Responses of stream macroinvertebrate communities to progressive forest harvesting: Influences of harvest intensity,stream size and riparian buffers

Harvesting of forests causes a range of disturbances, including changes to hydrology, nutrient inputs, water quality, food sources, habitat structure and channel morphology, which can impact streams over several years and are reflected in changes in community structure. We aimed to determine the relative magnitudes of impact and rates of recovery of benthic macroinvertebrate communities, and associated changes in biotic indices (Quantitative Macroinvertebrate Community Index and an Index of Biotic Integrity), in reaches of different sized streams within progressively logged catchments. We conducted annual summer surveys over seventeen years in fifteen New Zealand streams that differed in size (upstream catchment area between 40 and 2360 ha, mean channel widths between 2.5 and 16 m) and harvest intensity in the surrounding catchment. The largest post-harvest changes in biotic indices and community structures occurred in streams draining relatively small to medium catchments (<500 ha) where >40% of the upstream catchment had been harvested, and particularly after harvesting of overstorey riparian vegetation adjacent to study reaches. The impacts of harvest on invertebrate communities were less evident in wider streams draining catchments over 500 ha, but the largest changes from pre-harvest biotic indices and community structure still generally occurred after harvesting of riparian vegetation along these streams. The changes in community structure after harvesting of riparian vegetation typically included increases in the densities of Diptera, Mollusca and Oligochaetes, and decreases in the densities of Ephemeroptera. These results demonstrate that impacts on benthic macroinvertebrate communities increased as the proportion of upstream catchment harvested increased and/or after riparian vegetation was harvested. Some of the communities in headwater streams had largely recovered towards pre-harvest structures, whereas post-harvest recovery was less evident in relatively large streams, over the duration of the study.     

Litter decomposition can detect effects of high and moderate levels of forest disturbance on stream condition

Considerable research efforts have been devoted to determining what forest management practices most affect stream ecosystems, and how those impacts might be mitigated. Recent studies have stressed the relevance of litter decomposition to assess the conditions of headwater streams affected by riparian and upland forest harvest. Here we specifically examined whether litter decomposition can detect ecological effects of clearcutting to stream edges on headwater streams eight years after logging and if large (30 m) and narrow (10 m) riparian reserves (8-year post-harvest), and selection logging at 50% removal of basal area of riparian trees (1-year post-harvest), are effective protection measures for streams. We measured decomposition rates of red alder (Alnus rubra) leaf litter in sixteen stream reaches, including reference reaches in a 70-year-old forest. We further examined assemblages of two main litter consumer groups, shredder invertebrates in riffles and aquatic hyphomycete fungi developing on decaying alder leaves. Alder decay rate was significantly lower in clearcut reaches than in reference reaches, and we found no evidence that any alternative riparian management practices examined in this study were able to mitigate against such an effect of logging. In unlogged reaches, rapid litter decomposition (0.0050–0.0118 day⁻¹) was associated with high density and diversity of shredders (up to ten taxa). Slower litter decomposition in wide and narrow reserve reaches (0.0019–0.0054 day⁻¹) and clearcut reaches (0.0024–0.0054 day⁻¹) was attributed to lower density and richness of shredders. By contrast, the low decay rate in recently established thinned reaches (0.0031–0.0049 day⁻¹) was not associated with a numerical response of shredders. Smothering of submerged leaves by sediments may have caused the reduction in alder decay rate in thinned reaches. Across all forest treatments fungal biomass or diversity remained fairly similar. Our findings suggest that stream ecosystems are extremely sensitive to small changes in riparian and upland forest cover. We propose that litter decomposition as a key ecosystem function in streams could be incorporated into further efforts to evaluate and improve forestry best management practices.     

