Research Summaries

Manoukain, M. and C. B. Marlow.
2002. Historical trends in willow cover along streams in a southwestern Montana cattle allotment. Northwest Science 76:213-220.

Concern over the apparent scarcity of tall willows prompted changes in livestock grazing management in a southwestern Montana mountain valley to avoid degradation of riparian and aquatic habitats. We assessed potential improvement on the abundance of tall willows following .implementation of a new management strategy by determining the effect of historic grazing patterns on willows canopy within the Forest Service grazing allotment. Willow canopy cover by stream reach was measured from air photos taken in 1942, 1965, and 1987. Cover for each year was compared for change over the 46-year record. Willow canopy cover fluctuated along the streams in the allotment, but the general trend was upward from 1942 to 1987. Willow stem population demography was evaluated to ascertain whether historic grazing patterns had affected stem replacement. Stem age classes were normally distributed with a replacement cycle similar to those reported in other areas of the western U.S. and Canada. These data suggest that extended periods of rest (>3 years) are not necessary for willow recovery if livestock or wildlife use is closely controlled.

Harner, M. J. and J. A. Stanford.
2003. Differences in cottonwood growth between a losing and a gaining reach of an alluvial floodplain. Ecology 84:1453-1458.

Interstitial flow of river (hyporheic) water influences algal productivity, benthic assemblages, and locations of fish spawning. However, little is known of the effects of hyporheic flow in the growth of riparian vegetation. By increasing water availability and nutrient delivery, regional upwelling of hyporheic water may increase the growth of terrestrial vegetation. We tested and accepted the hypothesis that cottonwood trees (Populus trichocarpa) in a gaining reach of an alluvial floodplain grow faster than trees in a losing reach by comparing basal areas and ages on an expansive floodplain in western Montana. Trees in the gaining reach had basal areas twice the size of the trees in the losing reach, after correcting for tree age. In addition, the carbon-to-nitrogen ratios in leaves were 16% lower in the gaining reach. Lower cottonwood stem densities, deeper layers of fine sediments, and a higher water table occurred in the gaining compared to the losing reach. Each of these variables was significantly correlated with tree growth and likely interacted to influence the productivity of cottonwoods. We concluded that hydration and fertilization of riparian trees likely are mediated by hyporheic flow.

Ward, T. A., K. W. Tate, E. R. Atwill, D. F. Life, D. L. Lancaster, N. McDougald, S. Barry, R. S. Ingram, H. A. George, W. Jensen, W. E. Frost, R. Phillips, G. G. Markegard, and S. Larson.
2003. A comparison of three visual assessments for riparian and stream health. Journal of Soil and Water Conservation 58:82-88.

Visual assessments are integral components of several widely promoted efforts to assess the health of stream and riparian areas across the nation. The U.S. Environmental Protection Agency’s Habitat Assessment Field Data Sheet (HAFDS), USDA – Natural Resources Conservation Service’s Stream Visual Assessment (SVA), and the U.S. Department of Interior – Bureau of Land Management’s Proper Functioning Condition (PFC) assessment were applied to 234 rangeland riparian areas to determine: 1) how well the assessments correlate, and 2) how site-specific stream and riparian characteristics affect the outcome of each assessment and thus the comparison of outcomes across stream types. Habitat Assessment Field Data Sheet and Stream Visual Assessment are habitat driven assessments, which target similar parameters resulting in a strong positive correlation between these methods (r = 0.81). BLM’s Proper Functioning Condition focuses on parameters related to hydrologic function, thus a weaker correlation was found when comparing Proper Functioning Condition to the Habitat Assessment Field Data Sheet and the NRCS’ Stream Visual Assessment methods (r = 0.58 and 0.54). A combination of one habitat assessment and Proper Functioning Condition should be utilized to conduct a comprehensive assessment of riparian/stream health. Site characteristics, which were significantly associated with assessment outcomes, included entrenchment ratio, substrate size, channel width to depth, and slope. This presents a problem in that comparison of assessment outcomes across different streams and stream reaches are confounded by factors such as slope and substrate type, which may not always be indicative of riparian/stream health. The Rosgen Stream Morphology Classification was used to successfully control for the effect of these site-specific effects on assessment outcome, allowing for comparison of riparian/stream health assessments across streams.

