Bird species richness in a Bornean exotic tree plantation: A long-term perspective

To provide sustainable income from forestlands, large areas in the tropics are planted with “agricultural” trees, such as oil palm and rubber, and “industrial” trees, such as Acacia mangium and Gmelina arborea. To examine how native forest birds use such plantations, we surveyed in 2005 the avifauna at Sabah Softwoods, a plantation in southeastern Sabah, Malaysian Borneo. We focused on A. mangium, Albizia (Paraserianthes falcataria), oil palm (Elaeis guineensis), and logged native forest, and compared our results to those of a study conducted at the same plantation in 1982. The number of forest species in the industrial groves did not change dramatically between 1982 and 2005, even though the trees had been cropped several times and the plantation was, by 2005, completely surrounded by cleared land and far removed from primary forest. However, as is common in logged or isolated forests throughout the world, certain primary forest groups (e.g., muscicapine flycatchers) have been extirpated from the entire plantation area. The industrial groves also lacked some larger species of kingfisher, woodpeckers, and canopy frugivores. Nevertheless, numerous primary forest taxa (ca. 50% of species) were found in mature industrial tree groves. Albizia attracted the most species of birds, followed closely by Acacia. Both tree types underpinned relatively complex secondary forests that attracted forest birds. In contrast, younger groves of Acacia and Albizia held mainly open country and scrub species. Oil palm, as a remarkably simple and unusual habitat, attracted few bird species. Sustained occurrence of forest birds in all groves of exotic trees at Sabah Softwoods was substantially enhanced by the relatively rich avifauna of the logged native forest remaining in substantial stands throughout the plantation.     

Distance to edges, edge contrast and landscape fragmentation: Interactions affecting farmland birds around forest plantations

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.     

Threshold effect of eucalypt density on an aggressive avian competitor

General guidelines available to revegetation planners focus on the spatial context and dimensions of the revegetated site. However, site-specific habitat factors can have overarching importance for habitat value, especially where interactions with competitors or predators may play an important role. Current revegetation projects in Australia which aim to restore slow-growing buloke (Allocasuarina luehmannii) woodland, a threatened habitat important for bird conservation, usually include faster-growing eucalypts in plantings. This research aimed to identify whether eucalypt presence in buloke woodland facilitates invasion by the noisy miner (Manorina melanocephala), an aggressive competitor that is absent from pure buloke woodland. Birds were surveyed in buloke woodland remnants that contained eucalypts as a sub-dominant species at densities of 0-16 per ha. The probability of noisy miner presence in buloke woodland increased markedly where eucalypts were present at a density of approximately five per hectare. The presence of noisy miners resulted in a substantial difference in bird assemblage structure and composition. Small-bodied insectivorous birds which are experiencing population declines in southern Australia were recorded on average six times more often in transects without noisy miners (low-eucalypt density transects). Avian behaviour and habitat use was also altered, with birds flying more frequently in transects where noisy miners were present. A minor difference in habitat composition results in substantial degradation of the conservation value of non-eucalypt woodland in eastern Australia due to invasion by aggressive avian competitors. Revegetation and restoration practices should take into account the potential for such subtle floristic differences to result in substantial variation in conservation outcomes.     

Factors affecting site occupancy by woodland bird species of conservation concern

Significant biodiversity loss is characteristic of agricultural landscapes worldwide. Biodiversity recovery efforts in such landscapes can be hamstrung by a paucity of information on factors affecting species’ distributions, particularly for threatened and/or declining species. The temperate woodlands of south-eastern Australia have been extensively modified for agriculture and numerous bird taxa are declining. We have explicitly identified habitat and landscape attributes of woodland remnants affecting site occupancy by 13 woodland bird species of conservation concern.Using case-control data and linear logistic regression, we found that site occupancy for each species was related to both habitat and landscape variables. Habitat variables of particular importance included those in the ground layer (an abundance of leaf litter, an intact surface crust of mosses and lichens and a scarcity of annual grasses) and overstorey (a scarcity of eucalypt dieback and an abundance of mistletoe). Landscape variables strongly affecting site occupancy included the number of paddock trees and the area of native grass within 500 m of a site. Many of our study species were found most often in regrowth remnants.Our findings indicate a gap between current conservation practices and the actual habitat requirements of woodland bird species of conservation concern. Successful management will require protection and/or rehabilitation of the ground layer and overstorey of woodland remnants and sympathetic management of the surrounding landscape. It also will require managers to go beyond current practices of conserving old growth remnants and establishing replantings to maintaining and creating stands of woodland regrowth.     

Effects of forestry practices on vegetation structure and bird community of Kibale National Park, Uganda

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.     

