Long-term vegetation development on a wildfire slope in Innerzwain(Styria,Austria)

Forest fires in mountainous areas can cause severe defores-tation which can potentially trigger secondary natural hazards like debris falls and avalanches. We documented an extreme case study for the range of possible post-fire land cover （LC） dynamics. We investigated a 15-ha, steep （10°-65°） burnt slope in Styria （Austria） at elevation of 760-1130 m, which burned in 1946 and has not fully recovered to date. Seven 8-class legend LC maps were produced （1954, 1966, 1973, 1982, 1998, 2004, 2009） and integrated in a vector-based GIS, mainly by on-screen interpretation of aerial photos. Our aim was to clarify how post-wildfire LC dynamics take place on a severely damaged, steep slope and to give a basic projection of the future vegetation recovery process. The pre-fire Pinus sylvestrisstands have been mainly replaced by Picea abies and Larix decidua. Regeneration proceeded mainly from the base of the slope upwards. All tree species together still cover no more than 40% of the slope after more than 60 years of recovery, while grassland communities and rock/debris areas have expanded. Multitemporal analysis showed a slow but steady increase in woodland cover. Degraded rock/debris areas, however, expanded as well because soil erosion and related debris flows remained active. Slope angle （with a threshold value of approx. 35-40°） seemed to control whether erosion or regeneration prevailed. According to a simple extrapolation, the slope will not reach its former condition before 2070. This extreme disturbance window of more than 120 years is owed to the steepness of the slope and to the shallow soils on dolomitic bedrock that were severely damaged by the fire. The neglect of any game fencing is a further factor slowing regeneration.

Detecting abrupt change in land cover in the eastern Hindu Kush region using Landsat time series(1988-2020)

Land cover change in the semi-arid environment of the eastern Hindu Kush region is driven by anthropogenic activities and environmental change impacts. Natural hazards, such as floods presumably influenced by climatic change, cause abrupt change of land cover. So far, little research has been conducted to investigate the spatiotemporal aspects of this abrupt change in the valleys. In order to explore the abrupt change in land cover and floods as its possible drivers in the eastern Hindu Kush, a semi-arid mountain region characterized by complex terrain, vegetation variation, and precipitation seasonality, we analyzed long-term Landsat image time series from 1988 to 2020 using Breaks For Additive Seasonal and Trend(BFAST). Overall, BFAST effectively detected abrupt change by using Landsat-derived Modified Soil Adjusted Vegetation Index(MSAVI). The results of our study indicate that approximately 95% of the study area experienced at least one abrupt change during 1988-2020. The years 1991, 1995, 1998, 2007, and 2016 were detected as the peak years, with the peaks occurring in different seasons. The annual trend of abrupt change is decreasing for the study area. The seasonality of abrupt change at the catchment level shows an increasing trend in the spring season for the southern catchments of Panjkora and Swat. The spatial distribution patterns show that abrupt change is primarily concentrated in the floodplains indicating that flooding is the primary driver of the land cover change in the region. We also demonstrated the accurate detection of past flood events(2015) based on the two case examples of Ayun, Rumbur, and Kalash valleys. The detection of the flood events was verified by fieldwork and historical high-resolution Google Earth imagery. Finally, our study provides an example of applying Landsat time series in a dry mountain region to detect abrupt changes in land cover and analyze impact of natural hazards such as floods.