太白山红桦种群结构与空间分析

 为了揭示太白山红桦(Betula albo-sinensis)种群的维持机制, 结合径级结构、静态生命表和存活曲线, 对太白山红桦种群结构进行了研究; 并应用单变量、双变量K函数对不同径级立木与残干的空间格局、空间关联性进行了多尺度分析。研究显示, 太白山红桦种群在幼苗幼树阶段死亡率较高, 进入中龄期后死亡率有所降低, 随着年龄增长, 死亡率逐渐增加, 直至年龄极限。其存活曲线基本接近Deevey I型(曲线凸型)。其个体死亡方式主要为掘根和折干(由大雪所致), 能够为种群更新提供潜在空间。除海拔2 250 m立木整体格局呈集群分布外, 该地区红桦立木与残干在不同尺度下的整体格局均为随机分布。不同发育阶段的个体均呈集群分布, 表现为斑块状同龄群。在红桦更新所需的最适林窗大小尺度上, 红桦立木与残干的空间关联性为显著正相关。以上结果表明: 太白山红桦种群具有同龄集群生长的特性, 种群由时空上不连续的局部斑块同龄个体组成, 其更新有赖于以掘根及折干方式死亡个体所形成的林窗斑块, 这种以局部林窗斑块更新维持种群整体稳定的特性, 可能是其长期稳定存在的重要机制。     

Effects of disturbance and size structure on the regeneration process in a sub-boreal coniferous forest,northern Japan

The stand structure and disturbance history in a sub-boreal coniferous forest dominated byPicea jezoensis, Picea glehnii andAbies sachalinensis were investigated in four study plots set up in Taisetsuzan National Park, Japan. The effect of stand characteristics on the growth and mortality rates of understory trees was examined. Although all the stands showed inverse J-shape d.b.h. (diameter at breast height) distributions, the age structure and disturbance history differed amongst the stands. The stands with wide d.b.h. distribution (i.e. large CV and skewness) were more uneven-aged than those with narrow d.b.h. distribution (i.e. small CV and skewness). The disturbance-return interval based on the model of Hett and Loucks was 31 to 65 years. The gap ratio in the canopy was also different among the stands. These suggest that the variations in stand structure represent different occurrences of natural disturbances. Furthermore, the structural features such as size structure, canopy gap ratio and density of canopy trees also affected the growth dynamics of understory trees (≥2 m in height and <10 cm in diameter at breast height). The growth and mortality rates of understory trees changed with the canopy gap ratio and canopy tree density. The understory trees of stands with wide canopy d.b.h. distribution had higher growth and canopy recruitment rates than those of stands with narrow canopy d.b.h. distribution, contributing to the maintenance of continuous stand stratification. The understory trees of stands with narrow canopy d.b.h. distribution showed lower growth and higher mortality rates than those of stands with narrow canopy d.b.h. distribution, leading to the formation of a single-canopy structure. It is suggested that natural disturbance governs the regeneration process in the future by affecting the growth and mortality patterns of understory trees through the stand structure (size and age structure, canopy tree density, canopy gap ratio).     

管涔山青扦(Picea wilsoni)天然林年龄结构及其动态的研究

对种群年龄结构的研究表明,虽经人为频繁干扰,管涔山青扦天然林仍表现出异龄林结构特征,立木年龄范围超过一个龄级期,根据年龄结构特征值可分为相对同龄林、相对异龄林和异龄林３种类型。林下新一代种群的数量和结构受林冠郁闭度和结构的影响。具垂直郁闭型林冠的异龄林,林下更新数量充足,幼苗幼树年龄结构合理;而水平郁闭型林冠,不利于新一代种群的发生和发展。青扦种群年龄结构受种群发生和自疏两个过程的控制,林下种群的发生以小规模林冠空隙干扰下的连续更新为主。青扦华北落叶松混交林,在其共同适生范围内是某种干扰格局控制下的稳定群落     

