Bird communities in tropical agroforestry ecosystems: an underappreciated conservation resource

Tropical conservation and research focus primarily on protected areas and often ignore conservation values of surrounding agricultural lands. Understanding how species utilize agricultural land will maximize conservation efforts. We compared bird community composition in four habitats in northeastern Costa Rica: shade-grown cacao, live fences, riparian forest buffers, and preserved late-successional rainforest. Point counts over 2 months found 167 species from 36 families. Rainforest contained the most species unique to a habitat although richness per point was lower than in agricultural habitats. Half, 31, of the rainforest species did not occur in other habitats, while 106 species, mostly those preferring open areas, occurred in agroforest habitats but not rainforest. While agricultural habitats had fairly similar species composition to each other as determined by distance in an ordination, each also contained significant numbers, 9–30, of unique species. While intact rainforest remains central to conservation of tropical birds, agricultural lands with substantial trees, e.g., live fences, riparian buffers, and plantations with shade trees, can support a high richness of birds. These avian communities are not simply subsets of the rainforest species but include substantial numbers of unique species. Conservation contributions of these lands to species richness and complexity should be considered in conservation, and trees in these habitats preserved.     

Soil-water infiltration under crops, pasture, and established riparian buffer in Midwestern USA

The production-oriented agricultural system of Midwestern United States has caused environmental problems such as soil degradation and nonpoint source (NPS) pollution of water. Riparian buffers have been shown to reduce the impacts of NPS pollutants on stream water quality through the enhancement of riparian zone soil quality. The objective of this study was to compare soil-water infiltration in a Coland soil (fine-loamy, mixed, superactive, mesic Cumulic Endoaquoll) under multi-species riparian buffer vegetation with that of cultivated fields and a grazed pasture. Eight infiltration measurements were made, in each of six treatments. Bulk density, antecedent soil moisture, and particle size were also examined. The average 60-min cumulative infiltration was five times greater under the buffers than under the cultivated field and pasture. Cumulative infiltration in the multi-species riparian buffer was in the order of silver maple > grass filter > switchgrass. Cumulative infiltration did not differ significantly (P < 0.05) among corn and soybean crop fields and the pasture. Soil bulk densities under the multi-species buffer vegetation were significantly (P < 0.05) smaller than in the crop fields and the pasture. Other measured parameters did not show consistent trends. Thus, when using infiltration as an index, the established multi-species buffer vegetation seemed to improve soil quality after six years.This revised version was published online in November 2005 with corrections to the Cover Date.     

Vegetation structure,composition and effect of pine plantation harvesting on riparian buffers in New Zealand

The composition and structure of vegetation within riparian buffers prior to, and immediately post-harvesting in a managed radiata pine (Pinus radiata D.Don) forest is described and compared with riparian buffers in residual adjoining native forest on the Coromandel Peninsula, New Zealand. One hundred and twenty-one species (71% native) representing life forms from grasses to trees were recorded. The highest species richness, including both native and adventive (non-native) species, was found in riparian buffers in the post-harvest and native reference sites which had 18–25 species per site. Riparian buffers in mature pine plantations contained a mix of native species that was generally similar to, and not significantly reduced in species richness, from the reference native forest. Native species comprised 82–92% of the total cover in mature pre-harvest sites (irrespective of riparian width), and 99.8% in native reference sites. Compared with native forest the principal difference was a reduction of total cover in the upper tiers (5–12 m), and some increase in cover in the lower tiers. Adventive species in post-harvest sites comprised 16–67% of the total cover and were most frequently found in riparian areas highly disturbed by recent harvesting of the pines, particularly where riparian buffers were narrow or absent. Invasion by light-demanding adventives is expected to be temporary and most species are likely to be shaded out as the new rotation of pine trees develops. Radiata pine plantations in Whangapoua Forest can provide suitable conditions for the development of riparian buffer zones that will become dominated by native species, similar in richness and structure to neighbouring native forest.     

