Satellite-based monitoring of tropical seagrass vegetation: current techniques and future developments

Decline of seagrasses has been documented in many parts of the world. Reduction in water clarity, through increased turbidity and increased nutrient concentrations, is considered to be the primary cause of seagrass loss. Recent studies have indicated the need for new methods that will enable early detection of decline in seagrass extent and productivity, over large areas. In this review of current literature on coastal remote sensing, we examine the ability of remote sensing to serve as an information provider for seagrass monitoring. Remote sensing offers the potential to map the extent of seagrass cover and monitor changes in these with high accuracy for shallow waters. The accuracy of mapping seagrasses in deeper waters is unclear. Recent advances in sensor technology and radiometric transfer modelling have resulted in the ability to map suspended sediment, sea surface temperature and below-surface irradiance. It is therefore potentially possible to monitor the factors that cause the decline in seagrass status. When the latest products in remote sensing are linked to seagrass production models, it may serve as an early-warning system for seagrass decline and ultimately allow a better management of these susceptible ecosystems.     

A new forest cover map of continental southeast Asia derived from SPOT‐VEGETATION satellite imagery

Question: Can recent satellite imagery of coarse spatial resolution support forest cover assessment and mapping at the regional level? Location: Continental southeast Asia. Methods: Forest cover mapping was based on digital classification of SPOT4‐VEGETATION satellite images of 1 km spatial resolution from the dry seasons 1998/1999 and 1999/2000. Following a geographical stratification, the spectral clusters were visually assigned to land cover classes. The forest classes were validated by an independent set of maps, derived from interpretation of satellite imagery of high spatial resolution (Landsat TM, 30 m). Forest area estimates from the regional forest cover map were compared to the forest figures of the FAO database. Results: The regional forest cover map displays 12 forest and land cover classes. The mapping of the region's deciduous and fragmented forest cover remained challenging. A high correlation was found between forest area estimates obtained from this map and from the Landsat TM derived maps. The regional and sub‐regional forest area estimates were close to those reported by FAO. Conclusion: SPOT4‐VEGETATION satellite imagery can be used for mapping consistently and uniformly the extent and distribution of the broad forest cover types at the regional scale. The new map can be considered as an update and improvement on existing regional forest cover maps.     

A method for assessing evergreen habitats using phytodiversity and geospatial techniques in tropical rain forests of Southern Western Ghats (India)

We have used data generated using remote sensing and geographical information systems to categorize habitats, and then determined the relationship between the habitat categorizations and species-distribution patterns. A biologically rich hotspot—Kalakad-Mundanthurai Tiger Reserve, located at Southern Western Ghats, India, was chosen for this study. In order to spatially delineate areas of high species richness/diversity and endemic habitat zones, we have identified evergreen habitats in conjunction with landscape metrics, species assemblage, micro-habitats like slope, topography, species endemism, and proportion of core and edge species. A total of 236 species and 2,920 individuals were recorded using systematic stratified plots of 0.1 ha covering 47 plots. Hierarchical cluster analysis was done using Ward’s method. Plot information was used to identify clusters based on species density. The analysis showed five species assemblages that are quite distinct from each other in terms of dominant species. The distribution of endemic and edge species, land cover heterogeneity, and continuity of patches in these clusters were evaluated to understand the degree of disturbance and intactness at landscape scale. Integration of species assemblages and topography brought out four major elevation-slope complexes. Information on species composition (robust field survey) with spectral (hybrid classification) properties has shown 72% overall accuracy and distinguished four evergreen sub-groups and other land cover classes. The developed approach assumes great importance in the assessment of biodiversity and prioritizing the areas of conservation.     

