Research Summaries

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Compiled by Alan Carpenter

McAllister, L. S.
2008. Reconstructing historical riparian conditions of two river basins in eastern Oregon, USA. Environmental Management 42: 412-425.

As land use continues to alter riparian areas, historical information is increasingly needed to help establish reference conditions for monitoring and assessment. I developed and applied a procedure in the John Day and Deschutes river basins of eastern Oregon for synthesizing historical documentary records available across broad spatial areas to reconstruct 19th-century riparian conditions. The study area was stratified by ecoregion and stream physical characteristics to partition regional variability. Three primary data sources — General Land Office survey notes, historical photographs, and written accounts — provided descriptive records, which were grouped by topic to develop common riparian attributes. The number of records for each attribute was tallied by stratum to compare and contrast riparian structure and composition across strata and ecoregions. Detailed descriptions of historical riparian conditions using the original documentary records further illustrated the unique riparian conditions in each stratum. Similarities and differences in historical riparian structure and composition at the stratum and ecoregion levels were evident based on the distributional pattern and numbers of records of attributes across strata. A high number of repeated observations within and among primary data sources helped to corroborate descriptive data. Although these reference data cannot provide the detail needed for rigorous quantitative assessments, they do describe a range of conditions approaching a minimally disturbed condition and provide an important perspective for conducting riparian assessments in highly disturbed regions where least-disturbed reference sites are often poor examples of a desired condition.

 

Magner, J. A., B. Vondracek, and K. N. Brooks.
2008. Grazed riparian management and stream channel response in southeastern Minnesota (USA) streams. Environmental Management 42:377-390.

The U.S. Department of Agriculture-Natural Resources Conservation Service has recommended domestic cattle grazing exclusion from riparian corridors for decades. This recommendation was based on a belief that domestic cattle grazing would typically destroy stream bank vegetation and in-channel habitat. Continuous grazing (CG) has caused adverse environmental damage, but along cohesive-sediment stream banks of disturbed catchments in southeastern Minnesota, short-duration grazing (SDG), a rotational grazing system, may offer a better riparian management practice than CG. Over 30 physical and biological metrics were gathered at 26 sites to evaluate differences between SDG, CG, and nongrazed sites (NG). Ordinations produced with nonmetric multidimensional scaling (NMS) indicated a gradient with a benthic macroinvertebrate index of biotic integrity (IBI) and riparian site management; low IBI scores associated with CG sites and higher IBI scores associated with NG sites. Nongrazed sites were associated with reduced soil compaction and higher bank stability, as measured by the Pfankuch stability index; whereas CG sites were associated with increased soil compaction and lower bank stability, SDG sites were intermediate. Bedrock geology influenced NMS results: sites with carbonate derived cobble were associated with more stable channels and higher IBI scores. Though current riparian grazing practices in southeastern Minnesota present pollution problems, short duration grazing could reduce sediment pollution if managed in an environmentally sustainable fashion that considers stream channel response.

 

Kondolf, G. M, P. L. Angermeier, K. Cummins, T. Dunne, M. Healey, W. Kimmerer, P. B. Moyle, D. Murphy, D. Patten, S. Railsback, D. J. Reed, R. Spies, and R. Twiss.
2008. Projecting cumulative benefits of multiple river restoration projects: an example from the Sacramento-San Joaquin River system in California. Environmental Management 42:933-945.

Despite increasingly large investments, the potential ecological effects of river restoration programs are still small compared to the degree of human alterations to physical and ecological function. Thus, it is rarely possible to “restore” pre-disturbance conditions; rather restoration programs (even large, well-funded ones) will nearly always involve multiple small projects, each of which can make some modest change to selected ecosystem processes and habitats. At present, such projects are typically selected based on their attributes as individual projects (e.g., consistency with programmatic goals of the funders, scientific soundness, and acceptance by local communities), and ease of implementation. Projects are rarely prioritized (at least explicitly) based on how they will cumulatively affect ecosystem function over coming decades. Such projections require an understanding of the form of the restoration response curve, or at least that we assume some plausible relations and estimate cumulative effects based thereon. Drawing on our experience with the CALFED Bay-Delta Ecosystem Restoration Program in California, we consider potential cumulative system-wide benefits of a restoration activity extensively implemented in the region: isolating/filling abandoned floodplain gravel pits captured by rivers to reduce predation of outmigrating juvenile salmon by exotic warmwater species inhabiting the pits. We present a simple spreadsheet model to show how different assumptions about gravel pit bathymetry and predator behavior would affect the cumulative benefits of multiple pit-filling and isolation projects, and how these insights could help managers prioritize which pits to fill.

