Study On Process Of Burned Areas Forest Natural Restoration In Daxinganling

By using the methods of time instead of space,researched on the variation about forest soil physical and chemical properties,growth and regeneration of tress,the state of plants restoration in the burned areas which burned after at least 25 years from Betula platyhpylla -larix gmilini in Da Xing'an ling area.The results showed that:soil bulk density increased after burned 1 year,soil porosity and soil water content reduced after combustion.But the rate of variation with the time would gradually reduce and eventually be close to the level of unburned until the 12^th year;Soil organic matter in the upper and lower(soil genetic layers) layer between the first year and the 12^th year after burning had a descending trend,as the time going on,soil organic matter in the upper would gradually decrease the falling range,until the 20^th year after burning soil organic matter variation increased over the level of unburned.The variation of soil total nitrogen and soil total phosphorous between the first year and the 12^th year after burning increased first,as the time going on,the range was getting small,even was below the level of unburned.The variation of soil effective phosphorous decreased first and it increased later.The variation of soil available potassium in upper layer was irregular,but in the lower layer,it increased first and fell later.The variation of soil hydrolysis nitrogen in upper layer decreased in waves,but in the lower layer,the variation was similar to the one of soil available potassium.Growth and regeneration of trees had been changed after burning.Burned after past year and 4^th year,mean height and mean DBH of Larix gmilini in burned area had beyond the level of unburned,the variation of mean height and mean DBH was accordance basically;Burned after past year and 4^th year,mean height and mean DBH of Betula platyphylla in burned area had beyond the level of unburned during 12^th to 25^th after burning, but both mean height and mean DBH of Betula platyphylla had been lower than the level of unburned;Mean height and mean DBH of Populus davidiana had been always lower than the level of unburned;Variation of valid regeneration frequency of Larix gmilini and Populus davidiana in burned area wasn't significant with unburned area,however,variation of valid regeneration frequency of Betula platyphylla in burned area was significant with unburned area. During 5^th to 20^th year after burning,the forest composition of Larix gmilini had decreased.But at 25^th year after burning,valid regeneration amount of Larix gmilini had rose.Species diversity changed obviously with the time elapsed after burning in burned area.Species diversity index of different layers would fall first with restoring time elapsed after burning, then it rose up in short period but the rate of falling would stop and be stable;Species richness of arbor layer and shrub layer had the same trend after burning in burned area.The rate of change on both shrub layer and arbor layer was less,but the rate of change on herbage layer was large in the beginning of restoration,then it fell and kept stable.At 17^th year after burning it still went down again.In the beginning of restoration after burning,the community structure was simple.Betula platyphylla was dominant in the beginning of restoration;however,Larix gmilini would be a dominant population to seize the arbor layer again after about 20 years. Community structure was diverse before 20^th year after burning,but it would be suffered by shade tolerant plants from shrub layer and herbage layer after 20^th year.In the end of restoration,community structure would be simplexes.Through research of soil agents,the state of natural regeneration of trees,the species diversity and community dynamic,it will be important to the project of forest natural regeneration after burning with artificial aid.It will improve the forest ecology system restoration project.