Holm oak decline and mortality exacerbates drought effects on soil biogeochemical cycling and soil microbial communities across a climatic gradient

Holm oak decline is determined by shifts in fine root phenotypic plasticity in response to belowground stress

“…Thus, we speculate that the phenotypic plasticity associated with declining trees may not constitute an adaptive advantage (Stotz et al ., 2021) or an increase in fitness (Bonser, 2021) in the context of the Spanish dehesas. While holm oak trees are well adapted to the harsh environmental conditions where they have evolved (Moreno & Cubera, 2008; García‐Angulo et al ., 2020), Spanish dehesas are susceptible when subject to a sequence of different stochastic disturbances, including unusually or extreme long drought, clearing, ploughing, grazing and other anthropic land use‐related disturbances that expose holm oak to unpredictable changes in water and nutrient availability (Plieninger, 2006). All these factors may favour lower phenotypic plasticity and thus a conservative resource‐use strategy, such as the one we observed in healthy and susceptible holm oak trees (Fig.…”

Land-use practices (coppices and dehesas) and management intensity modulate responses of Holm oak growth to drought

“…Land-use classification was done based on orthophotos, which allowed to precisely estimate the crown coverage (i.e., percentage of trees per ha) of each of our ten study sites (MAGRAMA 2007;Sevilla et al, 2016;García-Angulo et al, 2020), and on in situ observations (i.e., presence or absence of livestock rearing and grazing). The analyses of the orthophotos was done with SigPac viewer (http://signa.ign.es/sign a/Pege.aspx) available from the Spanish Ministry of Transport, Mobility and Urban Agenda.…”

“…Based on this approach, we considered as being dehesas (i.e., DH) the sites where the crown coverage was low (~ 30% per ha) and where there were clear signs of livestock rearing and grazing. The sites where the crown coverage was high (>30% per ha) and there were not evident signs of livestock rearing and grazing, were considered as being coppices (i.e., FR) (García-Angulo et al, 2020). The ten study sites were further classified based on the vigor class of the Holm oaks by visually estimating the crown defoliation (% of foliage loss) of each Holm oak tree selected (see below).…”

“…Once collected, soil samples were immediately stored in a portable fridge where a 4 • C temperature was maintained until arrival to the laboratory (García-Angulo et al, 2020). Once in the laboratory, the soil within each bag was homogenized, dried at room temperature, sieved, and used for further analyses.…”

Micropropagation, Characterization, and Conservation of Phytophthora cinnamomi-Tolerant Holm Oak Mature Trees

“…Since the 1990s, and particularly in recent years, dehesas have been seriously affected by oak decline disease or "la seca", which jeopardizes the long-term survival of this valuable ecosystem. The etiology of the disease is multiple and usually results from the interaction of several factors [4], such as aging and low natural regeneration of trees [5], the appearance of extreme climate events promoted by climate change including increased temperatures and altered precipitation regimes [6][7][8], and the emergence of new diseases and outbreaks of soil pathogens, mainly Phytophthora cinnamomi Rands (Pc) [9,10]. The incidence of holm oak decline is increasing and affecting more and more areas in the Mediterranean region [11].…”