Asexual Propagation Of Quercus Variabilis And Its Role In Population Recovery

Natural Quercus variabilis forests in China have degraded because of over exploitingand cutting. Asexual propagation (sprouting) is an important reproduction mechanism insecondary Q. variabilis stands; however, limited information exists on the type of asexualreproduction, their positions and contributions to population recovery as well as factorsaffected sprouting in this species. The type of Q. variabilis sprouts, their positions in forestrestoration, time and space factors affected their contributions and growth were studied insecondary Q. variabilis forest, which is located in Qinling Mountains, through permanentplots survey and fixed experiments during2008~2010. Meanwhile, endogenous hormone indormant buds and sprouting buds of stump were detected to reveal the inner mechanism ofsprouting. The results were displayed below.(1) There were three different origins for Q. variabilis recruits in the research area,named as true seedling, stump sprout and stem base sprout, respectively, and stump sproutswere the main asexual recruits, and they contributed most to population restoration, trueseedlings were the second important recruits, and stem base sprouts just contributed a little topopulation restoration. Stump sprouts those were2~4years-old were abundant compared withother ages, while the age structure of true seedling was complete and the number of trueseedling declined with increasing age; base diameter, height, aboveground biomass and leafarea of stump sprouts were all higher than those of stem base sprouts and true seedlings; therewere drastic competition among stump sprouts, which was suggested by higher mortality rate.Stump sprouts were propitious to forestland recovering in short time because of their fastgrowth and abundant stems.(2) The relative importance of true seedlings and sprouts in different restoration stagesafter select logging for Q. variablilis population was evaluated in5,10and20yearspost-logging stands and unlogged stand. Sprouts especially stump sprouts were thepredominant recruitments in select-logged stands, while true seedlings were dominant inunlogged stand. The density of stump sprouts and sprouts number per stump, from high to low,were5years post-logging>10years post-logging>20years post-logging> unlogged stand, thedominant position of stump sprouts declined with increasing of post-logging age, the stumpsprouts contributed more to population recovery in the early stage after select-logging. True seedling’s contribution may be limited in the early stage after select-logging, but its densityincreased with prolong of population restoration time, meanwhile it benefits for forestlong-term development due to their ongoing age structure. Stem base sprouts, which wereshorter and smaller than other recruitments, were just observed in20years post-logging andcontrol plots and they contributed a little to population regeneration.(3) Slope aspect had no influence on population reproductive strategy, stump sproutswere the predominant recruits in both sunny slope and shady slope. But slope aspect didaffected the growth of recruits, the base diameter of stump sprouts and true seedlings in sunnyslope were greater than those in shady slope, and the height of these two kinds of recruitsdisplayed opposite trend. Q. variablilis took different reproductive strategies in understory,forest gap and forest edge: in understory, the positions of stump sprouts and true seedlingswere almost equal, but in forest gap and forest edge, stump sprouts occupied predominantposition implied by their largest base area and important value. Forest gap was a kind offriendly habitats which was beneficial for growth of sprouts and true seedlings compared withforest understory and forest edge. The number and growth of stem base sprouts were notinfluenced by slope aspect and micro-habitats, and there was no stem base sprout in forestgap.(4) Through surveying stump sprouting during3continuous years in clear-cutting Q.variabilis stand, we found that more than80%Q. variabilis stumps could keep live sproutsduring three years after cutting. All stumps sprouted in the first year after cutting, and stumpsurvival rate, sprout number, and sprout height growth declined with time after cutting.Stumps formed in December (dormant season) displayed greater sprouting ability than thosecut in growing season, but the effect of cutting season on sprouts growth disappeared in thesecond and third growing seasons after cutting. Stump diameter affected sprouting positivelythroughout the three years, while stump height influenced sprout number and sprout heightduring the first year, and the effect disappeared in the second and third years. So, larger basediameter (>15cm) and higher stump was beneficial for sprouting. It was essential toadjustment sprout number per stump in the early stage after cutting. After comparing thestump sprouts of understory, forest gap and forest edge, we found that forest gap was a kind offriendly habitat which was beneficial for stump sprouting and sprouts growth compared withforest understory and forest edge, although the mortality of stump sprouts in forest gap was alittle high.(5) The number and growth of stem base sprouts, which sprouted from mother trees indifferent DBH, were studied during two continuous growing seasons based on girdingexperiment. Q. variabilis mother trees in10cm~20cm DBH could form stem base sprouts easily after been girding, and the number of sprouts in these trees was stable, meanwhile, thesprout base diameter and height were both greater than those sprouts grew from other mothertrees during two years. However, sprouts mortality of these trees was lower than that of othermother trees. The relationship of sprouts number and mother tree DBH was negative, whichwas implied by sprouts number declining with increasing mother tree DBH（excpet first DBHclass）, as well as the sprouting time of large mother tree was later than that of small (smallDBH) mother tree.(6) Based on root-broken experiment that conducted in Q. variabilis mother trees withdifferent size, the broken root could form root sucker or not, as well as sprouts survival rateand growth were monitored during two continuous growing seasons. Adventitious buds weredetected in the broken root system of mother trees in10cm~20cm DBH, but these buds cannot develop to root sprouts. For Q. variabilis in Qinling Mountains, root sprouting was justaccidental phenomenon, and contribution of root sprouts to population regeneration waslimited.(7) The contents of four endogenous hormones, including ABA, IAA, GA3and Zeatin, insprouting buds and dormant buds of Q. variablilis stump were determined through highperformance liquid chromatography (HPLC). The sprouting of dormant bud was influencedintensely by the kinds and contents of endogenous hormones. The contents of IAA, GA3andZeatin in dormant bud were all far less than those in sprouting bud, while the content of ABAin dormant bud was as two times as that in sprouting bud. GA3played an important role inbreaking dormancy of dormant bud, and Zeatin promoted the initial sprouting of the dormantbud. IAA had little effect on dormant bud sprouting, while ABA inhibited and played abalancing act in sprouting. Higher value of GA3/ABA was better for dormant buds breakingdormancy.(8) During managing and conversion Q.variabilis secondary forest in the future, it wasbeneficial for stand fast recovery and polulation sustained development if applying asexualreproduction character reasonabley: cutting Q. variabilis with a larger base diameter (>15cm)at more than30cm high aboveground during the dormant season can maximize stumpsprouting, and the fast growth of stump sprouts can recover the ecological protection fuctionas soon as possible; meanwhile, after select cutting, keep the amount of true seedlings at areasonable level through protection and/or increasing the sowing density can increasepopulation gene diversity in cutting stand and be beneficial to true seedlings play a role inpopulation restoration in a long time; making girding to target Q.variabilis trees those were10cm~20cm in DBH first and then cut them after they sprouting, this method could helpcutting stand recover fastly; in the Q.variabilis secondary forest that was lack of recruits, cutting undergrowth Q. variablilis individuals appropriately to open forest gap, this measurecould promote population regeneration.