Influence of thinning on the shelter effect of windbreaks as clarified by a wind tunnel experiment

We measured the shelter effect of model windbreaks in a wind tunnel before and after adjustment thinning based on methods for managing overcrowded windbreaks. One of the aims of this experiment was to determine whether or not the actual thinning done on an actual windbreak would sustain the shelter effect. The shelter effects were evaluated based on the critical wind speed and the shelter distance. Six model windbreaks were set to model a windbreak after the thinning (AT1–6) and one was set to model it before the thinning (BT). In models AT1–3, the trees in the middle part of the windbreak were cut and the trees in both the windward and leeward parts were left. AT1 and AT2 were models that reproduced the actual windbreak after the thinning. In the other three models (AT4–6), which were set as additional thinning models based on AT3, trees in both the windward and leeward parts were cut. The thinning ratios of these models ranged from 21% (AT1) to 84% (AT6). The shelter effects of AT1–3 were sustained or only slightly decreased compared with that of BT. The shelter effects of AT4 (thinning ratio of 63%) and AT5 (79%) were the highest among all of the models. From these results, it was confirmed that the thinning done on an actual windbreak was able to sustain the windbreak’s shelter effect. If the trees at the edges are not felled, the shelter effect of the windbreak can be sustained or improved, even if the thinning is heavier than AT2.     

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.     

间伐对黑松海岸林风害的影响——基于风害危险率评价的理论推导

本文在“海岸林风害危险率评价的理论推导”(Journal of Forestry Research, 2002, 13(4))一文的基础上,对1997年12月经四种间伐处理的黑松海岸林进行了连续四个生长季的风害调查,同时,对黑松海岸林内与林外风速廓线和林分透光分层疏透度的分布也分别进行了观测。应用在这些观测数据,依据“海岸林风害危险率评价的理论推导”文中获得的风害危险率评价方法,对单株树木及林分的风害风险率进行了评估,结果表明,单独依据平均直径与结合风速廓线和林分结构的风害风险率,构成了评价海岸森林风害的重要指标。不同间伐强度和风害发生率之间的关系表明,在间伐初期林分的稳定性有所下降,这可能是由于林冠粗糙度和风负载的增加及周围树木的保护效应的减少而引起的。然而,经过一段时间后,间伐处理能够促进林分生长,从而提高了林分的稳定性和对强风的抵抗力。在本试验观察过程中只发现了强风对林冠的损害,而即使是在间伐海岸林外风速达到30.2 m·s-1的条件下,也没有发现风倒或风折。本次研究中获得的结果表明,尽管在间伐之初风害的概率增加了,但是,间伐作为一种最为有效的林分管理方法,可以成为保持海岸林健康、稳定的一种长期经营管理策略。图3表4参19。     

果树化学疏花疏果的研究现状与展望

疏花疏果是生产优质果品的重要栽培措施之一.为了摸清国内外化学疏花疏果的研究现状,以研究开发新型疏花疏果剂,对化学疏花疏果的主要药剂及其作用机理和影响疏除效果的因素等方面的研究结果与研究进展进行了综述,并指出了在深入研究疏除机理的基础上开发对食品和环境安全的天然化学疏除剂是未来相关研究的方向.     

抚育间伐对栓皮栎人工林直径和树高分布的影响

[目的]以河南登封林场栓皮栎人工林为研究对象,研究抚育间伐对林分不同生长阶段林木株数、林木直径分布和树高分布的影响,为制定科学合理的抚育经营措施奠定理论和技术基础.[方法]在株数强度为31.55％的间伐林分和条件基本一致的未间伐林分内,分别设置1个1 hm2样地,间伐作业2 a后获取每木检尺数据,分别利用Normal分...     

