Interactions between climate and nutrient cycles on forest response to global change: the role of mixed forests

Forest ecosystems are undergoing unprecedented changes in environmental conditions due to global change impacts. Modification of global biogeochemical cycles of carbon and nitrogen, and the subsequent climate change are affecting forest functions at different scales, from physiology and growth of individual trees to cycling of nutrients. This review summarizes the present knowledge regarding the impact of global change on forest functioning not only with respect to climate change, which is the focus of most studies, but also the influence of altered nitrogen cycle and the interactions among them. The carbon dioxide (CO2) fertilization effect on tree growth is expected to be constrained by nutrient imbalances resulting from highNdeposition rates and the counteractive effect of increasing water deficit, which interact in a complex way. At the community level, responses to global change are modified by species interactions that may lead to competition for resources and/or relaxation due to facilitation and resource partitioning processes. Thus, some species mixtures can be more resistant to drought than their respective pure forests, albeit it depends on environmental conditions and species' functional traits. Climate change and nitrogen deposition have additional impacts on litterfall dynamics, and subsequent decomposition and nutrient mineralization processes. Elemental ratios (i.e., stoichiometry) are associated with important ecosystem traits, including trees' adaptability to stress or decomposition rates. As stoichiometry of different ecosystem components are also influenced by global change, nutrient cycling in forests will be altered too. Therefore, a re-assessment of traditional forest management is needed in order to cope with global change. Proposed silvicultural systems emphasize the key role of diversity to assure multiple ecosystem services, and special attention has been paid to mixed-species forests. Finally, a summary of the patterns and underlying mechanisms governing the relationships between diversity and different ecosystems functions, such as productivity and stability, is provided.E.G.A. was funded by the TIMENUTRIENT project (ref. AGL2016-76463-P) granted by the Spanish Ministry of Economy and Competitiveness

Monitoring rainfed alfalfa growth in semiarid agrosystems using Sentinel-2 imagery

The aim of this study was to assess the utility of Sentinel-2 images in the monitoring of the fractional vegetation cover (FVC) of rainfed alfalfa in semiarid areas such as that of Bardenas Reales in Spain. FVC was sampled in situ using 1 m2 surfaces at 172 points inside 18 alfalfa fields from late spring to early summer in 2017 and 2018. Different vegetation indices derived from a series of Sentinel-2 images were calculated and were then correlated with the FVC measurements at the pixel and parcel levels using different types of equations. The results indicate that the normalized difference vegetation index (NDVI) and FVC were highly correlated at the parcel level (R 2 = 0.712), where as the correlation at the pixel level remained moderate across each of the years studied. Based on the findings, another 29 alfalfa plots (28 rainfed; 1 irrigated) were remotely monitored operationally for 3 years (2017–2019), revealing that location and weather conditions were strong determinants of alfalfa growth in Bardenas Reales. The results of this study indicate that Sentinel-2 imagery is a suitable tool for monitoring rainfed alfalfa pastures in semiarid areas, thus increasing the potential success of pasture management.Andres Echeverria was supported by a predoctoral fellowship from the Government of Navarra. This work was supported by the knowledge transfer contract 2018020023 UPNA-Bardenas Reales Committee with partial collaboration of the project PID2019-107386RB-I00/AEI/10.13039/ 501100011033 (MINECO/FEDER-UE)

Aplicaciones de SIG y teledetección en ecología: Guión de prácticas de la asignatura

Este trabajo surge como resultado del Proyecto de Innovación Docente de la Universidad Autónoma de Madrid – Convocatoria 2013: Adaptación de los recursos informáticos de la asignatura “Aplicaciones de SIG y Teledetección en Ecología” del Máster Oficial en Ecología para la utilización de herramientas de software libre, y elaboración del manual de las prácticas, coordinado por Juan Traba y con la participación de Javier Seoane y Manuel B. Morales; los tres son profesores titulares del Departamento de Ecología de la Universidad Autónoma de Madrid. Ester González de Andrés ha disfrutado de una beca financiada por la la UAM durante la realización de este proyecto. Queremos agradecer expresamente la imprescindible participación de Mª Paula Delgado, Irene Guerrero y Pablo Acebes en la docencia de la asignatura, la preparación y testado de materiales y en la revisión crítica de este documento

Modeling Climate Impacts on Tree Growth to Assess Tree Vulnerability to Drought During Forest Dieback