海南岛热带山地雨林天然次生林的功能群划分

热带林极高的物种丰富度使许多生态分析非常困难,把功能相似的物种划分为不同功能群,将为热带林的生态研究提供新的途径。以物种的7个功能特性因子(生长型、分布的海拔高度、分布的林型、木材密度、喜光性、演替地位和寿命)和9个林分结构因子(相对生物量、相对胸高断面积、相对树高、相对密度、相对频度、相对冠幅、相对更新数、相对死亡数和相对萌生数)为基础,应用数量化分析的方法,对海南岛典型的热带山地雨林天然次生林群落进行了功能群的划分。结果表明:(1)应用CCA分析林分结构因子时,可将山地雨林天然次生林的物种划分为6类功能群,它们的相对生物量、相对密度、相对频度、相对更新数、相对萌生数和相对死亡数等,随胸径和高度的增加而呈现有规律的变化;(2)应用CCA分析物种功能特性因子时,可将山地雨林天然次生林的物种划分为5类功能群,它们的功能特性都随演替过程而呈现有规律的变化;(3)在综合考虑两个不同角度CCA分析的基础上,最后将热带山地雨林天然次生林的物种共划分为11类功能群,它们能充分体现物种随胸径和高度结构的变化特点及其在演替过程中所处的阶段;(4)演替初期的灌木类功能群与各不同演替时期的乔木功能群共同分布于的中下层,但其大多处于死亡状态;(5)演替初期与演替中后期的乔木功能群则共同组成的主层林,但其死亡数量也较高。可见,海南岛热带山地雨林天然次生林目前正处不同功能群的激烈竞争阶段。     

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.     

Age structure and dynamics of Patagonian beech forests in Torres del Paine National Park,Chile

This study documents the stem size and age-structure in forests dominated by different species of Nothofagus in Torres del Paine National Park (51° S), in the Chilean Patagonian region. We also explored the relationship between the various types of Nothofagus forest and postglacial succession. Pioneer stands on moraine fields 1–2 km of the glacier front are dominated by Nothofagus betuloides and Nothofagus antarctica. Moraines appear to be first colonized by the evergreen N. betuloides, followed within 5–7 years by deciduous N. antarctica. Nothofagus antarctica may replace the former species and develop monospecific stands on glacial valleys. Most trees in the N. antarctica stand studied were older than 40 years and floods may cause a significant mortality of young trees. Recruitment from seed seems to be infrequent. Old-growth stands dominated by deciduous Nothofagus pumilio occupy more stable substrates, and probably represent the last stage of postglacial succession. This long-lived tree species had recorded ages over 200 years. The canopy of N. pumilio forests appears to be a mosaic of even-aged, old-growth patches. We propose that regeneration episodes follow the blowdown of a large portion of the canopy, with long intervals with little or no regeneration. Windstorms may be an important force influencing the regeneration of N. pumilio. Exogenous disturbances, such as floods and windstorms, are an integral part of the forest cycle in the Patagonian region.     

管涔山青扦(Picea wilsoni)天然林年龄结构及其动态的研究

地种群年龄的研究表明,虽经人为频繁干扰,管涔肝扦天然林仍表现出异龄林结构特征,立木年龄范围超过一个级期,根据年龄结构特征值可分为相对龄林、相对异龄林和异龄林３种类型林下新一代种群的数量和结构受林冠郁闭度和结构的影响。具垂直郁闭型林冠的异龄林,林下更新数量充足,幼苗幼树年龄结构合理;而服闭型林冠,不利于一代种群的发生和发展,青扦种群年龄结构受种群发生和自疏两个过程的控制,林下种群的发生以小规模林冠空     

Age distribution of trees in stationary forest system

A statistical theory for the age distribution of spatially dominant trees in a stationary forest system is developed. The result depends whether or not mortality is spatially correlated, as well as whether or not the stand boundaries are pre-determined. In the case of spatially non-correlated mortality, the tree age distribution is an exponential with survival rate as the base. In the case of spatially correlated mortality within a stand with pre-determined boundaries, the age distribution within the stand is an exponential with natural base. For a small stand, the median life span of the stand is inversely proportional to the number of trees (n); the median life span in relation to stand closure time is inversely proportional to n ln(n). For a large stand, the stand life does not extend to the closure time.The behaviour of a forest system without fixed stand boundaries depends on the dimensionality of the system. In the case of a one-dimensional system, the longevity distribution is exponential, most of the trees however having the same longevity. Consequently, the probability density of tree age is constant. However, the probability mass of size of catastrophe destroying a particular tree is evenly distributed. This is due to trees being rapidly born on empty areas in the beginning of the life cycle, and clusters rapidly growing into larger ones close to the end of tree life.     

