Study On The Ecological Characteristics Of Natural And Secondary Forest Of Fagus Pashanica

Five plots including Fagus pashannica mature forest in downhill position, F. pashannica mature forest, near-mature forest, half-mature forest, young forest in midhill and uphill position, were selected. The changes of ecological characteristics of F. pashannica forest after clear cutting in the process of natural regeneration was studied systematically, from the aspects of forest species component, diversity changes, photosynthetic productivity differences of constructive species seedlings, hydrological and ecological functional differences of litter fall and litter production, soil water conservation capacity, soil fertility, and soil carbon pool. The results were as follows:(1)The changes of richness index, Simpson index and comprehensive index of four forest type showed the similar trend: mature forest≈near-mature forest＜half-mature forest＜young forest. The evenness of each sample plot showed a similar trend with the changes of the Shannon-Wiener index: mature forestâ… , near-mature forest, and young forest had the lowest evenness, while half-mature forest and mature forestâ…¡had the highest.Research results of species diversity can be explained with Intermediate Disturbance Hypothesis. Studies on diameter structure and diseased tree of F. pashannica mature forest in the uphill and downhill position indicated that less light on downhill restricted arbor in lower tree layer, but the sapling quantity was more than that in the in midhill and uphill position due to humidity reasons. Species diversity of each sample plot was significantly correlated (mainly a negative correlation) with soil nutrient and physical property, it can provide new evidence for their complex relationship.(2) 18.8 trees ha^-1yr^-1 (5-20 cm DBH 16.8,＞20 cm DBH 2.1) were damaged in lower slope position mature stand. mortality rate per year of various size classes was about 1.4%(5-20 cm DBH 1.6%,＞20 cm DBH 0.7%).The expectation of further life was 71yr orerall(5-20 cm DBH 61yr,＞20 cm DBH 149yr).Turnover time was 61 yr (5-20 cm DBH) and 149yr (＞20 cm DBH).10.2 trees ha^-1yr^-1(5-20 cm DBH 7.6,＞20 cm DBH 2.7)were damaged in middle and upper slope position mature stand. mortality rate per year of various size classes was about 0.66%(5-20 cm DBH 0.68%,＞20 cm DBH 0.59%).The expectation of further life was 152yr orerall(5-20 cm DBH 147yr,＞20 cm DBH169yr), Turnover time was 147yr (5-20 cm DBH) and 169yr (＞20 cm DBH).(3) The order of net photosynthetic rate of F. pashannica seedlings in sample plots was: young forest＞mature forest in the downhill (mature forestâ… )＞mature forest in the midhill and uphill position (mature forestâ…¡). The variation of F. pashannica seedlings photosynthetic capacity with growing season was conformable: fast growth stage＞early growth stage＞last growth stage, and photosynthesis index had a large fluctuation and a high CO₂ compensation point during the early and last stage. Diurnal variation of photosynthes of of F. pashannica seedlings was single peak type. These indicated that water and light were closely related with F. pashannica regeneration, and downhill was more suitable than uphill for growth of F. pashannica seedling.(4) The annual litter production of litter layer, as well as water content in five sample plots was in the sequence of mature forest＞near-mature forest＞half-mature forest＞young forest. From the slope position, the litter production and water content of mature forestâ… was more than that of mature forestâ…¡. F. pashannica forest had obvious litter fastigium, and was single peak type. The sequence of annual litter production of each sample plot was: November＞September＞July＞May. Cumulation in each sample plot was a little different with the annual litter production. Determination results of water retention property of the litter by infusion method showed that young forest had the highest water retention property, while the mature forestâ…¡had the lowest. The results about comprehensive litter layer cumulation, water retention ratio and natural water content were as follows: (1)the maximum water capacity: mature forestⅠ＞mature forestⅡ＞near-mature forest＞half-mature forest＞young forest; (2) the maximum water amount of interception: mature forestⅡ＞mature forestⅠ＞near-mature forest＞half-mature forest＞young forest; (3)the modified water amount of interception: mature forestⅡ＞mature forestⅠ＞near-mature forest＞half-mature forest＞young forest.(5) Soil capacity characteristic at 0-20cm and 20-40cm soil layers was: mature forestⅠ＜near-mature forest＜mature forestⅡ＜half-mature forest＜young forest; non-capillary porosity was just opposite to this, mature forestâ… had the highest non-capillary porosity, reflected that mature forestâ… had well soil structure. There were differences in undergrowth soil water retention property of F. pashannica forest, the order was: mature forestⅠ＞near-mature forest＞mature forestⅡ＞half-mature forest＞young forest, and water retention property at 0-20cm＞at 20-40cm. Soil drainability at 0-20cm in each sample plot was all higher than that at 20-40cm, initial infiltration capacity was: mature forestⅠ＞near-mature forest＞mature forestⅡ＞half-mature forest＞young forest, among which initial infiltration capacity of mature forestâ…¡was close to near-mature forest, and half-mature forest was close to young forest.