Tree Height Class Research Articles

The Role of Forest Ecosystems for Carbon Sequestration and Poverty Alleviation in Ethiopia

The objective of the review was to examine and document the contributions of forests in Ethiopia to both climate change mitigation and poverty alleviation. A comprehensive analysis was conducted, encompassing several research articles from reputable journals and international report papers. The findings of the review reveal that Chilimo-Gaji forest exhibited the highest levels of above- and belowground biomass carbon sequestration, while the Egdu forest area demonstrated the highest soil organic carbon content. The variations in carbon sequestration capacity among forest areas can be attributed to several factors, including forest density, variation in diameter at breast height (DBH) among trees, tree height classes, altitude, slope, and aspect, which significantly influence carbon concentration. Furthermore, discrepancies in the application of allometric models to estimate forest biomass also contribute to these variations. In addition to their role in climate change mitigation, forests play an invaluable role in poverty alleviation, particularly in developing countries. Ethiopia has implemented various afforestation strategies to enhance the contribution of forest ecosystems to climate change mitigation and poverty alleviation.

African Elephant (Loxodonta africana) Impact on Selected Tree Species and Assessment of PiosphereGradients in Venetia-limpopo Nature Reserve

Trees utilised by elephants often undergo a significant amount of damage compared to trees utilised byother browsers. Woody plants play a crucial role in plant community dynamics, species composition, andthe savannah system’s functioning. As drivers ofecosystems, elephants are capable of transforming habitatsin terms of structure and species composition. In this paper, the damage caused by elephants on differentselected tree species in Venetia-Limpopo Nature Reserve was studied following a field-based approach.Field data collected for trees included the species name, GPS location, tree height class, extent, and type ofdamage resulting from elephant foraging. The Normalized Difference Vegetation Index (NDVI) was usedto evaluate vegetation’s vigour using Landsat-5 imagery. A Multiple Ring Buffer Tool was used to extractmean NDVI values of buffer rings spread around waterholes at 400-metre intervals. The impact on woodyvegetation along the vegetation gradient, ‘Piosphere’, was evaluated. NDVI values extracted for the differentyears indicate that the impact on woody vegetationdegradation along the Piosphere gradient is negligible.There was no statistically significant relationship (Pearson correlation r3= –0.500, P = 0.391), trend or patternbetween the number of damaged trees and the type of damage. Different trees at different height classeswere utilised inconsistently by elephants. The dominant (45%) type of damage was for Broken Main Stem(BMS), with the lowest (1%) damage being for BarkStripping (BS). Overall, there was a statistically significantdifference (Pearson correlation r3= 0.973, P = 0.146) between the number of trees selected by elephants inthe various height classes. Trees between 3 m and 4 mwere the most selected and the impact seemed to bestabilising at these tree heights. Additional studies need to be focused on the recruitment rates of elephantforaged trees in the reserve to prevent local extirpation of these species in the future.

Tree height effects on vascular anatomy of upper-canopy twigs across a wide range of tropical rainforest species

AbstractVessel diameter variation along the hydraulic pathway determines how much water can be moved against the force of gravity from roots to leaves. While it is well-documented that tree size scales with vessel diameter variation at the stem base due to the effect of basipetal vessel widening, much less is known whether this likewise applies to terminal sun-exposed twigs. To analyze the effect of tree height on twig xylem anatomy, we compiled data for 279 tropical rainforest tree species belonging to 56 families in the lowlands of Jambi Province, Indonesia. Terminal upper-canopy twigs of fully grown individuals were collected and used for wood anatomical analysis.We show that hydraulically weighted vessel diameter (Dh) and potential hydraulic conductivity (Kp) of upper canopy twigs increase with tree height across species although the relationship was weak. When averaged across given tree height classes irrespectively of species identity, however, a strong dependency of tree height on Dh and Kp was observed, but not on the lumen-to-sapwood area ratio (Al:Ax) or vessel density (VD).According to the comparison between actual tree height and the maximum tree height reported for a given species in the stand, we show that the vascular xylem anatomy of their terminal twigs reflects their canopy position and thus ecological niche (understory versus overstory) at maturity. We conclude that the capacity to move large quantities of water during the diurnal peak in evaporative demand is a prerequisite for growing tall in a humid tropical environment.

