滇西北亚高山针叶林林窗大小与更新的初步分析

分析了云南西北部碧塔海自然保护区的亚高山针叶林林窗大小对林窗植被和更新的影响。调查区域出现了1级林窗（面积＜50m^2)占36％,Ⅱ级（50－75m^2)21%,Ⅲ级（75－100m^2)19％,Ⅳ级（100－125m^2)13%和Ⅴ级（＞125m^2)11％。结果表明,亚高山针叶林因林窗大小不同而导致小环境条件的差异,使林窗植被和更新与林窗干扰密切相关。林窗大小对林窗植被的物种多样性,结果,密度分布以及云冷杉更新苗的空间分布都有不同程度的影响,小林窗（Ⅰ级）的物种多样性比大林窗（Ⅳ级和Ⅴ级）,中林窗（Ⅱ级和Ⅲ级）高。云冷杉更新幼苗以中,小林窗较多,且在小林窗中呈随机分布,主要分布在林窗中心和过渡区域（88％）;在大,中林窗中则呈集群分布,主发分布在过渡区域,占44％－50％。同时,研究表明该区亚高山针叶林有效更新的林窗阈值面积大约为75m^2。图4表3参22。     

林窗大小对2种针叶林更新效果的初步分析

为了解采伐林窗对2种人工林更新效果的影响,在浙江省丽水市白云山选择生境条件基本一致的马尾松林和杉木林,以林下为对照,比较了通过采伐获得的不同大小林窗(50～500 m~2)内人工和天然更新植物效果。结果表明:(1)10个人工更新树种在杉木林中生长优于马尾松林,马尾松林中枫香、无患子、山乌桕和细柄蕈树生长情况好于其他树种,杉木林中枫香、山乌桕、南方红豆杉、无患子和细柄蕈树生长情况好于其他树种。(2)林分类型显著影响南方红豆杉生长,特别是对树高的影响极为显著(P0.01),林窗大小对木荷地径和树高均有显著影响(P0.05),林分和林窗的交互作用对除朴树、闽楠和浙江楠外的其他树种均有显著影响。(3)不同大小林窗下天然更新植物物种数、Simpson生态优势度、Shannon多样性指数存在显著差异(P0.05),林分类型对物种数和Shannon多样性指数具有显著影响(P0.05),但对Simpson生态优势度没有影响。2种林分林窗间天然更新植物相似度介于0.4～0.9之间,同一林分林窗间物种相似度均大于林窗与对照之间。马尾松林阔叶化改造可采伐中等林窗(250 m~2),目标更新树种可选枫香、无患子、细柄蕈树和木荷;杉木林以大(500 m~2)或小林窗(50 m~2)为主,可选树种有枫香、南方红豆杉、山乌桕、无患子和细柄蕈树。     

林窗对马尾松人工林植物多样性的影响

为了解人工抚育调控林窗对马尾松人工林植物多样性的影响,以长江上游低山丘陵区39年生的马尾松人工林为研究对象,人为砍伐形成不同大小(100-1 600 m2)的林窗共计21个,研究了林窗、林窗边缘、林下的植物多样性.结果表明:马尾松人工林林窗内外的丰富度指数R0(物种数)、Simpson生态优势度指数(SP)、Shannon-Wiener物种多样性指数(SW)差异显著(P0.05),其丰富度指数的大小顺序是林窗林窗边缘林下.不同大小林窗之间的丰富度指数也有显著差异(P0.05),但Simpson生态优势度指数、Shannon-Wiener物种多样性指数和Pielou均匀度指数(Jsw)差异均不显著.不同大小林窗边缘的丰富度指数、优势度指数、多样性指数和均匀度指数均没有显著差异(P0.05).综合来看,林窗的形成显著提高了马尾松人工林林下植物的丰富度,林窗大小对林下植物的物种组成和丰富度也有显著影响.     

