Small Forest Fragments Research Articles

Forest structure in a mosaic of rainforest sites: The effect of fragmentation and recovery after clear cut

A variety of human-induced disturbances such as forest fragmentation and recovery after deforestation for pasture or agricultural activities have resulted in a complex landscape mosaic in the Una region of northeastern Brazil. Using a set of vegetation descriptors, we investigated the main structural changes observed in forest categories that comprise the major components of the regional landscape and searched for potential key descriptors that could be used to discriminate among different forest categories. We assessed the forest structure of five habitat categories defined as (1) interiors and (2) edges of large fragments of old-growth forest (>1000 ha), (3) interiors and (4) edges of small forest fragments (<100 ha), and (5) early secondary forests. Forest descriptors used here were: frequency of herbaceous lianas and woody climbers, number of standing dead trees, number of fallen trunks, litter depth, number of pioneer plants (early secondary and shade-intolerant species), vertical foliage stratification profile and distribution of trees in different diameter classes. Edges and interiors of forest fragments were significantly different only in the number of standing dead trees. Secondary forests and edges of fragments showed differences in litter depth, fallen trunks and number of pioneer trees, and secondary forests were significantly different from fragment interiors in the number of standing dead trees and the number of pioneer trees. Horizontal and vertical structure evaluated via ordination analysis showed that fragment interiors, compared to secondary forests, were characterized by a greater number of medium (25–35 cm) and large (35–50 cm) trees and smaller numbers of thin trees (5–10 cm). There was great heterogeneity at the edges of small and large fragments, as these sites were distributed along almost the entire gradient. Most interiors of large and small fragments presented higher values of foliage densities at higher strata (15–20 m and at 20–25 m height), and lower densities at 1–5 m. All secondary forests and some fragment edge sites showed an opposite tendency. A discriminant function highlighted differences among forest categories, with transects of large fragment interiors and secondary forests representing two extremes along a disturbance gradient determined by foliage structure (densities at 15–20 m and 20–25 m), with the edges of both large and small fragments and the interiors of small fragments scattered across the gradient. The major underlying processes determining patterns of forest disturbance in the study region are discussed, highlighting the importance of forest fragments, independently of its size, as forests recovery after clear cut show a greatly distinct structure, with profound implications on fauna movements.

Long-term erosion of tree reproductive trait diversity in edge-dominated Atlantic forest fragments

Habitat loss and fragmentation promote relatively predicable shifts in the functional signature of tropical forest tree assemblages, but the full extent of cascading effects to biodiversity persistence remains poorly understood. Here we test the hypotheses that habitat fragmentation (a) alters the relative contribution of tree species exhibiting different reproductive traits; (b) reduces the diversity of pollination systems; and (c) facilitates the functional convergence of reproductive traits between edge-affected and early-secondary forest habitats (5–32 years old). This study was carried out in a severely fragmented 670-km2 forest landscape of the Atlantic forest of northeastern Brazil. We assigned 35 categories of reproductive traits to 3552 trees (DBH⩾10cm) belonging to 179 species, which described their pollination system, floral biology, and sexual system. Trait abundance was calculated for 55 plots of 0.1ha across four habitats: forest edges, small forest fragments (3.4–83.6ha), second-growth patches, and core tracts of forest interior within the largest available primary forest fragment (3500ha) in the region. Edge-affected and secondary habitats showed a species-poor assemblage of trees exhibiting particular pollination systems, a reduced diversity of pollination systems, a higher abundance of reproductive traits associated with pollination by generalist diurnal vectors, and an elevated abundance of hermaphroditic trees. As expected, the reproductive signature of tree assemblages in forest edges and small fragments (edge-affected habitats), which was very similar to that of early second-growth patches, was greatly affected by both habitat type and plot distance to the nearest forest edge. In hyper-fragmented Atlantic forest landscapes, we predict that narrow forest corridors and small fragments will become increasingly dominated by edge-affected habitats that can no longer retain the full complement of tree life-history diversity and its attendant mutualists.

