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.     

Natural Regeneration in Thinned Douglas-fir Stands in Western Oregon

ABSTRACT

In response to interests by land management agencies to transform even-aged stands to structurally mimic old-growth forests, we evaluated whether thinning in 40- to 80-year-old Douglas-fir (Pseudotsuga menziesii) stands influenced amount and composition of advanced regeneration 5 to 7 years following treatment. We used data from two large-scale management experiments (Density Management Study and Young Stand Thinning and Diversity Study) conducted in western Oregon. Thinning focused on the removal of Douglas-fir, while maintenance of minor species was encouraged. Although both experiments showed higher tree regeneration after thinning, we found that variation in regeneration density was too high (3 orders of magnitude) to find statistical differences among thinning intensities. While seedlings of the major species, Douglas-fir and western hemlock (Tsuga heterophylla), were always present and dominated regeneration on nearly all sites, species trends were driven by high spatial and compositional variation throughout all units, treatments, and sites. Thinning increased the number of species within the regeneration layer. Hereby, species diversity was strongly related to overstory composition, suggesting seed source limitations for minor species. Hence, favoring rare species during thinning operations may be an effective method to increase regeneration species richness. Local conditions, as defined by overstory density appeared more influential than regional climate patterns in determining seedling densities. Shrub and grass competition did not prevent seedling establishment as their cover values were generally not as high as typically found in clearcuts in the region. The high variation in seedling density and species richness within the seedling stratum in the thinned stands may set the stage for development of structural complexity in even-aged Douglas-fir plantations.     

间伐强度对杉木人工林林下植被和土壤性质的影响

【目的】从发展林下植被、改善群落结构的角度,探讨适合杉木人工林的间伐强度,为提高人工林的稳定性和维护地力、维持人工林的可持续经营提供依据。【方法】2013年对福建省将乐国有林场的杉木人工林采取3种强度间伐:弱度间伐(LT,10%～25%)、中度间伐(MT,25%～35%)和强度间伐(HT,40%～50%),并设置对照样地(CK,未间伐)。于2016年对样地内林木进行每木检尺,调查林下植被物种多样性、盖度、生物量和土壤理化性质。对测定数据进行单因素方差分析,用Tukey法多重比较进行两两差异显著性检验,并对林下植被与土壤理化性质进行Pearson相关分析。【结果】间伐3年后,未间伐、弱度和中度间伐的盖度分别为25.52%、52.81%和58.98%,林下植被均未能形成群落,强度间伐的盖度为100%,林下形成灌木蕨类群落;灌木层物种丰富度、多样性指数、盖度和生物量均随间伐强度增加而增加,均匀度指数随间伐强度的增加而降低;草本层物种丰富度、多样性指数、均匀度指数、盖度和生物量均随间伐强度增加而增加;间伐3年后,弱度、中度、强度间伐林比未间伐林的表层土(0～10 cm)有机质含量分别增加71.41%、39.31%和98.10%,全氮含量分别增加82.76%、51.27%和115.87%,碱解氮含量分别增加49.47%、25.59%和42.22%,有效磷含量分别增加138.29%、112.23%和174.29%,速效钾含量分别增加-16.25%、-24.25%和16.27%,对表层土pH值、全磷含量和土壤物理性质的影响均不显著;灌木的盖度和生物量与土壤的有机质、全氮、全磷和有效磷含量均显著(P<0.05)正相关,此外灌木的盖度还与速效钾含量显著(P<0.05)正相关,草本盖度与土壤理化性质相关性不强,草本生物量与土壤有机质、全氮、全磷、碱解氮以及有效磷含量显著(P<0.05)正相关,林下植被的盖度和生物量均与土壤pH值和物理性质没有显著相关性。【结论】未间伐的杉木人工林林下植被的物种多样性、盖度和生物量均低,林下植被未能形成群落,缺乏稳定性;间伐能够促进林下植被的发育,增加林下植被生物多样性、盖度和生物量,林下植被能形成群落,可提高维护地力的能力,尤其是强度间伐;建议杉木人工幼龄林进行40%～50%强度的抚育间伐,将郁闭度调整到0.6～0.7较为合理。     

Effect of stand density and humus removal on regeneration of Pinus densiflora seedlings in a mixed conifer and broad-leaved forest

