Canopy structural changes in black pine trees affected by pine processionary moth using drone-derived data

Producción CientíficaPine species are a key social and economic component in Mediterranean ecosystems, where insect defoliations can have far-reaching consequences. This study aims to quantify the impact of pine processionary moth (PPM) on canopy structures, examining its evolution over time at the individual tree level using high-density drone LiDAR-derived point clouds. Focusing on 33 individuals of black pine (Pinus nigra)—a species highly susceptible to PPM defoliation in the Mediterranean environment—bitemporal LiDAR scans were conducted to capture the onset and end of the major PPM feeding period in winter. Canopy crown delineation performed manually was compared with LiDAR-based methods. Canopy metrics from point clouds were computed for trees exhibiting contrasting levels of defoliation. The structural differences between non-defoliated and defoliated trees were assessed by employing parametric statistical comparisons, including analysis of variance along with post hoc tests. Our analysis aimed to distinguish structural changes resulting from PPM defoliation during the winter feeding period. Outcomes revealed substantive alterations in canopy cover, with an average reduction of 22.92% in the leaf area index for defoliated trees, accompanied by a significant increase in the number of returns in lower tree crown branches. Evident variations in canopy density were observed throughout the feeding period, enabling the identification of two to three change classes using LiDAR-derived canopy density metrics. Manual and LiDAR-based crown delineations exhibited minimal differences in computed canopy LiDAR metrics, showcasing the potential of LiDAR delineations for broader applications. PPM infestations induced noteworthy modifications in canopy morphology, affecting key structural parameters. Drone LiDAR data emerged as a comprehensive tool for quantifying these transformations. This study underscores the significance of remote sensing approaches in monitoring insect disturbances and their impacts on forest ecosystems.Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación (AEI)/10.13039/501100011033 - (project PID2020-118444GA-I00)Junta de Castilla y León - (project VA171P20)Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (grant CLU-2019-01-IUFOR-UVa )Unión Europea-Next Generation EU, Ayudas Margarita Salas - (grant MS-240621)Ministerio de Ciencia, Innovación y Universidades, Ayudas María Zambrano, Universidad de Valladolid y Unión Europea-Next Generation EU - (grant #E-42- 2022-0000233)Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación (AEI)/10.13039/501100011033 y Fondo Social Europeo (FSE) - (grant PRE2021-098278)Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación (AEI)/10.13039/501100011033 - (grant IJC2019-040571-I

Forgotten giants: Robust climate signal in pollarded trees

Producción CientíficaTree ring records are among the most valuable resources to create high-resolution climate reconstructions. Most climate reconstructions are based on old trees growing in inaccessible mountainous areas with low human activity. Therefore, reconstruction of climate conditions in lowlands is usually based on data from distant mountains. Albeit old trees can be common in humanized areas, they are not used for climate reconstructions. Pollarding was a common traditional management in Europe that enabled trees to maintain great vitality for periods exceeding the longevity of unmanaged trees. We evaluate the potential of pollarded deciduous oaks to record past climate signal. We sampled four pollarded woodlands in Central Spain under continental Mediterranean climate. We hypothesized that pollarded trees have a strong response to water availability during current period without pollarding management, but also in the period under traditional management if pruning was asynchronous among trees. Moreover, we hypothesized that if climate is a regional driver of oak secondary growth, chronologies from different woodlands will be correlated. Pollard oaks age exceeded 500 years with a strong response to Standardized Precipitation-Evapotranspiration Index (SPEI) from 9 to 11 months. Climate signal was exceptionally high in three of the sites (r2 = 0.443–0.655) during low management period (1962–2022). The largest fraction of this climate signal (≈70 %) could be retrieved during the traditional management period (1902–1961) in the three sites where pollarding was asynchronous. Chronologies were significantly correlated since the 19th century for all the studied period, highlighting a shared climate forcing. We identified critical points to optimize pollard tree sampling schema. Our results show the enormous potential of pollarded woodlands to reconstruct hydroclimate conditions in the Mediterranean with a fine spatial grain. Studying pollarded trees is an urgent task, since the temporal window to retrieve the valuable information in pollarded trees is closing as these giants collapse and their wood rots.Junta de Castilla y León-Consejería de Educación [IR2020-1-UVA08; VA171P20]EU LIFE Soria Forest Adapt [LIFE19 CCA/ES/001181]Ministerio de Ciencia e Innovación - AEI (IJC2019-040571-I)Ministerio de Ciencia e Innovación - AEI (PRE2018-084106