Factors involved in the degradation of mangrove forests in Iran: A mixed study for the management of this ecosystem

In Iran, mangroves are located in the south of the country, where they fulfill essential ecosystem functions, but some parts of them have been destroyed for various reasons in recent years so that it seems necessary to have a management plan consistent with the conservation of this ecosystem. But, it needs knowledge of the trend of and reasons for the degradation of these forests. So, the primary idea of this research was to discover the factors involved in the degradation of these forests and how to manage them. So, the research first used the remote sensing technique to determine the rate of their degradation over the last 20 years. Then, using the Delphi technique, 45 factors were identified for the degradation of these forests and they were classified into five categories including climatic and environmental, anthropogenic, socioeconomic, psychological, and policymaking and legal. Finally, the analytic hierarchy process (AHP) was used to rank these factors within two management paradigms of remediability and preventability so that the ecosystem can be soundly managed by classifying these factors. Overall, the results can provide policymakers with new insights into forest management and the policies presented here can contribute to the sustainability of this ecosystem.     

Unified classification of European natural forests: the approach of the vegetation map of Europe

With the aim of evaluating the accessible data on vegetation structure and composition for the Vegetation Map of Europe as far as possible, a reasonable classification of natural vegetation has been proposed which facilitates the identification of vegetation units used in different Schools of vegetation science. The proposed universal classification makes full use of several different principles. The highest units are based on physiognomic-ecological features and correspond to formation units of different rank. The European natural forest vegetation (including shrubs) has been divided into 10 formation units. Each formation is further divided into subunits according to the most important features. Ecological and functional interpretation has priority in the hierarchic structure of the system which was used in the legend to the Vegetation Map of Europe. The resulting system shows the most important features of latitudinal (vegetation zones and subzones), longitudinal (oceanic to continental analogues) and altitudinal (vegetation belts) regularities, further azonal vegetation types and their differentiation as well as the edaphic, geographic and florogenetic varieties of the natural plant cover. This arrangement constitutes a framework in which the vegetation units of different Schools can be classed.     

Woody vegetation of a mosaic of protected areas adjacent to the Kruger National Park,South Africa

Question: How is pattern detected and spatial scale defined in a manner that is meaningful to management? Location: Protected areas to the west of the Kruger National Park, South Africa. Methods: A Two‐Way Indicator Species Analysis (TWIN‐SPAN) based on composition and structure was applied to woody survey data. The resulting TWINSPAN classes for individual monitoring sites were used in a supervised classification of Landsat ETM⁺ imagery across the study area. The training sample's co‐ordinates were fed into a GIS and the resulting TWINSPAN point‐feature shape file was processed using a 1 km theme‐buffer function. Results: The supervised classification using the theme‐buffer signatures yielded a satisfactory overall accuracy (κ= 0.75; r²= 0.80; p= 0.05) using a test sample compiled by reserve wardens throughout the study area. The derived vegetation map was smoothed using a majority filter and after on‐screen digitizing a small gabbro intrusion, it was accepted as the best representation of the woody vegetation of the study area at a scale of 1:250 000. Seven plant communities were identified in the current study and satisfactorily accommodated within various topographical units of four extrapolated Landscapes of the Kruger National Park. Conclusions: Vegetation patterns are described of the areas under conservation management to the west of the KNP at a spatial scale that allows for the meaningful examination and comparison of the structure, functioning, and ultimately effective management, of these savannas. This contribution thus links to the co‐ordinated effort extending into the Trans‐Frontier National Park in Mocambique. A key objective is to better understand the functioning of these savanna systems for effective management and we discuss some of the key ecological issues within the plant communities of each landscape. The latter illustrate the usefulness of the technique in practice.     

