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1.
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.  相似文献   

2.
Conversion of tropical forests is among the primary causes of global environmental change. The loss of their important environmental services has prompted calls to integrate ecosystem services (ES) in addition to socio‐economic objectives in decision‐making. To test the effect of accounting for both ES and socio‐economic objectives in land‐use decisions, we develop a new dynamic approach to model deforestation scenarios for tropical mountain forests. We integrate multi‐objective optimization of land allocation with an innovative approach to consider uncertainty spaces for each objective. These uncertainty spaces account for potential variability among decision‐makers, who may have different expectations about the future. When optimizing only socio‐economic objectives, the model continues the past trend in deforestation (1975–2015) in the projected land‐use allocation (2015–2070). Based on indicators for biomass production, carbon storage, climate and water regulation, and soil quality, we show that considering multiple ES in addition to the socio‐economic objectives has heterogeneous effects on land‐use allocation. It saves some natural forest if the natural forest share is below 38%, and can stop deforestation once the natural forest share drops below 10%. For landscapes with high shares of forest (38%–80% in our study), accounting for multiple ES under high uncertainty of their indicators may, however, accelerate deforestation. For such multifunctional landscapes, two main effects prevail: (a) accelerated expansion of diversified non‐natural areas to elevate the levels of the indicators and (b) increased landscape diversification to maintain multiple ES, reducing the proportion of natural forest. Only when accounting for vascular plant species richness as an explicit objective in the optimization, deforestation was consistently reduced. Aiming for multifunctional landscapes may therefore conflict with the aim of reducing deforestation, which we can quantify here for the first time. Our findings are relevant for identifying types of landscapes where this conflict may arise and to better align respective policies.  相似文献   

3.
Limited resources are available to address the world's growing environmental problems, requiring conservationists to identify priority sites for action. Using new distribution maps for all of the world's forest-dependent birds (60.6% of all bird species), we quantify the contribution of remaining forest to conserving global avian biodiversity. For each of the world's partly or wholly forested 5-km cells, we estimated an impact score of its contribution to the distribution of all the forest bird species estimated to occur within it, and so is proportional to the impact on the conservation status of the world's forest-dependent birds were the forest it contains lost. The distribution of scores was highly skewed, a very small proportion of cells having scores several orders of magnitude above the global mean. Ecoregions containing the highest values of this score included relatively species-poor islands such as Hawaii and Palau, the relatively species-rich islands of Indonesia and the Philippines, and the megadiverse Atlantic Forests and northern Andes of South America. Ecoregions with high impact scores and high deforestation rates (2000-2005) included montane forests in Cameroon and the Eastern Arc of Tanzania, although deforestation data were not available for all ecoregions. Ecoregions with high impact scores, high rates of recent deforestation and low coverage by the protected area network included Indonesia's Seram rain forests and the moist forests of Trinidad and Tobago. Key sites in these ecoregions represent some of the most urgent priorities for expansion of the global protected areas network to meet Convention on Biological Diversity targets to increase the proportion of land formally protected to 17% by 2020. Areas with high impact scores, rapid deforestation, low protection and high carbon storage values may represent significant opportunities for both biodiversity conservation and climate change mitigation, for example through Reducing Emissions from Deforestation and Forest Degradation (REDD+) initiatives.  相似文献   

4.
Tropical peat swamp forests (PSFs) are globally important carbon stores under threat. In Southeast Asia, 35% of peatlands had been drained and converted to plantations by 2010, and much of the remaining forest had been logged, contributing significantly to global carbon emissions. Yet, tropical forests have the capacity to regain biomass quickly and forests on drained peatlands may grow faster in response to soil aeration, so the net effect of humans on forest biomass remains poorly understood. In this study, two lidar surveys (made in 2011 and 2014) are compared to map forest biomass dynamics across 96 km2 of PSF in Kalimantan, Indonesia. The peatland is now legally protected for conservation, but large expanses were logged under concessions until 1998 and illegal logging continues in accessible portions. It was hypothesized that historically logged areas would be recovering biomass while recently logged areas would be losing biomass. We found that historically logged forests were recovering biomass near old canals and railways used by the concessions. Lidar detected substantial illegal logging activity—579 km of logging canals were located beneath the canopy. Some patches close to these canals have been logged in the 2011–2104 period (i.e. substantial biomass loss) but, on aggregate, these illegally logged regions were also recovering. Unexpectedly, rapid growth was also observed in intact forest that had not been logged and was over a kilometre from the nearest known canal, perhaps in response to greater aeration of surface peat. Comparing these results with flux measurements taken at other nearby sites, we find that carbon sequestration in above‐ground biomass may have offset roughly half the carbon efflux from peat oxidation. This study demonstrates the power of repeat lidar survey to map fine‐scale forest dynamics in remote areas, revealing previously unrecognized impacts of anthropogenic global change.  相似文献   

