基于无人机遥感的南岭山地树冠与树干性状关联研究

以南岭山地不同海拔高度的冠层树种为研究对象,通过无人机遥感手段获取冠幅、冠周长和冠面积(CA)等树冠性状,探讨其与基径(BD)、胸径(DBH)、2米径(D2)和4米径(D4)等树干性状间的关联性,并构建了冠面积与树干性状间的回归方程。结果表明：南岭山地树冠性状与树干性状的典型变量显著相关(R=0.89,P<0.01),并且这种相关性随海拔的升高(600 m到1 600 m)总体呈“M”型变化。其中,冠面积与树干性状间的相关性最高,可作为单一自变量反演树干性状,具体方程为：DBH=0.35CA+14.88 (R²=0.67),BD=0.41CA+17.89 (R²=0.82),D2=0.33CA+14.14 (R²=0.84),D4=0.35CA+11.3 (R²=0.86)。文章构建的冠面积与树干性状间的回归方程,可作为南岭山地森林生物量遥感反演的基础,也可用于指导南岭森林生态系统的长期监测。     

Forest transitions in tropical landscapes: A test in the Atlantic Forest biodiversity hotspot

Analyzing temporal changes in forest amount and configuration is paramount to better design future forest management interventions. Such analyses are especially required for tropical biomes, which are usually subject to dynamic and heterogeneous land uses. Recent studies have suggested that many tropical biomes are passing through the process of “forest transition”, i.e. an overall change from forest loss to forest gain. However, this hypothesis remains scarcely tested, due to the difficulty of obtaining detailed, quantitative historical records of forest cover. In this study, we investigate 38 years of land use change in Brazil's Atlantic Forest, a biodiversity hotspot, from 1976 to 2014, using multitemporal datasets from aerial photographs and satellite images. We classified the historical series to produce land use maps and calculated a set of landscape metrics, including total forest cover, patch size, patch shape and patch connectivity. Our results indicated non-linear changes through time in forest loss and gain and also in landscape structure, which can be classified into two distinct periods. The first period (1976–1996) was marked by expressive forest loss and fragmentation, whereas the second (1996–2014) was characterized by a much less intense forest dynamics, with little deforestation being balanced by forest regeneration. We attribute the forest dynamics observed to temporal changes in socioeconomic factors, such as increasing human settlements and changes in environmental protection policies. Our results show that current forests are a heterogeneous mosaic of forests with different ages, and support the hypothesis that forest transition is occurring in Atlantic Forest landscapes.     

Trends of tropical deforestation in Southeast Mexico

We assessed deforestation in Southeast Mexico (a surface area of 29 000 km² in seven states) through the comparison of land use/land cover maps at a scale of 1:250 000. This facilitated mapping of the land use/land cover change (LULCC) processes and calculation of the rates of change and the change matrix for the period 1978–2000. An original method was used to assess the accuracy of the LULCC map. The verification sites were selected through a stratified random sampling and were corroborated with aerial photographs for 1978 and 2000. Error matrices were elaborated using both hard and fuzzy set approaches in order to take into account the errors related to generalization of the map in fragmented landscapes. The results showed an average annual deforestation rate of 1.1 per cent which represents an average annual loss of 190 000 ha of forest, or an estimated total reduction of 4.2 million ha over 22 years. Furthermore, deforestation processes are concentrated in some areas such as Yucatan and Chiapas states, which registered major forest conversions to grassland and slash‐burning. The overall accuracy of the LULCC map, assessed with hard and fuzzy set approaches, was 72 per cent and 88 per cent respectively.     

Increases in fire risk due to warmer summer temperatures and wildland urban interface changes do not necessarily lead to more fires