Avian assemblages in eucalypt forests,plantations and pastures in northern NSW,Australia

Eucalypt plantations are expanding rapidly in Australia, and their value for native fauna requires investigation. The relative conservation value of young eucalypt plantations was investigated through assessment of avifauna richness, abundance and composition using transect surveys incorporating point counts in five broad habitat types—dryland forests, riparian forests, dryland plantations, riparian plantations, and riparian pastures (strips of riparian vegetation surrounded by pastures). A total of 73 species were recorded during formal surveys. Species richness and abundance were comparable among all habitat types except dryland plantations, which supported fewer species and in lower numbers. The avifauna assemblage differed according to broad habitat types. Forest habitats (dryland and riparian) harboured more forest- and woodland-dependent species, and a greater abundance of nectarivores and insectivores. Riparian plantations supported a similar number of forest- and woodland-dependent species to forest habitats, but also retained some open-country species. Riparian pastures had the highest cumulative species richness, reflecting a diverse mix of forest- and woodland-dependent birds and open-country species. It was the preferred habitat type for granivores and vertebrate eaters. Dryland plantations were dominated by common species and omnivores, and supported fewer forest- and woodland-dependent birds, insectivores and frugivores compared with other habitat types. The presence of riparian strips increased avifauna diversity and abundance in plantations and pastures to a greater extent than predicted by the proportional area of riparian habitat. The importance of riparian habitats needs to be recognised and incorporated into management policies if biodiversity conservation is to be an objective of plantation establishment.     

Faunal use of bluegum ( Eucalyptus globulus ) plantations in southwestern Australia

We examined the faunal use of Eucalyptus globulus plantations in southern Western Australia, and compared use of remnant vegetation, agricultural land and plantations in different positions relative to large tracts of remnant vegetation. In general, faunal use of plantations is less than in comparison with adjacent remnant vegetation, but more than in open pasture. For all faunal groups there were almost twice as many species recorded in the native vegetation than in any site in the plantations or on agricultural land and they were in greater abundance. Faunal use of plantation edges and interiors did not show consistent patterns. Generally, edges next to remnants were most frequently used, but individual species showed a wide range of patterns of use across the various habitat types studied. More species of bird identified as being “at risk” were found in plantation edges than in interiors. Adjacency to remnant vegetation increased plantation use by some species, but the overall differences between isolated plantations and those adjacent to remnant vegetation were relatively small. We conclude that plantations provide some value in terms of habitat for some species, including some of conservation concern, but that this value is limited by the lack of habitat complexity in the intensively-managed plantations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Establishing Conservation Easements on Forested Riparian Buffers: Opportunities for Long-term Streamside Protection

Forest riparian buffers are an important means of conserving land. The Conservation Reserve Enhancement Program (CREP) offers financial incentives to landowners to install forested riparian buffers under 10–15 year contracts. This study explores whether Pennsylvania CREP participants who had established a riparian buffer would also place it under a permanent conservation easement. A mail questionnaire was developed and administered to 685 CREP participants. It was found that the majority of the respondents are likely to leave their buffer intact when the CREP contract expires, but are hesitant to agree to conservation easements. Property rights, education and finances are among the key issues affecting acceptance of conservation easements.     

The role of land tenure in conservation of tree and shrub species diversity in miombo woodlands of southern Malawi

Biodiversity is declining throughout southern African miombo woodlands due to poor land use practices that are detrimental to soil, vegetation and habitat. We aimed at examining tree and shrub species diversity and distribution in Uapaca kirkiana-dominated woodlands under three land tenure types; forest reserves, customary and leasehold land. The study was conducted at different forest sites within similar agroecological zone in southern Malawi. Study sites were located at a range of altitudes between 900 and 1,200 m a.s.l. Three circular plots each with 32.60 m radius were established at each study site to sample tree and shrub species composition, structure and distribution under three land tenure types. We found that forest reserves had higher species diversity with an average of 16 tree families, 27 genera and 34 species as compared to only 10 tree families, 6 genera and 6 species on customary forest lands. Comparisons of diameter at breast height size class distributions showed that customary land had significantly low numbers of small (5.0–10.0 cm) and very large (≥30 cm) diameter classes suggesting lower levels of regeneration and high rate of anthropogenic activities. The high species diversity and richness in forest reserves and leasehold land indicate high potential for protected lands to restore tree species diversity. It is concluded that levels of human activities as influenced by land tenure type reduce tree species diversity, composition and distribution at the different sites, and this confirms the hypothesis that open access lands are not compatible with conservation of tree and shrub species diversity because of high anthropogenic activities.     

