Associational resistance to both insect and pathogen damage in mixed forests is modulated by tree neighbour identity and drought

Abstract

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‘Resistance Mixtures’ Reduce Insect Herbivory in Strawberry (Fragaria vesca) Plantations

“…Although the exact mechanisms of the effects of diversity and resistance behind our findings require further studies, both associational resistance and increased habitat complexity (increasing the structural complexity by increasing the number of varieties or increasing the functional complexity by increasing variation in plant traits) are likely to reduce herbivory via mutually nonexclusive ways by altering the likelihood of the herbivore encountering its preferred host or likelihood of leaving the food patch (Root, 1973;Duffy, 2002;Civitello et al, 2015;Garrett et al, 2017;Field et al, 2020). These attributes may decrease damage by herbivores through reductions in their colonization rates, reproductive performance, and/or lower consumption efficiency resulting from increases in search effort, lower host encounter rate, and/or diet mixing (Root, 1973;Peacock and Herrick, 2000;Duffy, 2002;McArt and Thaler, 2013;Civitello et al, 2015;Field et al, 2020), thereby relaxing the selection pressure for higher herbivore tolerance.…”

“…Increasing the diversity of agricultural systems can be accomplished by either increasing interspecies diversity via intercropping several crop species or by increasing intraspecies diversity via mixing several cultivars. There are several examples showing how increased interspecific diversity can reduce pest damage ( Jactel and Brockerhoff, 2007 ; Letourneau et al, 2011 ; Tooker and Frank, 2012 ; Field et al, 2020 , but see Vehviläinen et al, 2006 ). Although intercropping has proven to be a useful pest management tool, it has not been widely applied due to economic and practical reasons ( Lin, 2011 ; Letourneau et al, 2011 ; Tooker and Frank, 2012 ).…”

“…Similar to intercropping, cultivar mixing should decrease herbivore damage via multiple complementary mechanisms: According to the “variance in edibility,” “resource concentration,” and “dilution effect” hypotheses, the herbivore performance and population size of herbivores should be reduced in cultivar mixtures. This is because the increased heterogeneity of host plant populations should disrupt successful host location, increase the likelihood of leaving the food patch ( Root, 1973 ; Thiéry and Visser, 1987 ; Peacock and Herrick, 2000 ; Duffy, 2002 ; Civitello et al, 2015 ; Field et al, 2020 ), and/or force herbivores to consume nonpreferred plant cultivars as well (diet mixing; Peacock and Herrick, 2000 ; McArt and Thaler, 2013 ), thereby reducing the likelihood of the herbivores reaching outbreak levels. However, to date nearly all studies about cultivar mixing focus on its effects on pathogens ( Zhu et al, 2000 ; Mulumba et al, 2012 ; Yang et al, 2019 ; but see Peacock and Herrick, 2000 ; Ninkovic et al, 2002 ; and Doherty et al, 2019 for studies of herbivores).…”

Contributions of non-timber forest products to people in mountain ecosystems and impacts of recent climate change

“…The future vulnerability of these ecosystem services to climate change needs to be better understood and different management and adaptation initiatives implemented. For example, promoting the use of NTFP species which are more resilient to pests in regions with high incidence of pest attack, promoting mixed-species NTFPs (Field et al 2020), or managing healthy NTFPs by selective cutting of susceptible NTFPs which promote pest attack but have few defences against infestation. For the management of invasive plant species, control measures (e.g.…”

Landscape and tree community effects on the infestation of an endemic fungal pathogen in riparian forests were mediated by leaf traits

“…We quanti ed pathogen load by counting the number of symptomatic leaves out of 120 leaves on each individual. Then, ve leaves were haphazardly chosen on each branch, and the percentage of leaf area infected by pathogen was visually estimated and classi ed into seven classes: (1) 0%, (2) 1-5%, (3) 6-10%, (4) 11-25%, (5) 26-50%, (6) 51-75%, (7) 76-100%, after previous authors (Hantsch et al 2013(Hantsch et al , 2014aField et al 2020). Disease severity per tree individual was calculated by averaging damage percentage of all analysed leaves (20 leaves) of the individual.…”