Long-term impacts of even-aged timber management on abundance and body condition of terrestrial amphibians in Northwestern California

Conservation needs for amphibians in managed timberlands may differ based upon the species present and the timber harvesting methods employed. Clearcuts have been documented to be detrimental to amphibians but the impacts of associated silvicultural edges and alternative harvesting treatments are not well understood. The primary objective of this study was to determine if amphibian abundances and body condition differed in thinned forests and intact forests, and in clearcuts and associated silvicultural edges. We also examined which environmental attributes were important in explaining observed differences. We sampled clearcuts, silvicultural edges, and adjacent late-seral forests at 10 sites in northwestern California from October 1999 to July 2002. Clearcuts at these sites ranged in age from 6 to 25 years. Five of these forest stands were intact and five had been commercially thinned at least 10 years prior to our study. Amphibian abundances were similar in thinned and unthinned forests, but body condition of the most common species was lower in thinned forests. Abundances of amphibians were nearly twice as high in forests and at silvicultural edges than in clearcuts. Clearcutting at these sites appears to have affected amphibian numbers up to 25 years post-harvest, however, silvicultural edges were suitable habitats for amphibians. While commercial thinning did not reduce amphibian numbers, it is an intermediate treatment followed by clearcutting. Where conservation of amphibians is a concern, even-aged silvicultural systems may not provide the most appropriate method for maintaining viable populations on managed forestlands in the northwestern US.     

长白山森林的采伐更新方式

This paper discussed the characteristics of degenerated forest ecosystems in Changbai Mountain area,which include over-harvest natural forest,typical secondary forest,derived forest,and artificial forest.Forest cutting and regeneration methods that were historically used in the region were summarized.They lnclude diameter-class selective cutting,clearcutting,upbringing selective cutting,and selective sutting.We proposed cutting methods for the broad-leaved Korean pine mixed forest,spruce-fir forest,and larch forest.The measures for restoring the original mixed forest ecosystems were recommended.     

Productivity and Costs in Shelterwood Harvesting

Harvesting costs have a significant influence on the application and potential use of the shelterwood system. These costs are strongly related to the time needed for the logging operations. In this study, which was carried out in Norway spruce [Picea abies (L.) Karst.] stands in northern Sweden, the effective time (E ₀) of a single-grip harvester in shelterwood cutting, thinning of shelterwoods and clearcutting was measured. Based on these data the costs of shelterwood harvestings and clearcutting were calculated and compared. It was found that (1) the time per tree in shelterwood cutting and thinning of shelterwoods was greater than in clearcutting, (2) the time per cubic metre was higher in sparse shelterwoods than in dense shelterwoods, (3) most of this increase was due to longer driving time because fewer trees were harvested, and (4) the longer time and higher logging costs in the shelterwood system (compared with the clearcutting system) were mostly related to the establishment of the shelterwood. It was concluded that the shelterwood alternative is especially competitive when it is desirable to maximize the share of saw logs at the expense of pulpwood.     

Temperature sensitivity of mineral N transformation rates, and heterotrophic nitrification: possible factors controlling the post-disturbance mineral N flush in forest floors

