Above- and belowground responses to tree thinning depend on the treatment of tree debris

Mechanical mastication is increasingly prescribed for wildfire mitigation, yet little is known about the ecological impacts of this fuels treatment. Mastication shreds trees into woodchips as an alternative to tree thinning and burning the resulting slash, which can create soil disturbances that favor exotic plants. Previous research on mastication has not simultaneously considered both the responses of soil organisms and understory plant communities. We compared mastication to slash pile burning (both 6-months and 2.5-years post-treatment) and untreated controls in pinyon–juniper (Pinus edulis–Juniperus osteosperma) woodland and measured soil properties, arbuscular mycorrhizal fungi (AMF) and understory plant composition. Our results showed that slash pile burns had severely degraded soil properties and low AMF abundance and richness compared to untreated or mastication plots. Pile burns were dominated by exotic plant species and had approximately 6× less understory plant abundance and richness than untreated plots. Only two variables differed between mastication and untreated plots 6-months post-treatment: mastication had lower soil temperature and higher soil moisture. Mastication plots 2.5-years post-treatment had more plant cover and richness than untreated plots or pile burns, although non-native Bromus tectorum cover was also greater and AMF spore richness was lower than untreated plots. The structural equation model (SEM) we developed showed that plant cover strongly influenced AMF abundance (0.50) and both plant cover (0.36) and AMF (0.31) positively influenced soil stability. In the short-term, mastication is a preferable method as it creates fewer disturbances than pile burning; however long-term impacts of mastication need further study as this practice could affect native plant communities. Our results suggest that the manner in which woody debris is treated following tree thinning has an important influence on soil stability and native plant biodiversity.     

Response of antelope bitterbrush to repeated prescribed burning in Central Oregon ponderosa pine forests

Antelope bitterbrush is a dominant shrub in many interior ponderosa pine forests in the western United States. How it responds to prescribed fire is not well understood, yet is of considerable concern to wildlife and fire managers alike given its importance as a browse species and as a ladder fuel in these fire-prone forests. We quantified bitterbrush cover, density, and biomass in response to repeated burning in thinned ponderosa pine forests. Low- to moderate-intensity spring burning killed the majority of bitterbrush plants on replicate plots. Moderately rapid recovery of bitterbrush density and cover resulted from seedling recruitment plus limited basal sprouting. Repeated burning after 11 years impeded the recovery of the bitterbrush community. Post-fire seed germination following the repeated burns was 3–14-fold lower compared to the germination rate after the initial burns, while basal sprouting remained fairly minor. After 15 years, bitterbrush cover was 75–92% lower on repeated-burned compared to unburned plots. Only where localized tree mortality resulted in an open stand was bitterbrush recovery robust. By controlling bitterbrush abundance, repeated burning eliminated the potential for wildfire spread when simulated using a customized fire behavior model. The results suggest that repeated burning is a successful method to reduce the long-term fire risk imposed by bitterbrush as an understory ladder fuel in thinned pine stands. Balancing the need to limit fire risk yet provide adequate bitterbrush habitat for wildlife browse will likely require a mosaic pattern of burning at the landscape scale or a burning frequency well beyond 11 years to allow a bitterbrush seed crop to develop.     

Effects of selective thinning on growth and development of beech (Fagus sylvatica L.) forest stands in south-eastern Slovenia

We studied the effects of two types of selective thinning on beech stands formed by a shelterwood cut in 1910 — with lower number of crop trees and higher thinning intensity (T1) and higher number of crop trees with lower thinning intensity (T2). The stands were thinned in 1980, 1991 and 2001. Despite a lower stand density after thinning, the annual basal area increments of thinned stands in both thinning periods (1980–1991 and 1991–2002) were around 20% higher compared to those of the control (unthinned) stands. The mean annual basal area increment of dominant trees was 30–56% larger in the thinned plots compared to the control plots. Of 176 initial crop trees in the T1, 72% were chosen again during the last thinning. In the T2, 258 crop trees were chosen in the first thinning, and only 62% of these trees were chosen again during the last thinning. Only crown suppression and diameter classes of crop trees significantly influenced their basal area increment when diameter classes, crown size, crown suppression, and social status were tested. In the thinned stands, the dominant trees are more uniformly distributed if compared to the dominant trees in the control plots. Finally, the herbaceous cover and the species diversity were higher in the thinned plots.     