A digital land cover map of Wyoming,USA: a tool for vegetation analysis

Abstract. A Landsat Thematic Mapper (TM) based digital land cover map has been created for the state of Wyoming, USA, at moderate spatial (l-km² minimum mapping unit) and high typal (41 land cover types) resolution as part of the Wyoming Gap Analysis Program (WGAP). This map presents opportunities for regional characterization of land cover, especially vegetation, and for examination of ecological phenomena that manifest themselves over large areas. Using the digital land cover data, we describe Wyoming vegetation and examine positions of three prominent physiognomic transitions in Wyoming: the elevation of upper and lower treeline, and the position of the biogeographic boundary between shruband grass-dominated vegetation. By area, the three leading land cover types in Wyoming are Artemisia tridentata ssp. wyomingensis sagebrush (33.4 %), mixed grass prairie (17.5 %) and Pinus contorta forest (6.5 %). Average upper-treeline elevation in Wyoming is 2947 m, and decreases with increasing latitude at an average rate of about 0.5 m/km, less than the rate of about 0.9 m/km reported by Peet (1978) for a gradient from Mexico to Canada. Lower-treeline occurs at an average elevation of 2241 m, and decreases with increasing latitude and with southerly aspect. In Wyoming, shrub-dominated communities are more likely to occur than grass-dominated communities as summer precipitation decreases below 282 mm. All of these relationships are subtle, and it appears that for particular areas, local factors are more important than regional climatic trends in explaining the position of phytogeographic boundaries.     

Scale matters: fire–vegetation feedbacks are needed to explain tropical tree cover at the local scale

At a broad (regional to global) spatial scale, tropical vegetation is controlled by climate; at the local scale, it is believed to be determined by interactions between disturbance, vegetation and local conditions (soil and topography) through feedback processes. It has recently been suggested that strong fire–vegetation feedback processes may not be needed to explain tree‐cover patterns in tropical ecosystems and that climate–fire determinism is an alternative possibility. This conclusion was based on the fact that it is possible to reproduce observed patterns in tropical regions (e.g. a trimodal frequency distribution of tree cover) using a simple model that does not explicitly incorporate fire–vegetation feedback processes. We argue that these two mechanisms (feedbacks versus fire–climate control) operate at different spatial and temporal scales; it is not possible to evaluate the role of a process acting at fine scales (e.g. fire–vegetation feedbacks) using a model designed to reproduce regional‐scale pattern (scale mismatch). While the distributions of forest and savannas are partially determined by climate, many studies are providing evidence that the most parsimonious explanation for their environmental overlaps is the existence of feedback processes. Climate is unlikely to be an alternative to feedback processes; rather, climate and fire–vegetation feedbacks are complementary processes at different spatial and temporal scales.     

Prescribed moorland burning meets good practice guidelines: A monitoring case study using aerial photography in the Peak District,UK

Upland moors in the UK have been managed for centuries using rotational prescribed-burning, but in recent years there has been contentious debate over its continuing use due to varying effects on moorland ecosystem services. Prescribed-burning should only be carried out using good-practice codes, which include restrictions on the size, location and frequency of burns. Good burning practice is an indicator of management standards and habitat condition in moorland landscapes. However, there has been little attempt to assess management performance with respect to these restrictions. We investigated prescribed-burning on a case-study estate (Howden Moor) in the Peak District National Park from 1988 to 2009 using management maps and aerial photography. The annual area burned (0.9%) was far below recommendations (10%) and patches were in keeping with the target sizes specified (mean ± se: 2370 ± 70 m²). The risk of a large or escaped fire was very low, with less than 1% of fires greater than 15,000 m². However, only 28.9% of the total burnable area was burned, leaving the rest unmanaged and accumulating fuel. Future guidelines might recommend the application of prescribed-burning across the range of Calluna vulgaris growth phases, to reduce fuel load and promote biodiversity at the landscape scale. We show that vegetation mapping and aerial photography are an effective method for monitoring prescribed-burning practice on moorlands. The information derived from such monitoring studies should lead to greater confidence in the standard of prescribed-burning and adherence to good-practice guidelines and requirements imposed by statutory authorities.     

Spatial and temporal deforestation dynamics in protected and unprotected dry forests: a case study from Myanmar (Burma)