Retention patches as potential refugia for bryophytes and lichens in managed forest landscapes

Leaving small patches of forest intact at harvesting is now a standard procedure to mitigate negative effects on biodiversity. One purpose of the patches is to “life-boat” species over the forest regeneration phase, although the capacity of small forest fragments to do so is very uncertain. We investigated the survival of red-listed and indicator species of bryophytes and lichens in 74 retention patches in boreal Sweden. The patches were between 0.01 and 0.5 ha in size and of six different types with respect to tree species composition and location on the harvested area. Species presence and abundance were recorded shortly after harvest in transects covering the whole patches, and an identical inventory was carried out 6 years after the first. During this time, bryophytes generally decreased, most pronounced for liverworts. The largest decreases were found in buffer zones to streams and lakes and the smallest in tree groups dominated by deciduous trees. By contrast, among the lichens some species decreased while others increased, and there was no difference between retention patch types. Among the species abundant enough to be analyzed individually, the lichens Calicium parvum and Micarea globulosella decreased less in larger patches and the bryophyte Hylocomiastrum umbratum decreased more in patches of irregular shape. The results imply that retention patches of this size might be too small to function as refugia for sensitive bryophytes and lichens until the surrounding forest regenerates, but that some lichens appear to persist or even increase. Retention harvesting is still a young management practice and further studies on its long-term conservation benefits will be valuable.

Sex ratio and morphological characteristics of rufous gnateaters, Conopophaga lineata (Aves, Passeriformes) in Atlantic forest fragments

Unequal sex ratios lead to the loss of genetic variability, decreasing the viability of populations in the long term. Anthropogenic activities often disturb the natural habitats and can cause alterations in sex ratio and morphological characteristics of several species. Forest fragmentation is a major conservation concern, so that understanding its effects in natural populations is essential. In this study, we evaluated the sex ratio and the morphological characteristics of Rufous Gnateaters (Conopophaga lineata (Wied, 1831)) in small and large forest fragments in Minas Gerais, Brazil. Birds (n = 89) were sexed by plumage characteristics and molecular markers. The molecular analysis showed that plumage is not a totally reliable method for sexing Rufous Gnateaters. We observed that sex ratio did not differ between large and small forest fragments, but birds in small fragments had larger wings and tarsus. Wing and tarsus changes may affect the movement ability of individuals within and among forest fragments. In conclusion, Rufous Gnateaters have been able to survive in both small and large Atlantic rain forest fragments without altering their sex ratio, but morphological changes can be prejudicial to their long term survival.

Hormigas: relaciones especies-área en fragmentos de bosque seco tropical

We analyzed the effect of fragmentation on ant species-area and specimen frequency-area relationships in nine patches of tropical dry forest in the middle Cauca river basin in Colombia. Species richness and specimen relative frequency of ants were positively correlated with area, whereas no significant correlation was found between species richness and the degree of isolation calculated for the forest patches. As the fragmentation affects different functional groups in different ways, we analyzed the species-area relationship for separate functional groups of ants. According to the habitat requirements we found that the species richness increased faster as area increased for ants inhabiting decomposing wood, followed by ants associated with trees, while species richness of ants living under dead leaves did not correlate with area. According to the food preference, species richness was positively correlated with area for the army ant group, while no significant correlation was found for solitary hunters or for leaf-cutting ants. Ant species richness and specimen density were calculated from equal size samples and examined in relation to the habitat area. An inverse correlation was found only for specimen density, the opposite of what was expected. To our knowledge this is one of the first studies showing differential responses of functional groups of ants to habitat loss. Moreover, it emphasizes the conservation value of small forest fragments for ants in a tropical dry forest.

