低温对东北次生林主要树种早期更新的影响机制

Wind, snow and chilling damages are the major natural abiotic disturbances in the northern temperate forest ecosystem. These abiotic disturbances not only cause the reduction of timber production, but also induce the dramatic changes in forest environments; and futhrer affect the regeneration and succession of the forest ecosystems. The poor understanding on how the chilling damage influencing the regeneration in the secondary forest ecosystems has become one of the key problems in the studies of domiant tree species regeneration in the secondary forest of Northeast China. In this study, we selected the secondary forest stands with different stand strcutures or different size gaps, which produced by wind and snow damages, as the study sites. Three dominant tree species (Pinus koraiensis, Fraxinus mandshurica, Quercus mongolica) were chosen as the objective species. The methods of field observations and simulation in laboratory, together with the automatical temperature monitoring technique will be applied in combination in the study. The following aspects will be studied: 1) the effect of the stand stuctures (canopy openness or gap size) on the formation of chilling damage; 2) the impacts of chilling damage (various low temperaures) on the germination of seeds, and survival and growth of seedlings of the three dominant tree species; 3) dtermination of the threshold or range of low temperatures, which induce the failture of seed germination, and hinder the emergence, survival and growth of seedling for the three dominant tree species. In addition, the values of canopy openness or the position of the gaps, which would not cause the chilling damage will be determined. On the basis of the results obtained in this study, combined with the historical meteorological data, the probillity risk model of chilling damage will be established. At last, the tecniques for preventing or mitigating the impacts of chilling damage on the early stage of regeneration for the three dominant tree species will be proposed, which may be helpful for pormoting the regeneration of the dominant tree species in the secondary forests.

风、雪与低温灾害是北方温带森林生态系统重要的非生物自然干扰要素，在导致林业生产受损的同时，使森林环境发生巨大变化，影响森林生态系统更新演替。低温灾害对森林更新影响机制不清，已成为阻碍次生林主要树种更新的瓶颈之一。本项目以遭受风、雪干扰后形成的不同林分结构次生林生态系统为研究对象，选择受低温灾害影响严重的主要树种（红松、蒙古栎和水曲柳），采用野外定点观测与室内模拟分析相结合的试验方法，应用自动温度连续监测技术，重点研究林分结构对低温(灾害)形成过程的影响规律，明确低温对主要树种种子萌发、幼苗存活与生长影响过程，确定主要树种种子萌发、幼苗存活与生长所能忍受的低温极值和范围，明确可能规避低温灾害的林分郁闭度范围或林窗位置；依据试验结果和积累的气象数据，建立低温(灾害)发生的风险概率模型。提出防治低温(灾害)发生或降低其危害的技术措施；为人工促进次生林主要树种天然更新提供科学参考。

低温灾害是北方森林生态系统重要的自然干扰要素，是幼树幼苗存活与生长的主要限制因子之一。林窗形成后由于其林冠结构发生显著变化，从而使内部的光、温等环境因子发生显著改变，进而影响物种的早期更新。然而，林窗形成后是否加剧了低温灾害、继而影响林窗内幼苗存活与生长的机理尚不清楚。为此，本研究选择东北典型次生林生态系统为研究对象，以不同林分结构（林窗）样地为研究区，通过移植主要建群种（水曲柳、核桃楸等）苗木，采用野外定点观测与室内控温模拟相结合的方法，进行了温、光、种子萌发、苗木存活生长及苗木生理生态等指标的测定。旨在判明不同林窗内低温的变化特征和规律，并对林窗形成后能否加剧低温灾害、继而影响林窗内幼苗存活生长的科学问题进行了探讨，同时又结合室内控温模拟实验结果，揭示了低温环境因素对主要树种早期更新障碍的作用机制。该研究结果将为人工促进次生林天然更新、低温灾害的防御、以及次生林生态系统的可持续经营提供理论依据。.1、研究结果表明，不同坡向林窗内最低温度其位置、强度随时间不同而存在差异，从而使林窗内最低温度出现的早晚及空间位置也不同，这将对林窗内生长季初、晚期幼苗冻害的发生起决定性的作用，因此对林窗内低温小气候环境异质性的研究具有重要意义。.2、与非林窗样地相比，各林窗样地内的最低气温明显降低，而光强在林窗与非林窗及各林窗样地之间差异均较大。在光强较大的东南坡和东北坡林，林窗内低温灾害较重，西坡和对照样地由于光照较弱，并无低温灾害发生。由此说明，林窗形成后加剧了核桃楸幼苗低温灾害的发生，但不同林窗间苗木受害、生长差异明显，这主要是由林窗内不同光强所致。.3、从低温处理后幼苗生理指标及光合指标的初步结论来看，低温胁迫对主要树种早期更新的影响不仅与低温值有关，其中不同低温下的持续时间以及低温过后的光照强度均是低温受害的主要因子。