Potential Spatial Overlap of Heritage Sites and Protected Areas in a Boreal Region of Northern Canada

Abstract:  Under article 8-J of the Convention on Biological Diversity, governments must engage indigenous and local communities in the designation and management of protected areas. A better understanding of the relationship between community heritage sites and sites identified to protect conventional conservation features could inform conservation-planning exercises on indigenous lands. We examined the potential overlap between Gwich'in First Nations' (Northwest Territories, Canada) heritage sites and areas independently identified for the protection of conventional conservation targets. We designed nine hypothetical protected-area networks with different targets for woodland caribou ( Rangifer tarandus caribou ) habitat, high-quality wetland areas, representative vegetation types, water bodies, environmentally significant area, territorial parks, and network aggregation. We compared the spatial overlap of heritage sites to these nine protected-area networks. The degree of spatial overlap (Jaccard similarity) between heritage sites and the protected-area networks with moderate or high aggregation was significantly higher ( p < 0.001) than random spatial overlap, whereas the overlap between heritage sites and the protected-area networks with no aggregation was not significant or significantly lower ( p < 0.001) than random spatial overlap. Our results suggest that protected-area networks designed to capture conventional conservation features may protect key heritage sites but only if the underlying characteristics of these sites are considered. The Gwich'in heritage sites are highly aggregated and only protected-area networks that had moderate and high aggregation had significant overlap with the heritage sites. We suggest that conventional conservation plans incorporate heritage sites into their design criteria to complement conventional conservation targets and effectively protect indigenous heritage sites .     

Value of Semi-Open Corridors for Simultaneously Connecting Open and Wooded Habitats: a Case Study with Ground Beetles

Abstract:  To counteract habitat fragmentation, the connectivity of a landscape should be enhanced. Corridors are thought to facilitate movement between disconnected patches of habitat, and linear strips of habitat connecting isolated patches are a popular type of corridor. On the other hand, the creation of new corridors can lead to fragmentation of the surrounding habitat. For example, heathland corridors connect patches of heathland and alternatively hedgerows connect patches of woodland. Nevertheless, these corridors themselves also break up previously connected patches of their surrounding habitat and in so doing fragment another type of habitat (heathland corridors fragment woodlands and woodland strips or hedgerows fragment heathlands). To overcome this challenge we propose the use of semi-open habitats (a mixture of heathland and woodland vegetation) as conservation corridors to enable dispersal of both stenotopic heathland and woodland species. We used two semi-open corridors with a mosaic of heathland and woody vegetation to investigate the efficiency of semi-open corridors for species dispersal and to assess whether these corridors might be a suitable approach for nature conservation. We conducted a mark-recapture study on three stenotopic flightless carabid beetles of heathlands and woodlands and took an inventory of all the carabid species in two semi-open corridors. Both methodological approaches showed simultaneous immigration of woodland and heathland species in the semi-open corridor. Detrended correspondence analysis showed a clear separation of the given habitats and affirmed that semi-open corridors are a good strategy for connecting woodlands and heathlands. The best means of creating and preserving semi-open corridors is probably through extensive grazing .     

A spatially explicit model to predict future landscape composition of aspen woodlands under various management scenarios

Quaking aspen (Populus tremuloides) is declining across the western United States. Aspen habitats are among the most diverse plant communities in this region and loss of these habitats can result in shifts in biodiversity, productivity, and hydrology across a range of spatial scales. Western aspen occurs on the majority of sites seral to conifer species, and long-term maintenance of these aspen woodlands requires periodic fire. Over the past century, fire intervals, extents, and intensities have been insufficient to regenerate aspen stands at historic rates; however the effects of various fire regimes and management scenarios on aspen vegetation dynamics at broad spatial and temporal scales are unexplored. Here we use field data, remotely sensed data, and fire atlas information to develop a spatially explicit landscape simulation model to assess the effects of current and historic wildfire regimes and prescribed burning programs on landscape vegetation composition across two mountain ranges in the Owyhee Plateau, Idaho. Model outputs depict the future structural makeup and species composition of the landscape at selected time steps under simulated management scenarios. We found that under current fire regimes and in the absence of management activities, loss of seral aspen stands will continue to occur over the next two centuries. However, a return to historic fire regimes (burning 12–14% of the modeled landscape per decade) would maintain the majority of aspen stands in early and mid seral woodland stages and minimizes the loss of aspen. A fire rotation of 70–80 years was estimated for the historic fire regime while the current fire regime resulted in a fire rotation of 340–450 years, underscoring the fact that fire is currently lacking in the system. Implementation of prescribed burning programs, treating aspen and young conifer woodlands according to historic fire occurrence probabilities, are predicted to prevent conifer dominance and loss of aspen stands.     

