Growth trends and sensitivity to climate of declining Mediterranean open woodlands exhibiting widespread mortality in Southern Spain

We present two chronologies of dead and weakened Quercus ilex trees from declining open woodlands of Southern Andalusia and discuss climate's implication in the current widespread mortality in these ecosystems. Basal area increments were used to find out periods of growth decline preceding death. Absent rings became frequent since the 1970s, coinciding with increasing drought. Negative pointer years matched dry years and became more pronounced in the last decades. Growth was correlated with the annual Palmer Drought Severity Index and precipitations from previous October to May. Mean sensitivity increased recently, ranging between high values (0.35-0.5). Correlations with spring temperatures turned from positive to negative, positive correlations with current autumn precipitation arose whereas significant positive correlations with summer precipitations were no longer observed. These changes could suggest modifications on tree phenology. Intensively-used Mediterranean open woodlands of Southern Andalusia are vulnerable and the current dying process suggests that they are unlikely to overcome increasing stress climatic conditions

Identification of Old-Growth Mediterranean Forests Using Airborne Laser Scanning and Geostatistical Analysis

The protection and conservation of old-growth forests (OGFs) are becoming a global concern due to their irreplaceability and high biodiversity. Nonetheless, there has been little research into the identification and characterization of OGFs of the oldest tree species in Mediterranean areas. We used forest inventory data, low-density airborne laser scanning (ALS) metrics, and geostatistical analysis to estimate old-growth indices (OGIs) as indicators of old-growth forest conditions. We selected a pilot area in European black pine (Pinus nigra subsp. salzmannii) ecosystems where the oldest known living trees in the Iberian Peninsula are found. A total of 756 inventory plots were established to characterize standard live tree and stand attributes. We estimated several structural attributes that discriminate old growth from younger age classes and calculated different types of OGI for each plot. The best OGI was based on mean tree diameter, standard deviation of tree diameter, and stand density of large trees (diameter > 50 cm). This index is useful for assessing old-growthness at different successional stages (young and OGFs) in Mediterranean black pine forests. Our results confirm that the estimation of OGIs based on a combination of forest inventory data, geostatistical analysis, and ALS is useful for identifying OGFsThis work was supported by the following projects: “Iberian Heritage Project”, funded by the Netherlands Organization for Scientific Research (NWO, project number 236-61-001), National Geographic Society-Waitts Grant Program (“Millennia old black pines and Andalusian Cultural Heritage to unravel human-environment interactions in the Western Mediterranean”, W329-14), the Biodiversity Foundation of the Ministry of Agriculture and Fisheries, Food and Environment (“Bosques viejos frente al cambio climático. Vulnerabilidad, capacidad adaptativa e implicaciones frente a la gestión forestal”, PRCV00433) and Ministry of Economy, Industry and Competitiveness (MINECO) (“El final del ciclo envejecimiento, mortalidad y regeneración en pinares mediterráneos, y su papel en la adaptación ante un ambiente en cambio (OLDPINE), AGL2017-83828-C2-2-R). The Ministry of Agriculture and Environment of the Regional Government of Andalusia provided the AF forest inventory data. AH have been supported by PinCaR project (UHU-1266324, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020). We thank the Forest Service at Cazorla, Segura y Las Villas Natural Park, for providing the forest inventory data and for their interest in the project. Debería de ser más completo: We are grateful to Teresa Moro from the Natural Park, and Valentin Badillo from the Cazorla, Segura and Las Villas Natural Park, for their interest and support. The forestry engineering students Raúl García-Raga and Carlos Maeztu (University of Huelva), and Alex Boninsegna (University of Padova) contributed to the fieldwork as part of their final thesis undergraduate studie

Dendroclimatic signal in managed Mediterranean forests : a case study in SW Spain

Spanish Ministry of Economy and Competitiveness, the European Union (FEDER funds), Spanish National Agriculture Research Institute (project ref: RTA2013-00011-C02-02

Climate change-controlled dendroecological signal in Pinus pinea in Southern Spain

Researching the dynamic response to climatic variability of Mediterranean pine forests is a basic issue when evaluating the vulnerability of these ecosystems to climate change-induced abiotic stress. Tree-rings can provide valuable information to approach this purpose. We established five Pinus pinea ring-width chronologies in SW Spain. Tree-growth variability was analyzed using principal component analysis (PCA) for the period 1935-2011. A common climatic signal expressed by the first principal component (PC1) was found. Considering the PC1 scores as a regional chronology, significant correlations with meteorological data were found: correlation was positive for winter-spring precipitation and winter minimum temperatures, and negative for spring maximum temperatures. The PCA, the PC1-climate correlations and the inter-annual ringwidth variability (sensitivity) were computed for successive intervals to check whether the variance explained by the PC1, the climate-growth relationships and the intensity of growth response to climate varied over time. Both sensitivity and shared variance increased over the last decades. The correlation with winter precipitation and temperatures became stronger, spring precipitations lost significance and negative correlation with spring temperatures was enhanced. This indicates that climate became more limiting and a major force controlling growth in the recent decades. In agreement with our findings, meteorological series showed an increase of maximum temperatures in the warmer months, a decrease of minimum temperatures in winter and a marked increase of precipitation variability. Finally, running-interval correlations were performed between PC1 and three P. pinea reference chronologies from Central Spain: correlation increased significantly since the 1970s, indicating an enhanced common macroclimatic signal. Our study highlights the sensitivity of P. pinea to more restrictive climatic conditions and the synchronizing effect of climate change on P. pinea forest growth patterns at regional scale