A major forest disturbance such as clearcutting may bring on a flush of mineral N in organic forest floor horizons, but the magnitude of this flush can vary markedly from one ecosystem to another. For example, it was previously established that clearcutting in a high elevation Engelmann spruce-subalpine fir (ESSF) ecosystem results in significantly higher NH₄⁺ and NO₃⁻ concentrations, whereas clearcutting in an old-growth coastal western hemlock (CWH) ecosystem has little effect on mineral N dynamics. We hypothesized that the higher mineral N flush observed in the ESSF ecosystem is due to a greater temperature sensitivity of mineral N transformation rates, and to a lower proportion of heterotrophic nitrifiers, compared to the CWH ecosystem. To test these two hypotheses, we sampled forest floors several times over the growing season from clearcut and old-growth plots in both ecosystems, and measured gross mineral N transformation rates at field temperatures and at 10 °C above field temperatures, as well as with and without acetylene to inhibit autotrophic nitrifiers. Gross NH₄⁺ transformations rates ranged between 20 and 120 μg N (g forest floor)⁻¹ day⁻¹ at the ESSF site, and between 15 and 40 μg N (g forest floor)⁻¹ day⁻¹ at the CWH site. Higher temperature increased gross NH₄⁺ transformation rates in forest floor samples at both sites, but the average Q₁₀ value was higher at the ESSF site (3.15) than at the CWH site (1.25). Temperature sensitivity at the ESSF site was greater in clearcut plots (Q₁₀=4.31) than in old-growth plots (Q₁₀=1.98). Gross NO₃⁻ transformation rates ranged between 10 and 32 μg N (g forest floor)⁻¹ day⁻¹ at the ESSF site, and between 10 and 24 μg N (g forest floor)⁻¹ day⁻¹ at the CWH site, but there were no significant effects of temperature or clearcutting on gross NO₃⁻ transformation rates at either site. Likewise, there were no significant differences in the proportion of heterotrophic nitrifiers between sites. Overall, our results support the view that the temperature sensitivity of microbial processes may explain the magnitude of the NH₄⁺ flush in some coniferous ecosystems, but we lack the evidence relating the magnitude of the NO₃⁻ flush to the proportion of heterotrophic nitrifiers.     

Grapevine (Vitis spp.) dynamics in association with manual tending,physiography, and host tree associations in temperate deciduous forests

The role of lianas (woody vines) in the development and diversity of both tropical and temperate forests under differing management scenarios has not been thoroughly explored. We examined changes in grapevine (Vitis spp.) densities over time in clearcut stands as influenced by manual tending, physiography, and host tree associations. We used data from long-term studies on 66 clearcut stands dominated by temperate deciduous forest tree species on the Hoosier National Forest in south-central Indiana, USA. Fourteen of the stands had grapevines removed manually, approximately during the stem exclusion stage of development. Grapevine densities steadily increased from age 5 until age 15, which coincides with the period of stem exclusion of these stands. Subsequent grapevine mortality may have been related to light competition. Manually treated stands had similar grapevine densities as untreated stands after 20 years across sites, and it appeared that only on the most xeric area was the grapevine treatment effective in reducing grapevine densities. During early stand development, ranging from ages 5 to 17, grapevine density was strongly related to slope position, but as stands developed through the stem exclusion stage, aspect emerged as a stronger factor influencing grapevine density. Black cherry (Prunus serotina Ehrh.), walnut (Juglans spp.), and elm (Ulmus spp.) were the most common grapevine host trees under both treated and untreated scenarios, which may be associated with the crown architecture of these species. Results suggest lianas play a critical role in the early development of disturbed forest sites in temperate deciduous forests. With concerns that lianas are increasing in abundance and distribution in these forest types, understanding their role in forest dynamics, such as host tree associations at different stages of development, competition dynamics on different sites and corresponding influences on tree growth, species composition, and diversity, will be critical to decision-making processes in achieving desired management goals in the future.     

Water yield changes as a result of silvicultural treatments in an oak ecosystem

Interception loss represents an important factor of water balance. The reduction of interception loss through silvicultural treatments to the benefit of water yield is very important for countries with large periods of limited rainfall like Greece. In the context of climate change and its possible effects on water availability, oak ecosystems can play a significant role in water production, as they comprise the largest part of the forested area in Greece. The objective of this study is to investigate the relationships between water interception changes, as a result of different forest management treatments, and water yield. For this reason, experimental watersheds have been established for the study of the hydrological impacts of thinning and clearcutting in an oak ecosystem in northern Greece. Two watersheds were used as control while different combinations of thinning (removal 50% of basal area) and clearcutting treatments were used in the other three study watersheds. Canopy annual interception amounted for 9.0%, 6.7% and 1.8% of the total precipitation in the untreated, thinned and clearcut plots respectively. The practiced thinning and clearcutting operations increased the available amount of water by a mean annual average of 13.2 mm and 42.8 mm respectively compared to the control watersheds. The total water surplus represented 29.5%, 30.9% and 33.9% of the average annual precipitation for the control, thinned and clearcut plot respectively. Surface flow was very low even during large rainfall events, possibly due to the soil and bedrock attributes and the topography of the area. Analogous silvicultural treatments can increase water availability but they should incorporate reduced-impact logging and skidding practices and thus cause the least possible soil disturbance, by carefully selecting the best suited wood harvesting systems and methods.     