Habitat fragmentation reduces genetic diversity and connectivity among toad populations in the Brazilian Atlantic Coastal Forest

Tropical rainforests are becoming increasingly fragmented and understanding the genetic consequences of fragmentation is crucial for conservation of their flora and fauna. We examined populations of the toad Rhinella ornata, a species endemic to Atlantic Coastal Forest in Brazil, and compared genetic diversity among small and medium forest fragments that were either isolated or connected to large forest areas by corridors. Genetic differentiation, as measured by F ST, was not related to geographic distance among study sites and the size of the fragments did not significantly alter patterns of genetic connectivity. However, population genetic diversity was positively related to fragment size, thus haplotype diversity was lowest in the smallest fragments, likely due to decreases in population sizes. Spatial analyses of genetic discontinuities among groups of populations showed a higher proportion of barriers to gene flow among small and medium fragments than between populations in continuous forest. Our results underscore that even species with relatively high dispersal capacities may, over time, suffer the negative genetic effects of fragmentation, possibly leading to reduced fitness of population and cases of localized extinction.

Species compensation maintains abundance and raid rates of African swarm-raiding army ants in rainforest fragments

Habitat clearance and fragmentation is increasingly threatening the biodiversity of tropical rainforests, however, the response of many insect species, even of key organisms, is still little understood. Using an extensive data set spanning over four years, we analyzed the effects of clearance and fragmentation of a Congo-Guinean rainforest in western Kenya on the abundance and the raid rates of two species of swarm-raiding army ants, which are considered keystone organisms of tropical rainforests. The abundance of army ants was measured by transect monitoring and by short-term pitfall trapping while raid rates were measured by long-term pitfall trapping over a period of five months. Dorylus wilverthi was the most abundant army ant in undisturbed rainforest and its abundance and raid rate strongly declined in small forest fragments. In contrast, the abundance of Dorylus molestus increased with decreasing fragment size and compensated for the decline of D. wilverthi in terms of abundance and ecological functionality (i.e. raiding rates). D. molestus appears to have a higher ability of using the agricultural land surrounding the Kakamega Forest than D. wilverthi, which may explain the species-specific differences in the susceptibility to habitat fragmentation. Our study demonstrates that habitat fragmentation may have a differential effect on two ecologically highly similar keystone species. Moreover, it shows that species compensation might help in maintaining an important ecosystem function (i.e. raiding by swarm-raiding army ants) in fragmented tropical rainforests.

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.

Status and Conservation of Proboscis Monkeys (Nasalis larvatus) in Sabah, East Malaysia

The proboscis monkey (Nasalis larvatus) was surveyed in the East Malaysian state of Sabah to establish its population status and to assess threats to its survival. It was found to be more widespread and abundant than previously thought, with a minimum population size of c. 5,907 individuals found along major coastal river systems in Sabah. The distribution of proboscis monkeys appeared highly fragmented, with only five major centers of continuous distribution and numerous small isolated populations. Existing proboscis monkey habitats are increasingly threatened by human activities. Of particular concern is the clearing and conversion of important riparian and coastal mangrove habitats to plantations and human habitation, which result in fragmentation of otherwise continuous populations along rivers, and local extinction of remnant populations trapped in small forest fragments. Only 15.3% of the population estimated in this study was found within protected forest reserves, with much of the species' diminishing range habitats exposed to further conversion, extraction and disturbance. Urgent mitigating strategies are necessary to ensure the long-term survival of proboscis monkeys in Sabah. Immediate actions are needed to prevent small isolated populations from local extinction, and long-term efforts must be undertaken to protect important proboscis monkey habitats and re-establish connectivity between fragmented populations.