We studied the impact of stand density and forest floor humus removal on regeneration of Pinus densiflora in a mixed conifer and broad-leaved forest on the Daimonji-Yama Mountain,Kyoto,Japan.Three levels of stand density were set,i.e.,a clear-cut site,a heavily thinned site and a lightly thinned site.In each density treatment,comparisons were carried out between humus removal (A 0 -free)and humus intact(A 0 -intact)subplots.We counted the emergence of sown pine seeds and measured survival and growth of pine seedlings over the next four years.In addition,light conditions and the recovery of understory were monitored.Results show that thinning intensity and humus removal promoted the establishment and growth of seedlings.One exception,however,was that seedling growth was minimal in the heavily thinned A 0 -intact subplots.This was due to a strong response of understory vegetation growth on the treatment combination,which hindered the pine seedling growth.Furthermore,we found that the canopy openness measured at 1.3-m height remained at least 35%for the heavily thinned site in 2008.The results suggest that the removal of the A 0 layer after heavy thinning is the most effective and labor-saving operation for P.densiflora regeneration.     

粤西次生针阔混交群落的林下植被物种组成与多样性研究

季风常绿阔叶林是南亚热带的地带性植被类型,经采伐干扰和人工造林后形成大面积的次生林。参照CTFS样地建设技术规范,于2006年在广东粤西马尾松针阔次生林建立2 hm2固定监测样地。在对样地进行调查的基础上,分析了林下植被的物种组成与多样性。结果表明：（1）样地共有维管束植物207种,隶属于79科144属,数量优势科为茜草科、大戟科、樟科、番荔枝科、紫金牛科、禾本科和蔷薇科;单种属植物较多（101属）,占总属数的70.14%。林下植物泛热带和热带亚洲成分占绝对优势,具有南亚热带向中亚热带过渡的特征。（2）物种的丰富度指数表现出乔木幼苗〉灌木层〉藤本层〉草本层;Shannon-Wiener指数表现出乔木幼苗〉藤本层〉灌木层〉草本层;Simpson指数则为乔木幼苗〉藤本层〉草本层〉灌木层;均匀度指数为乔木幼苗〉藤本层〉灌木层〉草本层。     

间伐强度对柏木人工林生长及林下植物的影响

【目的】针对川中丘陵区普遍存在的柏木人工林密度过大、木材生产力低、林下灌草盖度低和天然更新不良等问题,开展生态疏伐试验,探讨间伐强度对林分生长和林下植物的影响,为开展柏木生态经济型防护林的营林活动提供参考。【方法】以25年生柏木人工林为研究对象,采用随机区组方法,设置4种间伐强度(20%～25%,15%～20%,10%～15%和对照)的处理,观察林分胸径、树高、蓄积量、生物多样性和天然更新幼苗数量,探讨间伐强度对其影响。【结果】不同强度间伐5年后林分平均胸径和胸径连年生长量在各处理之间均存在显著差异,胸径生长量随间伐强度加大而增加;平均树高以20%～25%间伐强度最大,达10.7 m,但20%～25%间伐强度与15%～20%间伐强度和10%～15%间伐强度之间无显著差异,而树高连年生长量在不同处理之间差异显著;20%～25%,15%～20%和10%～15%不同强度间伐5年后林分蓄积量分别为97.35,93.43和93.19 m3·hm －2,均比对照小,但蓄积连年生长量随间伐强度由高到低分别为6.11,4.58和3.66 m3·hm －2 a －1,均高于对照;20%～25%间伐强度林分的灌木和草本 Simpson 指数分别为0.7695和0.4446,Shannon-Wiener 指数分别为1.7025和0.7690,都比其他处理高;不同间伐强度天然更新幼苗株数仅在苗高5～30 cm 等级存在显著差异,30～50和50～150 cm 的幼苗在不同处理之间差异不明显;评价结果表明,综合得分以20%～25%间伐强度最大,且随间伐强度降低而减小。【结论】间伐后保留木的生长空间和营养空间得到有效改善,林分胸径和树高生长量随间伐强度增大而增加,但不同间伐强度蓄积量差异不显著;适度间伐可提高林下灌木和草本生物多样性指数;林分更新幼苗数量也随着间伐强度的增大而增加;就本研究的4种间伐强度而言,中龄阶段柏木人工林的适宜间伐强度为20%～25%。     

连栽杉木林不同生育阶段林下植被生物量

林下植被是森林生态系统的一个重要组成部分,亦是森林生态系统中有机物质的生产者,在森林生态系统的物质循环研究中具有重要作用(Chpin,1983;Chastain et al.,2006),如维持森林生物多样性(褚建民等,2007)、提高人工林的水土保持功能(袁正科等,2002)和保护环境(刘苑秋等,2004;Fabia et al.,2002;Kume et al.,2003;Taylor et al.,2006).对森林林下植被结构和生态功能的研究已有不少报道(Taylor et al.,2006;吴鹏飞等,2008;李春义等,2007;段劼等,2010).     

