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Understanding the interactive effects of global change drivers on tree demog-raphy 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.2. Here we aimed to fill this gap by experimentally exploring the effects of increas-ing 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 aggres-sive 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 during 3 years.3. We found that neutral or positive drought effects on regeneration dominated over negative effects in the tree community. Moreover, most positive drought ef-fects on the dominant species (Q. suber) were not direct, but indirectly mediated by soil-borne pathogens. This was shown by the fact that positive drought effects disappeared with fungicide application.4. 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 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

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 during 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 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 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 s

Climate change and exotic pests and pathogens are causing alarming forest declines worldwide. However, we still lack a comprehensive understanding of how damage caused by exotic pests and pathogens might vary under the different scenarios of water availability imposed by a changing climate, particularly in water-limited forests as those that occupy Mediterranean areas. In this paper we aimed to experimentally analyse the interactive effects of the aggressive exotic pathogen Phytophthora cinnamomi and climate change-related reductions in soil moisture on seedling performance of the Mediterranean host Quercus suber. We conducted a full-factorial greenhouse experiment where the physiology and growth of Q. suber seedlings was measured in soils with different combinations of P. cinnamomi inoculum density (0, 30, 60 and 120 colony forming units per gram of dry soil) and soil moisture (15%, 40%, 50% and 100% soil water holding capacity) simulating different invasion and climate change scenarios. We found additive effects of P. cinnamomi and drought on Q. suber performance aboveground, although these effects were not always negative. In fact, seedlings showed a compensatory physiological response to P. cinnamomi infection by increasing their net photosynthetic rates. Our results also supported important interactive effects of pathogens and soil moisture on belowground performance. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased. From a climate change perspective, these results suggest that an average drier climate might imply sub-optimal conditions for P. cinnamomi infections allowing for a slower advance of the disease in invaded areas. However, this effect will be modulated by the also predicted more frequent extreme climatic events. A higher frequency of extreme rain events that saturate the soil might be particularly beneficial for P. cinnamomi, boosting its soil density beyo

Water availability affects tree species performance and distributions in tropical forests. However, there are no studies that have measured detailed spatial variation in soil water availability within a tropical forest. This limits our understanding of how water availability shapes the demography and distributions of tree species within tropical forests. In this dissertation, I measured detailed spatial variation in soil water potential (SWP), the relevant measure of water availability for plant performance, in the seasonal tropical moist forest of the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama. In Paper 1, I mapped spatial variation in SWP across the 50-ha plot in various stages of the dry season using information on topography, soil type, dry season intensity and more. In Paper 2, I quantified the soil moisture niches of species in terms of demographic responses (growth and mortality) and species distributions. I related seedling growth and mortality responses to SWP of 62 species to their distributional centre along the SWP gradient, using data from 20 years of annual seedling censuses across 200 seedling census sites. I found that species that grew faster (slow) with increasing SWP were more common on wetter (drier) parts of the SWP gradient. Moreover, wet-distributed species grew faster on the wet side of the SWP gradient than dry-distributed species. Mortality was unrelated to species distributions but decreased strongly with seedling height. These findings indicate that species with a growth advantage with respect to SWP grow faster out of the vulnerable small size ranges, reducing their mortality in later seedling stages and thus shaping species distributions indirectly. This mechanism is a form of niche differentiation that contributes to species coexistence. In Paper 3, I related seedling growth and mortality responses to spatiotemporal variation in water availability with responses to light availability, another highly limiting resource i

Water availability affects tree species performance and distributions in tropical forests. However, there are no studies that have measured detailed spatial variation in soil water availability within a tropical forest. This limits our understanding of how water availability shapes the demography and distributions of tree species within tropical forests. In this dissertation, I measured detailed spatial variation in soil water potential (SWP), the relevant measure of water availability for plant performance, in the seasonal tropical moist forest of the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama. In Paper 1, I mapped spatial variation in SWP across the 50-ha plot in various stages of the dry season using information on topography, soil type, dry season intensity and more. In Paper 2, I quantified the soil moisture niches of species in terms of demographic responses (growth and mortality) and species distributions. I related seedling growth and mortality responses to SWP of 62 species to their distributional centre along the SWP gradient, using data from 20 years of annual seedling censuses across 200 seedling census sites. I found that species that grew faster (slow) with increasing SWP were more common on wetter (drier) parts of the SWP gradient. Moreover, wet-distributed species grew faster on the wet side of the SWP gradient than dry-distributed species. Mortality was unrelated to species distributions but decreased strongly with seedling height. These findings indicate that species with a growth advantage with respect to SWP grow faster out of the vulnerable small size ranges, reducing their mortality in later seedling stages and thus shaping species distributions indirectly. This mechanism is a form of niche differentiation that contributes to species coexistence. In Paper 3, I related seedling growth and mortality responses to spatiotemporal variation in water availability with responses to light availability, another highly limiting resource i

