Nate Hough-Snee

The Blurred Line between Form and Process: A Comparison of Stream Channel Classification Frameworks.

Stream classification provides a means to understand the diversity and distribution of channels and floodplains that occur across a landscape while identifying links between geomorphic form and process. Accordingly, stream classification is frequently employed as a watershed planning, management, and restoration tool. At the same time, there has been intense debate and criticism of particular frameworks, on the grounds that these frameworks classify stream reaches based largely on their physical form, rather than direct measurements of their component hydrogeomorphic processes. Despite this debate surrounding stream classifications, and their ongoing use in watershed management, direct comparisons of channel classification frameworks are rare. Here we implement four stream classification frameworks and explore the degree to which each make inferences about hydrogeomorphic process from channel form within the Middle Fork John Day Basin, a watershed of high conservation interest within the Columbia River Basin, U.S.A. We compare the results of the River Styles Framework, Natural Channel Classification, Rosgen Classification System, and a channel form-based statistical classification at 33 field-monitored sites. We found that the four frameworks consistently classified reach types into similar groups based on each reach or segment’s dominant hydrogeomorphic elements. Where classified channel types diverged, differences could be attributed to the (a) spatial scale of input data used, (b) the requisite metrics and their order in completing a framework’s decision tree and/or, (c) whether the framework attempts to classify current or historic channel form. Divergence in framework agreement was also observed at reaches where channel planform was decoupled from valley setting. Overall, the relative agreement between frameworks indicates that criticism of individual classifications for their use of form in grouping stream channels may be overstated. These form-based criticisms may also ignore the geomorphic tenet that channel form reflects formative hydrogeomorphic processes across a given landscape.

Multi-scale environmental filters and niche partitioning govern the distributions of riparian vegetation guilds

Across landscapes, riparian plant communities assemble under varying levels of disturbance, environmental stress, and resource availability, leading to the development of distinct riparian life-history guilds over evolutionary timescales. Identifying the environmental filters that exert selective pressures on specific riparian vegetation guilds is a critical step in setting baseline expectations for how riparian vegetation may respond to environmental conditions anticipated under future global change scenarios. In this study, we ask: (1) What riparian plant guilds exist across the interior Columbia and upper Missouri River basins? (2) What environmental filters shape riparian guild distributions? (3) How does resource partitioning among guilds influence guild distributions and co-occurrence? Woody species composition was measured at 703 stream reaches and each species morphological and functional attributes were extracted from a database in four categories: (1) life form, (2) persistence and growth, (3) reproduction, and (4) resource use. We clustered species into guilds by morphological characteristics and attributes related to environmental tolerances, modeling these guilds distributions as a function of environmental filters—regional climate, watershed hydrogeomorphic characteristics, and stream channel form—and guild co-existence. We identified five guilds: (1) a tall, deeply rooted, long-lived, evergreen tree guild, (2) a xeric, disturbance tolerant shrub guild, (3) a hydrophytic, thicket-forming shrub guild, (4) a low-statured, shade-tolerant, understory shrub guild, and (5) a flood tolerant, mesoriparian shrub guild. Guilds were most strongly discriminated by species rooting depth, canopy height and potential to resprout and grow following biomass-removing disturbance (e.g., flooding, fire). Hydro-climatic variables, including precipitation, watershed area, water table depth, and channel form attributes reflective of hydrologic regime, were predictors of guilds whose life history strategies had affinity or aversion to flooding, drought, and fluvial disturbance. Biotic interactions excluded guilds with divergent life history strategies and/or allowed for the co-occurrence of guilds that partition resources differently in the same environment. We conclude that the riparian guild framework provides insight into how disturbance and bioclimatic gradients shape riparian functional plant diversity across heterogeneous landscapes. Multiple environmental filters should be considered when the riparian response guild framework is to be used as a decision-support tool framework across large spatial extents.

