Crop Tree Release Research Articles

Retaining the largest aspen stems during motor-manual release allows to control aspen suckering in young mixedwood stands

Mixedwood stands containing aspens (Populus tremuloides or P. grandidentata) often convert to hardwood-dominated stands after harvesting due to the rapid regeneration of aspen from root suckers, even when sites are promptly replanted with conifer seedlings. Without the use of herbicides, this problem is usually dealt with several passes of motor-manual (“manual”) release of overtopped seedlings. The aim of this study was to test a variation of thinning from below treatment (thinning; only 20% of the largest aspens are retained), and to compare it against two traditional release treatments: broadcast brushing (brushing; 100% removal of aspen) or crop tree release (CTR; removal of competing vegetation 60 to 90 cm around planted spruce) and an un-treated control. The thinning treatment left the 20% larger aspen stems in place, in order that they continue exerting apical dominance on smaller suckers and limit re-suckering of the treated plots. Aspen suckering and growth of planted black spruce seedlings (Picea mariana (Mill.) B.S.P) were measured two- and four-growing seasons following treatments. Results four years after release application showed that the thinning and CTR treatments reduced aspen density by 61% compared to the brushing treatment. In addition, aspen individual stem volume in the thinning treatment was almost 10 times larger than the brushing and twice that of the CTR treatments. Spruce height and ground collar diameter (GCD; 5 cm aboveground line) were both measured, and while height increment was similar in all treatments, diameter increment was greater in the thinning treatment (+42%) compared to the control, brushing and CTR treatments (+17%). Thinning yielded better short-term results than the brushing release in terms of aspen re-suckering and aspen sawlog potential, highlighting the need for adapted silvicultural treatments based on the species’ ecology.

A comparison of initial harvest results from four partial harvest systems at the Blue Heron Demonstration Forest

Demonstration forests have been established across the northern hardwoods of the United States to assess the economic and environmental implications of partial harvest systems, such as single tree selection and diameter limit cutting. Single tree selection has been studied at several sites in the northern hardwoods of Canada, but there has not been a structured comparison of partial harvest systems within one site. We assessed the initial harvest results at the Blue Heron Demonstration Forest, in which four partial harvest systems – single tree selection (STS), financial maturity selection (FMS), diameter limit cutting (DLC), and crop tree release (CROP) – and a control treatment were implemented with multiple replicates within a typical northern hardwood forest in central Ontario. DLC harvested the most volume as well as basal area, followed closely by FMS. STS harvested the least basal area and volume and generated the lowest product values as well as the lowest stumpage revenue. However, STS did not harvest significantly more low vigour trees, nor did it significantly increase the proportion of basal area that is high vigour, suggesting that alternative partial harvest systems like FMS may achieve silvicultural objectives while yielding superior financial results over multiple cutting cycles.

Initial effects of crop tree release and traditional thinning on productivity and carbon storage of Cunninghamia lanceolata plantation

IntroductionThinning has a crucial impact on the carbon dynamics of forest ecosystems. The inconsistencies about the effects of thinning on carbon stocks in previous studies may be attributed to different thinning plans that designed to achieve different management goals.MethodsThis study focuses on Cunninghamia lanceolata as the research object and investigates three treatments: crop tree release (CTR), traditional thinning (TM), and no thinning (CK). The different thinning methods (CTR and TM) had different management objectives and selection of crop trees principle, although with the same thinning density. The short-term effects of CTR and TM treatments on tree growth and carbon storage in Cunninghamia lanceolata plantations were analyzed and compared.ResultsBoth CTR and TM were beneficial to the growth of individual trees when compared to CK, with CTR being more beneficial. The average annual increments in DBH, TH, and volume of a single tree in CTR increased by 62.50%, 61.29%, and 74.07% higher than CK, respectively. So CTR was the best for large-diameter timber yield, which was 77.40% higher than CK, whereas CK had a higher proportion of medium- and small-diameter timber yield. However, CTR had an insignificant short-term boosting effect on stand volume, and its timber volume was considerably higher than that in TM treatment, but not as high as in CK. Therefore, the carbon storage in the tree layer, litter, and different soil layers under different treatments showed that CTR and TM were significantly lower than CK. And the total carbon storage in the three treatments showed that CK > CTR > TM, with CTR showing a 13.07% higher than TM. On the contrary, thinning could effectively improve understory vegetation carbon storage. The carbon storage in the herb and shrub layers under CTR increased by 47.77% and 183.44%, respectively, compared to CK.DiscussionAlthough thinning could significantly promote the growth of individual trees and understory vegetation, their total carbon storage in the short term was lower than that in CK. CTR showed a higher carbon sequestration and sink capacity than TM. It suggests that CTR, as a special type of thinning method, should be encouraged to selected because it has the chance to achieve a faster carbon sequestration rate than traditional thinning and it also can produce higher-quality timber.