Thinning and chipping small-diameter ponderosa pine changes understory plant communities on the Colorado Front Range

Novel fire mitigation treatments that chip harvested biomass on site are increasingly prescribed to reduce the density of small-diameter trees, yet the ecological effects of these treatments are unknown. Our objective was to investigate the impacts of mechanical thinning and whole tree chipping on Pinus ponderosa (ponderosa pine) regeneration and understory plant communities to guide applications of these new fuel disposal methods. We sampled in three treatments: (1) unthinned forests (control), (2) thinned forests with harvested biomass removed (thin-only), and (3) thinned forests with harvested biomass chipped and broadcast on site (thin + chip). Plots were located in a ponderosa pine forest of Colorado and vegetation was sampled three to five growing seasons following treatment. Forest litter depth, augmented with chipped biomass, had a negative relationship with cover of understory plant species. In situ chipping often produces a mosaic of chipped patches tens of meters in size, creating a range of woodchip depths including areas lacking woodchip cover within thinned and chipped forest stands. Thin-only and thin + chip treatments had similar overall abundance and species richness of understory plants at the stand scale, but at smaller spatial scales, areas within thin + chip treatments that were free of woodchip cover had an increased abundance of understory vegetation compared to all other areas sampled. Relative cover of non-native plant species was significantly higher in the thin-only treatments compared to control and thin + chip areas. Thin + chip treated forests also had a significantly different understory plant community composition compared to control or thin-only treatments, including an increased richness of rhizomatous plant species. We suggest that thinning followed by either chipping or removing the harvested biomass could alter understory plant species composition in ponderosa pine forests of Colorado. When considering post-treatment responses, managers should be particularly aware of both the depth and the distribution of chipped biomass that is left in forested landscapes.     

Effects of thinning on plant species diversity and composition of understory herbs in a larch plantation

The effects of thinning on plant species diversity and composition of understory herbs in a larch plantation were investigated. The relationships between plant species diversity and composition of understory herbs and light conditions were established. Twenty-five 1 m × 1 m plots and fifteen 13 m × 1 m transects were set up in unthinned and thinned stands, respectively. All the transects in the thinned stands were set across the thinned rows and unthinned rows, and each of them was divided into nine 1 m × 1 m sub-plots. The herb diversity and light conditions were observed in each plot and sub-plot. The results show that there was a significant difference in herb diversity between the thinned and unthinned stands. All biodiversity indices except for evenness index in the thinned stand were higher than those of the unthinned stand, i.e., the herb diversity increased after thinning. According to the changes in herb densities and whether one species could be found in a stand or not before and after thinning, all herb species were classed into three types: positive, neutral and negative species, which referred to a species newly appeared and having an obviously increased density after thinning, with no obvious changes in its appearance and density after thinning, and disappeared and having an obviously decreased density after thinning, respectively. Many new species were found in the thinned stand like Corydalis pallida, Prenanthes tatarinowii, Vicia unijuga and Sonchus brachyotus etc. However, most species found in both the thinned and unthinned stands were negative species. In all nine subplots, only 11 and 10 species were found in spring and in autumn respectively, accounting for 17.74% and 15.15% of all the species in the thinned stand, respectively. All biodiversity indices were the highest in the center sub-plots and most of them tended to reduce from middle to side sub-plots. There was a close correlation between most of the three types of species and light conditions which was similar to each other in the thinned and unthinned stands. __________ Translated from Chinese Journal of Ecology, 2006, 25(10): 1201–1207 [译自: 生态学杂志]     

Can pine forest restoration promote a diverse and abundant understory and simultaneously resist nonnative invasion?