Canopy Temperature Is Regulated by Ecosystem Structural Traits and Captures the Ecohydrologic Dynamics of a Semiarid Mixed Conifer Forest Site

AbstractPlant canopy temperature (Tc) is partly regulated by evaporation and transpiration from the canopy surface and can be used to infer changes in stomatal regulation and vegetation water stress. In this study, we used a thermal Unmanned Aircraft Systems in conjunction with eddy covariance, sap flow, and spectral reflectance data to assess the diurnal characteristics of Tc and water stress status over a semiarid mixed conifer forest in Arizona, USA. Diurnal Tc dynamics were closely related to tree sap flow and changes in spectral reflectance associated with stomatal regulation. Consistent with previously reported deviations, we found that on average Tc was 1.8°C lower than the above canopy air temperature (Ta). However, the relationship between Tc and Ta varied significantly according to tree density and tree height classes, with taller and denser trees exhibiting relatively low |Tc‐Ta| (2.4 and 2.1°C cooler canopies, respectively) compared to shorter and less‐dense tree stands (1.7 and 1.5°C cooler canopies, respectively). We used these data to evaluate space‐borne diurnal measurements of Tc and water stress from the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) mission. We found that ECOSTRESS observations of Tc accurately tracked seasonal shifts in diurnal surface temperatures and vegetation water stress, and that site‐level observations of heterogeneity in forest composition and structure could be applied to separate the processes of canopy transpiration and soil evaporation within the ECOSTRESS footprint. This study demonstrates how proximal and satellite remote sensing approaches can be combined to reveal the diurnal and seasonally dynamic nature of Tc and water stress.

The effectiveness of ground‐based applications of Bacillus thuringiensis var. kurstaki for controlling oak processionary moth Thaumetopoea processionea (Lepidoptera: Thaumetopoeidae)

AbstractThe effectiveness of ground‐based applications of Bacillus thuringiensis var. kurstaki (Btk) for controlling oak processionary moth (OPM) was evaluated by comparing the numbers of larval nests on treated and untreated oak trees in Richmond Park, in west London, UK. A total of 760 oak trees (Quercus robur) were monitored over a period of 4 years from 2014 to 2017, and the effects of current treatment and previous treatment history on nest numbers were analysed using general linear mixed models. Two applications of Btk applied 7–10 days apart in the spring, just after egg hatch, reduced the numbers of larval nests by 86–94%. In 2015, the effectiveness of treatment decreased as tree height increased, whereas in 2016 and 2017 nest numbers were reduced by a similar percentage across all tree height classes. The effects of treatment were relatively short‐lived, because at the scale at which the insecticide applications were carried out, trees were re‐colonised rapidly by adult OPM flying in from the surrounding area. Consequently, nest numbers generally returned to pre‐treatment densities within 1–2 years.

Urban Green Areas and Woody Plant Composition: Dwelling Space Quality Factor in the Klokočina Housing Estate

Abstract The environment of a city is influenced by global and local climate changes, pollution load from transport, industry and local heat sources. Green spaces as part of the urban green infrastructure fulfil multiple ecosystem services and improve the environmental and residential quality of a city. The level of positive effects of green spaces depends on their area, distribution within the city and the proportion of trees. The aim of the paper was to evaluate land cover structure in a selected segment of the housing estate Klokočina in Nitra, Slovakia. The evaluation focused on the share of biologically active and inactive surfaces, as well as the parameters of woody plant structure in green spaces. Green areas account for 58.70%, while built-up areas, parking lots and roads cover in total 41.30%. Biologically inactive anthropogenic horizontal and of building envelope areas represent 67.30%. Biologically active green areas represent 32.70%. The share of areas with tree crown overlap on horizontal areas is 20.82%, other areas are paved surfaces or grassland. We calculated the indices of the quality of green spaces from the individual categories of areas: proportional green area index (PGAI), effective green area index (EGAI) and tree shade index (TSI). The tree species composition consists of 36 deciduous and 11 coniferous tree species, and 20 shrub species. We evaluated the biometric traits of trees as the tree height, crown width, stem girth and tree vitality class (TVC). The correlations between tree traits were statistically tested with a significant result. In the group of biologically active areas of greenery, we propose to increase the proportion of trees, to establish more natural lawns and xerophyte flower beds. In the category of inactive areas, we propose the reconstruction of parking lots to grass paved surfaces.

