Effects of Precommercial Thinning on Snowshoe Hares in Maine

Abstract: Snowshoe hares (Lepus americanus) are an important prey species and a dominant herbivore across much of their North American range, and researchers have questioned the influences of forestry practices that alter habitat for hares and the potential community-level effects on carnivores. We examined the effects of precommercial thinning (PCT) from 1 to 11 years posttreatment on snowshoe hares. In the commercial forests of northern Maine, USA, we counted and cleared hare pellets twice a year during 2001 and 2002 on >46 km of pellet transects across 30 regenerating conifer stands (17 treated with PCT) previously treated with an aerial application of herbicide. We compared densities of snowshoe hare pellets among 3 development classes with (1 yr after thinning, 6 yr after thinning, and 11 yr after thinning) and without thinning (stands with a similar history of clearcut and herbicide treatment but no thinning). During both years, densities of hares were lower in stands treated with PCT than in similar unthinned stands across the 3 development classes and during both leaf-off and leaf-on seasons (P < 0.001). Within both thinned and unthinned stands, hare density was greatest in stands in the 1-year development class when compared to the 6-year and 11-year development classes, but a statistical difference (P = 0.048) among classes was evident only during leaf-off seasons. Precommercial thinning was associated with densities of snowshoe hares that were approximately half of those in similar unthinned stands up to at least 11 years posttreatment; however, thinned stands may retain densities of hares greater than stands managed using other forest harvesting regimes. Our results apply to core portions of stands with crop trees spaced at 1.8–2.4-m intervals following complete overstory removal and herbicide treatment. We advocate caution when applying our results to other thinning regimes or across broader spatial scales.     

Huckleberry abundance, stand conditions, and use in western oregon: Evaluating the role of forest management

Huckleberries are major components of the understory vegetation in coniferous Pacific Northwest forests of the United States. Vaccinium species also have a long history of human use. However, little research has been done to ascertain how they respond to common forest management practices. We used data obtained from old-growth, young thinned, and young unthinned Douglas-fir stands in western Oregon to evaluate how forest management could potentially influence species abundance and product supply. Our analysis focused on three species: Vaccinium ovatum, V. parvifolium,and V. membranaceum. Results were variable, but indicate that overstory stand conditions and forest management can affect huckleberry species abundance. However, to assess fully the effects of forest management on these species, studies specifically designed to target areas where people harvest these products are needed. Measuring relevant product attributes such as commercial productivity is also critical.     

Understory vegetation response to thinning disturbance of varying complexity in coniferous stands

Question: Can augmented forest stand complexity increase understory vegetation richness and cover and accelerate the development of late‐successional features? Does within‐stand understory vegetation variability increase after imposing treatments that increase stand structural complexity of the overstory? What is the relative contribution of individual stand structural components (i.e. forest matrix, gaps, and leave island reserves) to changes in understory vegetation richness? Location: Seven study sites in the Coastal Range and Cascades regions of Oregon, USA. Methods: We examined the effects of thinning six years after harvest on understory plant vascular richness and cover in 40‐ to 60‐year‐old forest stands dominated by Douglas‐fir (Pseudotsuga menziesii). At each site, one unthinned control was preserved and three thinning treatments were implemented: low complexity (LC, 300 trees ha^?1), moderate complexity (MC, 200 trees ha^?1), and high complexity (HC, variable densities from 100 to 300 trees ha^?1). Gaps openings and leave island reserves were established in MC and HC. Results: Richness of all herbs, forest herbs, early seral herbs and shrubs, and introduced species increased in all thinning treatments, although early seral herbs and introduced species remained a small component. Only cover of early seral herbs and shrubs increased in all thinning treatments whereas forest shrub cover increased in MC and HC. In the understory, we found 284 vascular plant species. After accounting for site‐level differences, the richness of understory communities in thinned stands differed from those in control stands. Within‐treatment variability of herb and shrub richness was reduced by thinning. Matrix areas and gap openings in thinned treatments appeared to contribute to the recruitment of early seral herbs and shrubs. Conclusions: Understory vegetation richness increased 6 years after imposing treatments, with increasing stand complexity mainly because of the recruitment of early seral and forest herbs, and both low and tall shrubs. Changes in stand density did not likely lead to competitive species exclusion. The abundance of potentially invasive introduced species was much lower compared to other plant groups. Post‐thinning reductions in within‐treatment variability was caused by greater abundance of early seral herbs and shrubs in thinned stands compared with the control. Gaps and low‐density forest matrix areas created as part of spatially variably thinning had greater overall species richness. Increased overstory variability encouraged development of multiple layers of understory vegetation.     