Crustacean habitat potential mapping in a tidal flat using remote sensing and GIS

To make a macrofaunal (crustacean) habitat potential map, the spatial distribution of ecological variables in the Hwangdo tidal flat, Korea, was explored. Spatial variables were mapped using remote sensing and a geographic information system (GIS) combined with field observations. A frequency ratio (FR) and logistic regression (LR) model were employed to map the macrofauna potential area for the Ilyoplax dentimerosa, a crustacean species. Spatial variables affecting the tidal macrofauna distribution were selected based on abundance and biomass and used within a spatial database derived from remotely sensed data of various types of sensors. The spatial variables included the intertidal digital elevation model (DEM), slope, distance from a tidal channel, tidal channel density, surface sediment facies, spectral reflectance of the near infrared (NIR) bands and the tidal exposure duration. The relation between the I. dentimerosa and each spatial variable was calculated using the FR and LR. The species was randomly divided into a training set (70%) to analyse habitat potential using FR and LR and a test set (30%) to validate the predicted habitat potential map. The relations were overlaid to produce a habitat potential map with the species potential index (SPI) value for each pixel. The potential habitat maps were compared with the surveyed habitat locations such as validation data set. The comparison results showed that the LR model (accuracy is 85.28%) is better in prediction than the FR (accuracy is 78.96%) model. The performance of models gave satisfactory accuracies. The LR provides the quantitative influence of variables on a potential habitat of species; otherwise, the FR shows the quantitative influence of a class in each variable. The combination of a GIS-based frequency ratio and logistic regression models and remote sensing with field observations is an effective method to determine locations favorable for macrofaunal species occurrences in a tidal flat.     

Understanding the distribution of cattle production systems in the South American Chaco

ABSTRACT

Impacts of cattle production vary among different production systems, but data on their distribution is scarce for most world regions. In this work, we combine datasets on cattle vaccination locations and land cover in a regression framework to define and map major cattle production systems in the Argentinean Dry Chaco. We also explore how cattle occurrence relates to spatial determinants. Results indicate that the region harbors about 5.5 million heads. Cattle density was mainly described by the share of pasture (69.9%), cropland (28.1%) and aridity (23.8%). We identified 12-major cattle production systems: six cow-calf, three whole-cycle, and three fattening systems. Of these, four systems had high woodland cover (>85%). Data generated is available in a website. Understanding the distribution of cattle production systems is important to assess the environmental impacts of beef production at broad scales. Integrating vaccination data with land-cover information provides a promising avenue to identify livestock systems.     

Mapping "old" vs. "young" pi?on-juniper stands with a predictive topo-climatic model

