Studies on Natural Rgeneration and Heterogeneous Microsites of Dragon Spruce (Picea asperata Mast.) Plantation in Western Sichuan, China

川西亚高山针叶林是四川森林的主体，是长江上游重要的生态屏障。云杉作为亚高山针叶林人工更新的主要树种，已经在该地区形成了大面积的人工纯林。目前，许多云杉人工林分已经进入更新成熟龄，而这些人工林的持续更新却成为日益凸现的问题。探讨这些云杉人工林的自我更新潜力及云杉种子种群更新特点，可为培育后续森林资源提供科学依据。 本文以川西米亚罗亚高山60a云杉人工林为研究对象，并以该区域内相对稳定的植被群落——天然林为对照，采用种子收集器、土壤种子库筛选、室内外种子萌发实验及野外幼苗调查等方法，从异质性微生境的角度研究了种子雨下落之后，不同微生境对种子库、种子萌发、幼苗建立及分布这一前期更新过程的影响，得出如下结果： 1、通过对川西亚高山60a云杉人工林和天然林6年内种子雨雨量、形态特征、散步动态等的持续观测和综合比较可以发现，云杉林结实特点由于林木自身的特征存在着巨大的变动，2002年和2006年两个种子结实大年内，60a人工林种子雨强度分别达到1088.2 ± 52.3粒/m2和704.3 ± 48.9粒/m2，远大于天然林579.9 ± 28.9粒/m2 和507.5± 30.7粒/m2；且云杉林结实质量优于天然林。60a人工林结实量大，种子质量也最好，相对天然林来说对种群的天然更新以及群落的演替都有最大的贡献潜力。应该说，在川西亚高山云杉人工林的天然更新过程中，种源不是影响天然更新的因素。在种子结实大年里，达到更新成熟的云杉人工林有着优于该地区相对稳定植被群落——天然林的种源优势。至少在种子结实大年，种子供应不是该区域人工林天然更新的限制因子。 2、相对于天然林种子库，人工林种子库在种子萌发前能够有较多的有活力种子。虽然这其中有种子雨输入量有差别的因素存在，但两种林分种子库对种子的保存率的不同才是造成这种差异的主要因素。在人工林中，不同地被类型形成的微生境显著地影响了种子库中种子的密度、垂直分布。有地被物存在的微生境能够将种子雨的大部分截留在地被层中，成为幼苗出现的主要场所；同时不同的地被物对种子的保存情况存在显著的差异，苔藓和凋落物层能都较好地保持其中的种子，到种子萌发前，这两种种子库类型能分别为天然更新提供366.1粒/m2和302粒/m2的有效种子。从这点来看，林下地被物上的种子库能够为天然更新萌发阶段提供数量可观的物质基础。 3、种子的萌发和幼苗的定居是天然更新过程中种子库向幼苗库转化的关键环节。总的说来，米亚罗人工林区60a云杉人工林种子向幼苗的转化率十分低下，凋落物、苔藓、草本、裸地四种主要地被物以及天然林内种子/幼苗的转化率分别仅为2.22%、2.14%、0.57%、0.67%、1.05%。这种低的转化率成为云杉林天然更新的限制性因子。但在现有更新条件下，微生境对这一环节仍然显示出十分显著的影响，表现为凋落物和苔藓对现有更新的新幼苗的保存率高于其它类型及天然林。苔藓和凋落物在种子萌发，幼苗保存，以及幼苗分布上都要优于其它地被物类型；另外，微地形对天然更新过程的影响也很显著，凹立地上更适宜于种子的汇集、萌发和定居。 Subalpine coniferous forests dominate most parts of the forested areas in western Sichuan, and they are important ecological barriers in the upper reaches of the Yangtze River. Picea asperata is one of the keystone spruce species for re-afforestation after felling of the natural forests and there have been a total of ca. 13 000 ha of plantations dominate by this species established. Nowadays, many P. asperata plantations have reached reproductive maturity. However, continued regeneration becomes to an important problem in these plantations. Understanding their self-regeneration potential and the regeneration characteristics of seed populations in spruce plantations of these plantations can have some insights on the management of these plantations and the establishment of following forest resources. A subalpine 60a P. asperata plantation distributed in Miyaluo artificial forest area was studied in this paper, at the same time. Synchronously, a 150a natural spruce forest was studied as comparison. Using seed collecting traps, sieving method for soil seed bank, seed germination experiments and seedling investigations in the field, the effects of heterogeneous microsites on early natural regeneration processes after seed rain were studied, which included seed banks, seed germination, seedling establishment and distribution. The main results are as follows. 