Effects of even-aged timber harvest on stream salamanders: Support for the evacuation hypothesis

Habitats worldwide are increasingly threatened by degradation and conversion. Critical to the process of habitat loss is the organismal response, which can have effects on immediate conservation measures or future restoration. Among the most threatened and underappreciated habitats are headwater streams, which are small but abundant features of montane forests. These habitats comprise a significant proportion of the total stream length, can harbor remarkable biodiversity, and are critical for numerous ecosystem processes. One of the most abundant organisms in montane headwater ecosystems are salamanders, and therefore what happens to salamanders when the forest habitats surrounding headwater streams are altered? Three main hypotheses exist: (1) mortality hypothesis; (2) retreat hypothesis; and (3) evacuation hypothesis. To examine these hypotheses we evaluated the impacts of even-aged riparian timber harvest on stream-breeding salamanders. Riparian forests along headwater streams were logged, leaving riparian buffers of 0 m, 9 m, and 30 m. Responses to each riparian alteration were measured in terms of salamander terrestrial habitat use and growth in the riparian habitat, as well as changes in population density within headwater streams. Adult and juvenile salamander densities measured in headwater streams were significantly greater in logged riparian treatments than in unaltered riparian treatments. In addition, salamanders significantly reduced their terrestrial habitat use following riparian logging with both the average distance from the stream and the relative abundance of salamanders decreasing. It is unlikely that salamanders will persist in highly modified riparian habitats, as we measured significantly reduced body conditions over short periods of time at these sites. We present corroborative evidence that salamanders evacuate the riparian habitat following intensive riparian logging, emigrating to adjacent headwater streams. Our results underscore the sensitivity of stream salamanders to riparian habitat alteration as well as the importance of riparian buffers in preserving amphibian assemblages.     

Distribution and nest site selection of red-shouldered hawks (Buteo lineatus) in forests of northeastern Wisconsin (USA)

Red-shouldered hawks (Buteo lineatus) are threatened in Wisconsin and when nest sites are found during the cruising or marking stage of timber harvesting, the harvest is altered to accommodate the hawks. If nest site locations are known before initiation of timber harvest, foresters can employ a proactive approach to manage red-shouldered hawks while maintaining timber production. We searched for red-shouldered hawks nest sites on Marinette County Forest (MCF) which encompasses 94,000 ha in northeastern Wisconsin and is the second largest county forest in the state. We used a comparative modeling approach to evaluate distribution and habitat relationships of red-shouldered hawk nest sites in relation to a suite of environmental variables in MCF. Models were used to develop forest management recommendations for red-shouldered hawks in Wisconsin. During the spring of 2006 and 2007, we broadcasted conspecific calls to survey 1121 calling stations along forest roads and trails. We located 20 and 25 active nesting territories in 2006 and 2007, respectively (11 of which were active in both years). To understand nest site selection, we measured 22 habitat variables within 0.04-ha plots at active nest sites (n = 34) and at stratified random sites (n = 61). Logistic regression with information-theoretic model selection identified a model including greater tree species richness and closeness to forested wetland as the best-approximating model. Variable selection with Discriminant Function Analysis (DFA) indicated that nest selection was best explained by greater number of tree species, closer distance to forested wetlands, greater volume of downed woody debris, fewer small sawlogs, and increased proximity to streams. Univariate comparisons identified four of the five aforementioned variables in the DFA model as significant. Red-shouldered hawks are likely more common in Wisconsin than their state status suggests. Forest management for red-shouldered hawk nest sites should focus on increasing tree species richness, increasing down woody debris volume, and protecting forested wetlands. These recommendations may assist property managers to locate and plan for continued persistence of this species on MCF.     

