Natural Vegetation Changes Research Articles

Time-dependent change of natural vegetation on forest road fill slopes and its effects on erosion decrease

Time-dependent change of natural vegetation on forest road fill slopes and its effects on erosion decrease

Unveiling the impact of traditional land practices on natural vegetation using large-scale exclosures: National borders and military bases

Attributing the extent of changes in vegetation cover which are the result of human actions or of climate variability is challenging. The Negev Desert, bordered by two countries and the Palestinian Authority and crossing three climate zones, provides a natural laboratory for unveiling the impact of land practices on natural vegetation. Desert vegetation on both sides of the border was traditionally subject to herds grazing and bush gathering, but in recent decades; grazing policy, military training areas, and nature protection have excluded traditional uses. We used remotely sensed derived proxies of vegetation (the Normalized Difference Vegetation Index) and surface albedo from satellite images inside and outside of the large exclosures to estimate the anthropogenic impact on vegetation cover in the past four decades, and ultimately isolate the effect of traditional land uses on vegetation cover. Our results showed that the cross-border differences in land use led to a significant impact on vegetation cover outside the exclosed areas. These cross-border differences were more pronounced in the semi-arid - arid climate regions and decreased in the hyper-arid climate region. Exclosures provide a natural experiment which enables us the testing of the factors driving changes in natural vegetation.

One-Step High-Quality NDVI Time-Series Reconstruction by Joint Modeling of Gradual Vegetation Change and Negatively Biased Atmospheric Contamination

The normalized difference vegetation index (NDVI) can reflect the plant life cycle of growth and senescence and has become a widely used tool for many applications related to phenology, ecology, and environment. However, unwanted disturbance from cloud, snow, and other atmospheric effects greatly lowers the NDVI quality and hinders its further application. In this article, differing from the previous research attempting to approach the upper NDVI envelope by local adjustment or threshold-related iteration, a novel one-step global variational reconstruction (OGVR) method for NDVI time series is proposed via joint modeling of the gradual vegetation change and negatively biased atmospheric contamination. Two versions of the proposed method are designed for processing NDVI data with or without auxiliary flag information. Long-term and global-scale Advanced Very High Resolution Radiometer (AVHRR) global inventory monitoring and modeling system (GIMMS) data were applied in simulated and real-data experiments to verify the proposed method. The results show that the proposed method can successfully estimate the natural vegetation change from seriously contaminated NDVI time series and can conquer the problem of continuous low-value gaps. The qualitative and quantitative comparisons with five other widely used methods indicate that the proposed method has significant advantages in terms of both effectiveness and stability.

Slowdown of the greening trend in natural vegetation with further rise in atmospheric CO<sub>2</sub>

Abstract. Satellite data reveal widespread changes in Earth's vegetation cover. Regions intensively attended to by humans are mostly greening due to land management. Natural vegetation, on the other hand, is exhibiting patterns of both greening and browning in all continents. Factors linked to anthropogenic carbon emissions, such as CO2 fertilization, climate change, and consequent disturbances such as fires and droughts, are hypothesized to be key drivers of changes in natural vegetation. A rigorous regional attribution at the biome level that can be scaled to a global picture of what is behind the observed changes is currently lacking. Here we analyze different datasets of decades-long satellite observations of global leaf area index (LAI, 1981–2017) as well as other proxies for vegetation changes and identify several clusters of significant long-term changes. Using process-based model simulations (Earth system and land surface models), we disentangle the effects of anthropogenic carbon emissions on LAI in a probabilistic setting applying causal counterfactual theory. The analysis prominently indicates the effects of climate change on many biomes – warming in northern ecosystems (greening) and rainfall anomalies in tropical biomes (browning). The probabilistic attribution method clearly identifies the CO2 fertilization effect as the dominant driver in only two biomes, the temperate forests and cool grasslands, challenging the view of a dominant global-scale effect. Altogether, our analysis reveals a slowing down of greening and strengthening of browning trends, particularly in the last 2 decades. Most models substantially underestimate the emerging vegetation browning, especially in the tropical rainforests. Leaf area loss in these productive ecosystems could be an early indicator of a slowdown in the terrestrial carbon sink. Models need to account for this effect to realize plausible climate projections of the 21st century.

