Research Summaries

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Stanley, E. H. and M. W. Doyle.
2003. Trading off: the ecological effects of dam removal. Frontiers in Ecology and the Environment 1(1):15-22.

Dam removal is gaining credibility as a viable management option for dams that have deteriorated physically and are no longer economically practical. However, the decision to remove or repair a dam is often contentious and emotionally charged. Part of the acrimony arises from our limited scientific knowledge of the effects of dam removal. We believe that the ecological consequences are best understood by viewing the removal process as a disturbance. The resulting loss of reservoir habitat and movement of sediment can cause ecological and environmental change. Ecological outcomes will include changes that are both environmentally costly, such as invasion of exotic species, and environmentally beneficial, such as increasing access to spawning habitats for migratory fish. It has also become apparent that the wholesale aging of the US dam infrastructure will make dam removal even more common in the future. The challenge ahead is to better understand and manage the consequences of these removals.

 


Krueger-Mangold, J., R. L. Sheley, and B. D. Roos.
2002. Maintaining plant community diversity in a waterfowl production area by controlling Canada thistle using glyphosate. Weed Technology 16:457-463.

Our objective was to maximize Canada thistle control and plant community diversity in a waterfowl production area administered by the US Fish & Wildlife Service. We tested three rates (1.5, 3.0, and 4.5 kilograms active ingredient per hectare) of glyphosate applied during spring, summer or fall using two application methods. The lowest rate of glyphosate decreased Canada thistle density by about 30% relative to the control. Glyphosate applied in the fall decreased Canada thistle density below that of the control more consistently than when applied in spring or summer. Wick application resulted in less Canada thistle biomass than did broadcast application. Species richness was generally higher when glyphosate was wick applied, and all rates of this application method increased species richness when compared to the control. We recommend wick applied glyphosate in the fall at 1.5 kg active ingredient / ha to control Canada thistle near riparian areas. The application provided optimum Canada thistle control, while maintaining species richness important for waterfowl.

 


Salinas, M. J., and J. Guirado.
2002. Riparian plant restoration in summer-dry riverbeds of southeastern Spain. Restoration Ecology 10:655-702.

An evaluation was made of the development of two experimental plots where restoration of dominant riparian plant species. The evaluation was conducted in December 1991 along two semi-arid Mediterranean summer-dry watercourses. An overall comparison was made of the vegetation structure, species cover, floral composition, and species richness of the plots restored using vegetation from nearby undisturbed plots along the same watercourse. The monitoring was performed in October 1993, October 1995, September 1997, October 1999. In the restored zones previously rooted cuttings of the species most representative of these communities were planted, using the undisturbed zones as vegetation models. Climatological conditions (particularly the rainfall regime during the planting period) substantially favored the success of the planting. The results show that a simple planting technique accompanied by monitoring during the first year is adequate to schieve success in establishment of planting species. It is necessary to take precautions against herbivory of small plants of Cheaerops humilisFicus carica, and Retama sphaerocarpa. The planting itself causes some disturbance in the soil that may alter species composition, giving an advantage of ruderal species over others. More time is needed to attain coverage, frequency, and species composition comparable with that of undisturbed zones.

 


Sexton, J. P., J. K. McKay, and A. Sala.
2002. Plasticity and genetic diversity may allow saltcedar to invade cold climates in North America. Ecological Applications 12:1652-1660.

Two major mechanisms have been proposed to explain the ability of introduced populations to colonize over large habitat gradients, despite significant population bottlenecks during introduction: 1) Broad environmental tolerance — successful invaders possess life history traits that confer superior colonizing ability and/or phenotypic plasticity allowing acclimation to a wide range of habitats. 2) Local adaptation – successful invaders rapidly adapt to local selective pressures. However, even with bottlenecks, many introduced species exhibit surprisingly high levels of genetic variation and thus the potential for evolutionary increase in invasive traits and plasticity. Here we assess the invasive potential of Tamarix ramosissima by examining he degree of genetic differentiation within and among populations from the latitudinal extremes of its introduced range. Using growth chamber experiments we examined ecologically important variation in seedlings both in trait means and their reaction norms across temperature environments. Although we found no genetic variation for gas-exchange traits within or among populations, we did find significant genetic variation for growth traits, both in the trait means and in the degree of plasticity of these traits. Northern ecotypes invested more in roots relative to southern ecotypes, but only under low temperatures. Both ecotypes increased shoot investment in warm temperatures. Increased root investment in cold temperatures by northern ecotypes may increase their first winter survival. Genetic differences in seedling root investment may contribute to the ability of this species to successfully tolerate and invade a broader latitudinal range. Our data support a model in which both plasticity and adaptive evolution may contribute to the invasive potential of introduced species.

 


Purcell, A. H., C. Friedrich, and V. H. Resh.
2002. An assessment of a small urban stream restoration project in northern California. Restoration Ecology 10:685-694.

Stream restoration projects have become increasingly common, and the need for systematic post-project evaluation, particularly for small-scale projects, is evident. This study describes how a 70-meter restored reach of a small urban stream, Baxter Creek in El Cerrito, CA, was quickly and inexpensively evaluated using habitat, biological, and resident-attitude assessments. The restoration involved opening a previously culverted channel, planting riparian vegetation, and adding in-stream step-pool sequences and sinuosity. Replicated benthic macroinvertebrate samples from the restored site and an upstream unrestored site were compared using several metrics, including habitat taxa richness and a biotic index. Both biological and habitat quality improved in the restored compared with the unrestored section. However, when compared with a creek restored 12 years before, habitat condition was of lower quality in the recently restored creek. A survey of the neighborhood residents indicated that, overall, they were pleased with the restored creek site. The approach used in this demonstration project may be applicable to other small-scale evaluations of urban stream restorations.