林窗大小对川西马尾松人工林林下物种多样性和生物量的影响

林窗是植被演替和森林循环的重要驱动力,研究林窗大小对物种多样性和生物量的影响有利于揭示林窗干扰在生态系统恢复中的作用.以川西莲花山马尾松人工林为研究对象,划分出5种不同面积(81-625 m~2)的林窗共计15个和3个非林窗(林下)作对照(CK),对其群落物种组成、物种多样性水平(丰富度指数D、Simpson优势度指数H’、Shannon-Wiener指数H、Pielou均匀度指数J_(sw))和林下生物量(灌木层生物量、草本层生物量)进行调查研究.结果表明:(1)在总面积为5 493 m~2的样地中,共记录到维管植物99种,隶属56科84属;草本层和灌木层物种数随林窗面积增加均呈单峰格局,前者的物种数变化较后者明显.(2)总的来看,林窗下的D、H、J_(sw)值较林下大,H’值较林下小,且400-450 m~2面积的林窗下灌木、草本各物种多样性指数值达到一个较高水平.(3)林窗内的生物量显著大于林下生物量,200-250 m~2林窗下的生物量最大.(4)群落各层次物种多样性指数与对应层次地上、地下、全株生物量的相关性均不显著.因此认为,大面积林窗(400-450 m~2)有利于增加马尾松人工林林下群落物种丰富度,提升林下群落物种多样性水平;而中等面积林窗(200-250 m~2)则有利于增加林下生物量.     

单一斜率变点分析格氏栲幼苗的竞争范围

依据改进Hegyi单木竞争模型计算林窗和林下不同龄级格氏栲幼苗的竞争强度,采用指数平滑模型对幼苗竞争强度数据进行优化,对优化后数据应用单一斜率变点法确定格氏栲幼苗最佳竞争范围.结果表明:1)在格氏栲天然林中,林窗和林下格氏栲幼苗平均竞争强度随着竞争距离增大而逐步降低,初期下降较快,下降到一定程度后明显变缓,存在变化幅度的转折点,即为幼苗的竞争范围.2)林窗和林下格氏栲幼苗竞争强度的三次指数平滑值在最佳平滑系数α为0.8和0.7时其均方误差值分别为0.401 5和0.385 1,单一斜率变点分析得出林窗和林下格氏栲幼苗最佳竞争范围分别是距对象木1.70 m和1.90 m.研究结果可为格氏栲幼苗竞争格局研究中确定幼苗竞争范围提供科学理论依据.     

川西高山森林生态系统林下生物量及其随林窗的变化特征

作为森林生态系统的重要组成部分,林下植被及其残体的分布受到林冠层的影响,但迄今有关林窗对林下植被和残体生物量的影响尚无研究报道.于2013 年8 月2 日至20 日,以海拔3 600 m 的川西岷江冷杉原始林林下植被为研究对象,根据区域内的坡向和林分组成等因素设置3 个100 m×100 m 的典型样地,调查其生物量及其随林窗的变化特征.在每个样地内选择3 个大林窗,在林窗、林缘和林下分别设置3 个20 m×20 m 的样方,调查粗木质残体长度或高度、大小头直径、枯立木记录胸径、腐烂等级等;在林窗、林缘和林下分别设置3 个5 m×5 m 的样方,采用“收获法”收集样方内直径在2.5-10 cm之间的细木质残体和灌木生物量;在林窗、林缘和林下分别设置3 个1 m×1 m 的样方来调查凋落物储量和草本生物量;在1m×1 m 的样方内随机选择1 个20 cm×20 cm 的小样方来调查地被植物生物量.结果表明,（1）川西高山森林生态系统总生物量为72.75 t·hm^-2,其中林下生物量为67.92 t·hm^-2,占生态系统生物量的95.17%.活体植被以灌木为主,其生物量为9.81t·hm^-2;残体部分以粗木质残体为主,其储量为53.00 t·hm^-2;（2）林窗对灌木、草本、地被植物的影响各不相同,且不同物种的灌木生物量表现出不同的分布规律;草本生物量表现出明显的“边缘效应”,在林缘显著高于林下;林窗和林缘的地被植物生物量相对较低;（3）粗木质残体储量从林下到林窗呈现减小的趋势,但总体储量仍然较大,林窗和林缘的细木质残体储量高于林下.这些结果为认识高山森林生态系统林下生物量及其格局,以及林窗在森林生态系统的重要作用提供了基础理论依据.     

