Barba J., Curiel Yuste J., Poyatos R., Janssens I.A., Lloret F. (2016) Strong resilience of soil respiration components to drought-induced die-off resulting in forest secondary succession. Oecologia. 182: 27-41.LinkDoi: 10.1007/s00442-016-3567-8
How forests cope with drought-induced perturbations and how the dependence of soil respiration on environmental and biological drivers is affected in a warming and drying context are becoming key questions. The aims of this study were to determine whether drought-induced die-off and forest succession were reflected in soil respiration and its components and to determine the influence of climate on the soil respiration components. We used the mesh exclusion method to study seasonal variations in soil respiration (RS) and its components: heterotrophic (RH) and autotrophic (RA) [further split into fine root (RR) and mycorrhizal respiration (RM)] in a mixed Mediterranean forest where Scots pine (Pinus sylvestris L.) is undergoing a drought-induced die-off and is being replaced by holm oak (Quercus ilex L.). Drought-induced pine die-off was not reflected in RS nor in its components, which denotes a high functional resilience of the plant and soil system to pine die-off. However, the succession from Scots pine to holm oak resulted in a reduction of RH and thus in an important decrease of total respiration (RS was 36 % lower in holm oaks than in non-defoliated pines). Furthermore, RS and all its components were strongly regulated by soil water content-and-temperature interaction. Since Scots pine die-off and Quercus species colonization seems to be widely occurring at the driest limit of the Scots pine distribution, the functional resilience of the soil system over die-off and the decrease of RS from Scots pine to holm oak could have direct consequences for the C balance of these ecosystems. © 2016, Springer-Verlag Berlin Heidelberg.
Barba J., Lloret F., Yuste J.C. (2016) Effects of drought-induced forest die-off on litter decomposition. Plant and Soil. 402: 91-101.LinkDoi: 10.1007/s11104-015-2762-4
Aims: Drought-induced forest die-off and subsequent species replacement may modify environmental conditions and eventually affect litter decomposition. We aimed to disentangle the effects of tree species and die-off state on litter decomposition in a mixed forest where Pinus sylvestris populations experiencing severe drought-induced die-off are being replaced by Quercus ilex. Methods: Litter bags with leaves and fine roots from both species were placed under canopies representing three habitats of the die-off and replacement process (healthy and dead P. sylvestris and healthy Q. ilex). Mass was assessed over 3 years. Results: Species-specific chemistry of litter (C:N ratio) had a direct effect on mass loss, but also indirect effects, attributed to the decomposer microbial community associated with a given habitat-species. In their respective original habitats, oak leaves decomposed 44 % faster than pine needles, whereas oak roots decomposed 46 % slower than pine roots. Conclusions: Forest die-off and species replacement affected litter decomposition. This effect can have great implications in forest functioning, particularly if drought-induced die-off worsens in the next decades, according with the trend observed in the studied system. © 2015, Springer International Publishing Switzerland.
Cailleret, M., Jansen, S., Robert, E.M.R., Desoto, L., Aakala, T., Antos, J.A., Beikircher, B., Bigler, C., Bugmann, H., Caccianiga, M., Čada, V., Camarero, J.J., Cherubini, P., Cochard, H., Coyea, M.R., Čufar, K., Das, A.J., Davi, H., Delzon, S., Dorman, M., Gea-Izquierdo, G., Gillner, S., Haavik, L.J., Hartmann, H., Hereş, A.-M., Hultine, K.R., Janda, P., Kane, J.M., Kharuk, V.I., Kitzberger, T., Klein, T., Kramer, K., Lens, F., Levanic, T., Linares Calderon, J.C., Lloret, F., Lobo-Do-Vale, R., Lombardi, F., López Rodríguez, R., Mäkinen, H., Mayr, S., Mészáros, I., Metsaranta, J.M., Minunno, F., Oberhuber, W., Papadopoulos, A., Peltoniemi, M., Petritan, A.M., Rohner, B., Sangüesa-Barreda, G., Sarris, D., Smith, J.M., Stan, A.B., Sterck, F., Stojanović, D.B., Suarez, M.L., Svoboda, M., Tognetti, R., Torres-Ruiz, J.M., Trotsiuk, V., Villalba, R., Vodde, F., Westwood, A.R., Wyckoff, P.H., Zafirov, N., Martínez-Vilalta, J. (2016) A synthesis of radial growth patterns preceding tree mortality. Global Change Biology. : 0-0.LinkDoi: 10.1111/gcb.13535
Lloret F., García C. (2016) Inbreeding and neighbouring vegetation drive drought-induced die-off within juniper populations. Functional Ecology. : 0-0.LinkDoi: 10.1111/1365-2435.12655
Drought-induced episodes of forest die-off are being reported world-wide, and recent evidence shows that increases in temperature due to climate change are contributing to this decline. Several ecological mechanisms have been invoked at the plant level to explain the vulnerability of trees to this widespread drought-induced mortality. Apart from ecological factors, some genetic factors might also influence population responses to disturbances: it has been reported, for example, that genetic diversity enhances population resilience through genotypic complementarity, whereas genetic relatedness between conspecific individuals exerts a negative influence on variations in fecundity. However, we lack empirical data that prove any functional relationship between levels of individual inbreeding or kinship and patterns of drought-induced forest die-off resulting from field conditions. Here, we investigated the role of ecological, phenotypic and genetic factors in determining the response of trees to prolonged drought conditions. We focused on populations of the small tree Juniperus phoenicea L. that recently experienced severe drought-induced die-off in semi-arid woodlands from central Spain. We correlated mean individual inbreeding (f) and mean kinship between individuals within a plot (fij) with remaining green plant canopy and crop size. We found that f was negatively correlated with plant performance, whereas fij was not. Healthier canopy also tended to correspond with large plants and neighbourhoods dominated by trees and shrubs, suggesting a role for facilitative interactions and microsite heterogeneity. Accordingly, the probability of severe damage increased linearly with f, and individuals growing in open habitats with f values > 0·625 only had 15% chance of remaining unaffected after a period of prolonged drought. We show that both vegetative and reproductive responses to prolonged drought episodes are determined by multiple factors, including individual inbreeding. Therefore, any fuller understanding of phenomena such as drought-induced forest die-off needs to incorporate the contribution of individual genetic variations in conjunction with plant-plant interactions. © 2016 British Ecological Society.