Plant-soil biodiversity relationships and nutrient retention in agricultural riparian zones of the Sacramento Valley,California

Forested riparian buffers in California historically supported high levels of biodiversity, but human activities have degraded these ecosystems over much of their former range. This study examined plant communities, belowground biodiversity and indicators of multiple ecosystem functions of riparian areas across an agricultural landscape in the Sacramento Valley of California, USA. Plant, nematode and soil microbial communities and soil physical and chemical properties were studied along 50-m transects at 20 sites that represented the different land use, soil and vegetation types in the landscape. Riparian zones supported greater plant diversity and nearly twice as much total carbon (C) per hectare compared to adjacent land managed for agricultural uses, but had generally lower soil microbial and nematode diversity and abundance. When woody plant communities were present in the riparian zone, plant diversity and species richness were higher, and soil nitrate and plant-available phosphorus levels were lower. Belowground diversity and community structure, however, appeared to depend more on plant productivity (as inferred by vegetation cover) than plant diversity or species richness. Greater plant species richness, nematode food web structure, total microbial biomass, woody C storage and lower soil nitrate and phosphorus loading were correlated with higher visual riparian health assessment scores, offering the possibility of managing these riparian habitats to provide multiple ecosystem functions.     

Predicting breeding bird occurrence by stand- and microhabitat-scale features in even-aged stands in the Central Appalachians

Spatial scale is an important consideration when managing forest wildlife habitat, and models can be used to improve our understanding of these habitats at relevant scales. Our objectives were to determine whether stand- or microhabitat-scale variables better predicted bird metrics (diversity, species presence, and abundance) and to examine breeding bird response to clearcut size and age in a highly forested landscape. In 2004-2007, vegetation data were collected from 62 even-aged stands that were 3.6-34.6 ha in size and harvested in 1963-1990 on the Monongahela National Forest, WV, USA. In 2005-2007, we also surveyed birds at vegetation plots. We used classification and regression trees to model breeding bird habitat use with a suite of stand and microhabitat variables. Among stand variables, elevation, stand age, and stand size were most commonly retained as important variables in guild and species models. Among microhabitat variables, medium-sized tree density and tree species diversity most commonly predicted bird presence or abundance. Early successional and generalist bird presence, abundance, and diversity were better predicted by microhabitat variables than stand variables. Thus, more intensive field sampling may be required to predict habitat use for these species, and management may be needed at a finer scale. Conversely, stand-level variables had greater utility in predicting late-successional species occurrence and abundance; thus management decisions and modeling at this scale may be suitable in areas with a uniform landscape, such as our study area. Our study suggests that late-successional breeding bird diversity can be maximized long-term by including harvests >10 ha in size into our study area and by increasing tree diversity. Some harvesting will need to be incorporated regularly, because after 15 years, the study stands did not provide habitat for most early successional breeding specialists.     

Moving riparian management guidelines towards a natural disturbance model: An example using boreal riparian and shoreline forest bird communities

