Forest Regeneration Research of the Hovsgol Region
Mookhor Khishigjargal and Chultem Dugarjav
Northern Mongolian forest represents part of the southern boundary of the Siberian Taiga forest. The dominant tree is the Siberian larch (Larix sibirica), composing 90 to 95% of the forest, and at Hovsgol, the larch covers ridge tops and north-facing Mountain slopes. Therefore, the research of supporting and limiting factors on forest regeneration is very important. Although the forest regeneration rate is varies under different ecological conditions the most important factors are seed source rate, weather conditions, and seed bed conditions. The forest regeneration study usually covers a long time period (at least up to 20 years) and includes some stages of immature and mature tree growth (from seed germination to the mature growing trees). During the summers of 2002-2005, Hövsgöl field research, we concentrated our studies on seed source rates, saplings growing rates, and germination by considering and observing convenient growing conditions and forest regeneration rate within the project study site including experimental work and some forest ecotone research to define future forest expansion trends.
Relevant data were collected with a random sample design method in plots that were selected along line transects in the forests of the Hővsgől study valleys. A total of 72 plots and 216 sub-plots were sampled along the 4520 m transect line from the forest edge area to the top of the mountains in each valley. The data of seed source was collected cones from seed tree in each year by randomly in order to seed counting per cone. The seed germination, seedlings growing conditions and some seed predation impact on the seed emergency research based on the experiment that was various number seed planting in the enclosure and open site with enough replications for two years.
The forest ecotone research started from 2005 used random sample design method in plots that were selected in each zone which are forest, forest edge and steppe in the four valleys’s forest ecotone zone. A total of 120 plots, 360 sub plots sites along the transect lines. All data collected were processed by statistical analysis using one-way ANOVA and correlation using JMP IN, Sigma plot and Systat software.
During the survey, it was determined that there are several main environmental conditions available for seed growing in larch forests in the region and the most appropriate growing condition for seedlings is the moss covered areas. The main factor of seed growing rate in the dominant soil cover appears to be soil moisture content. The maximum soil moisture content is found in the moss covered forest soil.
The pilot study on larch regeneration has shown that after seeds have fallen to the ground, seed predators have strong negative impacts on the forest regeneration cycle and 84%-95% of the soil seed bank was removed by small mammals. The main seed predators are small rodents, which include Clethrionomus rufocanus. The experiment results of open and enclosure treatments have shown that 30% of seed germination rate was decreased by small mammal consumption in the open treatment. The significant difference of survived seed number in the enclosed site (p < 0.001) and defected seed number in open treatment (p < 0.007), investigated based on the seed counting data and analysis. Survived seedlings rate depends on various seed density that is number seed per square site, for 2004-2005.
As a result, the seed source was identified in varous amounts in each valley and years (no seed sourse rate in 2002, moderate in 2003, poor in 2004, moderate in 2005). It was identified that the seed source was depended on the distribution of seed insects. Main seed predator of cone is the larch fly, L. laricicola Karl.
During the survey, it represents that 24% of total trees is cone rich trees, 20% is cone poor trees and 56 % is no cone trees. The results of seed counting used seed traps in forest edge area shows 83.4% of total distributed seed was distributed within 20 m from forest, 14% was distributed within 20-30 m and 1-2% was distributed within 80-90 m from forest edge.
The selected six valleys significantly differ in their larch forest regeneration rate (p<0.01). The main criteria for forest regeneration is survival of saplings and young trees. Most of saplings’ heights are less than one meter. The average number of 5-20 year old saplings (10- 150 cm height) per hectare is 440. (This is the average number of saplings for the valleys). The results of seedlings and young trees that is 2-5 year old, 0-10 cm height, number per hectare was recorded 4200- 12500 in the Borsog, Dalbay and Shagnuul these valley’s growing capacity is enough for next generation. The lowest number was recorded about 1500 in Noyon, Turag, Sevsuul valleys. These results show that current saplings’ growing capacity is not enough for forest regeneration.
The initial result of forest ecotone study has shown that the forest expansion trend of northern valleys, that have heavy grazing impacted area, is decreasing and southern valley’s forest expansion trend is increasing according to the results on plant community, plant biomass, LAI – leaf area index, seedlings’ counting and other researches.