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1.
We studied a two-person game regarding deforestation in human-environment relationships. Each landowner manages a single land parcel where the state of land-use is forested, agricultural, or abandoned. The landowner has two strategies available: forest conservation and deforestation. The choice of deforestation provides a high return to the landowner, but it degrades the forest ecosystem services produced on a neighboring land parcel managed by a different landowner. Given spatial interactions between the two landowners, each landowner decides which strategy to choose by comparing the expected discounted utility of each strategy. Expected discounted utility is determined by taking into account the current and future utilities to be received, according to the state transition on the two land parcels. The state transition is described by a Markov chain that incorporates a landowner's choice about whether to deforest and the dynamics of agricultural abandonment and forest regeneration. By considering a stationary distribution of the Markov chain for land-use transitions, we derive explicit conditions for Nash equilibrium. We found that a slow regeneration of forests favors mutual cooperation (forest conservation). As the forest regenerates faster, mutual cooperation transforms to double Nash equilibria (mutual cooperation and mutual defection), and finally mutual defection (deforestation) leads to a unique Nash equilibrium. Two different types of social dilemma emerge in our deforestation game. The stag-hunt dilemma is most likely to occur under an unsustainable resource supply, where forest regenerates extremely slowly but agricultural abandonment happens quite rapidly. In contrast, the prisoner's dilemma is likely under a persistent or circulating supply of resources, where forest regenerates rapidly and agricultural abandonment occurs slowly or rapidly. These results show how humans and the environment mutually shape the dilemma structure in forest management, implying that solutions to dilemmas depend on environmental properties.  相似文献   

2.
We develop an agent-based model for forest harvesting to study how interactions between neighboring land parcels and the degree of information flow among landowners influence harvesting patterns. We assume a forest is composed of a number of land parcels that are individually managed. Each parcel is either mature forested, just-harvested, or immature forested. The state transition of each parcel is described by a Markov chain that incorporates the successional dynamics of the forest ecosystem and landowners' decisions about harvesting. Landowners decide to cut trees based on the expected discounted utility of forested vs. harvested land. One landowner's decision to cut trees is assumed to cause the degradation of ecosystem services on the downstream forested parcels. We investigated two different scenarios: in a strongly-connected society, landowners are familiar with each other and have full information regarding the behavior of other landowners. In a weakly-connected society, landowners do not communicate and therefore need to make subjective predictions about the behavior of others without adequate information. Regardless of the type of society, we observed that the spatial interaction between management units caused a chain reaction of tree harvesting in the neighborhood even when healthy forested land provided greater utility than harvested land. The harvest rate was higher in a weakly-connected society than that in a strongly-connected society. If landowners employed a long-term perspective, the harvest rate declined, and a more robust forested landscape emerged. Our results highlight the importance of institutional arrangements that encourage a long-term perspective and increased information flow among landowners in order to achieve successful forest management.  相似文献   

3.
Mitigating the negative impacts of declining worldwide forest cover remains a significant socio-ecological challenge, due to the dominant role of human decision-making. Here we use a Markov chain model of land-use dynamics to examine the impact of governance on forest cover in a region. Each land parcel can be either forested or barren (deforested), and landowners decide whether to deforest their parcel according to perceived value (utility). We focus on three governance strategies: yearly incentive for conservation, one-time penalty for deforestation and one-time incentive for reforestation. The incentive and penalty are incorporated into the expected utility of forested land, which decreases the net gain of deforestation. By analyzing the equilibrium and stability of the landscape dynamics, we observe four possible outcomes: a stationary-forested landscape, a stationary-deforested landscape, an unstable landscape fluctuating near the equilibrium, and a cyclic-forested landscape induced by synchronized deforestation. We find that the two incentive-based strategies often result in highly fluctuating forest cover over decadal time scales or longer, and in a few cases, reforestation incentives actually decrease the average forest cover. In contrast, a penalty for deforestation results in the stable persistence of forest cover (generally >30%). The idea that larger conservation incentives will always yield higher and more stable forest cover is not supported in our findings. The decision to deforest is influenced by more than a simple, “rational” cost-benefit analysis: social learning and myopic, stochastic decision-making also have important effects. We conclude that design of incentive programs may need to account for potential counter-productive long-term effects due to behavioural feedbacks.  相似文献   

