Browsing Herbivore–Woody Plant Interactions in Savannas

Scogings, Peter F.; Gowda, Juan H.

doi:10.1002/9781119081111.ch15

Cited by 8 publications

(13 citation statements)

References 163 publications

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“…Our results corroborated the findings of other studies of savanna woody plant responses to browsing that have shown that compensatory or over-compensatory shoot production is a common response to various intensities of browsing (Scogings & Gowda 2020). However, because reduced stem diameter can be indicative of C exhaustion (Hester et al 2006;Palacio et al 2014), this study suggested that extreme intensities of browsing early in the growing season, that may cause exhaustion of stored C during the same season, would retard saplings' long-term growth, and delay recruitment into the seed-producing adult stage (Swemmer & Ward 2020).…”

Section: Discussionsupporting

confidence: 91%

“…Low resource availability or high herbivory intensity can reduce C availability for both growth and defence (Herms & Mattson 1992; Scogings et al . 2011), and thus, the demand for nitrogen (N) is also reduced (Weaver & Herrmann 1997; He & Dijkstra 2014; Hernán et al . 2019).…”

Section: Introductionmentioning

confidence: 99%

“…However, these broad responses may be modulated by interactions between resource availability and herbivory intensity (Bagchi & Ritchie 2011; Scogings et al . 2011). While such generalised patterns may not hold equally within and among species (Hahn & Maron 2016), some studies have provided supporting evidence within species (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…A basic conceptual framework for predicting plant growth and secondary metabolism responses to nutrient availability and intensity of herbivory, based on Herms and Mattson (1992) and Scogings et al . (2011), with consideration of other renditions and insights, for example Stamp (2003), Gayler et al . (2007), Glynn et al .…”

Section: Introductionmentioning

confidence: 99%

“…). Increasing herbivory intensity has the same qualitative effect as decreasing nutrient availability because both factors have similar effects on carbon source–sink balances in the plant (Scogings et al 2011…”

Section: Introductionmentioning

confidence: 99%

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Severe simulated herbivory constrains Sclerocarya birrea saplings regardless of resource availability

Scogings¹,

Fortier

2020

Austral Ecology

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Allocation of carbon to growth and defences in plants is affected by resource availability and herbivory, two determinants of woody plant abundance in savannas. Both factors are critical at the sapling stage of woody plants, yet their combined effects on sapling growth and defence have been poorly studied in savannas. Sclerocarya birrea is an iconic keystone species in southern African savannas, widely used by herbivores and humans. We hypothesised that low resource availability or high herbivory intensity would reduce growth and nutritional value for herbivores, but high resource availability or low herbivory intensity would increase growth and nutritional value. Support for our hypothesis would imply that any level of browsing intensity (relative to unbrowsed plants), regardless of resource availability, would potentially hold saplings in a browser trap because of reduced growth or improved nutritional value. We explored responses of S. birrea saplings to five levels of nutrient fertiliser and six levels of simulated browsing intensity. Low fertiliser application rates did not affect growth, but the highest fertiliser rate increased canopy growth. The most severe intensities of simulated browsing negatively affected growth and nutritional value. Our results suggested that either resource limitation throughout the growing season, or extremely intense browsing early in the growing season, is potentially able to retard long‐term growth of saplings and delay recruitment of adults. Although saplings that are severely browsed early in the growing season might not be re‐browsed later in the same season because of their reduced nutritional value, their weakened nitrogen status would be an additional limitation to regrowth. No significant interactions between resource availability and herbivory intensity were detected, which we suggest resulted from responses to resource availability and herbivory operating at different temporal scales. We recommend that future experiments of this type include carefully timed measurements to detect transient responses.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Severe simulated herbivory constrains Sclerocarya birrea saplings regardless of resource availability

Scogings¹,

Fortier

2020

Austral Ecology

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Ungulates mitigate the effects of drought and shrub encroachment on the fire hazard ofMediterranean oak woodlands