Forest harvesting strategies that approximate natural disturbances have been proposed as a means of maintaining natural species’ diversity and richness in the boreal forests of North America. Natural disturbances impact shoreline forests and upland areas at similar rates. However, shoreline forests are generally protected from harvest through the retention of treed buffer strips. We examined bird community responses to forest management guidelines intended to approximate shoreline forest fires by comparing bird community structure in early (1–4 years) post-burned and harvested boreal riparian habitats and the adjacent shoreline forest. We sampled riparian areas with adjacent: (1) burned merchantable shoreline forest (n = 21), (2) burned non-merchantable shoreline forest (n = 29), (3) 10 m treed buffer with 25% retention in the next 30 m (n = 18), and (4) 30 m treed buffer (n = 21). Only minor differences were detected in riparian species’ abundance and bird community composition between treatments with greater differences in these parameters occurring between post-fire and post-harvest upland bird communities. Indicators of all merchantable treatments were dominated by upland species with open-habitat species and habitat generalists being typical upland indicator species of burned merchantable habitats and forest specialists typical upland indicators of harvested treatments. Riparian species indicative of burned riparian habitats were Common Yellowthroat (Geothlypis trichas), Le Conte’s Sparrow (Ammodramus leconteii) and Eastern Kingbird (Tyrannus tyrannus) and indicators of 30 m buffers were Alder Flycatcher (Empidonax alnorum) and Wilson’s Warbler (Wilsonia pusilla). Multivariate Redundancy Analysis (RDA) of the overall (riparian and upland birds) community showed greater divergence than RDA with only riparian species suggesting less effect of fire and forestry on riparian birds than on upland birds. Higher natural range of variability (NRV) of overall post-fire bird communities compared to post-harvest communities emphasizes that harvesting guidelines currently do not achieve this level of variability. However, lack of a large negative effect on common riparian species in the first 4 years post-disturbance allows for the exploration of alternative shoreline forest management that better incorporates bird community composition of post-fire riparian areas and shoreline forests.     

Understory plant diversity and biomass in hybrid poplar riparian buffer strips in pastures

Understory plant biomass, species richness and canopy openness were measured in six-year old hybrid poplar riparian buffer strips, in the understory of two unrelated clones (MxB-915311 and DxN-3570), planted along headwater streams at three pasture sites of southern Quebec. Canopy openness was an important factor affecting understory biomass in hybrid poplar buffers, with lower understory biomass observed on sites and under the clone with lower canopy openness. Although tree size was an important factor affecting canopy openness, relationships between total stem volume and canopy openness, for each clone, also support the hypothesis of a clonal effect on canopy openness. Understory biomass and canopy openness as low as 3.6 g m⁻² and 7.6% in 1 m² microplots were measured under clone MxB-915311 at the most productive site. This reduction of understory plant growth could compromise important buffer functions for water quality protection (runoff control, sediment trapping and surface soil stabilisation), particularly were concentrated runoff flow paths enter the buffer. On the other hand, tree buffers that maintain relatively low canopy openness could be interesting to promote native and wetland plant diversity. Significant positive relationships between canopy openness and introduced species richness (R ² = 0.46, p < 0.001) and cover (R ² = 0.51, p < 0.001) were obtained, while no significant relationship was observed between canopy openness and native (wetland) species richness and cover. These results suggest that planting riparian buffer strips of fast-growing trees can rapidly lead to the exclusion of shade-intolerant introduced species, typical colonisers of disturbed habitats such as riparian areas of pastures, while having no significant effect on native (wetland) diversity. Forest canopy created by the poplars was probably an important physical barrier controlling introduced plant richness and abundance in agricultural riparian corridors. A strong linear relationship (R ² = 0.73) between mean total species richness and mean introduced species richness was also observed, supporting the hypothesis that the richest communities are the most invaded by introduced species, possibly because of higher canopy openness, as seen at the least productive site (low poplar growth). Finally, results of this study highlight the need for a better understanding of relationships between tree growth, canopy openness, understory biomass and plant diversity in narrow strips of planted trees. This would be useful in designing multifunctional riparian buffer systems in agricultural landscapes.     

The importance of the surroundings: are bird communities of riparian galleries influenced by agroforestry matrices in SW Iberian Peninsula?

Context

The remaining riparian stretches are often the unique suitable habitats for forest breeding birds in Mediterranean landscapes undergoing long-term changes. Understanding the interactions between riparian zones and their surroundings is critical to establish successful management actions.