Forest fire frequency in Mediterranean countries is expected to increase with land cover and climate changes as temperatures rise and rainfall patterns are altered. Although the cause of many Mediterranean fires remains poorly defined, most fires are of anthropogenic origin and are located in the wildland urban interface (WUI), so fire ignition risk depends on both weather and land cover characteristics. The objectives of this study were to quantify the overall trends in forest fire risk in the WUI of the Alpes-Maritimes department in SE France over a period of almost 50 years (about 1960–2009) and relate these to changes in land cover and temperature changes. Land cover for two contrasting reference catchments (236 km² and 289 km², respectively) was mapped from available aerial photographs. Changes in fire risk over time were estimated using statistical relationships defined for each type of WUI, where isolated and scattered housing present a greater risk than dense and very dense housing. Summer monthly temperatures and spring and summer precipitation were quantified over the same temporal period as land cover. Finally, trends in fire frequency and burned area were analyzed over a shorter 37 year period (1973–2009) due to the lack of available fire data before 1973. Fire risk associated with WUI expansion increased by about 18%–80% over the 1960–2009 period (depending on the catchment). Similarly, mean summer minimum and maximum monthly temperatures increased by 1.8 °C and 1.4 °C, respectively, over the same period. Summer rainfall appears to decrease over time since about the 1970's but remains highly variable. Land cover and weather changes both suggest an overall increase in fire risk. However, the number of fires and burned area have decreased significantly since about 1990. This paradoxical result is due to a change in fire-fighting strategy which reinforced the systematic extinction of fires in their early stages. Technical support in the form of improved radio communication and helicopters contributed greatly to reducing fire frequency and burned area. Surveillance and legal reforms included the introduction of field patrols and restricted access to forests during high risk periods. Although this has proven highly successful in the short term, the risk of fuel load accumulation over time remains a risk which might contribute to the development of mega-fires in extreme climatic conditions in the future.     

Lithologic, structural, and geomorphic controls on ribbon forest patterns in a glaciated mountain environment

So-called “ribbon forests” have been attributed to snowdrift patterns and fire history without reference to geomorphology [Vegetatio 19 (1969) 192.]. This paper illustrates how site conditions of geomorphology and geology explain the origin of ribbon forests. In Glacier National Park, MT (USA), regional tectonic uplift associated with the Laramide Orogeny produced structural features that amplify lithologic differences. Pleistocene glaciation scoured deeply along the strike of bedding planes, highlighting this pattern and in some cases producing fine-scale parallel finger lakes between forested ribbon strips.Twelve ribbon forest sites on both sides of the Continental Divide were closely studied on stereoscopic aerial photographs, and several of these sites were examined in the field or from helicopter overflights. In all cases, geologic and geomorphic conditions explain the location and distribution of the ribbon forests. Change-detection of the distribution of trees versus nontree-covered surfaces in an area of ribbon forest on Flattop Mountain, a complex uplifted synclinal structure, was undertaken using panchromatic, low-altitude aerial photographs from 1966 to 1991. Areas changed from forest to meadow and from meadow to forest in roughly equal amounts in a generally random spatial pattern. No evidence was seen to suggest that the creation of one ribbon eventually created another downwind, as suggested by Billings. Aerial photograph interpretation, field examination and soils analyses of forest ribbons and adjacent unforested meadows clearly illustrated that trees occupy higher, parallel to subparallel, well-drained sites where the spatial pattern is in turn a distinct reflection of the spatial pattern of structure and stratigraphy. Meadows occupy topographically lower positions between ridges where erosion along bedding plane strike was concentrated. Topography sets conditions that allow tree growth in certain locations while precluding it in immediately adjacent areas. Ribbon forests there are thus a spatial manifestation of the interaction between structure, lithology, and topography.     

Forest conversion, conservation and forestry in Cross River State, Nigeria

This paper presents new data on the rate and patterns of loss of tropical moist forest cover to agriculture in Cross River State, Nigeria. Data from sequential aerial photographs and field surveys are used to derive an estimate of forest loss of 0.6 per cent per year. This rate is relatively modest, yet current conservation and forestry policy in the area is based on assumptions of rapid conversion of forest. The implications of these findings for debates about conservation and policy are discussed.     

