Edges Of Forest Fragments Research Articles

Split distance: a key landscape metric shaping amphibian populations and communities in forest fragments

AbstractAimHabitat split isolates forest fragments where terrestrial adults of many amphibian species live from aquatic‐breeding sites where their larvae develop, causing population declines and shifts in community structure. In contrast to most fragmentation theoretical frameworks which point to the relevance of fragment area and isolation, a recent theoretical model predicts that split distance, defined as the shortest distance between a forest fragment edge and the nearby stream, should affect negatively the abundance and occurrence probability of populations in forest fragments and, consequently, their total abundance and species richness. The model further predicts that the quality of the matrix between the two habitats, called split matrix, will modulate such responses. Here, we provide the first test of these theoretical predictions.LocationAtlantic Forest, Brazil.MethodsSplit distance was estimated for all fragments of the Brazilian Atlantic Forest, a highly disturbed biodiversity hotspot. Then, we selected 23 forest fragments, within a 1166‐km2 landscape, in a design that insured orthogonality between split distance (0–2000 m) and fragment size (1.7–30 ha). Split matrix quality (SMQ) and proximity, a measure of the availability of forest around the focal fragment, were estimated and controlled for in the analyses. Using multiple regression analyses with control for spatial autocorrelation, and AIC multimodel inference, we evaluated the relative importance of split distance, SMQ, fragment size and proximity to determine amphibian community and population attributes.ResultsMost Atlantic Forest fragments were affected by habitat split. Consistent with the theoretical predictions, species richness, abundance and the occurrence probability of many species declined with split distance and increased with SMQ, even when controlling for fragment size and isolation.Main conclusionsSplit distance can be used as a surrogate for conservation value of forest fragments for aquatic‐breeding amphibians in landscape planning and restoration enterprises.

Forest structure of artificial islands in the Tucuruí dam reservoir in northern Brazil: a test core-area model

Construction of hydroelectric dams in tropical regions has been contributing significantly to forest fragmentation. Alterations at edges of forest fragments impact plant communities that suffer increases in tree damage and dead, and decreases in seedling recruitment. This study aimed to test the core-area model in a fragmented landscape caused by construction of a hydroelectric power plant in the Brazilian Amazon. We studied variations in forest structure between the margin and interiors of 17 islands of 8-100 hectares in the Tucuruí dam reservoir, in two plots (30 and >100m from the margin) per island. Mean tree density, basal area, seedling density and forest cover did not significantly differ between marginal and interior island plots. Also, no significant differences were found in liana density, dead tree or damage for margin and interior plots. The peculiar topographic conditions associated with the matrix habitat and shapes of the island seem to extend edge effects to the islands' centers independently of the island size, giving the interior similar physical microclimatic conditions as at the edges. We propose a protocol for assessing the ecological impacts of edge effects in fragments of natural habitat surrounded by induced (artificial) edges. The protocol involves three steps: (1) identification of focal taxa of particular conservation or management interest, (2) measurement of an "edge function" that describes the response of these taxa to induced edges, and (3) use of a "Core-Area Model" to extrapolate edge function parameters to existing or novel situations.

Anurans of the Reserva Ecológica da Michelin, Municipality of Igrapiúna, State of Bahia, Brazil

We studied the richness and distribution of anuran species on different breeding sites at the Reserva Ecológica da Michelin (13° 50' S and 39° 10' W, approximately 90-400 m above sea level), Municipality of Igrapiúna, Bahia State, Brazil. The reserve includes fragments of Atlantic Rain Forest varying from 140 to 650 ha. Five types of environments were sampled: leaf litter inside forest fragments, streams inside forest fragments, dam on the edge of forest fragment, temporary pond inside forest, and temporary ponds inside banana and rubber groves along the eastern boundary of the reserve. We used active and passive sampling methods for surveys of amphibians, between March 2007 and December 2008. We captured 48 species distributed in 10 families (number of species in parentheses): Aromobatidae (1), Brachycephalidae (4), Bufonidae (2), Craugastoridae (1), Centrolenidae (1), Cycloramphidae (3), Hylidae (29), Leiuperidae (1), Leptodactylidae (3), and Microhylidae (3). Temporary ponds presented the highest number of species in reproductive activity (19 species in native forested areas, and 21 in plantation areas), while leaf litter presented the lowest (6 species). Two species were found in bromeliads (Phyllodytes melanomystax and P. luteolus). Twenty-two species were exclusive to fragments of forest, 11 were found only in anthropized areas (dam, and rubber and banana plantations) and 15 in both environments. Aplastodiscus cavicola and Dendropsophus giesleri had their geographic distribution extended to the State of Bahia. Phasmahyla timbo and Chiasmocleis cordeiroi known only from their type localities were found in the reserve.

