Assessing Harvested Sites in a Forested Boreal Mountain Catchment through Global Forest Watch

Fernando Rossi,Rasmus Astrup,Bruce Talbot,Stefano Puliti,Johannes Breidenbach

doi:10.3390/rs11050543

Fernando Rossi, Rasmus Astrup + Show 3 more

Open Access

https://doi.org/10.3390/rs11050543

Copy DOI

Journal: Remote sensing	Publication Date: Mar 6, 2019
Citations: 13	License type: CC BY 4.0

Affiliation: Norwegian Institute of Bioeconomy Research

Abstract

Global Forest Watch (GFW) provides a global map of annual forest cover loss (FCL) produced from Landsat imagery, offering a potentially powerful tool for monitoring changes in forest cover. In managed forests, FCL primarily provides information on commercial harvesting. A semi-autonomous method for providing data on the location and attributes of harvested sites at a landscape level was developed which could significantly improve the basis for catchment management, including risk mitigation. FCL in combination with aerial images was used for detecting and characterising harvested sites in a 1607 km2 mountainous boreal forest catchment in south-central Norway. Firstly, the forest cover loss map was enhanced (FCLE) by removing small isolated forest cover loss patches that had a high probability of representing commission errors. The FCLE map was then used to locate and assess sites representing annual harvesting activity over a 17-year period. Despite an overall accuracy of >98%, a kappa of 0.66 suggested only a moderate quality for detecting harvested sites. While errors of commission were negligible, errors of omission were more considerable and at least partially attributed to the presence of residual seed trees on the site after harvesting. The systematic analysis of harvested sites against aerial images showed a detection rate of 94%, but the area of the individual harvested site was underestimated by 29% on average. None of the site attributes tested, including slope, area, altitude, or site shape index, had any effect on the accuracy of the area estimate. The annual harvest estimate was 0.6% (standard error 12%) of the productive forest area. On average, 96% of the harvest was carried out on flat to moderately steep terrain (<40% slope), 3% on steep terrain (40% to 60% slope), and 1% on very steep terrain (>60% slope). The mean area of FCLE within each slope category was 1.7 ha, 0.9 ha, and 0.5 ha, respectively. The mean FCLE area increased from 1.0 ha to 3.2 ha on flat to moderate terrain over the studied period, while the frequency of harvesting increased from 249 to 495 sites per year. On the steep terrain, 35% of the harvesting was done with cable yarding, and 62% with harvester-forwarder systems. On the very steep terrain (>60% slope), 88% of the area was harvested using cable yarding technology while harvesters and forwarders were used on 12% of the area. Overall, FCL proved to be a useful dataset for the purpose of assessing harvesting activity under the given conditions.

Highlights

Mountain catchments play an increasingly important role in the provision of ecosystems services, of which supporting functions such as physical protection against avalanches [1], rock-falls and landand debris slides [2] are perhaps some of the most obvious
The forest cover loss map was enhanced (FCLE) by removing small isolated forest cover loss patches that had a high probability of representing commission errors
The confusion matrices and accuracy metrics (Table 1) for both maps were exactly the same. This is not surprising as only very small polygons were removed from the FCL map to create the FCLE map and, by chance, no reference observation was located in any of the removed polygons

Summary

Introduction

Mountain catchments play an increasingly important role in the provision of ecosystems services, of which supporting functions such as physical protection against avalanches [1], rock-falls and landand debris slides [2] are perhaps some of the most obvious. The continued support or enhancement of these services from mountain catchments in an era of climate change, together with perceived negative developments in size, location and extent of timber-harvesting operations, requires a management approach that is flexible and responsive to status change and risk. Mountain catchments are naturally characterised by steep terrain, the combination of harvesting system, harvesting site attributes and infrastructure imply an increased predisposition to natural hazards [11]. Research addressing these issues has typically focused on quantifying the effect or predicting the risk of negative externalities resulting from such operations. Depending on forest ownership structure, reliable and timely spatial information on the location and attributes of harvested sites can be difficult to access, while this information would be essential for an effective adaptive ecosystem management programme

Objectives

Methods

Results

Discussion

Conclusion