常绿阔叶林林冠环境对栲幼苗建成的影响

植物幼苗建成阶段是决定种群自然更新的关键生活史阶段。研究林冠环境对常绿阔叶林优势种幼苗建成阶段的影响对该类森林的恢复和管理具有重要意义。2014-2016年, 该研究在重庆市缙云山国家级自然保护区的常绿阔叶林的不同林冠环境(大林窗: >150 m ², 中林窗: 100-150 m ², 小林窗: 50-100 m ², 对照: 林下)下进行栲(Castanopsis fargesii)种子野外播种实验, 并对栲幼苗命运和生长情况进行了3年的持续监测。结果表明: (1)栲幼苗出土时间从7月持续到12月, 出苗时间较长, 大林窗对幼苗出土具有延迟作用; (2)栲种子野外平均萌发率为(62.8 ± 2.0)%, 第3个生长季(2016年)末幼苗平均存活率为(65.1 ± 2.2)%, 枯萎是栲幼苗死亡的主要原因; (3)林冠环境对栲种子萌发率及第1个生长季(2014年)末的幼苗存活率无显著影响, 对第2个(2015年)和第3个生长季末的幼苗存活率具有显著影响; (4)林冠环境在第1个生长季对幼苗生长无明显影响, 但在第2个和第3个生长季具有显著影响, 大、中林窗中幼苗总生物量、株高、基径、根长和叶片数显著高于林下, 比叶面积显著低于林下; (5) 3个生长季内, 4类林冠条件下栲幼苗的叶质量比和茎质量比升高, 根质量比和根冠比降低, 并且从第2个生长季开始大林窗中栲幼苗的叶质量比显著高于林下, 根质量比和根冠比显著低于林下。栲幼苗早期的存活和生长依赖种子储存的能量, 受林冠条件影响较弱, 后期则依赖光合作用, 受林冠条件影响较强, 从整个幼苗建成过程看, 大、中林窗更有利于栲幼苗定居。

Effects of forest canopy condition on the establishment of Castanopsis fargesii seedlings in a subtropical evergreen broad-leaved forest

Aims The establishment of seedlings is a key life-history stage during the regeneration of plant populations. This study is to investigate the effects of forest canopy condition (large-sized gap: >150 m ², medium-sized gap: 100-150 m ², small-sized gap: 50-100 m ², and understory as control) on the establishment of Castanopsis fargesii seedlings, and to guide in situ management and restoration of subtropical evergreen broad-leaved forests.Methods We conducted a 3-year in situ seed sowing experiment in the Jinyun Mountain National Nature Reserve under different canopy conditions, and monitored the growth and survival of C. fargesii seedlings for three years (2014-2016).Important findings We found that: (1) the emergence of the seedlings lasted from July to December, and the emergence of seedlings was delayed under large canopy gaps; (2) overall germination rate was (62.8 ± 2.0)%. The averaged survival rate during three growing seasons was (65.1 ± 2.2)%, with wither being the key type of seedling mortality; (3) there was no significant difference in the germination and survival rates under different canopy conditions in 2014, but significant difference in the survival rates in 2015 and 2016; (4) seedling growth among canopy conditions showed no difference in 2014, but distinct differences in 2015 and 2016. The seedling growth in large- and medium-sized gaps was significantly promoted compared with those growing under closed canopies in terms of total biomass, plant height, base diameter, root length and leaf number (except for the specific leaf area); (5) for each of the four types of canopy conditions, leaf mass ratio (LMR) and stem mass ratio (SMR) of seedlings growing increased within last three years, while root mass ratio (RMR) and root shoot ratio (RSR) decreased. The LMR in large-sized gaps was significantly higher than those in closed canopies, but not for the RMR and RSR. The results suggested that the initial survival and growth of C. fargesii seedlings may be supported by the nutrients stored in seeds, and thus less affected by canopy conditions. However, in late-establishment stages (i.e., the second and third years), gap size could become a key factor in affecting both the seedling survival and growth. And large- and medium-sized gaps could promote the seedling establishment success for C. fargesii.