Study On The Micro-Environment Characteristics And Seedlings Dynamic Regeneration In Castanopsis Kawakamii Natural Forest Gaps

Castanopsis kawakamii Hayata, a broad-leaved evergreen species of Fagaceae and of long growth periodcycle, is a relic plant of the Territory and endangered plant in the southern edge of mid-subtropics in China, whosedistribution is comparatively narrow. C. kawakamii natural forest, which is almost pure forest above700hm~2areain Fujian province of China, is a transitional type between central and southern subtropical evergreen broadleavedforests. The over mature population,species competition and human disturbance all could affect the dynamicperiodic fluctuations of C. kawakamii populations．Moreover, this forest has entered into a decline stage as a resultof severe fragmentation in the canopy layer, with increasing gaps in the forest canopy, the decreasing quantity ofmiddle age structure of C. kawakamii population, low germination rate of seeds and growth of seedlings in theforest and difficulties in regeneration of forest understory, which makes efficient protection, construct the optimalecological environment for its natural regeneration and improvement in its regeneration an urgent matter at thistime. The research of forest gap basic characteristics, micro-environmental characteristics, populationregeneration characteristics and seedlings regeneration dynamic were studied in this paper. The forest gapregeneration characteristics and restoration technology of C. kawakamii natural forest were firstly conducted andrevealed the C. kawakamii seedlings regeneration threshold, and propose the artificial practical measurements toimprove C. kawakamii regeneration.The minimum, maximum and average areas of canopy gaps were29.03m~2,98.92m~2and61.89m~2, and themaximum, minimum and average areas of expanded gaps were487.42m~2m~2,180.66m~2and327.83m~2in thecollected C. kawakamii natural forest gaps. The main tree species of gap border trees (GBTs) were C. kawakamiiwhose proportion was74.75%; the structure of DBH of GBTs showed a left-skew distribution, which consistentedwith the normal distribution, Weibull distribution and β distribution; the structure of tree height classes showed anormal distribution and mainly from15to30m; the GBTs' crown inclination was obvious, which was mainlyfrom0.5to0.8(70.71%). With exception for a few low diameter GBTs,most of GBTs were composed ofwell-developed medium or high diameter trees which were over mature compared with those of non-gaps, whichindicated that it was difficult to accomplish the forest gap regeneration by solely relying on GBTs and it wasindispensable to strengthen the protection of seedlings and young trees.Spatial and temporal distribution characteristics of illumination intensity were measured in C. kawakamiinatural forest gaps. The results showed that the illumination intensity in four seasons decreased form the gapcenter, canopy gap, expanded gap to non-gap, and the highest in gap center and lowest in non-gap. The directions of relatively high illumination intensity in canopy gap and expanded gap were different in four seasons. Thediurnal variation of average illumination intensity in C. kawakamii natural forest gaps demonstrated as normaldistribution curve and presented a low-high-low trend. The illumination intensity was low in the morning andevening, whereas reached the peak value in the noon. The illumination intensity was different among the smallgaps, medium gaps and large gaps, which were highest in large gaps, secondly with the medium gaps and thelowest average illumination intensity in small gaps.The differences between air temperature and relative humidity in spring, summer, autumn and winter wereextremely significant in forest gaps (P<0.01). The effects of four seasons on soil temperature0, soil temperature5and soil temperature10were highly significant (P<0.01). The diurnal variation of air and soil temperature andhumidity showed a single peak curve. The diurnal variations of relative humidity and soil water content werehigh-low-high trend. The differences between air temperature and relative humidity were extremely significant indifferent gap sizes of forest gaps. The air temperature of medium gaps was the highest, while with the lowestrelative humidity; the air temperature of small gaps was the lowest, while with the highest relative humidity. Thedifferences between soil temperature and moisture were extremely significant in different gap sizes of forest gaps.The difference of soil water content between small gaps and large gaps, moderate gaps were extremely significant.The air temperature, relative humidity, soil