Population Dynamics And Eco-hydrological Characteristics Of The Protection Forest In The Guansi River Basin

Located in southeastern of Qinghai-Tibet plateau and being reputed as an importantecological barrier of water and soil conservation for the upstream of Yangtz river,Mianyang Guansi river basin plays an important role in ecological function for its peculiarecological system structure integrity.In recent years, the population growth, theland-people relationship and human disturbances have in together affect the ecologicalstructure and function of the protection forest and pose a potential threat to the ecologicalenvironment of the downstream along Yangtz river. Evaluating the population andcommunity dynamics and eco-hydrological function is of strategical importance to furtherunderstanding the ecological functions and promoting the sustainable development of theprotection forest.Guided by the theories, principles and methods of Ecology, Hydrology, Soil scienceand Statistics, through field investigation and mathematical statistics, this paper analyzesthe renewal,succession and structure of the protection forest community in quantitativeand qualitative way. In terms of height class and size structure, the author classifies andgrades the four dominant population: Cupressus funebris, Pinus massoniana, Quercusvariabilis and Quercus acutissima. Based on the classification and grading, the paperexplores the structure, stability and renewal of the dominant population. By using thestatic life table and survival analysis, the paper explores the quantity dynamics andrenewal and succession law and predicts the development tendency of the dominantpopulation. Based on field sampling and indoor experiment, using statistical disposition,regression analysis and data fitting, the paper explores the water retention characteristicsand imbibition of the litter under the forest. The author also constructs the waterimbibition and retention model and analyses the basic physical nature and retentioncharacteristics. The author analyses the eco-hydrological function of the five forest standsin the quantitative perspective by using grey correlation analysis. Based on the abovestudy, the author draws the following results:(1) The renewal of the protection forest and species composition of the communityAfter20years’ renewal and succession, some stand types have changed greatly. Thelow Vitex negundo and Coriaria nepalensis shrubbery, mixed Alnus cremastogyne and Cupressus funebris forest have turned into Cupressus funebris forest. Quercus spp.andVitex negundo secondary shrubbery have become Quercus spp. forest; the Pinus elliottiiforest have turned into mixed Pinus massoniana and Pinus elliottii forest.Other standsremain the same, but the community species composition have changed a lot. Thereappears Quercus variabilis, Cyclobalanopsis glauca, Vernicia fordii, Broussonetiapapyrifera in the regeneration layer of Pinus massoniana forest and Cupressus funebrisforest. Some broadleaved evergreen trees such as Ormosia hosiei and Ligustrum lucidumhave expanded into the subtree layer.(2) The community vertical structure dynamics of the protection forestThe special distribution of each stand is experiencing changes and the commonspecies in vertical structure is increasing. As in sample plot3, the permanent sample plot ofQuercus spp.and Vitex negundo secondary shrubbery has changed into mixed Quercusvariabilis and Quercus acutissima forest. At the same time, due to vertical special changes,the representative sampling plot have changed too, as in sample plot6,(mixed Pinusmassoniana and Cupressus funebris forest). More broadleaved trees have appeared inlevel3to level6.(3) The dynamic changes of community stable rate in the protection forestThe community stable rate order of permanent sample plot is sample8>sample6>sample5>sample3>sample11>sample7>sample12>sample10>sample4>sample9>sample2>sample1. This demonstrates that the mature forest stand stable rate is betterthan the immature forest stand. The mixed forest is better than the pure forest, and theundisturbed forest stand is better than disturbed open forest stand. Compared with theprevious results by our predecessors, we find that in the past10years,except thedownward tendency of34.8%of sample10, the stable rate of other communities are rising.The sample1is up40.7%, sample2is up28.1%, sample5is up3.5%, sample6is up3.9%, sample7is up1.2%, sample9is up26.8%, sample12is up33.1%.(4) The structure of height class and size class of dominant population in theprotection forestIt can see from the height class structure that there are both growth form andsenescence form in the dominant tree population of the protection forest.For the Cupressusfunebris population, sample1stands for the growth form, sample2is in a growing form,but sample4,5,6,10are in the senescence form.For the Pinus massoniana population,the growth form includes sample9and sample11. The stable form includes sample8andthe senescence form includes sample6,7,10,12.For the Pinus elliottii population, thispopulation is in the senescence form; the Quercus variabilis and Quercus acutissima population stand respectively stable form and growth form.From the size class structurewe can conclude that there are less seedlings and samplings especially the seedlings in theage class of Ⅰ and Ⅱ. There is a higher percentage of middle and young age of trees.There are little mature age trees in Ⅵ and Ⅶ which demonstrates the unstablespindle-shaped structure that is totally different from the typical pyramid populationstructure.