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DeWine, J. M. and D. J. Cooper.: 2007. Effects of river regulation on riparian box elder (Acer negundo) forests in the canyons of the upper Colorado River Basin, USA. Wetlands 27:278-289.

Canyon riparian zone vegetation is vulnerable to effects of upstream river regulation. We studied box elder (Acer negundo) dominated canyon riparian forests intensively on the Green and Yampa rivers in Dinosaur National Monument, Colorado, and extensively in four other major rivers of the upper Colorado River Basin to determine the effects of river regulation on riparian tree establishment patterns. We: 1) aged individuals to determine if establishment was correlated with high annual peak flows, 2) mapped cohorts to determine if the areal extent of post-regulation cohorts was reduced on regulated compared to unregulated river reaches, and 3) measured the floodplain position of cohorts in regulated and unregulated rivers to determine if establishment was confined to lower landscape positions under regulated flow regimes. Box elder establishment was highly correlated with annual peak flows, with most recruitment occurring during years with unusually high peak flows. In regulated river reaches recruitment was facilitated by annual peak flows that were below average under a natural flow regime but were unusually high under the post-dam flow regime. The areal extent of post-regulation box elder cohorts was reduced on the regulated river compared to pre-regulation cohorts on all rivers, and recent cohorts on an unregulated river. Post-regulation cohorts on regulated rivers established at lower landscape positions than cohorts on unregulated rivers, resulting in inset floodplain forests on regulated rivers. The reduction in establishment height above the river was directly proportional to the magnitude of post-regulation peak flow reduction. Controlled high magnitude flood releases would facilitate forest regeneration across the full extent of historic forests, and peak flows that would mimic a lower magnitude natural hydrograph would facilitate establishment in the inset floodplain. In an era of increasing consumption of shrinking water supplies, opportunities for high magnitude reservoir releases are likely to diminish, increasing the need for active management of riparian forest ecosystems.

Patterson, L, and D. J Cooper.: 2007. The use of hydrological and ecological indicators for the restoration of drainage ditches and water diversions in a mountain fen, Cascade Range, California. Wetlands 27: 290-304.

An intact hydrologic regime and the presence of peat forming vegetation are critical for the persistence of fen wetlands. Fen restoration projects often focus on reestablishing water tables near the soil surface, with little effort directed toward identifying historic hydrologic regimes, hydrologic modifications, and the sources of degradation. We used inconsistencies in the modern hydrologic regime and historic hydrologic indicators present in the soil seedbank, vegetation, and organic soil composition to identify areas of Drakesbad Meadow, a mountain fen in Lassen Volcanic National Park, California, that had been degraded. A network of ground-water monitoring wells and piezometers were used to identify the hydrologic regime of the 4.7-ha site. The presence of thick organic soils in sites with deep late summer water tables, inconsistencies between species present in the seedbank and the existing vegetation, and the presence of dry meadow species such as Poa pratensis and Hordeum brachyantherum in areas with organic soils were used to determine that 2.4 ha of the site was degraded. A drainage ditch within the fen and diversions of the fen's water supply caused by a road outside of the fen were identified as the source of hydrologic modification and degradation. These were restored by blocking the flow of water in the main drainage ditch and by installing a series of channels to allow water to cross the road. Reconnecting flow beneath the road resulted in raising the summer water table from 80 cm below the soil surface to less than 10 cm in areas downslope of the road. The addition of five sheet-metal dams perpendicular to flow in the main drainage ditch resulted in raising the water table to within 10 to 20 cm of the soil surface in areas adjacent to and down gradient of the ditch. Before restoration, average late August water table levels across the entire site were 30 cm below the soil surface, while average post-restoration water table levels were 19 cm below the soil surface. One year following hydrologic restoration, the percent canopy cover of species indicative of uplands and wet meadows decreased - Deschampsia cespitosa, Hordeum brachyantherum, and Poa pratensis - while canopy cover of peat-forming species indicative of fens increased - Carex utriculata, Scirpus microcarpus, and Carex simulata. It is clear from our study that fens in this region will not persist under drought-like conditions created by water diversions, yet well-designed restoration projects can be used to restore modified hydrologic regimes and peat-forming vegetation necessary for the persistence of fen wetlands.

.H. L. Beyer, E. H. Merrill, N. Varley, and M. S. Boyce.: 2007. Willow on Yellowstone's Northern Range: evidence for a trophic cascade? Ecological Applications 17:1563-1571.

Reintroduction of wolves (Canis lupus) to Yellowstone National Park in 1995-1996 has been argued to promote a trophic cascade by altering elk (Cervus elaphus) density, habitat-selection patterns, and behavior that, in turn, could lead to changes within the plant communities used by elk. We sampled two species of willow (Salix boothii and S. geyeriana) on the northern winter range to determine whether (1) there was quantitative evidence of increased willow growth following wolf reintroduction, (2) browsing by elk affected willow growth, and (3) any increase in growth observed was greater than that expected by climatic and hydrological factors alone, thereby indicating a trophic cascade caused by wolves. Using stem sectioning techniques to quantify historical growth patterns we found an approximately twofold increase in stem growth-ring area following wolf reintroduction for both species of willow. This increase could not be explained by climate and hydrological factors alone; the presence of wolves on the landscape was a significant predictor of stem growth above and beyond these abiotic factors. Growth-ring area was positively correlated with the previous year's ring area and negatively correlated with the percentage of twigs browsed from the stem during the winter preceding growth, indicating that elk browse impeded stem growth. Our results are consistent with the hypothesis of a behaviorally mediated trophic cascade on Yellowstone's northern winter range following wolf reintroduction. We suggest that the community-altering effects of wolf restoration are an endorsement of ecological-process management in Yellowstone National Park.

W. B. Trowbridge.: 2007. The role of stocasticity and priority effects in floodplain restoration. Ecological Applications 17: 1312-1324.

This paper is a test of two widely held assumptions in the practice of riparian restoration: (1) if physical processes are restored, plant communities will naturally reassemble themselves, and (2) restored communities will resemble reference sites. Seasonal flooding was restored to two interconnected floodplains in the Central Valley of California (USA), and plant community establishment was studied for six years at 300 permanent vegetation plots. If these two assumptions are valid, then the two floodplains should end up with similar plant assemblages, and they should both have followed a similar trajectory. Then, once the relevant physical processes are restored, (1) plots with similar environmental conditions should have increasingly similar species compositions, (2) plant communities should become more stable and cohesive, (3) both species distributions and plant communities should respond to changes in environmental conditions, (4) plot diversity should decrease, and (5) perennial species should replace annuals.

The plots were classified into communities using TWINSPAN, and these communities differed significantly with respect to the main environmental gradient (inundation). Bray-Curtis similarities were calculated for each pair of plots. Patterns in similarity were used to test the strength of communities and the relative importance of proximity and inundation. On the northern floodplain, there was a trend of increasing similarity for plots with similar environmental conditions over the course of the study; plant communities became more stable and clearly responded to changes in environmental conditions. Plot diversity decreased, and the proportion of perennial species increased. On the southern floodplain, however, plots with similar environmental conditions became less similar, while plots that were close together became more similar; plant communities did not become more stable though they did shift in response to changes in environmental conditions. Taken together, this evidence suggests that assembly of communities is more stochastic than deterministic.

Posted on September 24, 2007.

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