Distinguishing Abrupt and Gradual Forest Disturbances With MODIS-Based Phenological Anomaly Series

Abstract

Capturing forest disturbances over time is increasingly important to determine the ecosystem's capacity to recover as well as aiding a timely response of foresters. With changes due to climate change increasing the frequencies, a better understanding of forest disturbances and their role in historical development is needed to, on the one hand, develop forest management approaches promoting ecosystem resilience and, on the other hand, provide quick and spatially explicit information to foresters. A large, publicly available satellite imagery spanning more than two decades for large areas of the Earth's surface at varying spatial and temporal resolutions represents a vast, free data source for this. The challenge is 2-fold: (1) obtaining reliable information on forest condition and development from satellite data requires not only quantification of forest loss but rather a differentiated assessment of the extent and severity of forest degradation; (2) standardized and efficient processing routines both are needed to bridge the gap between remote-sensing signals and conventional forest condition parameters to enable forest managers for the operational use of the data. Here, we investigated abiotic and biotic disturbances based on a set of ground validated occurrences in various forest areas across Germany to build disturbance response chronologies and examine event-specific patterns. The proposed workflow is based on the R-package “npphen” for non-parametric vegetation phenology reconstruction and anomaly detection using MODIS EVI time series data. Results show the potential to detect distinct disturbance responses in forest ecosystems and reveal event-specific characteristics. Difficulties still exist for the determination of, e.g., scattered wind throw, due to its subpixel resolution, especially in highly fragmented landscapes and small forest patches. However, the demonstrated method shows potential for operational use as a semi-automatic system to augment terrestrial monitoring in the forestry sector. Combining the more robust EVI and the assessment of the phenological series at a pixel-by-pixel level allows for a changing species cover without false classification as forest loss.

Earth-Observation-Based Monitoring of Forests in Germany—Recent Progress and Research Frontiers: A Review

“…The category of forest disturbance comprised 36 of 84 (43%) papers in this review [3,6,10,11,46,48,49,52,53,58,59,62,63,67,68,72,79,84,88,91,[94][95][96][97][98][99]103,110,111,[115][116][117][118]120] compared to 28 of 166 papers (17%) in our initial review [1]. Disturbances to forest systems include causes and effect; therefore, within this category of studies, broad themes emerged.…”

“…The European Forest Condition Monitor is a web-based tool created by Buras et al [49] for monitoring forests across Europe, characterizing forest condition and highlighting an increase in forest decline. Gnilke et al [62] presented a method for distinguishing abrupt and gradual forest disturbances using MODIS multi-temporal and multi-annual EVI data. A method utilizing Landsat thermal data was demonstrated by Barta et al [46] to identify increased and decreased surface temperature during the onset and recovery of disturbance events in a mixed forest over Bavarian Forest National Park.…”

“…Half of the papers concentrated solely on the topic of phenology [55,75,77,80,104,106], while one of them had a secondary focus on disturbance [118]. The remaining five papers dealt with phenology as a secondary research topic and had their main focus on disturbance [3,49,62,117] and biomass/productivity [47].…”

“…All of the studies used optical time series data, while one of them [118] combined optical with SAR (Sentinel-1) data. The pure optical analyses focused on MODIS [47,49,62,77,80], on Landsat [117], on Sentinel-2 [104,106], and on Sentinel-2 in combination with Landsat [75], MODIS [55], and Planet [3].…”

Natural forests for a safe climate: Enhancing ecosystem integrity, biodiversity and adaptive capacity for climate mitigation

“…In Germany, the average area burned since 1991-2018 was around 447 ha per year and only 283 ha between 2009 and 2018 with around 0.5 ha burned per fire, while the state of Brandenburg represents the area that burned the most (Fernandez-Anez et al, 2021). Most fires in Germany (65%) were recorded in coniferous forests (Gnilke and Sanders, 2021). The dominant forest type in the region of Brandenburg are Scots pine (Pinus sylvestris) monocultures on sandy soils that have replaced many of the previous and less-flammable broadleaved forest (Dietze et al, 2019).…”