Linear infrastructure such as roads, highways, power lines and gas lines are omnipresent features of human activity and are rapidly expanding in the tropics. Tropical species are especially ...vulnerable to such infrastructure because they include many ecological specialists that avoid even narrow (<30-m wide) clearings and forest edges, as well as other species that are susceptible to road kill, predation or hunting by humans near roads. In addition, roads have a major role in opening up forested tropical regions to destructive colonization and exploitation. Here, we synthesize existing research on the impacts of roads and other linear clearings on tropical rainforests, and assert that such impacts are often qualitatively and quantitatively different in tropical forests than in other ecosystems. We also highlight practical measures to reduce the negative impacts of roads and other linear infrastructure on tropical species.
ABSTRACT
We synthesize findings from one of the world's largest and longest‐running experimental investigations, the Biological Dynamics of Forest Fragments Project (BDFFP). Spanning an area of ∼1000 ...km2 in central Amazonia, the BDFFP was initially designed to evaluate the effects of fragment area on rainforest biodiversity and ecological processes. However, over its 38‐year history to date the project has far transcended its original mission, and now focuses more broadly on landscape dynamics, forest regeneration, regional‐ and global‐change phenomena, and their potential interactions and implications for Amazonian forest conservation. The project has yielded a wealth of insights into the ecological and environmental changes in fragmented forests. For instance, many rainforest species are naturally rare and hence are either missing entirely from many fragments or so sparsely represented as to have little chance of long‐term survival. Additionally, edge effects are a prominent driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage and a diversity of fauna.
Even within our controlled study area, the landscape has been highly dynamic: for example, the matrix of vegetation surrounding fragments has changed markedly over time, succeeding from large cattle pastures or forest clearcuts to secondary regrowth forest. This, in turn, has influenced the dynamics of plant and animal communities and their trajectories of change over time. In general, fauna and flora have responded differently to fragmentation: the most locally extinction‐prone animal species are those that have both large area requirements and low tolerance of the modified habitats surrounding fragments, whereas the most vulnerable plants are those that respond poorly to edge effects or chronic forest disturbances, and that rely on vulnerable animals for seed dispersal or pollination.
Relative to intact forests, most fragments are hyperdynamic, with unstable or fluctuating populations of species in response to a variety of external vicissitudes. Rare weather events such as droughts, windstorms and floods have had strong impacts on fragments and left lasting legacies of change. Both forest fragments and the intact forests in our study area appear to be influenced by larger‐scale environmental drivers operating at regional or global scales. These drivers are apparently increasing forest productivity and have led to concerted, widespread increases in forest dynamics and plant growth, shifts in tree‐community composition, and increases in liana (woody vine) abundance. Such large‐scale drivers are likely to interact synergistically with habitat fragmentation, exacerbating its effects for some species and ecological phenomena. Hence, the impacts of fragmentation on Amazonian biodiversity and ecosystem processes appear to be a consequence not only of local site features but also of broader changes occurring at landscape, regional and even global scales.
