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1.
以广东湛江特呈岛红树林自然保护区内的红海榄纯林、红海榄+木榄、红海榄+白骨壤、红海榄+木榄+白骨壤混交林4种群落类型为对象,运用最小距离指数、连接度指数分析红海榄支柱根的空间连接和分布规律;同时,采用分形维数与拓扑指数确定红海榄支柱根的分形特征,分析根系分支状况以及分形特征与支柱根性状之间的相关性.结果表明:红海榄同级支柱根之间的空间连接程度不高,近于随机分布格局;4种群落类型中红海榄支柱根均具有较好的分形特征,分形维数为1.468 5～1.554 5,具有较强的利用与占据生态空间的能力;红海榄支柱根拓扑结构复杂,拓扑指数为0.366 4～0.448 5,接近叉状分支模式,有利于扩展生态空间和增加植株的稳定性;根系分形维数与支柱根数量、平均连接长度等性状之间的相关关系显著. 相似文献
2.
Juliet C. Stromberg Melanie G.F. Tluczek Andrea F. Hazelton Hoori Ajami 《Forest Ecology and Management》2010
Populus–Salix forests are a valued riparian vegetation type in western North America. These pioneer, obligate phreatophytes have declined on some rivers, raising conservation concerns and stimulating restoration plantings, but have increased on others. Understanding patterns and causes of forest change is essential for formulating conservation, restoration and management plans. Our goal was to assess spatio-temporal patterns of vegetation change on the Upper San Pedro River in semiarid Arizona, USA, one of the few undammed rivers in the region. Over 100 years ago, intense floods initiated channel incision and substantially altered hydrogeomorphology. Pioneer trees began to establish in the widening post-entrenchment zone as the surfaces began to stabilize. Using a time-series of aerial photographs (1955–2003) we quantified recent change in area of riparian cover types. Analysis indicated that wooded area in the post-entrenchment zone nearly tripled from 1955 to 2003, at the expense of bare ground, and the active channel narrowed appreciably. This forest expansion represents a long-term response to river entrenchment, with the temporal pattern influenced by recent flood cycles and biogeomorphic feedbacks. Populus–Salix have established episodically during the infrequent years with high winter flood runoff, sequentially filling available recruitment space. Older cohorts cover wide swaths of the floodplain while young trees form narrow bands lining the channel. Barring extreme flooding, the pioneer forests are expected to senesce over the coming century. An additional factor that has shaped the pattern of post-entrenchment forest expansion is anthropogenic water withdrawal. Populus–Salix forest increase has been greatest within a conservation area, where stream flows are largely perennial. In drier, agricultural sectors, Populus–Salix have declined while the more deeply-rooted Tamarix has increased. Overall, the study reveals that long-term fluctuations in pioneer forest area and age structure are common on dryland rivers, and shows how past events such as extreme floods can interact with recent environmental practices such as freshwater withdrawal to influence riparian forest patterns. This underscores the necessity of a long-term perspective for forest conservation and management. 相似文献
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采用固定样地和样方法调查了小陇山林区百花林场3个实施不同经营措施的锐齿栎天然林林分特征和物种组成,运用4种常用的物种多样性指数对调查林分的乔木层、灌木层和草本层的物种多样性进行对比分析,结果表明:3种类型锐齿天然林的灌木层相对于其乔木层和草本物种组成丰富,多样性高;长期封育后的锐齿栎天然林群落在3种天然林类型中物种组成最丰富,乔木层、灌木层和草本层的Shannon-Wiener指数、Pielou指数和Margalef指数值在3个林分中最高;近自然技术单株经营后的锐齿栎天然林各层次的物种组成相对较少,多样性较低,但其林分中保留的乔木树种个体较大;结构优化抚育后的锐齿栎天然林的物种组成和多样性介于二者之间.抚育经营措施对林分的影响与抚育经营强度密切相关,适当的抚育经营强度能够促进林分多样性提高,否则会带来不利的影响,结构化森林经营技术是一种有效的经营方法. 相似文献
5.