Pi?on pine and juniper woodlands in the southwestern United States are often represented as an expanding and even invasive vegetation type, a legacy of historic grazing, and culpable in the degradation of western rangelands. A long-standing emphasis on forage production, in combination with recent hazard fuel concerns, has prompted a new era of woodland management with stated restoration objectives. Yet the extent and dynamics of pi?on-juniper communities that predate intensive Euro-American settlement activities are poorly known or understood, while the intrinsic ecological, aesthetic, and economic values of old-growth woodlands are often overlooked. Historical changes in pi?on-juniper stands include two related, but poorly differentiated processes: recent tree expansion into grass- or shrub-dominated (i.e., non-woodland) vegetation and thickening or infilling of savanna or mosaic woodlands predating settlement. Our work addresses the expansion pattern, modeling the occurrence of "older" savanna and woodland stands extant prior to 1850 in contrast to "younger" pi?on-juniper growth of more recent, postsettlement origin. We present criteria in the form of a diagnostic key for distinguishing "older," pre-Euro-American settlement pi?on-juniper from "younger" (post-1850) stands and report results of predictive modeling and mapping efforts within a north-central New Mexico study area. Selected models suggest a primary role for soil moisture in the current distribution of "old" vs. "young" pi?on-juniper stands. Presettlement era woodlands are shown to occupy a discrete ecological space, defined by the interaction of effective (seasonal) moisture with landform setting and fine-scale (soil/water) depositional patterns. "Older" stands are generally found at higher elevations or on skeletal soils in upland settings, while "younger" stands (often dominated by one-seed juniper, Juniperus monosperma) are most common at lower elevations or in productive, depositional settings. Modeling at broad regional scales can enhance our general understanding of pi?on-juniper ecology, while predictive mapping of local areas has potential to provide products useful for land management. Areas of the southwestern United States with strong monsoonal (summer moisture) patterns appear to have been the most susceptible to historical woodland expansion, but even here the great majority of extant pi?on-juniper has presettlement origins (although widely thickened and infilled historically), and old-growth structure is not uncommon in appropriate upland settings.     

Energy transition and its implications for environmentally sustainable development in Africa

SUMMARY

Energy transition is the process whereby there is an increase in the volume and proportion of commercial energy, to the extent that it replaces traditional fuels as the main source of energy and having enormous implications for the physical and biotic environment. This energy-environment process has rarely been the focus of research investigation in Africa. Using cross-national data drawn from the African continent, this paper examines and accounts for intercountry variations in the nature and extent of the energy transition process. The empirical analysis reveals that, for the continent as a whole, the extent to which commercial energy replaces traditional fuels is quite low. It varies between 33% and 39%. However, inter-country variations were found to be as high as 90% in countries such as Algeria, Egypt, Libya, Mauritania, Morocco and South Africa; and less than 15% for such countries as Benin, Burkina Faso, The Central African Republic, Ethiopia, Lesotho and Uganda. The key factors explaining intercounty variations in the energy transition process are the level of urbanization and the extent of forest and woodland resources. Other factors of secondary importance include economic growth, incidence of poverty, affordability of electrical appliances, energy trade status of the country in question and the price of commercial fuel. Finally, the paper shows that the identification of these key energy transition-inducing variables is a necessary prerequisite to an effective energy and environmentally sustainable development policy formulation in Africa.     

Ten years of contested enforcement of the Forest Law in Salta,Argentina. The role of land-change science and political ecology

ABSTRACT

In this study, we present a critical account of the enforcement of the Forest Law in the Province of Salta, Argentina. We discuss whether the objectives of this law were accomplished and we analyze the role that some technical tools, coupled with specific theoretical approaches, could play in its future enforcement. We illustrate our analysis with data from a case study in the Chaco region of this Province. We identified, mapped and analyzed land claims by indigenous communities and small-scale agricultural producers, and large-scale land acquisitions, and we discuss how these two variables could be used to improve the technical accuracy and the social legitimacy of the zoning map required by the Forest Law. We conclude that a balanced combination of land-change science methods and political ecology can be useful to improve the fairness of decision-making processes and the sustainability of social-environmental governance in agricultural frontiers.     

Changes in hydrology and salinity accompanying a century of agricultural conversion in Argentina