Long-Term Effects of Crop Tree Release on Growth and Quality in White-Oak (Quercus alba L.)-Dominated Stands

Abstract Crop tree release (CTR) can be an effective intermediate silvicultural treatment for culturing high-value stems in mixed hardwood stands. The lengthy rotation of hardwoods requires long-term evaluations if silvicultural treatment effectiveness is to be fully evaluated. Our study provides a 35-year evaluation of individual-tree and stand response to CTR imposed in small sawtimber-sized white-oak (Quercus alba L.)-dominated stands. The focus on white oak is justified based on the significant biologic and economic values of the species, and this study furthers our ability to optimize use of CTR as management tool for sustaining our oak resources. The replicated experiment included three treatment levels: 20 crop trees ac−1, 34 crop trees ac−1, and a control. Using a repeated-measures framework, we analyzed (1) how CTR affects growth and stem quality of white oak crop trees and (2) stand-level effects of CTR on basal area, stocking, and ingrowth. CTR increased crop tree diameter growth and proportion of crop trees reaching their maximum potential grade. However, crop tree diameter growth and proportion achieving maximum potential grade did not differ between the 20 and 34 crop trees ac−1 treatments. Finally, CTR stimulated stand-wide growth without altering the patterns of ingrowth density or species distributions.

The effects of crop tree thinning intensity on the ability of dominant tree species to sequester carbon in a temperate deciduous mixed forest, northeastern China

Forest management is one of the important nature-based solutions for climate mitigation. Thinning can indirectly influence tree physiology by changing the microclimate and directly change the stand biomass, which can impact forest carbon sequestration. However, previous results about how thinning might influence carbon stocks remain inconsistent regarding post-thinning carbon accretion. In this study, crop tree release (CTR) thinning in four intensities (CK: 0% of basal area removal, LT: 17.25%, MT: 34.73%, and HT: 51.87%) were conducted in a temperate deciduous forest in Jiaohe, northeastern China in 2011. Plot inventories in 2011, 2013, 2015, 2018 and 2021 and tree cores collected in 2017 and 2018 offered the opportunity to examine how are the interannual carbon sequestration ability of Korean pine and Manchurian ash responded to CTR thinning in four intensities. We quantify the carbon sequestration ability of trees by calculating individual stem carbon stock and annual carbon stock rate to examine whether the previous inconsistency was attributed to different responses of species, and the ignorance of frozen carbon content. The results show: (1) after thinning, the underestimation of carbon stocks of Manchurian ash decreased with the increasing thinning intensity. The greatest underestimation of Manchurian ash reaches 2922 kg ha−1, while that of Korean pine only reaches 283 kg ha−1. Compared with Manchurian ash, the conventional carbon fraction of 0.5 for Korean pine is more appropriate, and the misestimation of Korean pine didn't show an obvious pattern with the intensity of thinning. (2) Under light thinning, both species maintained a stable carbon stock growth, and the frozen carbon content of Korean pine was significantly increased. During the 10 years after light thinning, the individual stem carbon of Korean pine increased from 57 kg to 81 kg, and Manchurian ash increased from 201 kg to 268 kg. The average rate of increase of individual stem carbon is positively related to tree size. Removing such large-diameter trees from the stand is likely to decrease carbon stock rate. Therefore, it is essential to design carbon-friendly silviculture prescriptions worldwide under the consideration of species, sizes, and intensities.

