Regarding importance value as the quantitative factor Chinese fir communities with different age in Huitong，Hunan，were classified and ordinated by the use of floristic clas-sification and polar ordination．Communities from newly afforested stand to 37—year—old stand，consisting of 8 age classes，were divided into seven community types．Phys-iognomy structure and species composition were discussed for each community type．Fi-nally，the characteristics of understory succession were also analysed．

The dynamics of chemical elements in precipitation，throughfall，stemflow，surface runoff and underground runoff have been studied．The results showed that element con-tents in precipitation associated with the amount and its characteristics of a rainfall．Most element contents in throughfall and stemflow increased 2 to 24 times than in pre-cipitation．In Chinese fir plantations，the amount of most elements in surface runoff，such as K，Ca，Mg，Fe，and Cu，were larger than those in throughfall，while most element con-tents in underground runoff were lower than those in throughfall and surface runoff．The results can benefit the physical cycle in forest ecosystem and the large—scale evaluation of environment quality．

The biomass of understory in the secondary generation of chinese fir stand has been studied for 5 consecutive years at Huitong watersheds．Biomass dynamics in understory shrubs，herbs and litters were discussed．The results showed that the biomass of under-story in young chinese fir stand was 1.50—3.85t/hm²,the biomass of shrub decreasedas the stand age increasing．The biomass order of shrub was root>stem>leaf，while the biomass order of herb was under ground part>aboveground part．

Contents，accumulation and distribution of 13 nutrient elements in shrub，herb and litter stratum of the young Chinese fir stand war studied in Huitong．The results showed that contents of nutrient elements varied among species and among organs of the same species．Regarding accumulation of major nutrient elements，the order waS N>Ca>K>Mg>P in shrub stratum，N>K>Ca>Mg>P in herb stratum，and Ca>N>K>Mg>P in Litter。

Basde on observations from Chinese fir watersheds before and after artificial distur-bance,“excess storage model”was developed in the light of specific conditions of forest watersheds，the features and mechanisms of runoff yield and confluence analyzed and a comparative study of runoff dynamics under the influence of clearcutting and thinning made．The model was of high accuracy by which interflow could be prceisely separated from groundwater flow．The accuracy of modelling runoff at one—day intervals was 95．7％ in the clearcutting watershed and 92.3％ in the thinning watershed．The water holding capacity of crown and undergrowth amounted to more than 1—2mm．The final infiltration rate of surface water was 3.4—14.Omm/min.,most of which then turned in-to interflow and groundwater，while surfaceflow was only 0.4％ of total runoff．Simula-tion results showed that after clearcutting the storage capacity in the zone of aeration de-creased，time of throughflow concentration shortened，final infiltration capacity of groundwater dropped，and total storm runoff increased，while after thinning the water holding capacity in the zone of aeration decreased，time of throughflow concentration shortened slightly，infiltration rate of groundwater increased，thus its effect of storage control was greater than that in the clearcut watershed．The Chinese fir plantation reduces the flood flow and peak flow，and prolongs the time of concentration by means of aboveground storage control，transformation of direct runoff into groundwater and delay of throughflow confluence．

A four—year’S study on ecological restoration on temperature characteristics in the second generation of Chinese fir has been carried out at Huitong county，Hunan Provice，26°50′N，109°45′E．The results showed that the ecological restoration of temperature in young stands was very fast．Two years after afforestation，the ecological restoration could attain to 26％ of that of the mature stand，and 4 years later it could reach to 70％．In young stand，artificial disturbance of cultivation might decrease ecological restoration on surface soil temperature．Under natural condition，the ecological restoration speed on soil temperature within the young stand decreased as the soil layer deepened，and it was smaller than that of air temperature．This means that the soil physics within young stand will take a longer time to resorate to the level in mature stand．

