John D. Stednick

Monitoring the effects of timber harvest on annual water yield

Abstract Paired catchment studies have been used as a method to assess the effects of vegetation removal (timber harvesting) on streamflow responses including lowflows and peakflows, but particularly annual water yield. Paired catchment studies in the United States reporting on the effects of timber harvesting on annual water yields were compiled. In general, changes in annual water yield from forest cover reduction (or catchment area harvested) of less than 20% could not be determined by hydrometric or streamflow measurement methods. The catchment studies were discriminated by hydrologic region, defined by temperature and precipitation regimes. This regionalization suggested that as little as 15% of the catchment area (or basal area) could be harvested for a measurable increase in annual water yield at the catchment level in the Rocky Mountain region as compared with 50% in the Central Plains, although system responses are variable. Given changing world-wide objectives for forest land management, hydrologists will be asked to develop monitoring programs to assess the effects of multiple and temporally and spatially distributed land use activities on water resources. Less catchment area will be disturbed, thus monitoring programs must be carefully designed to obtain useful information. The concept of hydrologic recovery, i.e. return to pretreatment condition tends to be based on annual water yield, but also needs the evaluation of streamflow generation and routing mechanisms including lowflows and peakflows when compared with the pretreatment condition.

Bark beetle infestation impacts on nutrient cycling, water quality and interdependent hydrological effects

Bark beetle populations have drastically increased in magnitude over the last several decades leading to the largest-scale tree mortality ever recorded from an insect infestation on multiple wooded continents. When the trees die, the loss of canopy and changes in water and nutrient uptake lead to observable changes in hydrology and biogeochemical cycling. This review aims to synthesize the current research on the effects of the bark beetle epidemic on nutrient cycling and water quality while integrating recent and relevant hydrological findings, along with suggesting necessary future research avenues. Studies generally agree that snow depth will increase in infested forests, though the magnitude is uncertain. Changes in evapotranspiration are more variable as decreased transpiration from tree death may be offset by increased understory evapotranspiration and ground evaporation. As a result of such competing hydrologic processes that can affect watershed biogeochemistry along with the inherent variability of natural watershed characteristics, water quality changes related to beetle infestation are difficult to predict and may be regionally distinct. However, tree-scale changes to soil–water chemistry (N, P, DOC and base cation concentrations and composition) are being observed in association with beetle outbreaks which ultimately could lead to larger-scale responses. The different temporal and spatial patterns of bark beetle infestations due to different beetle and tree species lead to inconsistent infestation impacts. Climatic variations and large-scale watershed responses provide a further challenge for predictions due to spatial heterogeneities within a single watershed; conflicting reports from different regions suggest that hydrologic and water quality impacts of the beetle on watersheds cannot be generalized. Research regarding the subsurface water and chemical flow-paths and residence times after a bark beetle epidemic is lacking and needs to be rigorously addressed to best predict watershed or regional-scale changes to soil–water, groundwater, and stream water chemistry.

Biogeochemistry of beetle-killed forests: Explaining a weak nitrate response

A current pine beetle infestation has caused extensive mortality of lodgepole pine (Pinus contorta) in forests of Colorado and Wyoming; it is part of an unprecedented multispecies beetle outbreak extending from Mexico to Canada. In United States and European watersheds, where atmospheric deposition of inorganic N is moderate to low (<10 kg⋅ha⋅y), disturbance of forests by timber harvest or violent storms causes an increase in stream nitrate concentration that typically is close to 400% of predisturbance concentrations. In contrast, no significant increase in streamwater nitrate concentrations has occurred following extensive tree mortality caused by the mountain pine beetle in Colorado. A model of nitrate release from Colorado watersheds calibrated with field data indicates that stimulation of nitrate uptake by vegetation components unaffected by beetles accounts for significant nitrate retention in beetle-infested watersheds. The combination of low atmospheric N deposition (<10 kg⋅ha⋅y), tree mortality spread over multiple years, and high compensatory capacity associated with undisturbed residual vegetation and soils explains the ability of these beetle-infested watersheds to retain nitrate despite catastrophic mortality of the dominant canopy tree species.

