首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 45 毫秒
1.
  相似文献   

2.
Singapore Island suffered one of the highest known deforestation rates in the tropics from the mid-to-late 19th century when over 95% of its native lowland forest was cleared. We compared the current bird community structure and composition among three habitat types, i.e., old (>50 years, 7-935 ha) and young (?50 years, 29-49 ha) naturally regenerating secondary forests and abandoned wooded plantations (27-102 ha) dominated by exotic species. Forest patch area had the strongest influence on the current species richness. The overall bird richness was not greater in most mature forest patches, but 20 species were only found in the old secondary forests and five of these were found in <50% of these patches. The rapid decrease in the number of forest species in plantations was offset by an increase in the number of open habitat species. Comparisons with current bird communities in nearby mainland forest sites (Peninsular Malaysia) suggest that the forest avifauna of Singapore is depauperate. The preservation of larger mature and maturing forests is therefore required for conserving the extant forest avifauna in Singapore. Connecting isolated patches can also be envisioned to facilitate movements of forest birds that have low densities and restricted distribution.  相似文献   

3.
Woodpeckers (family Picidae) show promise as indicators of avian diversity in forests because their populations can be reliably monitored, and their foraging and nesting activities can positively influence the abundance and richness of other forest birds. A correlation between woodpecker richness and richness of forest birds is known to exist at the landscape scale, but uncertainty remains whether this correlation occurs at the smaller stand-level spatial scales where forest management activities take place. We used data collected under a diverse range of forest types, harvest treatments, and forest health conditions during a long-term study of bird communities in interior British Columbia, Canada, to examine two basic questions: (1) at the level of individual forest stands, is woodpecker richness correlated with bird richness (measured as richness of all other bird species)? and (2) do woodpecker richness and bird richness have similar habitat correlates? Bird richness was positively correlated with woodpecker richness (β = 0.59, SE = 0.22, 95% CI = [0.14 1.03]). Richness of both woodpeckers and all other birds were positively correlated with tree species richness and negatively correlated with density of pines, and the effect for forest harvest type was similar for both measures of avian richness (uncut < partial harvest < clearcut with reserves). The effect of density of lodgepole pines killed by mountain pine beetles differed between the two richness measures, being positive for woodpecker richness and negative for forest bird richness. We conclude that the richness of woodpeckers is indeed correlated with the richness of other birds at the stand-level, and can serve as a reliable indicator of overall bird richness in most forest stands and conditions, except during insect outbreaks when differential responses by woodpeckers and the rest of the avian community may decouple the relationship between bird richness and woodpecker richness.  相似文献   

4.
Unprecedented deforestation is currently underway in Southeast Asia. Since this trend is likely to continue, it is critical to determine the value of human-modified habitats (e.g., mixed-rural habitat) for conserving the regional native forest avifauna. The impacts of ongoing deforestation on the highly endemic avifauna (33%) of Sulawesi (Indonesia) are poorly understood. We sampled birds in primary and secondary forests in the Lore Lindu National Park in central Sulawesi, as well as the surrounding plantation and mixed-rural habitats. Species richness, species density and population density of forest birds showed a consistent decreasing trend in the following order: primary forests > secondary forests > mixed-rural habitat > plantations. Although primary forests contained the highest proportion (85%) of a total of 34 forest species recorded from our point count surveys, 40-yr old secondary forests and the mixed-rural habitat showed high conservation potential, containing 82% and 76% of the forest species, respectively. Plantations recorded only 32% of the forest bird species. Fifteen forest species had the highest abundance in primary forests, while two species had higher abundance outside primary forests. Our simulations revealed that all forest birds that were sensitive to native tree cover could be found in areas with at least 20% continuous native tree cover. Our study shows that although primary forests have the highest conservation value for forest avifauna, the potential of degraded habitats, such as secondary forests and the mixed-rural habitat, for conserving forest species can be enhanced with appropriate land use and management decisions.  相似文献   

