【作者】 许鹏辉；

【导师】 陈云明；

【作者基本信息】 西北农林科技大学 ， 水土保持与荒漠化防治， 2009， 硕士

【摘要】 水土流失严重与气候干旱是黄土丘陵半干旱区当前面临的两大生态问题。由于自然因素和人为因素的共同作用,黄土丘陵半干旱区部分人工植被如刺槐、小叶杨等存在退化现象,这一问题已经引起了人们的注意。为了正确认识该区人工植被退化的机理,采用野外试验与室内分析相结合的方法,在陕西安塞选取人工刺槐林,研究23、26、28、32、33、44、50林龄人工刺槐林生长状况及重新造侧柏林、皆伐后自然萌生、混交等不同更新方式下刺槐的生长情况,分析了刺槐林的退化特征,并对不同改造更新方式的效果进行分析,以期为该地区刺槐人工林的天然化培育提供依据。所取得的主要结论如下:1.通过刺槐纯林和混交林对生物量、冠幅、土壤物理特性、生物多样性的影响比较发现,黄土丘陵半干旱区刺槐纯林易发生退化。所调查不同林龄刺槐纯林均发生不同程度的退化。随林龄的增长,刺槐纯林退化程度加剧。生物量、径级、冠幅随林龄的增长而增加,林分密度降低,冠径比减小。蓄积量为26.07～84.79 m3/hm~2,林分密度为200～1417株/hm~2,径级为2～32cm。退化人工刺槐林平均冠幅为2.43～3.83 m,除33龄(W0°)外,其他纯林冠径比均大于1.2。不同林龄的退化刺槐林对土壤容重、孔隙度、有机质、饱和导水率的改善作用明显,不同林龄间差异十分显著。0～60cm土层内有机质含量为1.80g/kg～15.81 g/kg,平均值仅6.01g/kg。饱和导水率为0.30 mm/min～8.63 mm/min,平均饱和导水率50龄刺槐林最大为4.83 mm/min,33龄(W0°)最小为1.53 mm/min。土壤总孔隙度的变化范围为53.66%～59.90%。对黄土丘陵半干旱区不同林龄人工刺槐林的林分密度、蓄积量、比根长、土壤物理特性及生物多样性的分析认为,退化刺槐林的改造更新林龄在30年左右。2.退化刺槐林判断指标:a.退化人工刺槐林林相参差不齐,存在大量枯木;树体上枯枝多,萌生枝条多,萌生枝条存活率低,树冠冠形差;树体黑色,附生大量黄褐色地衣;b.刺槐胸径与树冠投影面积的相关性分析表明,若正相关系数在0.7以上,则没有发生退化,呈负相关或正相关性在0.7以下则发生退化。c.利用冠径比来进行判断。冠径比是两个垂直方向树冠投影直径的比值,冠径比可以描述两个垂直方向上刺槐冠幅的变化,两个垂直方向差异越大,冠径比就越大或越小。退化人工刺槐林的冠径比大于1.2或小于0.8,正常刺槐冠径比在0.8～1.2之间。d.人工刺槐林内,刺槐的自然死亡或人为破坏造成人工刺槐林发生退化,退化的刺槐林内林内郁闭度较低,草本生物多样性增加。3.不同改造更新方式下,林分密度、生物量都不相同,以混交林密度最合理,蓄积量最大。不同改造更新方式林分密度为1056株/hm~2～4667株/hm~2,乔木蓄积量为17.68m3/hm~2～50.73m3/hm~2。不同改造更新方式对土壤物理特性、生物多样性、冠幅的影响不同。其中以混交方式的作用最为明显,其次为皆伐萌生,重新造林效果最差。0～60cm土层总孔隙度在49.24%～62.58%范围变化,混交林大于萌生刺槐林和重新造林。土壤饱和导水率范围为0.73 mm/min～6.75 mm/min。土壤有机质在0.98g/kg～15.28g/kg之间。4.黄土高原地区在明确改造更新目的的情况下,对退化刺槐林改造更新时应遵循以下原则:a.急需改造更新且资金不足的退化人工刺槐林,可采用间伐加封育的措施进行适当的人工抚育。b.不提倡在退化刺槐林地上皆伐后进行重新造林,原因是重新造林成本过高,且易造成新的退化植被,并由于树种选择不当造成生态、经济效益不高。c.黄土高原地区降水量在200～500mm的地区可对退化人工刺槐林进行间伐或与灌木混交,灌木应以豆科经济灌木为主。d.不论采取何种改造更新措施,都必须加强抚育管理,以减少人为因素对刺槐林的影响。更多还原