Influences of woody encroachment and restoration thinning on overstory savanna oak tree growth rates

Midwestern savannas historically covered >10 M ha in central North America, but are now rare due to agricultural conversion and anthropogenic modifications to disturbance regimes - particularly fire suppression. Throughout this range, Midwestern savannas are characterized by scattered overstory trees; however, with fire suppression, these systems are invaded by non-savanna trees. Restoration of encroached savannas involves removal of invading trees, yet little is known about the impacts of encroachment or encroachment removal on the relict savanna overstory trees, which define these systems. Here, we use tree ring analysis to investigate savanna tree growth rates in encroached, non-encroached, and experimentally restored Midwestern oak savannas in central Iowa. We found that woody encroachment led to pronounced declines in growth rate (ring width) of relict overstory white oak (Quercus alba), relative to Q. alba trees in competition-free, open-grown conditions, or in an encroachment-free remnant woodland. To further understand effects of encroachment removal on relict Q. alba savanna trees, we conducted a large-scale restoration experiment, where encroaching trees were mechanically removed from four encroached savannas, with an additional four savannas retained as encroached controls. Restoration led to elevated tree growth rates, with these changes generally persistent through 7 years post-restoration (2003-2009). Over the course of this post-restoration study period, ring width, basal area increment, and relative basal area increased by 49%, 59%, and 55%, respectively, in trees from restored sites, relative to trees from encroached, control sites. These results suggest that woody encroachment has strong influence on overstory savanna trees, through increased competitive dynamics; however, woody encroachment removal may help to restore relict savanna tree growth rates, even after prolonged periods of encroachment (>40 years). To restore the oak savannas at our sites, and perhaps elsewhere, we advocate a three step process: (1) mechanical woody encroachment removal, (2) maintenance of the encroachment-free state through prescribed fire, and (3) promotion of a diverse understory layer, characteristic of oak savanna in our region. While promoting oak regeneration will be important for the long-term maintenance of these sites as oak savanna, relict savanna trees appear responsive to restoration and should maintain overstory conditions through the near-term.     

华北落叶松天然林目标树间伐释压与胸径生长关系研究

为探究华北落叶松所受竞争压力与胸径生长之间的关系,利用目标树中心样圆法对关帝山林区华北落叶松天然林间伐迹地进行调查研究。结果表明:受到不同竞争压力的目标树在1998年间伐后胸径生长量差异显著,且随着竞争强度的升高而减少;华北落叶松胸径连年生长量的变化由间伐释压前的下降趋势逐渐转变为缓释压力后的上升趋势;其中,间伐后受不同竞争压力的目标树胸径增长速率仍趋异化,弱度竞争目标树上升速率大于中度竞争目标树,而强度竞争目标树年平均胸径生长量上升最缓且趋势较不明显;竞争压力指数与伐后15 a胸径生长量呈幂函数关系,拐点出现在竞争压力指数为1处并在大于2后趋于平缓;以目标树为核心构建的经营体系能更加具有针对性,通过适度干扰及抚育间伐手段改良一定条件下的林木生长模式,进而精准提升森林质量。     

鲁山山区人工刺槐林抚育间伐对林木生长的影响

对淄博市国有鲁山林场人工刺槐林采取抚育间伐措施处理,对2000年所设对照、抚育标准样地在2001-2004、2005-2008、2009-2012年的数据整理后采用T检验法分析,结果表明:采用抚育间伐措施可有效促进胸径、单株材积、单位面积蓄积量的增长。该研究为人工刺槐林抚育间伐提供科学依据。     

Lipophilic extractives in different tree fractions and forestry assortments of Pinus sylvestris due for thinning or final cutting

The objectives were to determine the content and composition of lipophilic extractives, particularly fatty and resin acids, in three Scots pine trees from each of two stands in northern Sweden, one that was due for thinning and one due for final cutting. Extractives content of branches, needles, barks, stem discs from branch whorls, and sapwood and heartwood samples from various heights was measured. Fractions had very different concentrations and distributions of extractives due to differences in the composition of tissues. The needles had the highest total extractive concentration (around 150?kg/ton d.w.), followed by the branches, bark, timber from the final cut stand, and then the pulpwood and timber from the thinning stand. The final cut stand generally provided higher yields of extractives in assortments per hectare than the thinning stand; the difference was five-fold for timber, three-fold for whole trees, two-fold for branches, needles and bark and similar for pulpwood. This information on the content and composition of extractives in different tissues, and the dependence of these quantities on tree age could be used together with information on conventional stand data such as tree numbers and dimensions to guide the selection and management of feedstocks for biorefineries.     