(6) Changes of natural water content characteristic in every forest type were as follows: (1)time changes characteristic: July＞May＞November＞September. (2) forest type changes characteristic: mature forestⅠ＞near-mature forest＞mature forestⅡ＞half-mature forest＞young forest, and changes during every growing season was: mature forestⅡ＞mature forestⅠ＞near-mature forest＞half-mature forest＞young forest. The difference analysis of soil depth detected that natural water content at 0-20cm was higher than that at 20-40cm; and the change range of natural water content at 0-20cm was also higher than that at 20-40cm during every forest type. In the same quadrat, the most difference in natural water content between 0-20cm and 20-40cm was mature forestâ…¡, and then the near-mature forest, mature forestâ… , half-mature forest, the lowest was young forest.During each growing season, the contents of soil organic matter, total nitrogen, available nitrogen, ammonium nitrogen, nitrate nitrogen, total phosphorus, available phosphorus, total potassium and available potassium in 0-20cm and 20-40cm soil layer were all: mature forestⅠ＞near-mature forest＞ mature forestⅡ＞half-mature forest＞young forest, and these contents in 0-20cm were higher than these in 20-40cm, soil nutrient contents in different growing season were different, were: September＞May＞November＞July.F. pashannica mature forest and natural secondary forest's soil physical properties and nutrient content had a better correlation in 0-40cm soil layer. Bulk density was significantly or very significantly correlated with alkaline hydrolytic nitrogen, ammonium nitrogen, nitrate nitrogen, total phosphorus, available phosphorus, total potassium, available potassium. Total nitrogen was negative correlated with bulk density, and positive correlated with total pore, capillary pore, non-capillary pore, aeration porosity, capillary water capacity, non-capillary water capacity, primary permeability coefficient and stable permeability coefficient, but the correlation was not significant. Capillary water capacity was positive correlated with total nitrogen, alkaline hydrolytic nitrogen, total phosphorus, available phosphorus, total potassium, non-capillary water capacity positive correlated with all nutrient indexes, but the correlation was not significant. Capillary water capacity was positive correlated with ammonium nitrogen, nitrate nitrogen and available potassium. Soil organic matter was negative correlated with bulk density, it was very significantly correlated with capillary water capacity, and significantly correlated with other physical parameters. Other nutrients were significantly or very significantly positive correlated with soil physical properties.(7) In every season, the content of total organic carbon(C_T), free carbon(C_WS) and activity organic carbon(C_A) of soil displayed the character that mature forestⅠ＞near-mature forest＞mature forestⅡ＞half-mature forest＞young forest, and in every sample field, the content of total organic carbon in the 0-20cm soil layer was always higher than that in the 20-40cm soil layer, and every sample plot in different seasons had the same variational rule about total organic carbon: September＞May＞November＞July.In the five sample plots at 0-20cm soil layer of F. pashannica forest in July, soil volume, total pore, capillary pore, aeration porosity capillary interstice, capillary water capacity and initial infiltration index generally were significantly or very significantly correlated with C_WS, C_A, C_UA, C_WS / C_T, C_UA/ C_T, A and CPMI, but not significantly related with C_A/ C_T, there was no significant positive correlations between non-capillary water capacity and carbon pool index; non-capillary pore and steady infiltration index were not significantly correlated with C_UA/ C_T and A; soil volume was negative correlated with C_WS,C_A,C_UA,C_A/C_T,A,CPMI, while positive correlated with C_UA/C_T; total pore, non-capillary pore, initial infiltration index and steady infiltration index were significant positive related with C_WS,C_A C_UA,C_A/C_T,A,CPMI, and negative correlated with C_UA/C_T.(8) The change characteristics of soil urease activity, soil saccharase activity, soil phosphatase activity and catalase in every month among F. pashannica mature forest and three natural regeneration forests of were: matured forestⅠ＞near-mature forest＞mature forestⅡ＞half-mature forest＞young forest, and the soil enzyme activity at 0-20cm soil layer was higher than that at 20-40cm. The soil enzyme activity of each sample plot at different times had some differences, registered as September＞ July＞May＞November.(9) The changes of soil respiration had a obvious seasonal dynamics and was the single-peak type, which was, from the beginning of April, soil respiration gradually increased, and at August, reached the highest throughout the year (Mean of soil respiration rate reached 2.78μmol·m^-2·s^-1), and then gradually reduced. Daily changes of soil respiration showed a form of the single-peak curve, generally, the strongest appears between 14:00 and 15:00, and the weakest appears around 5:00 in the early morning. Daily changes of soil respiration were same with 5cm soil temperature changes, but slightly lagged behind the dynamic changes in surface temperature. Soil respiration rate of clear cutting was higher than F. pashannica forest, The maximum value of soil respiration rate of the clear cutting appeared at 14:00, while in the forest at 15:00-16:00, and the minimum both appeared around 5:00 in the early morning; compared with forest, the clear cutting reached the highest value about 1 hour ahead, and temperature was significantly related with soil respiration rate (p＜0.01).Research results showed that slope position had great influence on F pashannica seedling regeneration and growth, and downhill was more suitable than midhill and uphill position for growth of F. pashannica seedling. Protection of F. pashannica played a very significant role in enhancing hydrology and ecological functions of surface litter layer, increasing the water retention ability, reducing surface runoff loss of soil, improving natural water content of soil, soil nutrient content, soil enzyme activity and soil structure, increasing carbon content and carbon pool index. Proper disturb can enhance biodiversity of F. pashannica, but will weaken its ecological functions. Our study can provide evidence for F. pashannica protection, soil forest scientific management of its natural secondary forest and its forestation.