5.
Tropical deforestation varies temporally and spatially which can inhibit the ability of existing protected areas to stem forest loss. Identifying the spatial–temporal distribution of deforestation and its concentration can help decision makers decide conservation priorities and leverage limited resources. This study assessed how topographic and anthropogenic variables affect deforestation patterns within and outside protected areas on the islands of Sumatra and Kalimantan in Indonesia. Emerging hotspot analysis (EHA) was used to evaluate spatial and temporal trends of forest loss on the Hansen annual forest loss data for these islands from 2001–2018. For the two islands, most hotspots were detected outside protected areas; those within protected areas were mainly concentrated at boundaries, where lower elevation/slope and high human pressure could be observed. New hotspots were identified within the three PAs in Sumatra, while three kinds of hotspots (consecutive, oscillating, and sporadic) were found in the two PAs of Kalimantan (Kutai and Teluk Kelumpang). Areas with high human pressure (average human footprint higher than 12) were covered by a high density of hotspots. The results identify specific areas where forest loss has emerged recently, which could indicate a conservation priority. It is suggested that new protected areas be established in locations showing intensifying and persistent hotspots—those where deforestation has occurred for ≥16 of 18 years of the study period.

Emerging hotspot analysis, a new approach that can evaluate spatial and temporal trends of forest loss, was performed on annual forest loss data for these islands from 2001–2018. Most hotspots were detected outside PAs; those within PAs were mainly concentrated at boundaries, where lower elevation/slope and high human pressure could be observed. More hotspots were detected on Sumatra than Kalimantan and were mainly distributed in the island''s center  相似文献   

6.
Tropical forests account for more than half of the global carbon forest stock and much of the biological diversity on Earth. However, disturbances such as deforestation and forest degradation threaten the maintenance of these ecosystem services. This study aimed to understand how different disturbance histories affect the forest stand biomass, as well as species and functional diversity, and to what extent these differences can change the relationships between biomass and their drivers. We used data from forests with clear-cut and selectively logged disturbance histories, and from old-growth forests, situated in the Brazilian Atlantic forest. Forests with logging disturbances showed significant losses in their aboveground biomass compared to those of old-growth forests (50% loss in selectively logged forests and 80% loss in clear-cut forests). Interestingly, only clear-cut secondary forests showed differences in species and functional diversity, and were dominated by species with acquisitive trait values, commonly found early in succession. Shifts in stand biomass drivers were observed in selectively logged forests. The mass-ratio hypothesis (mainly through the functional trait of maximum height) was the most important biomass driver in clear-cut secondary and old-growth forests, whereas the importance of the niche complementarity hypothesis (through functional richness and dispersion) was higher in selectively logged forests. Our study highlights that disturbance histories can affect forest aboveground biomass and its drivers. Moreover, our results reinforce the need for conservation of intact forests but highlight the importance of including degraded forests in conservation mechanisms based in carbon stocks, as these forests retain high values of species and functional diversities that are crucial to biomass and consequently carbon stock acquisition.  相似文献   

7.
全球气候变化背景下,我国近地面臭氧浓度不断增加,已严重威胁到森林生态系统。但是,目前臭氧污染影响我国亚热带森林生物量的研究仍然具有较高的不确定性。本研究比较了不同模型和不同参数化方案评估的鼎湖山森林和林下草地生物量损失率的差别,比较了鼎湖山阔叶林和针叶林以及林下草地的生物量损失率与总初级生产力(GPP)损失率的一致性。2015—2016年臭氧污染造成的鼎湖山阔叶林生物量损失率为11.3%—11.69%,针叶林生物量损失率为3.97%—3.68%,草地生物量损失11.2%—14.6%;不同参数化方案估计的鼎湖山阔叶林的生物量损失率在9%—13%之间,针叶林的生物量损失率在3.68%—4.4%之间变化,草地在11.2%—14.6%之间。基于臭氧剂量响应关系模型估算的阔叶林GPP损失率为10%—12.6%,针叶林GPP损失率为1.81%—2.6%,草地GPP损失率为3.2%—3.3%。总的来看,鼎湖山阔叶林和针叶林的生物量和GPP损失具有较高的一致性,阔叶林生物量和GPP的损失率明显高于针叶林生物量和GPP的损失率。  相似文献   

