ID39: Mountain grasslands under global change
Mountain grasslands under global change
Session Part I: 10:00 - 12:00
Session Part II: 13:30 - 15:00
Richard Bardgett, Sandra Lavorel, Ursula Peintner and Ulrike Tappeiner
Assigned to Synthesis Workshop
1. Mountain Ecosystems under Global Change
climate warming, drought, land-use change, ecosystem functioning, biogeochemical cycles, plant-soil interactions, ecosystem services, shrub encroachment, mycorrhiza, microbial activity, grassland, biodiversity
Grasslands are an important component of mountain landscapes. They are a common ecosystem type above the treeline. In many mountain regions, subalpine and montane grasslands were created by humans to support livestock and thus human livelihood, making them important social-ecological systems which provide a broad range of ecosystem services. Over the recent decades mountain grasslands have been exposed to significant changes in land use and climate. Land-use changes have involved intensification, conversions from hay meadows to pastures and, most frequently, complete abandonment of grasslands. Climate warming has been particularly pronounced in many mountain regions, and in the coming decades is expected to favour the occurrence of severe droughts.
Individually and collectively, these global changes may affect mountain grasslands on multiple levels and scales. They may lead to changes in the vegetation, above-belowground interactions and biogeochemical cycles, with downstream consequences for productivity, nutrient cycling, greenhouse gas emissions and water yield. In this session we will explore the mechanisms underlying grassland responses to global changes and identify consequences for grassland functioning.
Abstract ID 438 | Date: 2022-09-12 10:00 – 10:10 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Halbritter, Aud H. (1); Klanderud, Kari (2); Austrheim, Gunnar (3); Telford, Richard J. (1); Goldberg, Deborah (4); Yang, Yan (5); Vandvik, Vigdis (1)
1: University of Bergen, Norway
2: Norwegian University of Life Sciences, Norway
3: Norwegian University of Science and Technology
4: University of Michigan
5: Institute of Mountain Hazards and Environment at Chinese Academy of Science
Keywords: Global Change, Alpine, Grazing, Biodiversity, Ecosystem Function
Climate warming, nitrogen deposition, and grazing pose major threats to alpine biodiversity. All of these can have complex effects on biodiversity and ecosystem function, and, especially for biodiversity, effects can often be negative. For plant communities, these impacts operate through many of the same ecological pathways, involving changes in plant productivity and biomass as well as carbon cycling processes. We us an experiment-based approach to (i) assess the single and interactive effects of these three global change drivers on alpine biodiversity and carbon cycling; and (ii) explore the circumstances under which grazing can be an effective tool for mitigating the ecological strains on biodiversity caused by climate warming and/or nitrogen deposition.
Warmer climate and nitrogen deposition significantly impact alpine biodiversity. In particular, they increase graminoid cover, while decreasing forb cover and species richness. However, grazing by sheep can mitigate these negative impacts to some extend. This study aims to understand impacts of global change on alpine ecosystems, and provide important information for farmers and policy makers in alpine areas to optimise the level of grazing on their land to improve biodiversity and ecosystem functions and is therefore highly relevant to society.
Abstract ID 730 | Date: 2022-09-12 10:10 – 10:20 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Garcia-Franco, Noelia (1); Wiesmeier, Martin (1,2); Berauer, Bernd Josef (3); Schuchardt, Max (3); Schucknecht, Anne (4); Schneider, Katrin (4); Schlingmann, Marcus (4); Andrade Linares, Diana (5); Schloter, Michael (5); Schulz, Stefanie (5); Schreiber, Mirella (4); Wolf, Bejamin (4); Jentsch, Anke (3); Kiese, Ralf (4); Dannenmann, Michael (4); Kögel-Kanbner, Ingrid (1,6)
1: Technische Universität München, Germany
2: Bavarian State Research Center for Agriculture, Freising, Germany
3: Department of Disturbance Ecology, University of Bayreuth, Bayreuth, Germany
4: Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research I (IMK-IFU), Garmisch-Partenkirchen, Germany
5: Helmholtz Zentrum München, Research Unit Comparative Microbiome Analysis, Neuherberg, Germany
6: Institute for Advanced Study, Technical University Munich, Garching, Germany
Keywords: Soil-Plant Mesocosms, Aggregates, Climate Change, Grasslands, Oc Stocks
Despite that alpine and pre-alpine grassland soils are hotspots for the soil organic carbon (SOC) sequestration, the information about the changes in SOC stocks and the aggregate distribution is limited. In our study, we selected grassland soils along an elevation gradient in the Northern Limestone Alps of Bavaria (Germany): Esterberg (1,260 m a. s. l.), Graswang at (860 m a. s. l.), and Fendt (600 m a s.l.). In 2016, the study sites were initially sampled before plant-soil mesocosms were translocated downslope along the elevation gradient to simulate climate change (temperature increase of +1 K from high- to mid- elevation, +2 K from mid- to low elevation, and +3 K from high- to low-elevation). In addition, two management practices (extensive vs. intensive) were implemented. After 4 years, in 2020, we took soil samples from each translocated soil-plant mesocosm to study the changes of SOC stocks and the SOC distribution according to different aggregate size classes. We observed a significant decrease of SOC and N contents after four years, but no significant effect on stocks due to inconsistent changes in bulk density. The analysis of soil aggregation showed a decrease in the OC associated with macroaggregates in both extensive and intensive management, while OC in microaggregates and the silt/clay-sized fraction increased. Our results showed evidence that climate change will lead to significant losses of C in these SOC-rich soils, which not only contributes to climate change but also probably deteriorates the functionality of these grassland soils.
Abstract ID 387 | Date: 2022-09-12 10:20 – 10:30 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Marchal, Lise; Gateuille, David; Poulenard, Jérôme; Naffrechoux, Emmanuel
Environnements Dynamiques et Territoires de la Montagne (EDYTEM), University Savoie Mont Blanc, France
Keywords: Moutain Soils – Alpine Grasslands – Pahs – Climate Change – Soil Organic Matter
However isolated they may be, Alpine soils are not spared from contamination by pollutants. In particular, they are affected by the atmospheric deposition of Polycyclic Aromatic Hydrocarbons (PAH). PAH are a large family of organic pollutants, mainly released into the atmosphere by the incomplete combustion of organic matter (OM). Today, the most important sources are household heating and road traffic. PAH are problematic because many of them are known to be toxic. Once released into the atmosphere, PAHs can be transported over long distances and deposite on vegetation and soils, where there are stored. Due to their high hydrophobicity and lipophilicity, these pollutants have a great tendency to bind to soil organic matter (SOM). By this way, soils store most of the PAHs present in the environment, giving them an essential role in the trapping and, in fine, the protection of aquatic ecosystems.