Tropical dry forests are more threatened, less protected and especially susceptible to deforestation. However, most deforestation research focuses on tropical rain forests. We analyzed spatial and temporal changes in land cover from 1972 through 2005 at Chatthin Wildlife Sanctuary (CWS), a tropical dry forest in Myanmar (Burma). CWS is one of the largest protected patches of tropical dry forest in Southeast Asia and supports over half the remaining wild population of the endangered Eld’s deer. Between 1973 and 2005, 62% of forest was lost at an annual rate of 1.86% in the area, while forest loss inside CWS was only 16% (0.45% annually). Based on trends found during our study period, dry forests outside CWS would not persist beyond 2019, while forests inside CWS would persist for at least another 100 years. Analysis of temporal deforestation patterns indicates the highest rate of loss occurred between 1992 and 2001. Conversion to agriculture, shifting agriculture, and flooding from a hydro-electric development were the main deforestation drivers. Fragmentation was also severe, halving the area of suitable Eld’s deer habitat between 1973 and 2001, and increasing its isolation. CWS protection efforts were effective in reducing deforestation rates, although deforestation effects extended up to 2 km into the sanctuary. Establishing new protected areas for dry forests and finding ways to mitigate human impacts on existing forests are both needed to protect remaining dry forests and the species they support.     

A comparison of cover calculation techniques for relating point-intercept vegetation sampling to remote sensing imagery

Accurate and timely spatial predictions of vegetation cover from remote imagery are an important data source for natural resource management. High-quality in situ data are needed to develop and validate these products. Point-intercept sampling techniques are a common method for obtaining quantitative information on vegetation cover that have been widely implemented in a number of local and national monitoring programs. The use of point-intercept data in remote sensing projects, however, is complicated due to differences in how vegetation cover indicators can be calculated. Decisions on whether to use plant intercepts from any canopy layer (i.e., any-hit cover) or only the first plant intercept at each point (i.e., top-hit cover) can result in discrepancies in cover estimates which are used to train remotely-sensed imagery. Our objective in this paper was to explore the theory of point-intercept sampling relative to training and testing remotely-sensed imagery, and to test the strength of relationships between top-hit and any-hit methods of calculating vegetation cover and high-resolution satellite imagery in two study areas managed by the Bureau of Land Management in northwestern Colorado and northeastern California. We modeled top-hit and any-hit percent cover for six vegetation indicators from 5m-resolution RapidEye imagery using beta regression. Model performance was judged using normalized root mean-squared error (RMSE) from a 5-fold cross validation. Any-hit cover estimates were significantly higher (α < 0.05) than top-hit cover estimates for forbs and grasses in the White River study area, but only marginally higher in Northern California. Pseudo-R² values for beta regression models of vegetation cover from RapidEye image information varied from 0.1525 to 0.7732 in White River and 0.2455 to 0.6085 in Northern California, with little pattern to whether any-hit or top-hit indicators produced better model fit. However, normalized RMSE was lower for any-hit cover (indicating better model performance) or minimally higher than top-hit cover for all indicators in each study area. Our results do not support the idea that top-hit cover estimates from point-intercept sampling are the most appropriate for remote sensing applications in arid and semi-arid shrub-steppe environments. In fact, having two sets of different indicators calculated from the same data may cause additional confusion in a situation where there is already considerable debate on how vegetation cover should be measured and used. Ultimately, selection of indicators to use for developing remote sensing classification or predictive models should be based first on the meaning or interpretation of the indicator in the ecosystem of interest, and second on how well the indicator performs in modeling applications.     

A method for studying vegetation dynamics when there are no obvious individuals: Virtual-population analysis applied to the tundra shrub Betula nana L.

A method is presented to study dynamics of plants that cannot be separated into individuals such as many grassland, salt marsh and tundra species. A virtual population is created by using a permanent transect line through the vegetation and individuals are defined as the branch segments distal to the intercept with the transect line. Addition and loss of individuals together with growth or shrinkage form the basis for constructing a size-structured transition matrix. A discrete-event simulation demonstrates that: 1) a virtual population of individuals grows at the same rate as the parent population; and, 2) size-structured transition matrices for a virtual population and parent vegetation have similar dominant and subdominant eigenvalues so a virtual population can be used to describe the dynamics of a parent vegetation.Dwarf birch, Betula nana L., was studied in the northern foothills of the Brooks Range, Alaska, by using photography to record branch intercepts along permanent transect lines. The distal branch segments constitute a virtual population of the parent vegetation. Transects were photographed in 1985 and again in 1986 and changes of branch segments were used to construct two transition matrices for shrubs with and without elevated fertilizer treatment. Analysis of the virtual populations suggests that although Betula nana may show increased branch growth with increased fertilizer, in the long run this shrub may decline in the tundra in response to such treatment.     