temperature and soil water in different locations of forest gaps weregradually decreased form the gap center, canopy gap, expanded gap to non-gaps.The results indicated that the wind speed of four seasons changed slowly in different points of C. kawakamiinatural forest gap, while the wind speed was the lowest in autumn and basically the same in spring, summer andwinter. The wind speed in autumn was significantly lower than in spring, summer and winter (P<0.01). Thediurnal variation of wind speed showed as a single convex peak curve in spring and summer of forest gaps, andthe diurnal variation of wind speed tended to be stable in autumn and winter during the daytime. The differencesof wind speed among the small gaps, medium gaps and large gaps were various, and the medium gaps were thehighest, secondly with the small gaps and large gaps the lowest. The wind speed in different locations of forestgaps showed that the canopy gap and expanded gap were relatively high, whereas relatively low in the gap centerand non-gap.Forest gaps in various sizes and development stages could improve soil pore space structure and watercharacteristics which may effectively promote water absorbing capacity of plant roots and plant growth, whichplayed an important role in plant regeneration. Soil pore space structure and water characteristics in small gapswere more obvious improvement, followed by the medium gaps. Soil pore space structure and watercharacteristics in late development stage gaps were more relatively improved, followed by the early developmentstage gaps. The contents of hydrolyzable N and available K in various sizes and development stages of forest gapswere higher than those of non-gaps, whereas the contents of total N, total P, available P, organic matter andorganic carbon were lower. The contents of total N, hydrolyzable N, available K, organic matter and organiccarbon in medium gaps were higher than those of large and small gaps. The contents of pH, hydrolyzable N andthe ratio of carbon to nitrogen(C/N) of forest gaps in various development stages were higher than those ofnon-gaps. The contents of total N, hydrolyzable N, total P, available P, organic matter and organic carbon in medium gaps were higher than those of medium and late development stage gaps.The average soil respiration rate in forest gaps and non-gaps were1.5211μmol CO2·m-2·s-1and1.5220μmolCO2·m-2·s-1, which had no significance with each other. There was no significant difference between soilrespiration rate with soil temperature and soil water content in forest gaps (p>0.05). There was no significantdifference between soil respiration rate with soil water content in non-gaps (p>0.05), whereas the extremelysignificant difference between soil respiration rate with soil temperature (p<0.01), the optimal regressionequation was y=0.0109e0.2761x. There was significance between soil respiration rate with Total P in forest gaps,whose the optimal regression equation was y=17.821x2-7.9157x+2.3536.The effect of forest gap disturbance on the stability of species in the regeneration layers of natural C.kawakamii forest were studied by improved M. Godron's stability methods in C. kawakamii natural reserve. Theplants in the tree layer of the forest gap were stable, but were unstable in the understory. The plants in the shrublayer of both the forest gap and understory were stable. The importance value of Litsea subcoriacea was thehighest in the tree layer of the forest gap and understory, which occupied an important role in forest regenerationand would likely have a greater impact on the regeneration of C. kawakamii population. The importance value ofC. kawakamii was relatively low in the tree layer of the forest understory, which affected its regeneration.However, forest gap disturbance improved the upward growth and importance value of C. kawakamii, whichcould achieve the regeneration and restoration of the C. kawakamii population effectively.The effect of forest gaps on species regeneration niche in regeneration layers was conducted by improvedmodels of regeneration niche width and niche overlap of C. kawakamii natural forest. Regeneration niche width ofC. kawakamii in forest gaps was higher than that of non-gaps. The regeneration niche width of Litsea subcoriaceain forest gaps and non-gaps was the most, while the regeneration niche overlaps between the population of L.subcoriacea and C. kawakamii were relatively high in forest gaps and non-gaps. High regeneration niche overlapsbetween the population of C. kawakamii and other species with sufficient available resources in early phase afterthe formation of forest gaps showed that the