Conversions of natural woodlands to agriculture can alter the hydrologic balance, aquifer recharge, and salinity of soils and groundwater in ways that influence productivity and sustainable land use. Using a land-use change chronosequence in semiarid woodlands of Argentina's Espinal province, we examined the distribution of moisture and solutes and estimated recharge rates on adjacent plots of native woodlands and rain-fed agriculture converted 6-90 years previously. Soil coring and geoelectrical profiling confirmed the presence of spatially extensive salt accumulations in dry woodlands and pervasive salt losses in areas converted to agriculture. A 1.1-km-long electrical resistivity transect traversing woodland, 70-year-old agriculture, and woodland, for instance, revealed a low-resistivity (high-salinity) horizon between approximately 3 m and 13 m depth in the woodlands that was virtually absent in the agricultural site because of leaching. Nine-meter-deep soil profiles indicated a 53% increase in soil water storage after 30 or more years of cultivation. Conservative groundwater-recharge estimates based on chloride tracer methods in agricultural plots ranged from approximately 12 to 45 mm/yr, a substantial increase from the <1 mm/yr recharge in dry woodlands. The onset of deep soil moisture drainage and increased recharge led to >95% loss of sulfate and chloride ions from the shallow vadose zone in most agriculture plots. These losses correspond to over 100 Mg of sulfate and chloride salts potentially released to the region's groundwater aquifers through time with each hectare of deforestation, including a capacity to increase groundwater salinity to >4000 mg/L from these ions alone. Similarities between our findings and those of the dryland salinity problems of deforested woodlands in Australia suggest an important warning about the potential ecohydrological risks brought by the current wave of deforestation in the Espinal and other regions of South America and the world.     

The importance of incorporating functional habitats into conservation planning for highly mobile species in dynamic systems

The distribution of mobile species in dynamic systems can vary greatly over time and space. Estimating their population size and geographic range can be problematic and affect the accuracy of conservation assessments. Scarce data on mobile species and the resources they need can also limit the type of analytical approaches available to derive such estimates. We quantified change in availability and use of key ecological resources required for breeding for a critically endangered nomadic habitat specialist, the Swift Parrot (Lathamus discolor). We compared estimates of occupied habitat derived from dynamic presence‐background (i.e., presence‐only data) climatic models with estimates derived from dynamic occupancy models that included a direct measure of food availability. We then compared estimates that incorporate fine‐resolution spatial data on the availability of key ecological resources (i.e., functional habitats) with more common approaches that focus on broader climatic suitability or vegetation cover (due to the absence of fine‐resolution data). The occupancy models produced significantly (P < 0.001) smaller (up to an order of magnitude) and more spatially discrete estimates of the total occupied area than climate‐based models. The spatial location and extent of the total area occupied with the occupancy models was highly variable between years (131 and 1498 km²). Estimates accounting for the area of functional habitats were significantly smaller (2–58% [SD 16]) than estimates based only on the total area occupied. An increase or decrease in the area of one functional habitat (foraging or nesting) did not necessarily correspond to an increase or decrease in the other. Thus, an increase in the extent of occupied area may not equate to improved habitat quality or function. We argue these patterns are typical for mobile resource specialists but often go unnoticed because of limited data over relevant spatial and temporal scales and lack of spatial data on the availability of key resources. Understanding changes in the relative availability of functional habitats is crucial to informing conservation planning and accurately assessing extinction risk for mobile resource specialists.     

Are existing vegetation maps adequate to predict bird distributions?

Bird species are selective on the vegetation types in which they are found but predictive models of bird distribution based on variables derived from land-use/land-cover maps tend to have limited success. It has been suggested that accuracy of existing maps used to derive predictors is in part responsible for the limited success of bird distribution models. In two areas of 4900 km² of Western Andalusia, Spain, we compared the predictive ability of bird distribution models derived from two existing general-purpose land-use/land-cover maps, which differ in their resolution and accuracy: a coarse scale vegetation map of Europe, the CORINE land-cover map, and a detailed regional map, the 1995 land-use/land-cover map of Andalusia from the SINAMBA (Consejerı́a de Medio Ambiente, Junta de Andalucı́a). We compared the bird distribution models derived from these general-purpose vegetation maps with models derived from two more accurate structural vegetation maps built considering directly variables that influence bird habitat selection, one built from satellite images for this study and another obtained by improving the resolution and accuracy of the SINAMBA map with satellite data. We sampled the presence/absence of bird species at 857 points using 15-min point surveys. Predictive models for 54 bird species were built with generalised additive models (GAMs), using as potential predictors the same set of landscape and vegetation structure variables measured on each map. We compared for each bird species the predictive accuracy of the best model derived from each map. Vegetation structure measured at bird sample points was used as ground-truth for comparing the accuracy of vegetation maps. Although maps differed in their resolution and accuracy, the results show that all of them produced similarly accurate bird distribution models, with a mixed map produced with both thematic and satellite information being the best. The models derived from the more accurate vegetation structure maps obtained from satellite data were not more accurate than those derived directly from the SINAMBA or CORINE maps. Our results suggest that some general-purpose land-use/land-cover maps are accurate enough to derive bird distribution models. There is a certain limit to improve vegetation maps above which there is no effect in their power to predict bird distribution.     