Åshild Ø. Pedersen Nigel G. Yoccoz Rolf A. Ims Therese Sigurdsen 《Forest Ecology and Management》2010
Voles and shrews are key species in northern forest ecosystems. Thus, it is important to quantify to what extent new forestry practices such as planting of non-native tree species impact these small mammals. In northern Norway stands of coastal subarctic birch forests have increasingly been converted to non-native spruce stands during the last century. This leads to changes in the forest floor vegetation and soil conditions that can be expected to negatively impact the community of ground-dwelling small mammals. In this 10-year trapping study we contrasted seasonal small mammal population abundances in spruce plantations with four birch forest varieties. Six different small mammal species were trapped (in descending order of abundance; common shrew Sorex araneus, red vole Myodes rutilus, field vole Microtus agrestis, grey-sided vole M. rufocanus, pygmy shrew S. minutus and water shrew Neomys fodiens). None of the voles appeared to exhibit temporal dynamics resembling population cycles. The three most numerous species were clearly less abundant in the spruce plantations compared to the other forest types. Autumn abundances were most impacted by spruce plantations, indicating that growth rates in the reproductive season were more influenced than winter declines. Species associated with productive forest habitats (i.e. field vole and common shrew) were most impacted by tree species conversion. Still young spruce plantations inter-mixed with birch trees and the ecotone habitat, sustained small mammal abundances comparable to the native birch forests. This implies that managing spruce plantations to maintain a mix of different tree species and high spatial heterogeneity (i.e. more ecotones), will reduce the negative impacts on the small mammal community. On the contrary, if young spruce plantations, as they age become spruce monocultures covering larger parts of the landscapes than they do presently, the negative effects on small mammal communities may be larger than observed in the present study. 相似文献
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The mountain pine beetle Dendroctonus ponderosae Hopkins is endemic to lodgepole pine, Pinus contorta var. latifolia Engelmann, forests in western Canada. However, the current beetle epidemic in this area highlights the challenges faced by forest managers tasked with prioritizing stands for mitigation activities such as salvage harvesting and direct control methods. In western Canada, the operational risk rating system for mountain pine beetle is based on biological knowledge gained from a rich legacy of stand-scale field studies. Due to the large spatial (millions of hectares affected) and temporal (over 10 years) extents of the current epidemic, new research into large-area mountain pine beetle processes has revealed further insights into the landscape-scale characteristics of beetle infested forests. In this paper, we evaluated the potential for this new knowledge to augment an established system for rating the short-term risk of tree mortality in a stand due to mountain pine beetle. New variables explored for utility in risk rating include direct shortwave radiation, site index, diameter at breast height, the temporal trends in local beetle populations, Biogeoclimatic Ecosystem Classification and beetle–host interaction variables. Proportional odds ordinal regression was used to develop a model for the Vanderhoof Forest District in west-central British Columbia. Prediction on independent data was assessed with the area under the receiver operator curve (AUC), indicating good discriminatory power (AUC = 0.84) for predicting levels of mountain pine beetle-caused pine mortality. 相似文献
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The forest growth model 4C was used to investigate how conversion management of a Scots pine (Pinus sylvestris L.) stand towards a mixed oak–birch stand would affect stand structural development – and hence biodiversity and productivity – in the long term. For this purpose the 4C model was parameterised for natural regeneration of light demanding species and extended for management of multi-layered stands. A series of structural indicators was selected to describe key factors of forest biodiversity at the stand scale. Two consecutive aspects of Scots pine conversion were tested: (1) the choice of conversion strategy between thinning and gap creation and (2) the choice of conversion regime in terms of cutting cycle, thinning type and pine tree retention. Three simulated conversion strategies aim at the gradual removal of the pine canopy but differ in the spatial organisation of pine cuttings and hence result in different light conditions for regeneration. Only the directed gap creation strategy was able to maintain and increase birch admixture to the stand and to approach natural stand structural development. Simulation of 12 conversion regimes for the directed gap creation strategy indicated that thinning type (from above or from below), pine tree retention at final felling (50% of the standing volume or none) and cutting cycle (6, 9 or 12 years) all significantly influence stand structural development. These effects were clearest for oak development. Birch occurred in a few mixed clusters, but tended to disappear when longer cutting cycles were used. Based on a multi-criteria analysis we conclude that the optimal conversion regime – in which both stand productivity and biodiversity objectives can be combined – implies thinning from above, pine tree retention, and cutting cycles of 6 years. The conceptual validity of the model as well as the applicability of the results are discussed. 相似文献