5.
Rivers and streams lined by narrow forest strips are common in the lowland countryside of south-western Costa Rica. We studied the importance of these gallery forests for understorey birds, especially forest species. Using mist-nets, we captured 1110 birds belonging to 90 species between June and September 2007 at 16 sites spread equally over four habitat types: forest interior, forest margin, gallery forest connected to closed forest, and isolated gallery forest. Though isolated gallery forests had the greatest number of expected species in total, they supported the lowest number of forest-specialist species, lower even than connected gallery forests. Granivorous birds showed an increase from forest to isolated gallery forest, all other feeding guilds however showed no change. The studied habitats differed from each other in their faunal composition. Assemblages of three species groups categorised by their habitat preferences (forest specialists, forest generalists, non-forest species) showed nested distribution patterns across the four habitats. There was no significant difference in the proportion of birds with brood patches or of recaptures across the studied habitat types, leading to the assumption that birds not only use gallery forests for movement and foraging but also for reproduction. Though of limited conservation value for most forest understorey birds, at least for a small fraction of forest species gallery forests constitute an important secondary habitat. More significantly, they can form corridors or stepping stones that allow movements within the matrix of human-dominated habitats, and represent an important landscape component benefiting total bird species richness in the Costa Rican countryside.  相似文献   

6.
The effects of habitat fragmentation on forest bird assemblages were analysed in 214 holm oak (Quercus ilex) remnants spread across the northern and southern plateaux of central Spain. Bird richness was highly dependent on fragment area for all species regardless of isolation, and barely affected by habitat traits. Geographical location was associated with high differences in richness of bird assemblages, which included 17 species exclusive to northern remnants and one exclusive to southern remnants. This supports the hypothesis that habitat suitability deteriorates sharply from north to south for forest birds in Spain. The species-area relationships of bird assemblages sampled in fragmented forests along a broad continental gradient (from Norway to southern Spain) showed that true forest birds only nest in woodlands >100 ha in southern Spain, whereas the full complement of forest species occurs in much smaller fragments in central-western Europe. Loss of species that are particularly sensitive to habitat fragmentation accounts for these differences between dry Spanish and mesic European woodlands. These results are explained by the low habitat suitability of Spanish woodlands, associated with the restrictive conditions for plant regeneration in the Mediterranean climate and long-standing human usage. There is, therefore, a particular need to develop management strategies that conserve birds, and probably other forest organisms, in Mediterranean regions by preventing habitat deterioration and decreases in fragment size, and by conserving all woods >100 ha.  相似文献   

7.
Despite the loss of 83% of native forests in the Philippines, little is known on the effects of this massive habitat loss and degradation on its forest biotas. This is a cause for concern because of the threat posed to the country’s large number of endemic taxa. To investigate the impacts of anthropogenic disturbance, forest birds and butterflies were surveyed in closed and open canopy forests, as well as suburban, rural and urban areas within the Subic Bay Watershed Reserve and Olongapo City in western Luzon. Measures of forest species richness and population densities for both taxa were similar in the two forest types, but showed different patterns in the other habitats. Indirect gradient analysis showed that forest bird species were positively correlated with vegetation variables (i.e., canopy cover, tree density, height to inversion and ground cover), while forest butterflies were not strongly correlated to any of the measured habitat variables. Community composition of birds in forests was distinct from those in modified habitats, while butterfly communities were more similar. A simulation showed that canopy cover of 60% or higher was required by 24 of the 26 bird species that were sensitive to canopy loss. Endemicity and nesting strata were the significant predictors of vulnerability to habitat disturbance for birds, while endemicity and larval hostplant specificity were significant for butterflies. Both taxa were negatively affected by anthropogenic disturbance but may respond to different components in the habitat (i.e., structure and resources), and thus cannot be used as surrogates of each other. Conservation of forests with contiguous canopy cover should be prioritized, and more ecological research is needed to improve the knowledge on the effects of disturbance on Philippine biodiversity.  相似文献   