Regeneration of a Coastal Pine (Pinus thunbergii Parl.) Forest 11 Years after Thinning,Niigata, Japan

To examine the effects of thinning intensity on wind vulnerability and regeneration in a coastal pine (Pinus thunbergii) forest, thinning with intensities of 20%, 30% and 50% was conducted in December 1997; there was an unthinned treatment as the control (total 8 stands). We re-measured the permanent sites to assess the regeneration characteristics 11 years after thinning. In the 50% thinned stand, seedlings aged from 2 to 10 years exhibited the highest pine seedling density and growth. The age composition ranged from 1–3 years with densities of 9.9 and 5.1 seedlings m⁻² in 30% and 20% thinned stands; only 1-year-old seedlings with a density of 6.1 seedlings m⁻² in the unthinned stand. Similar trends were found for the regeneration of broadleaved species such as Robinia pseudoacacia and Prunus serrulata. We speculate that the canopy openness and moss coverage contributed to the regeneration success in the 50% thinned stand, while the higher litter depth and lack of soil moisture induced the regeneration failure in the unthinned stand. The stands thinned at 20% or 30% were less favourable for pine regeneration than the stands thinned at 50%. Therefore, thinning with less than 30% canopy openness (20% and 30% thinned stands) should be avoided, and thinning at higher than 30% canopy openness (50% thinned stand, approximately 1500 stems ha⁻¹ at ages 40–50 years) is suggested for increasing regeneration in the coastal pine forest. The implications of thinning-based silviculture in the coastal pine forest management are also discussed. The ongoing development of the broadleaved seedlings calls for further observations.     

Diversity and succession of epiphytic macrolichen communities in low‐elevation managed conifer forests in Western Oregon

Abstract. We examined epiphytic macrolichen communities in Pseudotsuga menziesii (Douglas‐fir) forests across the western Oregon landscape for relationships to environmental gradients, stand age and structure, and commercial thinning. We used a retrospective, blocked design through the Coast and the western Cascade ranges of Oregon. Each of our 17 blocks consisted of a young, unthinned stand (age 50–110 yr); an adjacent, thinned stand of equivalent age; and an old‐growth stand (age > 200 yr). We found 110 epiphytic macrolichen taxa in the stands. Forage‐providing alectorioid lichens and the nitrogen‐fixing cyanolichen Lobaria oregana associated strongly with old‐growth stands and remnant old trees in younger stands (unthinned + thinned). Relative to unthinned stands, thinned stands had a slightly higher abundance of alectorioid lichens and a greater presence of Hypogymnia imshaugii. However, thinned stands hosted a lower landscape‐level (γ) diversity, lacking many species that occurred infrequently in the unthinned stands. Patterns in the lichen community composition correlated strongly with climatic gradients; the greatest variation in composition was between the Coast and Cascade ranges. The difference in communities between mountain ranges was greatest among stands 70–110 yr old, suggesting a difference in lichen successional dynamics between the ranges.     

Restoration of beech forest for saproxylic beetles—effects of habitat fragmentation and substrate density on species diversity and distribution

The influence of spatial location and density of beech snags on species diversity and distribution patterns of saproxylic beetles was studied in a 2,400 ha forest landscape in southern Sweden. Complete snag surveys were combined with a beetle survey using small window traps directly attached to the beech snags. The density of beech snags ≥30 cm dbh varied between one and seven snags per ha within the study area, corresponding to 1.1–5.1 m³/ha. A total of 2,610 specimens of 180 saproxylic beetles species were trapped, of which 19 species were red-listed. Within the study area, the number of red-listed and formerly red-listed species was highest around traps in old-growth stands, intermediate in managed stands contiguous with old-growth and lowest in managed stands isolated from old-growth by a two km-wide zone without beech forest. Logistic regressions revealed negative relationships between distance to old-growth forest and occurrence of eleven species, among them six red-listed or formerly red-listed species. The number of non red-listed species was not correlated with isolation from old-growth forest. The number of red-listed species also increased with snag density within 200–300 m around the traps. Our results suggest that red-listed species generally have a lower dispersal capacity than other saproxylic beetles. We conclude that retention of dead wood close to existing populations is more beneficial for red-listed species than an even distribution of snags across the forest landscape.     