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The management of burnt wood after a fire may affect seed predation by vertebrates due to the change produced in habitat structure. We analyze the effect of burnt wood management on post-dispersal seed predation in the Holm oak. Three plots were established in a burnt forest, with three treatments per plot: (1) non-intervention (NI, all trees left standing), (2) “partial cut plus lopping” (PCL, felling 90% of trees, cutting their main branches, leaving all the biomass in situ), and (3) “salvage logging” (SL, felling the logs for their removal and masticating the woody debris). Acorns were buried to mimic dispersal by jays or rodents two and three years after fire, with two trials per year (7200 monitored acorns), and the predation rate was evaluated until the time of seedling emergence. The spatial patterns of acorn predation were assessed by computing a transformed-Ripley's K function and Moran's I correlograms. There was a large spatial and temporal variability in acorn predation, with differences among trials, plots, and replicates within treatments and plots. Overall, PCL showed the lowest predation values (83.0% versus 87.4 in NI and 88.0 in SL). Predator species (mice versus wild boar) also differed among treatments, wild boar having a negligible effect in PCL, presumably due to the physical barrier of felled logs and branches. The results support that: (1) salvage logging offers no advantage against predators and (2) that post-fire burnt wood management alters the guild of acorn predators and may reshape the pattern of seedling establishment. 相似文献
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Forest recruitment is the outcome of local- and regional-scale factors such as disturbances and climate. The relative importance of local- and regional-scale factors will determine the spatial scale at which temporal pulses of recruitment occur. In seasonal tropical forests, where the annual dry-season is a critical bottleneck to seedling survival, multi-year periods of relatively cool, wet dry seasons may be required for successful tree recruitment. Consequently, when such conditions are present, region-wide synchronisation of recruitment may occur. To examine the case for regional synchronisation of forest dynamics in the seasonal tropical pine forests of northern Thailand, we investigated forest age structures at three spatial scales: stand, site and region. We compared forest age structures with instrumental climatic records beginning in 1902. We found significant statistical evidence of synchronous recruitment at the stand- and site-scales, but not at the regional-scale. While correlations between recruitment and climate were not statistically significant, recruitment success was often linked to favourable climatic conditions. For example, recruitment at all sites was associated with multi-year periods of cool-wet dry seasons. The lack of significant correlations between recruitment and climate appears to reflect complex interactions among local disturbance history, regional climate variability and pine recruitment. 相似文献
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João P.F. Carvalho 《Forest Ecology and Management》2011,262(10):1928-1937
Stand composition and structure of natural mixed-oak stands of common-oak (Quercus robur L.) and pyrenean-oak (Quercus pyrenaica Willd.) were studied. Diverse compositional and structural elements in early and late successional stand stages were analysed. The study was conducted in north and central Portugal where different natural mixed oak forests types are located. The following mixed-oak forest types involving common-oak and pyrenean-oak were studied: common-oak & other hardwoods; common-oak & cork-oak (Quercus suber L.); ash (Fraxinus angustifolia Vahl) & pyrenean-oak; and pyrenean-oak & madrone (Arbutus unedo L.). Measurements were made in early and late successional stand stages on the different mixed oak forest types. Different stand characteristics and indices were used to describe and compare stand structure and composition. The study showed changes in species diversity and stand structure. Most tree species in mature stands are present in early stages but with higher abundance. Shannon diversity index may change between 0.798 and 1.915. Significant differences on species diversity and abundance were found depending on the forest type and successional stage. Mature mixed-oak forests have high species diversity with an abundance of small to medium tree size species. Species distribution and diameter differentiation indices range from 0.30 to 0.70 and 0.52 to 0.82, respectively, revealing significant structural complexity. The average number of standing and downed dead trees was 265 and 83 trees ha−1 for early and late stage, respectively, with 6.9 and 65.4 m3 ha−1. Higher values of stand diversity index were 41 and 53 in more complex and developed forests. Later stand stages have complex structure, with a wider range of tree diameter distribution and higher degree of irregularity. 相似文献
12.
