Effects of insect attack to stems on plant survival, growth, reproduction and photosynthesis

116

118

The drivers of background tree mortality rates-the typical low rates of tree mortality found in forests in the absence of acute stresses like drought-are central to our understanding of forest dynamics, the effects of ongoing environmental changes on forests, and the causes and consequences of geographical gradients in the nature and strength of biotic interactions. To shed light on factors contributing to background tree mortality, we analyzed detailed pathological data from 200,668 tree-years of observation and 3,729 individual tree deaths, recorded over a 13-yr period in a network of old-growth forest plots in California's Sierra Nevada mountain range. We found that: (1) Biotic mortality factors (mostly insects and pathogens) dominated (58%), particularly in larger trees (86%). Bark beetles were the most prevalent (40%), even though there were no outbreaks during the study period; in contrast, the contribution of defoliators was negligible. (2) Relative occurrences of broad classes of mortality factors (biotic, 58%; suppression, 51%; and mechanical, 25%) are similar among tree taxa, but may vary with tree size and growth rate. (3) We found little evidence of distinct groups of mortality factors that predictably occur together on trees. Our results have at least three sets of implications. First, rather than being driven by abiotic factors such as lightning or windstorms, the "ambient" or "random" background mortality that many forest models presume to be independent of tree growth rate is instead dominated by biotic agents of tree mortality, with potentially critical implications for forecasting future mortality. Mechanistic models of background mortality, even for healthy, rapidly growing trees, must therefore include the insects and pathogens that kill trees. Second, the biotic agents of tree mortality, instead of occurring in a few predictable combinations, may generally act opportunistically and with a relatively large degree of independence from one another. Finally, beyond the current emphasis on folivory and leaf defenses, studies of broad-scale gradients in the nature and strength of biotic interactions should also include biotic attacks on, and defenses of, tree stems and roots.

Section: Discussionsupporting

confidence: 91%

Section: Discussionsupporting

confidence: 68%

Section: Implications For Characterizing the Strength Of Biotic Intermentioning

confidence: 51%

See 1 more Smart Citation

Why do trees die? Characterizing the drivers of background tree mortality

Das

Stephenson

Davis

2016

116

118

“…New lateral shoots on willow trees attracted additional insect herbivores and predators, resulting in a multilevel trophic cascade ). Interestingly, Stephens and Westoby (2015) show in their meta-analysis that stem-boring insects have overall positive effects on lateral growth of woody plants, suggesting that vegetative overcompensation may be widespread.…”

Section: Introductionmentioning

confidence: 99%

Overcompensation for insect herbivory: a review and meta‐analysis of the evidence

Garcia

Eubanks

2019

Not all herbivory is detrimental to plants. In some cases, plants can compensate for herbivory, maintain growth and fitness following damage, or even overcompensate for herbivory and perform better than if left undamaged. Examples of overcompensation to vertebrate herbivory are well known, but here we review the literature for examples of reproductive overcompensation (i.e., increased production of traits associated with fitness) and increased vegetative growth (i.e., vegetative overcompensation) following insect herbivory. We used a meta‐analysis to explore the effects of plant growth form, evolutionary history, herbivore feeding guild, and other plant and insect traits on the expression of reproductive and vegetative overcompensation by plants. Our literature search revealed 86 studies documenting examples of overcompensation for insect herbivory by 67 plant species representing 26 families. These plants included monocots and dicots, annuals and perennials, and woody and herbaceous plants. We also found that varied insect herbivores induce overcompensation, including 75 insect species in six orders representing 27 families and myriad feeding guilds. In our meta‐analysis, we calculated 53 effect sizes from 21 publications documenting reproductive overcompensation and 89 effect sizes from 40 publications documenting vegetative overcompensation. Variation in reproductive overcompensation was seen among plant growth forms, functional groups, cultivation, herbivore feeding sites, and plant and herbivore families. Variation in vegetative overcompensation was seen among plant families, herbivore families, and latitudinal gradients. We suggest overcompensation for insect herbivory may be far more prevalent than previously thought. Additional research focusing on the mechanisms, patterns, and ecological and evolutionary consequences of overcompensation for insect herbivory is likely to provide exciting new insights into this poorly understood and largely overlooked outcome of plant–insect interactions.

“…Second, herbivory may act to regulate established populations by reducing non‐native plant fitness, thereby limiting population growth and spread (Levine et al. , Schmitz , Stephens and Westoby ).…”

Section: Introductionmentioning

confidence: 99%

Pre‐damage biomass allocation and not invasiveness predicts tolerance to damage in seedlings of woody species in Hawaii

Lurie

Barton

Daehler

2017

Plant-herbivore interactions have been predicted to play a fundamental role in plant invasions, although support for this assertion from previous research is mixed. While plants may escape from specialist herbivores in their introduced ranges, herbivory from generalists is common. Tolerance traits may allow non-native plants to mitigate the negative consequences of generalist herbivory that they cannot avoid in their introduced range. Here we address whether tolerance to herbivory, quantified as survival and compensatory growth, is associated with plant invasion success in Hawaii and investigate traits that may enhance tolerance in seedlings, the life stage most susceptible to herbivory. In a greenhouse experiment, we measured seedling tolerance to simulated herbivory through mechanical damage (50% leaf removal) of 16 non-native woody plant species differing in invasion status (invasive vs. non-invasive). Seedlings were grown for 2 weeks following damage and analyzed for biomass to determine whether damaged plants could fully compensate for the lost leaf tissue. Over 99% of all seedlings survived defoliation. Although species varied significantly in their levels of compensation, there was no consistent difference between invasive and non-invasive species. Seedlings of 11 species undercompensated and remained substantially smaller than control seedlings 2 weeks after damage; four species were close to compensating, while one species overcompensated. Across species, compensation was positively associated with an increased investment in potential storage reserves, specifically cotyledons and roots, suggesting that these organs provide resources that help seedlings re-grow following damage. Our results add to a growing consensus that pre-damage growth patterns determine tolerance to damage, even in young seedlings which have relatively low biomass. The lack of higher tolerance in highly invasive species may suggest that invaders overcome herbivory barriers to invasion in other ways, such as resistance traits, or that herbivory does not play an important role in the seedling invasion dynamics of these woody species in Hawaii.