维持丛状结构特征可持续的沙柳防护林生态采伐调控机制研究

Stubble rejuvenation is necessary for care of shrub forest.It is useful for industrialization to fell branches. Plex structure is specialcharacter to play ecological function in the bushwood. Some investigations have beenpreviously studied on seasonal felling and stubble height. However, little is knownabout how to protect plex structure in flat stubble operation in the bushwood. Itwas mainly fell wide area of shrub in present. But this fell pattern of flat stubblecaused to expose earth’s surface and easily blow sand. Meantime, it has increasedto evaporate water in the soil, stopped growing, even dead after the bushwood werefelled, and resulted in ecological environment deterioration in desert area, whenthe earth’s surface lose suitable coverage of the bushwood. In the present, we providea new method that the branch is the minimum unit to focus on ecological functionof plex structure of the bushwood. We plan to study the mechanisms of the different pattern of felling more or less branches by turns on grow condition after felled the bushwood, and the mechanisms of retaining the different structure on the sand flow, evapotranspiration capacity and groundwater occurrence around the root in the bushwood. Thus, we can determine the best pattern of felling in salix psammophila plant, conclude a ecological theory of the felling the flat strubble to guide the production practice, and provide a theoretical foundation for reasonable utilization salix mongolica resource and formulating the rules associated felling shrub.

平茬复壮是灌木林抚育经营与利用的必要环节，灌丛生长结构是其所发挥生态功能的具体表征。当前，国内一些研究者只对灌丛采伐季节、留茬高度等方面有了一些研究，还没有人研究在采伐作业中如何保护其灌丛结构。灌木林采伐是区域性皆伐作业为主，造成地表裸露，易起风沙与破坏植被；加速了土壤水分蒸发，致使灌丛伐后长势退化甚至枯死，导致沙区生态环境恶化。本课题提出了以部分枝条为平茬单元来探索持续地保持其丛状结构特征的采伐新方法，关注灌丛自然结构的生态功能持续发挥。通过研究不同配置的丛状保留结构，分析采伐后沙柳灌丛生长状况及根蘖再萌动态；建立不同灌丛结构影响风沙流场的作用机制，采伐强度与方式对灌丛蒸发散、根部附近地下水分布的影响机理。确定沙柳灌丛最优的维持丛状结构特征的采伐作业方式，实现采伐-更新-采伐可持续的良性循环，形成灌木生态采伐平茬基础理论，为合理采伐利用灌木资源提供理论指导。

摘要：毛乌素沙地沙柳灌丛是当地防砂治沙的主要树种，依据沙柳自身的生物学特性，其生长到一定年限会出现衰退甚至枯死现象，平茬复壮是对沙柳灌丛林抚育经营与利用的必要环节。本项目按照基金申请书以及项目计划书的目标深入研究了毛乌素沙地沙柳灌丛林的平茬方法及其对灌丛抚育更新的影响机制，取得成果如下：平茬措施可提高沙柳的萌蘖枝条数和增加新枝条上的单叶面积，有利于沙柳的抚育更新；在进行沙柳灌丛平茬作业时，要综合考虑立地条件-沙柳灌丛-草本盖度三方面因素来确定平茬量；针对丘间低地上的沙柳灌丛，适于以能源林来培养，平茬以整块皆伐作业方式为优，皆伐平茬并不会发生风蚀现象，平茬周期4年可获得最大生物量；对于生长在迎风坡和丘顶的沙柳，应充分考虑沙柳丛生长结构所发挥生态功能，适合采取以部分枝条为平茬单元来保持其丛状结构特征可持续的平茬方法，针对单丛沙柳顺风向减小冠幅面积30%，基本不影响沙柳的固阻沙能力，但萌蘖枝条数明显要多于丘间低地；平茬作业可使沙柳枝条的茎杆液流速率增加，枝条的基径和枝高年生长量要高于未平茬对照；平茬后林地的水热条件得以改善，林地土壤呼吸速率加快，相较于未采伐样地，皆伐干扰样地的土壤养分含量变高，尤以有机质变化最为明显，增幅为11.8%。该系列研究成果基本形成了沙柳灌丛生态采伐平茬工艺，初步揭示了平茬措施在协调沙柳灌丛自身与其环境之间关系的调控机制，实现了采伐-更新-采伐可持续的良性循环，为合理采伐利用灌木资源提供了理论指导，更为今后继续深入研究沙地灌木资源的平茬问题积累了基础数据和经验。