Understanding forest dynamics and stand structures is crucial for predicting forest succession. However, many forests have been altered due to century-long land-use practices, which complicates the reconstruction of past and current successional trajectories. For a better understanding of successional processes, we suggest studying the intra- and interspecific competition among single trees across time. We introduce a tree-ring based competition index to reconstruct the competitive dynamics of individual trees over time. This new retrospective dynamic competition index combines a temporal and a spatial component by calculating the yearly ratio between the basal area increments (bai) of the neighbouring trees and the subject tree. The new index is applied to mixed Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) stands in the inner-Alpine dry-valley Valais, for which a change in species composition is hypothesised. The aim is to analyse current stand structures in terms of recent changes in the competitive interactions at the single tree level and to relate these competitive dynamics to land-use change and increasing drought due to climate change. On five plots, the positions of 456 trees were recorded and increment cores were taken to derive bai data. The individual dynamic competition index curves were aggregated in clusters, which define typical patterns of competitive dynamics in both tree species. A large percentage of the trees (87% in oak, 70% in pine) were clustered into a group of trees with constant competition at a relatively low level. However, a smaller group of pines (20%) had recently faced increasing competition. In addition, stand structure analyses indicated a change towards a higher proportion of oak. This change in the competitive ability between oak and pine was found to be related to drought, in that oak had a competitive advantage in dry years. Furthermore, the high proportion of dead branches in pines with decreasing competitive abilities indicated increasing competition for light as a consequence of natural development towards a later successional stage that favours the more shade-tolerant oak. The new retrospective dynamic competition index proved to be promising in studying forest succession. The tree-ring based method allows us to identify changes in the competitive ability of single trees with a high temporal resolution and without repeated assessments. 相似文献
13.
TM遥感图像光谱信息具有良好的综合性,其归一化指数（NDVI）是植物生长状态以及植被空间分布密度的最佳指示因子,利用这一特性,借助遥感软件（ENVI）和地理信息系统软件（GIS）,结合MATLAB小波分析和SPSS逐步回归分析方法,对湖南攸县黄丰桥林场杉木地位指数遥感估测的尺度选择进行研究。结果表明：NDVI在经过小波一级重构后的值是估测地位指数的最佳数据,即一尺度为最佳尺度;SPSS分析模型中,一尺度的标准偏回归系数为0.679,对估测的贡献率最大。 相似文献
14.