林下植被组成和功能研究进展

林下植被作为森林生态系统的一个重要组成部分, 在维护森林多样性、推动森林生态系统流程和功能中扮演着重要的角色。目前, 关于林下植被的研究已有上百年历史, 其中在森林群落分类、更新演替、养分循环及稳定生产力等方面做了大量研究。文中从林下植被的定义及其组成、演替和功能等方面综述了近年来林下植被的研究进展, 并探讨了如何综合研究演替以及干扰对林下植被组成的影响、林下植被对气候变化的可能响应以及如何将林下植被作用及功能的研究理论应用于近自然人工林建设和管理实践中。     

Influences of Thinning,Chipping, and Fire on Understory Vegetation in a Sierran Mixed Conifer Stand

Thinning implemented with a cut-to-length harvesting system coupled with on-site slash chipping and redistribution and followed by prescribed underburning were assessed for their impacts on a shrub understory in an uneven-aged Sierra Nevada mixed conifer stand. Overstory species consisted of California white fir (Abies concolor var. lowiana [Gord.] Lemm.), Jeffrey pine (Pinus jeffreyi Grev. & Balf.), sugar pine (Pinus lambertiana Dougl.), incense-cedar (Libocedrus decurrens Torr.), and red fir (Abies magnifica A. Murr.), while huckleberry oak (Quercus vacciniifolia Kellogg) was predominant among 10 understory shrubs. Herbaceous species were entirely absent from the site for the 4-yr duration of the study. The mechanized treatments exerted minimal detriment effects on overall understory cover and weight, and for prostrate ceanothus (Ceanothus prostratus Benth.) and creeping snowberry (Symphoricarpos mollis Nutt.)—two of the lesser shrubs—were stimulatory. In contrast, losses to the total understory from the underburn amounted to two-thirds of cover and weight in the absence of the mechanized treatments and more than three-quarters where they had been implemented, with huckleberry oak prevalence especially diminished. For almost all of the understory species individually as well as for the total, greater pretreatment abundance predisposed greater posttreatment prevalence. Results of this study provide insight into the understory impacts of restoration treatments that are deemed especially appropriate for sensitive sites in western U.S. forests.     

帽峰山米锥人工林林下植被结构特征研究

以广东省广州市帽峰山18 a生米锥人工纯林为研究对象,对林下植被结构特征进行调查,研究结果表明:米锥人工林林下植被表现出木本植物稀疏、垂直结构单一的特点。建议对该林分进行适当的结构管理,如适当的疏伐,借此促进林下植物的更新。     

Selective removal of paper birch increases growth of juvenile Douglas-fir while minimizing impacts on the plant community

Broadcast weeding of naturally regenerating paper birch (Betula papyrifera) to improve performance of conifer crop trees is common in forest plantations in British Columbia, Canada, but such treatments are costly, reduce biodiversity and may increase disease. To investigate whether alternative treatments can enhance conifer performance with minimal loss of other ecosystem services, we examined effects of selective removal of paper birch in two interior Douglas-fir (Pseudotsuga menziesii var. glauca) plantations on Douglas-fir growth and survival, and cover and height of residual birch and the understorey plant community. Douglas-fir-centred birch-free patches of varying radius (0–2.5?m) were created by single and repeated manual cutting and Triclopyr® application. The “threshold brushing radius,” defined as the birch removal radius at which Douglas-fir performance was optimized was 2.0?m at the more productive site and 1.5?m at the less productive one. Armillaria root disease, the major Douglas-fir mortality agent, spiked in the 1.0?m radius manual cutting treatment at one location. The greatest reductions in birch and understory plant abundance occurred following the most intensive treatments. Selective brushing treatments are an effective alternative to broadcast removal of paper birch for increasing conifer performance, and have less impact on the plant community.     