Türkiye’de Çevre Sorunları Başlığı Altında Hazırlanmış Kayıtlı Yüksek Lisanas ve Doktora Tezlerinin Bibliyometrik İncelenmesi

Countries in the world have begun to pay more attention to environmental problems in recent years. Because these problems have threatened human life in every aspect and without limit. Climate changes, rising temperatures, melting of glaciers, and the change of natural vegetation are among the threatening environmental issues and many countries act together in the international area on these issues. Protection of ecological balance and natural life, use of renewable energy sources, recycling of wastes, environmentally friendly production methods are strong solutions to be brought to environmental problems. In addition, original academic studies should be conducted to bring solution to the these issues. In this context, bibliometric studies, which is one of the most important reference sources of science policies, come to the fore. In these studies, publications produced by individuals or institutions are analyzed after determining their subject, period and region. In this context, the main purpose of this study is to investigate the master and doctorate theses registered under the title of environment problems in the Thesis Center of the Council of Higher Education between 1978-2018 in line with various parameters by using bibliometric analysis technique. In accordance with this purpose, environmental problems were written in the search section of the web page of the Thesis Center of the Higher Education Council and the master's and doctorate theses were analyzed in detail. 214 master's and doctoral theses have written under the title of urbanization in Turkey by the end of 2018. 36 of these theses are doctoral theses and 178 of them are master's theses. In the scope of the subject, bibliometric studies can be performed on topics such as environment, environmental policy and environmental law in the following years except for the title of environmental problems. In addition, in these subjects comparisons between countries, branches of science and public and private sectors producing publications will be useful for contributing to the literature.

Assessing multidimensional sustainability: Lessons from Brazil’s social protection programs

Examining linkages among multiple sustainable development outcomes is key for understanding sustainability transitions. Yet rigorous evidence on social and environmental outcomes of sustainable development policies remains scarce. We conduct a national-level analysis of Brazil's flagship social protection program, Zero Hunger (ZH), which aims to reduce food insecurity and poverty. Using data from rural municipalities across Brazil and quasi-experimental causal inference techniques, we assess relationships between social protection investment and outcomes related to sustainable development goals (SDGs): "no poverty" (SDG 1), "zero hunger" (SDG 2), and "health and well being" (SDG 3). We also assess potential perverse outcomes arising from agricultural development impacting "climate action" (SDG 13) and "life on land" (SDG 15) via clearance of natural vegetation. Despite increasing daily per capita protein and kilocalorie production, summed ZH investment did not alleviate child malnutrition or infant mortality and negligibly influenced multidimensional poverty. Higher investment increased natural vegetation cover in some biomes but increased losses in the Cerrado and especially the Pampa. Effects varied substantially across subprograms. Conditional cash transfer (Bolsa Familia [BF]) was mainly associated with nonbeneficial impacts but increased protein production and improved educational participation in some states. The National Program to Strengthen Family Farming (PRONAF) was typically associated with increased food production (protein and calories), multidimensional poverty alleviation, and changes in natural vegetation. Our results inform policy development by highlighting successful elements of Brazil's ZH program, variable outcomes across divergent food security dimensions, and synergies and trade-offs between sustainable development goals, including environmental protection.

Land Use / Land Cover Change And Impact On Carbon Stocks In The Atacora Chain Of Mountains, A Biodiversity Hotspot In Benin (West Africa)

