Complex agricultural landscapes host more biodiversity than simple ones: A global meta-analysis

Abstract

Managing agricultural landscapes to support biodiversity conservation requires profound structural changes worldwide. Often, discussions are centered on management at the field level. However, a wide and growing body of evidence calls for zooming out and targeting agricultural policies, research, and interventions at the landscape level to halt and reverse the decline in biodiversity, increase biodiversity-mediated ecosystem services in agricultural landscapes, and improve the resilience and adaptability of these ecosystems. We conducted the most comprehensive assessment to date on landscape complexity effects on nondomesticated terrestrial biodiversity through a meta-analysis of 1,134 effect sizes from 157 peer-reviewed articles. Increasing landscape complexity through changes in composition, configuration, or heterogeneity significatively and positively affects biodiversity. More complex landscapes host more biodiversity (richness, abundance, and evenness) with potential benefits to sustainable agricultural production and conservation, and effects are likely underestimated. The few articles that assessed the combined contribution of linear (e.g., hedgerows) and areal (e.g., woodlots) elements resulted in a near-doubling of the effect sizes (i.e., biodiversity level) compared to the dominant number of studies measuring these elements separately. Similarly, positive effects on biodiversity are stronger in articles monitoring biodiversity for at least 2 y compared to the dominant 1-y monitoring efforts. Besides, positive and stronger effects exist when monitoring occurs in nonoverlapping landscapes, highlighting the need for long-term and robustly designed monitoring efforts. Living in harmony with nature will require shifting paradigms toward valuing and promoting multifunctional agriculture at the farm and landscape levels with a research agenda that untangles complex agricultural landscapes' contributions to people and nature under current and future conditions.

Keywords: agroecology; landscape agronomy; landscape composition; landscape configuration; landscape heterogeneity.

Fig. 1.

(A) Data distribution across countries indicating effect sizes (number of articles). Effect sizes from multicountry articles are excluded from the figure (12 from four articles). (B) Percentage of articles assessing the landscape complexity effect on biodiversity during the last three decades. Country boundaries are from the Database of Global Administrative Areas (GADM) version 3.6.

Fig. 2.

Direction and strength of the effect on biodiversity of each landscape complexity dimension. *P ≤ 0.05, ***P < 0.001. The triangle in the center lists the different mechanisms or processes reported in the literature explaining the use of biodiversity’s natural and cultivated elements embedded in agricultural landscapes. The total percentage for articles is above 100% since one article can measure more than one dimension. Values next to icons indicate Pearson’s correlation estimated mean value. Linear elements are represented in configuration (e.g., live fences), whereas areal elements are represented in composition (e.g., patches of habitat). comp: composition, conf: configuration, herb: herbaceous, hete: heterogeneity, lu: land use, nat: natural, nd: no data, seminat: seminatural.

Fig. 3.

Landscape complexity effect (estimated mean and 95% confidence intervals) on biodiversity across the significant moderators with the most studied and strongest evidence (≥10 articles). Moderators (a to h) and their respective levels (nested labels) are grouped by theme: green, biodiversity; orange, cropping system; blue, landscape; gray, study design. Effects sizes are calculated as Pearson correlations; hence, values > 0 indicate larger biodiversity outcomes in complex than in simple landscapes, and confidence interval values overlapping zero indicates no significant difference between complex and simple landscapes. Numbers in parentheses indicate the number of effect sizes/number of articles with a significance level of ***P < 0.001, **P < 0.01, and *P < 0.05. The dotted line shows the mean overall estimate, and the size of the circles corresponds to the number of effect sizes. comp: composition, conf: configuration, herb: herbaceous, hete: heterogeneity, lu: land use, nat: natural, nd: no data, seminat: seminatural.