间伐对落叶松人工林内草本植物多样性及其组成的影响

通过对落叶松人工林间伐林分和未间伐林分林下草本植物的调查以及林下光照条件的测定,分析间伐对林下草本植物多样性、组成的影响及其与光照条件的关系。结果表明,除均匀度指数在春、秋季表现不同外,间伐林分的丰富度指数、多样性指数均高于未间伐林分,说明间伐后草本植物多样性明显增加。依据草本物种在间伐前后出现与否和密度变化情况将其划分为正反应种(间伐后密度明显增加和间伐后新出现的种)、中性反应种(间伐后密度变化不明显或没有变化的种)和负反应种(间伐后密度明显减小和间伐后消失的种),间伐后出现大量新的草本种类,同时在间伐和未间伐林分的共有种中有许多表现为负反应种。在间伐林分中,间伐行和未间伐行的共有种春季有11个、秋季有10个,分别占间伐林分草本总种数的17.74%和15.15%,表明各行草本植物组成差异较大;各指数均呈现了从间伐行到未间伐行逐渐减小的趋势。主要的正反应种、中性反应种和负反应种均表现出与光照具有一定的相关性,且这种相关性与间伐和非间伐林分之间各草本物种与光照的相关性基本一致。     

Seasonal prevalence of arthropods after line thinning of overstocked Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantations in central Japan

We investigated the seasonal changes in the abundance of coleopteran and hymenopteran functional groups to evaluate the ecological suitability of line thinning in overstocked Japanese cedar plantations in central Japan. In line thinning, 3- to 5-m-wide sections of the stand are harvested parallel to the mountain slope and perpendicular to the forest roads. The thinning intensity varies from 25 to 35% of the total number of trees. We compared the seasonal abundance between the thinned stand and the unthinned (control) stand in two plantation forests: a low-elevation Sugi site (4 years since thinning) and a high-elevation Kuchiotani site (6 years since thinning). Most coleopteran and hymenopteran functional groups were consistently more abundant in the thinned stand than in the unthinned stand. The differences in arthropod abundance between the thinned and unthinned stands were mainly caused by marked differences in the abundance of seasonally strongly changing functional groups during their peak seasons. The predators and parasitoids of insects as well as the plant and pollen feeders (plant-dependent functional groups) responded to seasonal changes in the vegetation (food and microhabitats) and microclimate. The ants were less affected by line thinning. Our results indicate that line thinning is an ecologically suitable silvicultural treatment for the improvement of biodiversity conditions in the overstocked plantation forests.     

Diversity of the Bialowieza Forest avifauna in space and time

The Biaowiea Forest (BF) is an extensive and relatively little changed forest complex on the Polish-Belarussian border. Data on the structure and diversity of its breeding avifauna have mostly been collected in primeval old-growth stands, preserved within the Biaowiea National Park (BNP). Mapping censuses repeated in space (plots, replicated in riverine, oak-lime-hornbeam and coniferous stands) and time (permanent plots, 28 years) reveal that the breeding bird assemblages are rich in species (29–52/season in a 25 to 33-ha plot), but of moderate overall density (40–120 pairs/10 ha). The latter is due to low, lower than in man-transformed areas, densities of the majority of particular species. Despite marked changes in vegetation structure, the composition of the breeding bird assemblage does not vary much across different primeval forest types, with a single breeding bird community inhabiting all of them, including treefall gaps. High richness of the BF avifauna stems from the Forests geographical locality, as well as from a high level of the primeval avifauna retention. Over 95% of the 135–140 pristine species still breed there. Especially species-rich groups are birds of prey, owls, woodpeckers and Sylvinae warblers. Bird communities in the BNP and primeval tropical rain forests share many features, suggesting that natural differences between temperate and tropical forests were less pronounced in the past. The combination of high species richness with low densities of individual species is probably a feature of all pristine forests, independent of climatic zone. The BF avifauna must once have been typical of the ancient European forests and it has become so exceptional chiefly because it has preserved most of its pristine features. The BF thus constitutes an indispensable reference site for future studies of woodland bird biology. To ensure its survival should become a priority. Commercial logging, taking place over 80% of the Polish BF part, severely changes the Forests structure and strongly affects the birds, especially species which depend on dead wood (Dendrocopos leucotos, Picoides tridactylus) and on old-growth stands. The small area protected as the BNP becomes an increasingly isolated island, in which preservation of the primeval forest features seems to be impossible. In order to retain them, it is necessary to protect the whole BF area.     

