@article{BoseScherrerCamareroetal.2021, author = {Bose, Arun K. and Scherrer, Daniel and Camarero, j. Julio and Ziche, Daniel and Babst, Flurin and Bigler, Christof and Bolte, Andreas and Dorado-Li{\~n}{\´a}n, Isabel and Etzold, Sophia and Fonti, Patrick and Forrester, David I. and Gavinet, Jordane and Gazol, Antonio and Gonz{\´a}lez de Andr{\´e}s, Ester and Karger, Dirk Nikolaus and Lebourgeois, Francois and L{\´e}vesque, Mathieu and Mart{\´i}nez-Sancho, Elisabet and Menzel, Annette and Neuwirth, Burkhard and Nicolas, Manuel and Sanders, Tanja G. M. and Scharnweber, Tobias and Schr{\"o}der, Jens and Zweifel, Roman and Gessler, Arthur and Rigling, Andreas}, title = {Climate sensitivity and drought seasonality determine post-drought growth recovery of Quercus petraea and Quercus robur in Europe}, series = {Science of The Total Environment}, volume = {784}, journal = {Science of The Total Environment}, publisher = {Elsevier}, issn = {1879-1026}, doi = {10.1016/j.scitotenv.2021.147222}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-2609}, pages = {13}, year = {2021}, abstract = {Recent studies have identified strong relationships between delayed recovery of tree growth after drought and tree mortality caused by subsequent droughts. These observations raise concerns about forest ecosystem services and post-drought growth recovery given the projected increase in drought frequency and extremes. For quantifying the impact of extreme droughts on tree radial growth, we used a network of tree-ring width data of 1689 trees from 100 sites representing most of the distribution of two drought tolerant, deciduous oak species (Quercus petraea and Quercus robur). We first examined which climatic factors and seasons control growth of the two species and if there is any latitudinal, longitudinal or elevational trend. We then quantified the relative departure from pre-drought growth during droughts, and how fast trees were able to recover the pre-drought growth level. Our results showed that growth was more related to precipitation and climatic water balance (precipitation minus potential evapotranspiration) than to temperature. However, we did not detect any clear latitudinal, longitudinal or elevational trends except a decreasing influence of summer water balance on growth of Q. petraea with latitude. Neither species was able to maintain the pre-drought growth level during droughts. However, both species showed rapid recovery or even growth compensation after summer droughts but displayed slow recovery in response to spring droughts where none of the two species was able to fully recover the pre-drought growth-level over the three post-drought years. Collectively, our results indicate that oaks which are considered resilient to extreme droughts have also shown vulnerability when droughts occurred in spring especially at sites where long-term growth is not significantly correlated with climatic factors. This improved understanding of the role of drought seasonality and climate sensitivity of sites is key to better predict trajectories of post-drought growth recovery in response to the drier climate projected for Europe.}, language = {en} } @article{KrauseSandersMundetal.2019, author = {Krause, Stuart and Sanders, Tanja G. M. and Mund, Jan-Peter and Greve, Klaus}, title = {UAV-Based Photogrammetric Tree Height Measurement for Intensive Forest Monitoring}, series = {Remote Sensing}, journal = {Remote Sensing}, number = {11(7)}, publisher = {MDPI}, issn = {2072-4292}, doi = {10.3390/rs11070758}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-3240}, pages = {18}, year = {2019}, abstract = {The measurement of tree height has long been an important tree attribute for the purpose of calculating tree growth, volume, and biomass, which in turn deliver important ecological and economical information to decision makers. Tree height has traditionally been measured by indirect field-based techniques, however these methods are rarely contested. With recent advances in Unmanned Aerial Vehicle (UAV) remote sensing technologies, the possibility to acquire accurate tree heights semi-automatically has become a reality. In this study, photogrammetric and field-based tree height measurements of a Scots Pine stand were validated using destructive methods. The intensive forest monitoring site implemented for the study was configured with permanent ground control points (GCPs) measured with a Total Station (TS). Field-based tree height measurements resulted in a similar level of error to that of the photogrammetric measurements, with root mean square error (RMSE) values of 0.304 m (1.82\%) and 0.34 m (2.07\%), respectively (n = 34). A conflicting bias was, however, discovered where field measurements tended to overestimate tree heights and photogrammetric measurements were underestimated. The photogrammetric tree height measurements of all trees (n = 285) were validated against the field-based measurements and resulted in a RMSE of 0.479 m (2.78\%). Additionally, two separate photogrammetric tree height datasets were compared (n = 251), and a very low amount of error was observed with a RMSE of 0.138 m (0.79\%), suggesting a high potential for repeatability. This study shows that UAV photogrammetric tree height measurements are a viable option for intensive forest monitoring plots and that the possibility to acquire within-season tree growth measurements merits further study. Additionally, it was shown that negative and positive biases evident in field-based and UAV-based photogrammetric tree height measurements could potentially lead to misinterpretation of results when field-based measurements are used as validation.}, language = {en} }