Growth, yield, and financial return through six decades of various management approaches in a second-growth northern hardwood forest

Evaluation of long-term studies provides information about the sustainability of forest management on a time scale valuable to forest managers. A long-term silvicultural study at the Argonne Experimental Forest in northern Wisconsin has been continuously maintained for over six decades, providing an opportunity to test differences in growth and yield between three partial cutting methods: single-tree selection, crop tree release, and diameter-limit cutting. Over 65 years, results showed that single-tree selection with low residual stocking (14 m2 ha−1 basal area) performed best in regard to financial returns, growth, and yield, with high financial returns, greater levels of ingrowth, lower mortality, and greater residual percent volumes of high quality sawtimber. Diameter growth was maximized in low to moderate (17 m2 ha−1 residual basal area) residual stocking selection. The diameter-limit cut (18 cm dbh limiting diameter) was not successful in producing high-quality trees or consistent yield. After 50 years the crop tree release treatment did increase percent of high-quality harvested volumes, but to a lesser extent than the selection treatments. Selection treatments removing more basal area provided an overall better return on investment, providing potential incentive for modification to traditionally practiced single-tree selection to higher residual basal areas.

Residual Stand Damage under Different Harvesting Methods and Mitigation Strategies

A major component of sustainable forest management are the stands left behind after the logging operation. Large mechanized harvesting equipment involved in current forest management can inflict damage on residual trees; and can pose a risk of mortality from diseases, natural calamities, and/or degrade future economic value. The primary objective of this study was to evaluate the residual stand damage under different harvesting methods and silvicultural prescriptions i.e., crop tree release (CTR), diameter limit cut (DLC), and overstory removal (OSR). The second objective was to evaluate the intensity and frequency of damage occurring on the bole, canopy, and root at tree and stand level. The third objective was to document strategies adopted globally to minimize stand damage due to timber harvesting. Five harvest blocks implementing three silvicultural prescriptions, were selected as the treatments across two different industrial timberlands in central and northern Maine (Study Site (SS) I and II, respectively). A hybrid cut-to-length (Hyb CTL) and whole-tree (WT) harvesting method were employed for conducting the harvest in SS I and II, respectively. Systematic transect sampling was employed to collect information on type, frequency, and intensity of damages. The inventory captured 41 and 8 damaged trees per hectare with 62 and 22 damages per hectare from SS I and SS II respectively. Bole damage was the most frequent damage across all treatments. The Hyb CTL had lower damage density (damage per ha) and severity compared to WT. The average number of trees damaged per ha was higher for CTR prescriptions compared to DLC. There were no significant differences in the height of the damages from the ground level between treatments within each study site; however, there was a significant difference between the study sites. Species damaged was directly related to the residual trees left behind and was dominated by American beech, yellow birch, sugar maple, and eastern hemlock. Finally, the study provides strategies that can be adopted at different forest managerial phases to mitigate residual stand damage.

Influencing plantation stand structure through close-to-nature silviculture

New silvicultural practices to meet the requirements of ecosystem-based forest management are being adopted operationally, even if the long-term outcomes remain unknown. In eastern Quebec, Canada, the conversion of plantations from even-aged to irregular or uneven-aged stands is being carried out in 10% of commercial thinning operations. Existing growth and yield simulators cannot be used to forecast stand development. Here we apply a novel individual tree-level simulator to plantations characterized by high levels of natural regeneration ingrowth, such as those observed in Quebec. The simulator user can either choose distance-dependent or distance-independent competition indices, depending on user preference or simulation needs. Calibration statistics and validation results indicate that both versions perform very well. When applied to operational silvicultural scenarios, the simulator shows that thinning does not influence total stand yield; however, tree spatial aggregation does change. Moreover, the variability among the different simulation runs is greater for spatial statistics than for stand yield. Overall, thinning from below has the greatest effect on stand structure, whereas the smallest is from early crop tree release, used as the initial conversion step. This pattern implies that the first and second thinnings of the conversion process towards irregular or uneven-aged stands may not have a major effect on stand structure. In the case of the conversion process, the consequences for stand structure must thus be viewed as a longer-term issue. More importantly, the conversion process does not reduce stand yield, thereby reducing one of the key concerns of forest managers.

