| Forest gap is the area in the forest created by old tree dying,insect,some diseases,or struck by lightning,blown over by the wind or storm,or are knocked down by other falling trees.The appearance of the gap enhances forest dynamics.Forest gap is a link between forest disturbance and forest succession.Therefore,the forest gap is important in maintaining the forest ecosystem.Gap creation has effects on microclimate,light intensity,soil temperature,air temperature and soil moisture,and can change when the canopy is opened.Solar radiation and soil temperature differed significantly among gap size and placement within the opening.The Castanopsis kawakamii natural forest,Sanming City,Fujian Province,China is a subtropical evergreen broadleaved forest dominated by the mature C.kawakamii(average age over 100 years),C.carlesii,Pinus massoniana and Schima superba,which is the biggest and purest C.kawakamii natural forest.Many studies have focused on this area.The results have reported that in different gap size and gap location,there are different features of air-soil temperature,relative humidity,and soil water content.This condition also varies seasonally.The different conditions in the microsite may influence seed germination and seedling establishment of C.kawakamii.The C.kawakamii population is reducing and the population age structure is not sustainable because of the seedlings and saplings of C.kawakamii is decreasing.The main reasons are the lack of seed germination,seedling establishment,and human disturbance.As aforementioned,the gap has an effect on species regeneration but present findings showed that most studies have focused on microclimate in forest gap.The spatial heterogeneity of microenvironment and effect of gap size on microenvironment are still unclear.The effect of gap size on seedling regeneration and how it respond to the microenvironment in forest gap are still unknown.In this study,we explored the effect of a gap on micro-environment and environmental factors that influence the leaf traits and investigated the respond of C.kawakamii seedling to micro-environment within the gap.The aims of this study 1)To investigate the effect of forest gap on the dynamics of micro-environment during the daytime.2)To reveal the effect of gap size on spatial variability of soil chemical-physical properties.3)To investigate the effect of light intensity on the micro-environment and on the leaf traits.4)To investigate the response of leaf traits to gap micro-environment in regeneration layer and 5)To investigate the effect of gap size and location within the gap on the C.kawakamii regeneration.The two hemispherical photographs(THP)method was used to calculate the gap area by using fish-eye lens camera.The area of nine forest gaps were measured.The largest area is 216.72 m2 and the smallest area is 30.28 m.According to the ranging of gap area,we classified the nine forest gaps into small(30-50 m2),medium(50-100 m2)and large gaps(>150 m2).The small gap size was created by branch fall,while the large and medium gap size were created by trees fall.Meanwhile,non-gap was selected as control groups with the areas 15m×15m.Sampling points were set by using the grid system size 3m×3m,which applied over the entire gap area and non-gap areas as well.In each sampling point,the micro-environments which include soil temperature at 0,5 and 10 cm depth(ST0,ST5 and ST 10),air temperature(AT),light intensity(LI),and air relative humidity(RH)were recorded in every 2 hours interval from 8 am to 6 pm.The data were collected on June 15tth-25th 2014 and on January 5th-15th 2015.We used geostatistical analysis to illustrate the spatial patterns of soil physical-chemical properties and soil enzyme activities variability within 9 gaps,and non-gap areas.To investigate the effect of gap size and microenvironment within the gap on leaf traits.Plots size 5m×5m in different five directions within gaps and non-gap areas were conducted for leaf samples collecting.We collected leave from regeneration layer(<2 cm DBH,height 2-5 m.)to measure the leaf traits in winter and summer seasons.The selected leaf traits were leaf area(LA),leaf dry mass(LDM),specific leaf area(SLA),Chlorophyll a(Chla),chlorophyll b(Chlb),total chlorophyll(TChl),and carotenoid(CAR),soluble sugars content,starch content,nitrogen content(N),carbon content(C),phosphorus content(P),potassium content(K)and leaf enzyme activity.For species management and conservation,we explored whether a forest gap has the potential to promote the regeneration of C.kawakamii seedlings and examined favorable locations for seedling regeneration within the gap.Numbers of C.kawakamii,the basal areas,and the height at four stages(tree,sapling,shrub,and seedling)in five locations in the gap(center,south,east,north,and west)were determined in the summer season.The results of this study are as follows:The results showed time-dependent variations for the micro-environments.In each gap size,the maximum LI was recorded at 10 am to 2 pm at the center of the gap,which was higher at the north and west directions than south and east directions,except for the north direction in large gap size.LI has a significant positive correlation with ST compared with that non-gap area.ST responded differently with respect to gap size.Unlike the small and medium gap sizes,the ST increased from morning to afternoon in large gap size with the highest during 12 to 2 pm.AT has a significant negative correlation with RH,both in gap sizes and non-gap.Gap size had a significant impact on the micro-environments and the variables in five directions varied depending on the LI.We found that every soil physical properties,except SCP and STP,significantly differed with gap size.Gap sizes generally improved the soil physical properties,especially in the small and large gaps,indicated that the soil is more suitable for plant growth than that of the non-gap area.The highest spatial variability of soil physical properties was observed in the large gaps.Most of the soil chemical properties vary by the gap sizes and seasons.Gap size influences the soil chemical properties,with a higher effect in the summer season when compared to the winter season.The results of this study showed that gap size may affect the soil chemical properties but in not regular patterns with respect to gap size.The soil pH in the small gap size was significantly lower when compared with the medium