Response of shrubland birds to regenerating clearcut area and shape

Conservation of birds that breed in early-successional forests will require an understanding of their response to patch size and shape during the early seral stages following disturbance. We modeled the effects of patch area, patch shape, and time period following harvest on territory densities of 5 shrubland bird species and bird community composition in 36 clearcuts from 1997 to 2014 in the Missouri Ozarks, USA. Our best-supported models indicated that densities of indigo bunting (Passerina cyanea), yellow-breasted chat (Icteria virens), and prairie warbler (Setophaga discolor) declined from the early time period (1–7 years post-harvest) to the late time period (12–18 years post-harvest), regardless of clearcut area or shape. Yellow-breasted chat density and bird species richness were positively related to clearcut shape complexity. Bird species richness increased, and bird species density decreased with clearcut area during both time periods. Non-metric multidimensional scaling indicated that bird community composition was strongly related to time since harvest. Within the spatial scale of our study, successional stage is more influential than clearcut size and shape, and some bird species may benefit from relatively small or irregularly shaped clearcuts. © 2019 The Wildlife Society.     

Thinning improves growth and resilience after severe droughts in Quercus subpyrenaica coppice forests in the Spanish Pre-Pyrenees

During the past years, growth and productivity of different oak species have been constrained by water shortage in seasonally dry regions such as the Mediterranean Basin. Thinning could improve oak radial growth in these drought-prone regions through the reduction of tree competition for soil water in summer. However, we still lack adequate, long-term assessments on how lasting are thinning treatments effects and to what extent they contribute to oak growth recovery after drought. Here we aim: (i) to study the radial growth sensitivity to drought of Quercus subpyrenaica in the Spanish Pre-Pyrenees, and (ii) to verify if thinning represents a suitable option to enhance growth resistance to drought and post-drought growth recovery. We analysed basal area increment (BAI) trends in the period 1960–2020 of formerly coppiced oak stands thinned in 1984 and compared them with unthinned plots and also with coexisting Scots pine (Pinus sylvestris) growing in thinned plots. We used the Standardized Precipitation Evapotranspiration Index (SPEI) to estimate the severity of droughts and we also assessed climate-growth relationships. Oaks in thinned plots showed higher BAI (369 mm²) than those in unthinned plots (221 mm²). Growth rates remained higher in thinned than in unthinned plots also under severe drought stress. A severe summer drought in 1986 caused abrupt BAI reductions in both oaks (- 40.5%) and pines (- 40.1%). The positive effect of thinning on growth lasted for over 20 years and slightly declined as canopies closed. In the thinned plots, trees with smaller diameter showed the greatest growth release. Oaks in unthinned plots and Scots pine were more sensitive to short-term droughts in terms of growth reduction than oaks in thinned plots, while long term droughts have similar effects on oaks from both thinned and unthinned plots. Oaks were resilient to drought, showing recovery periods lasting from 1 to 2 years in both thinned and unthinned plots. However, intense and prolonged droughts could strongly reverse the expected growth enhancement of thinned plots, and a greater frequency of droughts would limit coppice growth and productivity thus lengthening the rotation periods.     

