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Berlin Brandenburg

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  • 1
    In: Ecohydrology, November 2012, Vol.5(6), pp.721-732
    Description: Changes of the land surface affect the water balance components over seasonal, annual and decadal time scales. This study explored the role of vegetation cover transitions on evapotranspiration in forested watersheds of the North American West. We applied empirical time‐recovery functions describing the impact of forest removal and subsequent regrowth on actual evapotranspiration () or runoff. A generalized function () was adapted to the North American West and tested using three different datasets of observed or estimated in forest chronosequences: from flux towers equipped with eddy covariance sensors, estimated from the water balance in experimental paired watersheds and in a set of gauged watersheds with considerable forest cover history dating back to the 18th century. from the first two datasets showed a behaviour similar to the K‐curve, although the timing and the magnitude differed substantially. To reconstruct long‐term changes in for the gauged watersheds, we applied a transfer function approach linking the K‐curve and the reconstructed forest cover history at the watershed scale. In several watersheds, correlation coefficients between the reconstructed changes and the annual water balances suggest that changes in time were driven by the land cover transitions. In watersheds with low correlations, disturbance activities peaked before the 20th century, and the effects of vegetation have phased out in the period of streamflow observations. The findings of this paper suggest that trends in the observed water balance in forested watersheds can be associated to land cover disturbances well before the start of hydro‐climatic observations. Copyright © 2011 John Wiley & Sons, Ltd.
    Keywords: Forest Disturbance ; Recovery ; Evapotranspiration ; Stand Age ; North American West ; Water Balance ; Forest Cover History ; Eddy Covariance Fluxes
    ISSN: 1936-0584
    E-ISSN: 1936-0592
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  • 2
    Language: English
    In: Ecohydrology, March 2012, Vol.5(2), pp.145-159
    Description: Widespread, rapid, drought‐, and infestation‐triggered tree mortality is emerging as a phenomenon affecting forests globally and may be linked to increasing temperatures and drought frequency and severity. The ecohydrological consequences of forest die‐off have been little studied and remain highly uncertain. To explore this knowledge gap, we apply the extensive literature on the ecohydrological effects of tree harvest in combination with the limited existing die‐off ecohydrology research to develop new, relevant hypotheses. Tree mortality results in loss of canopy cover, which directly alters evaporation, transpiration, and canopy interception and indirectly alters other watershed hydrologic processes, including infiltration, runoff, groundwater recharge, and streamflow. Both die‐off and harvest research suggest that for most forests, water yield can be expected to increase following substantial loss of tree cover by die‐off. We hypothesize that where annual precipitation exceeds ∼500 mm or water yield is dominated by snowmelt, watersheds will experience significantly decreased evapotranspiration and increased flows if absolute canopy cover loss from die‐off exceeds 20%. However, recent observations suggest that water yield following die‐off can potentially decrease rather than increase in drier forests. To reliably predict die‐off responses, more research is needed to test these hypotheses, including observations of multiple water budget components and the persistence of ecohydrological effects with the post‐die‐off successional dynamics of tree recruitment, understorey growth, and interactions with additional disturbances. With die‐off, mitigation and restoration options are limited and costly, necessitating societal adaptation; therefore, die‐off ecohydrology should be a high priority for future research. Published in 2011. This article is a US Government work and is in the public domain in the USA.
    Keywords: Ecohydrology ; Die‐Off ; Tree Mortality ; Forest Mortality ; Evapotranspiration ; Recharge ; Water Yield ; Bark Beetle ; Tree Pests
    ISSN: 1936-0584
    E-ISSN: 1936-0592
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