The effects of extreme forest fragmentation on the bird community of Singapore Island

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.     

The value of forest strips for understorey birds in an Amazonian plantation landscape

Remnant forest strips are frequently proposed as valuable conservation tools in fragmented tropical landscapes, yet we currently lack evidence to evaluate their potential conservation value for native biota. We examined the potential value for understorey forest birds of 30-year-old riparian and terra firme (unflooded) primary forest strips within a large silvicultural landscape in the north-east Brazilian Amazon, where the matrix is dominated by Eucalyptus plantations. We conducted mist-netting in eight forest strips connected to continuous forest (four of each forest type), with a total of 24 replicate sampling sites located near to (<1 km), far from (2.5-9 km), and within undisturbed forest controls (i.e. 16 samples within the strips, and 8 in controls). Bird communities in both strip types changed with increasing distance along forest remnants into the plantation matrix. Matrix-embedded samples were characterised by a higher representation of birds typical of secondary growth forest but not those typical of the Eucalyptus-dominated matrix. While the long-term viability of the bird populations in these remnants remains unclear, our data demonstrate that forest strips can provide important habitat for many bird species that are otherwise rarely found outside primary forest. Forest strips therefore provide an important tool to enhance biodiversity conservation in plantation landscapes. The relative practical ease with which these areas can be selected and maintained means that the protection of forest strips as part of a wider conservation strategy is likely to have particular appeal to policy makers and landscape managers working in the human-dominated tropics.     

Land use and habitat gradients determine bird community diversity and abundance in suburban, rural and reserve landscapes of Minnesota, USA

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.     

Fauna conservation in Australian plantation forests - a review

A review of the value for fauna of conifer and eucalypt plantations in Australia is presented. Five key reasons highlight a need for wildlife conservation as part of plantation management. These are: (1) The plantation estate in Australia is set to triple in the coming decades, and where new plantations are located and how they are managed will influence the biota that currently exist in such landscapes. This is particularly critical in many semi-cleared former grazing landscapes where the establishment of new plantations is focused. This is because: (1) (a) native vegetation communities in these areas are poorly represented in the existing reserve system, and, (b) uses such as wood and pulp production need to be balanced with other management values such as wildlife conservation. (2) The maintenance of some elements of the biota within plantations could have benefits for key ecosystem processes like pest control. (3) Although some species cannot be conserved in plantation-dominated landscapes, many species can be through the adoption of (sometimes minor) modifications to forest management. (4) The maintenance (or loss) of biota in plantations is relevant for moves toward ecological standards and the certification of plantations in many parts of the world. And, (5) simple plantation forestry which has a narrow and intensive management focus on producing a forest crop for a limited array of purposes, may not meet societal demands for a range of outputs from plantations in addition to wood and pulp. It also may not be congruent with the principles of ecological sustainability.Our review showed that almost all research undertaken in Australian plantations, both in conifers and eucalypts, highlighted the importance of landscape heterogeneity and stand structural complexity for fauna conservation. At the landscape level, patches of retained native vegetation, strips of riparian vegetation, dams, open and clearing areas can significantly increase the number of native species that occur within plantations. Some species that occur in these areas can also use adjacent planted areas, a result common to conifer and eucalypt plantations. The spatial juxtaposition of stands of varying ages throughout plantation landscapes also can contribute to the maintenance of some populations of native taxa. At the stand level, structural complexity is also important for fauna with many species responding positively to the presence of native understorey plants, the presence of windrowed logs, and logging slash left on the forest floor.The management of plantations to promote landscape heterogeneity and stand structural complexity will, in many cases, involve trade-offs that will influence wood and pulp production. The extent to which this occurs will be dependent on the objectives of plantation management and how far they extend toward the complex plantation forestry model to incorporate social and environmental values in addition to wood and pulp production.     

Browsing down our natural heritage: Deer impacts on vegetation structure and songbird populations across an island archipelago

Declines in forest and woodland birds have largely been attributed to habitat loss and fragmentation. In the past decade, however, the potential for herbivores to influence bird species abundance and community composition via their direct impact on vegetation structure has also been recognised. We tested the hypothesis that deer influence vegetation structure and bird assemblages in a large island archipelago in western North America using surveys of 18 islands with deer densities ranging from 0 to over 1 deer/ha. Amongst these islands, reduced predation and hunting pressure has allowed deer populations to increase above those likely to have existed in pre-European times. Our results support a growing body of evidence that deer regulate both the cover and architecture of understory vegetation which in turn profoundly affects island bird assemblages. Deer-free islands supported the most abundant and diverse bird fauna. Iconic songbirds such as the rufous hummingbird, song and fox sparrow were abundant on islands with no deer but substantially reduced on islands with high deer densities. Only one bird species, the dark-eyed junco, preferred moderate and high density deer islands. Our observations suggest that current cohorts of palatable shrubs on islands with high deer densities are relatively old and potentially represent an impending extinction debt, where the full effects of high deer density on island biota may take decades to fully unfold. Our results suggest that deer densities below a threshold of 0.1 deer/ha should allow native vegetation to recover and a rich and diverse bird species assemblage to persist. We suggest that adaptive management be used to test the validity of this threshold, and that without active management of deer abundance, local extinctions of native flora and fauna appear likely to accelerate.     