Nitrate attenuation in a small temperate wetland following forest harvest

Elevated nitrate concentrations in streams and groundwater are frequently observed following forest harvest. In addition to depleting nutrients available for forest regeneration, elevated nitrate export following harvest can have deleterious effects on downstream aquatic ecosystems. As part of a forest harvest experiment conducted at the Turkey Lakes Watershed, Ontario, Canada, stable isotope techniques were employed to investigate nitrate attenuation in a natural wetland receiving high concentrations of nitrate as a result of clear-cutting in the catchment. Isotopic analysis of nitrate (δ¹⁸O, δ¹⁵N) and vegetation (δ¹⁵N) demonstrated that both denitrification and plant uptake of nitrate resulted in significantly lower nitrate concentrations in wetland outflow compared to incoming stream water. Although the 0.2-ha forested swamp (4% of catchment by area) was too small to be featured on standard topographic maps, the wetland remove 65–100% of surface water nitrate inputs, thereby protecting downstream aquatic habitats from the full effect of N release from forest harvest. The δ¹⁵N enrichment factor associated with nitrate attenuation in wetland surface water was lower than typically observed during denitrification in groundwaters, suggesting that nitrate removal is complete in some areas of the wetland. Plant assimilation of nitrate was also partially responsible for the low observed enrichment factor. Wetland plants recorded the high δ¹⁵N associated with denitrification activity in portions of the wetland. Apportionment of nitrate sources using δ¹⁸O–NO₃⁻ at the outlet weir was unaffected by the wetland nitrate attenuation under pre- and post-harvest conditions due to the mid-catchment position of the wetland. Future forest management practices designed to recognize and preserve small wetlands could reduce the potentially detrimental effects of forest harvest on aquatic systems.     

Amphibian distributions in riparian and upslope areas and their habitat associations on managed forest landscapes in the Oregon Coast Range

Over the past 50 years, forested landscapes of the Pacific Northwest have become increasingly patchy, dominated by early successional forests. Several amphibian species associated with forested headwater systems have emerged as management concerns, especially after clearcutting. Given that headwater streams comprise a large portion of the length of flowing waterways in western Oregon forests, there is a need to better understand how forest management affects headwater forest taxa and their habitats. Mitigation strategies include alternatives to clearcutting, such as harvests that remove only part of the canopy and maintenance of riparian buffer strips. Our study investigates effects of upland forest thinning coupled with riparian buffer treatments on riparian and upland headwater forest amphibians, habitat attributes, and species-habitat associations. Amphibian captures and habitat variables were examined 5–6 years post-thinning within forest stands subject to streamside-retention buffers and variable-width buffers, as well as unthinned reference stands. We found no treatments effects, however, our results suggest that ground surface conditions (e.g., amount of rocky or fine substrate) play a role in determining the response of riparian and upland amphibians to forest thinning along headwater streams. Distance from stream was associated with amphibian abundance, hence retention of riparian buffers is likely important in maintaining microclimates and microhabitats needed for amphibians and other taxa. Moderate thinning and preservation of conditions in riparian and nearby upland areas by way of variable-width and streamside-retention buffers may be sufficient to maintain suitable habitat and microclimatic conditions vital to amphibian assemblages in managed headwater forests.     

Windthrow and recruitment of large woody debris in riparian stands

To document the impacts of windthrow in riparian leave strips and identify the components needed for small stream large woody debris (LWD) recruitment modeling, we monitored nine small streams at a temperate rainforest site in coastal British Columbia. This study was a component of a larger integrated study of forest management impacts on small streams. A series of small clearcuts were harvested in 1998 in a 70-year-old second growth stand that had regenerated naturally following logging and wildfire. Three cutblocks each were assigned to 10 m and 30 m buffer width treatments and three areas were assigned as unharvested controls. Seven years after the 1998 logging, all logs greater than 10 cm diameter that spanned at least part of stream channel width were measured. A total of 179 logs were recorded. Post-harvest windthrow was higher in the 10 m buffer treatment, while competition-related standing tree mortality was higher in the controls. The major windthrow events had occurred in the first and second years after logging of adjacent stands. There was no significant difference in the number of spanning and in-stream logs in the 10 m, 30 m buffer and control treatments. More than 90% of the LWD was in the 10–30 cm diameter classes. The majority of logs were oriented perpendicular to the stream channel. At the time of measurement, the majority of these trees were still suspended above the stream channel, indicating that the recruitment of logs into the stream channel is a long-term process. Time to recruitment into the channel is dependent on log and valley geometry, log size, species, and log condition prior to toppling. Log height above stream was negatively correlated with log decay class and valley width. Log length was negatively correlated with state of decay, and many windthrown logs were in an advanced state of decay before they entered the stream.     