From clearfell coupe to old-growth forest: Succession of bird assemblages in Tasmanian lowland wet eucalypt forests

As forests undergo succession after major disturbance events their assemblages of birds also change. Thus the frequency and extent of wildfire or clearfelling in the landscape can potentially affect the species-richness and abundance of forest birds. We used a chronosequence approach to investigate succession of bird communities in Tasmanian lowland wet eucalypt forest, from shortly after disturbance through to old-growth forest aged approximately 200–250 years. The number of native bird species recorded per survey per site increased as a linear function of stand-age. However, succession did not involve a unidirectional transition in assemblage-composition because of differences in successional responses among individual species and also among guilds of birds that mostly inhabited different strata of the forest. This was exemplified by the crescent honeyeater, which was observed most frequently in the youngest (6–8 years) and oldest (200–250 years) forests that we surveyed, and by the superb lyrebird (introduced to Tasmania from mainland south-eastern Australia) which favoured mid-aged regrowth (42–43 years) after clearfelling. Forests aged 200–250 years had the greatest richness-per-survey of those native species that were observed mostly in the lower layer or mid-layer. However, the greatest richness-per-survey of canopy-dwelling species and the highest native species-richness across the survey period were found in forests aged around 150 years. Younger regrowth was generally less rich in birds, although regrowth in the first decade after clearfelling was the only seral stage inhabited by superb fairy-wrens. These results suggest that, in the Tasmanian lowland wet eucalypt forest landscape, species-richness of birds may be greatest when old-growth forest is interspersed with young regrowth forests. Hence for bird conservation, a challenge is to ensure that old-growth forest continues to prevail in the production forest landscape.     

The increasing scarcity of red oaks in Mississippi River floodplain forests: Influence of the residual overstory

Red oaks – cherrybark oak (Quercus pagoda Raf.), willow oak (Quercus phellos L.), water oak (Quercus nigra L.), and Nuttall oak (Quercus texana Buckley; aka: Quercus nuttallii Palmer) – are not regrowing in Mississippi Delta river floodplain forests in the southeastern United States in sufficient numbers to sustain the former species composition and timber and wildlife values. Even if vigorous red oak reproduction becomes established, partial harvesting that does not remove the taller trees will suppress understory red oak height growth more than it will suppress height growth of such other species as sugarberry (Celtis laevigata Willd.), American elm (Ulmus americana L.), cedar elm (Ulmus crassifolia Nutt.), swamp dogwood (Cornus foemina Mill.), green ash (Fraxinus pennsylvanica Marshall), and sweetgum (Liquidambar styraciflua L.). Consequently, the red oaks in these partially harvested stands become increasingly suppressed and probably die; and there is a shift in species composition to the other species. In addition to ensuring vigorous oak reproduction, silvicultural clearcutting or rapid removal of the residual trees following shelterwood or seed tree harvesting to provide full sunlight is needed to ensure red oaks become a dominant part of these future river floodplain stands.     