We analyzed indices of gap dynamics, i.e. gap formation and gap closure rates as well as turnover rates, in a montane conifer forest in the temperate zone and asked: (1) Are the characteristics of gap dynamics comparable with those of other temperate forests? (2) Do gap dynamics exhibit temporal trends, and (3) if so, are they related to recent climate change? We also addressed methodological issues concerning the differences observed at differing temporal and spatial scales of the used datasets. Thus, we asked further how the indices of gap dynamics are influenced (4) by differences in the length of observation periods and (5) by differences in gap size categories included in the study? 相似文献
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基于2005年森林资源一类清查数据,分析了六盘山区辽东栎林分结构和空间分布特征。结果表明:辽东栎林在六盘山主要分布于海拔1 900-2 300 m范围内,坡度为20-35°的半阴坡、半阳坡和阴坡上,与山杨林的分布生境相近。现有的辽东栎林多为幼龄林,平均林龄30 a,林分密度较大,平均1 046株·hm-2,树木平均高度7.8 m,平均胸径12.4 cm。胸径5-10 cm的辽东栎株数占50％以上,平均木材蓄积量仅为 39.9 m3·hm-2。随着海拔升高、坡位从坡上部到坡下部,坡向从半阴坡到半阳坡,林分密度增大,平均树高和胸径增加,这主要是因为沿此梯度林龄在增加,而且随着年龄的增加,辽东栎林的平均胸径以0.8 cm·a-1的速度增大,作为主要先锋伴生树种的山杨在林内的比重则下降,说明六盘山区的现有辽东栎林正处于正向演替阶段,更趋稳定。建议对辽东栎林采取近自然林业的管理方式,减少不利的人工干预,加速培养近自然森林。 相似文献
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Brian H. Aukema Jun Zhu Jesper Møller Jakob G. Rasmussen Kenneth F. Raffa 《Forest Ecology and Management》2010
Bark beetles are largely known for their ability to undergo intermittent population eruptions that transform entire landscapes and pose significant economic hardships. However, most species do not undergo outbreaks, and eruptive species usually exert only minor disturbances. Understanding the dynamics of tree-killing noneruptive species can provide insights into how beetles persist at low densities, and how some spatiotemporal patterns of host predisposition may more likely favor breaching eruptive thresholds than others. Elucidating mechanisms behind low-density populations is challenging, however, due to the requirement of long-term monitoring and high degrees of spatial and temporal covariance. We censused more than 2700 trees annually over 7 years, and at the end of 17 years, in a mature red pine plantation. Trees were measured for the presence of bark beetles and wood borers that breed within the primary stem, root weevils that breed in root collars, and bark beetles that breed in basal stems. We quantify the sequence of events that drive this decline syndrome, with the primary emergent pattern being an interaction between below- and above-ground herbivores and their fungal symbionts. This interaction results in an expanding forest gap, with subsequent colonization by early-successional vegetation. Spatial position strongly affects the likelihood of tree mortality. A red pine is initially very likely to avoid attack by tree-killing Ips beetles, but attack becomes increasingly likely as the belowground complex spreads to neighboring trees and eventually make trees susceptible. This system is largely internally driven, as there are strong gap edge, but not stand-edge, effects. Additional stressors, such as drought, can provide an intermittent source of susceptible trees to Ips beetles, and elevated temperature slightly accentuates this effect. New gaps can arise from such trees as they subsequently become epicenters for the full complex of organisms associated with this decline, but this is not common. As Ips populations rise, there is some element of positive feedback, in that the proportion of killed trees that were not first colonized by root organisms increases. This positive feedback is very weak, however, and we propose the slope between beetle population density and reliance on host stress as a quantitative distinction along a gradient from noneruptive through eruptive species. Almost all trees colonized by Ips were subsequently colonized by wood borers, likely a source of negative feedback. We discuss implications to our overall understanding of cross-scale interactions, between-guild interactions, forest declines, and eruptive thresholds. 相似文献
17.