Aims

We assessed the influence of surrounding matrix on riparian bird communities and the use of riparian galleries as surrogate habitats for the forest passerine communities of southwestern Iberia.

Methods

We used point counts in three simultaneous sampling stations, one in the riparian gallery and two in the adjacent matrix. Three matrix types were selected with a decreasing tree density gradient: dense montado, sparse montado, and open agricultural areas. Data were analysed with redundancy analysis and differences in species’ occurrences were tested with one-way ANOVA.

Results

In riparian galleries, we found bird species belong to three ecological guilds: riparian, woodland, and edge guilds. The richness of bird guilds and the occurrence of some species depended on the surrounding matrix type. Riparian bird richness was constant in all surrounding matrices, woodland bird guild was richer in galleries embedded in dense montados, and edge guild in riparian galleries surrounded by sparse montados. Five among 19 assessed species were influenced by matrix type, within particular a few strictly riparian species. Species richness increased close to riparian galleries, due to the increase in habitat heterogeneity and resource availability for birds in densely vegetated riversides. However, the occurrence of some bird species differed according to the type of surrounding matrix.

Conclusion

The matrix type explained most of the variance in riparian bird assemblages. Some woodland birds have used riparian galleries as surrogate habitat. Our study suggests that land use in the surrounding matrices must be taking into account for the management and rehabilitation of watercourses and bird conservation actions.     

Nutrient Attenuation in Agricultural Surface Runoff by Riparian Buffer Zones in Southern Illinois,USA

Nutrients in overland flow from agricultural areas are a common cause of stream and lake water quality impairment. One method of reducing excess nutrient runoff from non-point sources is to restore or enhance existing riparian areas as vegetative buffers. A field scale study was conducted to assess the ability of remnant giant cane (Arundinaria gigantea (Walt.) Muhl.) and forest riparian buffer zones to attenuate nutrients in agricultural surface runoff from natural precipitation events. Two adjacent, 10.0 m wide riparian buffers were instrumented with 16 overland flow collectors to monitor surface runoff for nitrate, ammonium, and orthophosphate. Measurements were taken at 3.3 m increments within each buffer. The forest buffer significantly reduced incoming dissolved nitrate-N, dissolved ammonium-N, total ammonium-N, and total orthophosphate masses in surface runoff by 97, 74, 68, and 78 , respectively within the 10.0 m riparian buffer. Nutrient reductions within the cane buffer were 100 for all three nutrients due to relatively high infiltration rates. Significant reductions of total ammonium- N and total orthophosphate were detected by 3.3 m in the cane buffer and at 6.6 m in the forest buffer. Results suggest that both giant cane and forest vegetation are good candidates to incorporate into riparian buffer restoration designs for southern Illinois as well as in other regions within their native range with similar climatic and physiographic conditions.     

紫蓬山区国家级森林公园春夏季鸟类群落生态的初步研究

１９９７年４～７月对紫蓬山区国家级森林公园的鸟类群落生态进行了调查,结果表明：８个鸟类群落中,针阔混交林中鸟类种类和数量最为丰富,优势种最多;针阔混交林、农田和岗坡灌丛群落鸟类多样指数较大,阔叶林、库塘、岗坡灌丛鸟类群落的均匀性指数较大;针阔混交林和针叶林鸟类群落极相似。鸟类群落的空间配置上的差异和生境特征以及植被类型相关,鸟类群落的多样性存在季节差异。     

Amphibian distributions in riparian and upslope areas and their habitat associations on managed forest landscapes in the Oregon Coast Range