An important goal of forest restoration is to increase native plant diversity and abundance. Thinning and burning treatments are a common method of reducing fire risk while simultaneously promoting understory production in ponderosa pine (Pinus ponderosa) forests. In this study we examine the magnitude and direction of understory plant community recovery after thinning and burning restoration treatments in a ponderosa pine forest. Our objective was to determine if the post-treatment community was a diverse, abundant, and persistent assemblage of native species or if ecological restoration treatments resulted in nonnative species invasion. This project was initiated at the Grand Canyon-Parashant National Monument, Arizona, USA in 1997. We established four replicated blocks that spanned a gradient of soil types. Each block contained a control and a treated unit. Treated units were thinned to emulate pre-1870 forest stand conditions and prescribed-burned to reintroduce fire to a system that has not burned since ∼1870. We measured plant cover using the point-line intercept method and recorded species richness and composition on 0.05 ha belt transects. We examined the magnitude of treatment responses using Cohen's d effect size analysis. Changes in community composition were analyzed using nonmetric multidimensional scaling (NMS). Native plant species cover and richness increased in the thinned and burned areas compared to the controls. By the last year of the study, annual species comprised nearly 60% of the understory cover in the treatment units. Cheatgrass (Bromus tectorum), a nonnative annual grass, spread into large areas of the treated units and became the dominant understory species on the study site. The ecological restoration treatments did promote a more diverse and abundant understory community in ponderosa pine forests. The disturbances generated by such treatments also promoted an invasion by an undesirable nonnative species. Our results demonstrate the need to minimize disturbances generated by restoration treatments and argue for the need to proactively facilitate the recovery of native species after treatment.     

Influence of conventional and chemical thinning on stand structure and diversity of plant and mammal communities in young lodgepole pine forest

Silvicultural practices that provide a wide variety of vegetative composition and structure (habitats) in young stands should help manage for biological diversity across forested landscapes. This study was designed to test the hypotheses that: (i) abundance and diversity of stand structure attributes (species diversity and structural diversity of herb, shrub and tree layers) and forest floor small mammal communities, and (ii) relative habitat use by large herbivores, will increase from unthinned to conventionally thinned to chemically thinned stands of young lodgepole pine (Pinus contorta) forest. Replicate study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had three treatments: a conventionally thinned, a chemically thinned and an unthinned stand. Pre-commercial thinning was conducted in 1993. Coniferous stand structure and understory vegetation were measured prior to thinning in 1993 and 5 years later in 1998. Small mammal populations were sampled intensively from 1993 to 1998. Relative habitat use by large herbivores was sampled in 1998.

Our results indicate that chemical thinning of young lodgepole pine stands produced an aggregated pattern of crop trees compared with stands subjected to conventional thinning. Diameter growth of crop trees in the chemically thinned stands was similar to that in the conventionally thinned, but also to that in unthinned stands. Although horizontal stratification (aggregates of trees) was enhanced, vertical stratification (structural diversity of vegetation) was less in the chemically than conventionally thinned stands. Abundance and diversity of understory vegetation and small mammal communities were generally unaffected by stand thinning in these particular installations. Relative habitat use by mule deer (Odocoileus hemionus) occurred in a gradient from highest in the conventionally thinned stand to lowest in the unthinned stand. Habitat use by snowshoe hares (Lepus americanus) tended to have the opposite trend. Moose (Alces alces) exhibited no difference in habitat use among stands. Thus, although there were few differences among treatment stands, chemical thinning could be used to develop an aggregated pattern of crop trees in pre-commercially thinned stands to maintain habitat for herbivores such as snowshoe hares and mule deer. Understory plant and forest floor small mammal communities would be maintained in these stands as well.     

Initial Response of Understory Vegetation to Three Alternative Thinning Treatments

This study compares initial understory vegetation response among three thinning treatments and a control in 30- to 50-year-old even-aged Pseudotsuga menziesii (Mirbel) Franco (Douglas-fir) stands. It was conducted on four sites on the western slope of the central Oregon Cascades. Treatments included a control (no thinning), a light thinning, and two treatments designed to encourage development of understory vegetation: a light thinning with gap creation and a heavy thinning. Vegetation response was measured during the first post-treatment growing season and 5–7 years later. At a treatment-scale, vegetation structure and composition differed between thinned and unthinned stands but varied little among thinning treatments. Thinnings resulted in initial declines of bryophytes, tall shrubs, and low shrubs followed by subsequent recovery and growth. Herbs displayed little initial response, but a release of early-seral species was evident in thinned stands by 5–7 years posttreatment. The addition of gaps resulted in differentiation of plant composition across the gradient from gap center to the thinned forest matrix, but this was only statistically detectable at a within-treatment scale. The causal mechanisms driving initial post-thinning response are discussed to better understand long-term implications and potential roles of thinning in managing for understory vegetation.     

