DOI: 10.5061/dryad.wstqjq2t3
title: Evidence for antagonistic effects of climate change and exotic pathogens on regeneration of Mediterranean forests

description: Understanding the interactive effects of global change drivers on tree
 demography is fundamental for realistic predictions of future forest
 dynamics. Multiple studies have shown increasing drought and exotic
 pathogens to severely threaten forest persistence by increasing mortality
 and decreasing growth of adult trees. However, much less is known about
 their effects on regeneration, and how they might affect seedling
 performance in additive and non-additive (synergistic or antagonistic)
 ways. Here we aimed to fill this gap by experimentally exploring the
 effects of increasing drought and soil-borne pathogens on tree
 regeneration in two types of mixed oak forests (Quercus suber-Q.
 canariensis and Q. suber-Olea europaea) invaded by the exotic soil-borne
 oomycete Phytophthora cinnamomi, one of the most aggressive plant
 pathogens on earth. We conducted a seed-sowing experiment with
 oomycete-specific fungicide taking advantage of rainfall exclusion
 infrastructures that excluded 30% of the annual rainfall, simulating
 predictions of climate change models for Mediterranean systems. Seedling
 emergence, survival and growth of the three tree species were followed
 over 3 years. We found that neutral or positive drought effects on
 regeneration dominated over negative effects in the tree community.
 Moreover, most positive drought effects on the dominant species (Q. suber)
 were not direct, but rather indirectly mediated by soil-borne pathogens.
 This was shown by the fact that positive drought effects disappeared with
 fungicide application.  Synthesis: Overall, our results suggest
 that rainfall reductions predicted by climate change models for the
 Mediterranean region might have minor direct negative effects on early
 regeneration of tree species, but that could play a major indirect role by
 limiting the negative effects of exotic pathogens on highly susceptible
 tree species. These findings highlight that antagonisms among global
 change drivers should be recognized as important forces that might slow
 down the current loss of tree health.
description: We conducted a sowing
 experiment using seeds of the two dominant species at each forest type:
 <em>Q. suber </em>and<em> Q. canariensis</em> in
 the closed forest, and <em>Q. suber </em>and<em> O.
 europaea</em> in the open woodland. In December 2016, two 25 × 25 cm sowing quadrats
 (“Control” and “Fungicide”) were established under each of the 86 study
 trees. At each quadrat we established 16 sowing points. In the closed
 forest, one acorn of <em>Q. canariensis </em>or<em> Q.
 suber w</em>as sown per point, making a total of 688 seeds per
 species (8 seeds × 2 treatments × 43 trees). In the open woodland, one
 acorn of<em> Q. suber </em>was also sown per point (n = 688
 acorns). However, we sowed a higher
 number of <em>O. europaea</em> seeds (17 seeds per point,
 11696 seeds in total) to compensate for the low germination rate of the
 species. Seeds in the fungicide quadrats were treated monthly
 with an oomycete-specific fungicide (Armetil 25 WP, 25% metalaxyl),
 whereas Control seedlings were treated with an identical volume of water.
 Seedling emergence,
 survival, and growth were followed monthly for 34 months. At each census,
 the state of each seed (emerged/not emerged) or seedling (alive/dead) was
 registered. In October 2019, all the living seedlings were harvested. Once
 in the lab, seedlings were divided into stem, leaves and roots.
 All plant material was
 dried at 70 ºC for a minimum of 48 h to estimate shoot and root
 biomass.
description: # Evidence for antagonistic effects of climate change and exotic pathogens
 on regeneration of Mediterranean forests
 [https://doi.org/10.5061/dryad.wstqjq2t3](https://doi.org/10.5061/dryad.wstqjq2t3) This dataset contains data of emergence, survival and growth of seeds of *Quercus sub*er, *Quercus canariensi*s and *Olea europaea* in experimental rainfall exclusions located in Mediterranean forests of Southern Spain. ## Description of the data and file structure The Excel file includes information about: * **site**: factorial variable with two levels (Gamir or Marrufo) * **block**: factorial variable with three levels to take into account the spatial nested design of the experiment (1, 2 or 3) * **n\_tree**: factorial variable representing each of the target trees (43 per site) * **quadrat**: factorial variable representing each of the sowing quadrats in the experiment (86 per site, 43 with fungicide and 43 without fungicide). * **seed\_weight**: weight (in grams) of *Quercus suber* and *Quercus canariensis* acorns used in the experiment. Weights are not available for Olea europaea seeds. * **fungicide**: factorial variable with two levels (fungicide and control). * **rainfall**: factorial variable with two levels (rainfall exclusion and control). * **tree\_sp**: factorial variable describing the species of the canopy tree under which seeds were sown (*Quercus suber*, *Quercus canariensis* or *Olea europaea*) * **seed\_sp**: factorial variable describing the species of the seeds sown (*Quercus suber*, *Quercus canariensis* or *Olea europaea*) * **emergence\_date**: number of days from the beginning of the experiment to the emergence of the seedling. Seedlings without this value (i.e. NAs) are seedlings that did not emerge. * **survival\_1**: binomial variable describing the state of each emerged seedling (0, dead; 1, alive) after the first summer of the experiment (after 10 months). Seedlings without this value (i.e. NAs) are mostly seedlings that did not emerge. An exception are seedlings of *Olea europaea* that emerged during the second year of the experiment. In this case, there is no data available for survival\_1, but there is data for survival\_2 and survival\_3. * **survival\_2**: binomial variable describing the state of each emerged seedling (0, dead; 1, alive) after the second summer of the experiment (after 22 months). Seedlings without this value (i.e. NAs) are seedlings that did not emerge. * **survival\_3**: binomial variable describing the state of each emerged seedling (0, dead; 1, alive) at the end of the study (after 34 months). Seedlings without this value (i.e. NAs) are seedlings that did not emerge. * **shoot biomass**: dry biomass (in grams) of the aerial parts (stem and leaves) of seedlings alive at the end of the experiment. Seedlings without this value (i.e. NAs) are seedlings that did not emerge or died along the experiment. In the case of *Quercus* species, each value represent the biomass of a single alive seedling. For *O. europaea*, each value represents the biomass of all alive seedlings per quadrat. * **root biomass**: dry biomass (in grams) of the fine roots attached to the tap root of each seedling alive at the end of the experiment. Seedlings without this value (i.e. NAs) are seedlings that did not emerge or died along the experiment. In the case of *Quercus species*, each value represent the biomass of a single alive seedling. For *O. europaea*, each value represents the biomass of all alive seedlings per quadrat.