1. Through a 6-year long term investigation of seed rain intensities, characteristic, dispersal dynamics of 60a P. asperata plantation, we could concluded that the seed setting properties of 60a P. asperata plantation have a great variation for the characteristics trees. In the mast seed year of 2002 and 2006, the seed rain intensities of plantation was 1088.2 ± 52.3 seeds/m2 and 704.3 ± 48.9 seeds/m2 respectively, which were much greater than that of natural spruce forest (579.9 ± 28.9 seeds/m2 in 2002, and 507.5± 30.7 seeds/m2 in 2006). Furthermore, the quality of seed rain in P. asperata plantation was better than that of natural spruce forest. Contrasting with natural spruce forest, 60a P. asperata plantation has a greater potential on natural regeneration of P. asperata population and succession of community for the reason of greater seed rain intensities and better seed quality. We can confirm that seed source was not a limiting factor which influences the natural regeneration progress of P. asperata population distributed in subalpine mountain zone, at least in the mast seed year. 2. Contrasting with natural spruce forest, P. asperata population had more viable seeds in seed bank before the germination. Although the difference of seed rain intensities of two forests has effect on this phenomenon, the difference of seed conservation ability in two forests was the main factor. In the P. asperata plantation, the seed densities and seed vertical distribution pattern were significant effected by the microsites, which posed by different ground cover types. In other word, Microsite with ground covers can obstruct most seeds and keep them in ground cover layer from seed rain, and these ground covers would be the main site for seed occurrence. There was a significant difference about seeds conservation ability among these ground covers. Litter and moss could better conserve P. asperata seeds which distributed in this two covers. Seed banks exist in litter and moss ground cover types could respectively provide 302seed/m2 and 366.1seed/m2 for natural regeneration before the seed germination. From this point of view, we could conclude that ground covers can ensure considerable numbers of seeds for the germination process. 3. Seed germination and seed establishment are key steps that the seeds invert to seedlings in natural generation process. In sum, the seed/seeding transform rate in 60a P. asperata plantation distributed in Miyaluo artificial forest area is very low. the seed/seeding transform rates in litter, moss, herb, soil surface and natural spruce forest were 2.22%、2.14%、0.57%、0.67%、1.05%, respectively. The low transform rate become to a limiting factor of P. asperata natural regeneration process. However, under the existing conditions of natural regeneration, microsit still had significant effect on this transform. The states of Seed germination, new seedling conservation, and older seedling distribution in litter and moss were better than in any other ground cover type or natural spruce forest. In addition, the micro-relief has significant effect on natural regeneration process. Concave site was more suitable for seed collection, seed germination and seedling distribution