林窗对川西亚高山云杉人工林土壤呼吸的影响

为了解林窗对川西亚高山粗枝云杉(Picea asperata)人工林土壤呼吸的影响,采用CO2通量全自动监测系统对川西亚高山粗枝云杉人工林林窗和林内土壤呼吸及土壤温度、水分进行为期两年的连续观测,比较分析林窗和林内环境因子和土壤呼吸速率的变化.结果表明:川西亚高山粗枝云杉人工林林窗和林内的土壤温度、土壤水分和土壤呼吸速率均具有显著的季节动态.在生长季节(4-10月),林窗效应使土壤温度、土壤水分和土壤呼吸速率较林内分别增加了48.8%、19.3%和18.6%;而冬季(11月-翌年3月)两种环境之间并无显著差异.林窗和林内土壤呼吸速率和土壤温度均呈显著指数相关(P0.01),与土壤水分呈显著线性相关(P0.05).林窗和林内的土壤呼吸温度敏感性(Q_(10))分别为2.46和3.01.综上所述,林窗效应对川西亚高山森林土壤呼吸具有显著刺激作用,且有明显的季节动态特征.(图3表1参33)     

马尾松人工林林窗内土壤动物对凋落物微生物生物量的影响

选择长江上游人工采伐形成的7种不同大小的马尾松人工林林窗(G1:100 m~2;G2:225 m~2;G3:400 m~2;G4:625 m~2;G5:900 m~2;G6:1 225 m~2;G7:1 600 m~2),探讨不同林窗大小、位置和凋落物分解时间下土壤动物对凋落物微生物生物量的影响.结果显示:中等林窗(G4和G5)内,土壤动物显著影响了凋落物的微生物生物量氮(MBN)(P0.05),MBN分别增加了28.16%和26.18%.同时,林窗边缘的土壤动物使凋落物的MBN增加了29.06%(P0.05).此外,分解30 d,土壤动物使凋落物的MBN增加了26.52%(P0.05);分解90 d,土壤动物使凋落物中微生物生物量碳(MBC)显著增加了49.10%(P0.05);但在180 d时,土壤动物显著降低了MBC(P0.05).这些结果说明,在马尾松人工林林窗内马尾松凋落物分解初期,土壤动物对微生物生物量的增加有一定的促进作用,但其作用大小受到林窗大小、林窗位置和凋落物分解时间的影响而表现出一定的差异.     

林窗大小对马尾松人工林更新植物生态化学计量特征的影响

为了解林窗大小对马尾松人工林林窗下更新过程中优势植物生态化学计量特征的影响,在长江上游低山丘陵区选取7种面积不等(100 m~2、225 m~2、400 m~2、625 m~2、900 m~2、1 225 m~2、1 600 m~2)的人为采伐形成的林窗,以林下为对照,分析更新优势植物油樟、芒萁、芒和皱叶狗尾草叶片化学计量特征.结果表明:4种植物化学计量特征对林窗大小响应不同,在各自林窗梯度中均有显著差异.4种植物C:N为17.0-37.7,C:P为152.5-748.0,N:P为6.4-21.5.随林窗面积增大,油樟、芒和皱叶狗尾草C:N均先升后降,C:P和N:P先降后升,芒萁变化不明显.油樟C、N、P元素分配最佳的林窗为625 m~2,芒萁为1 225 m~2,芒和皱叶狗尾草为1 600 m~2.4种植物在多数林窗中不受N、P限制,但900 m~2林窗中油樟和芒萁均处于缺P状态,400 m~2林窗中芒和皱叶狗尾草均受N限制.综上,更新油樟树种采用625 m~2林窗表现出较理想的效果,芒萁、芒和皱叶狗尾草的自然更新则在大面积林窗(1 225-1 600 m~2)中效果更好.     

