Phenology Modelling and Forest Disturbance Mapping with Sentinel-2 Time Series in Austria

Markus Löw,Tatjana Koukal

doi:10.3390/rs12244191

Abstract

Worldwide, forests provide natural resources and ecosystem services. However, forest ecosystems are threatened by increasing forest disturbance dynamics, caused by direct human activities or by altering environmental conditions. It is decisive to reconstruct and trace the intra- to transannual dynamics of forest ecosystems. National to local forest authorities and other stakeholders request detailed area-wide maps that delineate forest disturbance dynamics at various spatial scales. We developed a time series analysis (TSA) framework that comprises data download, data management, image preprocessing and an advanced but flexible TSA. We use dense Sentinel-2 time series and a dynamic Savitzky–Golay-filtering approach to model robust but sensitive phenology courses. Deviations from the phenology models are used to derive detailed spatiotemporal information on forest disturbances. In a first case study, we apply the TSA to map forest disturbances directly or indirectly linked to recurring bark beetle infestation in Northern Austria. In addition to spatially detailed maps, zonal statistics on different spatial scales provide aggregated information on the extent of forest disturbances between 2018 and 2019. The outcomes are (a) area-wide consistent data of individual phenology models and deduced phenology metrics for Austrian forests and (b) operational forest disturbance maps, useful to investigate and monitor forest disturbances to facilitate sustainable forest management.

Highlights

Worldwide forests are increasingly affected by changes and dynamics of various origin and at different scales [1,2,3]
Following the structure of the method section, the results section presents the main findings concerning (1) the phenology modelling with Sentinel-2 time series applied to the entire forest area of Austria (Section 2.3), and (2) the multiyear forest disturbance mapping, focusing on damages by the bark beetle infestation in Northern Austria (Upper and Lower Austria) between 2018 and 2019 (Section 2.4)
We present the first nationwide operational forest phenology modelling and forest monitoring system optimised for 10 m Sentinel-2 time series data and based on a Savitzky–Golay modelling approach

Summary

Introduction

Worldwide forests are increasingly affected by changes and dynamics of various origin and at different scales [1,2,3]. Without doubt there is an urgent need to safeguard forested areas worldwide and trace dynamics of altering site conditions caused by climate change [7,9]. The monitoring of unobtrusive and small scale land cover changes such as those caused by natural events (e.g., pest infestation, higher mortality due to altering site conditions) or forest management practices (e.g., thinning or selective timber extraction) becomes more and more crucial [8,11]. Natural forests are more resilient to altering environmental conditions and will provide valuable regulating ecosystem services in the future [16]. The monitoring of such small-scale forest management practices will be crucial to guarantee sustainable forestry, in Austria

Objectives

Methods

Results

Discussion

Conclusion