Mountain areas are fragile ecosystems that play important roles in people’s livelihoods and maintenance of the global ecosystem through the provision of many ecosystem services. Land use/cover (LULC) change is considered one of the major threats to mountain areas due to its effects on ecosystem services including carbon stocks. In this study we assessed LULC change between 1987 and 2015 and its impact on aboveground carbon stocks in the Atacora Chain of Mountains (ACM) in Benin, West Africa. Supervised classification was performed to delineate LULC classes on three dates (1987, 2001 and 2015), and forest measurements carried out in the land cover classes, to estimate the aboveground biomass and the subsequent carbon stocks. Seven land cover classes were delineated: gallery forests, woodlands, savanna, water, settlements, bare lands and farm lands. LULC changes were characterized by three transitions: 1) the change of man-made land cover into savanna, 2) the change of natural vegetation into man-made land cover and 3) the degradation of gallery forests and woodland into less wooded vegetation. The aboveground carbon stock in gallery forests, woodland and tree savanna were significantly greater than in shrub savanna. During the 28 years of assessment, LULC change in gallery forests, woodland and savanna caused an estimated overall aboveground carbon release of 17.10% in the ACM. From the aboveground carbon quantity in the ACM, it appeared that this ecosystem is a potential carbon reservoir. Because the aboveground carbon stock in shrub savanna is significantly lower as compared to gallery forests, woodland and tree savanna and the rates of degradation from gallery forests and woodland to savanna are high, 53.62% and 59.99% respectively in 28 years, LULC change may undermine the ACM ability to store carbon and contribute to climate change mitigation. There is a need to investigate the drivers of this degradation for actions to preserve the natural vegetation in the ACM. Keywords: Atacora Chain of Mountains; Land use/land cover (LULC); Benin; West Africa; Carbon stock DOI: 10.7176/JEES/10-6-13 Publication date: June 30 th 2020

Human-induced fire regime shifts during 19th century industrialization: A robust fire regime reconstruction using northern Polish lake sediments.

Fire regime shifts are driven by climate and natural vegetation changes, but can be strongly affected by human land management. Yet, it is poorly known how humans have influenced fire regimes prior to active wildfire suppression. Among the last 250 years, the human contribution to the global increase in fire occurrence during the mid-19th century is especially unclear, as data sources are limited. Here, we test the extent to which forest management has driven fire regime shifts in a temperate forest landscape. We combine multiple fire proxies (macroscopic charcoal and fire-related biomarkers) derived from highly resolved lake sediments (i.e., 3–5 years per sample), and apply a new statistical approach to classify source area- and temperature-specific fire regimes (biomass burnt, fire episodes). We compare these records with independent climate and vegetation reconstructions. We find two prominent fire regime shifts during the 19th and 20th centuries, driven by an adaptive socio-ecological cycle in human forest management. Although individual fire episodes were triggered mainly by arson (as described in historical documents) during dry summers, the biomass burnt increased unintentionally during the mid-19th century due to the plantation of flammable, fast-growing pine tree monocultures needed for industrialization. State forest management reacted with active fire management and suppression during the 20th century. However, pine cover has been increasing since the 1990s and climate projections predict increasingly dry conditions, suggesting a renewed need for adaptations to reduce the increasing fire risk.

Bird species diversity in Altai riparian landscapes: Wood cover plays a key role for avian abundance.

AimsWe aim to understand bird richness and variation in species composition (beta diversity) along a 630 km riparian landscape in the Altai Mountains of China and to test whether vegetation cover is the main explanation of species diversity.MethodsWe selected nine regions along a gradient of natural vegetation change. Bird surveys and environmental measurements were conducted at 10 points in each of the nine regions. We collected environmental land cover variables such as wood cover (area proportion of trees and shrubs with saplings in habitats; here trees are woody plant with a single trunk and higher than 3 m, shrubs and saplings are distinguished from trees by their multiple trunks and shorter height) and tree cover, and two climate factors which were Annual Mean Temperature (AMT) and Annual Precipitation (AP). We used Liner Regression Models to explore the correlation between bird species richness and environmental variables. We used Sørensen's dissimilarity index to measure birds' beta diversity, and quantified the contribution of environmental variables to this pattern using a Canonical Correspondence Analysis (CCA).ResultsWood cover was the strongest predictor of overall, insectivore, and omnivore bird richness. Regions with wood cover contained more bird species. Beta diversity was overall high in the studied regions, and turnover components occupied a major part of beta diversity. Wood cover and AP were significant predictors of bird species composition explaining 33.24% of bird beta diversity together.ConclusionsWood vegetation including trees, shrubs, and saplings, rather than only trees, contains high bird richness. High beta diversity suggests that expansion of the existing nature reserves is needed in the riparian landscapes to capture the variation in bird species composition. Thus all wood cover in the overall riparian landscapes of Altai Mountains should be protected from farming and grazing to improve bird conservation outcomes.OPEN RESEARCH BADGES This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available at Raw bird data in this study: osf.io/78qcw; Raw environment data: osf.io/qr5cw.