8.
OBJECTIVES--To compare the effects of maternal HIV-1 and HIV-2 infections on outcome of pregnancy, infant mortality, and child survival, and to measure serological concordance between mothers and children. DESIGN--Retrospective cohort study with cross sectional study of concordance for HIV antibodies. SETTING--Hospital, tuberculosis clinic, and maternal and child health centre in Abidjan, Côte d''Ivoire, west Africa. SUBJECTS--986 women who had had a total of 2758 pregnancies since 1980. The last born children of 194 of these women. MAIN OUTCOME MEASURES--Pregnancy outcomes; mortality for all children born since 1980; and outcome for last born children. Serological concordance between mothers and last born children. RESULTS--Women with HIV-1 and HIV-2 infections had higher rates of spontaneous abortion and stillbirth than uninfected women (86/769 in HIV-1 positive women, 48/421 in HIV-2 positive, 31/234 in dually reactive, and 96/1131 in uninfected). Compared with children born to uninfected mothers (mortality 10.3%), greater proportions of children of HIV-1 positive (20.6%) and dually reactive (20.3%) mothers had died; mortality in children of HIV-2 infected women (13.1%) was not significantly increased. Infant mortalities for the last born children of HIV-1 positive, dually reactive, HIV-2 positive, and seronegative women were, respectively, 133, 82, 32, and 40 per 1000 live births. Nine of 77 last born children of HIV-1 positive mothers were concordantly seropositive compared with none of 21 children of HIV-2 infected mothers. CONCLUSIONS--Maternal HIV-2 infection has less influence on child survival than infection with HIV-1, probably because of a lower vertical transmission rate.  相似文献   

9.
In the Amazon, deforestation and climate change lead to increased vulnerability to forest degradation, threatening its existing carbon stocks and its capacity as a carbon sink. We use satellite L-Band Vegetation Optical Depth (L-VOD) data that provide an integrated (top-down) estimate of biomass carbon to track changes over 2011–2019. Because the spatial resolution of L-VOD is coarse (0.25°), it allows limited attribution of the observed changes. We therefore combined high-resolution annual maps of forest cover and disturbances with biomass maps to model carbon losses (bottom-up) from deforestation and degradation, and gains from regrowing secondary forests. We show an increase of deforestation and associated degradation losses since 2012 which greatly outweigh secondary forest gains. Degradation accounted for 40% of gross losses. After an increase in 2011, old-growth forests show a net loss of above-ground carbon between 2012 and 2019. The sum of component carbon fluxes in our model is consistent with the total biomass change from L-VOD of 1.3 Pg C over 2012-2019. Across nine Amazon countries, we found that while Brazil contains the majority of biomass stocks (64%), its losses from disturbances were disproportionately high (79% of gross losses). Our multi-source analysis provides a pessimistic assessment of the Amazon carbon balance and highlights the urgent need to stop the recent rise of deforestation and degradation, particularly in the Brazilian Amazon.  相似文献   

10.
森林退化/衰退的研究与实践   总被引:7,自引:3,他引:4  
森林退化可以理解为森林面积减少、结构丧失、质量降低、功能下降;森林衰退则是森林退化的一种形式,指森林(树木)在生长发育过程中出现的生理机能下降、生长发育滞缓、生产力降低甚至死亡,以及地力衰退等状态.国内外研究表明,森林采伐/毁林是造成森林面积减少的最主要原因,有关森林采伐/毁林引起的森林退化研究主要集中在森林退化的后果、国家/国际政策的影响、加强全球性合作以及寻求解决途径等方面.森林衰退原因可归纳为:工、农业污染,自然胁迫/致衰因子,林分动态发生变化,森林衰退病或生态病,人工纯林以及纯林连栽导致的地力、生产力衰退等.中国的森林退化/衰退现状与世界各地森林退化基本一致,但由于历史原因,中国森林退化又有其自身特点:近一个世纪的强烈人为干扰,使大部分原始天然林退化为次生林;中国拥有世界上最多的人工林,且多数人工林均具有质量差、功能低等衰退特征.本文在综述森林退化/衰退研究与实践基础上,提出中国现代森林退化/衰退的的主要原因,给出中国森林退化/衰退的基本对策.  相似文献   