8.
Bird species’ community responses to land use in the suburbanizing Twin Cities, Minnesota, USA, were contrasted among reserves, rural lands, and suburbs. For each land use type, bird composition, diversity, and abundance were recorded for 2 years in ≈99 plots in three sampling units (each ≈4500 ha). A habitat gradient defined by canopy structure (grasslands to savannas to forests) was influenced by land use, so ≈300 plots were used to characterize simultaneous variation in bird communities along land use and habitat gradients. At broad scales (aggregate of 33 plots covering ≈4500 ha) suburbs supported the lowest bird richness and diversity and rural landscapes the most, with reserves slightly below rural. Although reserves were like rural lands in diversity of bird communities, they supported more species of conservation concern, particularly of grasslands and savannas. Differences among land use types varied with habitat structure. Suburbs, rural lands, and reserves had similar forest bird communities, but differed in grassland and savanna bird communities. The extensive rural forests are important for the region’s forest birds. Suburban grasslands and savannas had low shrub abundance, low native bird richness and high non-native bird richness and abundance. However, total bird richness and diversity were as high in suburban as in rural and reserve plots because high native richness in suburban forests and high non-native species richness in suburban grasslands and savannas compensated for lower native richness in suburban grasslands and savannas. Bird conservation here and in the Midwest USA should protect rural forests, expand grasslands and savannas in reserves, and improve habitat quality overall.  相似文献   

9.
We show how Chilean forest bird species richness, abundance and guild structure changes as a function of structural properties of forest stands. We surveyed bird assemblages in two old-growth (>200 years), two mid-successional (30-60 years), and two early-successional forest stands (4-20 years), from November 1999 to September 2000, on Chiloé Island, southern Chile (42°S). Birds were grouped into four habitat-use guilds: large-tree users, vertical-profile generalists, understory species, and shrub-users that occasionally use forests. We recorded a total of 24 bird species: 21 in old-growth, 14 in mid-successional and 16 in early-successional stands. Large-tree users and understory birds were most abundant in old-growth stands, vertical-profile generalists were common in both old-growth and mid-successional stands, and shrub-users were only common in early-successional stands. For nine bird species we found significant relationships between their local abundance and forest structural elements. Higher bird densities in old-growth forests were associated with greater availability of canopy emergent trees, snags, logs and understory bamboo cover in this habitat. Accordingly, bird species diversity in forest stands can be predicted by the presence of these structural elements, and forests should be managed to conserve structural elements that create favorable habitat for bird species in order to prevent future species losses due to logging practices.  相似文献   

10.
Despite the fact that Madagascar is classified a biological `hotspot' due to having both high levels of species endemism and high forest loss, there has been no published research on how Madagascan bird species respond to the creation of a forest edge or to degradation of their habitat. In this study, we examined how forest bird communities and different foraging guilds were affected by patch habitat quality and landscape context (forest core, forest edge and matrix habitat) in the threatened littoral forests of coastal southeastern Madagascar. We quantified habitat use and community composition of birds by conducting 20 point counts in each landscape contextual element in October and November 2002. We found that littoral forest core habitats had significantly (p<0.01) more bird species than forest edge and matrix habitats. Thirty-one (68%) forest dependent species were found to be edge-sensitive. Forest edge sites had fewer species, and a higher representation of common species than forest interior sites. Twenty-nine species were found in the matrix habitat, and the majority of matrix-tolerant forest species had their greatest abundance within littoral forest edge habitats. Guild composition also changed with landscape context. Unlike other tropical studies with which we are familiar, we found that frugivorous species were edge-sensitive while sallying insectivores were edge-preferring. The majority of canopy insectivores (n=15, 88%), including all six endemic vanga species, were edge-sensitive. When habitat quality was assessed, the distributions of nine edge-sensitive species were significantly (p<0.01) affected by changes in habitat complexity and vegetation vertical structure in core or edge point counts. Therefore, we believe that changes in vegetation structure at the edge of littoral forest remnants may be a key indicator of mechanisms involved in edge sensitivity of forest dependent species in these forests. Our findings indicate that habitat fragmentation and degradation affect Madagascan bird communities and that these processes threaten many species. With continued deforestation and habitat degradation in Madagascar, we predict the further decline of many bird species.  相似文献   