 

Heitke, J. D., R. C. Henderson, B. B. Roper, and E. K. Archer.
2008. Evaluating livestock grazing use with streambank alteration protocols: challenges and solutions. Rangeland Ecology and Management 61:647-655.

Appropriate management of livestock in riparian areas can help ensure that these ecosystems are maintained. We evaluated how one indicator of livestock grazing in riparian areas, streambank alteration, was affected by choices related to protocols and personnel used for these assessments. We found that although streambank alteration protocols were generally repeatable among observers, results were affected by factors not directly related to grazing intensity, including 1) training, 2) professional background, 3) location and intensity of measurements, and 4) the protocol used. Training reduced estimates of alteration and observer variability. Rangeland professionals had higher estimates of streambank alteration than seasonal technicians. Rapid assessments of alteration were correlated with more intensive estimates; however, the relationship was not 1∶1. Different protocols resulted in different alterations estimates when alterations at the same locations were estimated. Given the large number of monitoring programs, personnel, and methods used to assess streambank alteration, we suggest more thought be given on how to standardize monitoring efforts so results consistently reflect the true amount of alteration at a site. We also remind managers that no protocol can be implemented without some error. Managers should therefore be careful when taking action based on a single evaluation — especially when the result is near a management standard or threshold. When these concerns are addressed, indicators such as streambank alteration can help ensure management decisions maintain both sustainable allotments and landscapes.

 

Bork, E. W. and A. M. Burkinshaw.
2009. Cool-season floodplain meadow responses to shrub encroachment in Alberta. Rangeland Ecology and Management 62:44-52.

This study evaluated the impact of shrub encroachment within cool-season floodplain meadows in a portion of the Rocky Mountain Forest Reserve in southwestern Alberta, where nearly half of open grasslands have been lost since 1958. Sample transects situated in meadows, known formerly to be in open grassland, were assessed in 2001 (n=21) and 2002 (n=33) in areas ranging from 0% to 92% shrub cover. Shrub cover, density, and height were correlated to understory parameters, including herbaceous production, bunchgrass cover and density, and species richness and diversity. Additional data on soil horizon depths were obtained. Analysis was conducted using regression to assess empirical relationships between understory or soil characteristics and the overstory. Stronger empirical relationships (i.e., greater R2) were found in 2002, coincident with larger sample sizes and greater rainfall. Among independent overstory variables, aggregate shrub cover for all species accounted for the greatest variation in understory characteristics. Significant (P<0.01) negative nonlinear relationships were observed between shrub cover and herbage production, with the latter declining from 6629 kg·ha-1 in meadows containing less than 12% shrub cover, to 2797 kg·ha-1 in areas where shrub cover exceeded 35%. Negative linear trends were found (P<0.01) for bunchgrass density and cover in .relation to increasing shrub abundance in 2002. Understory diversity increased with shrub abundance, peaking at 64% shrub cover in 2002. Meadows with low and high shrub cover also coincided with thicker Ah and litter, fibric, and humic soil layer (LFH) horizons, respectively. Collectively, these results indicate shrub encroachment is threatening the sustainability of native bunchgrass communities and reducing forage availability. Meadow conservation in this area will require proactive management to protect or restore open grasslands.

 

Ficetola, G, F., Padoa-Schioppa, E., and F. De Bernardi.
2009. Influence of landscape elements in riparian buffers on the conservation of semiaquatic amphibians. Conservation Biology 23:114-123.

Studies on riparian buffers have usually focused on the amount of land needed as habitat for the terrestrial life stages of semiaquatic species. Nevertheless, the landscape surrounding wetlands is also important for other key processes, such as dispersal and the dynamics of metapopulations. Multiple elements that influence these processes should therefore be considered in the delineation of buffers. We analyzed landscape elements (forest cover, density of roads, and hydrographic network) in concentric buffers to evaluate the scale at which they influence stream amphibians in 77 distinct landscapes. To evaluate whether our results could be generalized to other contexts, we determined whether they were consistent across the study areas. Amphibians required buffers of 100-400 m of suitable terrestrial habitat, but interspecific differences in the amount of habitat were large. The presence of amphibians was related to roads and the hydrographic network at larger spatial scales (300-1500 m), which suggests that wider buffers are needed with these elements. This pattern probably arose because these elements influence dispersal and metapopulation persistence, processes that occur at large spatial scales. Furthermore, in some cases, analyses performed on different sets of landscapes provided different results, which suggests caution should be used when conservation recommendations are applied to disparate areas. Establishment of riparian buffers should not be focused only on riparian habitat, but should take a landscape perspective because semiaquatic species use multiple elements for different functions. This approach can be complex because different landscape elements require different spatial extents. Nevertheless, a shift of attention toward the management of different elements at multiple spatial scales is necessary for the long-term persistence of populations.