Over the past 50 years, forested landscapes of the Pacific Northwest have become increasingly patchy, dominated by early successional forests. Several amphibian species associated with forested headwater systems have emerged as management concerns, especially after clearcutting. Given that headwater streams comprise a large portion of the length of flowing waterways in western Oregon forests, there is a need to better understand how forest management affects headwater forest taxa and their habitats. Mitigation strategies include alternatives to clearcutting, such as harvests that remove only part of the canopy and maintenance of riparian buffer strips. Our study investigates effects of upland forest thinning coupled with riparian buffer treatments on riparian and upland headwater forest amphibians, habitat attributes, and species-habitat associations. Amphibian captures and habitat variables were examined 5–6 years post-thinning within forest stands subject to streamside-retention buffers and variable-width buffers, as well as unthinned reference stands. We found no treatments effects, however, our results suggest that ground surface conditions (e.g., amount of rocky or fine substrate) play a role in determining the response of riparian and upland amphibians to forest thinning along headwater streams. Distance from stream was associated with amphibian abundance, hence retention of riparian buffers is likely important in maintaining microclimates and microhabitats needed for amphibians and other taxa. Moderate thinning and preservation of conditions in riparian and nearby upland areas by way of variable-width and streamside-retention buffers may be sufficient to maintain suitable habitat and microclimatic conditions vital to amphibian assemblages in managed headwater forests.     

Live fences as tools for biodiversity conservation: a study case with birds and plants

Live fences may act as tools for biodiversity conservation by providing habitat for native species and increasing connectivity in the landscape. We studied the influence of live fence characteristics on species richness and fence use by birds by examining both local and landscape factors. We studied three types of live fences: planted fences of a native tree, planted fences of an exotic, and spontaneous. They were either connected to forest fragments or isolated, and were all within a pasture matrix. Spontaneous and planted live fences maintain a diverse plant (77 shrub and tree species) and bird communities (98 species). Fence types strongly differed in vegetation composition and structure. We found that by analyzing each fence characteristic independently, there was no difference in bird richness or abundance. However, there was a significant correlation when plant richness, structure, and connectivity were analyzed together. This could be the result of some variables counterbalancing each other. Birds used fences for a variety of purposes including foraging, breeding, and moving across the landscape. Native birds and plants used live fences as habitat and refuge in a landscape where large forest tracts have been lost for decades. Live fences in conjunction with small forest fragments maintain a diverse array of plant and birds species that are a subsample of the species originally found in the landscape before extensive deforestation. We recommend the establishment of live fences, allowing growth of spontaneous understory.     

Restoration of dry tropical forests in Central America: A review of pattern and process

Much information on restoration and management exists for wet tropical forests of Central America but comparatively little work has been done in the dry forests of this region. Such information is critical for reforestation efforts that are now occurring throughout Central America. This paper describes processes of degradation due to land use and provides a conceptual framework for the restoration of dry tropical forest. Most of this forest type was initially harvested for timber and then cleared for cattle in the last century (1930-1970). Only 1.7% remains largely restricted to infertile soils and remote areas on the Pacific coastal side of Panama, Costa Rica, Nicaragua and Mexico. These cleared areas are again in a state of transition due to a combination of decreasing land productivity, and land speculation for tourism development. Some farms have been sold to new landowners who are interested in reforesting to increase biodiversity and forest cover. Attempts have therefore been made to reforest by protecting the land from fire and cattle, by supplementing natural regrowth with enrichment planting, or through use of tree plantations. Experimental studies have demonstrated the ability of these lands to grow back to forests because of native species ability to sprout after cutting, and the capacity of remnant trees in field and riparian zones to provide seeds and to moderate edge environment for seed germination and seedling establishment. However, research also shows that on sites with long histories of land clearance, species diversity will remain low with functional groups missing unless some active management occurs. Under-planting with late-successional native tree species can add structure and diversity; enrichment planting with large-fruited shade-intolerant species can initiate new islands of more diverse regeneration beneath their canopies; and plantings of fast-growing, nitrogen-fixing trees that provide light canopy shade can moderate the environment below, promoting regeneration establishment of late-successional species. Plantations are the only option for lands that have lost almost all remnants of native forest, and where soils and vegetation have changed to new states of structure and function. Conversion of pastures to tree plantations that can facilitate natural regeneration beneath them is appropriate when pastures are prone to fire and/or lack immediate seed sources nearby. After the grasses have been shaded out, natural recruitment can slowly occur over a 10-15 years period. Under-planting of shade-tolerant late-successional species can supplement species composition and structure.