Interrelations between relief, vegetation, disturbances, and permafrost in the forest‐steppe of central Mongolia

Abstract. The central Mongolian forest-steppe is a sensitive ecotone, commonly affected by disturbances such as logging and forest fires. In addition, intensified drought events aggravate stress on the trees that are anyway at their drier limit in the forest-steppe. Climate change increases evapotranspiration and reduces the distribution of discontinuous permafrost. The motivation for this study came about through our previous observation that forest stands show great differences with respect to their recovery after disturbance by fire or logging. Sometimes, no regrowth of trees takes place at all. As water availability is the main limiting factor of forest growth in this region, we hypothesized that differences in hydrological soil properties control the forest-recovery pattern. To test this hypothesis, we analysed soil properties under forests, predominantly consisting of Siberian larch (Larix sibirica Ledeb.), in the forest-steppe of the northern Khangai Mountains in central Mongolia. We distinguished four vegetation categories: 1. near-natural forest (FOR), 2. steppe close to the forest (STE), 3. disturbed forest with regrowth of trees (DWIR), and 4. disturbed forest showing no regrowth of trees (DNOR). 54 soil profiles were described in the field and sampled for soil chemical, physical, and hydrological analysis. We found a significant difference in soil texture between soils under DWIR and DNOR. Sand generally dominated the soil texture, but soils under DWIR had more silt and clay compared to soils under DNOR. Soil pF curves showed that soils under DWIR had higher plant-available field capacity than soils under DNOR. In addition, hydraulic conductivity was higher in the uppermost horizons of soils under DWIR compared to soils under DNOR. Chemical properties of the soils under DWIR and DNOR showed no significant differences. We conclude that the differences in post-disturbance tree regrowth are mainly caused by soil hydrological properties. High plant-available field capacity is the key factor for forest recovery under semi-arid conditions. High hydraulic conductivity in the uppermost soil horizons can further support tree regrowth, because it reduces evaporation loss and competition of larch saplings with grasses and herbs for water. Another important factor is human impact, particularly grazing on cleared forest sites, which often keeps seedlings from growing and thus inhibits forest recovery. Permafrost was absent at all studied disturbed sites (DWIR, DNOR). We thus conclude that it is not a major factor for the post-disturbance tree-regrowth pattern, although it does contribute to water availability in summer.

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Geoecological parameters indicate discrepancies between potential and actual forest area in the forest-steppe of Central Mongolia

Forest Ecosystems ◽

10.1186/s40663-021-00333-9 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Michael Klinge ◽

Choimaa Dulamsuren ◽

Florian Schneider ◽

Stefan Erasmi ◽

Uudus Bayarsaikhan ◽

...

Keyword(s):

Forest Fires ◽

Forest Area ◽

Mean Annual Precipitation ◽

Forest Steppe ◽

Forest Stands ◽

Tree Biomass ◽

Living Tree ◽

Central Mongolia ◽

Forest Distribution ◽

Topographic Parameters

Abstract Background Forest distribution in the forest-steppe of Mongolia depends on relief, permafrost, and climate, and is highly sensitive to climate change and anthropogenic disturbance. Forest fires and logging decreased the forest area in the forest-steppe of Mongolia. The intention of this study was to identify the geoecological parameters that control forest distribution and living-tree biomass in this semi-arid environment. Based on these parameters, we aimed to delineate the area that forest might potentially occupy and to analyse the spatial patterns of actual and potential tree biomass. Methods We used a combination of various geographic methods in conjunction with statistical analyses to identify the key parameters controlling forest distribution. In several field campaigns, we mapped tree biomass and ecological parameters in a study area within the Tarvagatai Nuruu National Park (central Mongolia). Forest areas, topographic parameters and vegetation indices were obtained from remote sensing data. Significant correlations between forest distribution and living-tree biomass on one hand, and topographic parameters, climate data, and environmental conditions on the other hand, were used to delineate the area of potential forest distribution and to estimate total living-tree biomass for this area. Results Presence of forest on slopes was controlled by the factors elevation, aspect, slope, mean annual precipitation, and mean growing-season temperature. Combining these factors allowed for estimation of potential forest area but was less suitable for tree-biomass delineation. No significant differences in mean living-tree biomass existed between sites exposed to different local conditions with respect to forest fire, exploitation, and soil properties. Tree biomass was reduced at forest edges (defined as 30 m wide belt), in small fragmented and in large forest stands. Tree biomass in the study area was 20 × 109 g (1,086 km2 forest area), whereas the potential tree biomass would reach up to 65 × 109 g (> 3168 km2). Conclusions The obtained projection suggests that the potential forest area and tree biomass under the present climatic and geoecological conditions is three times that of the present forest area and biomass. Forest fires, which mostly affected large forest stands in the upper mountains, destroyed 43% of the forest area and 45% of the living-tree biomass in the study area over the period 1986–2017.

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Modelled potential forest area in the forest-steppe of central Mongolia is about three times of actual forest area

10.5194/bg-2020-13 ◽

2020 ◽

Author(s):

Michael Klinge ◽

Choimaa Dulamsuren ◽

Florian Schneider ◽

Stefan Erasmi ◽

Markus Hauck ◽

...