Stream size influences stream temperature impacts and recovery rates after clearfell logging

Water temperature has profound effects on stream ecosystems. We studied effects of clear-fell logging Pinus radiata plantations on mid-summer water temperatures and recovery times in streams with 2–12 m wide channels. Post-logging increases were 2–3.8 °C for summer daily means and 4–7.3 °C for summer daily maxima. Rates of recovery of thermal regimes after logging were strongly negatively correlated with stream size, as indexed by catchment area, channel width or baseflow (r² = 0.80–0.93). Summer daily mean and maximum temperatures declined during the riparian vegetation regrowth phase by 0.18 and 0.47 °C year⁻¹, respectively, for the largest stream and 1.4 and 1.9 °C year⁻¹ in the smallest stream. Thermal regimes were restored in small streams (2–4 m wide channels) about 6–8 years after clearfelling. In medium-sized streams (6–12 m wide channels), we predict this recovery will take 12–16 years.     

Efficacy of riparian buffers in mitigating local population declines and the effects of even-aged timber harvest on larval salamanders

Headwater streams are an important and prevalent feature of the eastern North American landscape. These streams provide a wealth of ecosystem services and support tremendous biological diversity, which is predominated by salamanders in the Appalachian region. Salamanders are ubiquitous throughout the region, contributing a significant biomass that supports ecological and ecosystem processes. One of the greatest threats to salamanders is loss of headwater-riparian habitat through timber harvest. In this study, we measured larval salamander abundance at five headwater streams with different riparian buffer widths retained following logging. By sampling larval salamanders using leaf litter bags, we assessed the impacts of even-aged timber harvest on aquatic larval salamander abundances, where it was found that larvae are negatively impacted by increased stream sedimentation and a decrease in riparian buffer width. We found that retention of a 9-m buffer was effectively no different than complete removal of all riparian forest, and as such, current regulations to protect headwater streams are ineffectual. Furthermore, no significant differences were observed between the 30 m buffer treatment and uncut control treatments suggesting that a 30 m or larger riparian buffer may assuage the in-stream effects of riparian timber harvest. Management guidelines for Appalachian forests should be revised to accommodate the biology of plethodontid salamanders.     

Riparian management and the tailed frog in northern coastal forests

Although the importance of aquatic environments and adjacent riparian habitats for fish have been recognized by forest managers, headwater creeks have received little attention. The tailed frog, Ascaphus truei, inhabits permanent headwaters, and several US studies suggest that its populations decline following clear-cut logging practices. In British Columbia, this species is considered to be at risk because little is known of its abundance, distribution patterns in the landscape, and habitat needs. We characterized nine logged, buffered and old-growth creeks in each of six watersheds (n = 54). Tadpole densities were obtained by area-constrained searches. Despite large natural variation in population size, densities decreased with increasing levels of fine sediment (<64 mm diameter), rubble, detritus and wood, and increased with bank width. The parameters that were correlated with lower tadpole densities were found at higher levels in clear-cut creeks than in creeks of other stand types. Tadpole densities were significantly lower in logged streams than in buffered and old-growth creeks; thus, forested buffers along streams appear to maintain natural channel conditions. To prevent direct physical damage and sedimentation of channel beds, we suggest that buffers be retained along permanent headwater creeks. Creeks that display characteristics favoring higher tadpole densities, such as those that have coarse, stable substrates, should have management priority over less favorable creeks. Measures should also be taken to minimize fine sediment inputs from roads and stream crossings.     