Ecological succession following forest decline in a xeric oak forest of south-central United States

Aims The loss of canopy trees associated with forest decline can greatly influence the species composition and structure of a forest and have major impacts on the ecosystem. We studied the changes in forest composition and structure 1 and 5 years following nearly total canopy mortality on several hundreds of hectares of xeric oak forests in south-central United States. Because the forests were within an ecotonal vegetation type composed of a mosaic of forest, savanna and grassland, we sought to learn whether forest decline areas would recover to forest or change to more open savanna and grassland conditions in the landscape pattern of vegetation. Because low intensity fire shaped the vegetation type, we sought to learn whether fire would keep the decline areas open.Methods The study was conducted in a xeric oak forest in east-central Oklahoma, USA. Randomly located vegetation and regeneration surveys were conducted in decline and non-decline stands 1 and 5 years following nearly total canopy mortality. Diameter at breast height (DBH), regeneration and sprout origin were recorded for all woody species.Important findings The major canopy species post oak (Quercus stellata Wangenh.), blackjack oak (Quercus marilandica Muenchh.) and black hickory (Carya texana Buckl.) suffered 85–92% mortality; however, minor canopy components experienced limited mortality. Mortality affected all size classes of canopy trees except those below 5cm breast height diameter. There was abundant regeneration of all species and fire seemed to maintain a high level of sprouting. Decline appeared to decrease the relative importance of stump sprouting and increase other types including root sprouts. Decline areas had abundant true seedlings, with stem origin from a root with the same diameter as the stem, which is very unusual for xeric oak forests. Regeneration height in decline areas was twice that of non-decline forests. Our findings suggest that forest decline may lead to: (i) reduced oak dominance and species change in the canopy, (ii) change in reproduction type to increase success of true seedlings and maintain genetic diversity of oaks.     

Legacy of Pre-Disturbance Spatial Pattern Determines Early Structural Diversity following Severe Disturbance in Montane Spruce Forests

Background

Severe canopy-removing disturbances are native to many temperate forests and radically alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity to ecosystem function after such events. Poorly understood is the degree to which the structural complexity of an old-growth forest carries over to the next stand. We asked how pre-disturbance spatial pattern acts as a legacy to influence post-disturbance stand structure, and how this legacy influences the structural diversity within the early-seral stand.

Methods

Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and dead trees, crown projections, down logs, and herb cover.

Results

Post-disturbance stands were dominated by an advanced regeneration layer present before the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus aucuparia), were strongly self-aggregated and also clustered to former canopy trees, pre-disturbance snags, stumps and logs, suggesting positive overstory to understory neighbourhood effects. Thus, although the disturbance dramatically reduced the stand’s height profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced advanced regeneration through microsite and light limitation. Under formerly dense canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater heterogeneity in heights.

Conclusion

These findings suggest that pre-disturbance spatial patterns of forests can persist through severe canopy-removing disturbance, and determine the spatial structure of the succeeding stand. Such patterns constitute a subtle but key legacy effect, promoting structural complexity in early-seral forests as well as variable successional pathways and rates. This influence suggests a continuity in spatial ecosystem structure that may well persist through multiple forest generations.     

