Marcella do Carmo Pônzio and Nielson Pasqualotto summarise their latest research in which they and colleagues investigated the effects of landscape heterogeneity and native vegetation cover on richness and composition of native and invasive mammals, across 55 landscapes in the Brazilian Savanna, Cerrado.

A global process and a knowledge gap

Intensive agriculture has significantly transformed landscapes by replacing native habitats and diversified small-scale farming into large monoculture crops. This process, known as “agricultural landscape simplification,” has led to a reduction in native vegetation cover and landscape heterogeneity (the variety of land cover types and their form, arrangement, and spatial distribution). While we know that this process impacts resource availability and distribution, we have yet to fully comprehend how these two landscape features affect, alone or together, biodiversity in agroecosystems.

This persistent knowledge gap is caused by several factors:

• first, native vegetation cover and landscape heterogeneity are strongly correlated in agroecosystems. For this reason, many studies have a limited investigation capacity or have findings closely associated with the quantity of native vegetation rather than the landscape heterogeneity
• second, most of the research adopts a binary landscape perspective – considering patches of native vegetation as “habitats” and the agricultural matrix as “non-habitats”, overlooking the permeability of agricultural areas to various species.

Sampling in the Brazilian Savanna

Overcoming these limitations is crucial to support actions to conciliate agricultural production and biodiversity conservation. Aiming to fill this knowledge gap, we conducted a study in the Brazilian Savanna, Cerrado, a region of global conservation significance and high agricultural production.

We sampled 55 landscapes, carefully selected to maximize uncorrelated variation between landscape heterogeneity and native vegetation cover, recording the occurrence of medium and large-bodied mammals.

The importance of native vegetation and heterogeneity in agroecosystems

Our findings demonstrate that landscape heterogeneity and native vegetation cover affect the richness of native and invasive mammals in opposite directions. The native species richness was best explained by the additive and positive effects of these both features, achieving the highest values in landscapes with higher heterogeneity and native vegetation cover.

The positive effect of landscape heterogeneity corresponds to 80% of the positive effect of native forest cover. The richness of invasive species was explained by either the simple and negative effect of native savanna cover or by the additive and negative effects of a native vegetation variable (savanna or total native vegetation) and a heterogeneity variable. The negative effect of landscape heterogeneity corresponds to 27% of the negative effect of savanna cover.

Therefore, we can regard the loss of landscape heterogeneity as a human-induced disturbance that leads to biotic homogenization (the replacement of native and specialist species by exotic and generalist species), similar to other well-known disturbances that also trigger this process. Although biotic homogenization had already been reported due to agricultural conversion, we demonstrated that beyond habitat loss, the loss of landscape heterogeneity is key to promote and explain this widespread biotic response.

Also, our results indicate the importance of native savanna for decreasing the richness of invasive species. Unfortunately, savannas’ conversion and afforestation are ongoing global processes that threaten their biodiversity and ecological services.

We also found that increasing landscape heterogeneity helps to control European hares and domestic dogs’ invasion in landscapes predominantly covered by native vegetation (> 40% cover), or wild boar invasion in deforested landscapes. Considering the study region has less than 20% of native remnants (as many agroecosystems), the increase in local landscape heterogeneity emerges as a fundamental tool to manage and control wild boar invasion, one of the most detrimental invasive species that has caused substantial economic losses to the agricultural sector.

Promoting a complex landscape to support biodiversity and agricultural production

Although smaller than the native vegetation cover effects, the landscape heterogeneity can help compensate the negative influence of native habitat loss on biodiversity in agroecosystems. Increasing the diversity and complexity of land cover can create agroecosystems that support more native species and control some invasive species. Beyond requiring that farmers set-aside areas of native vegetation, policies that stimulate crop diversity and small-scale agriculture are valuable additions for preserving biodiversity in productive areas.

Recognizing the importance of maintaining protected areas, there is an opportunity to plan agroecosystems with varying levels of native vegetation cover and landscape heterogeneity, tailored to local constraints and needs. However, it contradicts monoculture-based production – a system ineffective in the promotion of biodiversity conservation, end poverty, and food security.

On the other hand, it can be achieved through other systems such as:

• crop rotation
• intercropping
• and agroforestry.

Balancing agricultural production with nature conservation certainly involves more than landscape management – we need to consider social, environmental, and political issues – but the influence of landscape heterogeneity could be a powerful tool in advancing this mission.

Read the full article “Landscape heterogeneity can partially offset negative effects of habitat loss on mammalian biodiversity in agroecosystems” in Journal of Applied Ecology