Can Shrub Flammability be Affected by Goat Grazing? Flammability Parameters of Mediterranean Shrub Species under Grazing

Abstract

In this study, we evaluated changes in the potential flammability of different Mediterranean shrub species in a pine (Pinus pinea) forest in the Doñana Natural Park (of SW Spain) as a result of goat grazing. Plant height, total biomass, fine fuel biomass and leaves/wood ratio were measured in individual plants of each species in both grazed and ungrazed areas. Moisture content, mean time of ignition, mean time of combustion, gross heat of combustion (GHC) and flammability class of the studied shrub species were determined in the laboratory. The results of this experiment showed that grazing influenced the flammability characteristics of the studied shrub species. However, the strength of this effect was insufficient to modify the flammability index of these plants, except in the case of Myrtus communis, in which grazed plants presented a lower flammability index. According to Valette’s classification, Cistus salviifolius, Halimium halimifolium and Pistacea lentiscus are flammable species, Rosmarinus officinalis is a flammable-highly flammable species, and M. communis is non-flammable. The GHC values obtained were generally “intermediate”, except for those of R. officinalis, which were classified as “high”. The flammability parameters of the study species did not show a very marked trend in relation to grazing, but the vertical structure of plants did change by presenting reduced biomass of leaves and fine twigs. This change altered the physical characteristics of these plants and possibly acted to reduce the inherent fire risk of the shrublands.

Native herbivore browsing alters plant physical and chemical traits in a eucalypt forest understory

“…The leaf moisture content of two species increased in the presence of herbivores, an unexpected effect that may result from reduced competition at open sites (Figure 4), increasing water availability. This is in contrast to studies that find that herbivory typically removes moister leaf material (Blackhall et al, 2012;Mancilla-Leyt on al., 2021). Our study area was affected by heavy rainfall at the time of data collection, potentially influencing moisture content results.…”

“…At the individual plant level, herbivores can preferentially graze different biomass components within a plant (Mancilla-Leyt on et al, 2021). Preferential grazing can be driven by plant traits including chemical properties, physical leaf characteristics, and overall plant architecture (Archibald et al, 2019;.…”

“…Preferential grazing can be driven by plant traits including chemical properties, physical leaf characteristics, and overall plant architecture (Archibald et al, 2019; Rafferty & Lamont, 2007). For example, higher moisture content and specific leaf area (SLA) have been positively associated with increased biomass consumption (Jessen et al, 2020; Mancilla‐Leytón et al, 2021), whereas morphological defenses such as tough leaves deter herbivores (Hanley et al, 2007). Leaf nutritional content and chemical defense compounds can also influence herbivore vegetation preference (Archibald et al, 2019).…”

Effects of Diet Selection by Goats Grazing on the Vegetation of a Protected Pine Forest in Doñana Natural Park (SW Spain)

“…The study was carried out in a 100 ha pine forest located in the Doñana Natural Park limits, SW Spain (37 • 14 N, 6 • 20 W). The climate is Mediterranean, with wet and mild win-ters and long, dry summers; mean annual rainfall is 540 mm [8]. The vegetation comprises a Pinus pinea forest with an understory dominated by shrubs (the common species being Cistus salviifolius, Halimium halimifolium, H. calycinum, Myrtus communis, Pistacia lentiscus, and Rosmarinus officinalis).…”

“…Grazing selectivity has been considered to greatly influence species composition and abundance, through the control that it exerts over the population dynamics of plant species [4]. Accordingly, it is accepted that goats (Capra hircus) have modified, through selective feeding [5][6][7][8], the structure and composition of Mediterranean rangelands, which they have traditionally grazed. Goats are poliphagous animals that feed on a great variety of species, but they always select some species and avoid others [9].…”