Recovery Dynamics Of Understory Vegetation Following Closing Hillsides To Facilitate Afforestation

Closing hillsides to facilitate afforestation， which promoting stand regenerationby its own ability of self-recovery，may be one of the most efficient ways to facilitatevegetation recovery in limestone area. In this paper， I studied the recovery processesby selecting stands of different ages since hillside closing in Qiaomu village，Qingyang county， Anhui province. I addressed the following research： the structureand diversity of understory vegetation; the biomass of understory vegetation; physicaland chemical properties of soil; the correlation between biomass and diversity ofunderstory vegetation; the correlation between soil properties and biomass/diversity.The study examined the dynamic processes of diversity and biomass since hillsideclosing， aiming to provide theoretical guidance for wildly using of setting apart hillsfor forest recovery in limestone mountain. The result showed that：（1） Closing hillsides to facilitate afforestation could improve diversity ofunderstory vegetation. There were a total of24species belonging to21genera and17families in shrub layer， a total of7species belonging to5generas and7families inherb layer. Following closing, Margalef index and Shannon-wiener index of shrublayer increased first and then decreased later in the order of：20years>10years>30years>5years since closing>no closing. Margalef index and Shannon-wiener index ofherb layer also showed a trend of increasing first and decreasing later followingclosing, they followed the order：10years>30years>20years>30years sinceclosing>no closing.（2）Closed years had a significant impact on biomass of understory vegetation.With the increase of the closed years，biomass of shrub layer showed a trend ofincreasing first and decreasing later， they followed the order：20years>10years>30years>5years since closing>no closing. The maximum biomass of shrub layerwas4.61t hm^-2， the minimum was1.45t hm^-2. Herb layer biomass accounted foronly little ratio in whole understory biomass. Its changing trend was similar withdiversity， following as10years>5years>20years>30years since closing>noclosing. The maximum of which was0.54t hm^-2， the minimum was only0.12t hm^-2.（3）Closing hillsides to facilitate afforestation could significantly improve thewater and fertilizer conditions of soil. The soil properties had obvious differencesunder different closed years. After5years’ closing， the water content increased 21.6%， total porosity increased14.5%， the bulk density decreased23.1%. After20years’closing， the water content got its maximum， about55.27%， the soil bulkdensity decreased to0.43， the total porosity was up to83.08%. Soil nutrient improvesignificantly after closing hillsides. The pH of soil changed from7.69to6.21， after5years’ closing， the nitrogen of soil increased97.9%， the organic matter increased23.3%， the available phosphorus increased27.9%.（4）The biomass and diversity was significantly correlated. The total biomass hadsignificant correlation with biomass and diversity indexes of shrub layer. The biomassof understory vegetation also had significant correlation with diversity indexes inshrub layer. The herb layer biomass significantly correlated with diversity indexes.（5） The biomass and diversity index of shrub layer had a significant correlationwith soil properties. The biomass positively related to soil porosity， water content，available phosphorus， available potassium， organic matter and total nitrogen. It hada negative relation with soil bulk density，pH，potassium，calcium and magnesium.Its diversity index （Margalef index， Shannon-Wiener index） showed positivecorrelation with soil porosity， water content， available phosphorus， availablepotassium， organic matter and total nitrogen， and showed a significant negativecorrelation with soil bulk density， pH， potassium， calcium and magnesium. Thecorrelation of Herb layer biomass and diversity index and soil properties was notobvious.