ABSTRACT
Large old trees are some of the most iconic biota on earth and are integral parts of many terrestrial ecosystems including those in tropical, temperate and boreal forests, deserts, savannas, ...agro‐ecological areas, and urban environments. In this review, we provide new insights into the ecology, function, evolution and management of large old trees through broad cross‐disciplinary perspectives from literatures in plant physiology, growth and development, evolution, habitat value for fauna and flora, and conservation management. Our review reveals that the diameter, height and longevity of large old trees varies greatly on an inter‐specific basis, thereby creating serious challenges in defining large old trees and demanding an ecosystem‐ and species‐specific definition that will only rarely be readily transferable to other species or ecosystems. Such variation is also manifested by marked inter‐specific differences in the key attributes of large old trees (beyond diameter and height) such as the extent of buttressing, canopy architecture, the extent of bark micro‐environments and the prevalence of cavities. We found that large old trees play an extraordinary range of critical ecological roles including in hydrological regimes, nutrient cycles and numerous ecosystem processes. Large old trees strongly influence the spatial and temporal distribution and abundance of individuals of the same species and populations of numerous other plant and animal species. We suggest many key characteristics of large old trees such as extreme height, prolonged lifespans, and the presence of cavities – which confer competitive and evolutionary advantages in undisturbed environments – can render such trees highly susceptible to a range of human influences. Large old trees are vulnerable to threats ranging from droughts, fire, pests and pathogens, to logging, land clearing, landscape fragmentation and climate change. Tackling such diverse threats is challenging because they often interact and manifest in different ways in different ecosystems, demanding targeted species‐ or ecosystem‐specific responses. We argue that novel management actions will often be required to protect existing large old trees and ensure the recruitment of new cohorts of such trees. For example, fine‐scale tree‐level conservation such as buffering individual stems will be required in many environments such as in agricultural areas and urban environments. Landscape‐level approaches like protecting places where large old trees are most likely to occur will be needed. However, this brings challenges associated with likely changes in tree distributions associated with climate change, because long‐lived trees may presently exist in places unsuitable for the development of new cohorts of the same species. Appropriate future environmental domains for a species could exist in new locations where it has never previously occurred. The future distribution and persistence of large old trees may require controversial responses including assisted migration via seed or seedling establishment in new locales. However, the effectiveness of such approaches may be limited where key ecological features of large old trees (such as cavity presence) depend on other species such as termites, fungi and bacteria. Unless other species with similar ecological roles are present to fulfil these functions, these taxa might need to be moved concurrently with the target tree species.
Humans have altered terrestrial ecosystems for millennia 1, yet wilderness areas still remain as vital refugia where natural ecological and evolutionary processes operate with minimal human ...disturbance 2–4, underpinning key regional- and planetary-scale functions 5, 6. Despite the myriad values of wilderness areas—as critical strongholds for endangered biodiversity 7, for carbon storage and sequestration 8, for buffering and regulating local climates 9, and for supporting many of the world’s most politically and economically marginalized communities 10—they are almost entirely ignored in multilateral environmental agreements. This is because they are assumed to be relatively free from threatening processes and therefore are not a priority for conservation efforts 11, 12. Here we challenge this assertion using new comparable maps of global wilderness following methods established in the original “last of the wild” analysis 13 to examine the change in extent since the early 1990s. We demonstrate alarming losses comprising one-tenth (3.3 million km2) of global wilderness areas over the last two decades, particularly in the Amazon (30%) and central Africa (14%). We assess increases in the protection of wilderness over the same time frame and show that these efforts are failing to keep pace with the rate of wilderness loss, which is nearly double the rate of protection. Our findings underscore an immediate need for international policies to recognize the vital values of wilderness and the unprecedented threats they face and to underscore urgent large-scale, multifaceted actions needed to maintain them.
•Globally important wilderness areas are ignored in conservation policy•We reveal that extensive losses of wilderness have occurred in the last two decades•Efforts aimed at protecting wilderness areas are failing to keep pace with its loss•International policy must recognize the actions needed to maintain wilderness areas
Watson et al. discover that the Earth’s wilderness areas are disappearing at a rate that has significantly outpaced their protection over the past two decades. Despite their ecological, climatological, and cultural importance, wilderness areas are ignored in multilateral environmental agreements, highlighting the need for urgent global policy attention.
Island biogeography theory (IBT) provides a basic conceptual model for understanding habitat fragmentation. Empirical studies of fragmented landscapes often reveal strong effects of fragment area and ...isolation on species richness, although other predictions of the theory, such as accelerated species turnover in fragments, have been tested less frequently. As predicted by IBT, biota in fragments typically ‘relax’ over time towards lower species richness. Beyond these broad generalizations, however, the relevance of IBT for understanding fragmented ecosystems is limited. First, IBT provides few predictions about how community composition in fragments should change over time, and which species should be most vulnerable. Second, edge effects can be an important driver of local species extinctions and ecosystem change, but are not considered by IBT. Third, the matrix of modified vegetation surrounding fragments—also ignored by IBT—can strongly influence fragment connectivity, which in turn affects the demography, genetics, and survival of local populations. Fourth, most fragmented landscapes are also altered by other anthropogenic changes, such as hunting, logging, fires, and pollution, which can interact synergistically with habitat fragmentation. Finally, fragmentation often has diverse impacts on ecosystem properties such as canopy-gap dynamics, carbon storage, and the trophic structure of communities that are not considered by IBT. I highlight these phenomena with findings from fragmented ecosystems around the world.