Long-term Streamflow Changes Following Timber Harvesting

Studies under virtually every environmental condition indicate that vegetation removal results in increased annual water yield (Rothacher 1970; Harr 1976, 1979, 1983; Bosch and Hewlett 1982; Stednick 1996). However, treatment responses are variable and depend on the vegetation complex, landform, and climate of the particular watershed system studied (Hewlett and Hibbert 1967; Bosch and Hewlett 1982; Stednick 1996). Vegetative recovery, following harvest, leads to return of water yield to pretreatment levels, though at different rates for each climatic and geographic zone studied (Kovner 1956; Ziemer 1964; Harr 1979, 1983; Troendle and King 1985; Keppeler and Ziemer 1990; Stednick 1996). Thus the treatment response is time-dependent. There have been many papers written regarding short-term hydrologic changes resulting from both timber harvest and road-building in the United States (Rothacher 1970; Harr et al. 1975; Harris 1977; Harr 1980; Ziemer 1981; Harr et al. 1982, among others). Generally speaking, these studies have been short-term due to the expense and commitment required for long-term monitoring or the loss of a control watershed, i.e. land use activities (Stednick and Kern 1992). The monitoring techniques used at Alsea typify methods employed in most paired watershed studies. The effects of timber harvesting are measured by differences between preand post-logging hydrologic relations or hydrologic events of interest on Needle Branch and Deer Creek, compared to the control Flynn Creek. Regression equations developed to describe the prelogging relationships predict expected values for the dependent variables (Needle Branch or Deer Creek flow parameters) from observed values of the independent variable (Flynn Creek) (Rothacher and Miner 1967; Harris 1977). The results of the AlseaWatershed Study showed an increase in annual water yield and the three-day peak flow for Needle Branch, the clearcut watershed, and no significant change for any streamflow characteristic on Deer Creek, the

Managing bark beetle impacts on ecosystems and society: priority questions to motivate future research

Summary 1. Recent bark beetle outbreaks in North America and Europe have impacted forested landscapes and the provisioning of critical ecosystem services. The scale and intensity of many recent outbreaks are widely believed to be unprecedented. 2. The effects of bark beetle outbreaks on ecosystems are often measured in terms of area affected, host tree mortality rates, and alterations to forest structure and composition. 3. Impacts to human systems focus on changes in property valuation, infrastructure damage from falling trees, landscape aesthetics, and the quality and quantity of timber and water resources. 4. To advance our understanding of bark beetle impacts, we assembled a team of ecologists, land managers and social scientists to participate in a research prioritization workshop. 5. Synthesis and applications. We identified 25 key questions by using an established methodology to identify priorities for research into the impacts of bark beetles. Our efforts emphasize the need to improve outbreak monitoring and detection, educate the public on the ecological role of bark beetles, and develop integrated metrics that facilitate comparison of ecosystem services across sites.

The effects of acid rock drainage onCarex aquatilis leaf litter decomposition in rocky Mountain fens

Fens occur in many Colorado Rocky Mountain watersheds that have historically been affected by metal mining activities. A persistent effect of mining is acid rock drainage (ARD), which flows from mine adits and tailings piles. ARD water has low pH and high concentrations of heavy metals and can pollute surface and ground water supporting fens. There are few floristic differences between polluted and pristine fens, and it is unclear what long-term affects ARD has on fens. We investigated decomposition of native leaf litter and a standard litter for two years in fourCarex aquatilis-dominated subalpine fens. Two of the fens are affected by ARD, and their source waters have pH <4.0 and high concentrations of dissolved Zn, Cu, Mn, and Pb. The other two fens are relatively pristine, with source water pH > 6.0 and low metal concentrations. ARD significantly reduced native litter decomposition rates over two years (ANOVA, p <0.01) with 63% of the initial mass of leaf litter remaining at the most pristine site (Peru Creek fen), 47 % at a moderately polluted site (Argentine fen), and 23% at the most pristine site (Deer Creek fen). ARD also reduced the quality of litter produced. Standard litter decomposed more rapidly than native litter at all sites, particularly Peru Creek fen. Site, representing fen environment, and litter origin, representing native vs. standard litter, significantly affected decomposition rates (ANOVA, p < 0.0001) Pristine fens had decomposition rates comparable with boreal rich fens, while polluted fens had decomposition rates comparable with boreal poor fens and bogs. Acid rock drainage causes ecosystem-level responses in organic matter processing, peat accumulation rates, and most likely in nutrient cycling, which could have long-term affects on fen primary and secondary production and other functions.

The New Alsea Watershed Study

The original Alsea Watershed Study assessed the effects of timber harvesting on water, aquatic habitat, and salmonid resources using a paired-watershed approach. The New Alsea Watershed Study provides an opportunity to evaluate water resource and salmonid resource responses to current forest practices compared to undisturbed conditions. It also allows a comparison to the original study results that included an extreme manipulation in the 1960s. Flynn Creek was an undisturbed control watershed in the original study and remains an undisturbed Natural Research Area under the USDA Forest Service. Deer Creek was partially cut and demonstrated the effectiveness of streamside management zones in the original study. Needle Branch was completely clearcut with subsequent slash burning, with no streamside vegetative buffers. Needle Branch experienced some of the most dramatic water quality impacts for temperature and dissolved oxygen ever observed in response to forest management. Increases in discharge, sediment, and nutrients were also measured, although these changes were more subtle. The water quality impacts observed for Needle Branch, especially temperature, are sometimes erroneously cited as the inevitable consequence of clearcutting in the Pacific Northwest. The regenerated forest in the Needle Branch watershed is again ready for commercial harvest. The proposed timber harvesting plan in Needle Branch involves two harvesting units and will provide an opportunity to assess cumulative effects on water resources. This new study, using paired watersheds, synoptic surveys of water quality, and biological monitoring, will test how effective current forest practices are in maintaining water quality.