Direct and indirect drivers of instream wood in the interior Pacific Northwest, USA: decoupling climate, vegetation, disturbance, and geomorphic setting

Abstract Instream wood is a driver of geomorphic change in low-order streams, frequently altering morphodynamic processes. Instream wood is a frequently measured component of streams, yet it is a complex metric, responding to ecological and geomorphic forcings at a variety of scales. Here we seek to disentangle the relative importance of physical and biological processes that drive wood growth and delivery to streams across broad spatial extents. In so doing, we ask two primary questions: (1) is riparian vegetation a composite variable that captures the indirect effects of climate and disturbance on instream wood dynamics? (2) What are the direct and indirect relationships between geomorphic setting, vegetation, climate, disturbance, and instream wood dynamics? We measured riparian vegetation composition and wood frequency and volume at 720 headwater reaches within the American interior Pacific Northwest. We used ordination to identify relationships between vegetation and environmental attributes, and subsequently built a structural equation model to identify how climate and disturbance directly affect vegetation composition and how vegetation and geomorphic setting directly affect instream wood volume and frequency. We found that large wood volume and frequency are directly driven by vegetation composition and positively correlated to wildfire, elevation, stream gradient, and channel bankfull width. Indicator species at reaches with high volumes of wood were generally long-lived, conifer trees that persist for extended durations once delivered to stream habitats. Wood dynamics were also indirectly mediated by factors that shape vegetation: wildfire, precipitation, elevation, and temperature. We conclude that wood volume and frequency are driven by multiple interrelated climatic, geomorphic, and ecological variables. Vegetation composition and geomorphic setting directly mediate indirect relationships between landscape environmental processes and instream large wood. Where climate or geomorphic setting preclude tree establishment, reaches may remain naturally depauperate of instream wood unless wood is transported from elsewhere in the stream network.

Riparian vegetation as an indicator of riparian condition: Detecting departures from historic condition across the North American West

Floodplain riparian ecosystems support unique vegetation communities and high biodiversity relative to terrestrial landscapes. Accordingly, estimating riparian ecosystem health across landscapes is critical for sustainable river management. However, methods that identify local riparian vegetation condition, an effective proxy for riparian health, have not been applied across broad, regional extents. Here we present an index to assess reach-scale (500xa0m segment) riparian vegetation condition across entire drainage networks within large, physiographically-diverse regions. We estimated riparian vegetation condition for 53,250xa0km of perennial streams and rivers, 25,685xa0km in Utah, and 27,565xa0km in twelve watersheds of the interior Columbia River Basin (CRB), USA. We used nationally available, existing land cover classification derived from 30xa0m Landsat imagery (LANDFIRE EVT) and a modeled estimate of pre-European settlement land cover (LANDFIRE BpS). The index characterizes riparian vegetation condition as the ratio of existing native riparian vegetation cover to pre-European settlement riparian vegetation cover at a given reach. Roughly 62% of Utah and 48% of CRB watersheds showed significant (>33%) to large (>66%) departure from historic condition. Riparian vegetation change was predominantly caused by human land-use impacts (development and agriculture), or vegetation change (native riparian to invasive or upland vegetation types) that likely resulted from flow and disturbance regime alteration. Through comparisons to ground-based classification results, we estimate the existing vegetation component of the index to be 85% accurate. Our assessments yielded riparian condition maps that will help resource managers better prioritize sites and treatments for reach-scale conservation and restoration activities.

What are the Conditions of Riparian Ecosystems? Identifying Impaired Floodplain Ecosystems across the Western U.S. Using the Riparian Condition Assessment (RCA) Tool

Environmental stressors associated with human land and water-use activities have degraded many riparian ecosystems across the western United States. These stressors include (i) the widespread expansion of invasive plant species that displace native vegetation and exacerbate streamflow and sediment regime alteration; (ii) agricultural and urban development in valley bottoms that decouple streams and rivers from their floodplains and reduce instream wood recruitment and retention; and (iii) flow modification that reduces water quantity and quality, degrading aquatic habitats. Here we apply a novel drainage network model to assess the impacts of multiple stressors on reach-scale riparian condition across two large U.S. regions. In this application, we performed a riparian condition assessment evaluating three dominant stressors: (1) riparian vegetation departure from historical condition; (2) land-use intensity within valley bottoms; and (3) floodplain fragmentation caused by infrastructure within valley bottoms, combining these stressors in a fuzzy inference system. We used freely available, geospatial data to estimate reach-scale (500u2009m) riparian condition for 52,800u2009km of perennial streams and rivers, 25,600u2009km in Utah, and 27,200u2009km in 12 watersheds of the interior Columbia River Basin (CRB). Model outputs showed that riparian condition has been at least moderately impaired across ≈70% of the streams and rivers in Utah and ≈49% in the CRB. We found 84% agreement (Cohen’s ĸu2009=u20090.79) between modeled reaches and field plots, indicating that modeled riparian condition reasonably approximates on-the-ground conditions. Our approach to assessing riparian condition can be used to prioritize watershed-scale floodplain conservation and restoration by providing network-scale data on the extent and severity of riparian degradation. The approach that we applied here is flexible and can be expanded to run with additional riparian stressor data and/or finer resolution input data.