多伦县不同树种造林40年后林下植被结构与多样性研究

选取在相同立地条件下造林40年的油松林、华北落叶松林和白桦林作为研究对象,运用多样性指数、丰富度指数、均匀度指数和物种重要值等群落生态学统计方法,对其林下植被结构和物种多样性进行了研究。结果表明：①华北落叶松林林下植被具有最高的盖度、单位面积个体数和地上生物量,且灌木株高和冠幅最大;另外,油松林的林下植被盖度和地上生物量也高于白桦林。②油松林和华北落叶松林林下植物科属数目均多于白桦林,并且油松林和另外2种人工林分布以菊科和禾本科植物最多。③3种人工林灌木层重要值最大的分别是虎榛子、耧斗叶绣线菊和铁杆蒿;草本层重要值最大的均是黄囊苔草。④3种人工林灌木层的丰富度均较差,仅为5、4和4;而草本层各指数均是油松林〉华北落叶松林〉白桦林。     

上海半自然森林更新苗物种组成与多样性研究

城市半自然森林具有独特的群落结构和生物多样性特征,研究城市化影响的半自然森林更新特征,可以为城市生物多样性保育与地带性植被恢复重建提供借鉴。文章以上海辰山残存半自然森林1 hm^2固定监测样地为对象,调查分析半自然森林更新苗的物种组成特征。结果表明:1 hm^2样地更新苗共5 937株,分属22科32属37种,其中上海自然分布的乡土种占57.89%,明显高于城市人工林的乡土树种比例;香樟、构树、天竺桂、朴树和小蜡等5种更新苗占总数的57.2%,聚集性分布格局明显;在11个植被群落类型中,各类型更新苗的丰富度普遍较高,不同树种的更新苗存活和发育潜力存在差异。     

蒙古栎次生林林木竞争对不同抚育间伐方式的响应

目的 以长白山林区蒙古栎次生林为研究对象,分析其林木竞争关系及对不同抚育间伐方式的响应,为了解此类群落的生态适应机理及制定合理的经营措施提供依据。 方法 2013年在吉林汪清设置12块样地,开展传统经营（T1）、目标树经营密度1和密度2（T2,T3）以及对照试验（T0）,2018年进行了复测。通过有序样本聚类的方法确定Hegyi指数竞争木数量并分析了蒙古栎次生林的竞争关系以及各林层、优势树种及目标树的竞争关系对不同抚育间伐方式的响应。 结果 （1）蒙古栎次生林样地的优势树种为：蒙古栎、红松和白桦,Hegyi指数最佳相邻竞争木个数为8。（2）样地内主要树种的总竞争排序为：蒙古栎>红松>色木槭>糠椴>白桦>大青杨>落叶松>水曲柳>黑桦;主要树种的平均种间竞争略高于平均种内竞争。（3）T2,T3上林层竞争明显降低;4种抚育间伐方式均降低了白桦和蒙古栎的竞争强度,其中T3下降的幅度最大;红松的竞争强度仅在T0升高;对于优势树种来说,T2,T3来自糠椴和色木槭的种间竞争增大,而来自大青杨的种间竞争减小;T2和T3对目标树竞争的减缓作用明显优于T0和T1。 结论 基于目标树经营的抚育间伐能够有效降低蒙古栎次生林上林层及优势树种的竞争,从而可针对性培育目标树种,引导林分的正向演替,进一步验证了目标树经营的可行性和合理性。     

Predicting survival of planted Douglas-fir and ponderosa pine seedlings on dry,low-elevation sites in southwestern Oregon

Four equations were developed for predicting the probability of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine (Pinus ponderosa Dougl. ex Laws.) survival for the first (0–1) and first to third (1–3) growing seasons after applying mulching, scalping, or artificial shading (shade cards) treatments in plantations in southwestern Oregon, U.S.A. Variables describing conifer size, levels of competing vegetation, presence of silvicultural treatments, site factors, and climate factors were collected from 13 sites ranging from 0 to 6 years after planting and examined as potential predictors of survival. Age, stem diameter, a competition index for shrubs, severity of growing season at time of treatment, average annual precipitation, aspect, and slope angle were predictors of Douglas-fir survival during 0–1 and 1–3 growing seasons after treatment; the presence of silvicultural treatments was also a predictor only during the first growing season after treatment. Age, aspect, and slope angle were predictors of ponderosa pine survival over both 0–1 and 1–3 growing seasons after treatment; height-diameter ratio, competition indices for herbs, shrubs, and hardwoods, silvicultural treatment, severity of growing season at time of treatment, and average annual precipitation were also predictors only during the first growing season after treatment; crown width was a predictor of survival only during 1–3 growing seasons after treatment. When significant in the models, predicted probability of survival increases with treatments, less severe weather conditions, diameter, crown width, age, and precipitation; probability decreases with increasing height-diameter ratio and competition indices for herbs, shrubs, and hardwoods.     