Stand and landscape-level factors related to bird assemblages in exotic pine plantations: Implications for forest management

Plantations cover a substantial amount of Earth's terrestrial surface and this area is expected to increase dramatically in the coming decades. Pinus plantations make up approximately 32% of the global plantation estate. They are primarily managed for wood production, but have some capacity to support native fauna. This capacity likely varies with plantation management. We examined changes in the richness and frequency of occurrence of bird species at 32 plots within a Pinus radiata plantation (a management unit comprising multiple Pinus stands) in south-eastern Australia. Plots were stratified by distance to native forest, stand age class and thinning regime. We also assessed the landscape context of each plot to determine relationships between bird assemblages and stand and landscape-level factors. Bird species richness was significantly higher at plots ≥300 m from native forest and in mature (∼20 years since planting) and old (∼27 years since planting) thinned pine stands. We were able to separate the often confounding effects of stand age and thinning regime by including old stands that had never been thinned. These stands had significantly fewer species than thinned stands suggesting thinning regime, not age is a key factor to improving the capacity of pine plantations to support native species (although an age × thinning interaction may influence this result). At the landscape level, species richness increased in pine stands when they were closer to native riparian vegetation. There were no significant differences in species composition across plots. Our study indicates the importance of stand thinning and retention of native riparian vegetation in improving the value of pine plantations for the conservation of native fauna.     

Wildlife responses to thinning and burning treatments in southwestern conifer forests: A meta-analysis

After a century of fire suppression, conifer forests in the western United States have dramatically departed from conditions that existed prior to Euro-American settlement, with heavy fuel loads and an increased incidence of wildfire. To reduce this threat and improve overall forest health, land managers are designing landscape-scale treatments that strategically locate thinning and burning treatments to disrupt fuel continuity, allowing managed wildfires to burn the remaining area. A necessary step in designing and evaluating these treatments is understanding their ecological effects on wildlife. We used meta-analysis to compare effects of small-diameter removal (thinnings and shelterwoods) and burning treatments, selective harvesting, overstory removal (including clearcutting), and wildfire on wildlife species in southwestern conifer forests. We hypothesized that small-diameter removal and burning treatments would have minimal effects on wildlife compared to other treatments. We found 33 studies that met our criteria by (1) comparing density or reproductive output for wildlife species, (2) using forest management or wildfire treatments, (3) implementing control-impact or before-after control-impact design using unmanaged stands as controls, and (4) occurring in Arizona or New Mexico ponderosa pine (Pinus ponderosa) or mixed conifer (Abies/Picea/Pinus) forest. The 22 studies suitable for meta-analysis occurred ≤20 years post-treatment on sites <400 ha. Small-diameter harvest and burning treatments had positive effects but thin/burn and selective harvest treatments had no detectable effect on most small mammals and passerine bird species reported in studies; overstory removal and wildfire resulted in an overall negative response. We examined foraging guild responses to treatments; ground-foraging birds and rodents had no strong response. Aerial-, tree-, and bole-foraging birds had positive or neutral responses to the small-diameter removal and burning treatments, but negative responses to overstory removal and wildfire. Small-diameter removal and burning treatments as currently being implemented in the Southwest do not negatively impact most of the wildlife species in the studies we examined in the short-term (≤10 years). We believe a combination of treatments in a patchy arrangement across the landscape will result in the highest diversity and density. We recommend that managers implement thinning and burning treatments, but that future research efforts focus on long-term responses of species at larger spatial scales, use reproductive output as a more informative response variable, and target species for which there is a paucity of data.     