长白山阔叶红松林不同强度择伐后关键树种的竞争关系

天然林择伐改变了林分的树种组成和结构,导致林木竞争关系发生变化,进而影响树木的生长和种群的动态.关键树种在维持群落结构和生态系统功能方面具有至关重要的作用.为了弄清长白山区阔叶红松林典型林型关键树种竞争关系的特点,本研究以红松、紫椴和水曲柳为研究对象,运用Hegyi竞争指数分析了受不同程度采伐干扰后形成的原始林(未受干扰)、轻度择伐林、中度择伐林和重度择伐林的林分结构和竞争关系.结果表明: 与原始林相比,轻度择伐林中关键树种的种群结构没有显著变化;中度择伐林和重度择伐林中3个关键树种大树(胸径DBH≥20 cm)的密度和平均胸径均显著减少,但幼树(2 cm≤DBH<10 cm)的数量增加.所有样地中关键树种的竞争指数均随径级的增加而减小,且二者服从幂函数分布,而林木胸径生长到20 cm后,竞争指数进入稳定状态.在原始林、轻度和中度择伐林中,3个树种的幼树的竞争指数受到非冠层树种的影响最大,而红松小树(10 cm≤DBH<20 cm)和大树主要受红松种内和非冠层树种的影响;水曲柳主要受红松和非冠层树种的影响,紫椴主要受种内和红松的影响.重度择伐林中,白桦是3个树种的主要竞争来源,贡献率均超过50%.根据以上关键树种竞争关系的特点,抚育非冠层树种有利于3个关键种幼树的更新和生长;对于小树来说,还需要根据树种类型来采取相应措施,而大树不需要采用抚育措施.本研究对关键树种培育和天然林择伐后快速恢复具有指导意义.     

Regeneration in subalpine coniferous forests

The regeneration process of a subalpine coniferous forest, a mixed forest ofTsuga diversifolia (dominant species),Abies veitchii, Abies mariessi, andPicea jezoensis var.hondoensis, was studied on the basis of annual ring data. The age class distribution was discontinuous and four age groups occurred in the study plot (30m×30m). The canopy layer was a mosaic of patches (83.8–133.7 m² patch area), which had different mean ages. The recruitment of canopy trees was carried out only by advance regeneration in the plot. The diameter growth ofAbies andPicea exceeded diameter growth ofTsuga in the gap.Abies lived for 200–300 years and their trunks were susceptible to heart rot.Picea lived for 300–400 years andTsuga for more than 400 years. The regeneration process derived from the analysis of the plot consisted of three phases leading to the development of a even-aged patch; (1) the establishment of saplings before a gap opening, (2) the opening of a gap in the canopy and repair of the canopy by advance regenerated saplings dominated by rapid growth species,Abies andPicea, and (3) the dying off of canopy trees as each species reached the end of its life-span, resulting in pure patches of long-livedTsuga.     

Succession: A population process

Summary Recent critical reviews suggest the need for a reductionistic approach to the study of secondary plant succession. We propose viewing succession as the result of the underlying plant population dynamics. This approach is being developed using nearly 50 years of permanent sample plot records.After initial establishment Pinus taeda shows an exponential depletion with stands of various densities conforming to the reciprocal yield relationship. Uneven-aged hardwoods also show exponential depletion. Canopy disturbance can enhance the establishment process, though severe disturbance and the consequent abundant regeneration can lead again to dense, even-aged stands with low levels of establishment. These results suggest a general pattern of forest development wherein establishment is initially important, but is quickly replaced by mortality as the dominant process when the dense, even-sized stand starts to thin. Eventually, failing additional disturbance, natural mortality will again open the canopy allowing development of a balance between establishment, and mortality.This research was supported by National Science Foundation grants DEB-7708743 and DEB-7804043 to R.K.P. and DEB-7707532 and DEB-7804041 to N.L.C.     

Looking for age-related growth decline in natural forests: unexpected biomass patterns from tree rings and simulated mortality

Forest biomass growth is almost universally assumed to peak early in stand development, near canopy closure, after which it will plateau or decline. The chronosequence and plot remeasurement approaches used to establish the decline pattern suffer from limitations and coarse temporal detail. We combined annual tree ring measurements and mortality models to address two questions: first, how do assumptions about tree growth and mortality influence reconstructions of biomass growth? Second, under what circumstances does biomass production follow the model that peaks early, then declines? We integrated three stochastic mortality models with a census tree-ring data set from eight temperate forest types to reconstruct stand-level biomass increments (in Minnesota, USA). We compared growth patterns among mortality models, forest types and stands. Timing of peak biomass growth varied significantly among mortality models, peaking 20–30 years earlier when mortality was random with respect to tree growth and size, than when mortality favored slow-growing individuals. Random or u-shaped mortality (highest in small or large trees) produced peak growth 25–30 % higher than the surviving tree sample alone. Growth trends for even-aged, monospecific Pinus banksiana or Acer saccharum forests were similar to the early peak and decline expectation. However, we observed continually increasing biomass growth in older, low-productivity forests of Quercus rubra, Fraxinus nigra, and Thuja occidentalis. Tree-ring reconstructions estimated annual changes in live biomass growth and identified more diverse development patterns than previous methods. These detailed, long-term patterns of biomass development are crucial for detecting recent growth responses to global change and modeling future forest dynamics.     