At the same time, the current climate change has a significant impact on moutainous areas. In the Alps, minimal temperaturesare rising faster than on the global scale. These evolutions cause changes in soil compositions and properties, including notably a loss in organic carbon, i.e. OM.
In sum, in response to changing SOM dynamics due to climate change, PAH dynamics will in turn be impacted. Soil capacities to trap PAH could decrease and cause a remobilization of PAHs stocks built up over decades. This phenomenon could lead to a transfer of PAH to rivers, and thus to significant pollution of aquatic ecosystems. Given the potentially rapid response of soils to climate change, and in view of deleterious effects of PAH on ecosystems and human health, it seems essential to better understand these mecanisms.
Therefore, our study focused on the potential remobilization of PAH in French alpine grasslands. Between Galibier and Lautaret passes, pollutant and SOM contents in soils were investigated on several plots (~40 samples), in order to explore drivers of the constitution of PAH stocks and to better understand how changes may lead to pollutant remobilization.
Our results showed that all studied soils were polluted with PAH (> 200 ng/g for the sum of 14 compounds) and that a change in the quality and/or the quantity of OM can change the storage capacity of PAH in soils.
Abstract ID 550 | Date: 2022-09-12 10:30 – 10:40 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Tello-García, Elena (1); Mandolini, Edoardo (2); Tasser, Erich (3); Probst, Maraike (2); Peintner, Ursula (2); Tappeiner, Ulrike (1); Leitinger, Georg (1)
1: Department of Ecology, University Innsbruck, Austria
2: Department of Microbiology, University Innsbruck, Austria
3: Institute for Alpine Environment, Eurac Research, Bozen, Italy
Keywords: Drought, Plant-Soil Interactions, Plant Traits, Biomass Productivity, Roots
Drought compromises water availability, affects biomass productivity and acts as a filter that determines which plant species or functional groups persist. In grasslands, usually legumes such red clover (Trifolium pratense) are more influenced by drought than other functional groups like grasses or herbs. How plant species cope with stressors like drought depends mostly on their functional traits. Recently, it has been increasingly emphasized the importance of the belowground plant traits and the resulting plant-soil interactions in the plant's response to climate change. Plant roots host symbiotic microbes like arbuscular mycorrhiza fungi that enhance water retention and pathogen defence, or Rhizobia, which provide nitrogen to the plant. In this study, we analyse the effects of drought on plant-soil interactions and plant traits of red clover (Trifolium pratense), as well as how they affect plant productivity. To do so, we performed an experiment with pots with a soil collected in a meadow used for hay production located in the Austrian Alps. Half of the pots were filled with native soil, and the others were filled with the same soil, but sterilized. In these pots, we planted red clover and simulated two drought periods. We saw that the disruption of the soil microbial community by sterilization caused an increase in plant productivity under humid conditions. However, red clover in sterilized soil decreased productivity significantly under drought. Plant individuals showed a fast growth at the beginning of both drought periods, enhanced by a change on the plant traits. Leaves got thicker and smaller, the stomata density decreased, while roots got longer and thinner to increase the root absorption area. However, red clover in native soil did not show big changes on plant traits caused by drought, but had similar productivity than the humid variant. Therefore, we conclude that a stable plant-soil system with a more diverse microbial community and a higher abundance of Rhizobia can cope with drought easily, showing a conservative strategy. While in a disrupted system caused by sterilization, plants can grow faster because they give less energy to the few microorganisms, but they are less supported by the microorganisms under drought. Even when red clover changes plant traits, it is not enough to maintain the productivity rate that it had in humid conditions.
Abstract ID 605 | Date: 2022-09-12 10:40 – 10:50 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Forte, T'Ai G. W:; Carbognani, Michele; Chiari, Giorgio; Petraglia, Alessandro
University of Parma, Italy
Keywords: Ecosystem Respiration, Gross Ecosystem Production, Anpp, Plant Survival, Climate Extremes
As a result of climate change, increased frequency of drought events are predicted globally. In this scenario, the timing of dry events represents a crucial aspect in determining the degree to which limited water supply impacts ecosystem functions. Research on drought-timing effects on high-elevation grasslands, however, is still scarce. In particular, a study investigating moisture thresholds of ecosystem functions under different drought timings has yet to be carried out.
To fill this knowledge gap, a mesocosm experiment was implemented using monoliths from a Carex curvula grassland. The effects of different drought timings during the growing season was assessed on plant performance – i.e. aboveground net primary production (ANPP) and plant survival. Soil moisture and temporal thresholds (days without precipitation) of ecosystem respiration (ER) and gross ecosystem production (GEP) were also identified to assess whether these vary in different drought conditions – i.e. a dry event starting immediately after snowmelt (EARLY) vs one starting ca. 1 month later (MID). Three drought treatments were employed: early-season drought (ED) and mid-season drought (MD), both of which lasted 1 month; and full-season drought (FD) lasting 2 months, which was carried out to identify the thresholds triggering different ER and GEP rates. Full-rainfall exclusion was imposed and monoliths watered during the whole experimental period were used as controls (C).
The plant community was diversely affected by drought depending on its timing, with the greatest ANPP reduction in ED compared to C; plant survival, on the other hand, was lower in MD, while plants in ED exhibited similar C values. Threshold analysis revealed that soil moisture and temporal thresholds for ER and GEP were different according to drought timing, with thresholds under MID drought being reached at higher moisture values, and after a shorter dry period, compared to those under EARLY drought.
Overall, the impact of drought on ecosystem functions in alpine grasslands appears to be strongly dependent on the timing of dry spells during the growing season. In particular, the thresholds of key ecosystem processes differ according to when the extreme event is experienced – a result confirmed by the data on plant survival. Timing should, therefore, be factored in when ecological thresholds in response to water scarcity are investigated.