Is field-measured tree height as reliable as believed – Part II, A comparison study of tree height estimates from conventional field measurement and low-cost close-range remote sensing in a deciduous forest

Tree height is one of the most important tree attributes in forest inventory. However, using conventional field methods to measure tree height is a laborious and time-consuming process. Despite the great interest in the past to facilitate tree height measurements, new, upcoming solutions are not yet thoroughly investigated. In this study, we investigated the applicability of different close-range remote sensing options for tree height measurement in a complex lowland deciduous forest. Six sample plots in a pedunculate oak forest were measured in detail using conventional methods. Close-range remote sensing datasets used in this study represent solutions from low-cost sensors used for hand-held personal laser scanning (PLShh), unmanned–borne laser scanning (ULS) and unmanned aerial vehicle photogrammetry (UAVimage). Each tree in the sample plots was interactively measured directly from the point cloud, and correspondence of the field- and remote sensing measured trees was verified using tree positions collected during fieldwork. Cross-comparisons of different datasets were performed to evaluate the performances of different data sources in the tree height estimation with respect to crown class, tree height and species. All remote sensing data sources correlated well, e.g. biases between remote sensing sources were around ± 1%. The field-measured tree height in general correlated well with remote sensing data sources. The uncertainties and bias of the field measurements were dependent on the tree height and crown class. Field measurements tended to underestimate codominant and intermediate trees at the approximately 1 m magnitude, whilst remote sensing data sources were robust to crown classes. Low-cost ULS used in this study, and very likely in general, may not have enough penetration capability when measuring low and mostly occluded trees, causing missed treetops. PLShh gave tree height estimates closer to the real tree height than those derived from conventional field measurements for trees above 21 m height.

Tropical tree size-frequency distributions from airborne lidar.

In tropical rainforests, tree size and number density are influenced by disturbance history, soil, topography, climate, and biological factors that are difficult to predict without detailed and widespread forest inventory data. Here, we quantify tree size-frequency distributions over an old-growth wet tropical forest at the La Selva Biological Station in Costa Rica by using an individual tree crown (ITC) algorithm on airborne lidar measurements. The ITC provided tree height, crown area, the number of trees >10m height and, predicted tree diameter, and aboveground biomass from field allometry. The number density showed strong agreement with field observations at the plot- (97.4%; 3% bias) and tree-height-classes level (97.4%; 3% bias). The lidar trees size spectra of tree diameter and height closely follow the distributions measured on the ground but showed less agreement with crown area observations. The model to convert lidar-derived tree height and crown area to tree diameter produced unbiased (0.8%) estimates of plot-level basal area and with low uncertainty (6%). Predictions on basal area for tree height classes were also unbiased (1.3%) but with larger uncertainties (22%). The biomass estimates had no significant bias at the plot- and tree-height-classes level (-5.2% and 2.1%). Our ITC method provides a powerful tool for tree- to landscape-level tropical forest inventory and biomass estimation by overcoming the limitations of lidar area-based approaches that require local calibration using a large number of inventory plots.

Hollow-bearing characteristics of Populus euphratica in the lower reaches of Tarim River, China

We analzyed the hollow ratio of tree trunks, tree hole parameters, and its distribution characteristics among different DBH and tree height classes in a long-term monitoring plots of Populus euphratica forest at the Argan section in the lower reaches of Tarim River. The results showed that P. euphratica in the study area had a high hollow ratio, in that trees with hollowness accounted for 56% of the total individuals, with a absolute value of 159 tree·hm-2. The hollow ratio of P. euphratica showed significant difference among different DBH classes and tree height classes. The hollow ratio was positively correlated with DBH, and negatively correlated with tree height. The density of P. euphratica with hollowness was 560 ind·hm-2 and 2 ind·tree-1. Most of tree holes appeared on the tree trunk (57.1%) and mainly in the middle of the trunk (31.3%). The hole with a diameter of 5-15 cm accounted for the largest proportion (38.2%). The total number of tree holes, the number of tree holes per tree, and the diameter of holes were positively correlated with DBH and negatively correlated with tree height. The distribution of different tree hole types among different DBH classes and tree height classes was different, with inconsistent changing trends. The distribution of tree holes showed significant difference acorss orientations, with most of which mainly toward the west. The occurrence rate of tree hollow in P. euphratica desert riparian forest was more serious. The larger the DBH of poplar tree was, the more obvious the degree of hollow. Therefore, it is of great significance to strengthen the conservation of young poplar trees and to restore degraded desert riparian forests.