Understory abundance,species diversity and functional attribute response to thinning in coniferous stands

Alternative strategies for stand density management in even-aged coniferous forests may increase plant species and functional diversity. We examined the effects of fixed and variable density thinning on tree seedling regeneration as well as on abundance (indexed by cover) and richness of understory vascular plants 11 years after harvesting 45- to 66-year old forests dominated by Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) or western hemlock (Tsuga heterophylla (Raf.) Sarg.) at three sites in western Oregon. Each site contained an unthinned control (CON), and thinning treatments selected to enhance overstory structural diversity and spatial variability within stands (HD, high density treatment at 300 trees ha⁻¹; MD, moderate density treatment at 200 trees ha⁻¹; VD300, VD200 and VD100, variable density treatments at 300, 200 and 100 trees ha⁻¹). Leave islands are included in HD and the other thinning treatments contain both leave islands and gap openings. Tree seedling regeneration was highly variable and generally increased with thinning. Cover of all understory species was greater in VD100 than in the control whereas richness was greater in HD and MD. Cover and richness of early seral species were greater in most thinning treatments than in the control. Understory plant communities were overwhelmingly dominated by native species. In general, vegetation dynamics was accelerated by thinning, especially in variable density treatments. Cover of N-fixing understory species was greater in VD200 than in the other treatments, and in MD and VD300 than in the control, whereas richness of understory N-fixing species increased in all thinning treatments. Cover of understory species with intermediate soil water requirements was greater in MD, VD200 and VD100 than in the control, whereas richness of these species increased in VD200 compared to the control, HD and VD300. Thinning promoted higher diversity of understory conditions without reducing density and species richness of crop tree regeneration, and seemed to increase functional effect and response diversity.     

Eight years of seasonal burning and herbicidal brush control influence sapling longleaf pine growth,understory vegetation,and the outcome of an ensuing wildfire

To study how fire or herbicide use influences longleaf pine (Pinus palustris Mill.) overstory and understory vegetation, five treatments were initiated in a 5–6-year-old longleaf pine stand: check, biennial arborescent plant control by directed herbicide application, and biennial burning in March, May, or July. The herbicide or prescribed fire treatments were applied in 1999, 2001, 2003, and 2005. All prescribed fires were intense and averaged 700 kJ/s/m of fire front across all 12 burns. Using pretreatment variables as covariates, longleaf pine survival and volume per hectare were significantly less on the three prescribed fire treatments than on checks. Least-square means in 2006 for survival were 70, 65, 64, 58, and 56% and volume per hectare was 129, 125, 65, 84, and 80 m³/ha on the check, herbicide, March-, May-, and July-burn treatments, respectively. A wildfire in March 2007 disproportionately killed pine trees on the study plots. In October 2007, pine volume per hectare was 85, 111, 68, 98, and 93 m³/ha and survival was 32, 41, 53, 57, and 55% on the check, herbicide, March-, May-, and July-burn treatments, respectively, after dropping trees that died through January 2009 from the database. Understory plant cover was also affected by treatment and the ensuing wildfire. In September 2006, herbaceous plant cover averaged 4% on the two unburned treatments and 42% on the three prescribed fire treatments. Seven months after the wildfire, herbaceous plant cover averaged 42% on the two previously unburned treatments and 50% on the three prescribed fire treatments. Before the wildfire, understory tree cover was significantly greater on checks (15%) than on the other four treatments (1.3%), but understory tree cover was similar across all five treatments 7 months after the wildfire averaging 1.1%. The greater apparent intensity of the wildfire on the previously unburned treatments most likely resulted from a greater accumulation of fuels on the check and herbicide plots that also collectively had a higher caloric content than fuels on the biennially prescribed burned plots. These results showed the destructive force of wildfire to overstory trees in unburned longleaf pine stands while also demonstrating the rejuvenating effects of wildfire within herbaceous plant communities. They caution for careful reintroduction of prescribed fire even if fire was excluded for less than a decade.     