Abstract ID 888 | Date: 2022-09-12 10:50 – 11:00 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Capponi, Lisa (1); Neuner, Gilbert (1); Still, Christopher (2); Schaumberger, Andreas (3); Bahn, Michael (1)
1: University of Innsbruck, Austria
2: Oregon State University, Corvallis, Oregon, USA
3: HBLFA Raumberg-Gumpenstein, Irdning, Austria
Keywords: Mountain Grassland, Drought And Future Climate, Leaf Temperatures, Stomatal Conductance, Plant Stress
Multiple drivers of global change, including elevated CO2 concentrations, warming and drought, are increasingly affecting ecosystems worldwide. While their individual effects on plants and ecosystems have been comparatively well studied, their interactive effects are still poorly understood. Leaf temperatures are crucial for a range of plant processes and connect plant water relations to the energy balance and can thus be triggers and indicators of heat and water stress under extreme climate conditions. However, to date little is known on how they are affected by interacting global change drivers. In this study, based on a multi-factor global change experiment in managed mountain grassland, we investigated the individual and combined effects of summer drought, future warming (+3 °C) and future CO2 concentrations (+ 300 ppm) on leaf temperatures, stomatal conductance, and chlorophyll fluorescence, which was studied as an indicator of stress. Canopy and leaf surface temperatures were measured using Infrared imaging (IR); stomatal conductance and chlorophyll fluorescence were assessed at the leaf scale using a porometer combined with a fluorometer. Preliminary results show that, during sunny days, mid-summer warming and elevated CO2 increased leaf temperatures compared to ambient conditions. Drought caused significantly higher leaf temperatures compared to warming and elevated CO2. When drought was combined with future warming and CO2 concentrations, i.e., when all three global change drivers interacted, leaf temperatures were most strongly increased. Leaf temperatures were inversely related to stomatal conductance. No significant treatment-related effect was observed when measuring chlorophyll fluorescence. Interestingly, drought effects on leaf temperatures persisted also during the period of plant recovery from drought. Overall, we conclude that in a future warmer climate under elevated CO2, drought effects on leaf and canopy surface temperatures are much more pronounced compared to drought under ambient current conditions, potentially inducing or exacerbating plant stress and reducing grassland resistance to such extreme climatic events.
Abstract ID 523 | Date: 2022-09-12 11:00 – 11:10 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Varricchione, Marco; Carranza, Maria Laura; Stanisci, Angela
University of Molise, Italy
Keywords: Mediterranean Calcareous Grasslands, Endemic Species, Re-Visitation Study, Global Change
High mountain ecosystems contain 20% of the native flora of Europe and are hotspots of biodiversity, hosting a high number of cold adapted species, rich in endemic and rare plants. However, they are among the most threatened by global change, as they are exposed to a high risk of biodiversity loss.
As observed on several studies, climate change has a strong impact on species distribution in the high moutain alpine-nival ecological belts, with a general gain in species richness coming form the lower vegetation belts and a loss of cryophilous species. Such process, called thermophilization is mainly promoted by the increase in temperatures.
The present work aims to analyze temporal changes on plant species composition of high mountain vegetation ocurred during the last 20 years in Central Apennines and to explore temporal trends on endemic species cover and richness
We analyzed the Maiella National Park (MNP) which, comprised in the LTER network of central Apennine, assures continous and updated data describing the ecological effects of climate change on high mountains.
Specifically we studied temporal changes in species composition through a re-visitation study, using a set of 25 georeferenced historical relevés newly collected after 20 years on two high mountain calcareous grasslands: Sesleria juncifolia subsp. juncifolia community growing on steep slopes and the Kobresia myosuroides community growing on the windy ridges, both included in the 6170 EU Habitat (Alpine and subalpine calcareous grasslands).
We analyzed temporal changes on overall and endemic species richness and cover by the ANalysis Of SIMilarities (ANOSIM) through a one-way ANOSIM test. We used the nonparametric Kruskal-Wallis test for equal medians to determine the presence of significant differences over time. We also assessed the degree of change in the floristic composition by the Vegetation Turnover Index (Tveg).
Our results evidenced a decrease in the total number of species and in species cover and richness per plot in both high elevation plant communities. In the Sesleria juncifolia community we also registered a significant decrease in endemic species per plot (cover and richness). The Vegetation Turnover Index (Tveg) ranged between 0,29 for Sesleria juncifolia community and 0,36 on Kobresia myosuroides community.
These changes are partially in line with those observed in others Mediterranean calcareous summits, where similar reduction on species richness and endemic loss were explained by a combination of two climate parameters: the rise of temperatures and the decline of summer precipitations.
Abstract ID 704 | Date: 2022-09-12 11:10 – 11:20 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Tissink, Maud (1); Radolinski, Jesse (1); Reinthaler, David (1); Pötsch, Erich (2); Bahn, Michael (1)
1: Department of Ecology, University of Innsbruck, Sternwartestraße 15 A-6020 Innsbruck, Austria
2: Höhere Bundeslehr- und Forschungsanstalt für Landwirtschaft (HBLFA) Raumberg-Gumpenstein, Raumberg 38, A-8952 Irdning, Austria
Keywords: Mountain Grassland, Water Uptake, Roots, Root Traits, Global Change
Plants can modulate the source and magnitude of water uptake under environmental stresses, ultimately constraining water and energy fluxes across Earth's surface. These alterations are scarcely quantified for future climatic scenarios such as warming, elevated atmospheric CO2 (eCO2) and droughts, and their interactions. Here we used diurnal soil moisture dynamics throughout the 2019 growing season to quantify the impacts of these three global change factors on root water uptake across a multilayer 3–36 cm soil profile in a managed C3 mountain grassland in Austria; a key agricultural landscape within central Europe. We expected that 1) annual summer drought and eCO2 (+300 ppm) would reduce root water uptake relative to ambient conditions due to supply limitation and a lower stomatal conductance, whereas 2) greater vapour pressure gradients in warmed systems (+3 ℃) would elevate transpiration rates, increasing root water uptake. Furthermore, we determined the effects of these global change factors on root mass, length and further morphological traits using fine roots obtained from ingrowth root cores extracted three times during the season. We expected that 3) these root parameters would explain water uptake capacity across the global change treatments.
Plants reduced water uptake in droughted plots by ~35% by decreasing water extraction from the upper soil profile during the peak drought, also when additionally exposed to warming and eCO2. Contrary to our expectation, warmed plots had lower water uptake by 17-25% relative to control plots. Finally, vegetation in eCO2 plots displayed similar water uptake to plots under ambient conditions; however, eCO2 effects did buffer warming effects, such that plots with eCO2 and warming extracted less water than those subjected to warming alone. Treatments that affected root water uptake (drought, warming and multifactor treatments) generally increased root weight, length and some traits whilst decreasing others, whereas fine roots exposed to eCO2 remained similar to those under ambient conditions. Root water uptake capacity was related to fine root biomass and some root traits in ambient, drought, and eCO2 plots, yet no significant relationships were found for plots under warming or multifactor treatments. From our study, we conclude that eCO2, warming and drought have non-additive effects on grassland root water uptake, which are partially mediated by global change responses of root biomass and traits.