Climate change and exotic pests and pathogens are causing alarming forest declines worldwide. However, we still lack a comprehensive understanding of how damage caused by exotic pests and pathogens might vary under the different scenarios of water availability imposed by a changing climate, particularly in water-limited forests as those that occupy Mediterranean areas. In this paper we aimed to experimentally analyse the interactive effects of the aggressive exotic pathogen Phytophthora cinnamomi and climate change-related reductions in soil moisture on seedling performance of the Mediterranean host Quercus suber. We conducted a full-factorial greenhouse experiment where the physiology and growth of Q. suber seedlings was measured in soils with different combinations of P. cinnamomi inoculum density (0, 30, 60 and 120 colony forming units per gram of dry soil) and soil moisture (15%, 40%, 50% and 100% soil water holding capacity) simulating different invasion and climate change scenarios. We found additive effects of P. cinnamomi and drought on Q. suber performance aboveground, although these effects were not always negative. In fact, seedlings showed a compensatory physiological response to P. cinnamomi infection by increasing their net photosynthetic rates. Our results also supported important interactive effects of pathogens and soil moisture on belowground performance. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased. From a climate change perspective, these results suggest that an average drier climate might imply sub-optimal conditions for P. cinnamomi infections allowing for a slower advance of the disease in invaded areas. However, this effect will be modulated by the also predicted more frequent extreme climatic events. A higher frequency of extreme rain events that saturate the soil might be particularly beneficial for P. cinnamomi, boosting its soil density beyo

Water availability affects tree species performance and distributions in tropical forests. However, there are no studies that have measured detailed spatial variation in soil water availability within a tropical forest. This limits our understanding of how water availability shapes the demography and distributions of tree species within tropical forests. In this dissertation, I measured detailed spatial variation in soil water potential (SWP), the relevant measure of water availability for plant performance, in the seasonal tropical moist forest of the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama. In Paper 1, I mapped spatial variation in SWP across the 50-ha plot in various stages of the dry season using information on topography, soil type, dry season intensity and more. In Paper 2, I quantified the soil moisture niches of species in terms of demographic responses (growth and mortality) and species distributions. I related seedling growth and mortality responses to SWP of 62 species to their distributional centre along the SWP gradient, using data from 20 years of annual seedling censuses across 200 seedling census sites. I found that species that grew faster (slow) with increasing SWP were more common on wetter (drier) parts of the SWP gradient. Moreover, wet-distributed species grew faster on the wet side of the SWP gradient than dry-distributed species. Mortality was unrelated to species distributions but decreased strongly with seedling height. These findings indicate that species with a growth advantage with respect to SWP grow faster out of the vulnerable small size ranges, reducing their mortality in later seedling stages and thus shaping species distributions indirectly. This mechanism is a form of niche differentiation that contributes to species coexistence. In Paper 3, I related seedling growth and mortality responses to spatiotemporal variation in water availability with responses to light availability, another highly limiting resource i