Dynamics of wood recruitment in streams of the northeastern US

Wood is an important component of forested stream ecosystems, and stream restoration efforts often incorporate large wood. In most cases, however, stream restoration projects are implemented without information regarding the amount of wood that historically occurred or the natural rates of wood recruitment. This study uses a space-for-time analysis to quantify large wood loading to 28 streams in the northeastern US with a range of in-stream and riparian forest characteristics. We document the current volume and frequency of occurrence of large wood in streams with riparian forests varying in their stage of stand development as well as stream size and gradient. Linear models relating stream wood characteristics to stream geomorphic and forest characteristics were compared using Akaike's Information Criterion (AIC) model selection. The AIC analysis indicated that the volume and frequency of large wood and wood accumulations (wood jams) in streams was most closely associated with the age of the dominant canopy trees in the riparian forest (best models: log₁₀(large wood volume (m³ 100 m⁻¹)) = (0.0036 × stand age) − 0.2281, p < 0.001, r² = 0.80; and large wood frequency (number per 100 m) = (0.1326 × stand age) + 7.3952, p < 001, r² = 0.63). Bankfull width was an important factor accounting for wood volume per unit area (m³ ha⁻¹) but not the volume of wood per length of stream (100 m⁻¹). The empirical models developed in this study were unsuccessful in predicting wood loading in other regions, most likely due to difference in forest characteristics and the legacy of forest disturbance. However, these models may be applicable in other streams in the northeastern US or in streams with comparable riparian forests, underlying geology, and disturbance regimes—factors that could alter long-term wood loading dynamics. Our results highlight the importance of understanding region-specific processes when planning stream restoration and stream management projects.     

Impacts of selective logging on above-ground forest biomass in the Monts de Cristal in Gabon

Selective logging is an important socio-economic activity in the Congo Basin but one with associated environmental costs, some of which are avoidable through the use of reduced-impact logging (RIL) practices. With increased global concerns about biodiversity losses and emissions of carbon from forest in the region, more information is needed about the effects of logging on forest structure, composition, and carbon balance. We assessed the consequences of low-intensity RIL on above-ground biomass and tree species richness in a 50 ha area in northwestern Gabon. We assessed logging impacts principally in 10 randomly located 1-ha plots in which all trees ?10 cm dbh were measured, identified to species, marked, and tagged prior to harvesting. After logging, damage to these trees was recorded as being due to felling or skidding (i.e., log yarding) and skid trails were mapped in the entire 50-ha study area. Allometric equations based on tree diameter and wood density were used to transform tree diameter into biomass.Logging was light with only 0.82 trees (8.11 m³) per hectare extracted. For each tree felled, an average of 11 trees ?10 cm dbh suffered crown, bole, or root damage. Skid trails covered 2.8% of the soil surface and skidding logs to the roadside caused damage to an average of 15.6 trees ?10 cm dbh per hectare. No effect of logging was observed on tree species richness and pre-logging above-ground forest biomass (420.4 Mg ha⁻¹) declined by only 8.1% (34.2 Mg ha⁻¹). We conclude from these data that with harvest planning, worker training in RIL techniques, and low logging intensities, substantial carbon stocks and tree species richness were retained in this selectively logged forest in Gabon.     

Harnessing forest ecological sciences in the service of stewardship and sustainability: A perspective from ‘down-under’

Australia's native forests are predominantly Crown land, managed by the States. Regional Forest Agreements between four of the States and the Federal Government (1997–2001) resulted in a 36% increase in the area of conservation reserves and a 15% decrease in area of multiple-use (including timber harvesting) forests. The limited acceptance of timber harvesting in native forests, together with the rapid expansion of hardwood plantations, has diverted research focus away from native forests. Recent events including a prolonged drought and two forest fires totaling more than 3 million ha should have stimulated research in native forests on the effects of fire on ecosystem processes, on the management of fire and on management of water catchments; fires, far more than logging, are shaping our native forests in recent times. In particular, the use of prescribed fire to reduce fuels has decreased. We argue that Australian research effort in native eucalypt forests is lacking in two key areas – the effects of fire on carbon storage in forests and soils, and on the management of water yield from forested catchments. The results of forest research are variously published in the scientific journals, and increasingly in consultancy reports to governments or a to a range of organizations and industries. The question of who does the harnessing of knowledge coming from the science of forest ecology is compounded by constant changes in both political and management arrangements. If forest science is to assume a greater role in politics and forest management in Australia, scientists must enter the foray, using the fighting words of politics rather than maintaining the protective mantle of neutrality. With research in native forests being continually downgraded at both State and Federal levels, we take a somewhat less than optimistic view about how well ecological sciences will be harnessed in the service of forest stewardship and sustainability in Australia.     

