Using data from a water‐balance instrument cluster with spatially distributed sensors we determined the magnitude and within‐catchment variability of components of the catchment‐scale water balance, focusing on the relationship of seasonal evapotranspiration to changes in snowpack and soil moisture storage. Co‐located, continuous snow depth and soil moisture measurements were deployed in a rain–snow transition catchment in the mixed‐conifer forest in the Southern Sierra Nevada. At each elevation sensors were placed in the open, under the canopy, and at the drip edge on both north‐ and south‐facing slopes. Snow sensors were placed at 27 locations, with soil moisture and temperature sensors placed at depths of 10, 30, 60, and 90 cm beneath the snow sensor. Soils are weakly developed (Inceptisols and Entisols) and formed from decomposed granite with properties that change with elevation. The soil–bedrock interface is hard in upper reaches of the basin (>2000 m) where glaciers have scoured the parent material approximately 18,000 yr ago. Below an elevation of 2000 m soils have a paralithic contact (weathered saprolite) that can extend beyond a depth of 1.5 m, facilitating pathways for deep percolation. Soils are wet and not frozen in winter, and dry out in the weeks following spring snowmelt and rain. Based on data from two snowmelt seasons, it was found that soils dry out following snowmelt at relatively uniform rates; however, the timing of drying at a given site may be offset by up to 4 wk because of heterogeneity in snowmelt at different elevations and aspects. Spring and summer rainfall mainly affected sites in the open, with drying after a rain event being faster than following snowmelt. Water loss rates from soil of 0.5 to 1.0 cm d−1 during the winter and snowmelt season reflect a combination of evapotranspiration and deep drainage, as stream baseflow remains relatively low. About one‐third of annual evapotranspiration comes from water storage below the 1‐m depth, that is, below mapped soil. We speculate that much of the deep drainage is stored locally in the deeper regolith during periods of high precipitation, being available for tree transpiration during summer and fall months when shallow soil water storage is limiting. Total annual evapotranspiration for water year 2009 was estimated to be approximately 76 cm.

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Dead organic matter is an important structural and functional element in natural forests, but its quantity, quality, and spatial distribution are greatly modified by intensive harvesting and management through forestry. From the perspective of conflicts with biodiversity, the most important changes are associated with reductions in the abundance of snags, cavity trees, and coarse-woody debris, all of which are well known as critical habitat elements for a wide range of indigenous species. Changes in the depth and quality of the forest floor of managed stands are also important for some species and guilds of wildlife. Resolution of this conflict between forestry and biodiversity will require the design and implementation of management systems that accommodate the critical habitat qualities associated with dead organic matter, particularly with large-dimension deadwood and cavities. This goal may be most effectively achieved by an integrated strategy that involves (i) basing forest-management planning on shifting-mosaic habitat models of stand harvesting and replacement, designed to ensure a continuous availability of sufficient areas of stands old enough to sustain habitat features associated with dead organic matter, along with (ii) the provision of protected areas of mature and older growth forest, associated with riparian buffers, deer yards, and nonharvested ecological reserves and other kinds of protected areas. The protected areas are necessary to accommodate those elements of biodiversity that cannot tolerate the conditions of managed stands.Key words: biodiversity, managed forests, plantations, old-growth forests, coarse-woody debris, cavity trees, snags.

Export of dissolved organic matter (DOM) from California oak woodland ecosystems is of a great concern because DOM is a precursor for carcinogenic disinfection byproducts (DBPs) formed during drinking water treatment. Fresh litter and decomposed duff materials for the four dominant vegetation components of California oak woodlands: blue oak (Quercus douglassi H. & A.), live oak (Quercus wislizenii A. DC.), foothill pine (Pinus sabiniana Dougl.), and annual grasses, were exposed in natural condition for an entire rainy season (December to May) to evaluate their contributions of particulate (POC) and dissolved (DOC) organic carbon, particulate (PON) and dissolved (DON) organic nitrogen, inorganic nitrogen (NH4+ and NO3-), and trihalomethane (THM) and haloacetonitrile (HAN) formation potentials, to surface waters. Litter and duff materials can be significant sources of DOC (litter=29-126 mg DOC g(-1) C; duff=6.5-37 mg DOC g(-1) C) and THMs and HANs (up to 4600 mg-THMs g-C(-1) and 137 microg-HANs g-C(-1)). Blue oak litter had the highest yield of DOC, THM, and HAN precursors. When scaled to the entire watershed, leachate production yielded 445 kg-DOC ha(-1), as compared to DOC export via streams of 5.25 kg-DOC ha(-1). DOC transport to surface waters is facilitated by subsurface lateral flow through A horizons during storm events. The majority of DOM and DBP precursors was leached from plant materials in the initial rainfall events and thus may explain the seasonal stream pattern of a DOC pulse early in the rainy season.

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