Beleaguered Chimpanzees in the Agricultural District of Hoima, Western Uganda

With approximately 5,000 chimpanzees, Uganda is important for the conservation of the eastern subspecies Pan troglodytes schweinfurthii. The population distribution is highly fragmented, however, and the prospects for the long-term viability of many populations will be greatly improved if dispersal opportunities are maintained between major forests via migratory corridors. Chimpanzees in unprotected human-dominated habitat outside the main forest blocks are often ignored by research and conservation efforts. This study assessed the status and distribution of chimpanzees in northern Hoima District, western Uganda. The survey region covered 400 km2 between 1°26′–1°37′N and 31°09′–31°32′E, and separates two major forest blocks, Bugoma and Budongo. Chimpanzees use small forest fragments along watercourses throughout this region, both on private or communal land and in small government reserves, and a number of distinct groups (‘communities’) are present. There has been no evidence to indicate that chimpanzee populations are isolated; on the contrary chimpanzees appear highly mobile in this forest-farm habitat, confirming the region's corridor potential. At one site in the region, chimpanzees occur at an estimated density of 0.66 individuals/km2 which, if extrapolated across the survey area, implies a larger population than previously thought. Recent and rapid habitat change resulting from unregulated timber extraction and clearance of fragments for agriculture—particularly for cash crops such as tobacco—has exposed the chimpanzees, causing increased negative interactions between apes and farming communities. The chimpanzees in northern Hoima are unlikely to survive without immediate intervention.

Rare canopy species in communities within the Atlantic Coastal Forest in Rio de Janeiro State, Brazil

Rare species are one of the principal components of the species richness and diversity encountered in Dense Ombrophilous Tropical Forests. This study sought to analyze the rare canopy species within the Atlantic Coastal Forest in Rio de Janeiro State, Brazil. Six different communities were examined: Dense Ombrophilous alluvial Forest; Dense sub-montane Ombrophilous Forest; Dense Montane Ombrophilous in Serra do Mar and Serra da Mantiqueira. In each area the vegetation was sampled within forty 10 × 25 m plots alternately distributed along a linear transect. All trees with DBH (1.3 m above ground level) ≥5 cm were sampled. The canopy was characterized using the allometric relationship between diameter and height, and included all trees with BDH ≥10 cm and height ≥10 m. A total of 64 families, 206 genera, and 542 species were sampled, of which 297 (54.8%) represented rare species (less than one individual per hectare). The percentage of rare species varied from 34 to 50% in each of the different communities sampled. A majority of these rare trees belonged to the Rosidae, and a smaller proportion to the Dilleniidae. It was concluded that there was no apparent pattern to rarity among families, that rarity was probably derived from a number of processes (such as gap formation), and that a great majority of the rare species sampled were consistently rare. This indicates that the restricted geographic distribution and high degree of endemism of many arboreal taxa justifies the conservation of even small fragments of Atlantic Forest.

Patterns of Plant Composition in Fragments of Globally Imperiled Pine Rockland Forest: Effects of Soil Type, Recent Fire Frequency, and Fragment Size

Maintaining native plant diversity through fire management is challenging in the wildland-urban interface. In subtropical South Florida, fragments of fire-dependent, globally imperiled pine rockland forest are scattered throughout urban areas. To determine the effects of recent fire frequency, major soil type, and fragment size on species composition, we measured understory vascular plant presence and cover in 162 plots distributed among 16 publicly-owned pine rockland preserves in 1995 and 2003. Fragments received either 0, 1, or > 1 burn(s) between sampling periods. Native plant richness was very high overall. Major soil type, which varies regionally and is associated with latitude and elevation, strongly influenced the assemblage of species present at a given site. Native species cover was significantly different across different burn categories. Fragment size was positively associated with plant species richness, but small fragments had high variance in the total number of native plant species they supported, with some having nearly as many plant species as the largest fragment. Examining trends over time for rare native and invasive non-native plant species revealed the spread of the invasive grass Rhynchelytrum repens (Willd.) C.E. Hubb. and showed no major decreases in rare plant species. In general, this study provided encouraging results for managers of small urban forest fragments, showing that they can maintain high levels of native plant diversity, even when fire occurs infrequently.