Climate change and exotic pests and pathogens are causing alarming forest declines worldwide. However, we still lack a comprehensive understanding of how damage caused by exotic pests and pathogens might vary under the different scenarios of water availability imposed by a changing climate, particularly in water-limited forests as those that occupy Mediterranean areas. In this paper we aimed to experimentally analyse the interactive effects of the aggressive exotic pathogen Phytophthora cinnamomi and climate change-related reductions in soil moisture on seedling performance of the Mediterranean host Quercus suber. We conducted a full-factorial greenhouse experiment where the physiology and growth of Q. suber seedlings was measured in soils with different combinations of P. cinnamomi inoculum density (0, 30, 60 and 120 colony forming units per gram of dry soil) and soil moisture (15%, 40%, 50% and 100% soil water holding capacity) simulating different invasion and climate change scenarios. We found additive effects of P. cinnamomi and drought on Q. suber performance aboveground, although these effects were not always negative. In fact, seedlings showed a compensatory physiological response to P. cinnamomi infection by increasing their net photosynthetic rates. Our results also supported important interactive effects of pathogens and soil moisture on belowground performance. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased. From a climate change perspective, these results suggest that an average drier climate might imply sub-optimal conditions for P. cinnamomi infections allowing for a slower advance of the disease in invaded areas. However, this effect will be modulated by the also predicted more frequent extreme climatic events. A higher frequency of extreme rain events that saturate the soil might be particularly beneficial for P. cinnamomi, boosting its soil density beyo

Climate change and exotic pests and pathogens are causing alarming forest declines worldwide. However, we still lack a comprehensive understanding of how damage caused by exotic pests and pathogens might vary under the different scenarios of water availability imposed by a changing climate, particularly in water-limited forests as those that occupy Mediterranean areas. In this paper we aimed to experimentally analyse the interactive effects of the aggressive exotic pathogen Phytophthora cinnamomi and climate change-related reductions in soil moisture on seedling performance of the Mediterranean host Quercus suber. We conducted a full-factorial greenhouse experiment where the physiology and growth of Q. suber seedlings was measured in soils with different combinations of P. cinnamomi inoculum density (0, 30, 60 and 120 colony forming units per gram of dry soil) and soil moisture (15%, 40%, 50% and 100% soil water holding capacity) simulating different invasion and climate change scenarios. We found additive effects of P. cinnamomi and drought on Q. suber performance aboveground, although these effects were not always negative. In fact, seedlings showed a compensatory physiological response to P. cinnamomi infection by increasing their net photosynthetic rates. Our results also supported important interactive effects of pathogens and soil moisture on belowground performance. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased. From a climate change perspective, these results suggest that an average drier climate might imply sub-optimal conditions for P. cinnamomi infections allowing for a slower advance of the disease in invaded areas. However, this effect will be modulated by the also predicted more frequent extreme climatic events. A higher frequency of extreme rain events that saturate the soil might be particularly beneficial for P. cinnamomi, boosting its soil density beyo

Water availability affects tree species performance and distributions in tropical forests. However, there are no studies that have measured detailed spatial variation in soil water availability within a tropical forest. This limits our understanding of how water availability shapes the demography and distributions of tree species within tropical forests. In this dissertation, I measured detailed spatial variation in soil water potential (SWP), the relevant measure of water availability for plant performance, in the seasonal tropical moist forest of the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama. In Paper 1, I mapped spatial variation in SWP across the 50-ha plot in various stages of the dry season using information on topography, soil type, dry season intensity and more. In Paper 2, I quantified the soil moisture niches of species in terms of demographic responses (growth and mortality) and species distributions. I related seedling growth and mortality responses to SWP of 62 species to their distributional centre along the SWP gradient, using data from 20 years of annual seedling censuses across 200 seedling census sites. I found that species that grew faster (slow) with increasing SWP were more common on wetter (drier) parts of the SWP gradient. Moreover, wet-distributed species grew faster on the wet side of the SWP gradient than dry-distributed species. Mortality was unrelated to species distributions but decreased strongly with seedling height. These findings indicate that species with a growth advantage with respect to SWP grow faster out of the vulnerable small size ranges, reducing their mortality in later seedling stages and thus shaping species distributions indirectly. This mechanism is a form of niche differentiation that contributes to species coexistence. In Paper 3, I related seedling growth and mortality responses to spatiotemporal variation in water availability with responses to light availability, another highly limiting resource i