Abstract ID 645 | Date: 2022-09-12 11:20 – 11:30 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Pittarello, Marco (1); Gorlier, Alessandra (2); Ravetto Enri, Simone (1); Lonati, Michele (1); Lombardi, Giampiero (1)
1: Department of Agricultural, Forest and Food Sciences (DISAFA), University of Torino, Turin, Italy
2: School of Natural Resources and the Environment, University of Arizona, Tucson, AZ 85721, USA
Keywords: Grassland Restoration, Management, Botanical Composition, Livestock, Pastoral Value
In mountain environments, the cessation of extensive farming and inadequate management practices have led to serious vegetation changes, which negatively affect forage yield and quality and the ecosystem services provided by mountain grasslands. Besides promoting tree and shrub encroachment, the reduction of agricultural practices induces the invasion of competitive coarse grasses, such as Brachypodium rupestre (Host) Roem. & Schult. This species is highly competitive due to its elevated tiller density, branching frequency, and clonal growth. Moreover, silica-rich and hairy leaves make B. rupestre a low-quality forage species for livestock. The aim of this research was to assess the single and combined effects of mowing and mineral fertilization on the reduction of B. rupestre coverage in an abandoned grassland of the Western Italian Alps, over the long-term (10 years, from 2006 to 2015). The study area was a secondary grassland dominated by B. rupestre located at Gran Bosco di Salbertrand Natural Park, at 1360 m a.s.l. Four treatments were applied in the area: mowing (M), mineral fertilization (F, 120 kg/ha N – 80 kg/ha K2O – 80 kg/ha P2O5), mowing coupled with mineral fertilization (MF), and control (not mown and not fertilized). A split-plot experimental design was used with mineral fertilization in the main plot and mowing in the subplots, for a total of 16 2×5-m subplots (four replicates per each treatment). Botanical composition within each subplot was surveyed with the vertical point-quadrat method before treatment application. The cover of B. rupestre was similar amongst treatments in 2006 and 2007 whereas marked differences were measured in 2013 and 2015: M and MF had a lower cover of B. rupestre compared to F and control. All the treatments except were effective in reducing B. rupestre cover, while it did not change in the control. MF and M resulted in an increase of medium-high forage value species over time, as shown by a Principal Response Curve. Conversely, B. rupestre was replaced by plant species with medium and low forage values only in M.
The results of this research showed that the most effective practice to reduce B. rupestre cover was MF, followed by M. Conversely, F alone determined a negligible reduction. The advantage of combining mowing and fertilization was the increase of nutrient-demanding plant species, which are also characterized by a higher forage quality. However, effects on vegetation were evident only after six years of treatment application.
Abstract ID 146 | Date: 2022-09-12 11:30 – 11:40 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Volk, Matthias (1); Suter, Matthias (1); Wahl, Anne-Lena (1); Bassin, Seraina (2)
1: Agroscope, Switzerland
2: Pädagogische Hochschule Schaffhausen, Switzerland
Keywords: Climate Warming, Soil Carbon Sink, Net Ecosystem Carbon Balance Necb, C Stock, C Flux
Climate change is associated with a change in soil organic carbon (SOC) stocks, implying a feedback mechanism on global warming. Grassland soils represent 28% of the global soil C sink and are therefore important for the atmospheric greenhouse gas concentration.
In a field experiment in the Swiss Alps, we recorded changes in the ecosystem organic carbon stock under climate change conditions, while quantifying the ecosystem C fluxes at the same time (ecosystem respiration, gross primary productivity, C export in plant material and leachate water). We exposed 216 grassland monoliths to six different climate scenarios (CS) in an altitudinal transplantation experiment. In addition, we applied an irrigation treatment (+12-21% annual precipitation) and an N deposition treatment (+3 and +15 kg N ha-1 a-1) in a factorial design, simulating summer-drought mitigation and atmospheric N pollution.
In five years the ecosystem C stock, consisting of plant C and SOC, dropped dramatically by about -14% (-1034 ±610 g C m-2) with the CS treatment representing a +3.0 °C seasonal (Apr.-Oct.) warming. N deposition and the irrigation treatment caused no significant effects. Measurements of C fluxes revealed that ecosystem respiration increased by 10% at the +1.5 °C warmer CS site and by 38% at the +3 °C warmer CS site (P ≤ 0.001 each), compared to the CS reference site with no warming. However, gross primary productivity was unaffected by warming, as were the amounts of exported C in harvested plant material and leachate water (dissolved organic C). As a result, the five year C flux balance resulted in a climate scenario effect of -936 ±138 g C m-2 at the +3.0 °C CS, similar to the C stock climate scenario effect. It is likely that this dramatic C loss of the grassland is a transient effect before a new, climate adjusted steady state is reached.
Abstract ID 186 | Date: 2022-09-12 11:40 – 11:50 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Elsen, Paul R (1); Lewińska, Katarzyna Ewa (2); Zandler, Harald (3); Surya, Gautam (1); Jahed, Nasrat (4); Faryabi, Sorosh Poya (4); Radeloff, Volker C (2); Grantham, Hedley S (1)
1: Wildlife Conservation Society, Global Conservation Program
2: Department of Forest and Wildlife Ecology, University of Wisconsin-Madison
3: Bayreuth Center of Ecology and Environment Research, University of Bayreuth
4: Wildlife Conservation Society-Afghanistan
Keywords: Remote Sensing, Conservation, Rangelands, Ecosystem Integrity, Sustainable Development
Grasslands support billions of people and important biodiversity, but their ability to function as natural support systems is hindered by both climate change and human activities. Grassland degradation is especially problematic in Afghanistan, where political instability, overgrazing, and drought threaten grassland ecosystems, upon which most people critically depend. We applied spectral unmixing analysis and temporal segmentation to high-resolution satellite imagery to reveal detailed spatiotemporal patterns of three distinct grassland degradation processes over 20 years in Afghanistan's vital northeastern grasslands. Both green and dry vegetation loss occurred mainly in highly populated areas, while desiccation occurred widely from valley bottoms to high mountains. Model results were validated using data from field surveys of green vegetation cover in two opposing regions of the landscape. Annual trends in green vegetation were associated with reductions in precipitation and snow cover as measured by reanalysis and MODIS satellite data, respectively, but models also revealed vast areas of degradation unexplained by these factors adjacent to and likely driven by people and livestock. Protecting high integrity grasslands, restoring degraded grasslands, and establishing alternative livelihoods are essential to bolster adaptation potential and reduce pressure and reliance on grasslands.