Extending the rotation period in larch plantations increases canopy heterogeneity and promotes species richness and abundance of native beetles: Implications for the conservation of biodiversity

We studied the effects of extending the rotation period (long-rotation) and related ecological variables on the biodiversity of six beetle families in larch (Larix kaempferi) plantations. Beetle diversity in the forest understory and the canopy of long-rotation and middle-aged plantations was compared. The relationships between the species richness of each beetle family and 24 ecological variables were identified. We found that beetle diversity tended to increase with long-rotation and responded differently to the ecological variables in two woodland strata (understory and canopy); e.g., an increase in phytophagies occurred in the canopy. Among the 24 measured ecological variables, the species richness of naturally regenerated mature trees, their abundance, and the quality and quantity of coarse woody material (CWM) had the strongest influences on beetle diversity. The former two variables increased with long-rotation; however, most variables related to CWM did not increase because thinned trees were left in middle-aged plantations as fallen logs. Therefore, the occurrence of naturally regenerated native trees that had grown sufficiently tall to reach canopy height in long-rotation plantations underpinned the improved biodiversity in larch plantations, contributing to native beetle species richness in these woodlands. Long-rotation makes plantations more heterogeneous, particularly in the canopy, and promotes greater native beetle diversity.     

High sensitivity of montane bird communities to habitat disturbance in Peninsular Malaysia

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.     

Land use and conservation value for forest birds in Central Sulawesi (Indonesia)

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.     

Acari (mite) assemblages under plantations of bluegum, Eucalyptus globulus, in southwestern Australia

Farm forestry, in particular the planting of exotic bluegums Eucalyptus globulus, is a strategy increasingly used in southwestern Australia to mitigate the damaging effects of land clearing and to improve agricultural productivity. At the same time, such agroforestry systems have the potential to at least partially impede the biodiversity decline associated with habitat destruction and agriculture. The soil/litter habitat, an important repository of biodiversity in terrestrial systems, is one of the habitats most affected by clearing and conventional agricultural practices. Within this habitat, free-living mites are one of the most diverse and abundant animal groups contributing significantly to key ecosystem functions. This study compares the soil and litter mite assemblages of 7-year-old E. globulus plantations with those of adjacent native forest and pasture sites. The assemblages associated with E. globulus were substantially more diverse than those of the pasture soils but well below that of the native forest. Particularly low densities of oribatid mites were observed in the plantation sites. We suggest that the young plantation age, the exotic nature of the plantation species, and the homogeneous, mono-specific litter all contributed to limit the potential for these plantations to enhance mite biodiversity.     

Local and landscape factors determine functional bird diversity in Indonesian cacao agroforestry

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.     

Spatial and temporal variations in the use of rice-paddy dominated landscapes by birds in Japan

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.     

桉树林和针阔混交林对植物多样性的影响比较

为了系统评价桉树林和针阔混交林对生物多样性的影响,采用立地条件控制及空间代替时间法,对南亚热带桉树林（2代和1代）和针阔混交林（10～11 a生和5～7 a生）乔木层、灌木层和草本层生物多样性进行了比较。结果表明,针阔混交林Ⅰ（10～11 a生）有68种植物,隶属38科62属,桉树林Ⅱ（桉树2代）有41种,隶属26科39属,针阔混交林Ⅲ（5～7 a生）有53种植物,隶属30科48属,桉树林Ⅳ（桉树1代）有55种植物,隶属33科51属。针阔混交林乔木层重要值较大的科为杉科、樟科、金缕梅科、大戟科、山茶科、木兰科和楝科,灌木层为五加科和大戟科,草本层以禾本科、鳞始蕨科和乌毛蕨科为主。桉树林乔木层重要值较大的科为桃金娘科、芸香科、樟科、大戟科和漆树科,灌木层为冬青科、樟科、大戟科和芸香科,草本层以禾本科和里白科为主。4种试验林间乔木层、灌木层和草本层物种丰富度指数（S）、Shannon-Wiener指数（H’）、Simpson优势度指数（D）、Pielou均匀度指数（E）差异不显著（P > 0.05）。针阔混交林Ⅰ乔木层和灌木层H’指数、D指数及E指数显著高于草本层（P < 0.05）,桉树林Ⅱ乔木层、灌木层和草本层间H’指数、D指数及E指数均存在显著差异（P < 0.05）。针阔混交林乔木层均匀度指数（E）均大于桉树林。与针阔混交林Ⅲ相比,针阔混交林Ⅰ乔木层物种S,H’,D及E指数呈上升趋势,而灌木层和草本层呈下降趋势。与1代桉树林Ⅳ相比,2代桉树林Ⅱ灌木层和草本层S,H’和D指数呈下降趋势。研究结果为桉树人工林物种多样性保护和可持续经营提供科学依据。     