11.
The United Nations climate treaty may soon include a mechanism for compensating tropical nations that succeed in reducing carbon emissions from deforestation and forest degradation, source of nearly one fifth of global carbon emissions. We review the potential for this mechanism [reducing emissions from deforestation and degradation (REDD)] to provoke ecological damages and promote ecological cobenefits. Nations could potentially participate in REDD by slowing clear‐cutting of mature tropical forest, slowing or decreasing the impact of selective logging, promoting forest regeneration and restoration, and expanding tree plantations. REDD could also foster efforts to reduce the incidence of forest fire. Potential ecological costs include the accelerated loss (through displaced agricultural expansion) of low‐biomass, high‐conservation‐value ecosystems, and substitution of low‐biomass vegetation by monoculture tree plantations. These costs could be avoided through measures that protect low‐biomass native ecosystems. Substantial ecological cobenefits should be conferred under most circumstances, and include the maintenance or restoration of (1) watershed functions, (2) local and regional climate regimes, (3) soils and biogeochemical processes, (4) water quality and aquatic habitat, and (5) terrestrial habitat. Some tools already being developed to monitor, report and verify (MRV) carbon emissions performance can also be used to measure other elements of ecosystem function, making development of MRV systems for ecological cobenefits a concrete possibility. Analysis of possible REDD program interventions in a large‐scale Amazon landscape indicates that even modest flows of forest carbon funding can provide substantial cobenefits for aquatic ecosystems, but that the functional integrity of the landscape's myriad small watersheds would be best protected under a more even spatial distribution of forests. Because of its focus on an ecosystem service with global benefits, REDD could access a large pool of global stakeholders willing to pay to maintain carbon in forests, thereby providing a potential cascade of ecosystem services to local stakeholders who would otherwise be unable to afford them.  相似文献   

12.
Combining protected areas with natural forest timber concessions may sustain larger forest landscapes than is possible via protected areas alone. However, the role of timber concessions in maintaining natural forest remains poorly characterized.An estimated 57% (303,525 km2) of Kalimantan''s land area (532,100 km2) was covered by natural forest in 2000. About 14,212 km2 (4.7%) had been cleared by 2010. Forests in oil palm concessions had been reduced by 5,600 km2 (14.1%), while the figures for timber concessions are 1,336 km2 (1.5%), and for protected forests are 1,122 km2 (1.2%). These deforestation rates explain little about the relative performance of the different land use categories under equivalent conversion risks due to the confounding effects of location.An estimated 25% of lands allocated for timber harvesting in 2000 had their status changed to industrial plantation concessions in 2010. Based on a sample of 3,391 forest plots (1×1 km; 100 ha), and matching statistical analyses, 2000–2010 deforestation was on average 17.6 ha lower (95% C.I.: −22.3 ha–−12.9 ha) in timber concession plots than in oil palm concession plots. When location effects were accounted for, deforestation rates in timber concessions and protected areas were not significantly different (Mean difference: 0.35 ha; 95% C.I.: −0.002 ha–0.7 ha).Natural forest timber concessions in Kalimantan had similar ability as protected areas to maintain forest cover during 2000–2010, provided the former were not reclassified to industrial plantation concessions. Our study indicates the desirability of the Government of Indonesia designating its natural forest timber concessions as protected areas under the IUCN Protected Area Category VI to protect them from reclassification.  相似文献   

13.
J B Casterline 《Social biology》1989,36(3-4):186-212
Differentials in the probability of pregnancy loss are examined using pregnancy history data from eight WFS surveys in developing countries. Multiple logistic regression equations are estimated. The probability of loss varies substantially over the reproductive career. Both higher-order pregnancies and those conceived at older ages are more likely to terminate in loss. maternal age differentials are more pronounced for lower-order pregnancies. First and second pregnancies conceived over age thirty suffer especially high levels of loss. Pregnancies conceived relatively soon after the termination of the previous pregnancy are more likely to be lost, as are pregnancies conceived after long intervals. Risk of loss is higher for women previously experiencing loss, and the effect persists beyond the pregnancy following the loss.  相似文献   

14.

