Global patterns of insect herbivory in gap and understorey environments, and their implications for woody plant carbon storage

Abstract

Insect herbivory is thought to favour carbon allocation to storage in juveniles of shade-tolerant trees. This argument assumes that insect herbivory in the understorey is sufficiently intense as to select for storage; however, understoreys might be less attractive to insect herbivores than canopy gaps, because of low resource availability and -at temperate latitudes -low temperatures. Although empirical studies show that shade-tolerant species in tropical forests do allocate more photosynthate to storage than their light-demanding associates, the same pattern has not been consistently observed in temperate forests. Does this reflect a latitudinal trend in the relative activity of insect herbivory in gap versus understorey environments? To date there has been no global review of the effect of light environment on insect herbivory in forests. We postulated that if temperature is the primary factor limiting insect herbivory, the effect of gaps on rates of insect herbivory should be more evident in temperate than in tropical forests; due to low growing season temperatures in the oceanic temperate forests of the Southern Hemisphere, the effect of gaps on insect herbivory rates should in turn be stronger there than in the more continental temperate climates of the Northern Hemisphere. We examined global patterns of insect herbivory in gaps versus understories through meta-analysis of 87 conspecific comparisons of leaf damage in contrasting light environments. Overall, insect herbivory in gaps was significantly higher than in the understorey; insect herbivory was 50% higher in gaps than in understoreys of tropical forests but did not differ significantly between gaps and understories in temperate forests of either hemisphere. Results are consistent with the idea that low resource availability -and not temperature -limits insect herbivore activity in forest understoreys, especially in the tropics, and suggest the selective influence of insect herbivory on late-successional tree species may have been over-estimated.

Intermediate harvesting intensities enhance native tree performance of contrasting species while conserving herbivore diversity in a Patagonian woodland

“…increased harvested areas) as radiation, mean temperature and available water increase (Piotto et al, 2003;Pafundi, Urretavizcaya & Defossé, 2014;Gönc et al, 2015). However, these large openings would also lead to more days of frost in winter, more hydric stress in summer and potentially more herbivory (Piper, Altmann & Lusk 2018). In this context, facilitation from wild trees and bushes to the planted saplings could be critical in some landscapes (Pretzsch, Forrester & Bauhus, 2017).…”

Herbivory and leaf traits of Amazonian tree species as affected by irradiance

“…2). Although some studies have shown highest values of herbivory in the understorey (Goodale et al 2014; Mąderek et al 2017; Salgado‐Luarte & Gianoli 2017), others have indicated that the highest herbivory occurs in gaps or under high irradiance (Chacon & Armesto 2006; Richards & Coley 2007; Piper et al 2018), while others observed no differences between extremes in terms of light environment (Vasconcelos 1999; Ruhnke et al 2009). In addition, recent studies indicate that the environment can modulate leaf traits more intensely than phylogenetic characteristics among species (Nascimento et al 2020).…”

“…Although herbivory is a critical biotic factor affecting seedling survival and growth, mainly because foliar tissue is removed during feeding (Forrister et al 2019), the effects of the light environment on herbivory in tropical tree species remain controversial (Ruhnke et al 2009; Salgado‐Luarte & Gianoli 2017; Piper et al 2018). While high values of herbivory have been reported in shaded environments (low irradiance) (Liang & Stehlik 2009; Salgado‐Luarte & Gianoli 2017), other studies have reported the opposite, showing high herbivory rates under gap conditions (high irradiance) (Chacon & Armesto 2006; Piper et al 2018). Moreover, even under contrasting irradiance conditions, significant changes in herbivory may not be observed (Vasconcelos 1999; Baraza et al 2004; Plath et al 2011).…”

Weak effects of birds, bats, and ants on their arthropod prey on pioneering tropical forest gap vegetation

“…Abundance of herbivorous insects in regenerating tropical canopy gaps is generally higher than in mature forest ecosystems (Richards & Coley, 2007). Similarly, consumptive effects of herbivorous insects (e.g., increased leaf damage) are stronger on pioneering successional gap vegetation (Piper et al, 2018). Insectivorous birds, bats, and ants can effectively limit the abundance of tropical arthropods (Kalka et al, 2008; Morrison & Lindell, 2012; Sam et al, 2015; Wills et al, 2019).…”