Tree mortality and biomass loss in drought-affected forests of East Texas, USA

Changes in tree mortality due to severe drought can alter forest structure, composition, dynamics, ecosystem services, carbon fluxes, and energy interactions between the atmosphere and land surfaces. We utilized long-term (2000‒2017, 3 full inventory cycles) Forest Inventory and Analysis (FIA) data to examine tree mortality and biomass loss in drought-affected forests for East Texas, USA. Plots that experienced six or more years of droughts during those censuses were selected based on 12-month moderate drought severity [Standardized Precipitation Evaporation Index (SPEI) -1.0]. Plots that experienced other disturbances and inconsistent records were excluded from the analysis. In total, 222 plots were retained from nearly 4000 plots. Generalized nonlinear mixed models (GNMMs) were used to examine the changes in tree mortality and recruitment rates for selected plots. The results showed that tree mortality rates and biomass loss to mortality increased overall, and across tree sizes, dominant genera, height classes, and ecoregions. An average mortality rate of 5.89% year−1 during the study period could be incited by water stress created by the regional prolonged and episodic drought events. The overall plot and species-group level recruitment rates decreased during the study period. Forest mortality showed mixed results regarding basal area and forest density using all plots together and when analyzed the plots by stand origin and ecoregion. Higher mortality rates of smaller trees were detected and were likely compounded by density-dependent factors. Comparative analysis of drought-induced tree mortality using hydro-meteorological data along with drought severity and length gradient is suggested to better understand the effects of drought on tree mortality and biomass loss around and beyond East Texas in the southeastern United States.

The effect of pollen performance on low seed fertility in a Greek population of Juniperus excelsa

The Juniperus excelsa (Cupressaceae) forest in northern Greece has been facing a documented severe decline of natural regeneration over the last few years. In order to dissect the physiological components of the low regeneration, pollen originated from different sites as well as from trees of different height was investigated in terms of viability and in vitro germination capacity. In addition, embryo development and viability of the first year immature seeds were further assessed. Pollen was found to present high viability (61.5–93.2%) in all sites and tree height classes. However, pollen germination was quite low (maximum germination percentage recorded was 30.2%). The low pollen germination capacity recorded in trees above 6 m in height was reflected in the subsequent low percentages of successful embryo development and viability found in the produced seeds. These results suggest that low seed fertility in Juniperus excelsa is associated with reduced pollen germination, suggesting a complex regeneration mechanism and is considered an additional step in shedding light on the physiological basis of the low natural regeneration of Juniperus excelsa.

Vulnerability of Conifer Regeneration to Spruce Budworm Outbreaks in the Eastern Canadian Boreal Forest

Spruce budworm (Choristoneura fumiferana) is the main defoliator of conifer trees in North American boreal forests, affecting extensive areas and causing marked losses of timber supplies. In 2017, spruce budworm affected more than 7 million ha of Eastern Canadian forest. Defoliation was particularly severe for black spruce (Picea mariana (Mill.) B.S.P.), one of the most important commercial trees in Canada. During the last decades, intensive forest exploitation practices have created vast stands of young balsam fir (Abies balsamea (L.) Mill.) and black spruce. Most research focused on the impacts of spruce budworm has been on mature stands; its effects on regeneration, however, have been neglected. This study evaluates the impacts of spruce budworm on the defoliation of conifer seedlings (black spruce and balsam fir) in clearcuts. We measured the cumulative and annual defoliation of seedlings within six clearcut black spruce stands in Quebec (Canada) that had experienced severe levels of defoliation due to spruce budworm. For all sampled seedlings, we recorded tree species, height class, and distance to the residual forest. Seedling height and species strongly influenced defoliation level. Small seedlings were less affected by spruce budworm activity. As well, cumulative defoliation for balsam fir was double that of black spruce (21% and 9%, respectively). Distance to residual stands had no significant effect on seedling defoliation. As insect outbreaks in boreal forests are expected to become more severe and frequent in the near future, our results are important for adapting forest management strategies to insect outbreaks in a context of climate change.