Impacts of Future Crop Tree Release Treatments on Forest Carbon as REDD+ Mitigation Benefits

Sustainable forest management activities, such as future crop tree (FCT) release treatments, became part of the REDD+ strategy to avoid carbon emissions from forests. FCT release treatments are intended to achieve increased growth of FCTs by removing competitor trees. This initially leads to a reduction of the forest carbon pool and represents a carbon debt. We estimated that the time it takes for FCTs to offset the carbon debt through increased growth on experimental sites of 10 km² in Belize, Guyana, Suriname, and Trinidad and Tobago. We further investigated whether the costs of treatment can be compensated by the generated financial carbon benefits. An average of 2.3 FCT per hectare were released through the removal of an average of 3.3 competitors per hectare. This corresponds to an average above ground biomass (AGB) deficit of 2.3 Mg FCT−1. Assuming a 30% increase in growth, the FCT would need on average 130 years to offset the carbon loss. For carbon prices from US$ 5 to 100 Mg CO2e−1 an additional increment between 0.6 and 22.7 Mg tree−1 would be required to cover the treatment costs of US$ 4.2 to 8.4 FCT−1. Assuming a carbon price of US$ 10 Mg CO2e−1, the additional increment required would be between 5.8 and 11.4 Mg tree−1, thus exceeding the biological growth potential of most individual trees. The release of FCTs does not ensure an increase in forest carbon stocks, and refinancing of treatment costs is problematic.

Future crop tree release treatments in neotropical forests – an empirical study on the sensitivity of the economic profitability

Silvicultural treatments are a common tool for increasing commercial timber production. Their impact on the growth or mortality of the remaining stand is well researched. This study focuses on the economic aspects of silvicultural treatments in neotropical forests. We have selected liberation treatments and consider them to be investments that are expected to pay for themselves through the additional growth of released trees and corresponding timber prices following a 30-year rotation period. The study is based on empirical data collected on experimental sites of 10 km2 in Belize, Guyana, Suriname, Trinidad and Tobago. To determine the timber price or additional growth required to cover the treatment costs, we used a reverse approach based on net present values. The treatment costs range between US$4.5 and US$8.9 per released tree. The additional growth required per released tree to cover the expenses for silvicultural treatments depends on treatment costs and achievable timber prices and varies from 0.02 to 3.5 m3. Conversely, if a potential increase in growth is assumed, timber prices must be between 34 and 578 US$ m-3 to at least cover the cost of treatments. We found a high sensitivity of profitability related to the additional growth, the timber prices to be achieved, and the discount rate chosen, which significantly increases the financial risk of silvicultural treatments as an investment tool. The decision whether to use silvicultural treatments or not is often solely guided by the expected improvement in tree growth. We, however, show that growth alone is insufficient as a decision criterion. While treatment costs are known when the decision to implement the measures is made, future timber prices and harvesting costs as well as the additional growth actually achieved are subject to uncertainties. These uncertainties have a decisive influence on the economic risk assessment, which is reflected in the choice of the internal interest rate. Our study demonstrates that investments in silvicultural treatments involve a considerable financial risk and that the decision to carry out silvicultural treatments should always be the subject of a thorough investment calculation.

Crop tree release increased the density of soil nematodes and improved the food web structure

As a special thinning method, crop tree release (CTR) has a beneficial effect on forest environments and structures by changing forest light, heat, and water. However, the impact of CTR on underground biodiversity remains unclear. Therefore, we analyzed the composition, diversity, and metabolic footprints of soil nematode communities under three CTR (100, 150, and 200 trees·ha–1) treatments, as well as a no CTR treatment, in Pinus massoniana Lamb. plantations. The results showed that CTR increased the density of soil nematodes (P < 0.05), the number of omnivore–predator nematodes (P < 0.05), and the diversity (H′) of nematodes (P < 0.05) and enriched the food web structure of soil nematodes. In the medium CTR density treatment (150 trees·ha–1), the nematode density and diversity (H′) were the highest (P < 0.05), the number of omnivore–predator nematodes was also the highest (P < 0.05), and the enrichment index and structure index values of the soil nematodes reached the maximum at the depth of 0–10 cm (P < 0.05). Our results indicated that the community structure of soil nematodes became more stable and mature after CTR, which may be attributed to the changes of soil condition, especially soil organic matter, and plant diversity indirectly.