Effects of thinning on growth of six tree species in north-temperate forests of Lithuania

This paper summarises the results from 35 years-observed thinning experiments on 256 permanent sample plots in 10–60 year-old stands of ash, aspen, birch, oak, pine and spruce in Lithuania. Thinning enhanced crown projection area increment of residual trees. The largest effect was observed in stands of aspen and birch (growth increase by 200%), followed by ash and oak (over 100%), and spruce and pine (about 80%). Thinning also promoted dbh increment, especially in younger stands, and the increase of dbh increment was positively correlated with the thinning intensity. The strongest reaction was exhibited by oak and aspen, while ash, birch and conifers reacted to a lower extent. Low and moderate intensities of thinning stimulated volume production in younger stands while the opposite was observed in older stands with increasing removals. Spruce stands exhibited relatively strongest increase of volume increment and pine, –the weakest, while the effect on deciduous species was intermediate. The results demonstrate that significant increase in volume increment is achievable with thinning of only young forest stands, e.g. 10–20 year-old pine, birch and ash, or 10–30 year-old oak, aspen and spruce.     

Impact of precommercial thinning on tree growth,lumber recovery and lumber quality in Abies balsamea

Abstract

Precommercial thinning (PCT) is often used to improve stand growth and value. While PCT may accelerate tree growth and reduce mortality, it may also have a negative effect on product quality. This study examined the effect of moderate and heavy thinning on tree growth, lumber recovery and quality in a natural balsam fir [Abies balsamea (L.) Mill.] PCT trial 35 years after thinning. Compared with the control, the heavy thinning increased merchantable tree diameter, stem volume per tree and lumber volume recovery per tree by 41.1%, 100.9% and 92.7%, respectively, reduced the Select Structural grade (the best grade) recovery by 33.7%. Thinning did not affect the no. 2 and better grade yield. There was a 12.2% and 15.0% difference, respectively, in the lumber bending modulus of elasticity (MOE) and modulus of rupture (MOR) between the control and heavy thinning. Moderate thinning had little impact on the visual grade recovery, lumber bending MOE and MOR. Heavy thinning is recommended if the goal is to get sizeable sawlogs in the shortest time, whereas moderate thinning is preferable if the intention is to minimize the negative effects on lumber quality while retaining modest tree growth and lumber recovery. Overall, PCT of very dense young balsam fir stands appears to be an effective and viable silvicultural treatment.     

Modifying climate change habitat models using tree species-specific assessments of model uncertainty and life history-factors

Species distribution models (SDMs) to evaluate trees’ potential responses to climate change are essential for developing appropriate forest management strategies. However, there is a great need to better understand these models’ limitations and evaluate their uncertainties. We have previously developed statistical models of suitable habitat, based on both species’ range and abundance, to better understand potential changes of 134 tree species habitats in the eastern United States (http://www.nrs.fs.fed.us/atlas). Our focus here is to build on these results via a more robust assessment framework called modification factors (ModFacs) that is made up of five components. ModFac 1 addresses nine biological characteristics (e.g., shade tolerance and seedling establishment) that quantify the influence of species life-history traits. ModFac 2 considers 12 disturbance characteristics (e.g., insect pests, drought, and fire topkill) which address the capacity of a species to tolerate and respond to climate-induced changes in habitat. ModFac 3-5 distill the tree SDM results and facilitate communication of model uncertainty; we quantified the variability in projected change for General Circulation Models (GCM) and emissions scenarios (ModFac 3), the extent to which each species’ habitat intersects novel climate conditions (ModFac4), and accounted for long-distance extrapolations beyond a species’ current range (ModFac5). The life-history components of ModFacs 1 and 2 demonstrate the marked variability among species in terms of biological and disturbance characteristics, suggesting diverse abilities to adapt to climate change. ModFacs 3-5 show that the information from the SDMs can be enhanced by quantifying the variability associated with specific GCM/emission scenarios, the emergence of novel climates for particular tree species, and the distances of species habitat shifts with climate change. The ModFacs framework has high interpretive value when considered in conjunction with the outputs of species habitat models for this century. Importantly, the intention of this assessment was not to create a static scoring system, but to broadly assess species characteristics that likely will play an important role in adaptation to climate change. We believe these scores based on biological, disturbance, and model synthesis factors provide an important expansion of interpretive and practical value to habitat model projections.     