Tree resprout dynamics following fire depend on herbivory by wild ungulate herbivores

Abstract Savanna tree cover is dynamic due to disturbances such as fire and herbivory. Frequent fires can limit a key demographic transition from sapling to adult height classes in savanna trees. Saplings may be caught in a ‘fire trap’, wherein individuals repeatedly resprout following fire top‐kill events. Saplings only rarely escape the cycle by attaining a fire‐resistant height (e.g. taller than the minimum scorch height) during fire‐free intervals. Large mammalian herbivores also may trap trees in shorter size classes. Browsing herbivores directly limit sapling height, while grazing herbivores such as cattle facilitate sapling growth indirectly via grass removal. Experimental studies investigating how meso‐wildlife, megaherbivores and domestic livestock affect height of resprouts following fire are rare, but necessary for fully understanding how herbivory may reinforce (or counteract) the fire trap. In our study system, interactive fire–herbivore effects on transitions from sapling (<1 m) to adult tree (>1 m) height classes may be further influenced by plant defences, such as symbiotic ants. We used the Kenya Long‐term Exclosure Experiment (KLEE) to investigate how post‐fire resprout size of a widespread monodominant East African tree, Acacia drepanolobium was influenced by (a) herbivory by different combinations of cattle, meso‐wildlife (15–1,000 kg) and megaherbivores (>1,000 kg) and (b) the presence of acacia–ant mutualists that confer tree defences. We sampled height, stem length and ant occupancy of resprouts exposed to different herbivore combinations before and after controlled burns. Resprout height of saplings that were short prior to fire (<1 m) was reduced primarily by meso‐wildlife. Negative effects of elephants on post‐fire resprout height increased with pre‐fire tree size, suggesting that resprouts of the tallest trees (with the greatest potential to escape the fire trap cycle) were preferentially browsed and reduced in height by elephants. There were no significant cattle effects. Synthesis. We provide experimental evidence for two potential pathways through which large herbivores exert control over sapling escape from the fire trap: (a) post‐fire meso‐wildlife browsing of short (<1 m) resprouts and (b) elephant browsing of the largest size class of resprouts, which would otherwise be most likely to escape the fire trap.

Short‐ and long‐term effects of fire in subtropical cloud forests on an oceanic island

AbstractThe recurrence of fires has increased considerably due to human activity, affecting even forests where traditionally fire is uncommon. In this study, we verify the effects of degradation caused by fire in the Canarian laurel forests, which is a subtropical forest formation restricted to the humid montane areas of these Macaronesian islands. We evaluated the effect of fire by comparing a series of burned plots corresponding to fires from 1960, 1984, 1995, to 2012 with geographically proximate and comparable unburned plots in the Garajonay National Park (La Gomera Island, Spain). We focused on three aspects that are immediately altered by fire: forest structure, floristic composition, and microclimate. These aspects have been quantified using (a) tree density, the Pielou index using tree height classes, and DBH for the vertical structure of the forest; (b) DCA, the Bray Curtis dissimilarity index, and a species indicator analysis for the floristic composition; and (c) temperature and relative humidity for microclimate under three canopy cover conditions. Our results reveal that, overall, structural complexity and its composition in the burned areas have barely reached 40% and 35%, respectively, when compared with unburned areas, and recovery mainly depends on time since fire. Additionally, burned plots presented more pioneer species, a higher density of trees, and climatic variables tend to have a wider range throughout the day. These data reveal the long time span that this ecosystem needs for recovery to a prefire state and how it may be more prone to subsequent fire events.

