Assessing the effects of agricultural intensification on natural habitats and biodiversity in Southern Amazonia

Landscape changes in the Cerrado: Challenges of land clearing, fragmentation and land tenure for biological conservation

Land clearing, low levels of protection, and high biodiversity make the Brazilian Cerrado a hotspot for biological conservation. However, one of the most active agricultural frontiers in Brazil is located in this region. We thus aimed to evaluate the current trends of deforestation and fragmentation of the Cerrado, from 1986 to 2019; and the contribution of land tenure and farm size to the Cerrado conservation. We divided the Cerrado (∼2 Mkm2) into three sub-regions and calculated the distribution and size of the fragments; core areas and edge distance; isolation and importance of the smallest fragments for reducing isolation; and connectivity for the years 1986, 1997, 2008, and 2019. We then evaluated vegetation cover and landscape metrics for public lands and private farms. Since 1986, 22 % of the Cerrado's remnant vegetation was cleared and the number of fragments increased by 20 %. Currently, 10 % of the Cerrado vegetation is under the effect of a 30 m edge. Isolation increased in all the sub-regions and smaller fragments (>100 ha) are important for landscape configuration. 10.82 % of the vegetation is preserved in public lands and 57.9 % in private farms, where 377,901.5 km2 could be legally cleared. Compared to other Brazilian regions, the northern Cerrado is relatively well connected and less fragmented but land clearing still threatens biodiversity. Public lands are important for connectivity and habitat amount but play a minor role when compared to private lands. Our results highlight that avoiding further land clearing of the Cerrado is a challenge that requires the engagement of different stakeholders at different levels.

Conversion of steppe to cropland increases spatial heterogeneity of soil functional genes

The microbiome function responses to land use change are important for the long-term prediction and management of soil ecological functions under human influence. However, it has remains uncertain how the biogeographic patterns of soil functional composition change when transitioning from natural steppe soils (NS) to agricultural soils (AS). We collected soil samples from adjacent pairs of AS and NS across 900 km of Mollisol areas in northeast China, and the soil functional composition was characterized using shotgun sequencing. AS had higher functional alpha-diversity indices with respect to KO trait richness and a higher Shannon index than NS. The distance-decay slopes of functional gene composition were steeper in AS than in NS along both spatial and environmental gradients. Land-use conversion from steppe to farmland diversified functional gene profiles both locally and spatially; it increased the abundances of functional genes related to labile carbon, but decreased those related to recalcitrant substrate mobilization (e.g., lignin), P cycling, and S cycling. The composition of gene functional traits was strongly driven by stochastic processes, while the degree of stochasticity was higher in NS than in AS, as revealed by the neutral community model and normalized stochasticity ratio analysis. Alpha-diversity of core functional genes was strongly related to multi-nutrient cycling in AS, suggesting a key relationship to soil fertility. The results of this study challenge the paradigm that the conversion of natural to agricultural habitat will homogenize soil properties and biology while reducing local and regional gene functional diversity.

Can guava monocultures (Psidium guajava L.) function as refuge for bird conservation?

Agricultural intensification negatively affects bird communities, and the response of birds to these changes varies from those that survive and increase their populations (disturb-tolerant species) to those that cannot adapt to new conditions and are regionally extinct (disturb-sensitive species). Thus, the present study sought to investigate the bird community in 39 guava orchards in the semiarid region of the state of Sergipe, northeast Brazil. Field observations were made between July and October 2017, through a one-hour visit to each orchard. Samplings were conducted using the MacKinnon’s List method. In addition to bird sampling, walks were carried out in the orchards to observe nesting. Seventy-six species of birds belonging to 30 families were recorded using the guava orchards. The most frequent species were Vanellus chilensis, Columbina talpacoti, Columbina picui, Crotophaga ani, Pitangus sulphuratus and Sporophila albogularis. Of the 186 nests recorded in the orchards, the majority (n = 144 nests; 77.4%) belonged to Columbina picui, Columbina talpacoti and Columbina minuta. The results demonstrate that the bird community in the guava orchards is formed only by disturb-tolerant species, showing that the studied guava orchards are not favorable to the conservation of disturb-sensitive birds of the Caatinga domain.