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.     

Impact of three silvicultural treatments on growth,light-energy processing,and related needle-level adaptive traits of Pinus strobus from two regions

Our goal was to quantify and compare the impact of three silvicultural treatments (STs) on growth, light-energy processing, and needle-level morphological adaptive traits for eastern white pine (Pinus strobus L.) from large, central Ontario (ON) and small, isolated Newfoundland (NL) populations. The interest in STs is to reduce weevil (Pissodes strobi) incidence; however, there are potential adaptive changes and productivity trade-offs. The light levels for the STs were, on average, 100%, 42.0%, and 20.4% transmittance for the full-sun, and intermediate- and high-shade STs, respectively. After 8 years, overall height growth was 4.10, 3.25, and 1.70 m for full-sun, and intermediate- and high-shade STs, respectively (P < 0.001). Across all STs, ON populations had greater total height (14%), basal diameter (12%), current leader length (25%), and tree volume (49%) than NL populations (all P < 0.001). At low light levels (10 and 25 μmol m⁻² s⁻¹), high-shade ST trees had higher photochemical quenching (qP) and lower chlorophyll fluorescence (F_pc) compared with intermediate-shade and full-sun STs. At 100 μmol m⁻² s⁻¹ and beyond, full-sun ST trees had higher qP and lower F_pc than intermediate- and high-shade STs. Average total chlorophyll concentration (CHL) and content (CHLC), and carotenoid concentration (CAR), increased in response to the intermediate-shade ST but did not respond further, or decreased in the high-shade ST. Region was significant for CHL, CAR, chlorophyll a:b and CHL:CAR ratios and CHLC, with ON greater than NL, but was reversed for CHL:CAR ratio. Tree height and volume showed a curvilinear and linear relationship to light level, respectively. Tree height showed a positive linear relationship to qP, apparent photosynthesis, chlorophyll a:b ratio, and needle N (all P < 0.001). Tree height showed a negative linear relationship to F_pc, CHL:CAR ratio, specific needle area, C:N ratio, and needle area N⁻¹ (all P < 0.001). There were modest trade-offs between weevil protection and productivity in the intermediate ST due to the compensatory physiological and morphological adaptations to the limiting light, however, the trade-off with growth at the high-shade level was severe. For NL, consideration should now be given to the introduction and mixing of seed from local seed sources with more southern mainland seed sources, which would decrease the inbreeding effect and provide wider variation for natural selection for a more fit future population.     

Silvicultural treatments enhance growth rates of future crop trees in a tropical dry forest

Silvicultural treatments are often needed in selectively logged tropical forest to enhance the growth rates of many commercial tree species and, consequently, for recovering a larger proportion of the initial volume harvested over the next cutting cycle. The available data in the literature suggest, however, that the effect of silvicultural treatments on tree growth is smaller in dry forests than in humid forest tree species. In this study, we analyze the effect of logging and application of additional silvicultural treatments (liana cutting and girdling of competing trees) on the growth rates of future crop trees (FCTs; i.e., trees of current and potentially commercial timber species with adequate form and apparent growth potential). The study was carried out in a tropical dry forest in Bolivia where a set of 21.25-ha plots were monitored for 4 years post-logging. Plots received one of four treatments that varied in intensity of both logging and silvicultural treatments as follows: normal (reduced-impact) logging; normal logging and low-intensity silviculture; increased logging intensity and high-intensity silviculture; and, unlogged controls. The silvicultural treatments applied to FCTs involved liberation from lianas and overtopping trees. Results showed that rates of FCT stem diameter growth increased with light availability, logging intensity, and intensity of silvicultural treatments, and decrease with liana infestation degree. Growth rate increment was larger in the light and intensive silvicultural treatment (22–27%). Long-lived pioneer species showed the strongest response to intensive silviculture (50% increase) followed by total shade-tolerant species (24%) and partial shade-tolerant species (10%). While reduced-impact logging is often not sufficient to guarantee the sustainability of timber yields, application of silvicultural treatments that substantially enhanced the growth rates of FCTs will help move the management of these forests closer to the goal of sustained yield.     