Linking climate, annual growth and competition in a Mediterranean forest: Pinus pinea in the Spanish Northern Plateau

Climate, competition and site conditions are the main drivers controlling annual secondary growth in tree species. These factors do no act independently on tree growth, but by means of interactions, resulting in mediated interactive effects. For example, the stress gradient hypothesis postulates alleviated interspecific competition under limiting spatial (site) or temporal (climate) resources. According to this, models predicting annual growth and yield for a given forest should consider these issues in their formulation. In this study, we present a modelling approach based on using data from permanent plots and dendrochronological analysis in order to describe annual tree growth in pure, even-aged stands of Pinus pinea L. in the Spanish Northern Plateau, a highly limiting environment due to its Mediterranean continental climate. Our method is based on identifying the different sources of variability by means of a multilevel linear mixed model, and thereby identifying the potential covariates explaining observed variability at the different spatiotemporal scales. Our results indicate that site related factors such as site index or dominant height exert a greater influence on annual secondary growth than size-symmetric competition. In addition, we found that the controlling influence of water stress is greater than that of temperatures on tree growth. Furthermore, our results allow evidence to be identified for the stress gradient hypothesis in temporal intraspecific interactions, since trees exposed to a higher degree of competition tend to grow more than expected in dry periods. In contrast, the effect of competition on growth, on average, tends to be aggravated at very poor sites. Finally, our modelling approach allows us to conduct growth and yield simulations under different climate scenarios at different spatial scales, providing results which point to significant decreases in timber and cone production under the more severe scenarios, which can be alleviated through more intensive silviculture.This work has been carried out under the financial and functional framework of the National Projects RTA-2013-00011.C2.1, PCIN-2014-138 INFORMED, AGL-2017-83828-C2.1 and the PROPINEA agreement between INIA, ITACYL and Deputation of Valladolid. Authors wish to thank Forest Service of Valladolid for their permanent support with the inventory and maintenance of the experimental trials

Differences in stem radial variation between Pinus pinaster Ait. and Quercus pyrenaica Willd. may release inter-specific competition

Species complementarity by morphological and physiological trait differences could cause distinct temporal and spatial use of resources. Accordingly, mixed stands may enhance production, biodiversity and/or provide a better adaptation to future climate conditions. We aim to identify species differences in intra-annual stem radial variation patterns, and to recognize species-specific responses to contrasting weather conditions at key intraannual growth phases. Stem radial variation was recorded from high temporal resolution point dendrometers (2012-2014) installed on twelve dominant maritime pine and Pyrenean oak trees in two mixed stands in central Spain. Species differences in stem radial variation were analyzed by synchrony statistics, intra-annual pattern modelling, and evaluating the dependence of main intra-annual growth phases on climate conditions. Both species showed important differences on intra-annual radial increment pattern despite general stem radial variation synchrony. Radial increment onset was earlier for maritime pine during the spring and rainy autumns. Species-specific responses to weather indicate that stem radial variation increased with autumn temperature in maritime pine, but decreased in Pyrenean oak trees. However, summer vapor pressure deficit may reduce stem radial variation for maritime pine. Therefore, maritime pine would adapt more efficiently to warmer temperatures associated with climate change, although summer water stress may reduce this competitive bonus

La biodiversidad como herramienta en la gestión y certificación forestal : zonas de alto valor de conservación en montes madereros del suroeste peninsular

Este artículo presenta un estudio sobre la biodiversidad y el estado de ocho Zonas de Alto Valor de Conservación en la provincia de Huelva (localizada en el suroeste de la Península Ibérica), colindantes a plantaciones de especies de crecimiento rápido (Eucalyptus globulus). El estudio se incluye en el marco de un proceso de certificación forestal. Se han evaluado algunos parámetros de biodiversidad –riqueza, diversidad alfa, diversidad beta- y estado –regeneración, cobertura, densidaden 143 parcelas de comunidades leñosas. Se han registrado un alto número de taxones animales y vegetales, algunos de los cuales son especies amenazadas o endémicas. El uso de los índices de diversidad ha sido esencial; son simples abstracciones de la estructura altamente compleja de las comunidades, muy útiles para hacer comparaciones. Han mostrado la alta diversidad de las zonas estudiadas mediante datos cuantificables. Este tipo de estudios son muy importantes e útiles para conocer el estado de ecosistemas forestales y abordar su seguimiento, y por lo tanto para la gestión forestal.____________________________________This paper presents a study about the biodiversity and the status of eight Zones of High Conservation Value within the province of Huelva (located in the southwest of the Iberian Peninsula), near plantations of fast growing species (Eucalyptus globulus). The study is in the framework of a forest certification process. Some parameters of biodiversity –species richness, diversity alpha, diversity beta– and status – regeneration, cover, density– have been evaluated in 143 plots of woody communities. A high number of vegetal and animal species have been recorded; some of them are endangered or endemic species. The use of diversity indices has been essential; they are simple abstractions of the highly complex structure of communities, very useful for comparisons. They have shown the high biodiversity of the study areas using quantifiable data. Such studies are very important and useful to know the status of forest ecosystems and to address the monitoring of these ones, and therefore for forest management