Understanding Interaction Effects of Climate Change and Fire Management on Bird Distributions through Combined Process and Habitat Models

Abstract: Avian conservation efforts must account for changes in vegetation composition and structure associated with climate change. We modeled vegetation change and the probability of occurrence of birds to project changes in winter bird distributions associated with climate change and fire management in the northern Chihuahuan Desert (southwestern U.S.A.). We simulated vegetation change in a process‐based model (Landscape and Fire Simulator) in which anticipated climate change was associated with doubling of current atmospheric carbon dioxide over the next 50 years. We estimated the relative probability of bird occurrence on the basis of statistical models derived from field observations of birds and data on vegetation type, topography, and roads. We selected 3 focal species, Scaled Quail (Callipepla squamata), Loggerhead Shrike (Lanius ludovicianus), and Rock Wren (Salpinctes obsoletus), that had a range of probabilities of occurrence for our study area. Our simulations projected increases in relative probability of bird occurrence in shrubland and decreases in grassland and Yucca spp. and ocotillo (Fouquieria splendens) vegetation. Generally, the relative probability of occurrence of all 3 species was highest in shrubland because leaf‐area index values were lower in shrubland. This high probability of occurrence likely is related to the species’ use of open vegetation for foraging. Fire suppression had little effect on projected vegetation composition because as climate changed there was less fuel and burned area. Our results show that if future water limits on plant type are considered, models that incorporate spatial data may suggest how and where different species of birds may respond to vegetation changes.     

Modelling the spatial distribution of montane and subalpine forests in the central Alps using digital elevation models

The analysis of complex interactions between spatial distribution patterns of site factors and vegetation types is crucial for understanding high mountain ecosystems, especially in the view of a changing climate. Therefore, in the present study, a GIS and remote sensing-based approach is followed to produce a vegetation map for a study area in the Western Alps (Switzerland). Two major forest alliances are chosen for analysis: subalpine coniferous forest Vaccinio-Piceion/Larici-Pinetum cembrae and montane oak forest Quercion pubescenti-petraeae. As spatial information on site factors is commonly lacking in mountain areas, the use of a digital elevation model (DEM) is a potential substitute for use in vegetation analyses: it highly correlates with temperature, moisture, geomorphological processes and disturbance factors. Thus, it is important to analyse the capabilities of a DEM for indicating habitat conditions in a landscape characterised by high topodiversity and a patchwork of microclimatic habitats.For the purpose of identifying the potential of landform parameters for the indication of forest habitat structures in the present study, 24 primary and secondary landform parameters have been derived, indicating temperature and moisture distribution, exposure towards wind, snow, etc. Quantitative analyses were performed using statistical means such as contingency correlation coefficients and principal components analysis. The results formed the basis for the development of parallel-epiped-vegetation models (PED) used to simulate the spatial distribution patterns of the subalpine coniferous and the montane oak forest. It can be shown that topographic variables derived from a DEM at a spatial resolution of 25 m are very useful for indicating habitats of large forest types. Additionally potential forest sites in the cultural landscape, removed by human logging, can be reconstructed.Inaccuracies within the simulation results can partly be attributed to the insufficient parameterisation of geomorphologic activity and to poor spatial resolution of the DEM as compared to the vegetation data. Although the lack of information on the human dimension leads to some uncertainties in the interpretation of spatial patterns of vegetation, the exclusive use of topographic variables in vegetation models for the indication of forest habitats is very promising.     