Keyword(s):

Vegetation Index ◽

Arid Environment ◽

Forest Area ◽

Forest Steppe ◽

Forest Edges ◽

Climate Data ◽

Forest Stands ◽

Tree Biomass ◽

Central Mongolia ◽

The Mean

Abstract. The Mongolian forest-steppe is highly sensitive to climate change and environmental impact. The intention of this study was to identify, which geoecological parameters control forest distribution and tree growth in this semi-arid environment, and to evaluate the actual and potential tree biomass. For this purpose, we applied a combination of tree biomass and soil mapping, remote sensing and climate data analysis to a study area in the northern Khangai Mountains, central Mongolia. Forests of different landscape units and site conditions generally showed minor differences in tree biomass. We found no significant correlation between tree biomass and NDVI (normalized differentiated vegetation index). Tree biomass was reduced at forest edges, in small fragmented forest stands of the steppe-dominated area, and in large forest stands, compared to all other forest units. The tree biomass of forests on slopes ranged between 25 and 380 Mg ha−1. The mean tree biomass in forests of 10–500 ha was 199–220 Mg ha−1, whereby tree biomass at the forest edges was 50–63 Mg ha−1 less than in the interior parts of the forests. The mean tree biomass of forests > 500 ha was 182 Mg ha−1, whereas that of forests

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Hydrological soil properties control tree regrowth after forest disturbance in the forest steppe of central Mongolia

SOIL ◽

10.5194/soil-7-563-2021 ◽

2021 ◽

Vol 7 (2) ◽

pp. 563-584

Author(s):

Florian Schneider ◽

Michael Klinge ◽

Jannik Brodthuhn ◽

Tino Peplau ◽

Daniela Sauer

Keyword(s):

Hydraulic Conductivity ◽

Soil Properties ◽

Soil Texture ◽

Field Capacity ◽

Forest Growth ◽

Forest Recovery ◽

Forest Steppe ◽

Soil Hydrology ◽

Central Mongolia ◽

Disturbed Forest

Abstract. The central Mongolian forest steppe forms a transition between different ecozones and is as such particularly sensitive to environmental changes. It is commonly affected by disturbances such as logging and forest fires. Intensified drought events aggravate stress on the trees that are anyway at their drier limit in the forest steppe. Climate change increases evapotranspiration and reduces the distribution of discontinuous permafrost, which leads to drier soil conditions. The motivation for this study came about through our previous observation that forest stands show great differences with respect to their recovery after disturbance by fire or logging. Sometimes, no regrowth of trees takes place at all. As water availability is the main limiting factor of forest growth in this region, we hypothesised that differences in soil hydrology control the forest recovery pattern. To test this hypothesis, we analysed soil properties under forests, predominantly consisting of Siberian larch (Larix sibirica Ledeb.), in the forest steppe of the northern Khangai Mountains, central Mongolia. We distinguished the following four vegetation categories: (1) near-natural forest (FOR), (2) steppe close to the forest (STE), (3) disturbed forest with regrowth of trees (DWIR), and (4) disturbed forest showing no regrowth of trees (DNOR). A total of 54 soil profiles were described in the field and sampled for soil chemical, physical, and hydrological analysis. We found a significant difference in soil texture between soils under DWIR and DNOR. Sand generally dominated the soil texture, but soils under DWIR had more silt and clay compared to soils under DNOR. Soil pF curves showed that soils under DWIR had higher plant-available field capacity in their uppermost parts than soils under DNOR. In addition, hydraulic conductivity tended to be higher in the uppermost horizons of soils under DWIR compared to their counterparts under DNOR. Chemical properties of the soils under DWIR and DNOR showed no significant differences. We conclude that the differences in post-disturbance tree regrowth are mainly caused by different soil hydrology. High plant-available field capacity is the key factor for forest recovery under semi-arid conditions. High hydraulic conductivity in the uppermost soil horizons can further support tree regrowth because it reduces the evaporation loss and the competition of larch saplings with grasses and herbs for water. Another important factor is human impact, particularly grazing livestock on cleared forest sites, which often keeps seedlings from growing and, thus, inhibits forest recovery. None of the disturbed sites (DWIR and DNOR) had permafrost. We, thus, conclude that permafrost is no major factor for the post-disturbance tree regrowth pattern, although it generally supports tree growth in the forest steppe by preventing meltwater from seasonal ice from seeping below the root zone, thus increasing the water supply in summer.

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Merging Indigenous Knowledge Systems and Station Observations to Estimate the Uncertainty of Precipitation Change in Central Mongolia

Hydrology ◽

10.3390/hydrology5030046 ◽

2018 ◽

Vol 5 (3) ◽

pp. 46 ◽

Cited By ~ 5

Author(s):

Steven Fassnacht ◽

Arren Allegretti ◽

Niah Venable ◽

María Fernández-Giménez ◽

Sukh Tumenjargal ◽

...

Keyword(s):

Meteorological Data ◽

Rate Of Change ◽

Forest Steppe ◽

Rain Intensity ◽

Robust Estimate ◽

Central Mongolia ◽

Climate Change Uncertainty ◽

Consensus Score ◽

Indigenous Knowledge Systems ◽

The Mean

Across the globe, station-based meteorological data are analyzed to estimate the rate of change in precipitation. However, in sparsely populated regions, like Mongolia, stations are few and far between, leaving significant gaps in station-derived precipitation patterns across space and over time. We combined station data with the observations of herders, who live on the land and observe nature and its changes across the landscape. Station-based trends were computed with the Mann–Kendall significance and Theil–Sen rate of change tests. We surveyed herders about their observations of changes in rain and snowfall amounts, rain intensity, and days with snow, using a closed-ended questionnaire and also recorded their qualitative observations. Herder responses were summarized using the Potential for Conflict Index (PCI2), which computes the mean herder responses and their consensus. For one set of stations in the same forest steppe ecosystem, precipitation trends were similar and decreasing, and the herder-based PCI2 consensus score matched differences between stations. For the other station set, trends were less consistent and the PCI2 consensus did not match well, since the stations had different climates and ecologies. Herder and station-based uncertainties were more consistent for the snow variables than the rain variables. The combination of both data sources produced a robust estimate of climate change uncertainty.

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