11.
Large-scale intensification of smallholder cacao management is currently affecting the agroforestry landscapes of Sulawesi (Indonesia), the world’s third largest cacao producer. Little is known about how this shift from diverse plantations to full-sun cacao will affect functionally important biodiversity within the agroecosystem, and how this is related to landscape-wide patterns in land-use and natural ecosystems. We recorded birds in 43 cacao plots differing in woody and herbaceous vegetation as well as distance to forest in two valleys around the Lore Lindu National Park in Central Sulawesi. Species richness of frugivores and nectarivores decreased with increasing distance to forest, whereas granivorous birds increased in richness. Forest specialists, but not habitat generalists, responded positively to forest edge proximity. Species richness of all functional groups except seed eaters increased at higher density of tall shade trees. Greater species richness of shade trees was associated with higher species richness of frugivores and nectarivores, while herbaceous vegetation did not have a strong impact on the avifauna. The positive effect of shade trees was independent of distance to forest. In conclusion, our study shows the relative importance of local and landscape effects on bird diversity with shade trees being critical for bird conservation in cacao agroforestry landscapes.  相似文献   

12.
Effects of age and intensity of urbanization on farmland bird communities   总被引：1，自引：0，他引：1  
Urban sprawl is now occurring worldwide and considered as a major large-scale perturbation on ecosystems. Consequently, urban territory is replacing other habitats such as agricultural areas. As farmland biotic communities are already reported to be declining, it seems necessary to assess the urbanization impact on them. We conducted a bird survey on 92 plots of 1 × 1 km chosen after stratification on the proportion of urban area and farmland habitat (either 0%, 25%, 50%, 75%), focusing on farmland habitat. Two aspects of urbanization were studied: its intensity and its age. We found that farmland bird species richness did not vary with increasing proportion of urbanized habitat. Non-farmland bird species richness increased from 0% to 25% classes and was constant for other classes. No effect of the urbanization age on farmland bird species richness was found, whereas a positive one was found on the non-farmland birds’ species richness. Abundance of the most specialized farmland birds decreases with urbanization intensity and age. We also found that, the more urbanized and the more recently urbanized the plots, the more similar bird communities. A strong difference in farmland bird’s communities’ compositions was found between 0% and 25% of urbanization, whereas no distinction was found between 50% and 75%. Altogether, our results suggest that to maintain for farmland birds, it is better to add new urban habitat in place where it already exist, rather than to spread it in small lots throughout the landscape.  相似文献   

13.
Afforestation often causes direct habitat losses for farmland birds of conservation concern, but it is uncertain whether negative effects also extend significantly into adjacent open land. Information is thus required on how these species react to wooded edges, and how their responses are affected by edge and landscape characteristics. These issues were examined in Mediterranean arable farmland, using bird counts at 0, 100, 200, 300 and >300 m from oak, pine and eucalyptus edges, embedded in landscapes with variable amounts and spatial configurations of forest plantations. Bird diversity declined away from edges, including that of woodland, farmland and ground-nesting birds. Positive edge responses were also found for overall and woodland bird abundances, and for five of the nine most widespread and abundant species (Galerida larks, stonechat, linnet, goldfinch and corn bunting). Strong negative edge effects were only recorded for steppe birds, with reduced abundances near edges of calandra larks and short-toed larks, but not of little bustards and tawny pipits. Edge contrast affected the magnitude of edge effects, with a tendency for stronger responses to old and tall eucalyptus plantations (hard edges) than to young and short oak plantations (soft edges). There were also species-specific interactions between edge and fragmentation effects, with positive edge responses tending to be strongest in less fragmented landscapes, whereas steppe birds tended to increase faster away from edges and to reach the highest species richness and abundances in large arable patches. Results suggest that forest plantations may increase overall bird diversity and abundance in adjacent farmland, at the expenses of steppe birds of conservation concern. Clustering forest plantations in a few large patches and thus reducing the density of wooded edges at the landscape-scale might reduce such negative impacts.  相似文献   

14.
It has been suggested that an increase in the area of low-intensity land-use on arable land (e.g. set-aside fields and short-rotation coppice), and high or increased farmland habitat heterogeneity, may halt or reverse the observed population decline of farmland birds. We tested these hypotheses by undertaking farmland bird censuses during two contrasting periods of agricultural policies and land-use (i.e. 1994 and 2004) in a farmland region covering a gradient of forest- to farmland-dominated landscapes in Sweden. Local species richness (i.e. at 3 hectare sites) declined significantly between 1994 and 2004. Local species richness was positively related to habitat heterogeneity in both years of study whereas temporal change in species richness was not. Local change in species richness was positively associated with a change in the proportion of non-rotational set aside and short-rotation coppice (i.e. low-intensity land-use forms), but also to changes in the amount of spring-sown crops. However, the effect of low-intensity land-use was significantly dependent on the amount of forest in the surrounding landscape. An increase in low-intensity land-use was linked to an increase (or less marked decrease) in species richness at sites located in open farmland surroundings but to a decrease in richness at sites located in forest surroundings. This interaction between amount of forest and low-intensity land-use could be interpreted as a “rare habitat effect”, where an increase in a farmland habitat only positively affects biodiversity when it was originally uncommon (i.e. open farmland areas). Our results suggest that conservation measures of farmland biodiversity have to be put in a landscape context.  相似文献   

