| The Three Gorges Reservoir Area is the ecological barrier of middle and lower Yangtze River. The soil and water conservation of forest in this area has been a hot issue among many researchers. Pinus massoniana is one of the most widespread trees in this area. As the key measure of forest management, thinning has a great influence on forest growth. Proper thinning methods can improve the light condition of forest canopy and adjust the growth and development of trees. Thus, it can affect the main ecological functions of forest. We chose Pinus massoniana in Jiulingtou Forestry Station,Quyuan Town,Zigui County as research object, set up middle-aged, pre-mature and mature forest after different thinning measures(unthinned, thinning-from-below, thinning-from- above) according to the ideology of “substitute time with space” to study the water conservation of canopy layer, little layer and soil layer. The main results are as follows:(1)With the increasing of rainfall, forest canopy interception increased to a certain degree, and then decreased. In unthinned plots, forest canopy interception decreased with the increasing of forest age, while the data of thinned plots increased. In a short time after thinning, forest canopy interception decreased in the order of unthinned(14.92mm), thinning-from-below(13.52mm), thinning-from-above(9.19m). However, when it came to the mature forest, the amount of forest canopy interception was thinning-from-below(14.63mm) > unthinned(13.61mm) > thinning from above(12.40mm).(2)Compared with unthinned plots, the litter storage of thinned plots showed a tendency of decreasing. And the thinning-from-above decreased more. The amount of litter storages in different forest ages were pre-mature forest > mature forest >middle-aged forest. The maximum water-holding capacity in undecomposed layer varied from 4.05 to 7.15t/hm2. In half-decomposed layer, it varied from 5.59 to 11.48 t/hm2, which went with the litter storage. The effective retaining content among different forest ages increased in the order of middle-aged forest, pre-mature forest, mature forest. The effective retaining content among different thinning measures decreased in the order of unthinned, thinning-from-below, thinning-from-above. The amount of half-decomposed layer was always larger than that of undecomposed layer, which means that the water conservation ability of litter layer depended on half-decomposed layer.(3)The soil bulk density in different plots varied from 1.06 to 1.61 g/cm3 and they all increased with the deepening of soil layer. The soil bulk density among different forest ages decreased in the order of middle-aged forest, pre-mature forest and mature forest. The total porosity differed from 38,12 to 60.75%, the non-capillary porosity differed from 6.29 to 14.75%. The soil capillary porosity and total porosity among different forest ages showed the same tendency of middle-aged forest<pre-mature forest<mature forest. The effective water-holding capacity in unthinned plots increased in the order of middle-aged forest, pre-mature forest, mature forest. After thinning, the effective water-holding capacity were pre-mature forest>mature forest>middle-aged forest.(4)Choosing forest canopy interception, litter effective retaining content and soil effective water-holding capacity as calculation indexes of water conservation, we came to the conclusion that the total water conservation varied from 563.21 to 854.00 t·hm-2. Among the three function layers, soil was the highest, which contributed about 74.59 to 85.30%. Forest canopy was the second, the rate differed from 13.47 to 24.01%. The least was litter layer which only contributed less than 2%. In unthinned plots, the total water conservation increased in the order of middle-aged forest, pre-mature forest and mature forest. While in thinned plots, the order were pre-mature forest > mature forest >middle-aged forest. Compared with unthinned plots, the total water conservation in both the thinning-from-below plots and the thinning-from-above plots decreased in a short period. However, after a long time the total water conservation in thinned plots was higher than unthinned plots.(5)After thinning, the kinds of species increased, especially the light-preferring species. Compared with unthinned plots, the Simpson index and Shannon-Wiener index in thinned plots increased. The diversity index of shrub layer increased in the order of middle-aged forest, pre-mature forest and mature forest. But the index in herb layer didn’t show the same tendency. The evenness indexes varied between different thinning measures. In a word, the thinning-from-above plots had a larger biodiversity increasement than thinning-from-below plots, which suggested that heavy thinning was more effective to stimulate the undergrowth diversity.In conclusion, the water conservation ability would decrease in a short time after thinning. But after a relatively long time, the total water conservation in thinned plots was higher than unthinned plots. After thinning, the undergrowth diversity increased and the increasement of thinning-from-above plots was larger. Thus, we need to establish scientifically rational thinning methods to stimulate the water conservation and biodiversity of Pinus massoniana forest in Three Gorges Reservoir Area. |
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