Combining Satellite and UAV Imagery to Delineate Forest Cover and Basal Area after Mixed-Severity Fires

In northern Argentina, the assessment of degraded forests is a big challenge for both science and practice, due to their heterogeneous structure. However, new technologies could contribute to mapping post-disturbance canopy cover and basal area in detail. Therefore, this research assesses whether or not the inclusion of partial cover unmanned aerial vehicle imagery could reduce the classification error of a SPOT6 image used in an area-based inventory. BA was calculated from 77 ground inventory plots over 3944 ha of a forest affected by mixed-severity fires in the Argentinian Yungas. In total, 74% of the area was covered with UAV flights, and canopy height models were calculated to estimate partial canopy cover at three tree height classes. Basal area and partial canopy cover were used to formulate the adjusted canopy cover index, and it was calculated for 70 ground plots and an additional 20 image plots. Four classes of fire severity were created based on basal area and adjusted canopy cover index, and were used to run two supervised classifications over a segmented (algorithm multiresolution) wall-to-wall SPOT6 image. The comparison of the Cohan’s Kappa coefficient of both classifications shows that they are not significantly different (p-value: 0.43). However, the approach based on the adjusted canopy cover index achieved more homogeneous strata (Welch t-test with 95% of confidence). Additionally, UAV-derived canopy height model estimates of tree height were compared with field measurements of 71 alive trees. The canopy height models underestimated tree height with an RMSE ranging from 2.8 to 8.3 m. The best accuracy of the canopy height model was achieved using a larger pixel size (10 m), and for lower stocked plots due to high fire severity.

贵州赤水常绿阔叶林不同层次树木空间分布格局和竞争的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 贵州赤水常绿阔叶林不同层次树木空间分布格局和竞争的关系 DOI: 10.5846/stxb201709121640 作者: 作者单位: 南京林业大学，环境保护部南京环境科学研究所,南京林业大学，江苏省中国科学院植物研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 中央级公益性科研院所基本科研业务专项（2015） Spatial patterns and competition among trees of different height classes in Guizhou, Chishui evergreen broadleaved forest Author: Affiliation: Nanjing Institute of Environmental Sciences,Ministry of Environmental Protection of People''s Republic of China,nanjing forestry 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:在贵州赤水桫椤国家级自然保护区的亚热带常绿阔叶林中设置0.96 hm2的固定样地进行调查，将2299株乔木按树高分级（林木下层、中层、上层），进行空间定位并记录胸径和冠幅等个体指标。采用基于个体间距离的对数相关函数（Pair-correlation functions，PCF）和基于个体胸径、冠幅的标记点格局分析（Marked correlation functions，MCF）空间统计方法检测不同高度层内和层间的空间分布格局和潜在的竞争，结果表明：（1）样地内上层树种呈现随机分布，中下层树种在0-6 m的小尺度内呈聚集分布，在层间关系上表现为0-1 m尺度下显著的正相关关系。（2）在群落内上层个体中没有检测到显著的层内竞争，也未发现其与中、下层树种存在层间竞争关系。（3）群落中、下层树种的层内和层间竞争对两者间空间分布格局和个体大小均产生了一定影响，其相邻个体的胸径和冠幅呈现显著负相关关系。这说明在贵州赤水地区常绿阔叶林中群落中不同层次个体处于不同演替阶段，群落内层内和层间竞争对个体较大的林木上层物种的影响已经非常微弱，而主要发生在中、下层树种内，导致了个体较小的中下层更新树种在层间和层内都出现了小尺度下聚集分布格局，这解释了研究地内不同高度级别树种间竞争关系与共存策略，也验证了标记点格局分析方法在检测植物群落竞争中的敏感性。 Abstract:A 0.96 hm2 plot was established in a subtropical evergreen broad-leaved forest in the Chishui Alsophila National Nature Reserve, Guizhou province. The 2299 individual trees were stem-mapped and classified into three height classes:lower, intermediate, and upper height class. Diameter at breast height (DBH) and crown width (CW) were recorded as additional measures of individual growth and performance. In this study, the spatial distribution patterns, spatial associations, and competition among different tree height classes were analyzed PCF (Pair-correlation functions) Analysis based on individual distances. MCF (Marked correlation functions) based on individual DBH and CW were used to detect spatial patterns and within and between different size classes. We found that:(1) The upper tree species showed random distributions at almost all scales. The middle and lower tree species clustered on the small scales of 0-6 m, which showed positive associations with each other within a 1 m scale. (2) No intra-class competition of individual trees within the upper height class was detected, nor was there a significant association with other classes. (3) Intra-and interclass competition in the lower and intermediate height classes had some negative influence on the growth and spatial distribution of individuals. This suggested that individuals among different height classes were at different succession stages in the subtropical evergreen broad-leaved forest in Chishui. Intra-and interspecies competition had the least influence on the upper height classes, but significantly influenced the intermediate and lower size classes, resulting in an aggregated distribution of lower and intermediate height individuals at small scales. This study helps explain competition strategies and coexistence between different height classes. Additionally, it verified the high sensitivity of the marked correlation function analysis in the competition detection of a plant community. 参考文献 相似文献 引证文献