林窗对川西亚高山6种植物凋落叶纤维素降解的影响

凋落物纤维素降解是森林生态系统碳循环的关键过程,其可能受到林窗直接或间接的影响.采用凋落物分解袋法,通过3年连续监测,研究川西亚高山6种常见木本植物凋落叶(岷江冷杉、红桦、四川红杉、方枝柏、康定柳和高山杜鹃)在不同林冠环境下(林窗中心、林缘林窗、扩展林窗和郁闭林下)冬季和生长季纤维素降解特征.结果显示:川西亚高山6种凋落叶分解过程中纤维素含量和残留率均呈现下降趋势,分解3年后纤维素含量为5.5%-12.1%且残留率下降至23.1%-44.6%.林窗中心处整体上具有较低的凋落叶纤维素含量和残留率,但这种差异性在分解3年后消失.相关性分析表明凋落叶纤维素含量和残留率与均温、初始纤维素、木质素含量和C/N值呈显著负相关,与冻融循环和初始有机溶性组分含量呈显著正相关.表明林窗的形成通过提供较高的温度或减少冻融循环的发生促进凋落叶纤维素的降解,但这种差异随着分解进程逐渐减弱,且受到凋落叶初始质量所代表的物种差异的影响.本研究表明林窗通过改变林内微环境促进凋落叶纤维素早期的降解,上述结果有助于进一步认识林窗在亚高山森林生态系统物质循环中的生态作用和意义.(图4表2参39)     

Population maintenance of the short-lived shrub Sambucus in a deciduous forest

This study quantitatively clarifies the life history of a shrub, Sambucus racemosa ssp. sieboldiana, in an old-growth forest, the Ogawa Forest Reserve, Japan, by a demographic approach using a projection matrix model that incorporates interactions between demographic parameters and canopy height dynamics. S. racemosa is a common deciduous shrub in central Japan and is known to grow predominantly at forest edges or roadsides. This indicates that it is a highly light-demanding species, and occurrence in gaps in old-growth stands suggests its "fugitive," gap-dependent life history in old-growth forests. We found that one distinctive feature of this species was that its seedlings can survive well in shaded conditions by alternating stems every year like perennial herb species. Matrix model analyses demonstrated that S. racemosa can continuously regenerate under the present disturbance regime of this forest and is highly adaptable to the structural dynamics of the old-growth forest. The maturity of S. racemosa shrubs depends on their size, and nearly all (>90%) of the mature (reproducing) individuals were found in gaps or near gaps. But wide seed dispersal by birds and the ability to form both seed banks and seedling banks, the latter of which has been regarded as a common characteristic of shade-tolerant climax species, probably increase the species' chances to encounter canopy gaps. Dynamic-canopied matrix models showed that the greatest elasticity is with shaded seedling survival. The frequent stem alternation of shaded seedlings often makes the growth rate negative, but the survival rate of seedlings in low light awaiting new gap creation is remarkably high (0.93 yr(-1)). The lower survival rate of the larger individuals and smaller minimum size to start reproduction than other canopy or subcanopy shade-tolerant species indicate that S. racemosa has the potential to reproduce before the closure of the encountered gaps and to complete its life history rapidly.     

