Ungulates mediate trade‐offs between carbon storage and wildfire hazard in Mediterranean oak woodlands

Abstract

1. Ungulates influence ecosystem services in important ways, including by altering the amount of standing plant biomass and species composition. Browsing, for example, removes biomass and, in consequence, can decrease the risk of wildfires.The influence of ungulates on carbon storage is more complicated. Browsers reduce carbon stocks directly by consuming biomass, but if browsing reduces fine fuel loads, then long-term carbon storage may increase.2. We investigated how wild ungulates mediate trade-offs between carbon stocks and wildfire hazard in a Mediterranean oak woodland. We assessed the effects of deer (Cervus elaphus and Dama dama) on the colonization by gum cistus (Cistus ladanifer), a highly flammable Mediterranean shrub, through a long-term ungulate exclusion experiment. We established fenced (unbrowsed) and open (browsed) plots in areas whereshrubs were previously cleared, and compared shrub density, height, biomass, and above-ground carbon stocks 6 and 14 years after fencing.4. There were no significant differences in shrub density between treatments after 6 years of browsing exclusion but, by this point, height was already significantly greater in fenced plots. At the end of the experiment, shrub density and height were both significantly greater in fenced plots. Biomass and carbon stocks of gum cistus increased and reached a plateau in fenced plots, while in open plots biomass and carbon stocks increased initially but then decreased. Ungulates also prevented accumulation of litter carbon stocks, which was significantly higher in fenced plots after 14 years of browsing exclusion. 5.We also modelled fire behaviour in fenced and open plots. Browsing reduced fine fuel load, an important contributor to fire spread, by 80%. In browsed plots, modelled wildfire rate of spread, flame length, and fireline intensity decreased by 50%, 65%, and 90%, respectively, which also decreased the probability of canopy fire and of oak mortality.6. Synthesis and applications. By decreasing fire hazard and the probability of canopy fire, ungulates may ultimately increase ecosystem carbon stocks through improved adult oak survival. These critical, indirect trade-offs need to be assessed when addressing the effects of ungulates on ecosystems and the management of their populations. cork oak (Quercus suber). Woodland understorey was dominated by C. ladanifer, a Mediterranean shrub species, and annual grasslands primarily composed of grasses (e.g., Bromus madritensis, Gaudinia fragilis), with smaller proportions of forbs (e.g., Andryala integrifolia, Leontodon taraxacoides) and legumes (e.g., Vicia disperma, Ornithopus compressus). Cistus ladanifer is a highly flammable species because of the terpene-derived resin that impregnates its leaves and branches K E Y W O R D S above-ground biomass, Cistus ladanifer, ecosystem services, fire behaviour, fuel management, oak survival, shrub encroachment, ungulates | 701 Journal of Applied Ecology LECOMTE ET aL. S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be f...

Moisture availability and ecological restoration limit fine fuels and modelled wildfire intensity following non‐native ungulate removal in Hawaii

“…Ungulates mediate trade‐offs between wildfire risk, biodiversity and ecosystem services such as carbon storage and watershed conservation (Lecomte et al., 2019), as well as human recreation and economic activities. Land managers seeking to balance conservation and restoration objectives with wildfire risk should be cognizant of the impacts of non‐native ungulate removal on fuels and wildfire behaviour.…”

“…Ecosystems are threatened globally by increased frequency and severity of wildfires (Krawchuk et al., 2009). Wildfire activity globally is a dynamic ecological process that in many contexts poses a significant risk to human health and safety (Bowman et al., 2017), biodiversity (D'Antonio & Vitousek, 1992), watershed conservation (Ice et al., 2004; Trauernicht et al., 2018), primary productivity (Hawbaker et al., 2017; Lecomte et al., 2019) and other ecosystem goods and services (Moritz et al., 2014). In turn, wildfires are a widely distributed natural disturbance that plays an important role in many native ecosystems and can be a net benefit to overall ecosystem services (Pausas & Keeley, 2019).…”

Soil VOC emissions of a Mediterranean woodland are sensitive to shrub invasion

“…The impact of plants on soil physicochemical and biological properties can be particularly pronounced in grasslands and savanna-like ecosystems when the density of woody plants increases at the expense of the herbaceous layer through shrub propagation (Van Auken 2009;Eldridge et al 2011;Li et al 2016). This process can alter the ecosystem carbon stock (Li et al 2016;Lecomte et al 2019) water (Rascher et al 2011;Caldeira et al 2015;Haberstroh et al 2021) and nitrogen cycle (Hellmann et al 2011). Shrub propagation further alters soil microbial communities in the rhizosphere (Marschner et al 2001;Bakker et al 2013), litter quantity and quality (e.g.…”

“…Cistus ladanifer is a semi-deciduous shrub, known for its rapid colonization rates, associated high interspecific competition (mainly for water resources) (Caldeira et al 2015;Haberstroh et al 2021) and fire promotion (Frazão et al 2018;Lecomte et al 2019). Its leaves have numerous aromatic and pharmacological applications (Frazão et al 2018).…”

“…2018; Lecomte et al . 2019). Its leaves have numerous aromatic and pharmacological applications (Frazão et al .…”