A crop tree release variant of precommercial thinning using a backpack mounted chain saw

Although crop tree release (CTR) in hardwood stands is an accepted variant of precommercial thinning (PCT), the lack of an affordable and feasible method hinders its adoption. CTR implies selecting between 150 and 500 trees ha when trees are between 7 and 12 m high and cutting only stems competing with the target crop trees. We performed a field trial of a CTR variant of PCT in a 27.8 ha hardwood stand using a backpack mounted chain saw. A detailed time study was performed to document the trial over 13 days. Compared to conventional PCT performed earlier in the life of a stand, precommercial crop tree release required cutting larger stems, which showed to be feasible and productive using a backpack mounted chain saw. Productivity varied between 0.22 to 0.47 ha h during the trial, Although productivity could vary with stand characteristics and worker, this proof of concept trial demonstrates some of the potential uses that this new saw configuration offers and sets the basis for an eventual larger scale deployment of this treatment.–1–1

Thinning and species mixing in Chinese fir monocultures improve carbon sequestration in subtropical China

Mixed-species forests have potentially more benefits than monocultures particularly in terms of greater carbon sequestration. A 16-year-old Chinese fir (Cunninghamia lanceolata) monoculture in Zhejiang, China, was converted to a Chinese fir—broadleaved plantation by thinning from below (TFB) and crop tree release (CTR) methods coupled with planting of Chinese sweet gum (Liquidambar formosana) seedlings. Carbon pools in trees, snags, shrubs and herbs, seedlings, litterfall, forest floor, and mineral soil were measured for 5 years. The total tree biomass carbon increase in un-thinned control and CTR stands was approximately 15% higher than that in TFB. The average individual tree biomass C stock increased by 20.5% and 9.2% in CTR and TFB, respectively. Carbon flux through litterfall decreased after thinning but recovered, thereafter, to a level similar in the un-thinned control. Compared to the control, lower tree mortality and higher growth of seedlings in both converted stands resulted in no change in ecosystem C stocks. Carbon stocks in trees and seedlings increased more in CTR than in TFB stands, implying that CTR should be favored when converting pure plantations into mixed-species stands.

目标树经营初期对柏木人工林土壤线虫群落的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 目标树经营初期对柏木人工林土壤线虫群落的影响 DOI: 10.5846/stxb201806101296 作者: 作者单位: 四川农业大学林学院,四川农业大学林学院,四川农业大学林学院,四川农业大学林学院,四川农业大学林学院,四川农业大学林学院,四川农业大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 德国政府贷款四川林业可持续经营管理项目（G1403083）；科技部2017年度专项项目（2017YFD0600302-05） Effects of early crop-tree release on soil nematode communities in a Cupressus funebris plantation Author: Affiliation: College of Forestry, Sichuan Agricultural University,,,College of Forestry, Sichuan agriculture university,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为研究目标树经营初期对柏木人工林土壤线虫群落的影响，对遂宁市安居区处于竞争生长阶段的柏木林进行3种不同密度目标树经营，共计样地12个（目标树密度为6株/667 m2、9株/667 m2、12株/667 m2以及对照各3个）。在目标树经营1年后，采集春、夏、秋、冬4个季节样品共252个，采用改进的Baermann湿漏斗法分离土壤线虫，共鉴定出土壤线虫59科143属。其中Prionchulus为优势属，食细菌性线虫38属，食真菌性线虫12属，植食性线虫36属，杂食/捕食性线虫57属。土壤线虫生活史策略以c-p 4类群为主，占总数的44.33%，其中目标树密度为9株/667 m2整个样地（9N）的c-p 4占比最大。目标树经营增加了土壤线虫的数量，目标树密度为9株/667 m2的目标树单株（9C）线虫密度达到最大；目标树经营处理中均以杂食/捕食性线虫数量最多，其中9C杂食/捕食性线虫数量均高于其他处理；目标树经营提高了多样性指数（H'）、均匀度指数（J）、线虫营养多样性指数（TD）、线虫成熟度指数（MI），目标树经营改善了土壤线虫群落结构，其中目标树密度为9株/667 m2样地的土壤线虫群落结构最优。研究结果表明，采用目标树经营有利于提升土壤线虫群落多样性，使柏木人工林生态系统向更稳定的方向发展，其中目标树密度为9株/667 m2的效果最为显著。 Abstract:To study the impact of crop-tree release on the soil nematode community in a Cupressus funebris plantation, 12 plots were selected from the cedar forest of Anju District, Suining City (crop tree density 6 trees/667 m2, 9 trees/667 m2, and 12 trees/667 m2, and a control group for each of the three), 252 samples from four seasons (spring, summer, autumn, and winter) were collected, and a total of 143 genera belonging to 59 families were identified. Among them, Prionchulus was a dominant genus, Bacterivores were represented by 38 genera, fungivores by 12 genera, plant parasites by 36 genera, and omnivores/predators by 57 genera. The soil nematode colonizer persister was dominated by c-p 4 groups, accounting for 44.33% of the total. Among these, the whole plot with crop tree density of 9 trees/667 m2 (9N) had the largest proportion of c-p 4.The crop-tree release increased the number of soil nematodes. Among these, the crop trees with a crop tree density of 9 trees/667 m2 (9C) had the maximum nematode density. The number of omnivore/predator nematodes was highest in the crop-tree release, and the number of 9C omnivore/predator nematodes was higher than that of the other treatments. The crop-tree release increased the Shannon-Wiener index (H'), Pielou evenness index (J), Trophic Diversity (TD), and Maturity index (MI), which showed that the crop-tree release increased the diversity of soil nematode communities, and the crop tree density 9 had the best soil nematode community structure. The results showed that the use of crop-tree release was conducive to the enhancement of the diversity of soil nematode communities and the development of a Cupressus funebris plantation ecosystem to a more stable direction. Among these, the crop tree density of 9 trees/667 m2 had the most significant effect. 参考文献 相似文献 引证文献