Land change in the central Albertine rift: Insights from analysis and mapping of land use-land cover change in north-western Rwanda

Land change was assessed in the Albertine rift region (ARR) using its central section of north-western Rwanda as case study. This region is one of Africa's most ecologically sensitive environments under severe pressure from human activities. The study maps and quantifies the spatial extent of land use-land cover (LULC) changes between 1987 and 2016 from Landsat images. Transitions between five major land classes were identified in order to understand the trajectory of observed changes. In terms of gains, the forest class, the urban built-up and bare land class increased by 9% and 4% respectively over the study period. The gains of forest were mainly derived from the afforestation of some agricultural lands in the southern part, whereas the gains of built-up and bare lands were mostly from cultivated land which was a net losing class. Forest increase is in line with government's policy to increase the national forest cover to 30% by 2020. Forest losses occurred mostly outside protected areas due to land conversion for settlement and agricultural purposes. Much needed information about changes in LULC over the last three decades is provided. This study demonstrates in a timely manner how to analyse and monitor LULC change and the drivers in an environment where field based research is a challenge due to the mountainous terrain. The ecological richness of the region, which coincides with heightened human population pressure, necessitates the monitoring of land change as input for improving land use planning with focus on conserving biodiversity.     

Field validation of 1930s aerial photography: What are we missing?

Aerial photography from the 1930s serves as the earliest synoptic depiction of vegetation cover. We generated a spatially explicit database of shrub (Prosopis velutina) stand structure within two 1.8 ha field plots established in 1932 to address two questions: (1) What are the detection limits of panchromatic 1936 aerial photography?, and (2) How do these influence P. velutina biomass estimates? Shrub polygons were manually digitized on 1936 imagery and linked to 1932 field measurements of P. velutina canopy area. Aboveground 1932 P. velutina biomass was estimated using a site-specific allometric relationship for field-measured canopy area. Shrub canopy detection limits on the 1936 imagery were comparable to those reported for contemporary imagery. Based on a conservative shrub size detection threshold of 3.8 m², 5.8% of P. velutina biomass was missed. Spatial resolution (0.6 vs. 1.0 m) did not influence detection limits, but the overall accuracy of shrub cover estimates was greater on 1.0 m images. Presence of the sub-shrub Isocoma tenuisecta may also have significantly influenced estimates of P. velutina canopy area. These analyses illustrate the importance of standardizing aerial photo interpretation protocols, accounting for uncertainty estimating shrub biomass, and caution species-specific interpretations for historic aerial photography.     

High belowground biomass allocation in an upland black spruce (Picea mariana) stand in interior Alaska

The root system of forest trees account for a significant proportion of the total forest biomass. However, data is particularly limited for forests in permafrost regions. In this study, therefore, we estimated the above- and belowground biomass of a black spruce (Picea mariana) stand underlain with permafrost in interior Alaska. Allometric equations were established using 4–6 sample trees to estimate the biomass of the aboveground parts and the coarse roots (roots >5 mm in diameter) of P. mariana trees. The aboveground biomass of understory plants and the fine-root biomass were estimated by destructive sampling. The aboveground and coarse-root biomasses of the P. mariana trees were estimated to be 3.97 and 2.31 kg m^?2, respectively. The aboveground biomass of understory vascular plants such as Ledum groenlandicum and the biomass of forest floor mosses and lichens were 0.10 and 0.62 kg m^?2, respectively. The biomass of fine roots <5 mm in diameter was 1.27 kg m^?2. Thus, the above- and belowground biomasses of vascular plants in the P. mariana stand were estimated to be 4.07 and 3.58 kg m^?2, respectively, indicating that belowground biomass accounted for 47% of the total biomass of vascular plants. Fine-root biomass was 36% of the total root biomass, of which 90% was accumulated in the surface organic layer. Thus, this P. mariana stand can be characterized as having extremely high belowground biomass allocation, which would make it possible to grow on permafrost with limited soil resource availability.     

Landscape Controls on Structural Variation in Eucalypt Vegetation Communities: Woronora Plateau,Australia

Quantification of landscape-based vegetation structural variation and pattern is a significant goal for a variety of ecological, monitoring and biodiversity studies. Vegetation structural metrics, derived from airborne laser scanning (ALS or aerial light detection and ranging—LiDAR) and QuickBird satellite imagery, were used to establish the degree of plot-based vegetation variation at a hillslope scale. Topographic position is an indicator of energy and water availability, and was quantified using DEM-based insolation and topographic wetness, respectively, stratifying areas into hot-warm-cold and wet-moist-dry topographic classes. A range of vegetation metrics—maximum and modal canopy height, crown cover, foliage cover, NDVI and semivariance—were compared among randomly selected plots from each topographic class. NDVI increases with increasing landscape wetness, whereas ALS-derived foliage cover decreases with increasing insolation. Foliage cover is well correlated with crown cover (R ² =0.65), and since foliage cover is readily calculable for whole-of-landscape application, it will provide valuable and complementary information to NDVI. Between-plot heterogeneity increases with increasing wetness and decreasing insolation, indicating that more sampling is required in these locations to capture the full range of landscape-based variability. Pattern analysis in landscape ecology is one of the fundamental requirements of landscape ecology, and the methods described here offer statistically significant, quantifiable and repeatable means to realise that goal at a fine spatial grain.     