Thresholds in forest bird communities along woody vegetation gradients in the South American Dry Chaco

Abstract World‐wide, tropical savannas and dry forests are under increasing pressure from land use. The environmental impacts of agricultural expansion into these ecosystems have received much attention, yet subtler changes in natural vegetation remain severely understudied. We explored how bird communities vary along gradients of woody vegetation in the South American Dry Chaco by combining high‐resolution, satellite‐based tree, shrub and total woody cover with field data on the frequency of 82 bird species surveyed in 167 plots. We identified change points along woody cover gradients where the relative frequency of individual bird species dropped most strongly. Based on this, we identified forest indicator species and assessed evidence for community‐level thresholds. Most forest birds (71%) had clear change points in their frequencies along vegetation gradients, starting as high as 38% total woody cover. Many (41%) forest species declined drastically at woody cover levels of less than 11%. This general pattern was similar for tree and shrub cover. Only 7% of our study area had woody cover levels where we detected no response in forest bird communities. In contrast, 68% of the area had woody cover levels with incremental declines in forest bird species, and 25% of the study area had woody cover levels below the forest bird community threshold. We identified 11 indicator species strongly related to woody cover, with highest frequencies in the eastern and western Dry Chaco. Spatial distributions of these species corresponded well with areas above and below woody vegetation thresholds. Synthesis and applications. We found evidence for critical thresholds for forest birds along woody cover gradients in dry forests and implemented tools to map where these thresholds have been crossed. For the Chaco, we highlight the importance of maintaining woody cover levels above about 40%, such as in certain silvopastoral systems that can be much more wildlife‐friendly than other forms of agriculture. We identify remaining areas of potentially intact forest bird communities. More broadly, this study highlights the value of combining species‐level (indicator species' distributions) and ecosystem‐level (satellite‐based, continuous woody cover maps) surrogates for understanding biodiversity patterns and threats.

Simulating sediment supply from the Congo watershed over the last 155 ka

The Congo River is the world's second largest river in terms of drainage area and water discharge. Monitored for decades, a large dataset is available, onshore for both the hydrology and sediment load, and offshore by many paleo-environmental proxies compiled at the Late-Quaternary time-scale. These numerous data allow for accurate calibration of numerical modeling. In this study, we aim to numerically quantify the evolution of sediment supply leaving the tropical Congo watershed during the last 155 ka and to decipher the forcing parameters that control this sediment supply over glacial/interglacial stages. For this, a modified version of the model HydroTrend, that besides morphologic, climatic, hydrologic, lithologic, land cover and anthropogenic factors now also considers sediment deposition on the floodplain, is used. In addition, a method to quantify the impact of natural vegetation changes is developed.Simulations match well the present-day observed data. They indicate that a significant portion of suspended sediments is trapped on the floodplain. Long-term simulations indicate that environmental changes between glacial and interglacial stages account for a 30% maximum variation of sediment supply. Climatic changes - precipitation and temperature, account for a maximum decrease in sediment supply of 20% during cold periods while conversely, induced land cover changes (loss of forest during colder and dryer stages) lead to enhanced sediment supply up to 30%. Over a longer period, the average sediment supply remained almost constant during glacial and interglacial periods, while peaks may have occurred during a warming period, just before forests had time to recover the catchment, i.e. during post-glacial periods. These moderate changes in sediment export, despite major changes in climate and vegetation cover, can be explained by the efficiency of sediment trapping of large tropical catchments that buffer fluvial fluxes towards the ocean.