4.
This paper compares perfect information and passive–adaptive social learning models of forest harvesting using a simple Markov chain model for land-use dynamics. A perfect information model assumes that landowners know true utility values of forest conservation and harvesting. In contrast, a passive–adaptive social learning model assumes that landowners do not know true utility values and they learn these values by their past experiences and by exchanging information with others in a society. We determine conditions under which the same consequences expected from perfect information and passive–adaptive social learning models. We found that the outcome from a perfect information model resembles that from passive–adaptive social learning model only when the perfect information model incorporates little discounting for future values. The stability analysis of landscape dynamics predicts a cyclic overexploitation of forest resources in a passive–adaptive social learning model with short-term memory, while instability of landscapes is never expected in a perfect information model. We discuss the role of discounting the future and discounting the past in the context of forest management.  相似文献   

5.
Questions: With calls for afforestation to sequester carbon due to climate change, agricultural land will be converted to forests in the near future. Little is known about how the ecosystem services of reforested landscapes with an agricultural land-use history will differ from reference forests. Our objectives were to (i) test the hypothesis that forests with a history of agricultural land use can provide the same carbon storage and biomass ecosystem services as adjacent reference forests, given some recovery time; (ii) explore whether there is a lag in the recovery of forest community composition due to prior agricultural land use; and (iii) demonstrate how remote-sensing methods can improve our understanding of land-use legacies at large spatial scales. Location: Finger Lakes National Forest, NY, USA. Methods: Using historic air photos, landscape-scale lidar, and field surveys, we compared differences in biomass storage, forest structure, and vegetation communities between reference forests and post-agricultural forests at different stages of regeneration in the Finger Lakes National Forest, New York, USA. We also used lidar to create a spatial model of biomass across the landscape to analyze the spatial distribution of biomass across our study area. Results: We found biomass and forest structure in post-agricultural forests generally recovered to levels typical of reference forests within 50 years of abandonment. Conversely, we found the composition of woody and herbaceous communities still varied between reference and post-agricultural forests after 50 years of abandonment. Conclusions: Collectively our results indicate afforestation efforts can be effective for carbon sequestration at early stages of forest succession. Our spatial model of biomass indicated that biomass levels can be low in forests with extensive edge. Further research is needed to understand how contemporary landscape structure interacts with legacy effects of agriculture to affect biomass and other ecosystem services.  相似文献   

6.
Privately owned woodlands are an important source of timber and ecosystem services in North America and worldwide. Impacts of management on these ecosystems and timber supply from these woodlands are difficult to estimate because complex behavioral theory informs the owner’s management decisions. The decision-making environment consists of exogenous market factors, internal cognitive processes, and social interactions with fellow landowners, foresters, and other rural community members. This study seeks to understand how social interactions, information flow, and peer-to-peer networks influence timber harvesting behavior using an agent-based model. This theoretical model includes forested polygons in various states of ‘harvest readiness’ and three types of agents: forest landowners, foresters, and peer leaders (individuals trained in conservation who use peer-to-peer networking). Agent rules, interactions, and characteristics were parameterized with values from existing literature and an empirical survey of forest landowner attitudes, intentions, and demographics. The model demonstrates that as trust in foresters and peer leaders increases, the percentage of the forest that is harvested sustainably increases. Furthermore, peer leaders can serve to increase landowner trust in foresters. Model output and equations will inform forest policy and extension/outreach efforts. The model also serves as an important testing ground for new theories of landowner decision making and behavior.  相似文献   

7.
Understanding how climate change may influence forest carbon (C) budgets requires knowledge of forest growth relationships with regional climate, long‐term forest succession, and past and future disturbances, such as wildfires and timber harvesting events. We used a landscape‐scale model of forest succession, wildfire, and C dynamics (LANDIS‐II) to evaluate the effects of a changing climate (A2 and B1 IPCC emissions; Geophysical Fluid Dynamics Laboratory General Circulation Models) on total forest C, tree species composition, and wildfire dynamics in the Lake Tahoe Basin, California, and Nevada. The independent effects of temperature and precipitation were assessed within and among climate models. Results highlight the importance of modeling forest succession and stand development processes at the landscape scale for understanding the C cycle. Due primarily to landscape legacy effects of historic logging of the Comstock Era in the late 1880s, C sequestration may continue throughout the current century, and the forest will remain a C sink (Net Ecosystem Carbon Balance > 0), regardless of climate regime. Climate change caused increases in temperatures limited simulated C sequestration potential because of augmented fire activity and reduced establishment ability of subalpine and upper montane trees. Higher temperatures influenced forest response more than reduced precipitation. As the forest reached its potential steady state, the forest could become C neutral or a C source, and climate change could accelerate this transition. The future of forest ecosystem C cycling in many forested systems worldwide may depend more on major disturbances and landscape legacies related to land use than on projected climate change alone.  相似文献   