【Abstract】 Serious soil and water loss and arid climate were the two ecological problems faced by semi-arid loess hilly region. Because of the common effects of natural factors and human factors, there is degradation phenomenon in some artificial vegetation, such as locust, simon poplar, which has aroused the public attention. In order to correctly understand the degradation mechanism of artificial vegetation in this area, artificial locust forest which was located in Anshai of Shaanxi province was studied by using field test and laboratory analysis. The growth condition of artificial locust forest with 23, 26, 28, 32, 33, 44 and 50 forest ages and that with different regeneration modes (reforesting arborvitae forest, natural sprouting after clear cutting and mixed mode) were researched. what’s more, the degradation characteristics of locust forest and the effect of different reconstruction modes were analyzed in order to provide basis for natural cultivation of artificial locust forest in semi-arid loess hilly region. The main results were as follows:1.By comparing the effects of pure locust forest and mixed forest on biomass, crown width, soil physical properties and biodiversity, it was found that pure locust forest in semi-arid loess hilly region was easy to degrade. Pure locust forest with different forest age had degradation at different degree. The degradation degree, biomass,diameterclass, crown width increased with the increase of forest age, while the forest density and crown diameter ratio decreased. Volume amount was 26.07～84.79 m~3/hm~2, forest density was 200～1417 plant/hm~2, and diameter class was 2～32cm.The average crown width of degraded artificial locust forest was 2.43～3.83 m, the crown diameter ratios of other pure forests were all more than 1.2 except for the forest which was 33 forest ages. Degraded locust forest with different forest age had significant improving effect on soil bulk density, porosity, organic matter and saturated hydraulic conductivity. And the difference among forests with different forest age was significant. The organic matter content in 0～60cm soil depth was 1.80g/kg～15.81 g/kg, and the average was only 6.01g/kg. Saturated hydraulic conductivity was 0.30 mm/min～8.63 mm/min. For the average saturated hydraulic conductivity, the maximum in locust forest with 50 forest ages was 4.83 mm/min,the minimum in locust forest with 33 ages was 1.53 mm/min。The change range of total soil porosity was from 53.66% to 59.90%。Forest density, volume amount, specific root length, soil physical properties and biodiversity of artificial locust forest with different forest age in semi-arid loess hilly region were analyzed which showed that the forest age of degraded locust forest reconstruction was about 30.2.judgement indexes of degraded locust forest:a. Forest form of degraded artificial locust forest was uneven, and there were lots of withered wood; in the tree body, there were many dead woods and offshoots, the survival rate of offshoot was low, and the crown form was poor; the tree body was black with a lot of filemot lichens.b. Correlation analysis between diameter of locust and the projection area of crown showed that: when the positive correlation coefficient was more than 0.7, there was no degradation, and when it was negative correlation or the positive correlation coefficient was lower than 0.7, there was degradation.c. Crown diameter ratio was used as judgement index. Crown diameter was the ratio of crown projection diameter in two vertical directions, which could be used to describe the change of locust crown width in the two vertical directions. When the difference in the two vertical directions increased, crown diameter ratio was greater or smaller. The crown diameter ratio of degraded artificial locust forest was greater than 1.2 or smaller than 0.8, and the crown diameter ratio of normal locust was 0.8～1.2.d. Natural death of locust or human damage resulted in the degradation of artificial locust forest. In the degraded locust forest, canopy density was lower, and the diversity of herb organisms increased.3. Forest density and biomass were different under different reconstruction modes, the density of mixed forest was the most reasonable, and the volume amount was the most. The forest density with different reconstruction mode was 1056 plant/hm~2～4667 plant/hm~2,and the volume amount of arbor was 17.68m3/hm~2～50.73m3/hm~2.The effects of different reconstruction modes on soil physical properties, biodiversity, crown width were different. And the effect of mixed mode was the most significant, followed by clear cutting sprouting and reforestation. Total porosity in 0～60cm soil depth were between 49.24%～62.58%, and total porosity in mixed forest was more compared to sprouting locust forest and reforestation. Soil saturated hydraulic conductivity was 0.73 mm/min～6.75 mm/min, and soil organic matter changed form 0.98g/kg to 15.28g/kg.4. Under the condition of determining reconstruction aim, the reconstruction of degraded locust forest in loess plateau region must comply to the following principles:a. Suitable artificial tending could be taken in degraded artificial locust forest which urgently needed reconstruction by using intermediate cutting and exclusion measures if there was not enough capital.b. Reforestation in degraded locust forest was not advocated after clear cutting. The cost of reforestation was high and easy to cause new degraded vegetation, what’s more, the wrong choice of tree species could result in low ecological and economical benefit.c. Degraded artificial locust forest in area with precipitation between 200～500mm could use intermediate cutting or mixed plantation with shrub. And leguminosae economic shrub should be mainly chosen.d. Tending management must be enhanced no matter what reconstruction measures were applied in order to reduce the effect of human factor on locust forest.更多还原