This study was designed to answer questions about the patterns of understory diversity in managed forests of southern New England, and the factors that appear associated with those patterns. At the landscape-level, we used plot data to answer questions regarding the spatial distribution of forest understory plant species. Data from a combination of fixed area (understory vegetation) and variable radius (overstory trees) plot methods are combined with site variables for the analysis. Univariate and multivariate statistical methods are used to test for understory diversity relationships with overstory cover types and topography separately, and in combination. Analyses also test for relationships between specific understory species and cover types. In general the understory flora is dominated by four common clonal species that occur across the range of forest cover types: wild sarsaparilla (Aralia nudicaulis L.), Canada mayflower (Maianthemum candense Desf.), star flower (Trientalis borealis Raf.), and partridgeberry (Mitchella repens L.). Results also show that over story composition and structure can be used to assess understory species richness. Species richness follows a general trend among cover types of: hardwood ≥ regenerating forest, hardwood–pine, and pine ≥ mixed ≥ hardwood–hemlock > hemlock. Eastern hemlock (Tsuga canadensis L. Carriere) and mountain laurel (Kalmia latifolia L.) (which decreased in dominance from ridge to valley) both showed negative trends with understory species richness. Topographic position also appears associated with understory floristic patterns (particularly for the hardwood cover type), both in terms of species richness and compositional diversity which both increased from ridge, to midslope, to valley. However, overstory composition (covertype) appears to have a higher order influence on vegetation and mediates the role of topography. The results from this study provide foresters with a better understanding for maintaining floristic diversity and composition of the understory in managed forests. 相似文献
18.
Eucalyptus saplings are sensitive to weed competition. This can cause water stress which is the most important abiotic factor limiting survival during plantation establishment. Two provenances of Eucalyptus globulus subsp. maidenii viz. Murrabrine and Tantawanglo were used to examine the effect of water stress induced by weed presence during establishment on physiological responses of young saplings. Six-month-old saplings were transplanted into 220-L containers containing three weed cover levels (no weeds, low weed density, high weed density). Each provenance × weed cover combination was assigned to either a high or a low water availability level. Sapling water status was affected differentially by water competition induced by weeds. Murrabrine provenance showed higher pre-dawn relative water content, pre-dawn leaf water potential and noon leaf stomatal conductance than Tantawanglo. Water stress conditions induced osmotic (πadj) and elastic (?adj) adjustments. The magnitude of πadj varied according to the weed cover and water availability. Weed presence produced cell wall stiffening independently of water availability. Murrabrine provenance was less sensitive to weed cover, showing a significant change in wall stiffening only under high weed density. The two provenances had similar drought-tolerance mechanisms, but different responses to stress. Murrabrine had a larger water stress threshold than Tantawanglo that combined processes for “reduced water loss” and “maintenance of water uptake”. The relative importance of induced physiological drought-tolerance in response to weed interference during establishment is discussed. 相似文献
19.
Green-tree retention systems are an important management component of variable retention harvests in temperate zone coniferous forests. Residual live trees (“legacy trees”) provide mature forest habitat, increase structural diversity, and provide continuity in the regenerating stand. This study was designed to test the hypotheses that, at up to 8 years after harvest, abundance and species diversity of communities of (i) understory plants and (ii) forest-floor small mammals, and (iii) relative habitat use by mule deer (Odocoileus hemionus), will decline with decreasing levels of tree retention. Communities of plants and forest floor small mammals were sampled in replicated clearcut, single seed-tree, group seed-tree, patch cut, and uncut forest sites in mixed Douglas-fir (Pseudotsuga menziesii)—lodgepole pine (Pinus contorta) forest in southern British Columbia, Canada from 2000 to 2003 (5–8 years post-harvest). Habitat use by mule deer was measured during summer and winter periods each year from 1999 to 2003 in these same sites. 相似文献
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通过样地调查,分析了不同结构草类-落叶松林和杜香-落叶松林林木分布格局特征。研究表明:(1)年龄36 - 65年草类-落叶松林和年龄54 - 63年杜香-落叶松林分布格局中,均匀分布、随机分布和聚集分布所占比例分别为6.2%、50%、43.8%;(2)按林型分,草类-落叶松林分布格局中,均匀分布和随机分布所占比例均11.1%,聚集分布占77.8%。杜香-落叶松林分布格局均为随机分布;(3)树种组成在6落4阔 - 10落范围内,草类-落叶松林和杜香-落叶松林分布格局主要为聚集分布和随机分布两种类型。聚集分布主要集中在树种组成7落3阔 - 9落1阔范围内。 相似文献