Soil Amendment Increases Tree Seedling Growth but Reduces Seedling Survival at a Retired Gravel Mine

Without restoration, modernized bogs will likely have a delayed successional progression. Noticeable differences in biomass occurred between the sites, with restored sites having significantly higher herbaceous and woody biomass. Although species richness in 1m2 quadrats was not markedly increased by restoration, H indices for species diversity increased, perhaps by reducing dominance of the species suited to the uniformity of the former agricultural habitat. The heterogeneity created by the restoration activities has allowed for biomass to accumulate more rapidly than in the control or the peat-based bog, and although not significantly different, there is a measurably thicker hydric layer in the soil of the restored sites. These changes in vegetative communities and soil formation are essential for the ecosystem to regain functions of wildlife and plant habitat value, restoring the water holding capacity of the system to resist drought and assist in flood and erosion control. Compared with upland farms characterized by a homogenous landscape, the diverse habitats within cranberry farms create heterogeneity with various levels of anthropogenic disturbance (Wen 2010). This characteristic is particularly true for agricultural wetlands of the FPP. Our finding of lower species richness in the peat-based bog compared to modernized bogs is likely due to the fact that while cranberries were being grown, some native plant species coexisted within the intact wetland. After agriculture ceased and cranberry desiccated in winter, co-existing native wetland species gained dominance. In modernized bogs, however, cranberries were maintained in monoculture. After agriculture ceased, cranberry plants died and there were higher levels of species introduction and colonization. We found that the FPP plant community is closely linked to the degree of agricultural manipulation or restoration of the vegetation and soil. Through reintroducing a dynamic hydrology, mounded topography, and hydric soil, restoration activities instituted by the NJCF are accelerating succession of the modernized bogs into swamps. In addition to the restoration activities reported here, the NJCF is actively reintroducing Atlantic white-cedar (Chamaecyparis thyoides) and native forbs to many of the modernized cranberry bogs after the microtopography is restored, although planting activity did not occur yet in the sites selected for this study. The planting of red maple is not necessary, since that species is being naturally recruited on the site by neighboring intact swamps, as demonstrated by this research. The development of vegetative communities resulting from the NJCF activities is essential in order for the ecosystem to regain functions of wildlife and plant habitat value and restoring the water holding capacity of the system. References Ahn, C. and S. Dee. 2011. Early development of plant community in a created mitigation wetland as affected by introduced hydrologic design elements. Ecological Engineering 37: 1324–1333. Eck, P.1990. The American Cranberry. New Brunswick, NJ: Rutgers University Press. Forman, R.T.T 1998. Pine Barrens: Ecosystem and Landscape. New Brunswick, NJ: Rutgers University Press. Good, R. E. and N.F. Good. 1984. The Pinelands National Reserve: An Ecosystem Approach to Management. BioScience 34(3): 169–173 Mylecraine, K.A., G.L. Zimmermann, R.R Williams, and J.E. Kuser. 2004. Atlantic white-cedar wetland restoration on a former agricultural site in the New Jersey Pinelands. Ecological Restoration 22(2): 92–98. Peet, R.K., T.R. Wentworth, and P.S. White. 1998. A flexible, multipurpose method for recording vegetation composition and structure. Castanea 63(3): 262–274. Procopio, N.A. 2010. Hydrologic and morphologic of variability in streams with different cranberry agriculture histories. Journal of the American Water Resources Association 46: 527–540. Reiser, J. 2014. New Jersey State Atlas: 1930s Aerial Photography. Trenton, NJ: New Jersey Department of Environmental Protection and Office of Information Technology. (http:// njstateatlas.com/1930/Geo: 39.772444, -74.529383 USNG: 18S WK 4030 0260). United States Department of Agriculture, Natural Resources Conservation Service. 2010. Field Indicators of Hydric Soils in the United States, Version 7.0. L.M. Vasilas, G.W. Hurt, and C.V. Noble (eds). Washington, DC: USDA, NRCS, in cooperation with the National Technical Committee for Hydric Soils. Wen, A. 2010. Ecological functions and consequences of cranberry (Vaccinium macrocarpon) agriculture in the pinelands of New Jersey. PhD dissertation, Rutgers University.