A comparison of structural characteristics between old-growth and postfire second-growth hemlock–hardwood forests in Adirondack Park, New York, U. S. A.

1 This study compares the structural characteristics of 12 old‐growth and six postfire second‐growth hemlock–northern hardwood stands in north central Adirondack Park, New York, in order to test the null hypothesis that there are no differences in species composition, size structure, age structure and attributes such as dead wood and canopy gaps between old‐growth stands and this type of second‐growth forest. 2 The second‐growth forests of this study regenerated following widespread logging‐related fires in either 1903 or 1908; the old growth and second growth have similar environmental settings. 3 Estimates of stand ages, derived from an increment core of the oldest tree in each stand, range from 88 to 390 years. 4 Structural attributes are related to stand age (i.e. stage of development). In comparison with the second‐growth forests of this study, older stands are characterized as (a) a larger average diameter of canopy trees; (b) a greater basal area of trees; (c) a lower density of canopy trees and of all trees ≥ 10 cm d.b.h.; (d) a higher density of eastern hemlock (Tsuga canadensis (L.) Carrière) trees; (e) a higher density of large trees (≥ 50 cm d.b.h.); (f) larger canopy gaps; and (g) a greater volume of coarse woody debris (both logs ≥ 20 cm d.b.h. and snags ≥ 10 cm d.b.h.). 5 Despite differences between old growth and second growth, especially in species composition, it appears from observations of the 18 stands that second‐growth forests are developing some structural characteristics of old growth. 6 Structural attributes of the old‐growth forests are similar to characteristics of the same forest type in geographically distant areas in eastern USA.     

Patch to landscape patterns in post fire recruitment of a serotinous conifer

Obligate seeding species are highly specialized to fire disturbance and many conifers such as cypress, which are adapted to high intensity stand-replacing fires, have canopy seed banks stored in serotinous cones. Resilience of these trees to fire disturbance is a function of disturbance frequency and one focus of this study was to determine the effect of patch age on postfire recruitment. A second focus was to determine the extent to which fire induced a landscape level change in the location of the forest boundary. Prior to a fire in 1994, a large Cupressus sargentii forest was a mosaic landscape of different aged patches of nearly pure cypress bordered by chaparral. Patches less than 60 years of age were relatively dense with roughly one tree every 1–2 m² but older patches had thinned to one tree every 3–15 m². Older trees had substantially greater canopy cone crops but the stand level seed bank size was not significantly correlated with stand age. Fire-dependent obligate seeding species are sensitive to fire return interval because of potential changes in the size of seed banks – facing both a potential `immaturity risk' and a `senescence risk'. At our site, C. sargentii regeneration was substantial in stands as young as 20 years, suggesting that fire return interval would need to be shorter than this to pose any significant risk. Reduced seedling recruitment in stands nearly 100 years of age may indicate risk from senescence is greater, however, even the lowest density seedling recruitment was many times greater than the density of mature forests – thus this cypress would appear to be resilient to a wide range of fire return intervals. Changes in landscape patterning of forest and chaparral are unlikely except after fire. Factors that inhibit tree establishment within the shrubland, as well as factors that affect shrub establishment within the forest border likely affect the `permeability' of this ecotone. After the 1994 fire this boundary appeared to be stable in that cypress recruited best within the shadow of burned canopies and cypress were weak invaders of adjacent shrublands.     