Forest floor microbial communities in relation to stand composition and timber harvesting in northern Alberta

With the growing interest in silvicultural techniques that more closely emulate natural disturbance regimes, there is a need to better understand how partial harvesting affects the soil microbial community in stands with varying ecological characteristics, e.g., tree species composition. Four and a half and 5.5 years post-harvest, we used phospholipid fatty acid (PLFA) and substrate-induced respiration (SIR) analyses to compare the microbial biomass and microbial community structure of forest floors from stands dominated by white spruce (Picea glauca; SPRUCE) or by trembling aspen (Populus tremuloides; ASPEN) and from mixed-species (MIXED) stands in northern Alberta, Canada, that had been clearcut, partial-cut with 20% retention, partial-cut with 50% retention or left uncut (controls). PLFA and SIR analyses revealed that ASPEN forest floors supported a larger microbial biomass with a very different community structure than MIXED or SPRUCE forest floors. The microbial community structure of these soils appeared to be strongly affected by the presence of white spruce and the composition of the understory vegetation. There were no effects of timber harvesting detected within or across stand types on any of the variables measured, with the exception of the PLFA 16:1ω5, which was relatively more abundant in the clearcuts and 50% retention treatments than in the uncut controls, perhaps in response to an increased forest floor pH and grass cover in the disturbed areas. The resilience to timber harvesting of the forest floors from these stands may be the result of efforts to minimize soil disturbance during harvesting and to allow vegetation to regenerate naturally. From the perspective of the forest floor microbial community, partial harvesting does not appear to have any benefit over clearcut harvesting at these boreal forest sites.     

Initial recovery of soil carbon and nitrogen pools and dynamics following disturbance in jack pine forests: A comparison of wildfire and clearcut harvesting

Forests naturally maintained by stand-replacing wildfires are often managed with clearcut harvesting, yet we know little about how replacing wildfire with clearcutting affects soil processes and properties. We compared the initial recovery of carbon (C) and nitrogen (N) pools and dynamics following disturbance in jack pine (Pinus banksiana) stands in northern Lower Michigan, USA, by sampling soils (Oa+A horizons) from three “treatments”: 3-6-year-old harvest-regenerated stands, 3-6-year-old wildfire-regenerated stands and 40-55-year-old intact, mature stands (n=4 stands per treatment). We measured total C and N; microbial biomass and potentially mineralizable C and N; net nitrification; and gross rates of N mineralization and nitrification. Burned stands exhibited reduced soil N but not C, whereas clearcut and mature stands had similar quantities of soil organic matter. Both disturbance types reduced microbial biomass C compared to mature stands; however, microbial biomass N was reduced in burned stands but not in clearcut stands. The experimental C and N mineralization values were fit to a first-order rate equation to estimate potentially mineralizable pool size (C₀ and N₀) and rate parameters. Values for C₀ in burned and clearcut stands were approximately half that of the mature treatment, with no difference between disturbance types. In contrast, N₀ was lowest in the wildfire stands (170.2 μg N g⁻¹), intermediate in the clearcuts (215.4 μg N g⁻¹) and highest in the mature stands (244.6 μg N g⁻¹). The most pronounced difference between disturbance types was for net nitrification. These data were fit to a sigmoidal growth equation to estimate potential NO₃⁻ accumulation (Nit_max) and kinetic parameters. Values of Nit_max in clearcut soils exceeded that of wildfire and mature soils (149.2 vs. 83.5 vs. 96.5 μg NO₃⁻-N g⁻¹, respectively). Moreover, the clearcut treatment exhibited no lag period for net NO₃⁻ production, whereas the burned and mature treatments exhibited an approximate 8-week lag period before producing appreciable quantities of NO₃⁻. There were no differences between disturbances in gross rates of mineralization or nitrification; rather, lower NO₃⁻ immobilization rates in the clearcut soils, 0.20 μg NO₃⁻ g⁻¹ d⁻¹ compared to 0.65 in the burned soils, explained the difference in net nitrification. Because the mobility of NO₃⁻ and NH₄⁺ differs markedly in soil, our results suggest that differences in nitrification between wildfire and clearcutting could have important consequences for plant nutrition and leaching losses following disturbance.