The Characteristics Of The Understory Vegetation And Soil C,N,P Of Chinese Fir Plantation Under Burning Afforestation Conditions In The Central Subtropical Region, China

Chinese fir plantation is the special and fast growing tree of southern subtropical region, which has a long cultivation history. Maintaining a long-term productivity of Chinese fir plantation ecosystem is one of the hot issues in today’s ecology field. Controlled burning is one of the most common afforesting methods of Chinese fir plantation in southern China. The influences of the controlled burning on Chinese fir plantation ecosystem, especially on the understory vegetation and soil physical and chemical properties, was the most important basis to evaluate the impact of the controlled burning on Chinese fir plantation persistent productivity. In this study, we chose Chinese fir plantation as research objects in the subtropical region in Huitong county, Hunan province. The characteristics of the understory vegetation and soil of the Chinese fir plantation after different years (3,7,17,25 years) of controlled burning were studied, based on the spatial sequence instead of time successional sequence method. And we explored the long-term effects of controlled burning on the Chinese fir plantation ecosystem. The results are as follows:(1) The total number of the understory vegetation species was 194, and all of them belonged to 78 families, and 142 genera in the investigation of 5 Chinese fir plantation. In the contrast samples, there were 72 species in total, belonged to 36 families and 59 genera, mainly in Rosaceae, Rubiaceae. At 3 years old stand, there were 88 species in total, belonged to 46 families and 79 genera, mainly in Gramineae, Rubiaceae. At 7 years old stand, there were 60 species in total, belonged to 43 families and 56 genera, mainly in Rosaceae, Moraceae. At 17 years old stand, there were 76 species, belonged to 52 families and 64 genera, mainly in Dryopteridaceae, Rosaceae. At 25 years old stand, there were 68 species, belonged to 45 families and 63 genera, mainly in Gramineae, Saxifragaceae.(2) The stems density of shrub reached the maximum value at 7 years old, and then decreased; the stems density of herb reached the maximum value at 3 years old, and then decreased with the increasing of stand ages; the stems density of liana was basically unchanged. The average height of shrub increased with increasing stand ages; the height growth of herb reached the maximum at 7 years old, and then began to decrease; the average high of liana showed a downward trend. The understory vegetation coverage decreased with the increasing stand ages before 17 years, and then there was an increasing trend.(3) The dominant species of shrub, herb and liana were almost different between Chinese fir plantations after afforestation and CK sample stand. The important value of the same species in different stand were significant difference. Smilax china, Clerodendrum cyrtophyllum, Litsea cubeba were the dominant species in the shrub layers; Woodwardia japonica, Houttuynia cordata were the dominant species in the herb layers; Ampelopsis cantoniensis, Actinidia fulvicoma were the dominant species in the liana layer.(4) The Jaccard index of each other for understory vegetation was relatively lower after burning afforestation, which were lower than 55%. To contrast with the CK stand and the Jaccard index were increased with recovery time after the controlled burning afforestation.The Jaccard index of shrub, herb and liana reached a maximum at 25 years old. And the Jaccard index of liana was higher than that of the shrub and herb.(5) The species richness index of shrub reached the maximum at 3 years old, and then began to decrease; the species richness index of herb showed an obvious fluctuation (lower-higher-lower); but the species richness index of liana changed little. The Simpson and Shannon-Wiener indexs of shrub layer decreased over time; the indexs of herb layer increased at first, then declined, reached the maximum at 17 years; the liana layer changed little. The Pielou index of shrub layer was in a downtrend, and the index of herb layer increased at first, then declined, reached the maximum at 17 years; the index of liana layer showed an obvious fluctuation (lower-higher-lower).(6)The total biomass of understory vegetation soared at the initial burning afforestation, reached the maximum at 7 years (23.65 t·hm-2); the biomass of shrub layer decreased with stand ages, reached the minimum at 17 years (0.18 t·hm-2), then reached a small rise; the biomass of herb layer and litter layer reached the maximum at 7 years old, and then began to decline. The biomass of litter and shrub layer accounted for 44.4%-69.9% and 1.9%-37.0%, as the largest and the smallest proportion of the total biomass, respectively.(7) Influenced by the forest harvest, around the time of controlled burning, the pH value of soils was small. The controlled burning caused pH to rise, but the influence was not significant, at 3 years old, the pH value increased by 33.7%. The effects of controlled burning on soil bulk density was not significant. In the short term, the controlled burning reduced the content of soil organic carbon in 0-10cm layer significantly, but the content of soil organic carbon increased gradually with the passing time. The content of total nitrogen of two soil layers were down slightly after controlled burning, then increased gradually after the burning afforestation, reached maximum at 17 years old. The content of total phosphorus in two soil layers increased after controlled burning, but not significantly, the content of total phosphorus of two soil layers of 7,17 and 25 years after burning afforestation were significantly higher than thatbefore burning.