广东高要南部低丘桉树人工林下植被物种多样性分析

对广东高要南部低丘桉树（Eucalyptus spp．）人工林林下植被物种进行了调查分析。结果表明,林下植被物种最少有156种以上,分属56科和103属,乔木21种,灌木59种,藤本20种,草本36种,总体Shannon-Wiener指数为2．26。种群数目大于5％的优势种均为草本植物,其中芒箕（Dicranopteris dichotoma）占绝对优势（46．2％）,这是林下植被物种丰富度较高而多样性偏低的主要原因。林下植被物种组成、丰富度和多样性在不同地域之间均有显著的差异,但在林分龄级之间则没有明显的变化。     

乐都县下北山林场次生林抚育间伐效果分析

通过对1992～1999年期间抚育间伐效果的分析，并针对该场森林资源实际，提出了适宜间伐强度和间隔期，抚育间伐工作中应注意以森林经营方案和年度生产计划为依据搞好采伐作业设计，综合利用，实现森林永续利用。     

不同间伐强度天然次生林凋落物性质的研究

对近40年生以柞树为主的天然次生林采取不同抚育间伐措施后,定位研究林分凋落物的性质。结果表明:凋落物量每年从10月份开始增大,到12月末达到高峰,全年各个时期,凋落量最大的基本为弱度间伐区。枯枝落叶年凋落量和贮量以弱度间伐区最大,强度间伐区最小。凋落物总量的分解转化率以强度间伐区最高,对照区最小。研究认为,对天然次生林中的幼林采取适度抚育间伐可改善林地凋落物状况,有利于林地的养分供给。     

人工杉木过熟林林下草本植被分布情况初探

对张家界国家森林公园内杉木过熟林林下草本植被的分布情况开展初步调查研究.结果表明,杉木过熟林林下草本植物种类繁多,数量庞大;随着杉木林老化程度的加重,林下的阴生草本植物在减少,逐步出现阳生草本植物并在数量上有增加的趋势;下坡位的环境更适于草木植物生长.对林下草本植物的重要值分析结果,半边旗表现出最高的重要值,处于优势地位.     

毛乌素沙地杨树人工林林下植物群落特征

目的 研究人工林林下植物群落特征及其与林分因子的关系,对沙地植被恢复成效的评价和人工林管理具有重要意义。 方法 本研究以毛乌素沙地杨树人工林群落为研究对象,调查研究林下植物群落特征,并重点探讨了林分郁闭度、密度等林分因子对林下植被的影响。 结果 研究区杨树人工林林下共发现植物32种,隶属于12科28属,其中豆科、禾本科、菊科植物最多,占总植物种的62.51%;林下草本植物生活型以多年生草本植物为主,占总物种的78.13%,植物水分生态类型以旱生、中旱生植物为主,占总物种数的75.00%,其次为旱中生和中生植物;林下草本层Margalef丰富度指数变化范围为1.20～3.17,Simpson优势度指数变化范围为0.48～0.88,Shannon-Wiener多样性指数变化范围为0.95～2.34,Pielou均匀度指数变化范围为0.16～0.48,林龄32年生时林下物种多样性最高;结构方程模型结果显示林分郁闭度和密度与林下灌木层盖度之间存在负效应关系,人工林郁闭度较高时,林下无灌木层形成。林分郁闭度的增加有利于草本层的发育,而林分密度与草本层盖度、地上生物量、物种丰富度和Shannon-Wiener多样性指数之间存在负效应关系,灌木层对草本层的影响与乔木层相似。 结论 毛乌素沙地杨树人工林林下草本植物多样性较高,灌木种类较少,其大小受郁闭度和密度等林分因子的影响较明显。适当调控林分密度和结构,将有利于毛乌素沙地杨树人工林林下物种多样性的维持和近自然改造。