Tree diversity reduces herbivory by forest insects

Abstract

Biodiversity loss from plant communities is often acknowledged to affect primary production but little is known about effects on herbivores. We conducted a meta-analysis of a worldwide data set of 119 studies to compare herbivory in single-species and mixed forests. This showed a significant reduction of herbivory in more diverse forests but this varied with the host specificity of insects. In diverse forests, herbivory by oligophagous species was virtually always reduced, whereas the response of polyphagous species was variable. Further analyses revealed that the composition of tree mixtures may be more important than species richness per se because diversity effects on herbivory were greater when mixed forests comprised taxonomically more distant tree species, and when the proportion of non-host trees was greater than that of host trees. These findings provide new support for the role of biodiversity in ecosystem functioning across trophic levels.

Plant diversity effects on insect herbivores and their natural enemies: current thinking, recent findings, and future directions

“…Highly specialized herbivores should exhibit a strong response whereas generalist herbivores should exhibit weak responses because they are less limited to feeding on a specific host plant [21]. For example, in a meta-analysis, Jactel and Brockerhoff [33] found that increased tree diversity reduced herbivory by specialist species, whereas the response of generalist herbivores was variable. These predictions are supported by recent studies in both tropical [9 ] and temperate [31 ] forest systems.…”

Mixing of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) enhances structural heterogeneity, and the effect increases with water availability

“…Increases in species diversity and heterogeneity of other structural attributes can, e.g., stabilize and raise the productivity (Bielak et al, 2014;Lei et al, 2009;Liang et al, 2007;Jucker et al, 2014;Pretzsch et al, 2013Pretzsch et al, , 2015aRío and Sterba, 2009), stability (Griess and Knoke, 2011;Jactel and Brockerhoff, 2007), reduced sensitivity to drought (Grossiord et al, 2014;Metz et al, 2013), habitat diversity (Tews et al, 2004), plant and animal richness (Brunet et al, 2010;Ishii et al, 2004;Roth, 1976), and the aesthetic value (Schütz, 2002;Stölb, 2005) of forest stands. On the other hand more heterogeneous structures can have a negative effect on some taxa (Paillet et al, 2010), on the wood quality (Pretzsch and Rais, 2016), on the effort of forest inventory, planning, and management (von Gadow, 1998;von Gadow et al, 2002), and on the costs of opening up the stands to harvest the timber (Keegan et al, 1995;Kellogg et al, 1996).…”

“…For example, structural characteristics such as the canopy density, size distribution or tree morphology of mixtures and neighbouring monocultures may indicate a higher structural heterogeneity in mixtures. If so, they show how decisions to favour species mixing modifies stand structure and forest functions and services, such as stability (Griess and Knoke, 2011;Jactel and Brockerhoff, 2007), habitat diversity (Tews et al, 2004), or aesthetic value (Schütz, 2002;Stölb, 2005).…”

Forest Carbon Sequestration: The Impact of Forest Management

“…Mixed-species and other complex forests are potentially more adaptable to climate change, so promoting these forest types can help managers to cope with increasing uncertainty (Bolte et al, 2009;Kolström et al, 2011). Greater diversity of tree species can also limit damage from pests (Jactel and Brockerhoff, 2007) and diminish the risk of biological invasion, according to the associational resistance hypothesis (Barbosa et al, 2009). Helms (1998) defined silviculture as "the art and science of controlling the establishment, growth, composition, health and quality of forests and woodlands to meet the diverse needs and values of landowners and society on a sustainable basis".…”