Seed rain, soil seed bank and seedling regeneration in a 65-year Picea asperata plantation in subalpine coniferous, western Sichuan, China

川西亚高山人工针叶林已成为亚高山森林的重要组成部分,它们是否具有持续的自然更新能力,是决定川西亚高山针叶林群落演替方向和维持该区针叶林大面积存在的基础.以川西米亚罗亚高山人工云杉(Piceaasperata)林(65a)为研究对象,对种子雨量年际变化,土壤种子库动态,种子萌发和幼苗定居等更新过程的关键环节进行了连续7年(2002-2008年)的野外观测,以研究人工云杉林更新潜力及影响其更新的限制因素.结果表明:该区云杉林种子雨一般从每年的10月初开始下落,一直到翌年的1月底或2月初结束;云杉种子散落存在明显的大小年现象,种子散落周期为4年,且大小年之间种子产量差异极大;云杉种子从下落到土壤到种子完全失去活力不到1年时间,属于Thompson和Grime定义的第II类土壤种子库类型.腐烂死亡和动物取食是土壤种子库损耗的主要因素,而种子通过萌发真正转化为幼苗的比例非常低,仅占2002年下落种子总量的3.6%.种子萌发后,环境筛的作用导致云杉幼苗大量死亡,尤其是在种子萌发后的一个生长季节内,其死亡率高达78%.凋落物和苔藓是构成人工云杉林下地表的两种主要地被物类型,二者占所有调查幼苗数量的93%左右;两种地被物类型上0-2cm层幼苗存活率最高,分别占存活幼苗总数的76.07%和86.72%,随地被物厚度增加,幼苗存活率呈明显下降趋势,而幼苗死亡率呈明显升高的趋势,表明林下地被物厚度也是影响云杉幼苗定居的重要因素.两种地被物对幼苗生长的影响不同,除株高之外,分布在苔藓上的云杉幼苗生长参数(地径,分枝数,干重以及干重年增长率)明显高于分布于凋落物上的幼苗,表明苔藓地被物更有利于云杉幼苗定居.尽管该区大量云杉种子下落,但由于种子的高损耗率,幼苗的低输出率以及萌发幼苗的高死亡率,使得人工云杉林下种子通过萌发转为实生幼苗的数量非常少,最终真正能补充到云杉种群的个体数量非常有

WARMING EFFECTS ON GROWTH AND PHYSIOLOGY OF SEEDLINGS OF BETULA ALBO-SINENSIS AND ABIES FAXONIANA UNDER TWO CONTRASTING LIGHT CONDITIONS IN SUBALPINE CONIFEROUS FOREST OF WESTERN SICHUAN, CHINA

川西亚高山针叶林是青藏高原东部高寒林区的重要组成部分，也是研究全球变化对森林生态系统影响的重要森林类型。开展亚高山针叶林不同树种对气候变暖响应差异的研究，可为预测未来气候变暖背景下亚高山针叶林植被组成和森林动态提供科学依据。我们以川西亚高山针叶林两种主要树种红桦（Betula albo-sinensis）和岷江冷杉（Abies faxoniana）为研究材料，采用开顶式增温法（Open-top chamber,OTC）模拟气候变暖，研究了增温对全光条件和林下低光环境中（约为全光的10％）生长的红桦和岷江冷杉幼苗生长和生理的影响。在人工林环境下，OTC使增温框内平均气温和地表温度分别升高了0．51和0．33℃；而在林外空地处，OTC使二者分别升高了0．69和0．41℃。研究结果显示，增温总体上促进了两种幼苗的生长和生理过程，并促使幼苗将更多的生物量投入到其同化部位叶，使幼苗的根冠比（R/S）显著降低。增温通过增加叶片的光合色素含量和表观量子效率等光合参数，促进了幼苗的光合过程和生长。然而，增温对两种幼苗生长和生理的影响效果与植物种类及其所处的光环境有关。增温仅在林外全光条件下显著影响红桦幼苗的生长和生理过程。岷江冷杉幼苗对增温的响应与红桦相反，即增温仅在林下低光环境下对岷江冷杉幼苗的生长和生理过程有明显促进作用。这种响应差异可能赋予这两种植物在未来气候变暖背景下面对外界环境变化时具有不同的适应能力和竞争优势，从而对亚高山针叶林生态系统物种组成和森林动态产生潜在影响

增温对川西亚高山针叶林内不同光环境下红桦和岷江冷杉幼苗生长和生理的影响

川西亚高山针叶林是青藏高原东部高寒林区的重要组成部分,也是研究全球变化对森林生态系统影响的重要森林类型。开展亚高山针叶林不同树种对气候变暖响应差异的研究,可为预测未来气候变暖背景下亚高山针叶林植被组成和森林动态提供科学依据。我们以川西亚高山针叶林两种主要树种——红桦(Betula albo-sinensis)和岷江冷杉(Abies faxoniana)为研究材料,采用开顶式增温法(Open-top chamber,OTC)模拟气候变暖,研究了增温对全光条件和林下低光环境中(约为全光的10%)生长的红桦和