Borboletas (Lepidoptera) de um fragmento de mata urbano em Minas Gerais, Brasil

The butterfly fauna of a small forest fragment in the campus of the Pontifícia Universidade Católica de Minas Gerais was surveyed between March and November 2001. The adult butterflies were captured using hand nets and frugivorous traps. In addition, caterpillars were raised in the laboratory for identification after emergence. Ninety-one species of six families were recorded. Among them, 46.1% belonged in Nymphalidae; 28.5% in Hesperiidae; 15.4% in Pieridae; 4.4% in Riodinidae; 4.4% in Papilionidae; and 1.1% in Lycaenidae. At least 28.6% of the species are common in urban and other disturbed environments in Brazil and no rare or endangered species was recorded. On the other hand, the species in this fragment represent 18.7% of the species known to occur in the vicinities of the city of Belo Horizonte. Moreover, species of taxa considered as indicators of preserved environments, although in small absolute numbers, occurred in proportions similar to those found in large forest remnants across Brazil. It is concluded that the studied fragment, as well as other small urban fragments, are important refuges for conservation of butterflies within cities.

Profound impoverishment of the large-tree stand in a hyper-fragmented landscape of the Atlantic forest

Large tree species have a disproportional influence on the structure and functioning of tropical forests, but the forces affecting their long-term persistence in human-dominated landscapes remain poorly understood. Here we test the hypothesis that aging forest edges and small fragments (3.4–295.7 ha) are greatly impoverished in terms of species richness and abundance of large trees in comparison to core areas of forest interior. The study was conducted in a hyper-fragmented landscape of the Atlantic forest, northeast Brazil. Large tree species were quantified by recording all trees (DBH ≥ 10 cm) within fifty-eight 0.1-ha plots distributed in three forest habitats: small forest fragments ( n = 28), forest edges ( n = 10), and primary forest interior areas within an exceptional large forest remnant ( n = 20). Large tree species and their stems ≥10 cm DBH were reduced by half in forest edges and fragments. Moreover, these edge-affected habitats almost lacked large-stemmed trees altogether (0.24 ± 0.27% of all stems sampled), and very tall trees were completely absent from forest edges. In contrast, large trees contributed to over 1.5% of the whole stand in forest interior plots (2.9 ± 2.8%). Habitats also differed in terms of tree architecture: relative to their DBH trees were on average 30% shorter in small fragments and forest edges. Finally, an indicator species analysis yielded an ecological group of 12 large tree species that were significantly associated with forest interior plots, but were completely missing from edge-affected habitats. Our results suggest a persistent and substantial impoverishment of the large-tree stand, including the structural collapse of forest emergent layer, in aging, hyper-fragmented landscapes.

EFFECTS OF HABITAT FRAGMENTATION AND DEGRADATION ON FLOCKS OF AFRICAN ANT‐FOLLOWING BIRDS

Tropical rain forests are rapidly cleared, fragmented, and degraded in sub-Saharan Africa; however, little is known about the response of species and even of key ecological groups to these processes. One of the most intriguing (but often neglected) ecological phenomena in African rain forests is the interaction between swarm-raiding army ants and ant-following birds. Similar to their well-known Neotropical representatives, ant-following birds in Africa track the massive swarm raids of army ants and feed on arthropods flushed by the ants. In this study we analyzed the effect of habitat fragmentation and degradation of a mid-altitude Congo-Guinean rain forest in western Kenya on the structure of ant-following bird flocks. Significant numbers of swarm raids were located in all forest fragments and in both undegraded and degraded forest. Fifty-six different species of birds followed army ant raids, forming bird flocks of one to 15 species. We quantitatively differentiated the bird community into five species of specialized ant-followers and 51 species of opportunistic ant-followers. Species richness and size of bird flocks decreased with decreasing size of forest fragments and was higher in undegraded than in degraded habitat. This was caused by the decrease of the species richness and number of specialized ant-followers at swarms, while the group of opportunistic ant-followers was affected little by habitat fragmentation and degradation. The composition of bird flocks was more variable in small fragments and degraded forest, compared to undegraded habitat in large fragments. The effect of habitat fragmentation on flock structure was best explained by the strong decline of the abundance of specialized ant-followers in small forest fragments. To conserve the association of army ants and ant-following birds in its natural state, vast areas of unfragmented and undegraded tropical rain forest are necessary.