relationship of main tree populations in C. kawakamii forest gapswere not competition but a tendency of resource sharing. However, the main species with high regeneration nicheoverlaps may bring an obvious competition with the shortage of available resources in late phase of forest gaps.The further differentiation of niche width lead the species composition of forest gaps were under the situation ofdynamic balance and gradually filled the forest gaps to accomplish the forest regeneration finally. The future treespecies composition in C. kawakamii natural forest was a mixed community which mainly consisted by L.subcoriacea, Schima superba, Itea chinensis and C. kawakamii population. The whole community now ischanging in complex direction with diversity species composition.Seed rain, seed bank distribution characteristics and seedlings regeneration status in forest gaps and non-gapswere analyzed in C. kawakamii natural forest. Seed rain continued about2months and peaked at last ten-dayperiod of November to second ten-day of December. The seed rain quantities in the peak period occupied77.13%and74.5%of total seed rain quantities in forest gaps and non-gaps separately. Seed species in soil were low anddominated by C. kawakamii in forest. The vertical distribution of total seed bank quantities and C. kawakamii seedquantities both demonstrated with liter layer (about2/3)>humus layer (about1/3)> subsoil layer (less than1%). Conversion rate from total seed rain quantities to intact seed numbers in seed rain dispersal were relative high, andthen turned to intact seed numbers in seed bank and seedlings density in field practice presented a decreasingtrend. It should strengthen the protection of C. kawakamii seeds and seedlings for its extremely low conventionrate from seeds to seedlings.The effects of different treatments (seed sizes, temperatures, concentrations of gibberellins and seed capsules)on germination percentage, germination potential, germination index and average germination rate of C.kawakamii seeds were studied to improve the germination ability. The results showed that germination percentageof the large and medium C. kawakamii seeds were higher than that of small seeds; the favorable temperature were40℃and50℃and extreme temperature restrained the germination; different concentration of gibberellinspromoted the germination and the germination percentage of C. kawakamii seeds were over70%when treatedwith10,20and50mg/L gibberellins solution; removal of the seed capsule could improve the germinationpercentage. The germination rate of C. kawakamii seeds in wild was less than30%, and germinated seeds mainlywere small seeds, worm-eaten seeds and eaten by animals but have vigorous, whereas the germination rate wasabout60%during the indoor experiment, which indicated that low germination rate of C. kawakamii seeds in wildwas possibly affected by natural and human disturbance.The competition intensity of C. kawakamii seedlings were calculated by the improved competition model forindividual tree of Hegyi, which were optimized by the exponential smoothing model. The optimum competitionranges were confirmed by using the method of single slope change point. The results showed that: The averagecompetition intensity of C. kawakamii seedlings decreased with the increasing of competition distance withcompetition intensity decreased quickly at early stage while it had a slow down obviously after in a certain extentand existed a turning point in the change range called the seedlings competition zone of C. kawakamii naturalforest gaps and non-gaps. The minimum mean square errors of the third index smooth values of C. kawakamiiseedlings competition intensity in forest gaps and non-gaps were the least when the smoothing coefficient α=0.83and α=0.79respectively. By applying the method of single slope change point,the optimal sampling plotscompetition zone of C. kawakamii seedlings competition intensity were1.68and2.00meters distance from theobjective trees. We could investigated the competition trees around2meters distance from the objective trees tocalculate the competition intensity in field practice, which could demonstrated the competition pattern of C.kawakamii seedlings and improve the survey efficiency.The intraspecific and interspecific competitions intensity of C. kawakamii seedlings in C. kawakamii NatureReserve were quantitatively analyzed by using Hegyi's competition index model. The results showed that theintraspecific competition intensity in C. kawakamii seedlings decreased gradually with the increasing of heightclass. The intraspecific competition intensity of C. kawakamii seedlings at the