Drone‐based physiological index reveals long‐term acclimation and drought stress responses in trees

Abstract

Monitoring early tree physiological responses to drought is key to understanding progressive impacts of drought on forests and identifying resilient species. We combined drone-based multispectral remote sensing with measurements of tree physiology and environmental parameters over two growing seasons in a 100-yold Pinus sylvestris forest subject to 17-y of precipitation manipulation. Our goal was to determine if drone-based photochemical reflectance index (PRI) captures tree drought stress responses and whether responses are affected by long-term acclimation. PRI detects changes in xanthophyll cycle pigment dynamics, which reflect increases in photoprotective non-photochemical quenching activity resulting from drought-induced photosynthesis downregulation. Here, PRI of never-irrigated trees was up to 10 times lower (higher stress) than PRI of irrigated trees. Long-term acclimation to experimental treatment, however, influenced the seasonal relationship between PRI and soil water availability. PRI also captured diurnal decreases in photochemical efficiency, driven by vapour pressure deficit.Interestingly, 5 years after irrigation was stopped for a subset of the irrigated trees, a positive legacy effect persisted, with lower stress responses (higher PRI) compared with never-irrigated trees. This study demonstrates the ability of remotely sensed PRI to scale tree physiological responses to an entire forest and the importance of long-term acclimation in determining current drought stress responses.

UAV-Based Forest Health Monitoring: A Systematic Review

“…Moreover, needle or leaf samples were taken to identify the presence of nematodes [106,142,146], to quantify pigments under laboratory conditions [85,105], and to assess their water content and spectral properties [123,136]. Soil sampling was conducted to determine possible origins of nutritional deficiencies [109] and to measure the field capacity [147].…”

“…Repetitive UAV surveys of the same area were designed to collect time series as a database for change analysis. Hence, the scientists analyzed spectral and structural changes over time to assess mechanical crown damage [97,98], fire damage based on pre-and postfire data [99][100][101], phenological differences [89], and different stages of stress-induced symptoms evident in the tree canopy [92,94,[102][103][104][105][106][107][108][109][110][111][112]. The primary period of FHM typically lay within the growing season.…”

“…Others used the opportunity to get a clear view of the ground, enabling the creation of an improved photogrammetric digital terrain model (DTM) [114]. Only in six papers was the collection of UAV data over a period of more than a year described [97,98,105,106,108,115]. The longest and most comprehensive time series covered five years of monthly drone flights to study the influence of heavy rain events on tree fall and branch fall rates [97].…”

Effect of Drought and Heavy Metal Contamination on Growth and Photosynthesis of Silver Birch Trees Growing on Post-Industrial Heaps

“… There are modifications in the photosynthesis mechanism, enabling the adaptation of birch trees to the extreme conditions of the habitat. Recent scientific work [ 19 , 20 , 21 , 22 ] indicates the role of non-photochemical quenching (NPQ) in the adaptation to drought conditions, which is a key stress factor in heaps. It is possible to demonstrate physiological parameters, the modification of which enables birch trees to colonise extreme habitats as one of the first species.…”

“…There are modifications in the photosynthesis mechanism, enabling the adaptation of birch trees to the extreme conditions of the habitat. Recent scientific work [ 19 , 20 , 21 , 22 ] indicates the role of non-photochemical quenching (NPQ) in the adaptation to drought conditions, which is a key stress factor in heaps.…”