Ecological Studies Of Vegetation In Three Gorges Reservoir Hydro-Fluctuation Zone

A30m hydro-fluctuation zone (HFZ) was formed along the banks of Three GorgesReservoir (TGR) because of it’s operating scheme that high water level from April toSeptember while low water level from October to March of next year. That makes the HFZhaving a weak ecological carrying capacity and the ecological environment going worse.Vegetation investigation and samples collection was conducted at three elevation zone ofthe HFZ (145-155m,155-165m,165-175m) and one control elevation (more than175m) inChongqing section of TGR in April2011, July2011and September2011. The mainvegetation types, biodiversity characteristics, biomass and nitrogen and phosphoruscontents at the community level, as well as the phenology and adaptive strategy of thedominant species were analyzed. The above ground vegetation management scheme wasprovided furtherly with theory and data to maintain the ecological system stability of HFZ.The main conclusions of this study are as fallows.①TWINSPAN quantitative classification method was used to analyze plantcommunity types in the HFZ of TGR. The types at the early time, the middle time and theend of the non-subermerged period were6,5and8respectively. After the subermergedperiod, community types were less at the early time (April), but the community typesincreased at the end of non-subermerged period. At the early time of non-subermergedperiod, the communities types in which the crawl-type species were the dominant specieswere predominant. At the early time of non-subermerged period, there were significantdifferences of community types among the different elevations. As the recovery timeprolonged (July and September), this difference decreased gradually.②After the long subermerged period of the HFZ in TGR, the procumbentgrowth-form was the main form at the early time of the non-subermerged period. With theextension of the recovery time, the dominance of the procumbent growth-form speciesgradually reduced and other growth-form species increased. After the subermerged periodof the HFZ, the species richness, Shannon-Wiener and species evenness indices of thecommunities were all smaller than control elevation, and all the indices graduallydecreased along the high-low elevation gradient. As the vegetation restored at the middleand the end time of the non-subermerged period, all the indices increased and there wereno significant differences between the two terms of each elevation. The vegetation of HFZcan develop well and grow stably during the non-subermerged period. ③At the early time of non-subermerged period, the aboveground-biomass andbelowground-biomass of the HFZ vegetation were significantly small compared with thecontrol elevation and there was a significant difference between the two regions (P<0.05).At the middle and the end time of the non-subermerged period, the aboveground-biomassand below-ground biomass significantly increased. There was no significant difference(P>0.05) between the subermerged evaluation (165-175m&155-165m) andnon-subermerged evaluation (>175m).④The nitrogen and phosphorus contents of the HFZ vegetation at the early time ofthe non-subermerged period were higher than those at the middle and the end time of thenon-subermerged period. At the middle and the end time of the non-subermerged period,nitrogen and phosphorus contents didn’t have significant difference (P>0.05) between thesubermerged evaluation (165-175m&155-165m) and non-subermerged evaluation (>175m).The nitrogen and phosphorus accumulation of HFZ vegetation in TDR didn’t depend onthe nitrogen and phosphorus contents but the biomass.⑤The HFZ plants of TDR were more restrict to nitrogen when they were growing(N:P<7). The vegetation at control evaluation had a relatively stable N:P while those atHFZ had significant difference (P<0.01) between the middle and the end time of thenon-subermerged period. The unstable N:P during the non-subermerged period meant thevegetation was adapt to the changeable environment.⑥The results of study on the phenology of dominant species at HFZ showed thatannual plants, such as Chenopodium album, Polygonum hydropiper and Erigeron annuusadvanced their phenology and shortened life history cycle compared with those in normalhabitats. Phenology of perennial plants which have stolons or rhizomes, such asAlternanthera philoxeroides, Artemisia argyi and Humulus scandens was almost the sameas the actual situation. Dominant plants at HFZ were able to adapt to subermergencedisturbance, while there were some differences in their adaptation strategies.⑦Considering the ecological function, economic value and landscape of HFZ, weproposed a reasonable management strategy making a periodic harvest for the vegetationdeveloping at155-175m zone. The harvest could directly reduce the contribution ofnitrogen and phosphorus to the water of TGR, also could maintain the biological diversityof ecological system at HFZ.