How to effectively use long-term remotely sensed data to analyze the process of tree and shrub encroachment into open protected wetlands.

Succession caused by agricultural land abandonment is one of the most serious threats to the biodiversity of non forest ecosystems in Europe. The aim of the study conducted in the Biebrza National Park (NE Poland) was to develop a remote sensing method to analyze the process of tree and shrub encroachment into the open peatland area of the Lower Biebrza Basin of 245 km2. The study covered a period of 50 years, from 1966 to 2015. Tree and shrub coverage was analyzed independently on the basis of airborne imagery acquired in 1966, 1980, 1997, 2006, 2010 and hyperspectral and ALS data from 2015. The method used, which consisted in assigning the area covered by trees and shrubs to permanent reference areas in a grid of squares enabled us to analyze the succession process by integrating various types of airborne data retrieved from various sensors with different geometric, radiometric and spectral resolutions. Owing to this, the process of succession could be characterized on the map by illustrating the spatial distribution of tree and shrub area and the dynamics and directions of their changes in time, and quantitatively by calculating the area of trees and shrubs as well as the dynamics, pace and directions of its change over time. It will be possible to integrate the results of the analysis of archived data with those acquired in the future, which will contribute to even wider use of remote sensing in succession process monitoring. The findings suggest that in the study period the area covered by trees and shrubs increased by 3020 ha, and the open areas decreased from 75.78% of the study area in 1966 to 63.31% in 2015. During the last study period (2010-2015) encroachment of trees and shrubs was inhibited to the rate of 2.7 ha/year as a result of the conservation program being implemented in the Lower Biebrza Basin.