Comparación de la diversidad estructural de una selva alta perennifolia y una mediana subperennifolia en Tabasco, México

Debido a que el tamaño de los árboles puede influir significativamente en la estructura de una comunidad y consecuentemente en su diversidad, los índices de diversidad estructural constituyen estimadores más precisos que los índices de diversidad clásicos ya que incorporan el diámetro y altura de los árboles. Mediante el uso de ocho índices estructurales, considerando el área basal de la comunidad por clases de diámetro y altura de los árboles, se comparó la diversidad estructural de una selva alta perennifolia y una mediana subperennifolia en Tabasco, México. Para los árboles con diámetro a la altura del pecho mayor a 10 cm, se determinó especie, diámetro a la altura del pecho y altura total, y los índices se compararon estadísticamente entre las dos comunidades. La selva mediana subperennifolia presentó 27 especies, 211 árboles y 129 palmas por hectárea, diámetro promedio a la altura del pecho de 28.0 cm y 9 individuos > 20 m de altura. La selva alta perennifolia tuvo 66 especies y 591 árboles por hectárea, diámetro promedio a la altura del pecho de 21.2 cm y 36 árboles > 20 m de altura. Los índices de diversidad estructural de la selva alta perennifolia (2.76 – 6.737) fueron significativamente (p<0.01) mayores que los de la mediana subperennifolia (2.345 – 4.978). Los índices (Gini) de la selva alta perennifolia (0.61 y 0.494) indicaron que los árboles son más variables en su tamaño (diámetro y altura) que los de la mediana subperennifolia (0.583 y 0.419). Se concluye que los índices de diversidad estructural reflejan tanto la diversidad de especies como la complejidad estructural de la comunidad, siendo más diversa la selva alta perennifolia que la mediana subperennifolia. Se sugiere su uso para las comunidades arboladas.

Assessing urban tree condition using airborne light detection and ranging

With increased interest in urban forests on behalf of city dwellers and urban planners, there is a growing need for comprehensive information on urban tree condition. This study examines the potential of airborne light detection and ranging (LiDAR) for evaluating tree condition in the urban center of Surrey, Canada. An approach to detecting and outlining free-growing trees from LiDAR data augmented by a municipal tree inventory was developed and validated. Once the trees were located, LiDAR was used to estimate two field-measured indicators of tree condition: crown density and tree height. Tree heights estimated by LiDAR were, as expected, well correlated with field measurements (Pearson’s r=0.927, p<0.001), indicating accurate height estimates of successfully detected trees. Two LiDAR metrics, the percentage of non-ground LiDAR returns and the coefficient of variation of return height, were examined as predictors of crown density. While the percentage of non-ground returns performed relatively poorly (r2 between 0.005 and 0.23 across multiple tree height classes), the coefficient of variation of return height was able to predict crown density with an r2=0.617 for trees over 8 m. In addition, residuals derived using expected height growth from the known planting date and their LiDAR-derived height was found to be a useful tree condition metric. We conclude that despite the complexity of urban tree condition assessment, airborne LiDAR is a promising tool for detecting trees in an urban environment and measuring indicators of their condition.

Biomass Increases Go under Cover: Woody Vegetation Dynamics in South African Rangelands.

