Consistency in bird use of tree cover across tropical agricultural landscapes.

In tropical regions where forests have been replaced by agriculture, the future of biodiversity is increasingly dependent on the presence of remnant forest patches and on-farm tree cover within agricultural landscapes. While there is growing evidence of the importance of tree cover within agricultural landscapes, most studies have been conducted in a single landscape, making it difficult to ascertain whether the conservation value of different types of tree cover can be generalized across landscapes. To explore whether use of different forms of tree cover by birds is consistent across landscapes, we compared the number of individuals, species richness, and diversity of birds associated with different forms of tree cover in four agricultural landscapes in Central America, using a standardized methodology and sampling effort. In each landscape, we compared bird assemblages in six tree cover types (secondary forests, riparian forests, forest fallows, live fences, pastures with high tree cover, and pastures with low tree cover). We observed a total of 10 723 birds of 283 species, with 83-196 species per landscape. The specific patterns of bird species richness, number of individuals, and diversity associated with tree cover types varied across the four landscapes, but these variables were consistently higher in the forest forms of tree cover (riparian forests, secondary forests, and forest fallows) than in non-forest habitats. In addition, forest forms of tree cover had distinct species composition from non-forest forms in all landscapes. There was also consistency in the use of different types of tree cover by forest birds across the four landscapes, with higher richness and number of individuals of forest birds in forested than non-forested forms of tree cover, and more forest bird species in pastures with high tree cover than in pastures with low tree cover. Our findings indicate that riparian and secondary forests are consistently of higher value for bird conservation (particularly for forest species) than live fences and pastures with tree cover. Consequently, agricultural and land use policies that promote the retention of secondary and riparian forests and increase tree cover within pastures would greatly benefit bird conservation, regardless of the landscape in which they are applied.

More stable productivity of semi natural grasslands than sown pastures in a seasonally dry climate.

In the Neotropics the predominant pathway to intensify productivity is generally thought to be to convert grasslands to sown pastures, mostly in monoculture. This article examines how above-ground net primary productivity (ANPP) in semi-natural grasslands and sown pastures in Central America respond to rainfall by: (i) assessing the relationships between ANPP and accumulated rainfall and indices of rainfall distribution, (ii) evaluating the variability of ANPP between and within seasons, and (iii) estimating the temporal stability of ANPP. We conducted sequential biomass harvests during 12 periods of 22 days and related those to rainfall. There were significant relationships between ANPP and cumulative rainfall in 22-day periods for both vegetation types and a model including a linear and quadratic term explained 74% of the variation in the data. There was also a significant correlation between ANPP and the number of rainfall events for both vegetation types. Sown pastures had higher ANPP increments per unit rainfall and higher ANPP at the peak of the rainy season than semi-natural grasslands. In contrast, semi-natural grasslands showed higher ANPP early in the dry season. The temporal stability of ANPP was higher in semi-natural grasslands than in the sown pastures in the dry season and over a whole annual cycle. Our results reveal that, contrary to conventional thinking amongst pasture scientists, there appears to be no increase in ANPP arising from replacing semi-natural grasslands with sown pastures under prevailing pasture management practices in seasonally dry climates, while the temporal distribution of ANPP is more even in semi-natural grasslands. Neither sown pastures nor semi-natural grasslands are productive towards the end of the dry season, indicating the potential importance of the widespread practice of retaining tree cover in pastures.

Patterns of animal diversity in different forms of tree cover in agricultural landscapes.

As tropical regions are converted to agriculture, conservation of biodiversity will depend not only on the maintenance of protected forest areas, but also on the scope for conservation within the agricultural matrix in which they are embedded. Tree cover typically retained in agricultural landscapes in the neotropics may provide resources and habitats for animals, but little is known about the extent to which it contributes to conservation of animal species. Here, we explore the animal diversity associated with different forms of tree cover for birds, bats, butterflies, and dung beetles in a pastoral landscape in Nicaragua. We measured species richness and abundance of these four animal taxa in riparian and secondary forest, forest fallows, live fences, and pastures with high and low tree cover. We recorded over 20,000 individuals of 189 species including 14 endangered bird species. Mean abundance and species richness of birds and bats, but not dung beetles or butterflies, were significantly different among forms of tree cover. Species richness of bats and birds was positively correlated with tree species richness. While the greatest numbers of bird species were associated with riparian and secondary forest, forest fallows, and pastures with >15% tree cover, the greatest numbers of bat species were found in live fences and riparian forest. Species assemblages of all animal taxa were different among tree cover types, so that maintaining a diversity of forms of tree cover led to conservation of more animal species in the landscape as a whole. Overall, the findings indicate that retaining tree cover within agricultural landscapes can help conserve animal diversity, but that conservation efforts need to target forms of tree cover that conserve the taxa that are of interest locally. Preventing the degradation of remaining forest fragments is a priority, but encouraging farmers to maintain tree cover in pastures and along boundaries may also make an important contribution to animal conservation.