absences). We highlight future research needed to determine mechanisms underlying patterns so that we can better predict responses of bivalve communities to future scenarios, including climate change and restoration.

Understanding the ecology of blue elderberry to inform landscape restoration in semiarid river corridors.

Societal constraints often limit full process restoration in large river systems, making local rehabilitation activities valuable for regeneration of riparian vegetation. A target of much mitigation and restoration is the federally threatened Valley elderberry longhorn beetle and its sole host plant, blue elderberry, in upper riparian floodplain environments. However, blue elderberry ecology is not well understood and restoration attempts typically have low success rates. We determined broad-scale habitat characteristics of elderberry in altered systems and examined associated plant species composition in remnant habitat. We quantified vegetation community composition in 139 remnant riparian forest patches along the Sacramento River and elderberry stem diameters along this and four adjacent rivers. The greatest proportion of plots containing elderberry was located on higher and older floodplain surfaces and in riparian woodlands dominated by black walnut. Blue elderberry saplings and shrubs with stems <5.0 cm in diameter were rare, suggesting a lack of recruitment. A complex suite of vegetation was associated with blue elderberry, including several invasive species which are potentially outcompeting seedlings for light, water, or other resources. Such lack of recruitment places increased importance on horticultural restoration for the survival of an imperiled species. These findings further indicate a need to ascertain whether intervention is necessary to maintain functional and diverse riparian woodlands, and a need to monitor vegetative species composition over time, especially in relation to flow regulation.

Ecosystem engineering in space and time.

The ecosystem engineering concept focuses on how organisms physically change the abiotic environment and how this feeds back to the biota. While the concept was formally introduced a little more than 10 years ago, the underpinning of the concept can be traced back to more than a century to the early work of Darwin. The formal application of the idea is yielding new insights into the role of species in ecosystems and many other areas of basic and applied ecology. Here we focus on how temporal, spatial and organizational scales usefully inform the roles played by ecosystem engineers and their incorporation into broader ecological contexts. Two particular, distinguishing features of ecosystem engineers are that they affect the physical space in which other species live and their direct effects can last longer than the lifetime of the organism--engineering can in essence outlive the engineer. Together, these factors identify critical considerations that need to be included in models, experimental and observational work. The ecosystem engineering concept holds particular promise in the area of ecological applications, where influence over abiotic variables and their consequent effects on biotic communities may facilitate ecological restoration and counterbalance anthropogenic influences.

Using ecosystem engineers to restore ecological systems.

Ecosystem engineers affect other organisms by creating, modifying, maintaining or destroying habitats. Despite widespread recognition of these often important effects, the ecosystem engineering concept has yet to be widely used in ecological applications. Here, we present a conceptual framework that shows how consideration of ecosystem engineers can be used to assess the likelihood of restoration of a system to a desired state, the type of changes necessary for successful restoration and how restoration efforts can be most effectively partitioned between direct human intervention and natural ecosystem engineers.

The effects of dust on the federally threatened valley elderberry longhorn beetle.

We combined a natural experiment with field surveys and GIS to investigate the effects of dust from recreational trails and access roads on the federally threatened Valley elderberry longhorn beetle ("VELB," Desmocerus californicus dimorphus) and its host plant, elderberry (Sambucus mexicana). Dust is listed in the species recovery plan as a threat to the VELB and unpaved surfaces are common throughout the riparian corridors where the VELB lives, yet the effects of dust on the VELB have been untested. We found that dust deposition varied among sites and was highest within 10 m of trails and roads, but was similar adjacent to dirt and paved surfaces within sites. Elderberry density did not differ with distance from dirt surfaces. Despite similar within-site dust levels, elderberry adjacent to paved surfaces were less stressed than those near dirt ones, possibly because increased runoff from paved surfaces benefited elderberry. Dust deposition across sites was weakly correlated with elderberry stress symptoms (e.g., water stress, dead stems, smaller leaves), indicating that ambient dust (or unmeasured correlates) influenced elderberry. Direct studies of the VELB showed that its distribution was not negatively affected by the proximity to dirt surfaces. Dust from low traffic dirt and paved access roads and trails, therefore, affected VELB presence neither directly nor indirectly through changed elderberry condition. These results suggest that the placement of VELB mitigation, restoration, and conservation areas can proceed independently of access roads if dust and traffic levels do not exceed those in our study site. Furthermore, dust control measures are likely to be unnecessary under such conditions. The potential effects of increased traffic and dust levels are addressed through a literature review.