Effects of Quercus suber Decline on Woody Plant Regeneration: Potential Implications for Successional Dynamics in Mediterranean Forests

Abstract

15In the last decades widespread tree decline and mortality has been documented in forests 16 worldwide. These mortality events usually show certain level of host-specificity, translating 17 into rapid changes in the relative abundance of the adult community. Despite these short-term 18 changes, it is poorly understood whether the decline and mortality of certain tree species are 19 likely to result in long-term vegetation shifts. Trajectories of forest recovery and the 20 probability of occurrence of permanent vegetation shifts are to a large extent determined by 21 post-mortality regeneration dynamics. Using a spatially-explicit neighborhood approach we 22 evaluated the spatial patterns of natural regeneration of the woody plant community in mixed 23 Mediterranean forests affected by the decline of their dominant tree species, Quercus suber. 24 We predicted the abundance, survival and richness of the seedling and sapling bank as a 25 function of the distribution and health status of the tree and shrub community. Results 26 indicated that Q. suber decline had detectable effects on seedlings and saplings of coexistent 27 woody species from very different functional groups (trees, shrubs and lianas). The sign and 28 magnitude of these effects varied substantially among coexistent species, which could imply 29 shifts in the species ranking of seedling and sapling abundance, affecting successional 30 trajectories and potentially leading to vegetation shifts. Because most of these changes 31 pointed towards a loss of dominance of Q. suber, management strategies are urgently needed 32 in order to attenuate adult mortality or promote its regeneration, counteracting the negative 33 effects of global change drivers (exotic pathogens, climate change) on these valuable forests.34 35

Disentangling the climatic and biotic factors driving changes in the dynamics of Quercus suber populations across the species‘ latitudinal range

“…This alteration in dominance might imply important consequences in the next decades, since other species will have higher probabilities of replacing existing Q. suber trees, especially under current declining trends and rates of adult mortality already detected in many other populations across the species' distribution (Avila, et al, ; Gómez‐Aparicio et al, ). This pattern has been already described for some of the Spanish locations studied (Ibáñez et al, ), and we can now extend it to the southern distribution of the species. Our results also suggest far‐reaching consequences for the distribution of the species on the mid‐ to long term, since the low recruitment, aged demographic structure and lower understorey dominance of Q. suber at its southern range are indicative of ongoing range contraction (extinction debt, Jackson & Sax, ), while the northern edge of the species evidence the colonization credit to expand its distribution on the coming decades (Matías & Jump, ), jointly resulting in a potential range displacement of the species.…”

“…This result means that if the projected decrease in precipitation for the Mediterranean region is maintained (Giorgi & Lionello, 2008), it is very likely that recruitment failure would be the main constraint already detected in many other populations across the species' distribution (Avila, et al, 2017;Gómez-Aparicio et al, 2012). This pattern has been already described for some of the Spanish locations studied (Ibáñez et al, 2017), and we can now extend it to the south- (Matías & Jump, 2015), jointly resulting in a potential range displacement of the species.…”

“…In addition, Q. suber forests produce cork, a renewable resource of high economic importance that generates over 30,000 employments related to cork industry (Varela, 2013). However, the persistence of these important forests over the coming decades is uncertain due to the increasing adult mortality rates, overgrazing pressures and lack of regeneration detected in many Q. suber populations (Camilo-Alves, Clara, & Ribeiro, 2013;Ibáñez, Gómez-Aparicio, Ávila, Pérez-Ramos, & Marañón, 2017). Multiple global change drivers have been proposed to cause Q. suber decline, such as increasing drought (Camilo-Alves, Vaz, Clara, & Ribeiro, 2017) and the root-rot disease caused by the exotic soil-borne pathogen Phytophthora cinnamomi Rands.…”

Forest recovery following extreme drought in California,USA: natural patterns and effects of pre‐drought management

“…, Ibáñez et al. ). These changes may be exacerbated by the fact that mortality can modify wildfire behavior via changes in fuel loading (Harvey et al.…”

Pathogen-induced tree mortality interacts with predicted climate change to alter soil respiration and nutrient availability in Mediterranean systems

“…context-dependent (Ávila et al 2016;Cherubini et al 2002;Shearer et al 2009). Moreover, gaps opened after tree death will be very likely occupied by coexistent drought-tolerant shrubs not affected by the pathogen (Ibáñez et al 2017), which might lead the system to a condition of arrested succession for at least several decades (Acácio et al 2007). The substitution of trees by shrubs might indirectly cause a substantial alteration of soil functioning as a consequence of the contrasting footprint of these two life forms on soils, with shrubs showing lower litter production and litter quality than trees (Rolo et al 2012).…”