Nutrient concentration dynamics in an inland Pacific Northwest watershed before and after timber harvest

The nutrient loads of water draining forested watersheds are generally lower than the loads in water draining basins with other dominant land uses. Commercial forest management activities including timber harvesting, site preparation, road construction, and maintenance can alter the chemical properties of headwater forest streams, and there are concerns this can result in cumulative effects at downstream locations. Monthly water samples were collected from 1992 to 2006 in the Mica Creek Experimental Watershed (MCEW) in northern Idaho. This period of record included a pre-treatment time interval from 1992 to 1997; post-road construction period from 1997 to 2001; and post-harvest period from 2001 to 2006. Samples were analyzed for total Kjeldahl nitrogen (TKN), total ammonia nitrogen (TAN), nitrate + nitrite (NO₃ + NO₂), total phosphorus (TP), and orthophosphate (OP). Statistically significant increases (p < 0.001) were observed in NO₃ + NO₂ concentrations following both clearcut and partial cut harvest practices. Downstream of the clearcut harvest activity, mean monthly increases of 0.29 mg-N L⁻¹ were observed. Statistically significant increases were also observed at sites further downstream, but changes were smaller than those immediately below the harvest sites and reflected dilution and possibly instream processing and/or uptake. Continued monitoring at these sites will help evaluate nutrient concentration trends during stand regrowth and hydrologic recovery.     

Large wood abundance,distribution and mobilization in a third order Coastal mountain range river system,southern Chile

Large wood (LW) abundance, longitudinal distribution and mobilization were studied in the Vuelta de la Zorra channel draining a third order catchment located in the Coastal mountain range of southern Chile. Seventy-five percent of the 586.8 ha study catchment area is covered by evergreen native rainforests, 24% by Eucalyptus nitens plantations and the remaining 1% are different sites were native tree and shrub species are regenerating in areas that were prepared for forest replacement in the late 1980s but finally left unplanted. In a segment, 1557 m in length, surveyed between November 2008 and February 2009, a total of 484 pieces representing 181 m³ of LW were measured. Using bankfull width and length this volume corresponds to 109 m³ ha⁻¹ or 11.6 m³ 100 m⁻¹. LW was distributed along the channel in correlation with bankfull width. The channel segment was re-surveyed in December 2009 and we found that after one winter season 12% of the LW were transported downstream the river channel and 9 new wood elements were recruited. The LW traveled distance and traveled distance/piece diameter ratio decreased with increasing piece length/mean bankfull ratio. These results contribute to understand the complexity of LW abundance, mobilization and recruitment processes, and their effects on channel morphology, sediment routing and ecology in Chilean catchments.     

The response of planted trees to vegetation zonation and soil redox potential in created wetlands