Soil carbon fluxes and stocks in a Great Lakes forest chronosequence

We measured soil respiration and soil carbon stocks, as well as micrometeorological variables in a chronosequence of deciduous forests in Wisconsin and Michigan. The chronosequence consisted of (1) four recently disturbed stands, including a clearcut and repeatedly burned stand (burn), a blowdown and partial salvage stand (blowdown), a clearcut with sparse residual overstory (residual), and a regenerated stand from a complete clearcut (regenerated); (2) four young aspen ( Populus tremuloides ) stands in average age of 10 years; (3) four intermediate aspen stands in average age of 26 years; (4) four mature northern hardwood stands in average age of 73 years; and (5) an old-growth stand approximately 350-years old. We fitted site-based models and used continuous measurements of soil temperature to estimate cumulative soil respiration for the growing season of 2005 (days 133–295). Cumulative soil respiration in the growing season was estimated to be 513, 680, 747, 747, 794, 802, 690, and 571 g C m⁻² in the burn, blowdown, residual, regenerated, young, intermediate, mature, and old-growth stands, respectively. The measured apparent temperature sensitivity of soil respiration was the highest in the regenerated stand, and declined from the young stands to the old-growth. Both, cumulative soil respiration and basal soil respiration at 10 °C, increased during stand establishment, peaked at intermediate age, and then decreased with age. Total soil carbon at 0–60 cm initially decreased after harvest, and increased after stands established. The old-growth stand accumulated carbon in deep layers of soils, but not in the surface soils. Our study suggests a complexity of long-term soil carbon dynamics, both in vertical depth and temporal scale.     

Ecological study of pseudoscorpion fauna in the soil organic layer in managed and abandoned secondary forests

We surveyed pseudoscorpion fauna in the soil organic layer in managed and abandoned secondary forests in Hiroshima Prefecture, Japan, and studied the effects of forest management on the pseudoscorpions. The vegetation structure was generally more developed in abandoned stands than in managed stands. The depth of the soil organic layer was not significantly different between the two stand types. We observed a total of seven pseudoscorpion species belonging to five genera. Pseudoscorpion species richness and densities were higher in abandoned stands than in managed stands. We did not find any pseudoscorpions in stands where the summed vegetation cover was less than 150%.An erratum to this article can be found at     

Applying climate change refugia to forest management and old-growth restoration

Recent studies highlight the potential of climate change refugia (CCR) to support the persistence of biodiversity in regions that may otherwise become unsuitable with climate change. However, a key challenge in using CCR for climate resilient management lies in how CCR may intersect with existing forest management strategies, and subsequently influence how landscapes buffer species from negative impacts of warming climate. We address this challenge in temperate coastal forests of the Pacific Northwestern United States, where declines in the extent of late-successional forests have prompted efforts to restore old-growth forest structure. One common approach for doing so involves selectively thinning forest stands to enhance structural complexity. However, dense canopy is a key forest feature moderating understory microclimate and potentially buffering organisms from climate change impacts, raising the possibility that approaches for managing forests for old-growth structure may reduce the extent and number of CCR. We used remotely sensed vegetation indices to identify CCR in an experimental forest with control and thinned (restoration) treatments, and explored the influence of biophysical variables on buffering capacity. We found that remotely sensed vegetation indices commonly used to identify CCR were associated with understory temperature and plant community composition, and thus captured aspects of landscape buffering that might instill climate resilience and be of interest to management. We then examined the interaction between current restoration strategies and CCR, and found that selective thinning for promoting old-growth structure had only very minor, if any, effects on climatic buffering. In all, our study demonstrates that forest management approaches aimed at restoring old-growth structure through targeted thinning do not greatly decrease buffering capacity, despite a known link between dense canopy and CCR. More broadly, this study illustrates the value of using remote sensing approaches to identify CCR, facilitating the integration of climate change adaptation with other forest management approaches.     

A Decade of Streamwater Nitrogen and Forest Dynamics after a Mountain Pine Beetle Outbreak at the Fraser Experimental Forest,Colorado