Bird‐community responses to habitat creation in a long‐term,large‐scale natural experiment

Ecosystem function and resilience are compromised when habitats become fragmented due to land‐use change. This has led to national and international conservation strategies aimed at restoring habitat extent and improving functional connectivity (i.e., maintaining dispersal processes). However, biodiversity responses to landscape‐scale habitat creation and the relative importance of spatial and temporal scales are poorly understood, and there is disagreement over which conservation strategies should be prioritized. We used 160 years of historic post‐agricultural woodland creation as a natural experiment to evaluate biodiversity responses to habitat creation in a landscape context. Birds were surveyed in 101 secondary, broadleaf woodlands aged 10–160 years with ≥80% canopy cover and in landscapes with 0‐17% broadleaf woodland cover within 3000 m. We used piecewise structural equation modeling to examine the direct and indirect relationships between bird abundance and diversity, ecological continuity, patch characteristics, and landscape structure and quantified the relative conservation value of local and landscape scales for bird communities. Ecological continuity indirectly affected overall bird abundance and species richness through its effects on stand structure, but had a weaker influence (effect size near 0) on the abundance and diversity of species most closely associated with woodland habitats. This was probably because woodlands were rapidly colonized by woodland generalists in ≤10 years (minimum patch age) but were on average too young (median 50 years) to be colonized by woodland specialists. Local patch characteristics were relatively more important than landscape characteristics for bird communities. Based on our results, biodiversity responses to habitat creation depended on local‐ and landscape‐scale factors that interacted across time and space. We suggest that there is a need for further studies that focus on habitat creation in a landscape context and that knowledge gained from studies of habitat fragmentation and loss should be used to inform habitat creation with caution because the outcomes are not necessarily reciprocal.     

Spatial impacts of climate factors on regional agricultural and forestry biomass resources in north-eastern province of China

The dynamics of agricultural and forestry biomass are highly sensitive to climate change, particularly in high latitude regions. Heilongjiang Province was selected as research area in North-east China. We explored the trend of regional climate warming and distribution feature of biomass resources, and then analyzed on the spatial relationship between climate factors and biomass resources. Net primary productivity (NPP) is one of the key indicators of vegetation productivity, and was simulated as base data to calculate the distribution of agricultural and forestry biomass. The results show that temperatures rose by up to 0.37°C/10a from 1961 to 2013. Spatially, the variation of agricultural biomass per unit area changed from -1.93 to 5.85 t·km^–2·a^–1 during 2000–2013. More than 85% of farmland areas showed a positive relationship between agricultural biomass and precipitation. The results suggest that precipitation exerts an overwhelming climate influence on agricultural biomass. The mean density of forestry biomass varied from 10 to 30 t·km^–2. Temperature had a significant negative effect on forestry biomass in Lesser Khingan and northern Changbai Mountain, because increased temperature leads to decreased Rubisco activity and increased respiration in these areas. Precipitation had a significant positive relationship with forestry biomass in south-western Changbai Mountain, because this area had a warmer climate and stress from insufficient precipitation may induce xylem cavitation. Understanding the effects of climate factors on regional biomass resources is of great significance in improving environmental management and promoting sustainable development of further biomass resource use.

Open image in new window

     

The role of social learning for soil conservation: the case of Amba Zuria land management,Ethiopia

Social learning plays key roles in sustainable natural resource management; however, studies on its role show mixed results. Even though most current studies highlight positive outcomes, there are also negative effects of social learning with respect to natural resource management. This paper explores the influence of social learning outcomes on the adoption of soil conservation practices in Amba Zuria, Ethiopia. Data were collected through semi-structured interviews, group discussions and in workshops. The interviews were transcribed and analysed with the qualitative data analysis software ATLAS.ti. In addition, a review of pertinent documents and literature complements the analysis. We found that social learning results in positive outcomes in interactions among the actors, broader understanding on soil conservation, trust and mutual understanding, and the creation of opportunities to apply both indigenous and scientific knowledge. These outcomes, in turn, foster the adoption of stone terraces to conserve soils. No such positive results were found for farmers who were not involved in the learning process and who did not adopt stone terraces. The non-adoption can partly be explained by their exclusion from sharing the positive outcomes of social learning. The study also shows limitations related to the short duration of the learning platforms, insufficient representation of women and irregular patterns of learning schedules. Hence, Ethiopian soil conservation strategies should put emphasis on social learning in order to strengthen the collective processes of soil conservation measures.     