Climate change and exotic pests and pathogens are causing alarming forest declines worldwide. However, we still lack a comprehensive understanding of how damage caused by exotic pests and pathogens might vary under the different scenarios of water availability imposed by a changing climate, particularly in water-limited forests as those that occupy Mediterranean areas. In this paper we aimed to experimentally analyse the interactive effects of the aggressive exotic pathogen Phytophthora cinnamomi and climate change-related reductions in soil moisture on seedling performance of the Mediterranean host Quercus suber. We conducted a full-factorial greenhouse experiment where the physiology and growth of Q. suber seedlings was measured in soils with different combinations of P. cinnamomi inoculum density (0, 30, 60 and 120 colony forming units per gram of dry soil) and soil moisture (15%, 40%, 50% and 100% soil water holding capacity) simulating different invasion and climate change scenarios. We found additive effects of P. cinnamomi and drought on Q. suber performance aboveground, although these effects were not always negative. In fact, seedlings showed a compensatory physiological response to P. cinnamomi infection by increasing their net photosynthetic rates. Our results also supported important interactive effects of pathogens and soil moisture on belowground performance. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased. From a climate change perspective, these results suggest that an average drier climate might imply sub-optimal conditions for P. cinnamomi infections allowing for a slower advance of the disease in invaded areas. However, this effect will be modulated by the also predicted more frequent extreme climatic events. A higher frequency of extreme rain events that saturate the soil might be particularly beneficial for P. cinnamomi, boosting its soil density beyo

Aim of study: To assess the effectiveness for improving early seedling performance of the individual and combined application of (i) various doses of an innovative soil conditioner including polyacrylamide-free super-absorbent polymers, fertilizers, root precursors and humic acids; and (ii) innovative mulches based on renewable-biodegradable or recycled raw materials. The assessment was carried out in comparison with reference (commercial) soil conditioners and mulches.Area of study: Upper montane afforestation site located at 1,430 m altitude in the southern Pyrenees (NE Spain).Material and methods: We studied the effect of 15 treatments (various combinations of soil conditioners and mulches) on mountain ash (Fraxinus excelsior L.), testing survival, diameter and height growth and water and nutrient status during two growing seasons (2014-2015). We also assessed mulch durability during 2014-2016.Main results: The innovative soil conditioner improved diameter and height seedling growth (92% and 72% respectively) and water and nutrient status. The 40 g/seedling dosage was more cost-effective than the 20 and 80 g/seedling doses. The new formulation performed better in general than the commercial formulation. Mulches led to slight gains compared to control seedlings, and there were no major differences between the mulch models. The combined application of soil conditioners and mulches was not of particular interest.Research highlights: Soil conditioners consisting of synergic mixtures of water super-absorbent polymers, fertilizers, root growth precursors and humic acids can improve early seedling performance in coarse-textured, stony soils in montane conditions. Small mulches may be only of limited interest as long as weed competitiveness is poor.Keywords: ecotechnology; groundcovers; reforestation; seedling performance; restoration; water super-absorbent polymer; weed.Abbreviations used: GSn, growing season number ‘n’; leaf water potential, LWP; water super-absorbent

Aim of study: To assess the effectiveness for improving early seedling performance of the individual and combined application of (i) various doses of an innovative soil conditioner including polyacrylamide-free super-absorbent polymers, fertilizers, root precursors and humic acids; and (ii) innovative mulches based on renewable-biodegradable or recycled raw materials. The assessment was carried out in comparison with reference (commercial) soil conditioners and mulches.Area of study: Upper montane afforestation site located at 1,430 m altitude in the southern Pyrenees (NE Spain).Material and methods: We studied the effect of 15 treatments (various combinations of soil conditioners and mulches) on mountain ash (Fraxinus excelsior L.), testing survival, diameter and height growth and water and nutrient status during two growing seasons (2014-2015). We also assessed mulch durability during 2014-2016.Main results: The innovative soil conditioner improved diameter and height seedling growth (92% and 72% respectively) and water and nutrient status. The 40 g/seedling dosage was more cost-effective than the 20 and 80 g/seedling doses. The new formulation performed better in general than the commercial formulation. Mulches led to slight gains compared to control seedlings, and there were no major differences between the mulch models. The combined application of soil conditioners and mulches was not of particular interest.Research highlights: Soil conditioners consisting of synergic mixtures of water super-absorbent polymers, fertilizers, root growth precursors and humic acids can improve early seedling performance in coarse-textured, stony soils in montane conditions. Small mulches may be only of limited interest as long as weed competitiveness is poor.Keywords: ecotechnology; groundcovers; reforestation; seedling performance; restoration; water super-absorbent polymer; weed.Abbreviations used: GSn, growing season number ‘n’; leaf water potential, LWP; water super-absorbent