The estimation of wind exposure for windthrow hazard rating: comparison between Strongblow, MC2, Topex and a wind tunnel study

This paper compares five different methods of wind exposureassessment in an attempt to identify a method that could servein windthrow hazard assessment. The candidate methods that wereselected are: a wind tunnel simulation, two numerical modelsbased on air flow behaviour (MC2 and Strongblow) and two empiricalmethods (Topex and Topex-to-distance). Best correlations withthe wind tunnel results were observed with Strongblow and Topex-to-distance.For MC2, significant correlations were obtained at high windspeedsbut not at lower windspeeds. Ranking of windiness by topographicposition was identical for the wind tunnel, Strongblow and Topex-to-distance.Wind direction estimation by MC2 showed little sensitivity totopography, especially at higher windspeeds. This fact can beattributed both to the version of MC2 used and the conditionsin which the simulations were performed. The estimation of windspeedby direction obtained with Strongblow also appeared not to bevery reliable. The satisfactory performance of Topex-to-distanceand the ease with which this method can be calculated wouldmake it appropriate for inclusion in a windthrow hazard ratingsystem.     

Long-term growth and yield effects of respacing natural regeneration of Sitka spruce in Britain

Stands of Sitka spruce (Picea sitchensis (Bong.) Carr.) originating from natural regeneration can be extremely dense with high mortality, poor growth form and low volume production. Although costly, respacing (pre-commercial thinning) can reduce resource competition for the remaining trees, altering the final crop produced. Three experiments were established to examine the effect of respacing 1–2 m tall trees to different target densities. The impact on stand growth and yield was measured 11–17 years after respacing, and the longer-term impact was modelled to year 50. Unrespaced control treatments self-thinned at a similar and constant rate at two sites. At the third, extremely high initial density resulted in a higher rate of self-thinning and lower density after 11 years. Wider respacing treatments resulted in larger mean tree diameter, but there was no significant effect of respacing on stand volume 11–17 years after respacing; greater diameter growth did not compensate for low tree number. Results indicate a volume penalty associated with delaying respacing until trees were 4 m tall, but this treatment was unreplicated. Modelled stand volume in year 50 was higher for the 2.6 m × 2.6 m respacing treatment than for the 1.8 m × 1.8 m, 2.1 m × 2.1 m or 3.3 m × 3.3 m treatments. However, open-grown conditions may reduce timber quality compared to closer spacing treatments. The results are presented using a stand density management diagram for Sitka spruce growing in Canada and support recent suggestions that British stands have a shallower size–density relationship than Canadian stands.     

Spacing interval between principal tree windbreaks--Based on the relationship between windbreak structure and wind reduction

Relative windspeed reduction was measured behind nine relatively narrow, homogenous tree windbreaks with porosities between 0.13-0.33, and behind 28 combinations of model stubble barriers representing 25 different optical porosities (0.00-0.80). The optimum porosities observed were 0.25 and 0.13 for tree windbreaks and stubble barriers respectively. Based on the relationship between windbreak structure (optical porosity) and wind reduction, the chief indices for determining spacing interval, i.e., the windbreak structure index (δ) and the parameter of microclimate, represented by the problem wind (Lrp), were determined. Additionally, investigations on shelterbelt trees were carried out, and stem-analysis techniques were used, to develop a method for determining the mature height of tree windbreaks (H0). Optimal spacing intervals between windbreaks could be predicted from the indices of a given windbreak structure, percentage of reduction of windspeed desired and tree growth model. A hypothetical example for determining the spacing interval of principal poplar windbreaks is given at the end of this paper. The results can be applied not only to tree windbreak design but also to other plant materials and artificial barriers for wind protection.     

油茶丰产栽培技术

<正>油茶(camellia oleifera Abel)属山茶科茶属常绿小乔木,是我国长江流域以南地区的重要木本食用油料树种,寿命长,适应性强,丘陵、山地均可生长,不与粮、农争地。油茶花期长,是冬季蜜源植物。油茶树常绿,叶厚革质,树干光滑能起防火作用,是防火林带的优良树种,同时油茶能绿化荒山、保持水土、调节气候,具有良好的生态效益。