Long-term management impacts on carbon storage in Lake States forests

We examined carbon storage following 50+ years of forest management in two long-term silvicultural studies in red pine and northern hardwood ecosystems of North America’s Great Lakes region. The studies contrasted various thinning intensities (red pine) or selection cuttings, shelterwoods, and diameter-limit cuttings (northern hardwoods) to unmanaged controls of similar ages, providing a unique opportunity to evaluate long-term management impacts on carbon pools in two major North American forest types. Management resulted in total ecosystem carbon pools of 130-137 Mg ha⁻¹ in thinned red pine and 96-177 Mg ha⁻¹ in managed northern hardwoods compared to 195 Mg ha⁻¹ in unmanaged red pine and 224 Mg ha⁻¹ in unmanaged northern hardwoods. Managed stands had smaller tree and deadwood pools than unmanaged stands in both ecosystems, but management had limited impacts on understory, forest floor, and soil carbon pools. Total carbon storage and storage in individual pools varied little across thinning intensities in red pine. In northern hardwoods, selection cuttings stored more carbon than the diameter-limit treatment, and selection cuttings generally had larger tree carbon pools than the shelterwood or diameter-limit treatments. The proportion of total ecosystem carbon stored in mineral soil tended to increase with increasing treatment intensity in both ecosystems, while the proportion of total ecosystem carbon stored in the tree layer typically decreased with increasing treatment intensity. When carbon storage in harvested wood products was added to total ecosystem carbon, selection cuttings and unmanaged stands stored similar levels of carbon in northern hardwoods, but carbon storage in unmanaged stands was higher than that of thinned stands for red pine even after adding harvested wood product carbon to total ecosystem carbon. Our results indicate long-term management decreased on-site carbon storage in red pine and northern hardwood ecosystems, but thinning intensity had little impact on carbon storage in red pine while increasing management intensity greatly reduced carbon storage in northern hardwoods. These findings suggest thinning to produce different stand structures would have limited impacts on carbon storage in red pine, but selection cuttings likely offer the best carbon management options in northern hardwoods.     

Short- and long-term effects of thinning and prescribed fire on carbon stocks in ponderosa pine stands in northern Arizona

Euro-American logging practices, intensive grazing, and fire suppression have increased the amount of carbon that is stored in ponderosa pine (Pinus ponderosa Dougl. Ex Laws) forests in the southwestern United States. Current stand conditions leave these forests prone to high-intensity wildfire, which releases a pulse of carbon emissions and shifts carbon storage from live trees to standing dead trees and woody debris. Thinning and prescribed burning are commonly used to reduce the risk of intense wildfire, but also reduce on-site carbon stocks and release carbon to the atmosphere. This study quantified the impact of thinning on the carbon budgets of five ponderosa pine stands in northern Arizona, including the fossil fuels consumed during logging operations. We used the pre- and post-treatment data on carbon stocks and the Fire and Fuels Extension to the Forest Vegetation Simulator (FEE-FVS) to simulate the long-term effects of intense wildfire, thinning, and repeated prescribed burning on stand carbon storage.The mean total pre-treatment carbon stock, including above-ground live and dead trees, below-ground live and dead trees, and surface fuels across five sites was 74.58 Mg C ha⁻¹ and the post-treatment mean was 50.65 Mg C ha⁻¹ in the first post-treatment year. The mean total carbon release from slash burning, fossil fuels, and logs removed was 21.92 Mg C ha⁻¹. FEE-FVS simulations showed that thinning increased the mean canopy base height, decreased the mean crown bulk density, and increased the mean crowning index, and thus reduced the risk of high-intensity wildfire at all sites. Untreated stands that incurred wildfire once within the next 100 years or once within the next 50 years had greater mean net carbon storage after 100 years compared to treated stands that experienced prescribed fire every 10 years or every 20 years. Treated stands released greater amounts of carbon overall due to repeated prescribed fires, slash burning, and 100% of harvested logs being counted as carbon emissions because they were used for short-lived products. However, after 100 years treated stands stored more carbon in live trees and less carbon in dead trees and surface fuels than untreated stands burned by intense wildfire. The long-term net carbon storage of treated stands was similar or greater than untreated wildfire-burned stands only when a distinction was made between carbon stored in live and dead trees, carbon in logs was stored in long-lived products, and energy in logging slash substituted for fossil fuels.     