Influence of acorn size and storage duration on moisture content, germination and survival of Quercus petraea (Mattuschka)

This study was conducted to evaluate how acom size (small, medium and large) and acorn storage duration (0, 5 and 17 months) influenced Quercus petraea (Mattuschka) moisture content and germination. Acorn size and storage duration did not significantly affect acorn moisture content, but they significantly affected acorn germination performance. When averaged for three acorn sizes, loss of germination performance occurred after 17 months of storage even when the moisture content did not reduce significantly and remain at the initial level (32.6%). Maximum germination percentage was observed in large and medium size classes before storage (93 and 95%, respectively) and after 5-month storage (94 and 93%, respectively), but after 17-month storage medium acorn size class exhibited the highest germination (68%). Small seed size class exhibited the lowest germination percentage and rate in each acorn storage duration. Acorn size also significantly affected seedling emergence and survival in the nursery and seedling emergence and survival was the lowest in small seed size class (85 and 80%, respectively). Although seedling survival of one-year seedlings in the nursery increased up to large seed size class, maximum survival in nursery conditions was observed in large and medium size classes (89 and 91%, respectively). Thus, acorn size grading in Q. petraea may result in higher germination performance within in a seedbed.     

长苞铁杉林林隙自然干扰规律

从林隙的大小结构、形成方式及形成木的数量特征等几个方面 ,对长苞铁杉纯林及混交林林隙干扰状况进行了对比研究 .结果表明 :纯林冠空隙 (CG)平均面积为 16 .4 6m2 ,扩展空隙 (EG)平均面积为 96 .98m2 ,混交林CG、EG平均面积分别为 6 9.75m2 和 2 32 .93m2 ;在长苞铁杉纯林中 ,林隙主要以枯立木形成为主 ,占总形成木的一半以上 ,且以单株形成木和多株形成木综合形成 ,形成木径级主要集中在 2 0～ 4 0cm之间 ;混交林林隙以干基折断为主 ,且多由双形成木形成 ,由双形成木形成的林隙占林隙总数的 4 4 % ,形成木以 30～ 4 0cm径级的占最大比例 ,占形成木总数的 4 3.2 4 % ;纯林及混交林形成木高度都主要集中在 2 0～ 30m之间 ;形成木物种组成的比例大小基本上与其主林层树种所占的比例相对应 ;纯林林隙大多处于林隙发育的前、中期而混交林林隙则多集中在林隙发育的中后期 .图 3表 5参 19     

Untangling positive and negative biotic interactions: views from above and below ground in a forest ecosystem

In ecological communities, the outcome of plant-plant interactions represents the net effect of positive and negative interactions occurring above and below ground. Untangling these complex relationships can provide a better understanding of mechanisms that underlie plant-plant interactions and enhance our ability to predict population, community, and ecosystem effects of biotic interactions. In forested ecosystems, tree seedlings interact with established vegetation, but the mechanisms and outcomes of these interactions are not well understood. To explore such mechanisms, we manipulated above- and belowground interactions among tree seedlings, shrubs, and trees and monitored seedling survival and growth of six species (Pinus banksiana, Betula papyrifera, P. resinosa, Quercus rubra, P. strobus, and Acer rubrum) in mature pine-dominated forest in northern Minnesota, USA. The forest had a moderately open canopy and sandy soils. Understory manipulations were implemented in the forest interior and in large gaps and included removal of shrubs (no interactions), tieback of shrubs (belowground), removal of shrubs with addition of shade (aboveground), and unmanipulated shrubs (both below- and aboveground). We found that shrubs either suppressed or facilitated seedling survival and growth depending on the seedling species, source of interaction (e.g., above- or belowground), and ecological context (e.g., gap or forest interior). In general, shrubs strongly influenced survival and growth in gaps, with more modest effects in the forest interior. In gaps, the presence of shrub roots markedly decreased seedling growth and survival, supporting the idea that belowground competition may be more important in dry, nutrient-poor sites. Shrub shade effects were neutral for three species and facilitative for the other three. Facilitation was more likely for shade-tolerant species. In the forest interior, shrub shade negatively affected seedling survival for the most shade-intolerant species. For several species the net effect of shrubs masked the existence of both positive and negative interactions above and below ground. Our results highlight the complexity of plant-plant interactions, demonstrate that outcomes of these interactions vary with the nature of resource limitation and the ecophysiology of the species involved, and suggest that ecological theory that rests on particular notions of plant-plant interactions (e.g., competition) should consider simultaneous positive and negative interactions occurring above and below ground.     