early growth stage was at a mediumlevel. With the seedlings' height rising, the intraspecific competition of C. kawakamii seedlings was weakgradually, the interspecific competition of C. kawakamii seedlings was obvious increasingly and the C. kawakamiipopulation has the tendency of deterioration. In C. kawakamii natural forest gaps and non-gaps, the intraspecificcompetition intensity in C. kawakamii seedlings decreased gradually with the increasing of height class indifferent habitats. The order of the interspecific competition intensity in forest gaps was: Camellia octopetala> Photinia hirsute> Machilus grijsii> Litsea subcoriacea> Calamus thysanolepis> Antidesma japonicum>Engelhardtia fenzelii> Itea chinensis> Syzygium grijsii> Randia cochinchinensis> Syplocos lancifolia> Ardisiapunctata> Castanopsis fargesii> Diplospora dubia> Schima superba> Syzygium buxifolium> Maesa japonica.The order of the interspecific competition intensity in non-gaps was: L.subcoriacea＞C.octopetala＞M. grijsii＞S.superba＞Ilex pubescens＞D. dubia＞C.thysanolepis＞Neolitsea cambodiana＞A. japonicum＞A. punctata＞C.dentata＞S. lancifolia＞S. buxifolium＞S. grijsii＞C. kawakamii＞Distyliopsis dunnii＞M. japonica＞C. fargesii.The competition of C. kawakamii seedlings and samplings was mainly from interspecific competition whileintraspecific competition had little effect on it. Intraspecific competition and overall interspecific competition inforest gaps were higher than those of non-gaps. it should strengthen the protection of C. kawakamii seedlings inthe early stage of forest gaps and the gap environment should be created to accelerate the growth of C. kawakamiiseedlings and samplings after the height up to100~150cm in non-gaps which could effectively improve theconservation and regeneration of C. kawakamii population in forest gaps and non-gaps.The diurnal variation of net photosynthetic rate in5age classes of C. kawakamii seedlings of forest gapsand non-gaps in C. kawakamii natural forest showed that:5age classes of C. kawakamii seedlings of forest gapsand non-gaps showed single peak in four seasons. Photosynthetic rate was not high in the morning due to the lowphotosynthetically active radiation (PAR) and air temperature. Moreover, there was no obvious midday depressionat noon. Net photosynthetic rate (Pn) appeared after12:00and decreased gradually thereafter. The seedlingsgrowth rate of C. kawakamii seedlings in forest gaps was faster than that in non-gaps for the improvement oflight-temperature-water in forest gaps could promote the growth of C. kawakamii seedlings.The light response in5age classes of C. kawakamii seedlings of forest gaps and non-gaps in C. kawakamiinatural forest showed that: the orders of light compensation point (Lcp) in5age classes of C. kawakamii seedlingsof forest gaps were:3-4age class>5-6age class>7-8age class>9-10age class>1-2age class; the size order of Lspsof C. kawakamii seedlings were:5-6age class>7-8age class>3-4age class>9-10age class>1-2age class. Innon-gaps, the size order of Lcps in5age classes of C. kawakamii seedlings were:3-4age class>5-6age class>7-8age class>1-2age class>9-10age class; the size order of Lsps of C. kawakamii seedlings were:5-6age class>3-4age class>7-8age class>9-10age class>1-2age class. All of Lcps in5age classes of non-gaps were lower thanthose of forest gaps, shade-tolerant performed, however, C. kawakamii seedlings grew slowly in dim light, evenstoped growth, whose shade-tolerant ability cost of its growth. All of light saturation points in5age classes ofnon-gaps were lower than those of gaps, which showed that shading condition was not good for photosynthesis ofC. kawakamii seedlings which could be in disadvantage under community competition and very unfavorable forpopulation regeneration. Hence, C. kawakamii seedlings in forest gaps were more favorable for the regeneration.The CO2response in5age classes of C. kawakamii seedlings of forest gaps and non-gaps in C. kawakamiinatural forest showed that: When C. kawakamii seedlings in forest gaps were in initial period of low CO2concentration, apparent carboxylation reaction efficiency of7-8age class seedlings is higher than other four ageclasses, which showed that7-8age class seedlings could make use of low concentration CO2more efficiently. Netphotosynthetic rate of3-4age class seedlings was the highest in forest gaps when CO2saturated. When C.kawakamii seedlings in non-gaps were in initial period of low CO2concentration, apparent carboxylation reaction efficiency of5-6age class seedlings is lower than other four age classes, which indicated that5-6age classseedlings could take use of low concentration CO2for photosynthesis