Edge effects are major drivers of change in many fragmented landscapes, but are often highly variable in space and time. Here we assess variability in edge effects altering Amazon forest dynamics, ...plant community composition, invading species, and carbon storage, in the world's largest and longest-running experimental study of habitat fragmentation. Despite detailed knowledge of local landscape conditions, spatial variability in edge effects was only partially foreseeable: relatively predictable effects were caused by the differing proximity of plots to forest edge and varying matrix vegetation, but windstorms generated much random variability. Temporal variability in edge phenomena was also only partially predictable: forest dynamics varied somewhat with fragment age, but also fluctuated markedly over time, evidently because of sporadic droughts and windstorms. Given the acute sensitivity of habitat fragments to local landscape and weather dynamics, we predict that fragments within the same landscape will tend to converge in species composition, whereas those in different landscapes will diverge in composition. This 'landscape-divergence hypothesis', if generally valid, will have key implications for biodiversity-conservation strategies and for understanding the dynamics of fragmented ecosystems.
Habitat destruction and overhunting are two major drivers of mammal population declines and extinctions in tropical forests. The construction of roads can be a catalyst for these two threats. In ...Southeast Asia, the impacts of roads on mammals have not been well-documented at a regional scale. Before evidence-based conservation strategies can be developed to minimize the threat of roads to endangered mammals within this region, we first need to locate where and how roads are contributing to the conversion of their habitats and illegal hunting in each country. We interviewed 36 experts involved in mammal research from seven Southeast Asian countries to identify roads that are contributing the most, in their opinion, to habitat conversion and illegal hunting. Our experts highlighted 16 existing and eight planned roads - these potentially threaten 21% of the 117 endangered terrestrial mammals in those countries. Apart from gathering qualitative evidence from the literature to assess their claims, we demonstrate how species-distribution models, satellite imagery and animal-sign surveys can be used to provide quantitative evidence of roads causing impacts by (1) cutting through habitats where endangered mammals are likely to occur, (2) intensifying forest conversion, and (3) contributing to illegal hunting and wildlife trade. To our knowledge, ours is the first study to identify specific roads threatening endangered mammals in Southeast Asia. Further through highlighting the impacts of roads, we propose 10 measures to limit road impacts in the region.
Global Decline in Large Old Trees Lindenmayer, David B.; Laurance, William F.; Franklin, Jerry F.
Science (American Association for the Advancement of Science),
12/2012, Letnik:
338, Številka:
6112
Journal Article
Recenzirano
Odprti dostop
Large old trees are among the biggest organisms on Earth. They are keystone structures in forests, woodlands, savannas, agricultural landscapes, and urban areas, playing unique ecological roles not ...provided by younger, smaller trees. However, populations of large old trees are rapidly declining in many parts of the world, with serious implications for ecosystem integrity and biodiversity.
•Agriculture will increase dramatically in tropical nations this century.•This expansion will have major impacts on tropical forests and semi-arid environments.•The rapid proliferation of roads will ...strongly influence the footprint of agriculture.•Changes will be most dramatic in South America and Sub-Saharan Africa.
The human population is projected to reach 11 billion this century, with the greatest increases in tropical developing nations. This growth, in concert with rising per-capita consumption, will require large increases in food and biofuel production. How will these megatrends affect tropical terrestrial and aquatic ecosystems and biodiversity? We foresee (i) major expansion and intensification of tropical agriculture, especially in Sub-Saharan Africa and South America; (ii) continuing rapid loss and alteration of tropical old-growth forests, woodlands, and semi-arid environments; (iii) a pivotal role for new roadways in determining the spatial extent of agriculture; and (iv) intensified conflicts between food production and nature conservation. Key priorities are to improve technologies and policies that promote more ecologically efficient food production while optimizing the allocation of lands to conservation and agriculture.
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