Short-term responses of ground-active beetles to alternative silvicultural systems in the Warra Silvicultural Systems Trial,Tasmania, Australia

The Warra Silvicultural Systems Trial (SST) in Tasmania, Australia provides a framework for investigating the responses of beetles (Order: Coleoptera) to three alternative systems in lowland wet eucalypt forest: aggregated retention; dispersed retention; and understorey islands retained in clearfelled areas. Beetles from three families known to be sensitive to forest management, the families Carabidae (ground-beetles), Curculionidae (weevils) and Leiodidae (fungus-beetles), were collected with pitfall traps prior to harvest, and in the first and third years post-harvest. The retained aggregates in the aggregated retention system maintained beetle assemblages reasonably typical of mature forests, at least in these early years following harvesting. These aggregates appear to provide a stable habitat, with similar species composition in the first and third years post-harvest. In contrast, the harvested areas of the aggregated retention system contained low numbers of beetle species affiliated with mature forest, as did the understorey islands and the dispersed retention system. Relative to clearfelling, all alternative silvicultural systems appeared to be of some benefit to beetles affiliated with mature forest, but aggregated retention retained far greater numbers of these beetles compared to the other systems in Tasmanian wet eucalypt forest.     

A shifting algorithm to simulate thinnings from below and above

Thinning is a silvicultural practice to improve tree growth and health. Thinning from below for the even-aged silviculture and thinning from above for the uneven-aged silviculture are the two mainly applied thinning practices. In forest management simulations, algorithms that describe which individual trees to be removed from a forest have developed in five growth simulators (Söderbergh and Ledermann, 2003). We have developed a shifting algorithm that determines the proportion of trees to be thinned from different diameter classes to complement the individual tree selection algorithms. Sampled (or mapped) tree diameters are grouped into diameter classes. Given the target thinning volume, the algorithm automatically computes the thinning rate in each of the diameter classes using the three-parameter Weibull distribution. The thinning rate is obtained by shifting the location parameter of an estimated Weibull distribution either to the right or to the left for thinnings from below and above, respectively. A modified bisection method is used to search for the new location parameter that yields the desired thinning volume. The proposed algorithm is demonstrated in examples by using experimental forest datasets. A stand-alone program called Weibull_thinning is downloadable at http://www.it.abo.fi/suswood/weibull_thinning/.     

Ten-year regeneration responses to varying levels of overstory retention in two productive southern British Columbia ecosystems

We investigated survival and growth responses of planted and advance natural regeneration species of varying shade tolerance to partial retention harvesting in moist warm Interior Cedar-Hemlock (ICHmw2) and dry cool Montane Spruce (MSdk) ecosystems of southeastern British Columbia, Canada. Treatments included three levels of overstory basal area retention (none, light (∼25%), or heavy (∼50%)) installed by two harvest methods (handfelled or a pushover falling technique being tested for its ability to control the spread of root disease). After 10 years, growth of both planted and natural regeneration species of varying shade tolerance tended to increase with decreasing overstory retention and associated increases in light availability. In contrast, significant survival responses to retention level were lacking except in the case of shade-intolerant western larch. Harvest method had a variable effect on regeneration survival and growth. Where significant responses did occur, they were generally attributed to harvesting effects on the characteristics of planting microsites rather than root disease spread. Natural regeneration densities at the ICHmw2 site were high at all retention levels, whereas stocking was less consistent at the MSdk site. We concluded that moderately shade-tolerant to shade-tolerant interior spruce and western redcedar can, under conditions similar to those of our study sites, be successfully established under overstories of up to approximately 25 m²/ha basal area, but that growth performance is likely to be significantly lower than in clearcuts. Despite early survival issues, conclusions regarding Douglas-fir were similar. Poorer survival and vigour of shade-intolerant western larch suggested this species is not suitable for regeneration in partial retention systems where timber production is the primary objective. Where non-timber objectives predominate, survival and acceptable growth of even a small proportion of larch could add to the diversity of the regenerating stand.     

Commercial forest fertilization causes long-term residual effects in ground vegetation of boreal forests

Due to an increasing demand of forestry products, nitrogen (N) fertilization of coniferous forests may in the future become a standard silvicultural practice in parts of the boreal region that is not too remotely situated. Beside positive effects on productivity, forest fertilization may induce changes in species composition of the ground vegetation. More information on the magnitude of such side effects is needed to evaluate whether commercial forest fertilization is in accordance with principles of sustainable forestry and preservation of biodiversity.     