8.
Swidden agriculture, commercial logging and plantation development have been considered to be the primary common causes of degradation and loss of tropical rain forests in Southeast Asia. In this paper, I chose a part of northeastern Sarawak, East Malaysia as my case study area to analyze the changes in its land-use characteristics. In the study area, as well as primeval forests, we see that land use began about 100 years ago by a native group called the Iban; commercial logging began in the 1960s, and the development of oil palm plantations began recently. I describe the changes in land use as well as their social and economic causes by referring to aerial photographs, literature surveys, interviews with government officers and the Iban, and observation of land use. My analysis of land use demonstrates that on “state land”, where commercial logging and oil palm plantation development are occurring, large areas of forest have been disturbed in a short period of time. The objective is to benefit economically in response to the social and economic conditions surrounding the study area. On the other hand, in the “Iban territory,” where the Iban practice their land use, land conversion has not occurred on a large scale and in a short period of time, even though the forest has been cut and agricultural fields have been created in response to social and economic conditions as well. They disperse small agricultural fields throughout their forest land. Therefore, the landscape of the “Iban territory” is based on secondary forest, composed of patches of forest in various stages and with several types of agricultural land. Today in Sarawak, monocrop plantations are rapidly expanding and little primeval forest remains. Given these conditions, the land-use practices of natives such as the Iban will be evaluated from the viewpoint of ecosystem and biodiversity conservation. It could play an important role in providing habitats for natural wildlife.  相似文献   

9.
Shifting cultivation is a traditional agricultural practice in most tropical regions of the world and has the potential to provide for human livelihoods while hosting substantial biodiversity. Little is known about the resilience of shifting cultivation to increasing agricultural demands on the landscape or to unexpected disturbances. To investigate these issues, we develop a simple social-ecological model and implement it with literature-derived ecological parameters for six shifting cultivation landscapes from three continents. Analyzing the model with the tools of dynamical systems analysis, we show that such landscapes exhibit two stable states, one characterized by high forest cover and agricultural productivity, and another with much lower values of these traits. For some combinations of agricultural pressure and ecological parameters both of these states can potentially exist, and the actual state of the forest depends critically on its historic state. In many cases, the landscapes’ ‘ecological resilience’, or amount of forest that could be destroyed without shifting out of the forested stability domain, declined substantially at lower levels of agricultural pressure than would lead to maximum productivity. A measure of ‘engineering resilience’, the recovery time from standardized disturbances, was independent of ecological resilience. These findings suggest that maximization of short-term agricultural output may have counterproductive impacts on the long-term productivity of shifting cultivation landscapes and the persistence of forested areas.  相似文献   

10.
In West Virginia, USA, there are 24 conservation easement program wetlands enrolled in the Agricultural Conservation Easement Program (ACEP). These wetlands are located on private agricultural land and are passively managed. Due to their location within fragmented agricultural areas, wetlands enrolled in ACEP in West Virginia have the potential to add wetland ecosystem services in areas that are lacking these features. We evaluated ACEP wetlands compared to reference wetlands on public land in West Virginia by using surrounding land cover, vegetative cover, and wetland features and stressors such as the presence or absence of erosion, upland inclusion, algal mats, and evidence of impacts from the surrounding landscape as surrogate measurements of wetland function on 13 ACEP wetlands and 10 reference wetlands. ACEP wetlands had higher percentages of tree coverage and a higher proportion of agricultural land in the areas immediately surrounding the wetland. Reference wetlands had higher percent coverage of emergent vegetation and had a higher proportion of forest in the immediate landscape. Our findings suggest that ACEP wetlands provide valuable early successional and forested wetland cover in a state that is largely forested. Because of this, it is important to maintain and even expand ACEP in West Virginia to continue providing a valuable source of early successional wetland habitat.  相似文献   