Efeitos do substrato, bordas e proximidade espacial na estrutura da comunidade arbórea de um fragmento florestal em Lavras, MG

The present study aimed at detecting the influence of both edge effects and space substrate-related variables on the structural variations of the tree community in a small (4.0 ha) forest fragment in Lavras, Minas Gerais state, SE Brazil. Trees with diameter at breast height (dbh) > 5 cm were identified and measured in 29 (20 ×20 m), systematically distributed plots over the fragment. Substrate-related variables were obtained for each plot from the topography, laboratory analyses of soil samples and soil compaction measures. An 'edge factor' was calculated per plot from the fragment morphometry. Spatial variables were derived from the Cartesian coordinates of plot center. A canonical correspondence analysis of the species distribution abundance indicated significant correlations with some variables of the environmental and spatial matrices. The first ones were drainage classes, mean elevation, and saturation of bases, which explained 22.4% of the total variance. The spatial variables, x and x2*y, explained 12.7%, but the two sets shared, indistinctly, 4.6% of the total variance. Therefore, apart from the unexplained and stochastic variations (69.5%), the species distribution on the fragment is primarily influenced by spatial proximity, soil nutritional status and ground water regime.

Historical deforestation patterns and the conservation value of church forests in the northern Ethiopian highlands

Mountain forest plants have a limited capacity for migration because altitudinal gradients usually set strict limits to plant species’ ranges and often present physical barriers against dispersal. Innate ‘islands’ of biodiversity, mountain forests are therefore particularly vulnerable to the effects of climatic change and habitat fragmentation, both key drivers of global species loss. Conservation of these ecosystems must for that reason rely on protecting not only large fragments but also small habitat patches and relictual vegetation along a wide altitudinal range.When large fragments in such ecosystems are no longer available, small fragments become an environmental priority. Striking examples of small mountain forest fragments are the church forests of the northern Ethiopian highlands. In a landscape dominated by degraded semiarid savanna, sacred groves represent the majority of all remaining patches of Afromontane forest. Previous studies in the region only covered few fragments and could not adequately estimate the conservation value of these forests. For that reason, we digitized 394 church forests in an area of half a million hectares by systematically scanning high spatial resolution satellite images (pixel resolution 0.8 m) in eight blocks in the northern highlands and calculated area, density, shape, isolation and configuration metrics. Forest cover is only 0.2%, much lower than usually estimated in the literature (4%). Fragment shape and spatial configuration in the north and northeast of the surveyed area (irregular forests on northwestern slopes with churches near the forest edge) are consistent with forest conservation after fragmentation, while forests in the south and west (regular round forests surrounding a central church) indicate conservation prior to widespread deforestation. Fragments are small throughout the region (2.5 +- 0.2 ha) and need expansion, but known vegetation differences between church forests related to the two different historical fragmentation processes call for different strategies for forest conservation and restoration.

Historical deforestation patterns and the conservation value of church forests in the northern Ethiopian highlands

AbstractMountain forest plants have a limited capacity for migration because altitudinal gradients usually set strict limits to plant species’ ranges and often present physical barriers against dispersal. Innate ‘islands’ of biodiversity, mountain forests are therefore particularly vulnerable to the effects of climatic change and habitat fragmentation, both key drivers of global species loss. Conservation of these ecosystems must for that reason rely on protecting not only large fragments but also small habitat patches and relictual vegetation along a wide altitudinal range.When large fragments in such ecosystems are no longer available, small fragments become an environmental priority. Striking examples of small mountain forest fragments are the church forests of the northern Ethiopian highlands. In a landscape dominated by degraded semiarid savanna, sacred groves represent the majority of all remaining patches of Afromontane forest. Previous studies in the region only covered few fragments and could not adequately estimate the conservation value of these forests. For that reason, we digitized 394 church forests in an area of half a million hectares by systematically scanning high spatial resolution satellite images (pixel resolution 0.8 m) in eight blocks in the northern highlands and calculated area, density, shape, isolation and configuration metrics. Forest cover is only 0.2%, much lower than usually estimated in the literature (4%). Fragment shape and spatial configuration in the north and northeast of the surveyed area (irregular forests on northwestern slopes with churches near the forest edge) are consistent with forest conservation after fragmentation, while forests in the south and west (regular round forests surrounding a central church) indicate conservation prior to widespread deforestation. Fragments are small throughout the region (2.5 +- 0.2 ha) and need expansion, but known vegetation differences between church forests related to the two different historical fragmentation processes call for different strategies for forest conservation and restoration.