Forest dieback because of drought is a global phenomenon threatening particular tree populations. Particularly vulnerable stands are usually located in climatically stressing locations such as xeric sites subjected to seasonal drought. These tree populations show a pronounced loss of vitality, growth decline, and high mortality in response to extreme climate events such as heat waves and droughts. However, dieback events do not uniformly affect stands, with some trees showing higher symptoms of drought vulnerability than other neighboring conspecifics. In this study, we investigated if trees showing different vulnerabilities to dieback showed lower growth rates (Grs) and higher sensitivities to the climate in the past using dendroecology and the Vaganov-Shashkin (VS) process-based growth model. We studied two Pinus pinaster stands with contrasting Grs showing recent dieback in the Iberian System, north-eastern Spain. We compared coexisting declining (D) and non-declining (ND) trees with crown defoliation values above and below the 50% threshold, respectively. The mean growth rate was lower in D than in ND trees in the two stands. The two vigor classes showed a growth divergence prior to the dieback onset and different responsiveness to climate. The ND trees were more responsive to changes in spring water balance and soil moisture than D trees, indicating a loss of growth responsiveness to the climate in stressed trees. Such an interaction between water availability and vigor was reflected by the VS-model simulations, which provided evidence for the observation that growth was mainly limited by low soil moisture in both sites. Such an interaction between water availability and vigor was reflected by the VS-model simulations, which provided evidence for the observation that growth was mainly limited by low soil moisture in both sites. The presented comparisons indicated different stand vulnerabilities to drought contingent on-site conditions. Further research should investigate the role played by environmental conditions and individual features such as access to soil water or hydraulic traits and implement them in process-based growth models to better forecast dieback. © Copyright © 2021 Valeriano, Gazol, Colangelo, González de Andrés and Camarero

Chronically low nutrient concentrations in tree rings are linked to greater tree vulnerability to drought in nothofagus dombeyi

Forest dieback and mortality episodes triggered by droughts are receiving increasing atten-tion due to the projected increases in these extreme climate events. However, the role played by nutrient impairment in dieback is understudied, despite interactions among carbon-water balances and nutrition. Here, we followed a comparative analysis of long-term growth, intrinsic water-use efficiency (iWUE), oxygen isotopes (δ18O) and wood-nutrient composition patterns between living (L) and dead (D) trees of a Nothofagus dombeyi population, showing dieback in Argentina. The onset of the growth decline of D trees occurred ca. 40 years before death. These trees showed higher iWUE, pointing to higher drought stress. Their lower δ18O values, together with the uncoupling between δ18O and leaf-level processes, suggested a deeper source of water uptake for this vigor class. D trees showed a poorer nutritional status than L trees that likely amplified the dieback. This was supported by numerous positive associations of P-and K-concentrations in wood and related ratios with iWUE, δ18O and tree growth. Therefore, drought-related nutrient deterioration can significantly contribute to dieback and be an early warning signal of impending tree death.Fil: González de Andrés, Ester. Consejo Superior de Investigaciones Científicas. Instituto Pirenaico de Ecología; EspañaFil: Suarez, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Querejeta, José Ignacio. Consejo Superior de Investigaciones Científicas. Centro de Edafología y Biología Aplicada del Segura; EspañaFil: Camarero, J. Julio. Consejo Superior de Investigaciones Científicas. Instituto Pirenaico de Ecología; Españ

Reproductive phenology determines the linkages between radial growth, fruit production and climate in four Mediterranean tree species

The influence of climate on seed or fruit production and tree growth is a central question in forest ecology, with a key role on forest dynamics. However, the mechanisms linking inter- and intra-annual climate variability, fruiting and growth remain poorly understood, although they seem to be largely species-specific. The resource-matching hypothesis posits that fruit production responds to annual environmental variability, predicting a positive relationship between reproduction and growth, whereas other hypotheses such as resource switching or resource budget imply allocation trade-offs between reproduction and growth. Climate control over fruiting is thought to be more likely in variable, limiting environments such as those existing in seasonally dry Mediterranean forests. However, the studies about these forests are much scarcer than on temperate ecosystems, probably due to the sparseness and shortness of fruit production records. Here we analysed the relationships between monthly climate variables, tree-ring widths and fruit production at stand level in four tree species under different climatic conditions in Spain (12-27 trees and 24-54 radii were sampled in each site). For the species from xeric sites such as Pinus pinea, Castanea sativa and Quercus ilex, tree-ring width positively correlated with fruit production, as envisaged by the resource-matching hypothesis. This association was driven by prior wet winter climate conditions, which enhanced growth. Some of the significant correlations between climate variables and fruit yield corresponded to key reproductive phenophases. On the other hand, for the species from mesic sites (Abies alba) no positive growth–fruit production correlation was found, likely due to the mismatch in the effect of climatic factors on growth and fruiting. These results support the hypothesis that climatic conditions, particularly a positive water balance, play a major role as a proximate cause of fruit production in seasonally dry Mediterranean forests and underscore the importance of species-specific reproductive phenology traitsPublishe