Woody biomass dynamics are an expression of ecosystem function, yet biomass estimates do not provide information on the spatial distribution of woody vegetation within the vertical vegetation subcanopy. We demonstrate the ability of airborne light detection and ranging (LiDAR) to measure aboveground biomass and subcanopy structure, as an explanatory tool to unravel vegetation dynamics in structurally heterogeneous landscapes. We sampled three communal rangelands in Bushbuckridge, South Africa, utilised by rural communities for fuelwood harvesting. Woody biomass estimates ranged between 9 Mg ha-1 on gabbro geology sites to 27 Mg ha-1 on granitic geology sites. Despite predictions of woodland depletion due to unsustainable fuelwood extraction in previous studies, biomass in all the communal rangelands increased between 2008 and 2012. Annual biomass productivity estimates (10–14% p.a.) were higher than previous estimates of 4% and likely a significant contributor to the previous underestimations of modelled biomass supply. We show that biomass increases are attributable to growth of vegetation <5 m in height, and that, in the high wood extraction rangeland, 79% of the changes in the vertical vegetation subcanopy are gains in the 1-3m height class. The higher the wood extraction pressure on the rangelands, the greater the biomass increases in the low height classes within the subcanopy, likely a strong resprouting response to intensive harvesting. Yet, fuelwood shortages are still occurring, as evidenced by the losses in the tall tree height class in the high extraction rangeland. Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity. This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of ecosystem service provision. The structural implications of biomass increases in communal rangelands could be misinterpreted as woodland recovery in the absence of three-dimensional, subcanopy information.

小兴安岭阔叶红松混交林林隙特征

对小兴安岭阔叶红松混交林林隙基本特征进行了研究。结果表明:林隙的线状密度为31.78个/km,冠空隙和扩展林隙所占的面积比例分别为15.71%和30.78%;冠空隙的年干扰频率为0.46%,干扰轮回期约为434.8a。冠空隙的大小变化在42.12-372.52m²之间,平均为153.37m²;扩展林隙的大小变化在98.65m²-633.10m²之间,平均为300.44m²。冠空隙和扩展林隙面积分布格局均符合Weibull分布。林隙形成方式主要为干基折断,占总形成木总数的35.29%,其次为掘根风倒,占28.43%。平均每个林隙的形成木为4.98株,由红松、白桦、枫桦、冷杉形成,径级在20-30 cm之间,高度在15-30 m之间。冠空隙的直径与高度比值的相对频率的分布呈单峰型曲线,当比值为0.30-0.45时,出现峰值;而扩展林隙的直径与高度比值的相对频率的分布呈双峰型曲线,当比值分别为0.75-0.90和1.05-1.15时,出现峰值。林隙边缘木胸径级的多度分布和高度级多度分布符合Weibull分布,但不符合正态分布。约13.41%的边缘木未出现偏冠现象,偏冠率在0.5-0.7之间的边缘木占70.49%。;Gap characteristics were studied in the mixed broad-leaved Korean pine forest in Xiaoxing'an Mountains. The results showed that the linear gap density in the forest was 31.78 gaps/km. The canopy gaps and expanded gaps occupied 15.71%, and 30.78% of total investigated area, respectively. The yearly gap disturbance frequency was 0.46% and the disturbance rotation was 434.8 years. Canopy gaps varied from 42.12 to 372.52 m² and average area of canopy gaps was 153.37m². Expanded gaps varied from 98.65m² to 633.10m² and average area of expanded gaps was 300.44m². The distribution pattern in both canopy gap area and expanded gap area followed Weibull model. The major means of gap formation was breakage at base(35.29% of the total), and the second was uprooting (28.43%).The average number of gap makers was 4.98 per gap. Major gap makers were <em>Pinus koraiensis</em>,<em> Betula platyphylla</em>,<em> Abies nephrolepis</em>, <em>Betula costata</em>, of which the diameter at breast height (<em>DBH</em>) were between 20-30 cm and the height ranged from 15 to 30 m. For canopy gaps, their distribution in relative frequency of the ratio of their diameter to the height of forest gap (<em>d</em>_CG/<em>H</em>) presented single peak curve, the peak value occurred when the ratio of <em>d</em>_CG/<em>H</em> was between 0.30-0.45, but for expanded gap, their distribution exhibited double peak curves, the peak value came when the ratio of <em>d</em>_CG/<em>H</em> was between 0.75-0.90 and between 1.05-1.15, respectively, in the mixed broad-leaved Korean pine forest in Xiaoxing'an Mountains. The distribution of DBH classes and tree height classes of gap border trees followed Weibull distribution model but they did not follow the normal distribution model. About 13.41% of GBT had regular crowns, the GBT, of which the ratios of crown inclination (RCI) ranged from 0.5 to 0.7, comprised about 70.49% of total GBT.