11.
Land tenure has been considered one of the key factors that define patterns and change in land-use systems. This paper examines the implications of land reform for household decisions regarding patterns of land use, agricultural intensification, and forest conservation. We look at an Amazonian caboclo settlement in the Lower Amazon that had experienced land reform by the end of the 1980s. Results show that defined land tenure is not enough to guarantee agricultural intensification and forest conservation. In fact, several factors working at different scales are affecting land-use change in the region. At the settlement level, privatization of upland forest has led to an overall increase in cultivated land—pasture and annual crops—and increasing deforestation rates. However, at the farm-property level, different systems of agricultural production—intensive, extensive, or abandonment of land—occur according to availability of labor, and capital, and access to different natural resources.  相似文献   

12.
Secondary forests are increasingly important components of human-modified landscapes in the tropics. Successional pathways, however, can vary enormously across and within landscapes, with divergent regrowth rates, vegetation structure and species composition. While climatic and edaphic conditions drive variations across regions, land-use history plays a central role in driving alternative successional pathways within human-modified landscapes. How land use affects succession depends on its intensity, spatial extent, frequency, duration and management practices, and is mediated by a complex combination of mechanisms acting on different ecosystem components and at different spatial and temporal scales. We review the literature aiming to provide a comprehensive understanding of the mechanisms underlying the long-lasting effects of land use on tropical forest succession and to discuss its implications for forest restoration. We organize it following a framework based on the hierarchical model of succession and ecological filtering theory. This review shows that our knowledge is mostly derived from studies in Neotropical forests regenerating after abandonment of shifting cultivation or pasture systems. Vegetation is the ecological component assessed most often. Little is known regarding how the recovery of belowground processes and microbiota communities is affected by previous land-use history. In published studies, land-use history has been mostly characterized by type, without discrimination of intensity, extent, duration or frequency. We compile and discuss the metrics used to describe land-use history, aiming to facilitate future studies. The literature shows that (i) species availability to succession is affected by transformations in the landscape that affect dispersal, and by management practices and seed predation, which affect the composition and diversity of propagules on site. Once a species successfully reaches an abandoned field, its establishment and performance are dependent on resistance to management practices, tolerance to (modified) soil conditions, herbivory, competition with weeds and invasive species, and facilitation by remnant trees. (ii) Structural and compositional divergences at early stages of succession remain for decades, suggesting that early communities play an important role in governing further ecosystem functioning and processes during succession. Management interventions at early stages could help enhance recovery rates and manipulate successional pathways. (iii) The combination of local and landscape conditions defines the limitations to succession and therefore the potential for natural regeneration to restore ecosystem properties effectively. The knowledge summarized here could enable the identification of conditions in which natural regeneration could efficiently promote forest restoration, and where specific management practices are required to foster succession. Finally, characterization of the landscape context and previous land-use history is essential to understand the limitations to succession and therefore to define cost-effective restoration strategies. Advancing knowledge on these two aspects is key for finding generalizable relations that will increase the predictability of succession and the efficiency of forest restoration under different landscape contexts.  相似文献   

13.
Carabid beetle assemblages were studied to assess how diversity and community structure varied along a gradient of land-use. This gradient was composed of six 1 km2 quadrats with an increasing proportion of agricultural land reflecting the anthropogenic fragmentation and intensification of landscapes. Carabid species richness and abundance was predicted to peak in the most heterogeneous landscape, in accord with the intermediate disturbance hypothesis (IDH), and then decline as agricultural intensification increased. It was also predicted that the different landscapes would support beetle communities distinct from each other. The IDH was unsupported-in both years of this study carabid species richness and abundance was greatest in the most intensively managed, agricultural sites. Detrended correspondence analysis revealed a clear separation in beetle community structure between forested and open habitats and between different forest types. Canonical correspondence analysis revealed a significant correlation between beetle community structure and the environment, showing distinct beetle assemblages to be significantly associated with specific edaphic and botanical features of the land-use gradient. This study adds to increasing evidence that landscape-scale patterns in land-use significantly affect beetle community structure producing distinct assemblages.  相似文献   