Lecomte,

Bugalho,

Catry

et al. 2024

Ecological Applications

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Climate change is increasing the frequency of droughts and the risk of severe wildfires, which can interact with shrub encroachment and browsing by wild ungulates. Wild ungulate populations are expanding due, among other factors, to favorable habitat changes resulting from land abandonment or land‐use changes. Understanding how ungulate browsing interacts with drought to affect woody plant mortality, plant flammability, and fire hazard is especially relevant in the context of climate change and increasing frequency of wildfires. The aim of this study is to explore the combined effects of cumulative drought, shrub encroachment, and ungulate browsing on the fire hazard of Mediterranean oak woodlands in Portugal. In a long‐term (18 years) ungulate fencing exclusion experiment that simulated land abandonment and management neglect, we investigated the population dynamics of the native shrub Cistus ladanifer, which naturally dominates the understory of woodlands and is browsed by ungulates, comparing areas with (no fencing) and without (fencing) wild ungulate browsing. We also modeled fire behavior in browsed and unbrowsed plots considering drought and nondrought scenarios. Specifically, we estimated C. ladanifer population density, biomass, and fuel load characteristics, which were used to model fire behavior in drought and nondrought scenarios. Overall, drought increased the proportion of dead C. ladanifer shrub individuals, which was higher in the browsed plots. Drought decreased the ratio of live to dead shrub plant material, increased total fuel loading, shrub stand flammability, and the modeled fire parameters, that is, rate of surface fire spread, fireline intensity, and flame length. However, total fuel load and fire hazard were lower in browsed than unbrowsed plots, both in drought and nondrought scenarios. Browsing also decreased the population density of living shrubs, halting shrub encroachment. Our study provides long‐term experimental evidence showing the role of wild ungulates in mitigating drought effects on fire hazard in shrub‐encroached Mediterranean oak woodlands. Our results also emphasize that the long‐term effects of land abandonment can interact with climate change drivers, affecting wildfire hazard. This is particularly relevant given the increasing incidence of land abandonment.

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Herbivory mediates direct and indirect interactions in long‐unburned chaparral

Fox

Potts

2022

Ecological Monographs

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Community interaction webs describe both direct and indirect interactions among species. Changes in direct interactions often become noticeable soon after a perturbation, but time lags in the responses of many species may delay the appearance of indirect effects and lead to temporal or spatial variation in interaction webs. Accurately identifying these shifts in the field requires time‐specific, spatially differentiated interaction webs. We explore how variation in browsing affects interaction webs in a long‐unburned chaparral shrubland near the central California coast. Most prior work in chaparral focused on rapid changes for <5 years after a wildfire that were assumed to determine community patterns until the next fire. Here, we report the results of the first 15 years of an ongoing experiment monitoring how interaction webs in long‐unburned chaparral (at least 100 years postfire) respond to experimental variation in browsing by deer and rabbits on dominant shrubs (Arctostaphylos pumila, Ceanothus cuneatus var. rigidus, and Ericameria ericoides). We hypothesized that variation in browsing would directly affect foodplants, indirectly modify growth and survival of other shrubs, and impact habitat needed by herbaceous plants. We found a dynamic web of plant–herbivore and plant–plant interactions that responded rapidly to changes in deer browsing on Ceanothus followed by indirect interactions that continued developing over several years, affecting shrubs, open space, herbaceous plants, and small mammals. Experimental variation in the intensity of deer browsing led to temporal and spatial changes in interactions that produced three different community interaction webs. With deer, community webs were complex, having numerous direct and indirect interactions. Removing deer simplified the community web, changed outcomes of interactions, and reduced open space and herbaceous plant densities. Finally, changes in Ceanothus morphology without deer allowed woodrats to browse these shrubs, with negative impacts on Ceanothus growth and survival. General field observations also showed that all three alternative interaction webs occurred naturally at our fieldsite, varying across space and over time. Long‐unburned chaparral communities browsed by deer maintain high biological diversity, but maintenance of this diversity involves many key direct and indirect biotic interactions.

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Browsing Herbivore–Woody Plant Interactions in Savannas

Cited by 8 publications

References 163 publications

Severe simulated herbivory constrains Sclerocarya birrea saplings regardless of resource availability

Severe simulated herbivory constrains Sclerocarya birrea saplings regardless of resource availability

Ungulates mitigate the effects of drought and shrub encroachment on the fire hazard ofMediterranean oak woodlands

Herbivory mediates direct and indirect interactions in long‐unburned chaparral

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