Vegetation Characteristics And Its Responses To Water Condition In Liupan Mts

In Northwest China, vegetation restoration is an essential approach to ecological environment improving, and soil and water conservation. It is the basis of vegetation restoration to learn the structure, spatial distribution of vegetation, and its relationship with soil water condition in this area. In this study, the structure, spatial distribution and its growth of main vegetation types was analyzed by data of forest resources inventory held in 2005 and measured data on plots in Liupan Mts. The results showed that as following:1. Main forest types and their distributionIn Liupan Mts., forest cover ratio reached to 72.8% in 2005. The natural secondary forests, which was mainly consisted with Quercus liaotungersis, Betula albo-sinensis, Betula platyphlla, Betula utilis, Salix cathayana, Populus davidiana, accounts for 68.7% of all forests of Liupan Mts.. Larix principris-upprechtii plantation is mainly artificial forest type, which amounts to 31.3% of forests in Liupan Mts.. The ordination of important value of key tree species in Liupan Mts. was that as following: Salix cathayana (54) >Quercus liaotungersis (44.6) > Betula spp. (44.3) > Larix principris-upprechtii (41.5) > Populus davidiana (36.1).Quercus liaotungersis forest mainly distributed the sites with the elevation of 1840～2420 m, the aspects of shady slope, half shady slope and sunny slope. It usually distributed in steep slopes such that 96.4% of Quercus liaotungersis forest locates on slope with degree of more than 15. In Quercus liaotungersis forest, soil is thick compared to that of other forest types. For example, the area with soil thickness of 30-60cm accounts 78.6% of all Quercus liaotungersis forest. But humus and litter of Quercus liaotungersis forest is less than that of other forest types. 75% of Quercus liaotungersis forest is with soil humus of less than 10 cm as well as 64.3% of Quercus liaotungersis forest is with litter layer of less than 5 cm.Birch forests (Betula. albo-sinensi, Betula platyphlla, and Betula Utilis) inhabited in sites with the elevation of 1780～2840m, any aspects from sunny slope to shady slope with the degree of more than 15°. As the pioneer forest of succession, Populus davidiana forest distributes the slopes with the elevation of 2340～2690m, the aspects of half shady slope(41.7%), sunny slope(33.3%), and semi-sunny slope(25%). Larix principris-upprechtii plantation was planeted on the lower parts of slopes with the elevation of 1740～2700m%.2. The Structure of main forest typesQuercus liaotungersis forest is with the density of 1204 trees/hm2 and DBH of 11.9cm in average. DBH and tree height of Quercus liaotungersis Forest increases according to elevation increase. Quercus liaotungersi is only constructive species of Quercus liaotungersis Forest, which is associated with Populus davidiana, Betula albo-sinensis, Betula platyphlla, Betula utilis, and Tilia panciostata. In Quercus liaotungersis Forest, the shrub is fully developed with cover ratio of more than 50%. Otherwise, its herb layer does not well grow with low cover ratio.Compared with Quercus liaotungersis forest, Birch forest has low density as 756 trees/hm2. But it DBH is 12.2cm in average, which is similar to that of Quercus liaotungersis forest. But its mean DBH keeps stable according to elevation increase. Mean tree height increased with elevation increase like that of Quercus liaotungersis forest. The density of Populus davidiana forest is 900 trees/hm2 in average and mean DBH is 11.1 cm. This showed that all secondary natural forests are young.Larix principris-upprechtii plantation is also young with mean density of 627 trees/hm2 and mean DBH of 9.9 cm. In Larix principris-upprechtii plantation, he shrub and herb does not well grow such that 93.3 of Larix principris-upprechtii plantation is with shrub and herb cover ratio of less than 50%. Additionally, there is little seedling in Larix principris-upprechtii plantation. This remind us Larix principris-upprechtii plantation would hardly, naturally renew.3. the ralationship between plant growth and soil water conditions1) Larix principris-upprechtii: The growth rate of Larix principris-upprechtii is close related to soil water conditions. When the soil water content is more, Larix principris-upprechtii grows more rapid. For example, lateral branch has grown the length of 8.8 cm from May to Sep. on the upper part of slope with mean soil water content of 23.2% in weight but it is only 4.7cm in the middle part of slope with mean soil water concent of 20.3%. Although forest density impacts soil water availability to each tree, the rate of tree growth of first year after thinned is related to forest density before thinned rather than that after thinned.2) shrub: The structure of shrub community strongly impact on the plant growth. For example, the lateral branch of Larix principris-upprechtii in shrub plot No. 2 with Larix principris-upprechtii (28%) grow more rapid than that in shrub plot No.1 with Larix principris-upprechtii (2%). But the soil mositure in plot No. 2 decreased faster than that in Plot No. 1 due to more evapotranspiration in Plot No. 2.3) grassland on sunny slope: The average of soil moisture and its fluctuation together influences herb growth of grassland on sunny slope due to soil water limitation. Herbs in the middle part of slope with moderate fluctuation of soil moisture grew best with largest height and coverage of grass. When the grassland was watered, the herb growth would improved. But In different part of growing season, the response of herb growth is different. At the beginning of growing season, the herb grew better with large height and coverage of grass under waterring of 15mm/10day than that under watering of 5mm/10days and 10mm/10days. But the second part of growing season, herb growth was not significantly related to the volume of water added. When same volume of water was added in grassland, the herb grew better under watering of 10mm/5days than that under watering of 20mm/10days and 30mm/15days during the beginning of growing season. Since more times of watering with a little water will provides more aviliable soil water for herb. But at the second part of growing season, the herb grew better under the watering of 20mm/10days.