Landscape structure and live fences in Andes Colombian agrosystems: upper basin of the Cane-Iguaque River

Changes in land use have generated a new landscape configuration in the Andino orobiome (mountain range) of the tropical Andes, resulting in a mosaic of cultivation and pastures interrupted by small fragments of forest and live fences. This has resulted in an ongoing decrease in the biodiversity of this biome. In the upper basin of the Cane-Iguaque River (Villa de Levya-Boyacá, Colombia), located 2,600-3,000 m above the Cordillera Oriental, over three time periods in 1960, 1984, and 2004, we characterized the structure, patterns, and evolution of the overall landscape and of the live fences (used as tools in biodiversity conservation and considered to be desirable alternatives to nonlive fences in farming production systems) within an agricultural landscape. To do this, we interpreted high-resolution satellite images using a landscape ecology approach and applied landscape map metrics. We found that the natural forests have been transformed by pastures and cultivation, and that although live fences cover only a small portion of the total landscape (4.6%), they have an important effect on landscape structure and biodiversity. There has been an increase in live fences, especially between 1960 and 1984, as well as an increase in their density. However, there has been a reduction in the average length of live fences over the periods that we studied. This could be due in part to changes in the types of agricultural products that have been cultivated in recent years, with an increase in potatoes and a decrease in other vegetables, and also by resource extraction of timber and fuel wood. In the studied area, agricultural production was sustained while biodiversity conservation was improved by the use of live fences. Therefore, live fences should be considered not only as part of an agriculturally productive area, but also as an important element of a multi-functional landscape that contributes to the maintenance of biodiversity and provides resources of economic and ecological interest, decreasing the pressure on natural forest. Improving the network of live fences constitutes an important strategy for the sustainable management of the rural landscape of the Andino orobiome of Colombia and similar areas in the tropics.

SURVIVAL OF FLEDGLING HOODED WARBLERS (WILSONIA CITRINA) IN SMALL AND LARGE FOREST FRAGMENTS

Studies on the effects of forest fragmentation on the reproductive ecology of forest songbirds have focused almost exclusively on the egg and nestling stages. Little is known about survival or habitat use of fledglings in their first weeks out of the nest. We radiotracked adult Hooded Warblers (Wilsonia citrina) attending fledglings from large (>150-ha) and small (<30-ha) forest fragments during 2002 and 2003. Mark–recapture models were used to assess the effects of forest-fragment size and age of the attending adult on the survival of young. We also examined the structure of nesting- versus postfledging-habitat used by fledglings. Only 19% of fledgling Hooded Warblers survived the 28-day fledgling period prior to independence, and fledglings' daily survival probability was lowest in the first four days after they left the nest (1–2 days postfledging: 0.72; 3–4 days postfledging: 0.69). Fledgling survival did not differ between large and small forest fragments. Large fragments were more likely to contain older adults, and age of parent had a positive influence on fledgling survival, independent of fragment size. As in many other studies, overall productivity was higher within larger fragments; this was largely attributable to differences in number fledged rather than fledgling survival. Habitat used by fledglings was more structurally complex than habitat at nest sites, which indicates that fledglings may seek habitat with high cover to avoid predation. Fledgling survival was much lower than estimates used in demographic models, which suggests that for many species, these models may need re-evaluation. Supervivencia de Volantones de Wilsonia citrina en Fragmentos de Bosque Pequeños y Grandes