Abstract
Increasing temperature and drought intensity is inducing the phenomenon of the so-called “hotter drought”, which is expected to increase in frequency over the coming decades across many areas of the globe, and is expected to have major implications for forest systems. Consequences of hotter drought could be especially relevant for closely related species overlapping their distributions, since differences in response can translate into range shifts. We assessed the effect of future climatic conditions on the performance of five ecologically distinct pine species common in Europe: Pinus halepensis, P. pinaster, P. nigra, P. sylvestris and P. uncinata. We hypothesised that Mediterranean species inhabiting dry, low-elevation sites will be less affected by the expected warming and drought increase than species inhabiting cold-wet sites. We performed a controlled conditions experiment simulating current and projected temperature and precipitation, and analysed seedling responses in terms of survival, growth, biomass allocation, maximum photochemical efficiency (Fv/Fm) and plant water potential (Ψ). Either an increase in temperature or a reduction in water input alone reduced seedling performance, but the highest impact occurred when these two factors acted in combination. Warming and water limitation reduced Ψ, whereas warming alone reduced biomass allocation to roots and Fv/Fm. However, species responded differentially to warmer and drier conditions, with lowland Mediterranean pines (P. halepensis and P. pinaster) showing higher survival and performance than mountain species. Interspecific differences in response to warmer, drier conditions could contribute to changes in the relative dominance of these pine species in Mediterranean regions where they co-occur and a hotter, drier climate is anticipated.
Highlights
Air temperature has increased during the last decades at a planetary scale, and it is expected to continue rising to at least the end of the present century, with the potential to increase atmospheric water vapour pressure deficit and, water stress for plants (IPCC 2013)
Besides receiving the same amount of water, soil moisture differed among species (F = 13.2, P \ 0.001), decreasing from P. nigra to P. uncinata (10.5 ± 0.4%), P. sylvestris (9.4 ± 0.3%), P. halepensis (8.8 ± 0.3%) and P. pinaster (7.3 ± 0.3%)
Under current climate (CT ? CP scenario), survival was 100% for all species, but the combination of FT and FP scenarios reduced it for almost all species: P. uncinata survival reduced to 81.8%, P. nigra to 90.9%, P. sylvestris and P. pinaster to 95.5%, and P. halepensis was not affected
Summary
Air temperature has increased during the last decades at a planetary scale, and it is expected to continue rising to at least the end of the present century, with the potential to increase atmospheric water vapour pressure deficit and, water stress for plants (IPCC 2013). Mediterranean-type ecosystems are among the areas where hotter droughts will increase thorough the current century (Giorgi and Lionello 2008) This phenomenon can potentially alter forest structure and functioning (Coomes et al 2014) due to episodes of tree mortality (Allen et al 2010; Plaut et al 2013), lack of regeneration (Castro et al 2004; Mendoza et al 2009a; Matıas et al 2012a), reduction in biodiversity (Matıas et al 2011a; Mendoza et al 2009b) or changes in species distribution (Jump and Penuelas 2005; Matıas and Jump 2015). Forecasting the impact of the combined effect of warmer and drier conditions on different tree species is of paramount importance to predict forest dynamics and its consequences on the ecosystem services they provide (Ibanez et al 2007; Morin and Thuiller 2009)
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