Taiga forest and steppe grassland form distinct alternating bands in the valleys of northern Mongolia. Taiga forest, which consists almost exclusively of Siberian larch (Larix sibirica), occurs on north-facing slopes and steppe grassland occurs on south-facing slopes. The ecotone between forest and grassland on the ridge between north and south facing slopes is sharp, and this pattern is extensive throughout northern Mongolia, yet no data on the ridge-top ecotones in this region exist.

We characterized this ecotone using transects in summer 2009. Data were collected along 24 transects that ran north-south near the peak of the south-facing slope in Dalbay Valley along the east coast of Lake Hövsgöl in northern Mongolia [51°01'36.54"N, 100°45'54.23"E]. Each transect began at singleton trees clearly outside the forest and extended up to 100 m into the forest. Diameter at breast height (DBH), distance to nearest neighbor, and nearest neighbor’s DBH were measured for all trees within 0.5 m of each side of the transect line. 

Results/Conclusions

Our results suggest that the first two trees in each transect (T1 and T2) are definitively located within the ecotone rather than in taiga or steppe. By viewing the data for NN and DBH centered on the third tree in each transect (T3), it can be seen that beyond T3 the distributions of these variables become noticeably regular. For DBH of T1-T2, the mean is 19.01 cm and standard deviation is 18.94 cm, while for DBH of T4-T12, the mean is 20.25 cm and the standard deviation is 14.06 cm. For NN of T1-T2, the mean is 4.13 m and standard deviation is 3.91 m, while for NN of T4-T12, the mean is 1.43 m and standard deviation is 0.91 m. T3 can be used to approximate where the ecotone ends and the forest begins. Our results also indicate that T1 differed the most from the rest of the counted trees in terms of all variables measured. 

It is currently unclear whether this ecotone exists primarily due to natural phenomena or to what extent it is affected by local-scale anthropogenic effects of grazing by domestic animals and the cutting of trees by nomadic herders. Understanding this transition from steppe grassland to taiga forest is relevant because this region is undergoing environmental changes due to global climate change that may affect the position and character of this ecotone.