Effects of Timber Harvesting on Streamflow in the Alsea Watershed Study

The Alsea Watershed Study was the nation’s first long-term watershed study to simultaneously consider the effects of timber harvesting on water and water related resources (fish habitat and fish populations) (Brown 1972). The study began in 1957 as a cooperative effort between Oregon State University (then Oregon State College) and other federal and state agencies to address the effects of integrated land management on the stream environment (Harr and Krygier 1972; Moring 1975; Harris 1977). The Alsea River Basin, in the Oregon Coast Range, was selected because of the diversity of land ownership, active timber harvesting, and its close proximity to the university. The initial goal to assess these potential effects at the large watershed level proved to be too ambitious and was reduced to three small watersheds in the Alsea River Basin. The final selection of the watersheds reflected similar geographic location, exposure, elevation, and land ownership of the participants, namely the USDA Forest Service and Georgia Pacific Company (nowPlumCreekTimberCompany), a private timber company. The temperate coniferous forest in the western United States typically consists of well-developed overstories and understories. The overstory plant community of the temperate coniferous forest is dominated by Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). The understory consists of vine maple (Acer circinatum), red alder (Alnus rubra), salmonberry (Rubus spectabilis), rhododendron (Rhododendron macrophyllum), and others (Meehan 1991). The temperate coniferous forest of the Pacific Northwest of the United States extends from central Alaska to central California, including the Coastal Range of Alaska, British Columbia, Washington, Oregon, and California (Chamberlin et al. 1991). Rain is the dominant form of precipitation in the temperate coniferous forest of the Pacific Northwest of the United States and drives the hydrology of small forested streams (Chamberlin et al. 1991). The climate of the Alsea watersheds is a maritime climate with mild temperatures, winter precipitation, and

Effects of mountain pine beetle-killed forests on source water contributions to streamflow in headwater streams of the Colorado Rocky Mountains

Natural or human-influenced disturbances are important to the health and diversity of forests, which in turn, are important to the water quantity and quality exported from a catchment. However, human-induced disturbances (prescribed fire and harvesting) have been decreasing, and natural disturbances (fires and insects) have been increasing in frequency and severity. One such natural disturbance is the mountain pine beetle (MPB), (Dendroctonus ponderosae) an endemic species. A recent epidemic resulted in the mortality of millions of hectares of lodgepole pine (Pinus contorta) forests in Colorado, USA. Beetle-induced tree mortality brings about changes to the hydrologic cycle, including decreased transpiration and interception with the loss of canopy cover. This study examined the effect of the mountain pine beetle kill on source water contributions to streamflow in snowmeltdominated headwater catchments using stable isotopes (2H and 18O) as tracers. Study catchments with varying level of beetle-killed forest area (6% to 97%) were sampled for groundwater, surface water, and precipitation. Streams were sampled to assess whether beetle-killed forests have altered source water contributions to streamflow. Groundwater contributions increased with increasing beetle-killed forest area (p = 0.008). Both rain and snow contributions were negatively correlated with beetle-killed forest area (p = 0.035 and p = 0.011, respectively). As the beetle-killed forest area increases, so does fractional groundwater contribution to streamflow.

Research Opportunities in Hydrology and Biology in Future Watershed Studies

The effects of timber harvesting practices on water resources are mostly known from paired watershed studies. The first paired watershed study in the United States was in Colorado and designed to assess the effects of timber harvesting on water yield (Bates and Henry 1928). Many of these studies were designed to have demonstrable effects on water resources, specifically the timber harvesting was large in comparison to the watershed area (up to 100%), streamside vegetation buffers were not used, all timber including non-merchantable materials were removed, or the forest regeneration was suppressed by herbicide applications. Although these experiments helped identify the hydrologic processes affected by timber harvesting, they do not necessarily represent the effects of normal forest operations. The scope of watershed studies was soon expanded beyond water quantity and the processes of the hydrologic cycle to include water quality. Measurements of inputs and outputs, as precipitation and streamflow, were used for chemical budgets. In the 1960s, 150 forested experimental watersheds were being studied; only 12 of these remain relatively active and half of those are long term ecological research sites (Ziemer and Ryan 2000). Many of the active research watersheds tend to focus on ecological processes in the watershed, rather than focus on hydrological processes as related to ecology. Nonetheless, several lessons learned from Alsea and other watershed studies (Stednick et al. 2004) are worth repeating. The original AlseaWatershed Study and the ongoing research have provided some very useful lessons in forest hydrology and the effects of timber harvesting on hydrological responses. Timber harvesting of a large area in a watershed (Needle Branch) resulted in increased annual water yield. These water yield increases are higher in wetter years and lower in wetter years. As vegetation grows and the hydrological processes of interception, transpiration, and storage