Differentiating vegetation types from eastern South American ecosystems based on modern and subfossil pollen samples: evaluating modern analogues

In south and southeast Brazil land use caused profound changes in natural vegetation and consequently the value of the pollen composition in surface samples as modern analogues. In order to test the capability of modern pollen to represent the natural vegetation, three different time slices of pollen assemblages from 27 sites spread over southern and south-eastern Brazil and the Misiones Province in Argentina were collated. Pollen samples from the pre-colonization period, selected from the moment just before abrupt changes evidenced on pollen diagrams caused by the colonization process throughout the last 500 years, were assumed to represent the natural vegetation conditions once the climate remained stable within this period. Thus we used pre-colonization assemblages to compare with modern samples to explore to what extent surface pollen may be biased in representing the natural vegetation types. Furthermore, to compare man made vegetation change to climate driven vegetation change we also compared to these 20 out of 27 samples dated to 3,000 years bp. Guided by ordination and cluster analysis, but using abundance thresholds of indicator taxa we classified the pollen spectra of pre-colonization time into seven groups consistent with the main vegetation types in the area. Ordination analyses capture the differentiation between grassland and forested vegetation and between tropical and subtropical vegetation types. Comparing the pre-colonization with other time slices we observed that based on Poaceae abundance, 70 and 85 % respectively of sites from 3,000 bp and modern assemblages maintained their classification. Based on finer classification criteria these values decreased to 40 and 52 % respectively. Square chord dissimilarity indicates that colonization impact altered the pollen composition as strongly as 3,000 years of climate induced vegetation change. The surface samples still represent important environmental gradients; however, their use as modern analogue requires careful treatment and eventual exclusion of highly impacted sites.

River connectivity and road crossing effects on floodplain vegetation of the upper Columbia River, Canada

ABSTRACTFloodplain wetlands in the upper Columbia River valley are governed by the flood pulse. Water flows from the river into adjacent wetlands through channels incised through levees or over the top of the levees. This floodplain is relatively pristine with few road crossings restricting the flow of water in a 110 km length of the floodplain. We describe the floodplain vegetation at three points over 60 years to detect natural vegetation changes and contrast that with changes downstream of roads transecting the wetlands. We mapped eight landscape cover types within 40 floodbasins and four 2 km sections downstream of road crossings at three dates, over 60 years, using historical aerial photographs. Over 60 years the area of open water increased by 77% within the wetlands, and there was a decrease of 14.5% and 40% of marsh and shrub vegetation, respectively. During this time, floodbasins became more connected to the river. We observed greater change within the natural wetlands than in sections downstream of the road crossings. Since floodplain ecosystems are inherently complex due to their highly dynamic nature, isolating specific causes of trends is difficult. However, large-scale loss of vegetation and increase in open water has dramatically changed the wetlands.

The mutual importance of anthropogenically and climate‐induced changes in global vegetation cover for future land carbon emissions in the MPI‐ESM CMIP5 simulations

AbstractBased on the Max Planck Institute Earth System Model simulations for the Coupled Model Intercomparison Project Phase 5 and on simulations with the submodel Cbalone we disentangle the influence of natural and anthropogenic vegetation changes on land carbon emissions for the years 1850 until 2300. According to our simulations, climate‐induced changes in distribution and productivity of natural vegetation strongly mitigates future carbon (C) emissions from anthropogenic land‐use and land cover change (LULCC). Depending on the assumed scenario, the accumulated carbon emissions until the year 2100 are reduced between 22 and 49% and until 2300 between 45 and 261%. The carbon storage due to climate‐induced vegetation change is generally stronger under the presence of LULCC. This is because the natural vegetation change can reestablish highly productive extratropical forests that are lost due to LULCC. After stopping anthropogenic vegetation changes in the year 2100 the refilling of depleted C pools on formerly transformed land takes (dependent on the scenario) time scales of centuries.

Analysis of the changes in vegetation of the Sapanca Lake Basin (in Turkey) using multitemporal satellite data

<p>The Lake Sapanca Basin is located in an area where urbanization and industrialization is rapidly increasing because of its geographical location. The Sapanca Lake Basin was opened to settlement densely after 1980 due to recreational activities for urbanization and industrialization. The aim of this study is to investigate and evaluate the changes in natural vegetation and settlement caused by the effects of human activities in the Sapanca Lake Basin. For this purpose, Landsat 5 TM (1987) and Landsat 8 (2013) satellite images have been used. These images have been analyzed using ERDAS and ArcGIS software’s and this was supported and confirmed by the carried land studies. The results showed that there has been an % 12.8 decrease in the high density green vegetation areas. It is concluded that the natural vegetation of Sapanca Lake Basin damaged rapidly in the period between the years of 1987-2013.</p>

