TY - JOUR A1 - Wieczorek, Mareike A1 - Kolmogorov, Alexei A1 - Kruse, Stefan A1 - Jacobsen, Inga A1 - Nitze, Ingmar A1 - Nikolaev, Anatoly N. A1 - Heinrich, Ingo A1 - Pestryakova, Luidmila Agafyevna A1 - Herzschuh, Ulrike T1 - Disturbance-effects on treeline larch-stands in the lower Kolyma River area (NE Siberia) JF - Silva Fennica : a quarterly journal for forest science N2 - Tree stands in the boreal treeline ecotone are, in addition to climate change, impacted by disturbances such as fire, water-related disturbances and logging. We aim to understand how these disturbances affect growth, age structure, and spatial patterns of larch stands in the north-eastern Siberian treeline ecotone (lower Kolyma River region), an insufficiently researched region. Stand structure of Larix cajanderi Mayr was studied at seven sites impacted by disturbances. Maximum tree age ranged from 44 to 300 years. Young to medium-aged stands had, independent of disturbance type, the highest stand densities with over 4000 larch trees per ha. These sites also had the highest growth rates for tree height and stem diameter. Overall lowest stand densities were found in a polygonal field at the northern end of the study area, with larches growing in distinct " tree islands". At all sites, saplings are significantly clustered. Differences in fire severity led to contrasting stand structures with respect to tree, recruit, and overall stand densities. While a low severity fire resulted in low-density stands with high proportions of small and young larches, high severity fires resulted in high-density stands with high proportions of big trees. At waterdisturbed sites, stand structure varied between waterlogged and drained sites and latitude. These mixed effects of climate and disturbance make it difficult to predict future stand characteristics and the treeline position. KW - treeline KW - Larix cajanderi KW - Siberia KW - fire KW - stand structure Y1 - 2017 U6 - https://doi.org/10.14214/sf.1666 SN - 0037-5330 SN - 2242-4075 VL - 51 IS - 3 PB - The Finnish Society of Forest Science CY - Helsinki ER - TY - JOUR A1 - Nitze, Ingmar A1 - Grosse, Guido A1 - Jones, Benjamin M. A1 - Arp, Christopher D. A1 - Ulrich, Mathias A1 - Fedorov, Alexander A1 - Veremeeva, Alexandra T1 - Landsat-Based Trend Analysis of Lake Dynamics across Northern Permafrost Regions JF - Remote sensing N2 - Lakes are a ubiquitous landscape feature in northern permafrost regions. They have a strong impact on carbon, energy and water fluxes and can be quite responsive to climate change. The monitoring of lake change in northern high latitudes, at a sufficiently accurate spatial and temporal resolution, is crucial for understanding the underlying processes driving lake change. To date, lake change studies in permafrost regions were based on a variety of different sources, image acquisition periods and single snapshots, and localized analysis, which hinders the comparison of different regions. Here, we present a methodology based on machine-learning based classification of robust trends of multi-spectral indices of Landsat data (TM, ETM+, OLI) and object-based lake detection, to analyze and compare the individual, local and regional lake dynamics of four different study sites (Alaska North Slope, Western Alaska, Central Yakutia, Kolyma Lowland) in the northern permafrost zone from 1999 to 2014. Regional patterns of lake area change on the Alaska North Slope (-0.69%), Western Alaska (-2.82%), and Kolyma Lowland (-0.51%) largely include increases due to thermokarst lake expansion, but more dominant lake area losses due to catastrophic lake drainage events. In contrast, Central Yakutia showed a remarkable increase in lake area of 48.48%, likely resulting from warmer and wetter climate conditions over the latter half of the study period. Within all study regions, variability in lake dynamics was associated with differences in permafrost characteristics, landscape position (i.e., upland vs. lowland), and surface geology. With the global availability of Landsat data and a consistent methodology for processing the input data derived from robust trends of multi-spectral indices, we demonstrate a transferability, scalability and consistency of lake change analysis within the northern permafrost region. KW - lake dynamics KW - lake change KW - permafrost region KW - Landsat KW - Alaska KW - Siberia KW - thermokarst KW - trend analysis KW - machine-learning Y1 - 2017 U6 - https://doi.org/10.3390/rs9070640 SN - 2072-4292 VL - 9 PB - MDPI CY - Basel ER - TY - JOUR A1 - Nitze, Ingmar A1 - Grosse, Guido T1 - Detection of landscape dynamics in the Arctic Lena Delta with temporally dense Landsat time-series stacks JF - Remote sensing of environment : an interdisciplinary journal N2 - Arctic permafrost landscapes are among the most vulnerable and dynamic landscapes globally, but due to their extent and remoteness most of the landscape changes remain unnoticed. In order to detect disturbances in these areas we developed an automated processing chain for the calculation and analysis of robust trends of key land surface indicators based on the full record of available Landsat TM, ETM +, and OLI data. The methodology was applied to the similar to 29,000 km(2) Lena Delta in Northeast Siberia, where robust trend parameters (slope, confidence intervals of the slope, and intercept) were calculated for Tasseled Cap Greenness, Wetness and Brightness, NDVI, and NDWI, and NDMI based on 204 Landsat scenes for the observation period between 1999 and 2014. The resulting datasets revealed regional greening trends within the Lena Delta with several localized hot-spots of change, particularly in the vicinity of the main river channels. With a 30-m spatial resolution various permafrost-thaw related processes and disturbances, such as thermokarst lake expansion and drainage, fluvial erosion, and coastal changes were detected within the Lena Delta region, many of which have not been noticed or described before. Such hotspots of permafrost change exhibit significantly different trend parameters compared to non-disturbed areas. The processed dataset, which is made freely available through the data archive PANGAEA, will be a useful resource for further process specific analysis by researchers and land managers. With the high level of automation and the use of the freely available Landsat archive data, the workflow is scalable and transferrable to other regions, which should enable the comparison of land surface changes in different permafrost affected regions and help to understand and quantify permafrost landscape dynamics. (C) 2016 Elsevier Inc. All rights reserved. KW - Trend analysis KW - Permafrost thaw KW - Thermokarst KW - Thermoerosion KW - Land cover disturbances KW - River delta KW - Arctic tundra KW - Vegetation greening KW - Vegetation change KW - Coastal dynamics KW - Siberia Y1 - 2016 U6 - https://doi.org/10.1016/j.rse.2016.03.038 SN - 0034-4257 SN - 1879-0704 VL - 181 SP - 27 EP - 41 PB - Elsevier CY - New York ER -