A five—year’s study was carried out at Huitong county，southwest Hunan Provice．The results showed that once the young stand established，its ecological restoration start-ed．The restoration of runoff and that of maximum flood discharge in the one—year—old young stand was 9％ and 6％ of that in the mature stand respectively，while those in the four—year—old young stand reached to 44％ and 19％，respectively．The occurrence of artificial disturbance and precipitation could change the ecological restoration speed in young stands．Other factors，such as the height distribution，the root distribution,and the water storage capacity of litter in the stand,as well as vegetation restoration，could regulate the runoff．In subtropical zone，the full ecological restoration in the second gen-eration of Chinese fir，afforested after clear cutting of the first generation，will take more than 10 years．

Biomass and productivity of a 7—year second generation of Chinese fir plantation were studied in Huitong ecological station of Hunan Province，and compared with the same aged stand of first generation．The results showed that biomass of the second gen-eration of Chinese fir stand decreased 14.18t/hm²,net productivity decreased 2.04 t/hm²·a than those of the first generation，and the decrease range reached 31.47％．Therefore more attentions should be paid by foresters．

The energy storage and its distribution in Chinese fir plantations was comparatively studied at Huitong and Zhuting of Hunan Province respectively．The former is in the 0-riginal distribution centre of Chinese fir，the latter is in its enlarged planting areas．The results showed that the energy fixed by the 11—year—old stand at Huitong is 16833×10⁸J/hm²,while only 11381×10⁸J/hm² at Zhuting；Energy distribution in the forest com- ponents is in the following order；stem>root>leaf>branch．Energy stored in stem at Huitong is larger than that at Zhuting，but energy in branch and leaf at Huitong is less than that at Zhuting．The energy fixed by the stand decreased with its density increas-ing，the energy decrease occurred mostly in the stem’s accumulation．The energy vertical distribution of the forest showed that the soil surface layer and 2/3 canopy height take up most of the energy．It indicated that in an ecosystem，where most energy flows to and accumulated in the place where nutrients and water are most needed．In Zhuting stand，the economic value of energy fixed by photosynthesis(of stem) is 20％ less than that in Huitong，and the photosynthetic ability of leaf and branch is only 70％ that of the latter．

The dynamic characteristics of soil water were studied in Chinese fir ecosystems un-der different modes of artificial disturbance．Results showed that after clearcutting the storage capacity of forest land decreased，fluctuations of soil moisture increased,varia-tions in soil water content among soil layers became slighter．While after thinning fluctu-ations subsided．Soil water content at depths of O-30cm in the control and thinning wa-tershed was greater than that in the clearcutted watershed，but fluctuations of water content lower；the result turned out contrary at greater depths due to the root system．The greater artificial disturbance，the more similar variation of soil moisture at different depths，which resulted in poor capacity for soil water regulation．Based on standard devi- ation，statistical test of differences of standard deviation and coefficient of vertical varia-tion of soil moisture，the soil profile could be divided into three layers—changeable lay-er，active layre and less active layer．According to the two indicators—the ratio of evapo-transpiration to rainfall and daily mean evapotranspiration，the soil water evolution in a calendar year could be divided into three periods，i．e．，relatively stable period，recharge period and loss period．The fluctuations and vertical variations of soil moisture at differ-ent locations of slope in the three watersheds decreased in the order of hillside>downhill>foothill，and after thinning the effect of soil water regulation at different locations was greater.

Dynamic data analysis and harmonic wave theory are applied to simulate and ana-lyze perildic changes in soil moisture under different modes of artificial disturbnce in Chinese fir plantation．Results showed that soil moisture series on the forest land is sup-perposed by a stochastic component，which is a reflection of the effect of stochastic flue-tuations of climate on soil water content，and a perildic deterministic process，which is a reflection of periodic changes in climate or combinations of the water requirements of trees and periodic variations of climate．Simulation of the soil moisture series of clearcut-ting，control and thinning watersheds demonstrates that the additive model is of high precision for modelling long term change process of soil water．Periodic vibration de- creases in the order of：thinning>control>clearcutting，and the vibration of the three watersheds abates significantly with the increasing of soil depth．

The study on the soil C0₂ release from three land types of Chinese fir plantation in Huitong，Hunan showed that：①The soil C0₂ release from the afforested land or the def-forested land is evidently higer than that of the closed woodland，the soil C0₂ release from the afforested land is somewhat higher than that of the deforested land；②The soil C0₂ release is positive linear correlation with the soil temperature and soil moisture at a certain range，and also with the soil C/N ratio；③The soil C0₂ release change with a regular circadian rhythm；④The soil C0₂ release from the defforested lands with differ-ent treatments is evident difference in a certain time lapse．