基于土地利用/覆被分类系统估算 碳储量的差异——以海南岛森林为例

土地利用/覆被分类系统是碳蓄积研究的依据,然而各种碳蓄积研究所采用的土地利用/覆被分类系统不尽相同。根据1993年海南林业资源二类调查资料,我们按照USGS土地利用/覆被、LCCS土地覆被和中国科学院土地资源三种分类系统所定义的类别进行分类并计算了各自的碳储量和碳密度,为碳储量的进一步精确估算和土地覆被分类系统研制提供重要的科学依据。结果发现,（1）不同的土地利用/覆被分类系统所对应的总碳储量以及平均碳密度都有了明显的差别。林业调查资料的植被分类、FAO 土地覆被分类系统(LCCS)、USGS 土地利用/土地覆被分类系统以及我国学者常用的中国科学院土地资源分类系统的碳蓄积量(Tg C)分别是28.98、28.71、21.04和21.04;碳密度(t C/ha)分别是31.24、30.95、22.68和22.68。（2）土地利用分类系统和土地覆被分类系统之间的结果具有较大差异,其碳储量相差7.67～7.94 Tg C,碳密度则相差8.27～8.56 t C/ha;差距在26.47%～37.74%之间。与其他学者研究结果比较发现,土地利用/覆被分类系统造成的碳蓄积差异的变化方向是不定的,取决于具体的分类系统和材积-生物量函数。不同土地利用/覆被分类系统对于植被划分的不同,导致了材积-生物量回归方程和类别面积的差异是造成碳蓄积和碳密度估算差异的根本原因。目前常用的土地利用/覆被分类系统在估算碳蓄积中存在一定问题,不适合于高精度的碳蓄积计算。体现地表植被生物量差异、植被叶型和外貌特征、种类及树龄差异等内涵的土地利用/覆被分类系统利于陆地碳循环研究的深化。     

World heritage and landscape change – heritage buildings and their changed visibility in the coastal landscape of Vega,Norway

Part of the Vega archipelago in north-western Norway is a cultural landscape listed as a UNESCO World Heritage site. Its buffer zone comprises most of the main island of Vega, where agriculture is an important land use. The authors describe interdisciplinary research carried out in the buffer zone. The research revealed the significant role of agriculture for the maintenance of the traditional open coastal landscape. The finding was further underlined by the fact that many visitors to the site never reach the outer archipelago, which is the core of the listed site. Based on interpretations of aerial photographs, land cover maps were produced for three cross-sections in time (1965, 1986, and 2009). A further reclassification of the land cover was performed to capture the change in openness due to change in land cover. Viewshed maps of each building found on the aerial photographs were overlain with the openness classes to capture the visual consequences of the buildings due to changes in land cover. A marked decrease in open land surrounding the buildings was found in the study area, which comprised Holand and Floa-Kjul in Vega Municipality, which in turn comprises the islands of the Vega archipelago. The regrowth of the land seemed to be happening regardless of building category.     

Assessment of biophysical properties of Royal Belum tropical forest,Malaysia

The Royal Belum forest reserve is one of the oldest tropical rainforests in the world and it is one of the largest virgin forest reserves in Malaysia. However, not many studies have been conducted to understand the ecology of this forest. In this study we estimated the aboveground biomass (AGB) of the forest using diameter at breast height (DBH) and height of trees (h ), tree species and hemispherical photographs of tree canopy. We estimated AGB using five allometric equations. Our results demonstrated that the AGB given by the one tree species specific allometric equation does not show any significant differences from the values given by the non‐tree species specific allometric equations at tree and plot levels. The AGB of Intsia bijuga species, Koompassia malaccensis species and Shorea genera were comparatively higher, owing to their greater wood density, DBH and h. This has added importance because some of these species are categorized as threatened species. Our results demonstrated that mean AGB values in this forest (293.16 t ha^‐1) are the highest compared to some studies of other areas in Malaysia, tropical Africa and tropical Bazilian Amazonia, implying that the Royal Belum forest reserve, is an important carbon reservoir.     

