Editor’s Choice 57:04 – Enhancing biodiversity through more heterogeneous field designs

In Journal of Applied Ecology’s April Editor’s Choice, Alignier et al. present a way of promoting farmland biodiversity without sacrificing land needed for agricultural production. Associate Editor, Pieter De Frenne (Forest & Nature Lab, Ghent University, Belgium), introduces their exciting research.

Researchers and policymakers are constantly testing, assessing and implementing different techniques to reduce the negative impacts of current agricultural practices on biodiversity. This is important because biodiversity in agricultural landscapes is still strongly under threat in many parts of the globe (see Foley et al. 2005 and Pe’er et al. 2014 for examples).

Agri-environment schemes, in which farmers are paid to (partly) adjust their farm management, have been designed to moderate and reverse farmland biodiversity loss and protect the environment or landscapes. Agri-environment schemes have been implemented since the 1990s, but have also been criticised for their ineffectiveness at protecting or enhancing biodiversity in particular circumstances (for example, Kleijn et al. 2001; Pe’er et al. 2014 ). This means that we still need additional techniques to counteract biodiversity loss in agricultural landscapes.

Grass Buffer_BertReubens
Grass buffer strips are among the agri-environment schemes that can help to control water and soil quality and protect biodiversity. Photo: Bert Reubens

In their Journal of Applied Ecology Editor’s Choice article, Alignier et al. shed light on an often-overlooked technique: stimulating plant biodiversity within croplands (thus growing between or below the crop) by enhancing the heterogeneity of the crop mosaic itself. They investigated no less than 1451 agricultural fields across Europe and North America, managed as grassland or farmland with crops such as cereals, maize, soybean, oilseed rape, rice, beans and potato. They then went on to quantify the relative importance of the composition and configuration of the croplands on plant biodiversity within the fields. They quantified composition by counting the amount of crop species while the field edge density (or field size) represents configurational heterogeneity.

Semi-natural land cover_JonathanLenoir
Semi-natural land cover in agricultural landscapes is important for biodiversity and ecosystem services. Photo: Picardy, France, by Jonathan Lenoir

Using transect surveys in the field borders and interiors, Alignier and colleagues identified nearly 900 plant species across the 1451 fields. They detect that higher total field border length, and thus higher variation in the configuration of patches, resulted in higher alpha and gamma plant biodiversity in the field interiors. These beneficial effects were nearly equally high as those of having more semi-natural habitats in the landscape such as small forest patches, grasslands, and wetlands. The amount of semi-natural cover indeed also had important positive effects on the plant biodiversity within the fields. Adding to the importance of semi-natural land cover, small woodland patches in agricultural landscapes can disproportionally contribute important ecosystem services such as carbon sequestration, at even more efficient rates per area than larger forests.

The presence of such non-crop plant species in field interiors can be negative if the competition with the crop is strong but they can also provide important ecosystem services, for example as nectar and pollen sources for pollinators. Likewise, another recent pan-European analysis also detected strong beneficial effects of higher edge densities and more semi-natural landscape elements on biodiversity of arthropods.

Silvoable_BertReubens
In silvoarable agroforestry systems, crops are mixed with trees. Photo: Bert Reubens

Increasing heterogeneity of the crop fields is comparable to another technique to increase the structural heterogeneity, i.e., agroforestry (defined by the F.A.O. as land-use systems where woody perennials are deliberately used on the same land-management units as agricultural crops and/or animals). Also agroforestry has been shown to increase landscape-level biodiversity, for instance in arthropods. If the combination of crop and tree species is well thought through, e.g. by using winter cereals such as wheat and barley which perform a significant part of their growth before tree canopy flush, crop yield losses can be negligible.

A strong selling point of the proposed technique is that higher heterogeneity of the crop matrix does not require any land to be taken out of agricultural production. Unquestionably, smaller patches of any given crop may result in less efficient agricultural operations for the farmer. Indeed, crop-specific sowing, fertilisation, pesticide manipulations, and harvesting all have to be performed on smaller patches of varying shapes with less easy tractor manoeuvres – this may be an important drawback to implement this technique from a farmer’s viewpoint. Nonetheless, implementing more variation in the configuration of arable fields emerges as a simple management recommendation that could be considered in future agricultural policies to promote farmland plant biodiversity.

The full Editor’s Choice article, Configurational crop heterogeneity increases within‐field plant diversity, is free to read for a limited time in Journal of Applied Ecology.

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