Abstract ID 757 | Date: 2022-09-12 11:50 – 12:00 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Biasi, Christina; Voigt, Carolina; Marushchak, Maija; Kou, Dan; Martikainen, Pertti
University of Eastern Finland, Finland
Keywords: Permafrost Soils, Greenhouse Gases, Nitrous Oxide, Nitrogen Cycle, Arctic Soils, Alpine Soils
Nitrous oxide (N2O) is a strong greenhouse gas with a global warming potential about 300 times that of CO2 for a 100-year timescale. Soils are sources of N2O globally, but N2O emissions from permafrost-affected soils underlying large parts of high-latitude and alpine regions have been considered negligible owing to nitrogen (N) limitation in these cold soils. Recent measurements of N2O emissions have challenged this view, and a review of published studies (Voigt et al. 2020) showed that vegetated soils in permafrost regions are often small but evident sources of N2O during the growing season (~30 μg N2O–N m−2 day−1). Moreover, barren or sparsely vegetated soils, common in harsh climates, can serve as substantial sources of N2O (~455 μg N2O–N m−2 day−1), demonstrating the importance of permafrost-affected soils in Earth's N2O budget. Here we will discuss N2O fluxes from arctic, antarctic and alpine permafrost regions, including areas that likely serve as sources (such as peatlands) and as sinks (wetlands, dry upland soils), and estimate N2O emissions from global permafrost-affected soils. The average N2O emissions were 38 (mean) and 288 (median) μg N2O–N m−2 day−1, and were not significantly different between arctic, antarctic and alpine soils; however, data from alpine ecosystems were particularly rare and mostly restricted to the Tibetan Plateau. We outline the below-ground N cycle in permafrost regions and examine the environmental conditions influencing N2O dynamics. Global-change-related impacts on permafrost ecosystems and how these could alter N2O fluxes are discussed, including effects of warming, altered precipitation and snow pack, permafrost collapse, enhanced availability of mineral nitrogen and effects of management practices such as grazing on N2O emissions from alpine soils. Finally, we will introduce first modelling efforts to simulate N2O fluxes from permafrost regions. The need for more research to better constrain the global impact of permafrost N2O emissions is highlighted.
Voigt, Carolina & Marushchak, Maija & Abbott, Benjamin & Biasi, Christina & Elberling, Bo & Siciliano, Steven & Sonnentag, Oliver & Stewart, Katherine & Yang, Yuanhe & Martikainen, Pertti. (2020). Nitrous oxide emissions from permafrost-affected soils. Nature Reviews Earth & Environment 1, 1-15.
Abstract ID 621 | Date: 2022-09-12 13:30 – 13:40 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Protti Sanchez, Fabrizzio (1); Janssens, Ivan (2); Sigurdsson, Bjarni D. (3); Sigurdsson, Páll (3); Bahn, Michael (1)
1: Department of Ecology, University of Innsbruck, Innsbruck, Austria
2: Department of Biology, University of Antwerp, Antwerp, Belgium
3: Faculty of Environmental & Forest Sciences, Agricultural University of Iceland, Hvanneyri, Iceland
Keywords: Soil Co2 Efflux, Soil Carbon, Warming, Subarctic, Geothermal Gradient
Soil respiration is a key process of the terrestrial carbon (C) cycle, composed of the carbon dioxide (CO2) respired by soil microorganisms feeding on soil organic matter (heterotrophic source component) and the respiration of plant roots and their associated rhizomicrobial community (autotrophic source component). It is expected that global warming will accelerate metabolic rates leading to higher soil respiration and larger soil C losses, which could cause positive feedbacks to climate change. This is especially relevant in higher-elevation and/or high-latitude ecosystems, such as the arctic and the subarctic, where large amounts of C are stored in the soil. Our current understanding of warming effects on soil C dynamics is largely restricted to short-term warming experiments (1-5 y of warming), which limits our capacity to project the longer-term consequences of a warming climate.
In this study, which contributes to the EU-project FutureArctic, we investigated the effects of 13 years of geothermal warming on soil CO2 efflux and its main source components in subarctic grasslands. We measured soil CO2 efflux along a soil warming gradient ranging from +0 to +14°C above ambient soil temperature using continuously operating automated long-term soil chambers. To distinguish between biogenic and geogenic soil CO2 in this geothermal system, we measured the isotopic composition of soil CO2 efflux by coupling an isotope analyser to the automated long-term soil chambers in some field campaigns. Additionally, during the growing season, we manually measured soil CO2 efflux in shallow and deep soil collars (trenching approach) to partition between the autotrophic and heterotrophic components of soil respiration.
Preliminary results indicate that soil CO2 efflux showed strong seasonal dynamics and increased along the soil warming gradient throughout the whole year. Heterotrophic respiration was the main source component of soil respiration in this subarctic grassland ecosystem. Interestingly, autotrophic, and heterotrophic respiration increased in response to warming to a similar degree. From our first results, we conclude that medium-term warming leads to soil C losses by higher microbial and root respiration in subarctic grasslands.
Abstract ID 600 | Date: 2022-09-12 13:40 – 13:50 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Nagy, Laszlo (1); Buscardo, Erika (2,3)
1: University of Campinas, Brazil
2: University of Brasília, Brazil
3: University of Coimbra, Portugal
Keywords: Alternative Stable State, Grassland, Fire, Climate, Land Use
Treeless vegetation in mountains is associated either with land use in the montane zone or with climate limitation (temperature at the alpine treeline, or precipitation in dry climates). Removal of grazing in European anthropogenic montane grasslands is usually followed by secondary forest regrowth. In many parts of the world the existence of open grassy-shrublands has been attributed to top-down regulation either by herbivore consumers or by fire, leading to an alternative stable state. In the south-eastern Brazilian mountain range where climatically determined treeline is by far above the elevation of the mountains, there are extensive mosaics of vegetation formed by tropical montane rain forest and open grassy shrubby formation (locally called 'campo'). The various hypotheses proposed regarding their origin and maintenance include fires naturally lit by lightening, climate change (retarded response by trees to colonise open areas since the last maximum [LGM] extension of glaciation), soil (shallow skeletal soil with insufficient water-holding capacity for tree growth) and man-made fires to clear and maintain pastureland. We undertook a landscape-scale modelling of soil water availability to test the hypothesis that shallow soil would store insufficient plant available water to support tree growth. After a recent survey of recent fire history (1984-2020) in the Parque Estadual de Campos do Jordão, we ran a landscape scale water availability model under current mean and minimum annual precipitation years, future IPCC scenarios and LGM and mid-Holocene optimum scenarios. We found that in an average year, there is no month with water shortage in the areas currently occupied by open vegetation. We further discuss to what extent, if at all, the permanence of these 'mountain grasslands' may be attributable to extreme precipitation years.
