Productivity And Its Control Mechanisms Of Phyllostachys Pubescens Forest In Anhui Province

Phyllostachys pubescens is a very important forest type and resource in South China.This bamboo species is widely distributed,with the largest cultivation area and the highest economic value.Based on the investigation and analysis of the characteristics of site conditions and soil nutrients of Ph.pubescens forest in the main production areas of Anhui Province,this study aimed at determining the controlling factors on the growth and productivity of Ph.pubescens forest,so as to fully understand the productivity formation mechanisms and its regulations,and to provide basis for their sustainable management.The major results are as follows.?1?The mean DBH,mean height,mean density,mean ABH,and mean AGS of Ph.pubescens forest in four production areas in Anhui Province were,respectively,10.91 cm,14.67 m,2958 culms·hm^-2,28.31 m²·hm^-2,and 0.35.Based on the bamboo stock density,the productivities of Moso bamboo forests in areas of the south,north slopes of Dabie Mountains and southwest Anhui belonged to middle-class stands and to low-yield stands in area of the southeast Anhui.?2?The biomass of Ph.pubescens forest in various production areas of Anhui Province was ordered as North slope of Dabie Mountains(93.56 t·hm^-2)>South slope of Dabie Mountains(88.04 t·hm^-2)>Southwest Anhui(86.65 t·hm^-2)>Southeast Anhui(58.77 t·hm^-2).The proportion of culm biomass was the highest,and the proportions of the other components such as branches,leaves and roots were relatively small.The stand biomass of Ph.pubescens forest in different slope directions was ranked as sunny slope>shady slope>semi-sunny slope.The stand biomass of Ph.pubescens forest was greater at the downhill than at the mid-slope.With the increase of altitude,the total biomass and component biomass increased.Altitude at 500-700 m is suitable for growth of Ph.pubescens.With the increase of soil thickness,the total biomass and component biomass also increase.?3?The soils of Ph.pubescens forest were acidic.The mean soil bulk density was1.23 g cm^-3 that was suitable for bamboo growth.Soil SOC,TN and TP are abundant and have obvious surface accumulation,and their contents decrease with soil depth.The average value of soil C/N ratio was lower than the national level of Ph.pubescens forests.The C/P ratio was far lower than the national average level.The N/P ratio was far lower than the average value in China.Therefore,the productivity of Ph.pubescens forest in Anhui may be limited by N to some extent.The NO₃^–-N content in various soil available nutrients in each production area of Ph.pubescens forest showed a trend of first increasing and then decreasing with the deepening of the soil layer,and other nutrients showed a decreasing trend with the increase of soil depth.The content of soil AN was generally low.The stability of soil DOC and DON was poor and easy to be leached.Soil AP content was low.The content of soil AK was relatively rich.In the study area,however,the soil of Ph.pubescens forest appeared lack of AMg and ACa.There was significant or extremely significant correlation between soil nutrient factors of Ph.pubescens forest.Soil thickness and altitude had significant effects on soil nutrient regime,and different slope positions had significant effects on soil NO₃^–-N,AP,SOC,ACa and TN in Ph.pubescens forest.?4?The contents of SOC,TN and TP in the soil was positively correlated with Ph.pubescens height,AGS,DBH,ABH and biomass.The contents of NH₄⁺-N,NO₃^–-N,DON,DOC,AP,AK,ACa and AMg in the soil was positively correlated with bamboo height,DBH,ABH,AGS and biomass.The contents of AK and ACa in soil was positively correlated with the stand density of Ph.pubescens,and soil AP content was negatively correlated with stand density.?5?The factors controlling Ph.pubescens forest biomass in Anhui were analyzed by using Random Forest algorithm.The results showed that NH₄⁺-N,NO₃^–-N,SOC,DON,DOC,AMg,TN,soil thickness,altitude and slope position were the main factors controlling soil nutrient and site index and stand biomass of Ph.pubescens.The structural equation model explained 33.5%of the biomass change of Ph.pubescens forest.The soil thickness had the most direct and total impact on stand biomass.The altitude range in thi s study had a positive impact on biomass of Ph.pubescens forest,but the direct impact is not significant.The indirect impact of soil thickness and altitude on stand biomass was greater than their direct impact.The direct effect of AN was the most,and the direct effect of DON was the least.