Crop Tree Release Guidelines for 71- to 94-Year-Old Oak Stands Based on Height and Financial Maturity

Crop Tree Release Guidelines for 71- to 94-Year-Old Oak Stands Based on Height and Financial Maturity

Precommercial thinning as a silvicultural option for treating very dense conifer stands

ABSTRACTLack of available workforce in motor-manual operations has led to increased interest in mechanized precommercial thinning (PCT) treatments. We evaluated 15 years of growth and yield development of a very dense (27,000 stems ha–1) balsam fir (Abies balsamea (L.) Mill) and black spruce (Picea mariana (Mill.) B.S.P.) stand after six PCT treatments: (1) motor-manual (MAN), (2) motor-manual with crop tree release (MAN-C), (3) mechanized (MEC), (4) mechanized with residual patches (MEC-P), (5) semi-mechanized (mechanized followed by motor-manual, MEC-S), and (6) unthinned control (CON). Compared to CON, both MAN and MEC-S increased height of balsam fir study trees by 53–56% and diameter at breast height (DBH) by 57–58%. MAN-C and MEC-S increased DBH of black spruce study trees by 15–31% over all other treatments. The proportion of merchantable basal area (BA) was higher in MAN (62%) and MEC-S (56%) than in CON (22%) and MEC (25%), without a reduction in total BA. PCT treatments that provided a uniform distribution of potential crop trees (MAN, MEC-S) performed better than MAN-C and MEC-P, while MEC yielded the poorest responses. Our findings highlight the need to develop new tailored mechanized systems for high wood production and low operational cost.

Twenty-five year response of non-crop trees to partial release during precommercial crop tree management

An underappreciated component of precommerical crop tree release (PCTR) is the inevitable partial release of non-crop trees. While the response of fully released crop trees is increasingly understood, few studies have examined the response of non-crop trees. The effects of precommercial crop tree release at canopy closure on upper canopy persistence, mortality, and diameter growth over 25-years were examined on seven study areas established in Connecticut in 1988. Each area had nine 8m×8m plots for each of two treatments: PCTR and unmanaged controls. The equivalent of 156 crop trees per hectare were completely released by cutting all stems with adjacent crowns. This resulted in the inadvertent partial release on two or more sides of 480 upper canopy, non-crop trees per hectare. Diameters and crown classes of all stems (DBH>2cm) were measured annually. For those stems in the upper canopy at when treated, partial release increased the proportion of oaks, but not maples or birches, which persisted in the upper canopy. Partial release increased the proportion of intermediate oaks that ascended into the upper canopy and reduced mortality. Partial release increased 25-year diameter growth of oaks. However, releasing upper canopy, sapling oaks on only one side did not increase upper canopy persistence or diameter growth. PCTR increased the proportion of oaks among the largest 300 trees per hectare twenty-five years after treatment. Where predicted oak densities are below management goals, precommercial crop tree release should be considered as a tool to increase survival and growth of quality oak saplings.