Effects of silvicultural treatments and seasonal patterns on foliar nutrients in young post-fire Pinus halepensis forest stands

Tree growth and health status appear to be related to foliar nutrient contents. Foliar nutrient concentration might be the result of a complex interaction between soil nutrients and effective availability caused by climate, water and other site and treatment effects. This study examines foliar macronutrient (N, P, K, Ca, Mg) and organic C concentrations in Aleppo pine (Pinus halepensis) needles (between 5 and 18 months old), as well as time course variability (nine dates, from July 1999 to November 2001). Variability was assessed depending on quality site (two sites, Yeste and Calasparra; SE Spain) and seven silvicultural treatments including thinning, scrubbing, pruning and particular combinations of them. Foliar macronutrient concentrations for Aleppo pine in South-eastern Spain were slightly lower (N, P, K,) or higher (Mg, Ca) than the considered as adequate ranges for Aleppo pine and Pinus genera. However, our results agree well with other normal ranges reported for Aleppo pine in Spain and for other North American Pinus species such as P. elliottii, P. taeda and P. palustris. Site, treatment and date (season) affected significantly the foliar macronutrient and C concentration, although the most important was the date, likely due to the two growth periods per year that Aleppo pine has in Mediterranean sites. Silvicultural treatments affected foliar nutrient concentration, so that the concentrations of N, P and K were higher when treatments included thinning than those that did not. The contrary was true for Mg and Ca. However, treatments did not affect the time course of the concentration, i.e., seasonality was not broken due to treatments. Moreover, the effect of the treatments was markedly high along the first year after they were applied but the differences were attenuate 2 years later. Site affected the time course of N, K, Mg and C in a different way: while for N, K and C, at the end of study period, they were higher in Calasparra than in Yeste, for Mg the contrary was true. Nutrient ratios had a different behaviour regarding to single nutrient: although date was significant, we did not appreciate seasonality. In addition, some nutrient ratios were not affected by treatments (N/P, N/K, Ca/Mg,) or by site (N/Ca, K/Ca). Average foliar N concentration and Ca/Mg ratio explained significantly the mean diameter and height growth, so that higher is the foliar N concentration and lower is Ca/Mg, higher is the growth.     

杉木栽培制度的理论探讨

杉木栽培制度是栽培方式及其相应的栽培技术系列的综合体系。栽培制度是杉木林培育过程的组织和管理体系，亦为用地和养地相结合的重要手段，其实质是杉木林生态系统的调节控制体系。建立杉木栽培制度的根本目标在于实现林地持续利用和人工林持续速生丰产，其建立过程必须遵循一定的程序。文中还分析了现行栽培制度存在的问题，并提出改进意见和发展构想。     

Growth,carbon sequestration,and management of native tree plantations in humid regions of Costa Rica

The Costa Rican government has provided incentives for reforestation programs since 1986 and initiated a Payment for Environmental Services program in 1996. These incentives yielded native species reforestation programs throughout the country. This research aims to provide information about growth, carbon sequestration, and management of seven native tree species (Vochysia guatemalensis, Vochysia ferruginea, Hyeronima alchorneoides, Calophyllum brasiliense, Terminalia amazonia, Virola koschnyi, and Dipteryx panamensis) growing in small and medium-sized plantations in the Caribbean and Northern lowlands of Costa Rica. A total of 179 plots were evaluated in 32 farms. Overall, I found that V. guatemalensis, V. ferruginea, H. alchorneoides, and T. amazonia were the species with the fastest diameter, total height, and volume growth; and T. amazonia and D. panamensis sequestered more carbon. Moreover, I found that the plantations that had been thinned before this assessment had the best growth. The results of the present research enhance the criteria elaborated in previous research findings to improve species choices for reforestation and silvicultural management in Costa Rica and in other regions with similar ecological features. Furthermore, they support the concept that tropical plantations can serve diverse economic, social, and ecological functions that may ultimately help reduce atmospheric CO₂ accumulation.