Tree Diversity Limits the Impact of an Invasive Forest Pest.

Virginie Guyot,Aude Vialatte,Hervé Jactel,Federico Selvi,Bastien Castagneyrol,Filippo Bussotti,Marc Deconchat,Andrew Hector

doi:10.1371/journal.pone.0136469

Abstract

The impact of invasive herbivore species may be lower in more diverse plant communities due to mechanisms of associational resistance. According to the “resource concentration hypothesis” the amount and accessibility of host plants is reduced in diverse plant communities, thus limiting the exploitation of resources by consumers. In addition, the “natural enemy hypothesis” suggests that richer plant assemblages provide natural enemies with more complementary resources and habitats, thus promoting top down regulation of herbivores. We tested these two hypotheses by comparing crown damage by the invasive Asian chestnut gall wasp (Dryocosmus kuriphilus) on chestnut trees (Castanea sativa) in pure and mixed stands in Italy. We estimated the defoliation on 70 chestnut trees in 15 mature stands sampled in the same region along a gradient of tree species richness ranging from one species (chestnut monocultures) to four species (mixtures of chestnut and three broadleaved species). Chestnut defoliation was significantly lower in stands with higher tree diversity. Damage on individual chestnut trees decreased with increasing height of neighboring, heterospecific trees. These results suggest that conservation biological control method based on tree species mixtures might help to reduce the impact of the Asian chestnut gall.

Highlights

Biological invasions have been responsible for more than 74% of known species extinctions [1,2], being one of the major causes of biodiversity loss
Observations showed that 100% of the chestnut trees that we sampled were attacked by D. kuriphilus
Damage by D. kuriphilus was significantly higher on trees with higher apparency: chestnut trees that were taller than their neighbors were subject to twice as much damage as shorter trees on average (t = 3.95, P < 0.001, Fig 2)

Summary

Introduction

Biological invasions have been responsible for more than 74% of known species extinctions [1,2], being one of the major causes of biodiversity loss. Two temperate forest tree species came close to extinction in the 20th century due to exotic pathogens: the American chestnut (Castanea dentata (Marsh.) Borkh) due to chestnut blight introduced from Asia, and the European elms following the introduction of elm disease from North America. The emerald ash borer (Agrilus planipennis Fairmaire), which was introduced from Asia, is threatening the survival of the Fraxinus genus in the US [3]. The paradox is that biodiversity is itself considered a main driver of resistance to invasion. Since the seminal work of Elton [4], it is commonly assumed that ecosystem invasibility, i.e. susceptibility to invasion by non-resident.

Methods

Results

Discussion

Conclusion