14.
Market-based conservation instruments, such as payments, auctions or tradable permits, are environmental policies that create financial incentives for landowners to engage in voluntary conservation on their land. But what if ecological processes operate across property boundaries and land use decisions on one property influence ecosystem functions on neighboring sites? This paper examines how to account for such spatial externalities when designing market-based conservation instruments. We use an agent-based model to analyze different spatial metrics and their implications on land use decisions in a dynamic cost environment. The model contains a number of alternative submodels which differ in incentive design and social interactions of agents, the latter including coordinating as well as cooperating behavior of agents. We find that incentive design and social interactions have a strong influence on the spatial allocation and the costs of the conservation market.  相似文献   

15.
The composition of a landscape is a fundamental indicator in land-cover pattern assessments. The objective of this paper was to evaluate a landscape composition indicator called ‘landscape mosaic’ as a framework for interpreting land-cover dynamics over a 9-year period in a 360,000 km2 study area in the southern United States. The indicator classified a land parcel into one of 19 possible landscape mosaic classes according to the proportions of natural, developed, and agriculture land-cover types in a surrounding 4.41-ha neighborhood. Using land-cover maps from remote sensing, the landscape mosaics were calculated for each 0.09-ha pixel in the study area in 1996 and 2005. Mosaic transition matrices estimated from the pixel change data were then used to develop two Markov chain models. A “landscape mosaic” model was a temporal model of the shifting landscape mosaic, based on the probability of landscape mosaic change for all pixels. A “forest security” model was the same, except that the Markov states were defined by both the landscape mosaic and the land-cover of each pixel, which allowed interpreting forest land-cover dynamics in the context of a shifting landscape mosaic. In the forest security model, the overall percentage of forest decreased from 33% in 2005 to 17% at steady-state, and there was little change in the relative distribution of existing forest area among landscape mosaic classes. In contrast, the landscape mosaic steady-state was reached later, and indicated that a maximum of 10% of total area was available for forest. The implication was that forest security depended ultimately on the dynamics of the landscape mosaics that contained forest, not on forest dynamics within those landscape mosaics.  相似文献   

16.
Aim Climate, topography and soils drive many patterns of plant distribution and abundance across landscapes, but current plant communities may also reflect a legacy of past disturbance such as agricultural land use. To assess the relative influences of environmental conditions and disturbance history on vegetation, it is important to understand how these forces interact. This study relates the geographical distribution of land uses to variation in topography and soils; evaluates the consequences of land‐use decisions for current forests; and examines the effects of agricultural land use on the chemical properties of forest soils. Location Tompkins County occupies 1250 km2 in central New York's Finger Lakes region. Like much of eastern North America, this area underwent forest clearance for agriculture during the 1800s and widespread field abandonment and forest recovery during the 1900s. The current landscape consists of a patchwork of forests that were never cleared, forests that developed on old fields and active agricultural lands. Methods We investigated relationships among topography, soils and land‐use decisions by gathering information about land‐use history, slope, aspect, elevation, soil lime content, soil drainage and accessibility in a geographic information system (GIS). To assess the effects of agriculture on forest soil chemistry, we measured pH, organic matter content and extractable nutrient concentrations in field‐collected soil samples from 47 post‐agricultural and uncleared forests. Results Steeper slopes, less accessible lands and lower‐lime soils tended to remain forested, and farmers were more likely to abandon fields that were steeper, farther from roads, lower in lime and more poorly drained. Slope had by far the greatest impact on patterns of clearance and abandonment, and accessibility had a surprisingly strong influence on the distribution of land uses. The effects of other factors varied more, depending for example on location within the county. Current forest types differed accordingly in topography and soil attributes, particularly slope, but they also showed much overlap. Post‐agricultural and uncleared forest soils had similar chemical properties. Forests on lands abandoned from agriculture 80–100 years before had slightly higher pH and nutrient concentrations than adjacent, uncleared forests, but these changes were small compared to environmental variation across the county. Main conclusions Despite differential use of lands according to their topography and soils, the substantial influence of accessibility and the relatively small scale of land‐use decisions allowed for broad similarity among forest types. Thus, the topography and soil differences created by land‐use decisions probably contribute little to landscape‐level patterns of diversity. Subtle changes in forest soil chemistry left from past agriculture may nevertheless affect plant distribution and abundance at finer scales.  相似文献   