15.
In this paper data on the bird community overwintering in the subalpine zone of Sagarmatha National Park (Khumbu Himal area, Nepal) are presented, with particular emphasis on habitat structure and bird-habitat relationships. The impact of land use and management on the conservation of diversity is analysed and discussed. Four habitat types were considered: mixed forest, pure juniper forest, dwarf rhododendron shrubbery and cultivations. Mixed forest supports the richest avifauna, but forest birds are sensitive to over-exploitation of their habitat: bird density, species richness and diversity are significantly lower in heavily utilised forest. Here, the lower density of rhododendrons, firs and birches, together with their younger age, seem to be unattractive to insectivorous gleaners and granivores, which prefer tree- and understorey-rich spots of unutilised forest. Terraced cultivations also are a rich habitat for wintering birds, and traditional cultivations with hedgerows and scattered bushes have a great potential for bird conservation. Juniper woods are important habitats mainly for frugivores, whereas dwarf rhododendron shrubberies support the poorest avifauna. This study emphasises that forest birds and habitats are severely threatened. As deforestation is the consequence of the tourist pressure for fuelwood along the trekking route to Mt. Everest Base Camp, a strict regulation of tourist-related developments is essential to preserve biodiversity and manage land uses within sustainability.  相似文献   

16.
Agricultural landscapes with spatial and temporal variations interact with each other to affect the existing biodiversity. Though rice fields provide important habitats for birds all over the world, studies so far have rarely explored the effects of landscape heterogeneity on bird species in rice paddy areas. This study investigated the effects of habitat cover and landscape variables on the species richness and the abundance of birds in rice paddy areas in Japan. Data on bird occurrence and the environment were collected at 32 grid squares (1 × 1 km) in the Tone River basin. The richness and the abundance of agricultural wetland species were particularly high in landscapes with large areas of rice fields in summer, when rice fields were irrigated, but in those with large areas of open water in winter, when rice fields were drained. It is important to maintain a combination of rice fields and open water to satisfy multiple habitat requirements by agricultural wetland species throughout the year. Grassland species were positively associated with a rich diversity of land cover including fallow fields and open water, indicating the importance of a simultaneous existence of multiple landscape elements. Forest cover in landscapes positively affected edge species and woodland species. Since forest cover had a relatively strong correlation with edge density, the responses of bird species to changes in forest cover and edge density need to be explored further. This study illustrates the importance of spatial and temporal landscape complementation for bird species in rice paddy areas.  相似文献   

17.
I examined the lingering effects of past timber management practices on the vegetation structure and bird community of Kibale National Park, Uganda. I compared four forest treatments: unlogged native forest (UL), two that were selectively logged at low (LL) and high (HL) intensities in the 1960s, and a conifer plantation (PL). Forest-dependent birds were best represented at UL. LL was similar to UL in both vegetation structure and bird community composition, although some forest-dependent bird species were missing from the former. HL had significantly less canopy closure and lower tree density than other plots as a result of the combination of extensive secondary damage and natural disturbance patterns that prevented the reclosure of the forest canopy. Thirty-one percent of the forest-dependent bird species observed during the study were not detected at HL. At PL, bird species richness and bird abundance were about a third of those observed in other plots. There were significant correlations between heterogeneity of tree distribution (horizontal heterogeneity) and abundance and species richness of birds across plots. Abundance and species richness of all, forest-dependent, and forest generalist birds were highest in plots with intermediate measures of horizontal heterogeneity, which were mostly unlogged or lightly logged. If reduced-impact logging practices are not implemented during selective logging operations in tropical forests, consequent long-term changes in vegetation structure may result in significant declines in the populations of some forest-dependent species, as was observed in Kibale National Park.  相似文献   