Background

Chronic obstructive pulmonary disease (COPD) is a leading cause of death, particularly in developing countries. Little is known about the effects of economic development on COPD mortality, although economic development may potentially have positive and negative influences over the life course on COPD. We took advantage of a unique population whose rapid and recent economic development is marked by changes at clearly delineated and identifiable time points, and where few women smoke, to examine the effect of macro-level events on COPD mortality.

Methods

We used Poisson regression to decompose sex-specific COPD mortality rates in Hong Kong from 1981 to 2005 into the effects of age, period and cohort.

Results

COPD mortality declined strongly over generations for people born from the early to mid 20th century, which was particularly evident for the first generation to grow up in a more economically developed environment for both sexes. Population wide COPD mortality decreased when air quality improved and increased with increasing air pollution. COPD mortality increased with age, particularly after menopause among women.

Conclusions

Economic development may reduce vulnerability to COPD by reducing long-lasting insults to the respiratory system, such as infections, poor nutrition and indoor air pollution. However, some of these gains may be offset if economic development results in increasing air pollution or increasing smoking.  相似文献   

15.
Accurate estimates of forest biomass stocks and fluxes are needed to quantify global carbon budgets and assess the response of forests to climate change. However, most forest inventories consider tree mortality as the only aboveground biomass (AGB) loss without accounting for losses via damage to living trees: branchfall, trunk breakage, and wood decay. Here, we use ~151,000 annual records of tree survival and structural completeness to compare AGB loss via damage to living trees to total AGB loss (mortality + damage) in seven tropical forests widely distributed across environmental conditions. We find that 42% (3.62 Mg ha−1 year−1; 95% confidence interval [CI] 2.36–5.25) of total AGB loss (8.72 Mg ha−1 year−1; CI 5.57–12.86) is due to damage to living trees. Total AGB loss was highly variable among forests, but these differences were mainly caused by site variability in damage-related AGB losses rather than by mortality-related AGB losses. We show that conventional forest inventories overestimate stand-level AGB stocks by 4% (1%–17% range across forests) because assume structurally complete trees, underestimate total AGB loss by 29% (6%–57% range across forests) due to overlooked damage-related AGB losses, and overestimate AGB loss via mortality by 22% (7%–80% range across forests) because of the assumption that trees are undamaged before dying. Our results indicate that forest carbon fluxes are higher than previously thought. Damage on living trees is an underappreciated component of the forest carbon cycle that is likely to become even more important as the frequency and severity of forest disturbances increase.  相似文献   

16.
The intellectual abilities of 242 children born to women who had been hypertensive during pregnancy were assessed at the age of 7 1/2 years. Associations between 15 maternal, fetal, perinatal, postnatal and environmental factors, and test scores were investigated. After adjustment for confounding variables children in the upper social classes, born to non-smokers, who were first born, breast fed, and with birth weights above the 10th centile had significantly higher scores in some aspects of ability than the rest. Children whose mothers had developed superimposed pre-eclampsia had higher scores than those whose mothers had not suffered preeclampsia; and children delivered by elective caesarean section had lower scores than those delivered spontaneously. In a small subgroup of women with particularly high risk pregnancies perinatal mortality had been 10 times greater than in the rest of the sample. At 7 1/2 years the intellectual ability of the survivors in this subgroup did not differ from that of the rest. These findings do not support the notion that there is a quantitative continuum of "reproductive casualty" from mortality to morbidity.  相似文献   

17.
This study provides monitoring and spatial analysis of forest fragmentation based on high-resolution remote sensing, in order to give a framework for assessing residual biodiversity in the Guiglo-Taï region. Massive deforestation has taken place, mainly in the last 20 years, 79% of unprotected forests have been eliminated on the 100 × 100 km study area. Deforestation is also beginning to encroach on protected areas. Forest fragments are mainly found close to the deforestation front. In areas which were first deforested, forest fragments are very scarce and are restricted to less productive soils; they are often severely degraded. Young secondary forests develop on abandoned fields, but primary forest regeneration seems unlikely in light of the distance from seed sources and the increase in population pressure. Conservation initiatives in this zone of high biodiversity should focus on protected areas, taking into account short and long term benefits for the local population.  相似文献   

