Effects Of Fire Severity On Forest Communities In The Northern Great Xing'an Mountains

The effects of fire severity on the the forest commuity of Larix gmelinii, L. gmelini- Betula platyphylla, Pinus svlvestris-L. gmelini were studied in this thesis. Based on the vegetation analysis in different layers of trees, under-canopy and herbs layers in the three communities under the different fire severity, the results showed that the Larix gmelinii and Pinus svlvestris dbh (diameter at breast height) -class distribution followed the model of one peak in all plots, while the Betula platyphylla followed negative-exponential model; the peak value increased and the smaller dbh-classes missed with the fire severity; in all three communities the tree layers which were divided into five stratum in the unburned plots and lost the lowest one by the fire; in the Larix gmelini- Betula platyphylla community the importance value of the Larix gmelinii increased while the Betula platyphylla decreased; in the Pinus svlvestris-Larix gmelini community the importance value of the Pinus svlvestris increased while the Larix gmelini decreased.The diversity and evenness indexes of the under-canopy in all three communities showed a rise-fall pattern. In the under-canopy layers the diversity indexes of the vegetation reached at the peak value under low-medium severity and then fell slowly but all of indexes were higher than those in undisturbed areas. The richness indexes followed the same pattern but the indexes in the intensive plots were lower then the ones in the unburned in the Pinus svlvestris-Larix gmelini community and Larix gmelini community.The trend of three indexes observed in the herb layers was just reverse to those in the under-canopy layer: the lowest value appeared at the low-medium severity plots.Juveniles of Larix gmelini and Pinus svlvestris always appeared in the low, low-medium and medium-intensive severity plots, no one in the intensive severity plots; in the unburned plots there were juveniles in the Larix gmelini community.