Abstract ID 380 | Date: 2022-09-12 13:50 – 14:00 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Niu, Yujie (1); Schuchardt, Max (1); Berauer, Bernd (2); Heßberg, Andreas (1); Jentsch, Anke (1)
1: University of Bayreuth, Germany
2: University of Hohenheim, Germany
Keywords: Climate Extreme, Mountain Grasslands, Community Stability, Dominance, Species Gain And Loss
Plant community stability is essential to the predictability and reliability of ecosystem functioning. Understanding the drivers of stability of diversity (hereafter referred to species richness) and productivity (biomass production) in face increasing climate fluctuation has emerged as a pressing issue, especially with the increasing frequency and severity of climatic extremes. However, the effects of climatic extremes on plant communities and the stability mechanisms under climate fluctuation remain poorly understood. Here, we investigate community composition, and species gains and losses in considering dominance, as well as temporal stability of species richness and biomass production of six representative grassland communities (ranging from lowland mesic, montane, subalpine to alpine) along an elevational gradient within the European Alps exposed to the impacts of 2018 summer drought event on Central European. We found that only three out of six grasslands experienced extreme drought and heat during the growing season. Climatic extreme significantly decreased the species richness through higher species losses and lower gains, but did not decrease biomass production compared with the pre-extreme year. For the sites without climatic extreme, there were no significant difference in species richness between 2018 and 2017, but significant differences of biomass production in montane and alpine grasslands were found. The transition between different dominance groups was achieved through the common species, and the direct transition between rare and dominant species was extremely low. Species gains and losses were mainly to and from rare species, however during the community recovery, newly gained species were mainly to common species. The temporal variability of species gains and losses did not influence the stability of different dominance groups, and the stabilities of different dominance groups did not directly influence the stability of biomass production. The stability of biomass production was directly determined by stability of species richness. Furthermore, species richness stability was positively determined by the stability of common species, and negatively determined by the variability of species losses. Our results demonstrated that rarity forecast disproportionate species losses and gains, and the presence of non-dominant species increases plant community stability against increasing climate fluctuations.
Abstract ID 377 | Date: 2022-09-12 14:00 – 14:10 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Laorden-Camacho, Lucía (1); Tello-García, Elena (1); Lyonnard, Blandine (3); Binet, Marie-Noëlle (3); Grigulis, Karl (3); Peintner, Ursula (2); Tappeiner, Ulrike (1); Lavorel, Sandra (3); Leitinger, Georg (1)
1: Department of Ecology, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria
2: Department of Microbiology, University of Innsbruck, Technikerstraße 25d, Innsbruck, 6020 Austria
3: Univ. Grenoble-Alpes, Univ. Savoie Mont Blanc, CNRS, LECA, 38000 Grenoble, France
Keywords: Alpine Ecosystems, Shrub Encroachment, Biogeochemical Cycles, Climate Change, Land-Use Change
Changes in climate and land-use are two key factors for shrub-encroachment in alpine and arctic tundra ecosystems. In the Alps, the trend of abandoned grassland has continued to grow since the 1950s, yet there is poor knowledge of its consequences, specially under future climate change scenarios. Several studies have already pointed out significant differences in ecosystem functioning with shrub-encroachment in sub-alpine grasslands, such as shifts in biogeochemical cycles, microbial communities, and plant-soil stoichiometry. For instance, the presence of shrubs promotes the accumulation of more recalcitrant compounds with lower decomposition rates, leading to lower N-availability and nutrient-poor soils. The morphology of shrubs, which differ from those of forbs and graminoids, can also have an impact on soil moisture through shading. However, there is still a gap in knowledge regarding how these changes play along the succession. We hypothesize that rather than a continuous change, shrub encroachment results in a tipping point in the functioning of ecosystems. The LUCSES project – forecasting impacts of land-use and climate change on ecosystem services from shrub-encroached mountain grassland- is addressing these questions in the French and Austrian Alps. The Austrian site is located in the Stubai valley (1900-2200 m) near Neustift, where we are studying 10 x 10 m plots with different degrees of shrub encroachment in sub-alpine grassland. Samples were collected between the months of June and September 2021. We collected soil samples for biochemical analysis as well as for profiling fungal communities. Our results show lower pH, higher soil water content (SWC), higher soil organic matter (SOM), and higher leave and soil C:N ratios in shrub-encroached plots. Our results also suggest that there is a tipping point in these trends along the shrub-encroachment gradient. Our data suggests that the presence of shrubs alters the biogeochemical cycles of grasslands and therefore may result in lower diversity and important changes in ecosystem functioning, which might possibly have spillovers in the delivery of ecosystem services.
Abstract ID 458 | Date: 2022-09-12 14:10 – 14:20 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Vázquez-Ramírez, Jerónimo; Venn, Susanna E.
Deakin University, Australia
Keywords: Warmer Temperatures, Decrease In Precipitation, Fire, Seed Germination, Seedling Establishment.
Early plant life-history stages, such as germination and seedling establishment, are considered highly vulnerable to climate change and are important to species persistence because they could represent a bottleneck to future recruitment. The strong relationship between the changing climatic factors and these life stages suggests that they will be significantly affected in the future. Here, we present the results of a field manipulative experiment where we looked at how (i) seed maturation, (ii) seed germination and (iii) seedling establishment of ten alpine grassland species (graminoids and forbs) will respond to future warmer temperatures, a decrease in precipitation and more frequent fires. For this, during two snow-free seasons (2020-2021 and 2021-2022), we established a two-factorial experiment at the Australian Alps where our factors were: a future drier and warmer climate and post-fire conditions. We created warmer and drier conditions by using modified open-top chambers that simultaneously increased the soil temperature and reduced the soil moisture. To simulate post-fire conditions, we burnt small patches of vegetation and added smoke water. Then, to determine the effects of our experimental treatments in the studied life stages, we: (i) collected seeds from plants inside the chambers and contrasted their mass, size, viability and cotyledons size and greenness against seeds collected in control plots; (ii) we buried seeds from studied species inside mesh bags and recorded their monthly germination; and (iii) we planted seedlings of studied species and measured their monthly growth and survival. Overall, we find negative and neutral effects of our experimental treatments in the studied life stages. (i) Seeds from plants inside the chambers were significantly lighter and smaller and had smaller and less green cotyledons in almost all species. (ii) The final proportion of germinated seeds was negatively affected by warmer and drier conditions in all species. More importantly, warmer and drier conditions also affected the germination time, where most germination occurred later in the snow-free season compared to control sites. We did not detect any effect of post-fire treatment in seed germination. (iii) Seedling survival and growth were strongly affected by post-fire conditions, where most planted seedlings did not survive. Seedlings were affected less by warmer and drier conditions, but we still recorded more mortality and less growth than control plots. Finally, we discuss some of the potential implications of our findings and their significance to our understanding of future plant recruitment in alpine areas.
