Study On Characteristics And Comprehensive Assesment Of Sand-fixation Plantations In Northern Hebei Province

The north of Hebei province is located in the upstream of Beijing, it is not only the sourceof sandstorm, but also the channel of wind and sand, it plays an important role in protecting theecological security for Beijing, Tianjin and Hebei. Many plantations have afforested innorthern Hebei in recent decades. In order to understand the growth, structure and ecologicalfuction of sand fixation plantation in northern Hebei, on the basis of sandification land division,aimed to2types of heavy sandification land--east Bashang forest-steppe and northwestbasin-mountain,15type stands composed of different tree species including Larixprincipis-rupprechtii Mayr, Pinus sylvestnis, Populus X beijingensis, Ulmus pumila L.,Platycladus orientalis, Populus simoniiCarr., Populus simonii×(Populus pyramidalis+Salixmatsudana) cv. Poplaris and Populus bolleana were studyed by the method of sample-plotsurvy.32indices including diameter at breast height(DBH), tree height(H), crown breadth, treenumber, crown density, biomass were chose as the main factors to represent the whole status ofstands. Then, the model of comprehensive aseesment for sand-fixation plantations was built byprincipal component analysis method, Characteriscs of stand were evaluated in the end. Themain results for this paper are listed as the follows:(1) Sand fixation plantations generally grow very slow due to the harsh surroundings innorthern Hebei, Pinus sylvestnis has the biggest growing rate of volume in both averageincrement and current annual increment. The maxium value happened at13years old forest inHuangyangtan, followed by30years old Larix principis-rupprechtii Mayr and24years oldPinus sylvestnis in Bashang. The least amount of growth was found in Platycladus orientalisstand. The result shows that Populus X beijingensis grows not very slow but easy to be affectedby surroundings. Ulmus pumila L. is the tree species with satisfying performance inHuangyangtan. All of the stands grow lower than normal at the rate of71-6007kg/hm~2·a.(2)The distribution rule of DBH was analysied by5methods including normaldistribution, lognormal distribution, Welbull distribution, Gamma distribution and βdistribution, the result shows that normal distribution, Welbull distribution and β distribution can well match the distribution rule of DBH with the ratioes of84.6%、76.9%and69.2%respectively for15stands, and stands fitting all the three distributions at the same time reach aratio of69.2%, but lognormal distribution doesn’t fit any of these stands.(3)The Shannon-Wiener diversity indices for15types of stand fall into0.804-2.221,indicates that the diversities under sand-fixation plantations are very low. The fisrt three standsowning big diversity are No.7, No.1, No.2in order of numerical size.Coniferous stand hashigher diversity than deciduous one. Evenness index has the same order as Shannon-Wienerdiversity index. Margalef richness indices keep between0.806and3.733with big difference.As the tree grows older, the amount of undercanopy species can reach and keep a steady level.(4) The results also shows that sand-fixation plantations have played an important role inblocking sand, reducing wind erosion. Different type stands have different sand transportingrates, but35.3%-63.1%of sands was shifted only under the height of4cm above ground,64.7%-90.9%under the height of4cm. Sand transporting rate in vertical direction distributesregularly in the order of0-2cm>2-4cm>4-6cm>6-8cm>8-10cm>10-12cm. In this survy,sand has never been transported again in the stands of30years old Larixprincipis-rupprechtii Mayr and24years old Pinus sylvestnis in Bashang, which completelymet the objective of reducing wind and blocking sand. Since Pinus sylvestnis grows very slow,with weak ability of defendence, it has higher sand transporting rate, but Ulmus pumila L..stand blocks sand very well with no any transported sand. Sand transporting rate has very closecorrelativy with canopy densey, which has played an important role in horizontal direction.(5) Soil porosity in sand fixation plantations is from32％to54％, with morenoncaplillary porosity than caplillary one. The soil has lower ability of keeping water andfertilizer. The scale of water holding capacity is from10.54%to37.24%. In northwest Hebei,the content of soil organic is rather low, however, it is pretty high in Bashang. The highest soilorganic content for coniferious planted forest land happens in Bashang, which means that thesoil still keeps a typical characteristic of forest steppe or meadow steppe with no heavysandification. The composition of soil nitrogen has the same rule as organic. Both totalphosphorus and available phosphorus are in the extremely low level. To total potassium, Bashang is very different from scattered sandy land in the northwest, it is very low in Bashangbut very high in the northwest.(6) Comprehensive aseesment model for sand fixation plantations has been built by themethod of principle component analysis, the result of aseesment shows as the following order:5>2>3>10>11>9>1>8>4>14>15>13>7>6>12. the first three stands are24years old Pinussylvestnis,30years old Larix principis-rupprechtii Mayr, and8years old Pinus sylvestnis, allof them locate in Bashang sandy land, the last four stands based on the aseesment order are8year-old Populus simoniiCarr.,7and17year-old Platycladus orientalis, and15year-oldPopulus simoniiCarr.According to the aseesment result,15stands were divided into5groups including the best,better, middle, worse and the worest, in the end of this paper, optimizing managementcountermeasures have also been proposed to develop the sand fixation forest. In general, Larixprincipis-rupprechtii Mayr, and Pinus sylvestnis are the first choice for Bashang forest-steppetype. Ulmus pumila L.. is good for the scattered sandy land of northwest basin-mountain, orPopulus bolleana and Populus simonii×(Populus pyramidalis+Salix matsudana) cv. Poplarisin some special part, however, they are not recommended to be used as the planting treespecies because of their high water consumption and poor resistence to the evironment.