more efficiently. Net photosynthetic rate of5-6age class seedlings was the lowest in non-gaps when CO2saturated. Both of the CO2saturation points and CO2compensation points of C. kawakamii seedlings in forest gaps were higher than those in non-gaps with5-6ageclass seedling contrary, which might due to the decrease of wind speed from gap center, canopy gap and thenexpanded gap gradually and intercellular CO2concentration decreased in forest gaps.There was a very significant logarithmic functional relation between the length×width and area of adultleaves, presented as y=4383.232lnx-34519.789. There were extremely significant power functional relationsbetween the length×width and area of C. kawakamii seedlings' leaves in forest gaps and non-gaps, presented asy=0.255(lnx)1.092and y=0.866(lnx)0.944, respectively. The relative chlorophyll contents of C. kawakamii seedlings'leaves in different age classes of forest gaps and non-gaps both tended to increase firstly and then decrease. Therelative chlorophyll contents in5-6age class of C. kawakamii seedlings' leaves were the highest, whereas1-2ageclass the lowest in forest gaps and non-gaps. The relative chlorophyll contents of C. kawakamii seedlings' leavesin same ages of forest gaps were lower than those of non-gaps. The relative chlorophyll contents in three parts ofC. kawakamii seedlings' leaves generally shower as: leaf apex>leaf middle>leaf base. The explanation of relativechlorophyll contents in leaf middle to the average relative chlorophyll contents were the highest.The biomass and nutrition content of C. kawakamii seedlings in different age classes of forest gaps andnon-gaps were different, and the biomass of seedlings increased with the increasing of age. The total dry weight in1-2age class,3-4age class in forest gaps were lower than those of non-gaps, whereas the total dry weight werehigher than those of non-gaps during the5-6age class and thereafter. As a result of the initial stages of C.kawakamii seedlings need to live in shade and humid environment, the total N content of3-6age class of C.kawakamii seedlings in forest gaps was lower than that of non-gaps, while with slow growth rate. With thegrowing of seedlings and the demanding to light increasing, because of forest gaps could provide moreappropriate environment for the survival of seedlings, the total N content of7-8age class and growth rate of C.kawakamii seedlings in forest gaps was developing, which also illustrated in the9-10age class of C. kawakamiiseedlings in forest gaps.The difference analysis of regeneration threshold affected factors of C. kawakamii seedlings indicated thatthe growth rate of3-6age class of C. kawakamii seedlings in forest gaps was lower than that of non-gaps due tothe initial stages of C. kawakamii seedlings need to live in shade and humid environment. The Seedlings total dryweight, root dry weight, stem dry weight, leaf dry weight and total N content of7-8age class and growth rate of C.kawakamii seedlings in forest gaps were higher than those of non-gaps. Moreover, the all regeneration impactfactors of9-10age class of C. kawakamii seedlings in forest gaps were higher than those of non-gaps. Using theattribute reduction algorithm method of rough set to screen the degree of importance of evaluation indices, and theevaluation of C. kawakamii seedlings' growth was studied by using the Catastrophe Progression Method. Theresults showed that the light illumination may have certain limitation to the C. kawakamii seedlings growthduring the1-2age class, which growth rate was lower than that of non-gaps. As a result of micro-habitatheterogeneity of forest gaps, it could provide more sufficient available nutrition which could promote the C. kawakamii seedlings growth and continues increasing of the growth rate. In non-gaps, it could provide betterclosed environment for the initial growth period of C. kawakamii seedlings and had a relatively fast growth rate.However, the growth rate of C. kawakamii seedlings during5-6age class later decreased gradually as a result ofthe light illumination hardly satisfied the demand of seedlings growth. With the growing of seedlings andthe demanding to light and temperature increasing, meanwhile the improvement of light-temperature-water inforest gaps could promote the growth of C. kawakamii seedlings, it indicated that7-8age class of C. kawakamiiseedlings was the critical stage of seedlings regeneration, called as seedlings regeneration threshold. As for7-8age class of C. kawakamii seedlings in non-gaps, it should take certain of tending measures to created a forestgaps to improve the regeneration of C. kawakamii seedlings.