Soil drying in a tropical forest: Three distinct environments controlled by gap size

Soil water and temperature regimes in the tropical moist forest on Barro Colorado Island, Panama, were simulated directly from meteorological data using the model SWEAT. Separate field observations from root-exclusion, litter-removal and control treatments in one small and one large forest gap were used for calibration and validation. After irrigating all treatments to field capacity, soil matric potential and temperature were measured over 17 days at four depths ≤50 mm using the filter-paper technique and bead thermistors. Understorey environments were also simulated under the same initial conditions. The results suggest that three distinct scenarios, controlled by gap size, describe how the above- and below-ground processes controlling soil drying are coupled: (1) in the large gap, root water extraction by surrounding trees is negligible so soil drying is dominated by evaporation from the soil surface. Soil temperature is dominated by direct solar heating and cooling due to evaporation. (2) In the small gap, root water extraction dominates soil drying with soil evaporation playing a minor role. Soil temperature is still dominated by direct sunlight with some cooling due to evaporation. (3) In the understorey, root water extraction dominates soil drying. Soil temperature is dominated by heat conduction from deep soil layers with some evaporation and sensible heat transfer. The contrasting soil drying regimes imposed by variation in canopy structure enhance micro-environmental heterogeneity and the scope for differential germination and seedling establishment in coexisting tropical tree species.     

Seed predation by Neotropical rain forest mammals increases diversity in seedling recruitment

Seed dispersal and seedling recruitment (the transition of seeds to seedlings) set the spatiotemporal distribution of new individuals in plant communities. Many terrestrial rain forest mammals consume post-dispersal seeds and seedlings, often inflicting density-dependent mortality. In part because of density-dependent mortality, diversity often increases during seedling recruitment, making it a critical stage for species coexistence. We determined how mammalian predators, adult tree abundance, and seed mass interact to affect seedling recruitment in a western Amazonian rain forest. We used exclosures that were selectively permeable to three size classes of mammals: mice and spiny rats (weighing <1 kg), medium-sized rodents (1-12 kg), and large mammals (20-200 kg). Into each exclosure, we placed seeds of 13 tree species and one canopy liana, which varied by an order of magnitude in adult abundance and seed mass. We followed the fates of the seeds and resulting seedlings for at least 17 months. We assessed the effect of each mammalian size class on seed survival, seedling survival and growth, and the density and diversity of the seedlings that survived to the end of the experiment. Surprisingly, large mammals had no detectable effect at any stage of seedling recruitment. In contrast, small- and medium-sized mammals significantly reduced seed survival, seedling survival, and seedling density. Furthermore, predation by small mammals increased species richness on a per-stem basis. This increase in diversity resulted from their disproportionately intense predation on common species and large-seeded species. Small mammals thereby generated a rare-species advantage in seedling recruitment, the critical ingredient for frequency dependence. Predation by small (and to a lesser extent, medium-sized) mammals on seeds and seedlings significantly increases tree species diversity in tropical forests. This is the first long-term study to dissect the effects of various mammalian predators on the recruitment of a diverse set of tree species.     