The distribution of the soil microorganisms in Chinese fir plantation watershed in Huitong varies with different ages of stand．With the increment of the stand age，the bac-teria show a decrease tendency，actinomyces and fungi show an increse tendency．Most nitrifying bacteria occurs in the 8-year-old Chinese fir plantation，while least in the 30-year-old plantation．The results of the studies indicate that the quantities distribution of the soil microbes varies with forest eco-environment．They have important effects on the soil fertility and tree nutrient．

Based on the investigation in 8 age-class stands (from age 0.3 to 37 years old)in Huitong，Hunan，the changing process of species diversity of the Chinese fir plantation community was studied，the relationship between species diversity and community stabil-ity was also discussed．The results showed that the species diversity index of each age-class stand is 2.2—3.5 and the evenness is 0.64—O.85，the ecological dominant values is 0.04—O.18．The study would provide scientific basis for biodiversity conservation and sustainable utilization of the artificial forest．

This study was conducted to reveal the characteristics of biological and biogeologi-cal cycles in a 7-year-old second-generation Chinese fir plantation．The results showed that the total amount of N，P，K，Ca and Mg in precipitation in thd watershed is 58.110kg/hm²·a，while the amount in runoff is 42.290kg/hm²·a,the net accumulation of nutrients is 15.820kg/hm²·a．It indicates that the young Chinese fir forest ecosystem is just in the ecological recovery process．

Based on the data observed in successive years，the dynamic effects and its parame-ters in a Chinese fir plantation catchment was studied by aerodynamic principles．The re-sults could be presented as follows：the length of zero plane displacement is 9.52—9.95m，the canopy roughness 2.32—2.53m,the mixed length of the upper canopy sur-face 0.274m，the coefficiency of leaf resistance 0.367，the wind delay factor in the canopy 1.98,and the turbulanee force and friction velocity decrease as the depth of the canopy increase．Dynamic parameters have significant correlation with the velocity of airstream which is strongly effected by temperature layer sum and forest structural charaeteris-tics．Owing to the delay of airflow by leave and branches in the canopy，the turbulance and its spread characteristics above the upper canopy are quite different from that within the canopy．In the catchment，heat vapour of the canopy and gravity play an important role in the formation and development of the turbulance stream．

An integrated stand growth model (ISGM) of Chinese fir in Huitong was estab-lished in this paper．ISGM describes the interrelationship of the principal quantitative factors in Chinese fir stand in Huitong．Basal area model，predominant height model，av-erage height model and form-height model are included．And validations of the modelsare tested respectively．

Based on data from 92 permanent plots and 283 sample trees of Chinese fir，thechange pattern of LAI at different density，age and site type in two regions was ana-lyzed.The results showed that the relation between LAI and age can be expressed by the formula：LAI=—1.669+1.040a—0。027a² and there was one point of LAI culmination at the age of 19．With increasing of stands density，LAl increases and ultimately reaches to a certain value．The better site type is，the higher LAI gets．Intermediate cutting has a positive effect on trees growth and LAI can restore as before in a specific time after intermediate cutting．

According to the study on the relation between stand volume and biomass of Chi-nese fir plantation，this paper developed the integrated stand forecast models for stand biomass based on the integrated stand growth mode (ISGM) of Chinese fir plantation in Huitong．The models are W_i=a₁EXP{a₂L^a₃[1一EXP(-a₄S^a₅o>)^a₆FH} i=1，2，3，4，5 The precision of the models is greater than 96％ except for root．Through the t test，there is |t|0．05(55) for all organs．Thinking of no distinct difference between the esti-mative value and obser red data，the models can meet the needs of forest management．