We examined interrelationships among natural vegetation zones, soil redox potential (Eh), and metrics of tree seedling performance (i.e survival, growth, and photosynthesis) for planted Fraxinus pennsylvanica, Acer saccharinum, Quercus palustris, and Quercus bicolor at two created perched wetlands (two years and five years old) in Michigan, USA. Vegetation zones apparently associated with hydrology were fully developed at both sites. Wetland zones always had lower mean Eh than upland zones, indicating mostly anaerobic and aerobic root environments, respectively. Eh values for transition zones were similar to aerobic upland zones at the five-year-old site, and changed from anaerobic to aerobic conditions over the growing season at the two-year-old site. At the five-year-old site, transition zone trees of all species generally had greater height growth, survival, and were less likely browsed by deer than upland trees. They also had much greater survival and endured shorter periods of anoxia stress than wetland trees. Photosynthesis was positively related to survival and Eh, suggesting that unfavorable carbon balance may help explain low survival in the anoxic wetland zone. Management implications include: (1) vegetation zonation is a good indicator of wetland hydrological factors important to planted tree performance; (2) targeting developed transition vegetation zones for tree planting could increase the success and efficiency of efforts to create forested wetlands; and (3) transition zones extended over only a 9.3 cm vertical elevation gradient, indicating the importance of precise grading when creating perched forested wetlands.     

Biomass variation across selectively logged forest within a 225-km region of Borneo and its prediction by Landsat TM

Estimates of biomass integrated over forest management areas such as selective logging coupes, can be used to assess available timber stocks, variation in ecological status and allow extrapolation of local measurements of carbon stocks. This study uses fifty 0.1 ha plots to quantify mean tree biomass of eight logging coupes (each 450–2500 ha) and two similarly sized areas in un-logged forest. These data were then correlated with the spectral radiance of individual Landsat-5 TM bands over the 15 km × 15 km study area. Explanation of the differences in radiance between the ten forest sites was aided by measurements of the relative reflectance of selected leaves and canopies from ground and helicopter platforms.     

Small mammals and retention islands: An experimental study of animal response to alternative logging practices

The integration of forest biodiversity conservation with wood production is a key part of ecologically sustainable forest management. This can be a particular challenge at the stand-level when high-intensity silvicultural systems like clearfelling are employed. Alternative logging practices to clearfelling that result in partial stand retention are being widely promoted in many parts of the world. We present new findings from a replicated block experiment designed to examine the responses of small terrestrial mammals to the retention of islands of forest within otherwise clearfelled harvest units. Our experiment was conducted in the Mountain Ash (Eucalyptus regnans F. Muell) forests of the Central Highlands of Victoria, south-eastern Australia. We quantified the effects of four treatments on small terrestrial mammal abundance: (1) an uncut (‘control’) area of forest; (2) a 1.5 ha retained island within an otherwise clearfelled area; (3) three 0.5 ha retained ‘islands’ within an otherwise clearfelled area; and (4) a traditionally clearfelled area of forest, over the different stages of harvesting operations from pre-cut to post-cut to post-burn.     

Tree species composition influences differences in water use efficiency of upland forested microwatersheds

Water use efficiency (WUE) was compared in three upland South Moravian forested microwatersheds in the light of effects of global climate change on forest ecosystems (GCC). The experimental catchments were characterized as upland headwater forested microwatersheds of similar size and morphology and silvicultural system, but each with different dominant tree species in the stands (over 50% of forest stand composition in living stock): Norway spruce, European beech and mixed forest. WUE was evaluated according to mean daily streamflow reduction, measured at the discharge points of the recipients of the individual catchments in precipitation-free periods lasting more than 5 days. During these times, streamflow dynamics are mainly influenced by evapotranspiration processes occurring in the forest stands. Four precipitation-free periods were observed, two in the middle of the growing season and two at its end. Two of these periods were long (15 days or more), and two were shorter (6 days). The results indicated that WUE of upland forested catchments can be very different, depending upon the dominant tree species and the seasonal phase. Highest WUE at the catchment scale (never decreasing below 80%) was exhibited by beech predominating site. WUE of mixed forest was high as well, never decreasing below 69%. The lowest WUE was exhibited by spruce predominating site, especially during a long precipitation-free period in the summer where it decreased down to 39%. In the context of the landscape, upland microwatersheds with pure spruce stands could cause its accelerated dry out in the summer and pose a significant threat to sustainable water and forest management of these areas. In comparison, mixed forests stands where spruce is not the dominant species or beech stands should still be a viable option even under the effects of GCC.