Land use/cover, landforms and fragmentation patterns in a tropical dry forest in the southern Pacific region of Mexico

In spite of widely documented studies of deforestation rates and land use/cover changes in tropical dry forests in Mexico, relatively little is known about fragmentation patterns in such forests. This study defines the spatial distribution of landforms and land use/cover types the lower Papagayo River basin and examines their influence on fragmentation patterns and biological diversity in a tropical dry forest in that southern Pacific region. The land use/cover map was constructed from aerial photographs, Landsat TM imagery (2000) and fieldwork. Landform units were defined based on altitude, slope, lithology and morphology. Landscape fragmentation parameters were obtained using FRAGSTATS (version 3.3) considering the numbers of patches, mean, minimum and maximum patch size, edge density, total edge and connectivity. Results show tropical dry forest to be remnant vegetation (~11 per cent), characterized by isolation and low connectivity. Land use/cover types have different effects on fragmentation patterns. Agriculture and cattle raising produce similar numbers of patches, but with a different mean size; and human settlements have a scattered distribution pattern. The abandonment of rural agricultural livelihoods has favoured the expansion of secondary tropical dry forest characterized by continuity and high connectivity, which suggests a high regeneration potential from land abandonment. It can be concluded that tropical dry forest fragmentation and recovery at regional scales depend on such landscape attributes as lithology, slope, geomorphology and management.     

Changes in soil nutrients, vegetation structure and herbaceous biomass in response to grazing in a semi-arid savanna of Ethiopia

The effect of grazing was studied on vegetation structure, herbaceous biomass, basal and bare ground covers, together with soil nutrient concentrations in two locations in an Ethiopian semi-arid savanna. The lightly grazed sites had significantly higher herbaceous diversity, total abundance, basal cover and aboveground biomass, and a lower percentage of bare ground compared with the heavy grazed sites. Grazing pressure had no effect on the density and number of woody species as well as on the proportion of encroaching woody species. The light grazing sites had higher organic carbon, phosphorus and exchangeable bases, and therefore a higher pH and higher electrical conductance, indicating an improved soil nutrient status compared with heavy grazing sites, mainly attributed to the higher basal cover and standing biomass at light grazed sites, and the export of nutrients through grazing and dung collection from the heavily grazed sites. There were significantly higher soil nutrients, species diversity, aboveground biomass and basal cover in the light grazing sites compared with heavy grazing sites. We concluded that changes in herbaceous vegetation, standing biomass and soil compositions are caused by interactions between grazing, soil and vegetation, and these interactions determine the transitions of semi-arid savannas.     

Patterns and Controls of Hurricane-Caused Forest Damage: A Landscape-Scale Analysis of Treefall Direction Following Hurricane Katrina∗

To clarify broad-scale patterns and controls of treefall directionality from Hurricane Katrina, we examined fall directions across a 4,500 km² landscape mosaic in southern Mississippi using georeferenced, planar-rectified aerial photographs. Analyses using directional statistics, measures of local spatial autocorrelation, and general linear modeling indicated that treefall was significantly directional for nearly all of our locations and constrained primarily by mesoscale surface wind directions and landscape setting. None of our plots exhibited fall angles consistent with damage caused by wind reversals following the passage of the storm or by microbursts or tornadoes spawned by the hurricane. When coupled with results from other studies focused on hurricane-caused damage, these results suggest that it is possible to develop empirical, landscape-scale models of wind impacts or stand vulnerability using basic site information (e.g., topography, soils), biotic conditions (e.g., land cover, forest attributes), and generalized, but readily available, estimates of surface wind flow patterns.     

