AUTHOR=Gazol Antonio , Oliva Jonàs , Valeriano Cristina , Colangelo Michele , Camarero Jesús Julio 

TITLE=Mixed Pine Forests in a Hotter and Drier World: The Great Resilience to Drought of Aleppo Pine Benefits It Over Other Coexisting Pine Species

JOURNAL=Frontiers in Forests and Global Change

VOLUME=5

YEAR=2022

URL=https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2022.899425

DOI=10.3389/ffgc.2022.899425

ISSN=2624-893X

ABSTRACT=<p>Drought is an important driver of forest dynamics in the Mediterranean region. The forecasted increase in drought frequency and severity can notably influence tree growth, forest structure, composition and productivity. Understanding how coexisting tree species respond to drought is thus crucial to understand which are less vulnerable and will perform better in a warmer and drier world. To assess drought vulnerability, we used dendrochronology to study the radial growth trends and responses to a drought index of four pine species (<italic>Pinus halepensis</italic>, <italic>Pinus pinea</italic>, <italic>Pinus nigra</italic>, and <italic>Pinus sylvestris</italic>) coexisting in North-eastern Spain. We reconstructed the growth of each species and evaluated their short- and long-term growth response to drought for the common period 1980–2017. The growth of the four pine species depended on water availability and high early spring temperatures impacted the growth of <italic>P. nigra</italic> and <italic>P. sylvestris</italic> negatively. The occurrence of a severe drought between 2005 and 2007 lead to marked growth reductions in the four species, but it was greater in magnitude in <italic>P. pinea</italic> and <italic>P. halepensis</italic> in 2005, and in <italic>P. nigra</italic> in 2007. The results of basal area increment models at the individual tree level suggested that <italic>P. halepensis</italic> trees grow more than the rest of species. After accounting for age and drought effects, <italic>P. nigra</italic> and <italic>P. sylvestris</italic> displayed negative growth trends in the 2008–2017 period while <italic>P. pinea</italic> and <italic>P. halepensis</italic> displayed positive growth trends. <italic>P. sylvestris</italic> was the most resistant species and <italic>P. pinea</italic> the less resistant. Conversely, <italic>P. halepensis</italic> and <italic>P. pinea</italic> were slightly more resilient than <italic>P. sylvestris</italic>. Moreover, <italic>P. sylvestris</italic> was the species displaying the highest autocorrelation and the lowest coefficient of variation in ring-width indices. A marked drop in the autocorrelation of <italic>P. pinea</italic> ring-width index was observed in response to the 2005 drought. These results indicate that all study species are vulnerable to drought but in different degrees. The strong resilience capacity of <italic>P. halepensis</italic> suggests that it will better thrive in a drier future, but mixed pine forests, such as the one here studied, may contract or become rare due to the strong sensitivity of <italic>P. pinea</italic> to drought and the lower post-drought performance of <italic>P. nigra</italic> and <italic>P. sylvestris</italic>.</p>