Abstract ID 944 | Date: 2022-09-12 14:20 – 14:30 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Sumner, Emma Elizabeth (1); Williamson, Virginia (1); Gleadow, Roslyn (2); Wevill, Tricia (1); Venn, Susanna (1)
1: Deakin University, Australia
2: Monash University, Australia
Keywords: Heatwave, Drought, Stress, Thermal Tolerance
The effects of climate change in the Australian alps are already apparent, with warming temperatures and declining snowfalls. While severe soil moisture deficits can occur during the drier summer months, periods of drought are expected to increase in frequency and severity, as are summer heatwaves. These increasing extreme climate events are of particular concern as it is the extremes, not averages, that determine species distributions. There is no knowledge of heat tolerances amongst Australian alpine plants. Further, the co-occurrence of stress factors (such as heat and drought) is frequently observed in nature, but they are infrequently studied. Indeed, how alpine plants respond to simultaneous abiotic stressors is largely unknown – a major concern, given future climate predictions for the Australian alps. Our objective was to determine the independent and interactive effects of drought and heatwave exposure on thermal tolerance thresholds and recovery within a common Australian alpine grass species. We found that both heat stress exposure and water deficits had an additive effect in driving acclimation of heat tolerance, and that water deficits improved freezing tolerance. Rapid growth following heat and drought treatments indicate a high capacity for acclimation to and recovery from combined abiotic extremes.
Abstract ID 941 | Date: 2022-09-12 14:30 – 14:40 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Zhumanova, Munavar Ortikovna (1); Tomaszewska, Monika A. (1); Henebry, Geoffrey M. (1,2)
1: Center for Global Change and Earth Observation, Michigan State University, East Lansing, MI, USA
2: Department of Geography, Environment, and Spatial Sciences, Michigan State University, East Lansing, MI, USA
Keywords: Resurvey, Homogenization, Mountain Pastures, Degradation, Digital Photo Analysis
The United Nations General Assembly declared 2022 as the International Year of Sustainable Mountain Development based on the proposal of the Kyrgyz Republic. Few studies investigate vegetation changes in montane pastures arising from long-term grazing and environmental changes. Using resurveys and image analysis, we explored the responses of mountain vegetation to management and environmental changes in the Western and Central Tien-Shan to investigate (1) whether the plant communities in six vegetation types (ecozones) had changed over 44 years, (2) whether changes were related to management or ecological causes, and (3) whether used analysis methods enable to acquire environmental changes impacts. Ecological indicator values (EIVs) offer integrated signals of species-environmental relationships at the level of communities and vital information about long-term changes in environmental conditions at the site. As a complementary method in 2021, we took 102 near-nadir digital photographs at 47 sites along with a pair of 100 m orthogonal transects. Based on historic vegetation data (1973–1987), six ecozones were resurveyed annually from 2008 to 2021 and connected with species' management-related traits and EIVs. Overall, homogenization of vegetation within and among ecozones was observed. Mountain steppe, meadow-steppe, and subalpine meadows showed the strongest convergence towards dominance of mesic shrubs, related to increasing precipitation changing soil moisture, and soil-salt regimes. In high mountain steppe and alpine ecozones, cushion dwarf shrubs increased, driven by increased soil moisture following faster snowmelt. Changes in the semidesert were related to highly variable spring soil moisture. Compositional changes accelerated over time. We identified six types of pasture degradation and their inter-linkages to illustrate how semiarid landscapes undergoing vegetation transitions may function in future climatic conditions under unchanged grazing practices. Analysis of digital photos enables us to glimpse hidden stages of vegetation change. Image-based data collection and analysis is less biased, making permanent resource records available for reanalysis when data are questioned or when management objectives change.
Abstract ID 663 | Date: 2022-09-12 14:40 – 14:50 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Gaudard, Joseph (1,2); Töpper, Joachim P. (1,3); Halbritter, Aud H. (1); Vandvik, Vigdis (1)
1: University of Bergen, Norway
2: Bjerknes Centre for Climate Research, Norway
3: Norwegian Institute for Nature Research, Norway
Keywords: Carbon, Grazing, Nitrogen, Grassland
Mountain areas provide important habitats for many plant and animal species, but they also contribute with important ecosystem functions and services such as carbon storage or areas for livestock grazing. At the same time, mountain ecosystems are particularly vulnerable to climate change.
Climate warming, nitrogen deposition and grazing are important global change drivers with impacts on carbon cycling. Warmer temperatures might both increase soil decomposition and plant productivity. The impact on carbon storage will then depend on which of those is the strongest. Nitrogen deposition might mostly impact plant productivity, eventually increasing carbon storage, but with a negative impact on biodiversity. Grazing reduces biomass, but also increases the nutrient input in ecosystems which also increases plant productivity. The intensity of grazing is however important for how grazing affects carbon storage, a too strong grazing pressure affecting negatively plant productivity.
Climate change, nitrogen deposition and grazing pressure operate simultanously in nature. In order to understand their impacts on carbon fluxes, we need to investigate their relative effects and interactions together.
We designed a field experiment in south west Norway to investigate those complex interactions. In a full-factorial design, alpine plant communities were exposed to (i) a warmer climate by transplanting turfs to a lower elevation (~400m, corresponding to a 3°C temperature increase), different (ii) grazing pressures (grazing exclusion, one clipping per year, two clippings per year, and natural grazing), and (iii) nitrogen deposition concentrations (0, 0.5, 1, 5, 10, 50, 100, 150 kg N/ha/yr). Carbon fluxes were measured four times during the growing season using a closed loop chamber system. Both gross ecosystem production and ecosystem respiration were measured, and, in some of the plots, soil respiration was also measured.