Assessing and monitoring forest health using a forest fragmentation approach in Sariska Tiger Reserve,India

The relationship between trajectories of forest cover change and fragmentation due to physical and anthropogenic activities in Sariska Tiger Reserve is addressed in the article. The authors conducted a field visit to the reserve to collect groundtruth data and perform a village survey. Thereafter, their main method consisted of using Landsat TM images for three days, one in each of the years 1989, 1994, and 2014, to assess spatial-temporal variation in forest cover. A fragmentation model was used to examine the extent and pattern of forest degradation. The results showed an overall increase in forest cover in Sariska Tiger Reserve from 53% in 1989 to 55% in 2014. However, the fragmentation statistics revealed a deterioration in forest health. There was an increase in the fragmentation categories perforated, edge, and patch in their respective areas, while the core areas decreased at the expense of other fragmentation classes. The existence of villages, roads, and pilgrimage sites had increased the pace of degradation and fragmentation of forest in the reserve. The authors conclude that the fragmentation model was effective for analysing forest degradation and identifying the priority areas for strategic planning of nature conservation.     

黄河三角洲湿地柽柳林生长动态密度结构的响应特征

为了阐明滨海湿地不同密度柽柳(Tamarix chinensis)林的生长动态,探索滨海湿地柽柳林的密度合理性,在黄河三角洲莱州湾南岸的山东昌邑海洋生态特别保护区内,利用标准木树干解析法,对10a生的3种密度(2400株/hm2、3 600株/hm2和4400株/hm2)的柽柳林地上生物量、林木生长动态和基径分布特征进行研究.结果表明,3种密度林分的地上生物量、树高生长量和林木基径生长过程差别较大.随着林分密度增大,林木单株生物量和基径减小,但单位面积林分生物量增加;树高、基径的速生期都出现滞后现象.3种密度林分基径分布的偏度系数(SK)差别较大;密度为3 600株/hm2林分的SK值为0.085,接近正态分布,林分密度结构和基径分布较为合理;密度为2 400株/hm2和4 400株/hm2林分的SK值分别为-0.842和0.303,偏离正态分布,林分密度结构不合理.密度为2 400株/hm2林分的峰度系数(K)为0.017,林木生长相对整齐;密度为3 600株/hm2和4 400株/hm2林分的K值相差不大;密度因素对林木分化作用较小.若不考虑10a间的林木间伐利用,该区柽柳人工造林合理的初植密度建议为3 600株/hm2(株行距约2.0 m×2.0 m).     

Spatial analysis of rockfall activity, bounce heights and geomorphic changes over the last 50 years – A case study using dendrogeomorphology

Tree-ring series have been used to reconstruct 50 years of rockfall behavior on a slope near Saas Balen (Swiss Alps). A total of 796 cores and 141 cross sections from 191 severely injured conifer trees (Larix decidua Mill., Picea abies (L.) Karst. and Pinus cembra L.), combined with a series of aerial photographs, were used to investigate the evolution of the forest stand so as (i) to reconstruct past rockfall rates; (ii) to analyze the spatial behavior of maximum bounce heights; and (iii) to analyze the spatial comportment of rockfall activity over the last five decades.Tree-ring analysis permitted the reconstruction of the age distribution at the study site; results were in perfect agreement with the afforestation process shown in the aerial photographs. The oldest are located in the lower, central part of the study site; the youngest individuals at its uppermost lateral boundaries. Reconstructed rockfall rates reveal strong interannual variations and single event years with increased activity, namely in 1960/1961 and 1995. Spatial analysis of the maximum bounce heights indicate highest values at the lateral boundaries and lowest heights in the lower central part of the forest stand, where a big boulder seems to shield trees growing below it. The spatial analysis of past rockfall activity shows high active zones at the uppermost north-facing boundaries of the forest and least active zones in the lowermost central part of the studied stand. The high rockfall activity at the slope is expressed by a mean rockfall rate of > 1 event m^− 1 y^− 1.     

MAPPING OF FORESTED WETLAND: USE OF SEASAT RADAR IMAGES TO COMPLEMENT CONVENTIONAL SOURCES

Distinguishing forested wetland from dry forest using aerial photographs is handicapped because photographs often do not reveal the presence of water below tree canopies. Radar images obtained by the Seasat satellite reveal forested wetland as highly reflective patterns on the coastal plain between Maryland and Florida. Seasat radar images may complement aerial photographs for compiling maps of wetland. A test with experienced photointerpreters revealed that interpretation accuracy was significantly higher when using Seasat radar images than when using only conventional sources.