Study of Landcover Change in Yelwa-Heipang Area of Plateau State, North-Central Nigeria: A Geoinformatics Approach

Abstract. This study is a research programme carried out to detect the change in land use/land cover of Yelwa-Heipang area of Plateau State, North Central Nigeria. It lies within the South-Eastern part of the Jos-Plateau. It is about 40 km South of Jos city. It is located between latitude 9°35'16.65" N, longitude 8°52'29.91" E and Latitude 9°38'38.92" N, longitude 8°57'03.87" E (Naraguta topomap, sheet 168S.E). Two sets of Landsat images of 1975, 1986 and NigeriaSat-X image of 2012 were subjected to various image processing techniques and a supervised classification was carried out on the various images using ILWIS (Integrated land and water information system) software. The classification scheme used are bare-surface, built-up, farmland and vegetation. A follow up field work was carried out to confirm the results of the classification. The results were subjected to various statistical analyses and it shows natural vegetated area coverage increased from 5.80 sqkm in 1975 to 18.47 sqkm in 1986 and later reduced to 16.85 sqkm in 2012. Non-vegetated area which comprised built-up area, farmlands and bare surface, decreased from 42.2 sqkm in 1975 to 33.82 sqkm in 1986, then to 35.86 sqkm in 2012.The rate of change of natural vegetation between 1975 and 1986 was 1.152 sqkm per annum, while that of 1986 and 2012 was 0.108 sqkm per annum. Loss of naturally vegetated area in Yelwa-Heipang Barkin-Ladi is mainly as a result of urban growth and expansion, farming and gully erosion. Another important issue in the study area is the problem of soil erosion. In the past mining activity had led to accelerated gully erosion which has stripped substantial areas of lands of their vegetations. This has led to the formation of bare surface. Land cover of the study area during the period between 1975 and 2012 changed from a forested area to other land uses as a result of increase in population, demand for land for agricultural purposes and increase in the demand for firewood.

Monitoring of Vegetation Dynamics in the Mongolia Using MODIS NDVIs and their Relationship to Rainfall by Natural Zone

Vegetation plays a very important role conserving the natural environment and improving the living environment for humans. Thus, investigating spatio-temporal changes in vegetation is a crucial indicator to understand natural environmental changes. We explored the spatio-temporal trends of changing vegetation cover in Mongolia from 2002 to 2010 by investigating changes in the normalized difference vegetation index (NDVI) with rainfall. The 16-day composite NDVI time series Terra MODIS (MOD13A2) and the gridded rainfall data of the Inter-governmental Panel on Climate Change (IPCC) were used to identify the relationship between vegetation dynamics and rainfall. Residual NDVI trends were computed. Following our general procedure, monthly NDVI and annual rainfall were correlated for each pixel. The resulting regression equation represented the statistical association between observed NDVI and rainfall, and the model predicted NDVI according to rainfall. Residuals of NDVI (differences between the observed and predicted NDVI) for each pixel were calculated, and the trends in these residuals was analyzed by linear regression. From the 12 months NDVI and rainfall values they determine a linear regression line for each pixel. The positive or negative slope of this line is considered to reflect an increase or decrease in green biomass. Our results show that vegetation cover changes in Mongolia were caused by both natural factors and human activities. The natural vegetation change, such as those in forests was influenced by climate change, whereas human activities were the main reason for the change in vegetation planted.

Large-Scale Water Productivity Assessments with MODIS Images in a Changing Semi-Arid Environment: A Brazilian Case Study