Lloret F., de la Riva E.G., Pérez-Ramos I.M., Marañón T., Saura-Mas S., Díaz-Delgado R., Villar R. (2016) Climatic events inducing die-off in Mediterranean shrublands: are species’ responses related to their functional traits?. Oecologia. : 1-13.LinkDoi: 10.1007/s00442-016-3550-4
Extreme climatic episodes, likely associated with climate change, often result in profound alterations of ecosystems and, particularly, in drastic events of vegetation die-off. Species attributes are expected to explain different biological responses to these environmental alterations. Here we explored how changes in plant cover and recruitment in response to an extreme climatic episode of drought and low temperatures were related to a set of functional traits (of leaves, roots and seeds) in Mediterranean shrubland species of south-west Spain. Remaining aerial green cover 2 years after the climatic event was positively related to specific leaf area (SLA), and negatively to leaf water potential, stable carbon isotope ratio and leaf proline content. However, plant cover resilience, i.e. the ability to attain pre-event values, was positively related to a syndrome of traits distinguished by a higher efficiency of water use and uptake. Thus, higher SLA and lower water-use efficiency characterized species that were able to maintain green biomass for a longer period of time but were less resilient in the medium term. There was a negative relationship between such syndromes and the number of emerging seedlings. Species with small seeds produced more seedlings per adult. Overall, recruitment was positively correlated with species die-off. This study demonstrates the relationship between plant traits and strong environmental pulses related to climate change, providing a functional interpretation of the recently reported episodes of climate-induced vegetation die-off. Our findings reveal the importance of selecting meaningful traits to interpret post-event resilience processes, particularly when combined with demographic attributes. © 2016 Springer-Verlag Berlin Heidelberg
Martínez-Vilalta J., Lloret F. (2016) Drought-induced vegetation shifts in terrestrial ecosystems: The key role of regeneration dynamics. Global and Planetary Change. 144: 94-108.LinkDoi: 10.1016/j.gloplacha.2016.07.009
Ongoing climate change is modifying climatic conditions worldwide, with a trend towards drier conditions in most regions. Vegetation will respond to these changes, eventually adjusting to the new climate. It is unclear, however, how close different ecosystems are to climate-related tipping points and, thus, how dramatic these vegetation changes will be in the short- to mid-term, given the existence of strong stabilizing processes. Here, we review the published evidence for recent drought-induced vegetation shifts worldwide, addressing the following questions: (i) what are the necessary conditions for vegetation shifts to occur? (ii) How much evidence of drought-induced vegetation shifts do we have at present and where are they occurring? (iii) What are the main processes that favor/oppose the occurrence of shifts at different ecological scales? (iv) What are the complications in detecting and attributing drought-induced vegetation shifts? (v) What ecological factors can interact with drought to promote shifts or stability? We propose a demographic framework to classify the likely outcome of instances of drought-induced mortality, based upon the survival of adults of potential replacement species and the regeneration of both formerly dominant affected species and potential replacement species. Out of 35 selected case studies only eight were clearly consistent with the occurrence of a vegetation shift (species or biome shift), whereas three corresponded to self-replacements in which the affected, formerly dominant species was able to regenerate after suffering drought-induced mortality. The other 24 cases were classified as uncertain, either due to lack of information or, more commonly, because the initially affected and potential replacement species all showed similar levels of regeneration after the mortality event. Overall, potential vegetation transitions were consistent with more drought-resistant species replacing less resistant ones. However, almost half (44%) of the vegetation trajectories associated to the 35 case studies implied no change in the functional type of vegetation. Of those cases implying a functional type change, the most common one was a transition from tree- to shrub-dominated communities. Overall, evidence for drought-induced vegetation shifts is still limited. In this context, we stress the need for improved, long-term monitoring programs with sufficient temporal resolution. We also highlight the critical importance of regeneration in determining the outcome of drought-induced mortality events, and the crucial role of co-drivers, particularly management. Finally, we illustrate how placing vegetation shifts in a biogeographical and successional context may support progress in our understanding of the underlying processes and the ecosystem-level implications. © 2016 Elsevier B.V.
Martínez-Vilalta, J., Sala, A., Asensio, D., Galiano, L., Hoch, G., Palacio, S., Piper, F.I., Lloret, F. (2016) Dynamics of non-structural carbohydrates in terrestrial plants: A global synthesis. Ecological Monographs. 86: 495-516.LinkDoi: 10.1002/ecm.1231
Matías, L., Gonzalez-Díaz, P., Quero, J.L., Camarero, J.J., Lloret, F., Jump, A.S. (2016) Role of geographical provenance in the response of silver fir seedlings to experimental warming and drought. Tree Physiology. 36: 1236-1246.LinkDoi: 10.1093/treephys/tpw049
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