Forest cover dynamics in the Selva Maya of Central and Southern Quintana Roo,Mexico: deforestation or degradation?

ABSTRACT

Forest cover dynamics (1993-2018) was assessed in two regions on the Yucatan Peninsula: Zona Maya (ZM), 67% indigenous with shifting cultivation and community forestry; and Bacalar–Rio Hondo (BRH), mainly commercial agriculture and pastureland. Degradation (12,915 ha y^?1) exceeded deforestation (5882 ha y^?1) and was worse in BRH. In BRH there was a net forest loss (?1.6% y^?1) associated with pastureland and commercial agriculture. In ZM, mature forest recovery (1.4% y^?1) and dynamic forest cover (continuous loss and gain) were associated with shifting cultivation. Changes were more intense during 2011–2018 and gains of mature forest in ZM and deforested areas in BRH targeted secondary vegetation. Fragments of mature and secondary vegetation decreased, and connectivity improved in ZM, but opposite trends occurred in BRH. Reporting and monitoring deforestation using Global Forest Watch data is inadequate since 62% of forest cover loss represent degrading or recovering forest cover.     

红壤丘陵区LAI与土壤侵蚀分布特征的关系

叶面积指数(LAI)是常用的一个用于描述植被覆盖的方面指数,土壤侵蚀的分布又与植被的覆盖状况息息相关,这就意味着LAI与土壤侵蚀有一定的相关性,目前有关这二者的相关性研究还鲜有文献报道。基于这此,本研究首先利用2000年的遥感影像(TM)解释出该年度的土壤侵蚀强度图,再利用该遥感影像通过图像的代数运算得出该地区的NDVI栅格图,通过实测该县不同典型植被条件的LAI值,得出实测的LAI与图像NDVI值之间的函数关系式,由图像的代数运算把NDVI图转换成LAI图,即实现了遥感图像的实测LAI纠正。在GIS软件的帮助下,通过将LAI栅格图与土壤侵蚀强度图的空间叠加分析,得到不同LAI条件下的土壤侵蚀分布。结果表明,LAI与土壤侵蚀的分布表现为:大致以LAI=2为分界线,当LAI<2时,土壤侵蚀并未随LAI的增加而迅速减少,LAI>2时,土壤侵蚀的分布随植被指数的增加而减少,当LAI=2左右时,土壤侵蚀的面积最大。这种情况对于轻度、中度及强度土壤侵蚀的影响是类似的,都呈类正态分布的曲线形式,但在曲线的两侧土壤侵蚀类型是有本质区别的,在曲线的左侧土壤侵蚀类型的分布是中度和强度为主,而在曲线右侧则以轻度为主。表明LAI这个指标与土壤侵蚀有很好的相关性,可以用于土壤侵蚀方面的相关研究工作。     

Assessment of soil salinisation in the Ejina Oasis located in the lower reaches of Heihe River,Northwestern China

Recognition of the spatial-temporal distribution characteristics of soil salinity has become an important basis for the formulation of strategies required in the utilisation and sustainable development of soil resources in arid and semi-arid area. In this paper, based on vegetation cover dataset during 1998–2015 in Ejina region combined with the collected soil salinity data, geostatistical methods were used to explore the temporal and spatial dynamic characteristics of soil salinity and its impact on vegetation in the study area. The results showed significant differences in soil salinisation characteristics with a large variability in the soil salinity among the different soil depths, with a variation coefficient ranging from about 0.97–1.47. Soils are represented by a continuous variation, both in space and time. Soil salinity showed an obvious spatial autocorrelation, with a plaque type distribution. The areas of the salinised soil found for the years 2003, 2011 and 2015 were approximately 18,565, 23,206 and 17,721?km², respectively. From the relationships deduced between the normalised difference vegetation index (NDVI) and soil moisture and salt content in different soil depths, the present study ascertains that the soil moisture content is the most important limiting factor of vegetation growth in Ejina Oasis.