gap size,while OM,TN,TC,C/N ratio were lowest in medium gap size and highest in large gap size.The effect of gap size on TP and TK were the same patterns,the value of TP and TK were increased by gap size.AP and AK have the greatest value in the small gap size when compared with another gap size.The average value of soil OM,TP,TK AP,UA,CA,TN,TC and C/N ratio in the winter season were higher than in the summer season.We found a strong significant correlation among TN,TC,C/N ratio and OM.The highest OM in large gap size indicating the high potential of nutrient supply for the plant growth of soil in the large gap size.Besides,the OM has a negative significant correlation with soil pH.However,the soil pH range in this study area may affect the availability of plant nutrients.The spatial variability of soil chemical properties varies by the season.The variability of soil pH was less,while variability for soil OM in every gap size and non-gap area were moderated.Soil TN and TC had a same value of variability,with a little difference from soil C/N ratio.The variability of soil TP,TK,AP,AK,and HN in every gap size and non-gap area were moderate.The spatial variability in each soil chemical property was not in the same pattern depending on the gap characteristics and also other factors that have an effect on its.The study of the spatial variability of soil chemical properties in gap provides the database for the gap management and species conservation in this study area.Each gap has theirown environment,which affects species growth.Light changes when gap creates.We found that LI had a positive significant correlation with the ST and AT but the negative significant correlation with the RH,the correlation was inversed in the non-gap area.There was significant difference of LI among the gap sizes which was highest in the large gap size and lowest in the small one.The spatial heterogeneity of LI differ among the gap depends on the topography,slope direction,and location of trees at each direction.In medium and large gap size,LI had a negative significant correlation with the SLA(r =-0.248,p = 0.04 and r =-0.264,p = 0.008).At all directions,the SLA increased with decreasing LI.The effect of gap size on the average Chla,Chlb,TChl and CAR varies by the season.During the summer season,we recorded the highest chlorophyll contents in the small gap size and the lowest in the non-gap area,while during the winter season,the highest values of these chlorophyll contents appeared in the medium gap size.Moreover,the directions within the gap in the medium gap size of the summer season had an effect on the Chla and TChl.However,the average soluble sugar and starch contents did not differ significantly which might be due to the fact that these parameters are species specific.Gap size did affect the average K content in leave both in summer and winter seasons,while the effect on the average P content occurs in winter.The C and N contents were not affected by the gap size.Gap size had an effect on the average soluble protein content in the summer season and enzyme activity SOD(U/g)in the winter season.For other enzymatic activities,we did not find any significant difference among the gap sizes.Results from the RDA analysis between leaf traits and environment variables showed the difference between summer and winter seasons,while leaf traits in the summer correlated with environmental variables more than in the winter season.This result indicates that the environment in the summer season had more effect on the leaf traits when compared to the winter season.The p-value showed that during the summer season,the leaf traits were more correlated with soil chemical properties than soil physical properties.Moreover,the p-value of soil chemical properties in the summer was more significant than in the winter season.Summer is the growing season of this study area,which might have contributed to the plant response to the environmental factors better than winter season.We found a significant positive relationship between the number of C.kawakamii and gap area(r = 0.815,p=0.007).The number of C.kawakamii was predicted using a linear regression model:Number of C.kawakamii= 0.124× Gap area + 10.597,R2 = 0.664,p = 0.007.Higher number of C.kawakamii was found in the large gap size compared to the small gap size(p = 0.031).We found that the number and size of seedlings in the center of the gap were significantly different(p-0.041 and p = 0.017)than those of other locations within the gap.However,the interaction between C.kawakamii and the environment was complex and depended on shifts in species niche.We concluded that gap area at C.kawakamii natural forest was driven by the species diversity and altered the environment within the gap when compared to the non-gap areas.Gap area had an effect on the microenvironment within the gap,which had a duration fluctuated and varies by the season.Gap size had an effect on soil physical-chemical properties.The soil composition in the gaps was better than non-gap area.Introducing gap areas would improve the soil water storage better than non-gap area.The spatial variability of soil chemical-physical properties data in this study was a good database for the forest gap management.In each direction of different gap sizes,LI had effect on micro-environment and SLA when compared with non-gap.In addition,SLA had a positive significant correlation with N and P contents in leaves.The result showed that the average SLA value was lowest at the center of the gap.Gap size affected the leaf traits differently.Each leaf trait is varied by the species,age,seasonal,environmental factors etc.In this study few species that were affected by the environmental factors in different gap sizes were due to the limited number of leaf samples of these species.LI had an effect on the SLA and chlorophyll in some species,while the leaf enzyme activities in this study were not good parameters to study the effect of a gap on it.Gap area in this study also promoted the C.kawakamii regeneration.C.kawakamii seedling needs gap area to regenerate,especially in the large gap size.For the species conservation,forester must focus on the center of the gap with the best suitable for C.kawakamii seedling regeneration.The result from this study is the prime knowledge for the forest management and conservation at C.kawakamii natural forest. |
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