18.
Over the past few decades, the montane forests of Peninsula Malaysia have been severely impacted by the cultivation of exotic crops and urban sprawl. To guide conservation initiatives, montane bird communities were studied to determine their response along a disturbance gradient with the aim of identifying key factors influencing their distribution. Habitat types surveyed included primary and secondary montane forests, a tea plantation, rural, and urban areas in Cameron Highlands and Fraser’s Hill. Response variables included species richness and density quantified via point counts and mistnet surveys. Explanatory variables measured were related to vegetation structure, food abundance and land-use cover. Estimated ‘true’ species richness was higher for pristine and minimally disturbed sites, lower in tea plantation and lowest in heavily developed town centres. Nonmetric multidimensional scaling revealed that both vegetation structure (e.g. canopy density) and land-use cover (e.g. proportion of forest cover) influence species distribution; certain invasive lowland birds were tolerant of extreme development and native montane birds, in general, endured only slight habitat disturbances. A simulation indicated that montane forest dependant species richness started to decline when more than 20% of the canopy cover was lost. Less than a third of the species richness remained when more than 40% of the canopy cover was cleared. The logistic regression model suggested that sensitive species nested lower, were restricted to montane habitats and foraged in mid or high canopy. The dominance of lowland invasives in highly developed urban sites reveals that homogenisation of bird communities can occur even at higher altitudes (>1400 m a.s.l.). The results indicated that native montane birds communities are sensitive to habitat loss and degradation. Thus, any development in the highlands must proceed with minimal disturbance to montane forests, of which, keeping the canopy cover intact should be a crucial consideration.  相似文献   

19.
Small aspen stands are disappearing from the landscape in the Southwest, so it is important to understand their contribution to the avian community. We sampled birds in 53 small, isolated aspen stands and 53 paired plots within the ponderosa pine forest in northern Arizona, during the 1996 and 1997 breeding seasons. Bird species richness and abundance were higher in aspen than in pine. However, bird species richness and abundance did not vary with size of the aspen patch or isolation index. In addition, direct ordination of species distributions with habitat factors suggested no distinct avian communities. This suggests that aspen stands do not harbor separate populations, but rather are locations where the regional avifauna reaches high local density and richness and may be crucial to birds in years of resource scarcity. Thus it is important for avian conservation to maintain many aspen stands across the landscape, encompassing a diversity of vegetation structure and composition.  相似文献   

20.
In South-East Asia patterns of forest loss can predict the number of threatened birds. On the oceanic islands of Wallacea, small-scale agriculture, rather than commercial logging, is the main cause of forest loss and conversion, but few studies have directly examined their responses to land use. In 2001, I studied the birds of primary forest and anthropogenic gardens on the well-forested, and remote, Damar Island (198 km2) in the Banda Sea. Furthermore, I examined broad changes to the islands bird fauna by comparing baseline bird lists obtained in the 19th century with 2001 data. The conversion of primary forest to garden resulted in substantial changes in avifaunal composition, and to the abundance of individual bird species, particularly to frugivorous and globally restricted-range species. Of 15 common birds, four were significantly more abundant in primary forest (blue-tailed imperial pigeon Ducula concinna, northern fantail Rhipidura rufiventris, golden whistler Pachycephala pectoralis and red-chested flowerpecker Dicaeum maugei) and one (scaly-breasted honeyeater Lichmera squamata) was more abundant in garden habitat. Incidental observations provided further evidence that many forest specialists (including the island endemic Damar flycatcher Ficedula henrici) rarely, if ever, used garden habitats notwithstanding its relative proximity. The number of resident birds recorded in 2001 (39) was similar to the 1890s (38), but six forest-dependent passerines were extirpated between samples. These losses are associated with the conversion of 25% of the primary forest to modified habitat since the 1890s, but given the sparse species and environmental change data available it is impossible to definitively pinpoint this as the only cause underlying the species losses. This study demonstrates that remote and relatively well-forested islands are not immune to the threatening processes impacting bird populations elsewhere in South-East Asia.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号