Data on decomposition rate, vegetation analysis and biomass are also being collected.
We hypothesized that medium grazing level could mitigate the loss of carbon storage by stimulating plant productivity without damaging the ecosystem, while also mitigating the effects of nitrogen deposition on biodiversity.
Our preliminary results show that gross ecosystem production was not affected by warming, while ecosystem respiration increased. At the current point of the study, no strong effect on carbon fluxes from grazing and nitrogen deposition were detected, suggesting that warming is the main driver. However, taking into account soil respiration and decomposition rate data might provide more insights on that matter.
Abstract ID 639 | Date: 2022-09-12 14:50 – 15:00 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Lyonnard, Blandine (1); Hert, Laura (1); Binet, Marie-Noëlle (1); Colace, Marie-Pascale (1); Perigon, Sophie (1); Grigulis, Karl (1); Arnoldi, Cindy (1); Laporte, Frederic (1); Laorden-Camacho, Lucía (2); Tello-Garcia, Elena (2); Leitinger, Georg (2); Mouhamadou, Bello (1); Lavorel, Sandra (1)
1: Univ. Grenoble-Alpes, Univ. Savoie Mont Blanc, CNRS, LECA, 38000 Grenoble, France
2: Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
Keywords: Soil Fungal Ecology, Soil Microbial Activity, Mycorrhizae, Subalpine Grasslands, Shrub Encroachment
In the subalpine belt of many mountain areas, mowing and domestic grazing have contributed to maintaining semi-natural, anthropogenic grasslands. These grasslands have multiple benefits to biota and human societies. They store large amounts of carbon, host a rich biodiversity, provide nutritionally rich resources for herbivores, and contribute to a mosaic of ecosystems which together enhance the resilience of mountain areas to various disturbances. Changes in agropastoral systems in the past decades in Europe – i.e. cessation of mowing, extensification of grazing of less productive or accessible pastures and abandonment – have led to the initiation of secondary successions with shrub encroachment.
The modifications in plant community composition induced by shrub encroachment have been shown to impact soil properties and biogeochemical cycling. Previous studies have shown that the carbon to nitrogen ratio increases with shrub encroachment while nitrogen availability generally decreases. Microbial community composition was also impacted in different ways depending on colonising shrub species. However, a clear understanding of the mechanisms involved and of the specific role of saprotrophic and mycorrhizal fungi in those processes is still lacking.
The LUCSES project – forecasting impacts of land-use and climate change on ecosystem services from shrub-encroached mountain grassland – aims to fill these knowledge gaps, with study sites in the French and Austrian Alps. In the French Alps, we investigate changes following shrub expansion, across plots selected along gradients of encroachment by various deciduous and evergreen shrubs, from pure grassland to approximately 80% shrub cover. To observe the local effects of shrubs on fungal communities and their activities, we sampled soil and plant roots directly underneath shrubs and underneath herbaceous vegetation within each plot. We quantified potential lignin-modifying enzymatic activity and assessed saprotrophic and mycorrhizal fungal community composition using DNA metabarcoding. We also measured community-level variables in each plot, such as plant functional traits, soil properties, nutrient availability, and potential functional enzymatic activity, hypothesised to influence fungal communities.
Our results highlight potential tipping points in ecosystem functioning following shrub encroachment in subalpine grasslands and its linear effects on plant and soil parameters, and the specific role of saprotrophic and mycorrhizal fungi in the underpinning mechanisms.
Abstract ID 181 | Date: 2022-09-12 15:00 – 15:10 | Type: Oral Presentation | Place: THEOLOGIE – Madonnensaal |
Clark, Vincent Ralph (1); Dlomu, Muxe Gladmond (1); Le Roux, Peter Christiaan (2); Toucher, Michele Lynn (3)
1: Afromontane Research Unit & Department of Geography, University of the Free State: QwaQwa Campus, Phuthaditjhaba, South Africa
2: South African Environmental Observation Network, Grassland, Forest & Wetland Node, Pietermaritzburg, South Africa
3: Department of Plant & Soil Science, University of Pretoria, Hatfield, South Africa
Keywords: Leucosidea Sericea, Species Diversity, Maloti-Drakensberg, Bush Encroachment, Grassland
Globally, there is a trend of indigenous woody species converting grassland systems into woody systems through the process of bush encroachment. Along southern Africa's eastern Great Escarpment, there is a potential for the endemic shrub/small tree Leucosidea sericea (L. sericea) (Cheche (Sotho), Umtshitshi (Zulu), Ouhout (Afrikaans), and Oldwood (English)) to dominate biodiversity-rich mesic montane grassland, impacting negatively on water production, grassland conservation, and rangeland-based livelihoods. The aim of the study was to determine the impact of L. sericea on plant diversity in the Maloti-Drakensberg (MD). We hypothesise that L. sericea encroachment replaces rich grassland diversity with depauperate proto-forest diversity. Vegetation sampling was conducted at three sites in the MD: Cathedral Peak Research Catchments (Catchment IX) (CPK), Golden Gate Highlands National Park (GGHNP), and Witsieshoek (Batlokwa Tribal Authority) (WB), during mid-summer (December 2020–January 2021) and in late-summer (March–April 2021). At each site, the number of species, the number of individuals per species, and percent coverage per species were recorded in 30 paired 1 x 1 m quadrats, one set in L. sericea thickets, and one set in adjacent grassland. Plots in each pair were placed 3 m apart, and pairs were separated by 10 m. The effect of L. sericea on species composition and species diversity was analysed using non-metric multidimensional scaling and t-tests comparing Shannon diversity indices, respectively. The species composition in CPK (p=0.001) and WB (p=0.004) was significantly, albeit weakly (r2 <10%, PERMANOVA), affected by the occurrence of L. sericea, which may be due to old mature L. sericea riparian forest supporting a greater proportion of shade-tolerant and nutrient-demanding species. There was no significant difference in species diversity in CPK (p=0.27) and GGHNP (p=0.98) between L. sericea and grassland plots. However, there was a statistical difference in species diversity in L. sericea plots in WB (p=0.04). This suggests that L. sericea encroachment does not have an overall negative impact on plant diversity. However, the type of species occurring in these sites may be impacted by L. sericea encroachment, and therefore a comparison of the threat status of the species associated with Leucosidea or open grassland habitats may still provide additional insights into the conservation implications of woody encroachment in this system.