Efectos del clima sobre las variaciones diarias del radio del tronco y el crecimiento diametral de la encina durante siete años en una dehesa del suroeste de España (Huelva)

En el presente estudio se han analizado mediante dendrómetros electrónicos puntuales de alta resolución las variaciones diarias del radio del tronco de 9 encinas y los efectos del clima en sus patrones de crecimiento intraanual durante un periodo de 7 años (2005-2012). Nuestros resultados muestran ciclos diarios de expansión-contracción del tronco estrechamente relacionados con cambios en procesos ecofisiológicos a nivel intradiario. A nivel intraanual la encina presenta dos fases de crecimiento. La primera fase sucede generalmente durante el final del invierno y la primavera; y la segunda durante finales del verano y el otoño. Entre estas fases aparecen dos periodos de bajo crecimiento, parada o incluso contracciones del tronco, que se producen generalmente durante finales de la primavera y el verano, y durante finales del otoño y el invierno. La evapotranspiración de referencia afectó negativamente al incremento del tronco durante todo el año. La precipitación tuvo un efecto positivo solo durante las dos fases intraanuales de crecimiento. Las altas temperaturas tuvieron un efecto negativo, excepto en el periodo de meses más fríos. Las variaciones diarias del contenido de agua extraíble relativa tuvieron un efecto positivo, excepto durante el periodo de parada y contracción de final de la primavera y verano

Crown individualisation in holm oaks (Quercus Ilex l.) by the use of image segmentation and object classification techniques

A la hora de caracterizar una masa forestal, se hace imprescindible conocer la densidad, lo que puede hacerse a través de la individualización de las copas de cada árbol o pie. En el presente artículo se muestra el flujo de trabajo desarrollado para la individualización de copas en encinares mediante el empleo de técnicas de segmentación y clasificación basada en objetos (OBIA), analizando su efectividad en cuatro formaciones caracterizadas por alta/baja densidad y presencia/ausencia de estrato arbustivo. Para ello se combinaron los productos del Plan Nacional de Ortofotografía Aérea correspondientes a ortofotografía NIR y primera cobertura lidar. El estudio se llevó a cabo en cuatro áreas de entre 23.20 y 50.09 ha localizadas en la hoja Calañas-Huelva H50-0959, cada una de ellas representativa de una formación. Como entrada en el proceso de segmentación se emplearon las cuatro bandas espectrales de la ortofotografía NIR y un modelo digital de vegetación (MDV) obtenido mediante la nube de puntos lidar. El flujo de segmentación se desarrolló de forma iterativa mediante el software eCognition Developer. Se realizaron sucesivas segmentaciones y clasificaciones de objeto, de tal manera que los objetos que cumplieron una serie de criterios mínimos de individualización salieron del flujo y quedaron caracterizados como individuos. Los resultados de la metodología propuesta mostraron una alta capacidad de individualización de copas de entre el 81.23 % y el 96.86 % de acierto según el tipo de masa estudiado, posibilitando la individualización en encinares con tangencia de copas y adyacentes a matorral.When characterising a forest cover, it is of utmost importance to know its density, which can be done through the crown individualisation of each tree or foot. The present article shows the work flow developed for crown individualisation in holm oaks by means of segmentation and classification by objects techniques (OBIA), analysing its effectiveness in four forest formations characterised by high/low density and presence/absence of shrub stratum. For this, we combined the products of “Plan Nacional de Ortofotografía Aérea” relating to NIR orthophotography and first coverage lidar data. The study was conducted in four areas between 23.20 and 50.09 ha within the map sheet Calañas-Huelva H50-0959, each representing a formation. As input in the segmentation process, we employed the four spectrum bands of the orthophotography and a digital vegetation model (DVM) obtained by the cloud lidar point. The segmentation flow was iteratively run through the eCognition Developer software. We performed successive segmentations and object classifications, in such a way that the objects which met a series of minimum requirements of individualisation got out of the flow and remained characterized as individual objects. The results of the proposed methodology showed a high capacity for crown individualisation, between 81.23 % and 96.86 % of success rate depending upon the type of formation studied, enabling the individualisation in holm oaks with crown tangent and adjacent to shrub.Este estudio ha sido realizado bajo el proyecto “Centro Ibérico para la Investigación y Lucha contra Incendios Forestales” CILIFO (0753_CILIFO_5_E) y financiado por el Programa de Cooperación Transfronteriza Interreg VA España-Portugal - Interreg POCTEP (2014-2020) dentro de la línea de modelización, cuantificación y aprovechamiento de la biomasa orientado a la prevención de incendios forestales