18.
Papua New Guinea (PNG) is an extensively forested country. Recent research suggests that despite commencing a trajectory of deforestation and degradation later than many counties in the Asia–Pacific region, PNG is now undergoing comparable rates of forest change. Here we explore the bioregional distribution of changes in the forest estate over the period 1972–2002 and examine their implications for forest protection. This is undertaken through the development of a novel bioregional classification of the country based on biogeographic regions and climatic zones, and its application to existing forest cover and forest‐cover change data. We found that degradation and deforestation varied considerably across the 11 defined biogeographic regions. We report that the majority of deforestation and degradation has occurred within all the lowland forests, and that it is these forests that have the greatest potential for further losses in the near term. The largest percentage of total change occurred in the east of PNG, in the islands and lowlands of the Bismarck, D'Entrecasteaux, East Papuan Islands and in the South‐East Papua–Oro region. The only region with a significant highlands component to undergo deforestation at a comparable magnitude to the islands and lowland regions was the Huon Peninsula and Adelbert region. Significant changes have also occurred at higher elevations, especially at the interface of subalpine grasslands and upper montane forests. Lower montane forests have experienced proportionally less change, yet it is these forests that constitute the majority of forests enclosed within the protected area system. We find that protected areas are not convincingly protecting either representative areas of PNG's ecosystems, nor the forests within their borders. We conclude by suggesting a more expansive and integrated approach to managing the national forest estate.  相似文献   

19.
In spite of the high importance of forests, global forest loss has remained alarmingly high during the last decades. Forest loss at a global scale has been unveiled with increasingly finer spatial resolution, but the forest extent and loss in protected areas (PAs) and in large intact forest landscapes (IFLs) have not so far been systematically assessed. Moreover, the impact of protection on preserving the IFLs is not well understood. In this study we conducted a consistent assessment of the global forest loss in PAs and IFLs over the period 2000–2012. We used recently published global remote sensing based spatial forest cover change data, being a uniform and consistent dataset over space and time, together with global datasets on PAs’ and IFLs’ locations. Our analyses revealed that on a global scale 3% of the protected forest, 2.5% of the intact forest, and 1.5% of the protected intact forest were lost during the study period. These forest loss rates are relatively high compared to global total forest loss of 5% for the same time period. The variation in forest losses and in protection effect was large among geographical regions and countries. In some regions the loss in protected forests exceeded 5% (e.g. in Australia and Oceania, and North America) and the relative forest loss was higher inside protected areas than outside those areas (e.g. in Mongolia and parts of Africa, Central Asia, and Europe). At the same time, protection was found to prevent forest loss in several countries (e.g. in South America and Southeast Asia). Globally, high area-weighted forest loss rates of protected and intact forests were associated with high gross domestic product and in the case of protected forests also with high proportions of agricultural land. Our findings reinforce the need for improved understanding of the reasons for the high forest losses in PAs and IFLs and strategies to prevent further losses.  相似文献   

20.
Tropical dry forests are the most threatened forest type in the world yet a paucity of research about them stymies development of appropriate conservation actions. The Paranã River Basin has the most significant dry forest formations in the Cerrado biome of central Brazil and is threatened by intense land conversion to pastures and agriculture. We examined changes in Paranã River Basin deforestation rates and fragmentation across three time intervals that covered 31 yr using Landsat imagery. Our results indicated a 66.3 percent decrease in forest extent between 1977 and 2008, with an annual rate of forest cover change of 3.5 percent. Landscape metrics further indicated severe forest loss and fragmentation, resulting in an increase in the number of fragments and reduction in patch sizes. Forest fragments in flatlands have virtually disappeared and the only significant forest remnants are mostly found over limestone outcrops in the eastern part of the basin. If current patterns persist, we project that these forests will likely disappear within 25 yr. These patterns may be reversed with creation of protected areas and involvement of local people to preserve small fragments that can be managed for restoration.  相似文献   

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