The accumulation distribution and biological cycling of nine nutrient elements (N、P，K，Ca、Mg，Fe，Mn，Zn、Cu) in a natural secondary Quercus fabri forest in Yuanling，Hunan,was studied．The results indicated that the total accumulation of the nine nutri-ent elements in the ecosystem is 192.08t/hm²．In arbor layer，the annual absorbtion is 0.179t/hm²·a。the annual return is 0.125t/hm²·a，and the average cycling rate is 0.7．This research could provide base data for culturing artifieal mixed forests．

The biomass and nutrient contents of a natural secondary broadleaved-coniferous forest with dominant of Quercus fabri located in Yuanling，Hunan，has been studied．The results showed that the biomass of the community was 150.77t/hm²，the biomass and net production of the arbor layer were 112.65t/hm² and 8.78t/hm²．Nutrient contents were significantly different inter main tree species and between organs of the same species．

The accumulation and distribution of nutrient elements in a 12-year-old Castanopsis fissa plantation was studied．The results showed that the net-accumulation of nutrient elements is 81.59kg/hm²·a，in which K is 51.5％and N is 31.6％．Net-accumulation of mieronutrients is 2.756kg/hm²·a，in which Fe is 53.6％and Mn is 38.7％．The net-ac-cumulation of nutrient elements in leaves is higher than that in other organs．The re- quirement to produce one ten dry biomass is 10.25kg for nutrient elements and 346.2g for micronutrients．

The annual amount of litter and nutrient return in different density Slash pine plan-tations，the existing storage of the litter，and the content of elements in the litter were measured and analysed．The results show that the annual amount of litter is 6191.5—7123.9kg/hm²·a．the existing storage of the litter on the stands is 9.75—17.4t/hm²．The annual return amount of litter nutrient is 90.43—105.09kg/hm²·a，and the total amount of nutrient stored in the litter is 191.16—281.89kg/hm²，in which the highest storage was occurred at the density of 3000 stems/hm²．The data above proves that forest litter forms a huge storage of nutrient，which plays an important role in main-taining site quality and raising forest productivity．

The results showed that in 12 to 31-year-old Pinus massoniana forests，the produc-tivity of 25-year-old forest in the highest,which is 9.07t/hm²．The nutrient content in leaves of 21-year-old forest is the largest，which indicated that the forest is of physio-logical exuberance．Ca accumulates mainly in the bark．The requirement of nutrient ele-ments to produce one ton dry biomass is 3.0763kg and 4.695kg for 12-and 21-year-old forest respectively．

By study on a lot of sample plots and individual trees of Pinus Massoniana,it is proved that there is a close relationship between the biomass and the volume,so that the biomass of stem，branch，leaf，and root can be estimated very well respectively by the use of diameter at breast height and tree height．The single-tree biomass growth can be precisely predicted by the Richards model．The stand biomass change can be regulated by mean stand diameter，stand height and stand density，while the undergrowth biomass can be controlled by the cover-degree according to stand types．

According to the observed data，we established the models for stand growth，yield forecast，stand density effect and hydrological function prediction of Masson pine forest for water and soil conservation．On the basis of these，applying the principle that forest function depend on the stand structure，combining the mathematic method for plan opti-mization and the means of computer simulation，we developed the simulation software for managerial regulation of Masson pine for water and soil conservation，and the opti-mal managerial strategy of Loropetalum chinese-Pinus massoniana forest was presented，which fits to various managerial purposes．The results indicated that with the increasing of stand diameter，tree height and biomass，the capacity of stand retaining rainfall and conserve water increased，whereas the earth's surface runoff and soiI erosion module de-creased，and the integrative grade of water-holding function increased correspon-dently.While there are larger differance in biotic yield and hydrological benefit at the same site with different managerial purposes．

The biomass dynamics of Cryptomeria japonica (L．F)D．Don was studied by the use of Richards model·The stand biomass (W，t/hm²)can be calculated by the followingfunctions， W=318．0349 (1-e^-O．1414sst)^1/1-0.664835，where t is the sand age in years． The result showed that the growth process of Cryptomeria japonica to 16 years can be divided into three stages：1 to 5—year is young growth stage：5—10th year is pole stage；after 10th year will be submature stage．The calculating result is that the maxi-mum biomass will amount to 318．Ot/hm²．