The influence of river regulation and land use on floodplain forest regeneration in the semi‐arid upper Colorado River Basin, USA
ABSTRACT Flow regulation effects on floodplain forests in the semi-arid western United States are moderately well understood, whereas effects associated with changes in floodplain land use are poorly documented. We mapped land cover patterns from recent aerial photos and applied a classification scheme to mainstem alluvial floodplains in 10 subjectively selected 4th order hydrologic units (subbasins) in the Upper Colorado River Basin (UCRB) in order to document land use patterns (floodplain development) and assess their effects on Fremont cottonwood forest (CF) regeneration. Three of the mainstem rivers were unregulated, five were moderately regulated and two were highly regulated. We classified polygons as Undeveloped (with two categories, including CF) and Developed (with five categories). We ground-truthed 501 randomly selected polygons (4–28% of the floodplain area in each subbasin) to verify classification accuracy and to search for cottonwood regeneration, defined as stands established since regulation began or 1950, whichever is most recent. From 40% to 95% of the floodplain area remained undeveloped, but only 19–70% of the floodplain area was classified as forest. Regeneration occupied a mean of 5% (range 1–17%) of the floodplain. The likelihood of the presence of regeneration in a polygon was reduced 65% by development and independently in a complex manner by flow regulation. Our analyses indicate that floodplain forests may be in jeopardy on both regulated and unregulated rivers and that information on historical forest extent is needed to better understand their current status in the UCRB. Conservation efforts need to be coordinated at a regional level and address the potentially adverse affects of both flow regulation and floodplain development. Published in 2007 by John Wiley & Sons, Ltd.
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ABSTRACT: In forested wetlands, hydrology exerts complex and sometimes compensatory influences on tree growth. This is particularly true in semi-arid ecosystems, where water can be both a limiting resource and a stressor. To better understand these relationships, we studied hydrologic and edaphic controls on the density, growth, tree architecture and overall productivity of forested wetlands dominated by the tree species Alnus glutinosa and Salix atrocinerea in Southern Europe. We sampled 49 plots set within 21 stands in the Atlantic coastal zone of the Iberian Peninsula, and quantified woody composition, size structure (diameter and height), and radial growth using dendrochronology. Plots were grouped into three saturation classes to compare tree growth characteristics (tree density, degree of sprouting, live basal area and productivity) across levels of saturation. We used Principal Component Analysis (PCA) to create integrated explanatory factors of hydrology, soil nutrient status and soil texture for use in linear mixed models to predict stand characteristics. Increased site saturation favoured a shift in species dominance from Alnus to Salix and resulted in a higher degree of multi-stemmed tree architecture (‘shrubbiness’), particularly for Alnus. Radial growth was negatively correlated with long-term soil saturation; however, annual productivity on a per-tree basis varied by species. Alnus growth and tree density were negatively correlated with waterlogging and fine-textured soils, possibly due to anaerobiosis in the rooting zone. In contrast, Salix growth was more influenced by nutrient limitation. Overall site productivity as measured by annual basal area increment decreased with prolonged saturation. In summary, soil saturation appears to act as a chronic stressor for tree species in this ecosystem. However, these species persist and maintain a dominant canopy position in the most permanently flooded patches through increased sprouting, albeit at a reduced rate of overall biomass accumulation relative to well-drained sites. The diversity in functional responses among wetland forest species has important implications for the conservation and management of these ecosystems. The sustainable management of these ecosystems is directly tied to their vulnerability to changing hydrological conditions. Non-equilibrium modifications to the hydrologic regime from land use and climate change, which are particularly severe in semi-arid regions, may further decrease productivity, integrity and resilience in these stress-adapted communities.Forest Ecology and Management. 01/2010;
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ABSTRACT: In arid regions of the world, the conversion of native vegetation to agriculture requires the construction of an irrigation infrastructure that can include networks of ditches, reservoirs, flood control modifications, and supplemental groundwater pumping. The infrastructure required for agricultural development has cumulative and indirect effects, which alter native plant communities, in parallel with the direct effects of land use conversion to irrigated crops. Our study quantified historical land cover change over a 150-year period for the Walker River Basin of Nevada and California by comparing direct and indirect impacts of irrigated agriculture at the scale of a 10,217 km2 watershed. We used General Land Office survey notes to reconstruct land cover at the time of settlement (1860–1910) and compared the settlement-era distribution of land cover to the current distribution. Direct conversion of natural vegetation to agricultural land uses accounted for 59 percent of total land cover change. Changes among nonagricultural vegetation included shifts from more mesic types to more xeric types and shifts from herbaceous wet meadow vegetation to woody phreatophytes, suggesting a progressive xerification. The area of meadow and wetland has experienced the most dramatic decline, with a loss of 95 percent of its former area. Our results also show Fremont cottonwood, a key riparian tree species in this region, is an order of magnitude more widely distributed within the watershed today than at the time of settlement. In contrast, areas that had riparian gallery forest at the time of settlement have seen a decline in the size and number of forest patches. La conversión de vegetación nativa en agricultura en las regiones áridas del mundo demanda la construcción de una infraestructura de irrigación que incluya redes de canales, reservorios, obras para el control de inundaciones y bombas para extraer agua subterránea suplementaria. La infraestructura necesaria para el desarrollo agrícola en esas regiones tiene efectos indirectos y acumulativos, que afectan las comunidades de plantas nativas, paralelamente con los efectos directos de la conversión del uso del suelo a cultivos irrigados. En nuestro estudio se hizo la cuantificación del cambio histórico de la cubierta del suelo sobre un período de 150 años en la Cuenca del Río Walker de Nevada y California, comparando los impactos directos e indirectos de la agricultura de irrigación en un ámbito de 10.217 km2 de cuenca. Utilizamos las notas de los estudios realizados por la Oficina General de Tierras para reconstruir la cobertura del suelo en los tiempos del poblamiento del área (1860–1910) y comparamos la distribución de la cubierta del suelo durante la era del poblamiento con la distribución actual. La conversión directa de la vegetación natural en usos agrícolas representó el 59 por ciento del cambio total de la cobertura de la tierra. Los cambios experimentados en la vegetación no agrícola incluyeron transformaciones desde tipos más mésicos a otros más xéricos, lo mismo que cambios de vegetación de pradera herbácea húmeda a freatofitos leñosos, lo cual indica una xerificación progresiva. El área de praderas y humedales ha experimentado la declinación más dramática, con una pérdida del 95 por ciento de su extensión anterior. Nuestros resultados también muestran que el álamo de Fremont, una especie arbórea ribereña clave de la región, se encuentra hoy en un orden de magnitud más ampliamente distribuida dentro de la cuenca de lo que estuvo en tiempos del poblamiento. Por contraste, las áreas que tenían bosque de galería ribereño en tiempos del poblamiento han visto una declinación en el tamaño y número de los parches de arbolado.Annals of the Association of American Geographers 05/2012; 102(3):531-548. · 2.17 Impact Factor
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ABSTRACT: This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.Annals of the Association of American Geographers 01/2012; 1023:531-548. · 2.17 Impact Factor