TY - JOUR A1 - Tabares Jimenez, Ximena del Carmen A1 - Zimmermann, Heike Hildegard A1 - Dietze, Elisabeth A1 - Ratzmann, Gregor A1 - Belz, Lukas A1 - Vieth-Hillebrand, Andrea A1 - Dupont, Lydie A1 - Wilkes, Heinz A1 - Mapani, Benjamin A1 - Herzschuh, Ulrike T1 - Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers JF - Ecology and evolution N2 - Shrub encroachment has far-reaching ecological and economic consequences in many ecosystems worldwide. Yet, compositional changes associated with shrub encroachment are often overlooked despite having important effects on ecosystem functioning. We document the compositional change and potential drivers for a northern Namibian Combretum woodland transitioning into a Terminalia shrubland. We use a multiproxy record (pollen, sedimentary ancient DNA, biomarkers, compound-specific carbon (delta C-13) and deuterium (delta D) isotopes, bulk carbon isotopes (delta(13)Corg), grain size, geochemical properties) from Lake Otjikoto at high taxonomical and temporal resolution. We provide evidence that state changes in semiarid environments may occur on a scale of one century and that transitions between stable states can span around 80 years and are characterized by a unique vegetation composition. We demonstrate that the current grass/woody ratio is exceptional for the last 170 years, as supported by n-alkane distributions and the delta C-13 and delta(13)Corg records. Comparing vegetation records to environmental proxy data and census data, we infer a complex network of global and local drivers of vegetation change. While our delta D record suggests physiological adaptations of woody species to higher atmospheric pCO(2) concentration and drought, our vegetation records reflect the impact of broad-scale logging for the mining industry, and the macrocharcoal record suggests a decrease in fire activity associated with the intensification of farming. Impact of selective grazing is reflected by changes in abundance and taxonomical composition of grasses and by an increase of nonpalatable and trampling-resistant taxa. In addition, grain-size and spore records suggest changes in the erodibility of soils because of reduced grass cover. Synthesis. We conclude that transitions to an encroached savanna state are supported by gradual environmental changes induced by management strategies, which affected the resilience of savanna ecosystems. In addition, feedback mechanisms that reflect the interplay between management legacies and climate change maintain the encroached state. KW - climate change KW - fossil pollen KW - land-use change KW - savanna ecology KW - sedimentary ancient DNA KW - state and transition KW - tree-grass interactions Y1 - 2019 U6 - https://doi.org/10.1002/ece3.5955 SN - 2045-7758 VL - 10 IS - 2 SP - 962 EP - 979 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Klemm, Juliane A1 - Herzschuh, Ulrike A1 - Pestryakova, Luidmila Agafyevna T1 - Vegetation, climate and lake changes over the last 7000 years at the boreal treeline in north-central Siberia JF - Quaternary science reviews : the international multidisciplinary research and review journal KW - Tundra-taiga ecotone KW - Larix gmelinii KW - Palynology KW - Sediment geochemistry KW - Mean July temperature KW - Ordination KW - WA-PLS KW - Procrustes rotation Y1 - 2016 U6 - https://doi.org/10.1016/j.quascirev.2015.08.015 SN - 0277-3791 VL - 147 SP - 422 EP - 434 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Tian, Fang A1 - Herzschuh, Ulrike A1 - Mischke, Steffen A1 - Schluetz, Frank T1 - What drives the recent intensified vegetation degradation in Mongolia - Climate change or human activity? JF - The Holocene : an interdisciplinary journal focusing on recent environmental change N2 - This study examines the course and driving forces of recent vegetation change in the Mongolian steppe. A sediment core covering the last 55years from a small closed-basin lake in central Mongolia was analyzed for its multi-proxy record at annual resolution. Pollen analysis shows that highest abundances of planted Poaceae and highest vegetation diversity occurred during 1977-1992, reflecting agricultural development in the lake area. A decrease in diversity and an increase in Artemisia abundance after 1992 indicate enhanced vegetation degradation in recent times, most probably because of overgrazing and farmland abandonment. Human impact is the main factor for the vegetation degradation within the past decades as revealed by a series of redundancy analyses, while climate change and soil erosion play subordinate roles. High Pediastrum (a green algae) influx, high atomic total organic carbon/total nitrogen (TOC/TN) ratios, abundant coarse detrital grains, and the decrease of C-13(org) and N-15 since about 1977 but particularly after 1992 indicate that abundant terrestrial organic matter and nutrients were transported into the lake and caused lake eutrophication, presumably because of intensified land use. Thus, we infer that the transition to a market economy in Mongolia since the early 1990s not only caused dramatic vegetation degradation but also affected the lake ecosystem through anthropogenic changes in the catchment area. KW - central Mongolia KW - grain size KW - human impact KW - lake eutrophication KW - pollen KW - vegetation degradation Y1 - 2014 U6 - https://doi.org/10.1177/0959683614540958 SN - 0959-6836 SN - 1477-0911 VL - 24 IS - 10 SP - 1206 EP - 1215 PB - Sage Publ. CY - London ER -