• Energy Research

Abstract Background and Aims Anthropogenic disturbances are causing a co-occurring increase in biotic (ungulate herbivory) and abiotic (drought) stressors, threatening plant reproduction in oak-dominated ecosystems. However, could herbivory compensate for the adverse impact of drought by reducing evapotranspiration? Thus, we investigated the isolated and joint effects of herbivory and drought on oak seedlings of two contrasting Mediterranean species that differ in leaf habit and drought resistance. Methods California oak seedlings from the evergreen, and more drought-resistant, Quercus agrifolia and the deciduous Q. lobata (n = 387) were assigned to a fully crossed factorial design with herbivory and drought as stress factors. Seedlings were assigned in a glasshouse to three to four clipping levels simulating herbivory and three to four watering levels, depending on the species. We measured survival, growth and leaf attributes (chlorophyll, secondary metabolites, leaf area and weight) once a month (May–September) and harvested above- and below-ground biomass at the end of the growing season. Key Results For both oak species, simulated herbivory enhanced seedling survival during severe drought or delayed its adverse effects, probably due to reduced transpiration resulting from herbivory-induced leaf area reduction and compensatory root growth. Seedlings from the deciduous, and less drought-resistant species benefited from herbivory at lower levels of water stress, suggesting different response across species. We also found complex interactions between herbivory and drought on their impact on leaf attributes. In contrast to chlorophyll content which was not affected by herbivory, anthocyanins increased with herbivory – although water stress reduced differences in anthocyanins due to herbivory. Conclusions Herbivory seems to allow Mediterranean oak seedlings to withstand summer drought, potentially alleviating a key bottleneck in the oak recruitment process. Our study highlights the need to consider ontogenetic stages and species-specific traits in understanding complex relationships between herbivory and drought stressors for the persistence and restoration of multi-species oak savannas.

Abstract Key message We test the potential benefits of planting 2-year vs. 1-year-old seedlings to restore Mediterranean oak-dominated systems. Planting 2-year-old Quercus suber L. seedlings is recommended for improved survival and resilience against wild boar (Sus scrofa L.) and drought in dry sandy soils. The removal of acorns in seedlings did not apparently influence leaf biochemical traits and could reduce wild boar damage, particularly in 1-year-old seedlings. Context In the face of anthropogenic global change, Mediterranean oak-dominated ecosystems confront increased biotic (ungulate herbivory) and abiotic (drought) stressors, compromising forest regeneration. Restoration measures are imperative to address this scenario. Aims This study assesses the impact of different mitigation measures on the survival and biochemical traits of two oak species. Methods We planted Quercus ilex L. and Q. suber L. seedlings in Cabañeros and Doñana National Parks (Spain), subjecting them to three treatments: cotyledon/acorn removal, seedling age (1- vs. 2-year-old), and herbivore protection (fenced vs. non-fenced). Results Wild boar (Sus scrofa L.) damage peaked in winter and early spring, while drought prevailed from late spring to fall. In sandy soils, wild boar uprooted 1-year-old more often than 2-years-old seedlings (40% vs. 18%). One-year-old seedlings without acorns showed higher survival rates against wild boar only in sandy soils. The removal of acorns in seedlings did not influence plant biochemical traits. Conclusions Planting 2-year-old seedlings in sandy soils may mitigate wild boar damage and improve drought resilience. Seedling age seems more important than acorn removal against biotic and abiotic stressors although acorn removal could reduce wild boar damage in 1-year-old seedlings. Our results underscore the importance of considering multiple stressors in oak restoration strategies.

Abstract Hopkins’ Bioclimatic Law predicts geographical patterns in phenological timing by establishing a correspondence between latitudinal and altitudinal gradients. First proposed for key phenological events of plants, such as leaf sprouting or flowering dates, this law has rarely been used to assess the geographical equivalence of key life‐history traits of mammals. We hypothesize that (H1) parturition dates of European roe deer Capreolus capreolus are delayed and more synchronized at higher latitudes and altitudes, (H2) parturition timing varies along latitudinal and altitudinal gradients in a way that matches the Hopkins’ Bioclimatic Law and (H3) females adjust parturition timing to match the period of high energy demand with peak resource availability. We used parturition dates of 7,444 European roe deer from Switzerland to assess altitudinal variation in birth timing and synchrony from 288 to 2,366 m a.s.l. We then performed a literature survey to compare altitudinal results with those from different populations along the species’ latitudinal range of distribution. Finally, we performed spatial analysis combining our highly resolved altitudinal data on parturition dates with plant phenology data. As expected, parturition dates were delayed with increasing latitude and altitude. This delay matched the Bioclimatic Law, as the effect of 1º increase in latitude was similar to 120 m increase in altitude. However, while parturitions were more synchronized with increasing altitude, we did not detect any trend along the latitudinal gradient. Finally, plant phenology explained altitudinal variation in parturition timing better than a linear effect of altitude. Our findings clearly demonstrate the ability of a large herbivore to match parturition timing with phenological conditions across the altitudinal gradient, even at the smallest spatial scales.