菇渣用作无纺布容器育苗成型机配套基质的研究

为探讨菇渣在无纺布容器育苗成型技术中作为配套容器基质应用的可行性,研究了育苗成型机制备的菇渣(发酵后)和草炭容器基质的基本理化性质、盐分淋洗特征及其对火炬树和侧柏出苗及生长的影响。结果表明:菇渣基质的容重、通气状况与草炭基质之间无显著差异,pH值虽显著高于草炭基质,但适宜多数植物生长;相对于草炭基质,菇渣基质的持水能力不足,保肥性能较差;菇渣基质的适宜水分范围(36.1%~143.5%)明显小于草炭基质(41.9%~193.8%),有效水绝对含量较低;菇渣基质的电导率(3.71 mS.cm-1)虽高于安全育苗的临界值(≤2.6 mS.cm-1),但随着浇水次数的增加可逐渐降到安全值以下;菇渣基质的全氮、全磷和全钾含量显著高于草炭基质。在充足的水分和养分条件下,菇渣和草炭容器基质对侧柏和火炬树出苗及成活的影响基本一致,但菇渣基质对火炬树的育苗效果优于草炭基质。可见,只要保证充足水分,菇渣基质在无纺布容器育苗成型技术中可以替代草炭基质用于火炬树和侧柏的育苗。     

岷江干旱河谷灌木幼苗的土壤养分适应性研究

岷江上游干旱河谷地区的植被恢复是目前急需解决的问题,小马鞍羊蹄甲（Bauhinia faberi var. microphylla）是干旱河谷地区的优势乡土灌木,并作为当地植被恢复过程中的重要备选物种,因而进行小马鞍羊蹄甲种群在土壤贫瘠的干旱河谷的养分限制研究十分必要。针对性地进行施肥将影响到小马鞍羊蹄甲幼苗存活、生长和定殖,而如何有效提高该物种的存活和生长速率对于干旱河谷植被恢复将具有重要的意义。采用野外调查与模拟实验相结合的方法,分别研究了干旱河谷地区3个典型群落（干旱河谷的核心区——飞虹,干旱河谷灌丛与亚高山森林的过渡区——北部的石大关、干旱河谷灌丛与温性森林的过渡区——南部的蓝新镇）中小马鞍羊蹄甲幼苗叶片的化学计量特征,和施肥试验[w（有效氮）分别为100、280、460 mg·kg–1、w（有效磷）分别为12、24、48 mg·kg–1、w（氮）分别为40、70、100 mg·kg–1、w（磷）分别为12和24 mg·kg–1]中叶片化学计量特征及幼苗生长参数（叶片数、基径和株高）和各器官（根茎叶）生物量。结果表明：在野外各演替阶段的小马鞍羊蹄甲幼苗生物量和营养元素质量分数都随着磷肥的增加而增加,表明磷素是植物生长的限制因子,同时N∶P比均大于16,也暗示其受到P养分的限制;在室内施肥试验中,施加N肥没有促进小马鞍羊蹄甲生物量的积累,反而抑制了幼苗生长;施加P肥促进了幼苗生物量的积累,表明幼苗缺乏P元素,养分限制类型为P限制。     

Growth performance and range shift of the subalpine fir (Abies fargesii) in the Qinling Mountains,China

Trees in the subalpine environment, a particularly vulnerable area being the first to reflect climate changes, are most likely to show strong effects of climate variability. The aim of this study was to identify growth responses of subalpine fir (Abies fargesii) to climate variability, and investigate range shifts along an altitudinal gradient in the subalpine region of the Qinling Mountains, China. Standard correlation functional analysis showed different growth responses of fir trees to climatic variables between north and south aspects. In the north aspect, radial growth was significantly positively correlated with temperatures in early spring (February–April) and summer (July) of the current year, while radial growth was significantly positively correlated with temperatures in November and December of the previous year and early spring (February–April) of the current year in the south aspect. Analysis of age structure distribution displayed a decrease in number of mature fir trees and an increase in number of saplings along the altitudinal gradient on both aspects. Fir saplings/seedlings only occur in the treeline environment, and this fir population was significantly younger than that at lower elevations. Thus, fir trees show different radial growth patterns in response to climatic variability between north and south aspects, and age-class distributions along the altitudinal gradient imply an upward shift in range in the subalpine region during the past century in the Qinling Mountains of China.