Forests of western North America are currently experiencing extensive tree mortality from a variety of bark beetle species, and insect outbreaks are projected to increase under warmer, drier climates. Unlike the abrupt biogeochemical changes typical after wildfire and timber harvesting, the outcomes of insect outbreaks are poorly understood. The mountain pine bark beetle (Dendroctonus ponderosae) began to attack lodgepole pine (Pinus contorta) at the Fraser Experimental Forest in 2002 and spread throughout the research area by 2007. We compared streamwater nitrogen (N) from 2003 through 2012 with data from the previous two decades in four watersheds with distinct forest management histories, stand structures, and responses to the beetle outbreak. Watersheds dominated by old-growth had larger trees and lost 85% of overstory pine and 44% of total basal area to bark beetles. In contrast, managed watersheds containing a mixture of second-growth (30–60 year old) and old-growth (250- to 350-year old) had higher density of subcanopy trees, smaller mean tree diameter, and lower bark beetle-induced mortality (~26% of total basal area). Streamwater nitrate concentrations were significantly higher in old-growth watersheds during the outbreak than pre-outbreak levels during snowmelt and base flow seasons. In mixed-age stands, streamwater nitrate concentrations were unaffected by the outbreak. Beetle outbreak elevated inorganic N export 43 and 74% in two old-growth watersheds though the amounts of N released in streamwater were low (0.04 and 0.15 kg N ha^?1) relative to atmospheric inputs (<2% of annual N deposition). Increased height, diameter, and foliar N of measured in residual live trees augmented demand for N, far in excess of the change in N export during the outbreak. Reallocation of soil resources released after pine mortality to overstory and understory vegetation helps explain high nutrient retention in watersheds affected by bark beetle outbreaks.     

Restoration of Old Forest Features in Coast Redwood Forests Using Early‐stage Variable‐density Thinning

To accelerate development of old forest features in coast redwood, two thinning treatments and an unthinned control were compared in three treatment areas in north coastal California. One thinning treatment was designed to restore old forest densities of 125 trees/ha and the other 250 trees/ha representing a one‐step and partial treatments to the desired stand density. Four years after treatment, numbers of trees had increased in the thinning treatments due to recruitment of new trees, but had decreased in the control due to self‐thinning. Residual trees increased in stem volume following thinning by 128% in low‐density thinning compared to 70% in the controls indicating thinning accelerated stand development. The thinning treatments also moved the species composition of these stands to a greater proportion of redwood. Considerable slash was produced by the thinning treatments but was decomposing rapidly. Black bears damaged approximately 15% of all trees and more than 38% of residual trees in the thinned treatments compared to less than 2% of all trees in the control. This damage included killing some trees and damaging other trees that survived. Decisions over restoration densities in these stands are complicated by prolonged stand development, and balancing risks and costs. In this case, the bears represent a stochastic factor that dramatically increases risk. Thinning appears to be an effective means of enhancing old forest development by accelerating tree growth, modifying species composition, and increasing stand‐level variability. Continued monitoring will be necessary to evaluate long‐term trends in density relative to effects of bear damage.     

Effects of Wildlife Forestry on Abundance of Breeding Birds in Bottomland Hardwood Forests of Louisiana

ABSTRACT Effects of silvicultural activities on birds are of increasing interest because of documented national declines in breeding bird populations for some species and the potential that these declines are in part due to changes in forest habitat. Silviculturally induced disturbances have been advocated as a means to achieve suitable forest conditions for priority wildlife species in bottomland hardwood forests. We evaluated how silvicultural activities on conservation lands in bottomland hardwood forests of Louisiana, USA, influenced species-specific densities of breeding birds. Our data were from independent studies, which used standardized point-count surveys for breeding birds in 124 bottomland hardwood forest stands on 12 management areas. We used Program DISTANCE 5.0, Release 2.0 (Thomas et al. 2006) to estimate density for 43 species with >50 detections. For 36 of those species we compared density estimates among harvest regimes (individual selection, group selection, extensive harvest, and no harvest). We observed 10 species with similar densities in those harvest regimes compared with densities in stands not harvested. However, we observed 10 species that were negatively impacted by harvest with greater densities in stands not harvested, 9 species with greater densities in individual selection stands, 4 species with greater densities in group selection stands, and 4 species with greater densities in stands receiving an extensive harvest (e.g., >40% canopy removal). Differences in intensity of harvest influenced densities of breeding birds. Moreover, community-wide avian conservation values of stands subjected to individual and group selection, and stands not harvested, were similar to each other and greater than that of stands subjected to extensive harvest that removed >40% canopy cover. These results have implications for managers estimating breeding bird populations, in addition to predicting changes in bird communities as a result of prescribed and future forest management practices.