Neighborhood diversity simultaneously increased and decreased susceptibility to contrasting herbivores in an early stage forest diversity experiment

Abstract

1. Forest structure and diversity can regulate tree vulnerability to damage by insects and pathogens. Past work suggests that trees with diverse neighbours should experience less leaf herbivory and less damage from specialist herbivores and diseases, and that the effect of neighbourhood diversity should be strongest at small spatial scales.2. In an early stage temperate tree diversity experiment, we monitored damage from leaf removing herbivores, specialist (gallers and leaf miners) herbivores, and two specialist fungal diseases (maple leaf anthracnose and cedar apple gall rust) over 3 years. The experimental design included treatments that varied independently in phylogenetic and functional diversity and we made our analyses across four spatial scales (1-16 m 2 ).3. Neighborhood diversity simultaneously increased leaf removal for some species, decreased it for others, and had no effect on yet others. Height apparency-the difference between a focal plant's height and its neighbours'-was the best single predictor of leaf removal across species and spatial scales, but the strength and direction of its effect were also species-specific. 4. Specialist pathogens and fungal foliar diseases showed signs of associational resistance and susceptibility. Oaks (Quercus spp.) were more resistant to leaf miners and maples were more resistant to anthracnose when surrounded by diverse neighbours (associational resistance). In contrast, birches (Betula papyrifera) were more susceptible to leaf miners and eastern red cedars (Juniperus virginiana) were more susceptible to cedar apple gall rust (Gymnosporangium juniperi-virginianae) infection in diverse environments (associational susceptibility). 5. Herbivore and pathogen damage was better predicted by community structure and diversity at small spatial scales (1 and 4 m 2 ) than large scales (9 and 16 m 2 ), suggesting a characteristic spatial scale for these biodiversity-ecosystem functioning effects. 6. Synthesis. Humans control forest diversity through selective harvesting and planting in natural stands and plantations. Our experimental demonstration of the role of local community structure and diversity in suppressing some forms of pest and Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Grossman JJ, Cavender-Bares J, Reich PB, Montgomery RA, Hobbie SE. Neighborhood diversity simultaneously increased and decreased susceptibility to contrasting herbivores in an early stage forest diversity experiment. J Ecol. 2019;107:1492-1505. https://doi.

More diverse tree communities promote foliar fungal pathogen diversity, but decrease infestation rates per tree species, in a subtropical biodiversity experiment

“…This supports former evidence suggesting that foliar fungal pathogens have the potential to maintain competitive differences between tree species (Spear & Mordecai, 2018) and can be regulated by the diversity of the surrounding tree community (Grossman et al, 2019).…”

Complementarity effects are strengthened by competition intensity and global environmental change in the central boreal forests of Canada

“…First, it may reflect increasing complementarity effects dependent on the dispersion of functional traits not correlated with shade tolerance dissimilarity (Paquette et al ). Second, higher phylogenetic dissimilarity may buffer trees against the negative effects of specialist pest and pathogen outbreaks (Parker et al ; Grossman et al ). Studies have suggested that outbreaks of pests such as spruce budworm have increased in intensity in our study region (Boucher et al ) and regions previously inaccessible to the pest due to cold temperatures will become more susceptible as the climate warms (Pureswaran et al ).…”

“…Furthermore, phylogenetic dissimilarity may affect tree growth through a reduction in susceptibility to species–specific pests, pathogens and/or predators. Originally developed to describe patterns of seedling recruitment (Janzen ; Connell ), this theory has been extended to mature plants in the form of the resource concentration hypothesis (Parker et al ; Grossman et al ). The theory stipulates that mature plant communities with high abundances of phylogenetically close host species are more susceptible to specialised pest and pathogen outbreak than those with higher phylogenetic dissimilarity.…”

Forest Understorey Vegetation: Colonization and the Availability and Heterogeneity of Resources

“…Here, for reference, we include stand-replacing fire, a common disturbance type of stand-replacing disturbances in North America as an example. Previous studies have revealed that resource conditions are liable to be affected by stand-replacing fire disturbances [8,12,[33][34][35], which result in increased light, soil nutrients, pH, and soil temperatures, and a decrease in the organic layer depth [15]. Immediately after fire, adequate growth space and resource availability greatly favor the establishment of vascular plants, which are fast-growing, nutrient-demanding, and shade-intolerant [8].…”