Comparison of potential non-timber forest products in intensively managed young stands and mature/old-growth forests in south-central British Columbia

Development of understory vegetation has been influenced by the many densely stocked second-growth forest stands in North America, which have an extended stem exclusion successional stage. Understory composition and structure is important for ecosystem functioning, while also having social and economic value through the harvest of certain herb and shrub species. The potential for co-management of young and mature, managed and unmanaged stands for timber and non-timber forest products (NTFPs) was assessed in two separate replicated experiments. Experiment A examined pole-sized lodgepole pine (Pinus contorta) stands that had been pre-commercially thinned (PCT) to target densities of 250, 500, 1000, and 2000 stems/ha. Half of each of these four thinning units was repeatedly fertilized, resulting in eight experimental units. Experiment B examined six different stand types: young plantations, pole-sized lodgepole pine stands either PCT, PCT plus repeated fertilization, or unthinned, mature, and old growth. Fifty-four herb and shrub species were identified as potential NTFPs, with the responses of individual species, as well as mean total herb, shrub, berry-producing and overall total NTFPs being assessed. In Experiment A, mean total abundance (crown volume index) of NTFPs, as well as mean total herb NTFPs were significantly greater in fertilized than in unfertilized stands. Thinning treatments did not significantly affect NTFP volume, however, fertilization treatments produced five significant responses by individual species (Achillea millefolium, Epilobium angustifolium, Taraxacum officinale, Arctostaphylos uva-ursi, Rubus idaeus). In Experiment B, four of the six species responses that were significant had greater abundance in young, managed stands (young plantation, thinned, or thinned-fertilized) than in the unmanaged stands. Mean total NTFP volume and mean total herb NTFP volume also followed this pattern. A. uva-ursi, E. angustifolium, Lonicera involucrata, Sorbus sitchensis and Thalictrum occidentale all had significantly higher abundance in young, managed stands than in all other treatments. Results suggest that co-management for timber and NTFPs is possible in this ecosystem, with further research needed to evaluate livelihood values of these crops.     

Line thinning promotes stand growth and understory diversity in Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantations

We studied the effects of line thinning on stand structure, microclimate and understory species diversity of two Cryptomeria japonica D. Don plantations in south-central Japan. In each of two study sites we compared stand structure between the thinned stand and an adjacent unthinned stand and found that line thinning increased the growth rate of residual trees such that stand basal area may recover within 10 years after thinning. In the thinned stand, more open canopy conditions resulted in higher maximum temperatures on the forest floor during the early growing season than in the unthinned stand. The thinned stand had greater understory plant species richness and biomass than the unthinned stand. This study suggested that line thinning could potentially enhance biodiversity while simultaneously increasing tree-growth rates in overstocked Cryptomeria japonica plantations.     

Spatial variability in microclimate in a mixed-conifer forest before and after thinning and burning treatments

In the western United States, mechanical thinning and prescribed fire are common forest management practices aimed at reducing potential wildfire severity and restoring historic forest structure, yet their effects on forest microclimate conditions are not well understood. We collected microclimate data between 1998 and 2003 in a mixed-conifer forest in California's Sierra Nevada. Air and soil temperatures, relative humidity, photosynthetically active radiation (PAR), wind speed, soil heat flux, and soil volumetric moisture were measured at the center of 18 four-ha plots. Each plot was assigned one of six combinations of thinning and burning treatments, and each treatment was thus given three replications. We found that spatial variability in microclimate, quantified as standard deviations among monthly values of each microclimatic variable across different locations (n ≤ 18), was significantly high and was influenced primarily by elevation and canopy cover. The combination of thinning and burning treatments increased air temperature from 58.1% to 123.6%. Soil temperatures increased in all thinned plots. Air moisture variables indicated that treatments made air drier, but soil moisture increased in the range 7.9–39.8%, regardless of treatment type. PAR increased in the range 50.4–254.8%, depending on treatment type. Treatments combining thinning and burning increased wind speed by 15.3–194.3%. Although soil heat flux increased dramatically in magnitude in some plots, overall treatment effects on G were not statistically significant. We discussed the significance and implications of the spatial variability of microclimate and the treatment effects to various ecological processes and to forest management.     

Growth and structure development of semi-natural larch-spruce-fir (Larix olgensis–Picea jezoensis–Abies nephrolepis) forests in northeast China: 12-year results after thinning

Analyzing and understanding the structure and growth dynamics of semi-natural plantations is useful for their management. Since 1987, 16 plots with 4 treatments (CT: control; LT: light thinning; MT: medium thinning; and HT: heavy thinning) by 0, 20, 30 and 40% of basal area removal, respectively, and four replications were established in semi-natural larch-spruce-fir forests in northeast China. The structure and growth dynamics of semi-natural larch-spruce-fir stands and the effects of thinning on the growth, structure and diversity were examined. A mixed model repeated measures analysis of variance (RMANOVA) was used to test the effects of treatment and time.

