植物群落类型和围栏封育对高山林线岷江冷杉幼苗成活的影响

林线树种幼苗的生长紧密关系着高山林线的形成。通过室内发芽实验测定了岷江冷杉种子萌发能力。2015年春,在川西巴郎山岷江冷杉林线之上的高山林线交错带,通过播种处理(播种和不播种),研究了不同植物群落类型(灌木和草地群落)和围栏处理(围栏和不围栏)对岷江冷杉幼苗成活率的影响,以期为进一步探讨高山林线形成机制提供科学参考。结果表明:(1)岷江冷杉室内发芽率31.4%,成活率随时间下降。(2)灌木群落的全年日平均空气温湿度显著高于草本群落,而两群落的全年日平均土壤温度无显著差异。(3)未播种样地没有发现岷江冷杉幼苗,说明林线交错带缺乏岷江冷杉种子。(4)与不围栏样地相比,围栏封育分别显著提高了岷江冷杉幼苗成活率2.0%(2015年)和2.2%(2016年);与灌木群落相比,草本群落中岷江冷杉幼苗成活率显著提高0.8%(2015年)和1.2%(2016年),说明灌木对林线交错带幼苗更新具有更强的竞争作用。围栏处理下,草本群落中岷江冷杉幼苗成活率显著高于灌木群落;不围栏处理下,草本群落中岷江冷杉幼苗成活率显著低于灌木群落,2017年在不围栏样地没有幼苗存活,说明动物干扰对林线交错带森林更新有阻碍作用。研究表明,高山林线交错带森林更新,受种子、植物竞争和动物干扰(例如,放牧)等多方面因素的共同影响,可以通过播种、植物剔除(去除竞争)和围栏等促进幼苗更新和成活。

Effects of plant community types and fencing on survival of Abies faxoniana in the alpine treeline ecotone

The growth of seedlings in the alpine treeline ecotone is closely related to the formation of the alpine treeline. An ex situ germination of Abies faxoniana was conducted in greenhouse. A full factorial experiment with community type (shrub vs. herb community), seeds (sowing vs. non-seed addition), and fencing (with vs. without) was carried out in situ in the alpine treeline ecotone beyond the A. faxoniana treeline on Balang Mts., western Sichuan, to study the effects of community types and fencing on the survival and growth of A. faxoniana seedlings in the alpine treeline ecotone. The results showed that (1) the ex situ germination rate of A. faxoniana was 31.4%, and the survival rate decreased with time. (2) The annual mean daily air temperature and humidity were significantly higher in shrub community than in herbaceous community, whereas the annual mean soil temperature did not differ between the two communities. (3) A. faxoniana seedlings were not found in the plots without seed addition, indicating that the treeline A. faxoniana trees did not provide seeds to the treeline ecotone. (4) Compared to non-fence plots, fencing significantly increased the survival rate of A. faxoniana seedlings by 2.0% (2015) and 2.2% (2016). Compared to the shrub community, the survival rate of A. faxoniana in the herb community increased significantly by 0.8% (2015) and 1.2% (2016), suggesting that the shrubs have much stronger competitive effects on seedlings than herbs. Within the fence treatment, the survival rate of A. faxoniana was significantly higher in the herb community than in the shrub community. Within the non-fence treatment, the survival rate of A. faxoniana seedlings was significantly lower in the herb community than in the shrub community, and no seedlings survived in the non-fence plots in 2017, indicating that animal disturbance strongly impedes survival and growth of seedlings in the treeline ecotone. The present study showed that the recruitment of trees in the alpine ecotone is strongly determined by seed availability, plant competition, and animal disturbance. Therefore, target seed addition, vegetation removal, and fencing can be used to promote recruitment and growth of trees in the alpine treeline ecotone.