Rich, T. D.
2002. Using breeding land birds in the assessment of western riparian systems. Wildlife Society Bulletin 30:1128-1139.

In the western U.S., riparian ecosystems are among the highest priorities for improved management and restoration. Riparian vegetation has been widely destroyed or seriously degraded by livestock grazing, water diversions, altered flood regimes, and other human activities. Riparian degradation has led to a major federal initiative to assess riparian areas and prioritize them for restoration. Proper Functioning Condition (PFC) assessment has served as the main methodology for assessing riparian health by the U.S. Bureau of Land Management (BLM), U.S. Forest Service, U.S. Fish & Wildlife Service, and U.S. Natural Resources Conservation Service. PFC is a rapid qualitative assessment method whose purpose is to assess “how well the physical processes are functioning”. Here, I propose a simple method for incorporating an assessment of the breeding land bird community into the PFC methodology. This would bring the PFC assessment closer to an evaluation of biotic integrity. Experts identified 77 species as obligate or dependent breeding riparian land birds in the western U.S., and their occurrence serves as the standard to which data can be compared. The method is illustrated with sample data from the Boise River in southwestern Idaho. The first step was to construct a list of riparian obligate and dependent land bird species that should occur on the site during the breeding season. Relative abundance data from the Breeding Bird Survey could be used to fine-tune the list of expected obligate and dependent species. The simplest scoring was to calculate the percentage of potential obligate and dependent species which actually occurred (i.e., 44%, N=25) in this example. Knowledge of the ecology of those species actually on the site and those missing should be used along with the score to determine conservation priority.

Nagler, P. L., E. P. Glenn, and T. L. Thompson.
2003. Comparison of transpiration rates along saltcedar, cottonwood and willow trees by sap flow and canopy temperature methods. Agriculture and Forest Meteorology 116:73-89.

Transpiration, measured by stem flow gauges, and canopy and air temperature differential of Populus fremontiiSalix goodingii, and Tamarix ramosissima were compared to determine if remotely sensed canopy temperatures could be used to estimate transpiration or water stress in these trees in desert riparian zones of the U.S. and Mexico. Controlled experiments were conducted in which containerized plants were placed closely together and allowed to grow into a single, dense canopy over a summer in a desert climate. At the end of the growth period, two canopies of each species are measured for transpiration and temperature differential over 11 days, first under unstressed conditions then under water or salt stress. Transpiration and temperature differential were significantly (P< 0.05) correlated for all species. Correlation coefficients improved when a radiation term was included in the equation predicting transpiration from temperature differential. During the non-stress part of the experiment, canopies of all three species had similar rates of transpiration, but saltcedar maintained higher transpiration rates and lower stomatal resistance that the native trees on the stress treatments. For each species, models were developed, using both meteorological data and a canopy, energy balance equation, to predict daily transpiration and stomatal resistance; these models had standard errors of 15-22% when compared with measured transpiration over the unstressed portion of the experiment.


Stillings, A. M., J. A. Tanaka, N. R. Rimbey, T. Delcurto, P. A. Momont, and M. L Porath.
2003. Economic implications of off-stream water development to improve riparian grazing. Journal of Range Management 56:418-424.

Livestock grazing in riparian areas is an important management issue on both private and public lands. A study was initiated in northeastern Oregon to evaluate the economic and ecological impacts of different cattle management practices on riparian areas. The effect of off-stream water and salt on livestock distribution and subsequent impact on riparian use, water quality, and livestock production was evaluated. A multi-period bioeconomic linear programming model was used to the long-term economic feasibility of this management practice with a riparian utilization restriction of 35% for a 300 cow-calf operation. The utilization restriction resulted in economically optimal herd sizes 10% smaller than the baseline herd size. With the management practice, cattle were distributed more evenly, consumed more upland forage before maximum riparian utilization was reached, and gained more weight. The economic impacts of these outcomes were increased with expected annual net returns to the ranch for the project ranging between $4,500 and $11,000 depending on cattle prices and precipitation levels.