Although maternal environmental effects are increasingly recognized as an important source of phenotypic variation with relevant impacts in evolutionary processes, their relevance in long-lived plants such as pine trees is largely unknown. Here, we used a powerful sample size and a strong quantitative genetic approach to analyse the sources of variation of early seedling performance and to identify seed mass (SM)-dependent and -independent maternal environmental effects in Maritime pine. We measured SM of 8924 individual seeds collected from 10 genotypes clonally replicated in two environments of contrasting quality (favourable and stressful), and we measured seedling growth rate and biomass allocation to roots and shoots. SM was extremely variable (up to 14-fold) and strongly determined by the maternal environment and the genotype of the mother tree. The favourable maternal environment led to larger cones, larger seeds and reduced SM variability. The maternal environment also determined the offspring phenotype, with seedlings coming from the favourable environment being 35% larger and with greater root/shoot ratio. Transgenerational plasticity appears, thus, to be a relevant source of phenotypic variation in the early performance of this pine species. Seed provisioning explained most of the effect of the maternal environment on seedling total biomass. Environmental maternal effects on seedling biomass allocation were, however, determined through SM-independent mechanisms, suggesting that other epigenetic regulation channels may be involved. © 2013 Macmillan Publishers Limited All rights reserved.

Allelopathic interactions between invasive and native species have been suggested to be an important mechanism for the success of some of the most aggressive plant invaders. However, field experiments that test the effects of natural levels of allelopathic compounds on coexisting native species are exceptionally rare.2In this study, we analyzed the allelopathic effects of the invasive tree Ailanthus altissima on seedling emergence, survival and growth of three native tree species (Acer rubrum, A. saccharum and Quercus rubra) in temperate forests of the northeastern United States. We used activated carbon (AC) to reduce potential allelopathic interference, and developed neighbourhood models that explain the observed spatial variation in the effects of the AC treatments on seedling performance as a function of the size, abundance and distribution of Ailanthus trees in the neighbourhood.3Our results showed that the addition of AC to the soil did not affect seedling emergence or survival, but caused a significant increase in seedling growth of all three species. Moreover, the AC shifted the overall interaction between Ailanthus and maple seedlings from neutral or slightly positive to very positive for A. rubrum, and from negative to positive for A. saccharum, whereas the net interaction between Ailanthus and Q. rubra was always negative. As Ailanthus has the ability to increase soil fertility, these species-specific responses are presumably influenced by among-species differences in the net effects of both allelopathy and changes in resource availability caused by the presence of Ailanthus.4The cumulative allelopathic effects of Ailanthus were proportional to the density of Ailanthus in the neighbourhood, regardless of their size. In contrast, Ailanthus effects were strongly influenced by distance from a tree, generally dropping to zero within 5 m from the trunk.5Synthesis. Taken together, our results indicate that allelopathy is an important mechanism to take into acco

Tobacco seed performance is traditionally measured as percentage germination at 14 d under controlled laboratory conditions. However, under greenhouse conditions, seed lots with equal 14-d germination may exhibit substantial differences in uniformity of early seedling growth and spiral root incidence that impact the number of usable transplants. A seedling performance index (SPI) was developed to quantitatively describe greenhouse tobacco seedling performance. The 14-d emergence, relative leaf area uniformity, and seedling leaf area determined by computer image analysis were used to calculate the index. Greenhouse tobacco seed trials demonstrated that seed with the Rickard pellet had higher emergence, but the higher spiral root incidence associated with the Rickard pellet lowered the SPI compared to the Cross Creek pellet. Primed seed lots of flue-cured cultivars (NC 72 and NC 71) had a significantly higher SPI than the nonprimed seed lots at one location but not at a second location. Seed lots sown in Premier Pro-Mix TA commercial medium had a higher spiral root incidence, which resulted in a lower SPI compared to Carolina Choice, Carolina Gold, and Sunshine LP5 commercial media. The index quantitatively determined differences in seedling performance under greenhouse conditions not reflected by standard germination tests. Significant differences in the SPI were observed among seed lots with certified 90% germination. The SPI is a simple method to describe seedling performance because the data used to calculate the SPI is obtained from one seed tray image. In contrast, frequent counting and seedling evaluations are involved with standard germination and vigor tests.