In the Brazilian semi-arid region, the intensification of agriculture results in a change of natural vegetation by irrigated crops. To quantify the contrast between these two ecosystems, the large-scale values of water productivity components were modelled in Petrolina (PE) and Juazeiro (BA) municipalities. The SAFER (Simple Algorithm For Evapotranspiration Retrieving) algorithm was used to acquire evapotranspiration (ET), while the Monteith's radiation model was applied for estimating the biomass production (BIO). Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images were used together with agro-meteorological data. In Petrolina and Juazeiro, the mean monthly ET values for irrigated crops were 938 and 739 mm∙month−1, with the corresponding ones for natural vegetation of 385 and 194 mm∙month−1.Water productivity (WP) was analysed by the ratio of BIO to ET, defined here as the ratio of the net benefits from the mixed agricultural systems to the amount of water required for producing those benefits. The highest incremental WP values, as a result of the irrigated crops introduction, happened outside the rainy period. More spatial WP uniformity occurred in natural vegetation, when comparing with irrigated crops. The most frequent WP values in Petrolina were between 1.6 and 2.2 kg∙m−3 while in Juazeiro this range was from 1.0 to 1.6 kg∙m−3. The differences between the municipalities can be mainly explained by differences in precipitation and soil water storages conditions, promoting better rainfall use efficiency by the natural vegetation in the first one. The results of the current research are important for appraising the land use change impacts in situations of expanding irrigation areas.

Disease risk in temperate amphibian populations is higher at closed-canopy sites.

Habitat loss and chytridiomycosis (a disease caused by the chytrid fungus Batrachochytrium dendrobatidis - Bd) are major drivers of amphibian declines worldwide. Habitat loss regulates host-pathogen interactions by altering biotic and abiotic factors directly linked to both host and pathogen fitness. Therefore, studies investigating the links between natural vegetation and chytridiomycosis require integrative approaches to control for the multitude of possible interactions of biological and environmental variables in spatial epidemiology. In this study, we quantified Bd infection dynamics across a gradient of natural vegetation and microclimates, looking for causal associations between vegetation cover, multiple microclimatic variables, and pathogen prevalence and infection intensity. To minimize the effects of host diversity in our analyses, we sampled amphibian populations in the Adirondack Mountains of New York State, a region with relatively high single-host dominance. We sampled permanent ponds for anurans, focusing on populations of the habitat generalist frog Lithobates clamitans, and recorded various biotic and abiotic factors that potentially affect host-pathogen interactions: natural vegetation, canopy density, water temperature, and host population and community attributes. We screened for important explanatory variables of Bd infections and used path analyses to statistically test for the strength of cascading effects linking vegetation cover, microclimate, and Bd parameters. We found that canopy density, natural vegetation, and daily average water temperature were the best predictors of Bd. High canopy density resulted in lower water temperature, which in turn predicted higher Bd prevalence and infection intensity. Our results confirm that microclimatic shifts arising from changes in natural vegetation play an important role in Bd spatial epidemiology, with areas of closed canopy favoring Bd. Given increasing rates of anthropogenic habitat modification and the resulting declines in temperate and tropical frogs, understanding how vegetation cover and disease interact is critical for predicting Bd spread and developing appropriate management tools for wild populations.

DELIMITATION OF GUAVA WATER PRODUCTIVITY IN THE BRAZILIAN NORTHEAST

The intensification of agricultural crops in the Brazilian northeast results in a change of natural vegetation, making the quantification and evaluation of the additional water use important. Applications of a Geographic Information System (GIS) are presented in this paper to estimate the guava water productivity (GWP) on a large scale. Long-term weather data were used together with regression models involving crop coefficient (Kc), reference evapotranspiration (ET0) and accumulated degree days (DDac) to quantify the guava water requirements (GWR) in the Brazilian Northeast producer states, considering an average growing season of six months and the cultivar ‘Paluma’ as a reference. By coupling GWR data with total precipitation for a growing season, it was possible to quantify the guava water deficit (GWD) giving an estimate about irrigation needs. Considering the whole region, the variation of the averaged GWD values ranged from 50 mm for pruning dates in January to 520 mm, with pruning done in May. Associating the average GWR values with yield data for 2010 from the Brazilian Geographical and Statistical Institute (IBGE), the average biophysical and economic values of GWP were estimated for each guava producer state. The biophysical values were between 0.86 and 4.95 kg m -3 for pruning dates in July and January in Rio Grande do Norte and Pernambuco states, respectively, while the economic ones ranged from 0.40 to 3.18 R$ m -3 for the same pruning periods, however, with the lowest averaged value being for Paraiba state. The states of Pernambuco, Bahia and Piaui presented the largest biophysical and economic GWP values. The spatially presented analyses can subsidize programs for the expansion of rainfed guava crop as well as water allocation criteria under irrigation conditions, aiming at improvements for water resource use.