Is landscape context important for riparian conservation? Birds in grassy woodland

An important challenge for riparian management is to determine the extent to which landscape context influences the faunal assemblages of riparian habitats. We examined this challenge in the variegated landscapes of southeastern Queensland, Australia where riparian vegetation is surrounded by both extensive grazing and intensive cropping. We investigated whether riparian habitats adjacent to different landuses support similar bird assemblages. Three types of riparian habitat condition were sampled (uncleared ungrazed; uncleared grazed; cleared grazed) in four different land-use contexts (ungrazed woodland; grazed woodland; native pasture; crop) although only six of the 12 possible treatment combinations were available. Eighty percent of bird species responded significantly to changes in both riparian habitat condition and landscape context, while fewer than 50% of species were significantly influenced by landscape context alone. The influence of landscape context on the bird assemblage increased as the surrounding land use became more intensive (e.g., woodland to native pasture to crop). Riparian zones have been shown to have consistently high biodiversity values relative to their extent. These findings suggest it is not enough to conserve riparian habitats alone, conservation and restoration plans must also take into consideration landscape context, particularly when that context is intensively used land.     

Landscape supplementation in adjacent savannas and its implications for the design of corridors for forest birds in the central Cerrado, Brazil

We examined landscape supplementation (sensu [Oikos 65 (1992) 169]) by forest birds along forest/savanna boundaries in central Brazil to: (1) verify the role of savanna vegetation in providing resources to forest bird communities; (2) suggest minimum amounts of savannas to be conserved within corridors, to provide adequate foraging habitat for forest birds outside reserves. Transect counts parallel (n=64) and perpendicular (n=64) to forests were conducted in eight savannas (cerrado sensu stricto) between February 2000 and January 2001. Patterns of species richness and abundance of birds in relation to distances from forests were examined using Generalised Linear Mixed Models. Omnivores were the most abundant birds foraging in savannas, followed by insectivores and frugivores. Landscape supplementation in savannas was proportional to the density of savanna vegetation. Also, it was higher in the breeding season than in the non-breeding period. These two patterns suggest that surrounding savannas play a major role in providing additional foraging areas for forest bird species. We suggest that the environmental policy currently protecting 20 m of gallery forests along each side of rivers be modified to include at least 60 m of savanna along these forests through central Brazil. The study suggests that appropriate conservation efforts should also encompass the surrounding matrix to which the home ranges of target species are expanded, and not only their major habitat.     

Avian assemblages along a gradient of urbanization in a highly fragmented landscape

Our goal was to evaluate how avian assemblages varied along a gradient of urbanization in the highly fragmented landscape of coastal southern California. We measured species richness and abundance of birds within continuous blocks of habitat, within urban habitat fragments that varied in landscape and local habitat variables, and within the urban matrix at different distances from the wildland interface. These comparisons allowed us to characterize patterns of avifaunal response to a gradient of urban fragmentation. At the fragment scale, we found that fragment area was a strong, positive predictor of the total number of breeding species detected per fragment; total bird abundance per point count also increased with fragment size. Tree cover was higher in small fragments, as was the abundance of birds that typically occupy wooded habitats. Comparisons between core, fragment, and urban transects revealed differing patterns of response of individual bird species to urbanization. In unfragmented habitat, we recorded a relatively high diversity of urbanization-sensitive birds. In urban transects, these species were rare, and a relatively few species of non-native and anthropophilic birds were common. These urbanization-enhanced birds were also recorded in previous urban gradient studies in northern California and Ohio. Bird communities along the urban gradient reached their highest richness and abundance in fragments. The marked difference in vegetation structure between urban and natural landscapes in this arid shrubland system likely contributed to this pattern; the presence of native shrubs and exotic trees in fragments enabled both shrub and arboreal nesters to co-occur. As is characteristic of biotic homogenization, urban fragmentation in coastal southern California may increase local diversity but decrease overall regional avifaunal diversity.