Morphological, photosynthetic and water relations traits underpin the contrasting success of two tropical lichen groups at the interior and edge of forest fragments

Forest edges created by fragmentation strongly affect the abiotic and biotic environment. A rarely studied consequence is the resulting impact on non-vascular plants such as poikilohydric lichens, known to be highly sensitive to changes in the microenvironment. We evaluated the impact of forest edge and forest interior on the distribution of two groups of crustose lichens characterized by the presence or absence of a cortex and sought explanations of the outcome in terms of photosynthetic response and water relations. Microclimate, distribution patterns and physiology of cortical and non-cortical lichens were compared at the edge and in the interior of an Atlantic rainforest fragment in Alagoas, Brazil. Ecophysiological aspects of photosynthesis and water relations were studied using chlorophyll a fluorescence analysis, and hydration and rehydration characteristics. Cortical and non-cortical functional groups showed a clear preference for interior and edge habitats, respectively. The cortical lichens retained liquid water more efficiently and tolerated low light. This explains their predominance in the forest interior, where total area cover on host tree trunks reached ca. 40 % (versus ca. 5 % for non-cortical lichens). Although non-cortical lichens exchanged water vapour efficiently, they required high light intensities. Consequently, they were able to exploit well-lit edge conditions where they achieved an area cover of ca. 19 % (versus ca. 7 % for cortical lichens). We provide some of the first data for lichens giving the relative quantity of incident light absorbed by the photosystem (absorptivity). The cortical group achieved higher absorptivity and quantum efficiencies, but at the expense of physiological plasticity; non-cortical lichens showed much decreased values of F(v)/F(m) and electron transport rates in the forest interior. Morphological and physiological features largely determine the ecophysiological interaction of lichen functional groups with their abiotic environment and, as a consequence, determine their habitat preference across forest habitats. In view of the distinctiveness of their distribution patterns and ecophysiological strategies, the occurrence of cortical versus non-cortical lichens can be a useful indicator of undisturbed forest interiors in tropical forest fragments.

The effects of forest fragmentation on euglossine bee communities (Hymenoptera: Apidae: Euglossini)

Despite scientific and media attention on pollinator declines, there is still only a rudimentary understanding of the response of bees—the most important group of pollinators worldwide—to ongoing land use changes. Euglossine bees are an ecologically important Neotropical clade of forest-dependent pollinators. Despite the fact that euglossines are well studied relative to other groups of tropical bees, only three previous studies, all from Brazil, address the response of euglossines to forest fragmentation. In this study, I tripled the maximum sample size of previous efforts by sampling male euglossines in 22 forest fragments ranging in area from 0.25 ha to 230 ha in southern Costa Rica, using chemically baited Van Someren traps. Abundance of euglossine bees was significantly positively related to forest fragment size, negatively related to shape (edge:area ratio), and marginally related to fragment isolation. Euglossine species richness showed similar, but weaker trends: richness was significantly positively related to the quantity of forest edge, marginally negatively related to fragment area, and not related to fragment isolation. The positive relationship between euglossine richness and abundance and forest fragment edge is consistent with other studies that have found high euglossine density in secondary or disturbed forest. The data suggest that individual euglossines move between forest fragments, as has been shown in other systems. Still, forest fragmentation appears to affect euglossine bees more strongly than other bee groups in the study region. Their large flight range and positive relationship with forest edges may help to buffer the negative effects of fragmentation, allowing euglossines to utilize even the very smallest forest fragments in the study area.

The effects of forestry on carabid beetles (Coleoptera: Carabidae) in boreal forests

As compared to natural forests, managed boreal forests are younger, more homogeneous in terms of tree age and species composition, and consist of smaller fragments. Here we examine the effects of such characteristics caused by forestry on carabid beetles (Coleoptera, Carabidae) in the boreal region. The main results are the following. (1) Fragmentation of forests and the size of a fragment appear not to be crucial for the survival of the majority of forest carabids, as they tend to be distributed over various successional stages, but species requiring old-growth habitats suffer. (2) For carabids there appear to be no or very few edge specialist species, and forest-open land edges appear to be effective barriers for species associated with forest or open habitat. However, generalist species easily cross the edge, and edges of forest fragments may be invaded by species from the surrounding open habitat. (3) Habitat change following clear-cutting dramatically changes the composition of carabid assemblages: species restricted to mature forests disappear and open-habitat species invade, while habitat generalists survive at least in the short term. Carabid diversity can probably best be maintained if forest management mimics natural processes, maintains natural structures and includes the natural composition of vegetation and other structural elements (such as dead wood) within the stands, provided that these forest features can be maintained and recreated through forest management practices. At a larger scale, the whole spectrum of forest types and ages (especially old-growth forests), and different successional processes (especially fire) should be maintained. These require the development and use of innovative logging methods, and the planning, implementation, and assessment of landscape-scale ecological management strategies.

Factors Limiting the Survival of Native Tree Seedlings Used in Conservation Efforts at the Edges of Forest Fragments in Upland Madagascar

Abstract We tested four reforestation techniques in tropical forest fragments that were damaged by fire in upland Madagascar. We conducted a full‐factorial experiment on the survival of transplanted seedlings of five native tree species in grassland plots adjacent to the forest fragments in the Ambohitantely Forest Reserve. The species studied were Dodonaea madagascariensis, Filicium decipiens, Olea lancea, Podocarpus madagascariensis, and Rhus taratana. A total of 480 seedlings were planted; 207 survived the 15 months of the experiment. The factors examined were distance of the reforestation plots from the forest, mixing of forest soil into the plots, application of chemical fertilizers, experimental shading of plots, and the cover of naturally establishing shrubs. Both increasing the distance of plots from the forest edge and adding chemical fertilizers significantly reduced the survival of all seedlings. The surprising negative effects of fertilization may be partly due to increased competition from naturally establishing shrubs that are adapted to exploit high nitrogen levels. Mixing soil from the forest areas into the plots did not change seedling survival. Shading reduced the survival of D. madagascariensis seedlings and did not increase the survival of any species. These findings suggest that the success of reforestation projects can be increased by planting seedlings close to the existing forest fragments. Reforestation of similar tropical forests is likely to be more successful if efforts are focused on expanding the size of existing fragments of tropical forest, rather than on establishing new fragments in grassland openings.