(5) The dynamic changes of the dominant populations in the protection forestThe static life table analysis shows that the mortality rate of Cupressus funebris andPinus massoniana is basically the same, but the mortality rate of Quercus variabilis andQuercus acutissima is apparently different. Except Quercus variabilis, the peak value oflife expectancy of Cupressus funebris, Pinus massoniana and Quercus acutissima occursbefore the age class with the highest death rate. It shows that after fierce competitionwithin and outside the same population, the seedlings and samplings have lower lifeexpectancy. The survival curve shows that the curve of Cupressus funebris, Pinusmassoniana, Quercus variabilis and Quercus acutissima is more likely to be like Deevey-Ⅱ, which demonstrates a stable transition within certain period. But there are certaindifferences between the sample plot.Survival function curve shows that in the Cupressusfunebris population, it grows in the preterm, regresses in the mid-term and stabilizes in thelater period. The Pinus massoniana grows in the preterm, stabilizes in the mid-term andregresses in the later period. The Quercus variabilis regressed in the preterm, grows in themid-term and regresses in the later period. The Quercus acutissima stabilizes in thepreterm, grows in the mid-term and regresses in the later period.(6) Eco-hydrological characteristics of litter under protection forestsThe thickness and storage of litter under various forest showed similar trend, Quercusspp.forest, mixed Cupressus funebris and Pinus massoniana forest, Pinus massonianaforest, Cupressus funebris forest and mixed Pinus massoniana and Pinus elliottii forest indeclining order. The thickness of litter range from2.00cm to7.33cm, and the storage was4.11t/hm2to9.15t/hm2. Litter maximum water holding capacity and effective retainingcontent follow the order as follows, Quercus spp. forest, mixed Cupressus funebris andPinus massoniana forest, Cupressus funebris forest, Pinus massoniana forest and mixedPinus massoniana and Pinus elliottii forest, specifically, litter maximum water holdingcapacity range from6.78t/hm2to15.21t/hm2while effective retaining content was4.09t/hm2to10.61t/hm2. The water holding process of different layers of the a forest ordifferent type of forest exhibit similar characteristics. Water-holding capacity almostreached the maximum at the very beginning four to five hours, and stop increase after ten to fifteen hours of submerge. The relationship of immersion time with the water-holdingcapacity of undercomposed litter layer or intermediate decomposed litter layer maydescribed as Q=ln(t)+b, and the relationship of litter water absorbing rate and time maydescribed as V=a t-b. Both of these two formulas was significant at0.01, demonstratingthat these two formulas can be used to simulated the dynamic of litter water-holdingcapacity, litter water-holding rate and absorb rate.(7) Eco-hydrological characteristics of soil under protection forestVolume weight of soil under the protection forests declined in the order of mixedCupressus funebris and Pinus massoniana forest(1.42g/cm3), Pinus massoniana forest(1.395g/cm3), Quercus spp. forest(1.38g/cm3), Cupressus funebris forest(1.375g/cm3)and mixed Pinus massoniana and Pinus elliottii forest (1.32g/cm3). The soil total porositydeclined in the contrary direction as mixed Pinus massoniana and Pinus elliottii forest(50.45%), Cupressus funebris forest(48.55%), Quercus spp. forest(48.51%), Pinusmassoniana forest (48.37%), mixed Cupressus funebris and Pinus massonianaforest(47.41%). The water holding capacity and capillary moisture capacity follow thesame declining order as mixed Cupressus funebris and Pinus massoniana forest,Cupressus funebris forest, Quercus spp. forest, Pinus massoniana forest and mixed Pinusmassoniana and Pinus elliottii forest. The maximum water holding capacity range from227.03mm to262.62mm, the capillary moisture capacity was193.19mm to226.71mm.The available soil water storage, ranging from33.57mm to37.02mm, differed from theformers as its orders were Cupressus funebris forest, mixed Cupressus funebris and Pinusmassoniana forest, Quercus spp. forest, mixed Pinus massoniana and Pinus elliottii forestand Pinus massoniana forest. Compared to the study of Wang et al.(1992), the availablesoil water storage of corresponding protection forest significantly increased, and theimprovement of soil ecological hydrology function was about2.41~7.26%.(8) Eco-hydrological Function evaluation of protection forestThe result of grey correlation method showed that the comprehensiveeco-hydrological functions of the five protection forest deceased in order of Quercus spp.forest (0.89), mixed Cupressus funebris and Pinus massoniana forest (0.82), Cupressusfunebris forest (0.77), Pinus massoniana forest (0.71) and mixed Pinus massoniana andPinus elliottii forest (0.68). Quercus spp. forest as well as mixed Cupressus funebris andPinus massoniana forest exhibited better hydrological and ecological function and soil andwater conservation benefits than the pure Cupressus funebris forest and Pinus massonianaforest. Moderate modification is need to improve the structure of these pure needle forest,such as declining the forest density and supplement broad-leaf species, making it possible for these protection forest to better perform their ecological function and improve its waterand soil conservation ability in a longer time.