Dynamics of an old evergreen coppice in southwestern Japan with special focus on a typical coppice species (Castanopsis cuspidata) and a climax species (Distylium racemosum)

We investigated stand dynamics of an abandoned evergreen coppice (c.a. 100 years old) over the course of 21 years in south Kyushu, Japan. The study stand showed a change in species composition from being dominated by Castanopsis cuspidata to Distylium racemosum, that is, from a typical coppice species to a typical climax species of the region. However, the relative dominance of Castanopsis spp. appeared to remain very high in the study stand compared to that in the Aya Research Site, a typical old-growth forest in the region, due to abundant C. cuspidata canopy trees of coppice origin. This suggests that the species composition of the study stand remained distinct from that of climax forests in the region. On the other hand, D. racemosum did not show a significant change in diameter at breast height (DBH) class frequency distribution from 1996 to 2017, probably due to the slow growth of this species. However, generalized linear models (GLMs) were used to identify the factors affecting better DBH growth of this species in the gap, indicating the potential for further development of the population structure when small trees are released from suppression of canopy trees. This suggests, inversely, that the development of the D. racemosum population was heavily suppressed by abundant C. cuspidata canopy trees of coppice origin that survived to the age of nearly 100 years. Further, large typhoons are suggested to cause severe canopy disturbances that remove canopy trees of C. cuspidata, which might be important for promoting further forest succession, even for a nearly 100-year-old evergreen old coppice.

     

Community dynamics of evergreen broadleaf forests in southwestern Japan

The process and rate of revegetation in gaps in an evergreen oak forest were studied by comparing the species composition, tree density, frequency distribution of tree height, and relation between diameter at breast height and tree height among different aged stands. For estimating stand ages, the ages of gap indicators, such as,Symplocos prunifolia andAcer rufinerve, were very useful. It took about 70 years for gaps to be filled by large fully-grown trees. Since the mean residence time of the forest canopy was 180 years, the trees that attain the forest canopy were expected to be canopy trees for 110 years on the average. Tree densities of all broadleaved evergreens exceptS. prunifolia, were independent of stand age. On the other hand, densities of gap indicators,S. prunifolia andA. rufinerve, decreased as stand age increased. Other deciduous broadleaf and coniferous species were scarce as a whole. According to the frequency distributions of height of live and dead trees in different aged stands, it was suggested that shorter trees were more susceptible to death than taller trees. The self-thinning in revegetation process in gaps approximately followed the 3/2 power law, though the power was larger (−1.32) than expected from the law.     

林分结构对烟台黑松海岸防护林天然更新的影响

为阐明黑松(Pinusthunbergii)海岸防护林天然更新的影响机制,在对烟台2个典型样地6条样带共60个样方(10m×10m)调查的基础上,采用拟合模型和多重回归分析技术,探讨林分结构指标中,垂直结构(树冠指数、小树比例和大树比例)和密度因素(基面积、郁闭度和灌木盖度)对黑松种群天然更新的影响。结果表明在垂直结构变量中,树冠指数(CI)与幼龄植株个数之间存在典型的抛物线关系,在CI5-6范围内,幼龄植株个数达到最高;幼龄植株个数与小树比例关系较弱,但与大树比例表现出显著的正线性关系。在密度变量中,幼龄植株随着郁闭度的增加,个体数呈上升趋势,而随着灌木盖度的增加,则表现出显著的下降倾向;幼龄植株个数与基面积关系不明显。幼龄植株个体数变化取决于垂直结构变量CI和密度变量郁闭度和灌木盖度共同作用的影响。理解这些更新规律,是黑松海岸防护林可持续管理的前提。     

Natural Regeneration of Trees in Three Types of Afforested Stands in the Taihang Mountains,China

Natural regeneration is the natural process by which plants replace themselves. It is a cost-effective way to re-establish vegetation, and it helps to preserve genetic identity and diversity. In this study, we investigated the natural regeneration of trees in three types of afforested stands in the Taihang Mountains, China, which were dominated by Robinia pseudoacacia (black locust), Quercus variabilis (Chinese cork oak) and Platycladus orientalis (Chinese arborvitae) respectively. A consistent pattern was found among the three types of stands, being that the density of seedlings was positively correlated with the overstory canopy cover and negatively correlated with the covers of shrub, herb and litter layers. While a positive correlation between the density of seedlings and stand age was found for the conifer stands, negative correlations were found for the two types of broadleaf stands. Correlations between the density of saplings and the stand attributes were not consistent among the three types of stands. The two types of broadleaf stands had higher densities of seedlings and saplings than the conifer stands. While the broadleaf stands had adequate recruits for regeneration, the conifer stands did not have enough recruits. Our findings suggest that the overstory canopy should be prevented from being disturbed, any reduction of the canopy cover will decrease the recruits and affect the regeneration.