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

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 < 10 ha in the steppe-dominated area was only around 142 Mg ha⁻¹. Forests in alluvial plains had maximum tree biomasses of 440–688 Mg ha⁻¹. In contrast to tree biomass, the spatial extension of forests showed distinct relationships with topographic and climatic parameters. Presence of forest was controlled by elevation (< 2600 m a.s.l.), aspect (no southern slopes below 2100 m a.s.l.), slope (< 25°), mean annual precipitation (160–340 mm) and mean growing season temperature (6.5–10.8 °C).

The actual forests of the study area covered 1,086 km². In 1986, prior to extensive forest fires, it was 1,898 km². The actual tree biomass of 20 × 109 g represented 57 % of that in 1986. Modelling of the potential forest area resulted in 3,552 km², with 65 × 109 g tree biomass (based on topographic parameters) and 3,113 km² with 58 × 109 g tree biomass (based on climatic parameters), respectively. The modelled potential forest area was thus about three times the actual forest area.