17.
魏冲  宋轩  陈杰 《生态学报》2014,34(2):517-525
景观的空间配置与类型组成能够对流域的产流、产沙及非点源污染产生影响。在以往SWAT模型研究中,往往默认水文模型考虑了该影响。为分析SWAT模型对不同景观格局变化的敏感性,根据老灌河流域2000年土地利用在各子流域的组成,模拟研究区更为破碎、复杂的景观空间配置,通过设置多套试验参数,利用SWAT模型生成基于不同景观格局的模拟结果。结果表明,SWAT模型不能反映除坡度和面积变化之外的景观水平下各斑块之间因景观空间格局改变对流域产流、产沙以及非点源污染的影响;模型通过其他参数的调整,弥补了模型分析数据的不足,使实测数据与模型部分结果高度吻合。这表明,一个能够反映流域部分水文特征的SWAT模型,未必是对研究区真实情形的模拟,而是各个参数间平衡的结果。因此,在利用SWAT模型分析模拟景观变化时,不应默认模型能够模拟景观空间格局改变对流域水文过程的影响,同时研究者可以通过划分坡度带,提高模型对不同坡度土地利用的敏感性。  相似文献   

18.
西双版纳勐仑地区景观格局变化定量分析   总被引:11,自引:1,他引:10  
利用景观空间格局定量化分析软件FRAGSTATS和西双版纳勐仑地区1988、2003年两期Landsat影像解译结果,定量分析和比较了两时期景观格局的组成、各类型斑块特征、不同类型斑块间空间分布关系及其动态变化,并进一步分析了其生态效应.结果表明,15年来研究区内以经济林为主的人工景观组分剧烈增加,景观多样性上升;橡胶园等人工种植园地的扩张使得有林地破碎化:平均斑块面积由44km2减至21km2,斑块数由368增至441,同时边缘密度增加;导致其核心区缩小,斑块连接度下降;城镇建设用地的扩展也使得耕地(主要是水田)趋于破碎化.景观中不同斑块的交错分布格局也趋于简单.人工经济林的大面积发展和城市化使该区景观中人为影响显著增强,并产生了生物生境恶化及生态环境质量下降等不良生态效应.未来土地利用规划中应借鉴景观生态学原则,以尽量减少对生态环境的进一步破坏.  相似文献   

19.
This paper shows how the prospect of a forest carbon market in Papua New Guinea added a new element of instability to national forest policy and property processes that were already moving in contradictory directions. In particular we examine attempts by foreign investors to forge voluntary carbon agreements with customary landowners after the Bali climate change conference of 2007, and the mobilization of state institutions to counter these ‘private dealings’. We highlight the connection between the ways that these processes played out at both national and local scales, with a focus on the highly contentious Kamula Doso forest area in Western Province. We conclude with some observations on the way that the constitutional protection of customary land rights inhibits the formalization of marketable rights in forest resources, including forest carbon, and creates an inconclusive circularity in the operation of forest policy and property processes at different levels of social and political organization.  相似文献   

20.
广西滨海区域景观格局分析及土地利用变化预测   总被引:4,自引:0,他引:4  
研究滨海湿地景观动态及其发展趋势对于维持沿海地区可持续发展具有重要意义。利用移动窗口法分析广西滨海湿地景观格局时空变化,同时提取珍珠湾、茅尾海和丹兜海典型区进一步分析景观变化趋势,最后采用土地利用变化模型(Land Change Modeler,LCM)预测区域未来的景观演化趋势。结果表明,2000—2014年间,草地、乔木园地和常绿阔叶灌木林面积减少,而工业用地面积明显增加。研究区总体的景观异质性变化不大,破碎化趋势不明显。比较景观格局指数发现,边缘密度和多样性指数的空间分布特征相似,多样性指数较大的区域,边缘密度也大,并且多集中于珍珠湾、茅尾海和研究区的中东部。3个典型区的格局变化趋势相似,景观多样性指数降低而均匀度增加,其中,湿地斑块数目减少且所占面积比也减少。LCM模型结果表明,至2020年,草本湿地与森林灌丛湿地面积进一步降低,而工业用地和居民区则持续增长;其中,3个典型区土地利用变化均受到了工业发展的影响,以珍珠湾土地利用动态度最高,茅尾海其次,而丹兜海最小。当前,区域景观的变化明显降低了湿地植被的质量,加强湿地植被保护,限制工业区域的无序发展是维持区域生境完整和安全的有效途径。  相似文献   

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