利用遥感技术实现作物模拟模型区域应用的研究进展

作物模拟模型从单点发展到区域应用时,模型中一些宏观资料的获取和参数的区域化方面出现困难,利用遥感技术将实现作物模拟模型的区域应用．文中综述了近年来遥感反演作物模型所需的地表生物物理参数的方法、利用遥感信息直接获取生物量的途径和遥感信息与作物模拟模型之间时空匹配问题等方面的研究概况,重点介绍了利用遥感技术实现作物模拟模型区域应用的3种解决方案(强迫型、调控型和验证型)及其研究进展,并讨论了目前存在的问题和今后研究的方向．     

Identifying Amsterdam's nutrient hotspots: A new method to map human excreta at building and neighborhood scale

Recovering nutrients from human excreta and wastewater has been receiving increasing attention as a means to supplement or replace synthetic fertilizer production. Apart from technologies for nutrient recovery at centralized wastewater treatment plants, numerous decentralized, source‐separated sanitation systems, also known as new sanitation systems, have been developed to facilitate recovery. Decision‐making for the planning and implementation of new sanitation systems would benefit from a spatially explicit inventory of nutrient hotspots in urban areas. To provide visual representations of nutrient loads, we developed a methodology that combines spatial‐temporal modeling with geographic information system analysis, and used it for the city of Amsterdam. The methodology is new in the field of nutrient mapping, especially at the smallest geographical scale: building. Nitrogen, phosphorus, and potassium loads and hotspots are mapped at both building and neighborhood scale, drawing attention to the need for multiple scale analyses in decision‐making. This study concludes with a discussion on the potential to further develop the method proposed to include more detailed and verified data and to identify nutrient hotspots that are promising as nutrient recovery sites with new sanitation systems.     

Genetic structure of an insect-pollinated and bird-dispersed tropical tree in vegetation fragments and corridors: implications for conservation

In the vegetation corridors that connect small remnants of undisturbed primary forest in the Lavras landscape (Brazil), Protium spruceanum is a representative of a mass-flowering insect-pollinated and bird-dispersed tree. Allozyme variation was quantified from five forest remnants (N = 150) from secondary vegetation corridors linking them (N = 80) to generate information for genetic conservation. The species adhered to H-W equilibrium in all fragments in most of the loci. The results indicated high gene diversity in the fragments and corridors positively correlated with the plant density (r = 0.742, R ² = 0.551, d.f. = 4). We did not find evidence of inbreeding within fragments nor overall The genetic differentiation among remnants was low Evidence of recent bottlenecks by anthropogenic disturbance was detected in fragments (P < 0.05, Wilcoxon sign-rank test). The minimal viable population was estimated for conservation in situ, indicating fragments with possibilities of maintaining genetic equilibrium diversity in the short term (except F3) and in the long term (only F5). The ratios was also calculated to contribute to vegetation enrichment, area recovery or creation of new vegetation corridors. We found high levels of gene diversity in the vegetation corridors, genetic identity with the fragments and absence of inbreeding. Thus, our results suggest that landscape management strategies should therefore consider both the creation of new vegetation corridors and the protection of extant ones.     

A 10-year study of changes in forest vegetation on Silhouette island, Seychelles

A 10 year study of forest communities on Silhouette island, Seychelles demonstrates stability of forest composition in most areas over this time-scale. Areas with heavy invasion by alien species were found to be regenerating, particularly with the rapid loss of Clidemia hirta. This is attributed to the abundance of well-adapted native plants allowing competitive exclusion to take place, throughout competition for light. It was noted that invasive plant species tend to be unstable on the rocky slopes covered by native high forest. A high rate of tree fall and limited seed dispersal may reduce the impact of the invasive tree Paraserianthes falcataria in the future. Other species such as Cinnamomum verum and Psidium cattleianum may persist as major invaders due to wider seed dispersal.