Results showed that differences in periodic annual increment (PAI) of stand basal area and volume and the individual diameter and volume among treatments changed over time in a complex statistical interaction. Thinning, however, had a significant effect on growth at tree and stand levels 12 years after thinning while the PAI of the diameter, basal area and volume was positively correlated with thinning intensity. No significant differences were found in the total stand yield among treatments. Composition of tree species group (larch, other conifers and deciduous trees) during monitoring years did not change significantly. Moreover, no significant differences were observed in tree species and size diversity among treatments in the years following thinning. Both thinning and control plots had similar understory plant diversity after the 12 year period. Univariate point pattern analysis revealed that clumped and random distributions were dominant for tree species groups in this study. The current species composition and regeneration dynamics within these semi-natural plantations suggested a development towards mixed coniferous and broad-leaved forests. Management implications for the transformation from larch plantations towards mixed broad-leaved Korean forests with a more diverse structure, the climax vegetation in this region, were discussed.     

Silviculture as a disturbance regime: the effects of clear-cutting,planting and thinning on polypore communities in mixed forests

The structure of modern forest landscapes is profoundly affected by human-caused disturbances, particularly forest management; however, the effects and prospects of individual silvicultural techniques are insufficiently understood. This study distinguishes the effects of clear-cutting, planting and thinning on species richness and community composition of polypore fungi. In 2008–2009, 181 forest compartments (ranging from naturally regenerated deciduous stands to planted Picea abies stands and 0–137 years post clear-cutting) were explored in a hemiboreal landscape subjected to even-aged management. Altogether 104 polypore species were recorded. For species richness, time since clear-cutting was the most influential factor at both stand and landscape scales, followed by thinning. Clear-cuts had distinct polypore communities (including several red-listed species) whose species richness declined in time. Following 20 years post clear-cutting, species richness started to increase along different community–composition pathways determined by regeneration type. The communities developed after planting were moderately species rich at stand scale but homogeneous over larger areas. Thus, at landscape scale, mature unmanaged naturally regenerated stands hosted most species; thinning reduced species richness by approximately 15%, and among thinned stands, planted areas had a further 9–22% fewer species than naturally regenerated areas. In such variably managed landscape, silviculture appeared to create particularly distinct communities in young stands on nutrient-rich soils, which naturally provide polypores with a rich supply of small deciduous snags absent from stands artificially planted with P. abies and intensively thinned.     

Woody understory plant diversity in pure and mixed native tree plantations at La Selva Biological Station,Costa Rica

Tree plantations can be an important tool for restoration of abandoned pasturelands in the tropics. Plantations can help speed up secondary forest succession by improving soil conditions, attracting seed-dispersal agents, and providing shade necessary for understory growth. In this study, abundance and richness of understory regeneration was measured in three native tree plantations 15–16 years of age at La Selva Biological Station in the Costa Rican Caribbean lowlands. Each plantation contained tree species in pure plots, a mixture of the species, and natural regeneration plots (no trees planted). The greatest abundance of regeneration was found in the understory of pure plots of Jacaranda copaia (Aubl.) D.Don., Vochysia guatemalensis Donn.Sm., Dipteryx panamensis Benth, Vochysia ferruginea Mart., and in two mixed stands, while the lowest was found in the natural regeneration treatments with about half the values as in the plantation stands. There was a significant negative correlation between percent canopy openness and abundance of regeneration in the understory. Two distinctive clusters separated the regeneration treatments from the mixed and pure plantations at a very low Bray–Curtis similarity value. The natural regeneration treatments are separated from mixed and pure plantations in the two-dimensional ordination. The lack of difference between the understory make-up of pure and mixed plantations in abundance, species richness, and seed-dispersal syndromes of understory species suggests that planting mixed stands is not necessarily superior to planting pure stands for promoting understory diversity of woody species. While regeneration of woody species can be faster under pure- or mixed-species plantations than in open pastures, the abundance, richness and species composition depends on each plantation species, or species assemblages in case of the mixtures.