Evaluation of Cleanings to Maintain Oak Forests on the Allegheny National Forest

Ten-year results for an administrative study on the Allegheny National Forest (ANF) that examined their cleaning (precommercial thinning) prescriptions and standards for success in maintaining oak (Quercus spp.) composition in young stands and maintaining oak stems in a competitive position are presented. Two studies were installed. One study was in a 25- to 30-year-old stand where we released intermediate and suppressed oak species, in particular white oak (Quercus alba), to see if they would survive and improve in crown class. The other study was installed in two 16-year-old stands where cleanings using crown-touching crop-tree release treatments were done, with untreated control plots reserved. A total of eight treated and eight control plots in two stands were examined. In the first study, mortality of white oaks in the lower canopy (intermediate or overtopped) was 83 and 39% in control versus treated areas, respectively. The cleaning treatments were successful in keeping trees alive, but crown vigor declined and no trees increased in crown class. In the second study, the mortality of crop trees was 15 and 2% in control versus treated stands, respectively. The proportion (number of stems) of crop trees of all species in the upper canopy (dominant or codominant) dropped 22% versus 1% for control versus treated trees over the 10 years. Stand-level oak composition in control stands was 11.3% of basal area after 10 years (11.7% initially). In treated stands, it was 18.3% of basal area after 10 years (10.7% initially), a 71% increase in oak. The treatments successfully increased survival, growth, and composition of oak.

Silvicultural Rehabilitation of Cutover Mixedwood Stands

We investigated rehabilitation of mixedwood stands degraded by exploitative cutting on the Penobscot Experimental Forest in Maine. Three precommercial rehabilitation treatments were applied: control (no rehabilitation), moderate rehabilitation (crop tree release [CTR]), and intensive rehabilitation (CTR, timber stand improvement [TSI], and red spruce fill planting). Crop trees (primarily red maple, paper birch, spruce, aspen, and eastern hemlock) were selected and released based on their potential for improved growth and value, spacing, and species composition. Rehabilitation reduced sapling basal area, density, and hardwood abundance and increased crop tree diameter increment. Fill planting increased spruce stocking, but many planted seedlings were browsed. Long-term projections suggested that future stand value will repay costs of moderate rehabilitation (CTR); intensive rehabilitation (CTR-TSI-planting) as applied in this study requires greater investment than can be repaid through quality and growth improvements of low-value hardwoods and softwoods. Although simulations suggested no difference in future stand value between treated and untreated stands, improvements in composition, growth, and quality after rehabilitation will facilitate later commercial thinning and shelterwood regeneration in stands which otherwise have few management options.

Stand Structure and Composition 32 Years after Precommercial Thinning Treatments in a Mixed Northern Conifer Stand in Central Maine

Abstract The effects of four precommercial thinning (PCT) treatments on an even-aged northern conifer stand in Maine were investigated by examining stand structure and composition 32 years after treatment. Replicated treatments applied in 1976 included: (1) control (no PCT), (2) row thinning (rowthin; 5-ft-wide row removal with 3-ft-wide residual strips), (3) row thinning with crop tree release (rowthin+CTR; 5-ft-wide row removal with crop tree release at 8-ft intervals in 3-ft-wide residual strips), and (4) crop tree release (CTR; release of selected crop trees at 8×8-ft intervals). PCT plots had more large trees and fewer small trees than the control in 2008. There were no other significant differences between the rowthin and control. The rowthin+CTR and CTR treatments had lower total and hardwood basal area (BA) and higher merchantable conifer BA than the control. CTR also resulted in more red spruce (Picea rubens [Sarg.]) and less balsam fir (Abies balsamea [L.]) than the other treatments. Although stand structures for rowthin+CTR and CTR were similar, the percentage of spruce in CTR was greater. Although the less-intensive rowthin+CTR treatment may provide many of the same benefits as CTR, the latter would be the preferred treatment if increasing the spruce component of a stand is an objective. Overall, early thinning treatments were found to have long-term effects on key stand attributes, even more than 30 years after treatment in areas with mixed species composition and moderate site potential.