Patterns of bryophyte diversity in peatlands of continental western Canada
Patterns of bryophyte diversity in peatlands of continental western Canada
复制标题
加拿大西部大陆泥炭地苔藓植物多样性模式
DOI：
10.2307/3243306
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
R. Belland
中科院分区：
文献类型：
--
作者：
D. Vitt;Yenhung Li;R. Belland
在加拿大西部大陆，96 个泥炭地中发现的 110 个物种中，62% 出现在以泥炭藓为主的沼泽和贫瘠沼泽中，而 71% 则出现在以棕色苔藓为主的肥沃沼泽中。在富含沼泽的沼泽梯度上，α（位点）多样性非常均匀。伽玛（景观）多样性在极其丰富的沼泽中最高，这是所调查的五种泥炭地类型中变化最大的。地点层面的物种丰富度与栖息地异质性高度相关。气候因素并不那么重要；然而，栖息地异质性 (46%) 和温度 (15%) 共同解释了 61% 的变化。当单独检查五种泥炭地类型时，贫瘠沼泽地的物种丰富度随着 pH 值的增加而增加，极端丰富的沼泽地的物种丰富度随着 pH 值的增加而降低，而在泥炭高原、大陆沼泽和中等富裕的沼泽地中，无论 pH 值如何，物种丰富度都保持相对恒定。由于大陆沼泽的地毯和水池生境异质性有限，泥炭高原的物种丰富度始终高于大陆沼泽。百分之二十五的物种只被发现过一次；这些物种在该地区被认为是稀有的。其中百分之六十只发生在极其肥沃的沼泽地。栖息地异质性，加上某些泥炭地类型的 pH 值或温度，可以有效地用来预测地点的生物多样性。生物地理学家长期以来一直对物种丰富度模式感兴趣。解释这些物种发生模式的尝试多种多样，从历史导向的（Fischer 1960）到平衡的、认为丰富度模式归因于当前条件的（Rosenzweig 1975）。假设解释丰富度模式的过程包括生产力、栖息地恶劣性、气候稳定性、种间竞争和栖息地异质性。泥炭地是独特的生态系统，由于植物生产和分解速度不均而积累碳，如泥炭。根据水文和地理学标准，泥炭地可以很容易地与非泥炭形成的生态系统分开，并且它们拥有很大程度上独特的苔藓植物区系。在泥炭地内，生态系统年龄、生产力、稳定性和生境异质性存在很强的梯度，并且泥炭地发生在不同的区域气候下。许多人认为泥炭地生态系统压力较大，当仅利用维管束植物与其他栖息地进行比较时，泥炭地的物种丰富度通常相对较低。根据水文学，泥炭地可分为沼泽浅营养系统或沼泽矿营养系统。 Wheeler（1993）比较了英国这两种水文类型的物种丰富度，在沼泽中发现了 464 种维管植物和 189 种苔藓植物，总计 653 种，而在沼泽中他只发现了 109 种维管植物和 84 种苔藓植物，总计 193 种。显然，沼泽的物种比沼泽更多。然而，这是一个不平等的比较。沼泽和沼泽是水文单位，而不是植被单位。当泥炭地根据植被进行分类时，早已认识到四种类型（Sj6rs 1952；Vitt & Chee 1990）。在永久冻土影响很大的加拿大西部，沼泽可根据植被分为两种类型，即大部分位于永久冻土之下的沼泽，称为泥炭高原，以及没有永久冻土的沼泽，称为大陆沼泽（Belland & Vitt 1995）。沼泽地可分为三种类型，即贫瘠沼泽地、中等富裕沼泽地（有些人错误地将其称为中等沼泽地）和极度富裕沼泽地。因此，在加拿大西部大陆，物种丰富度的比较需要使用五种植被类型，而不是两种泥炭地水文类型。五种植被类型中的三种以泥炭藓为主（泥炭高原、大陆沼泽和贫瘠沼泽），而另外两种则以棕色苔藓为主（中等和极端丰富的沼泽）。当杜雷茨（DuReitz，1949）最初提出沼泽可以分为他所说的贫沼和富沼时，他的贫沼和富沼术语是基于沼泽中存在的指示物种的数量。贫瘠的沼泽地的指示物种比富裕的沼泽地少。如果这个指示物种概念沿着bog-fen梯度继续延伸到沼泽，则sup0007-2745/95/218-227$1.15/0 此内容于2016年7月6日星期三05:30:35 UTC从157.55.39.100下载 全部使用服从http://about.jstor.org/terms 1995] VITT ET AL.：泥炭地多样性 219 据称沼泽的指示物种数量最少。这些指示物种概念经常被错误地应用于化学条件和总体物种丰富度。因此，许多研究人员基于对富人和穷人概念的错误解释，认为富裕的沼泽地比贫穷的沼泽地具有更高的物种丰富度。此外，总体植物物种丰富度的这些明显模式通常仅基于维管植物成分，不包括苔藓植物。对苔藓植物重要的环境因素与对维管植物重要的环境因素不同。 Vitt 和 Chee (1990) 使用多变量方法表明，苔藓植物模式很大程度上遵循酸度和碱度梯度，而维管植物模式则倾向于遵循养分梯度（尤其是氮和磷）。可以预期，这两组植物的物种丰富度模式也表现出不同的模式。这在海拔和纬度梯度上很明显（Vitt 1991），其中苔藓植物多样性沿着海拔梯度增加，而沿着纬度梯度保持相对稳定。尽管 Glaser (1992) 最近在北美东部的区域范围内检查了沼泽中的维管植物多样性，但没有人使用综合区域数据集检查沼泽沼泽梯度上苔藓植物的物种多样性模式，也没有人提出为什么在这些泥炭地中发现的模式可能会出现这种情况。我们的目标是回答以下问题：1）景观中的苔藓植物物种丰富度（即伽马多样性）如何沿着富含沼泽的沼泽梯度变化？ 2）苔藓植物物种丰富度与泥炭地分类中重要的环境因素相关吗？ 3）当比较沼泽、贫瘠沼泽和富饶沼泽时，地点水平的苔藓植物物种丰富度（即α多样性）如何变化？ 4）可以使用适当的因子来预测苔藓植物物种丰富度吗？
In continental western Canada, 62% of the 110 species found in 96 peatlands occur in Sphagnum-dominated bogs and poor fens, whereas 71% occur in brown moss-dominated rich fens. Alpha (site) diversity is remarkably uniform over the bog-rich fen gradient. Gamma (landscape) diversity is highest in extreme-rich fens, which are the most variable of the five peatland types surveyed. Species richness at the site level is most highly correlated with habitat heterogeneity. Climatic factors are not as important; however, habitat heterogeneity (46%) and temperature (15%) together explain 61% of the variation. When the five peatland types are examined individually, species richness in poor fens increases with pH, in extreme-rich fens decreases with pH, and in peat plateaus, continental bogs, and moderate-rich fens remains relatively constant regardless of pH. Peat plateaus consistently have greater species richness than continental bogs due to limited carpet and pool habitat heterogeneity in the latter. Twenty-five percent of the species were found only once; these species are considered rare in the region. Sixty percent of these occurred only in extreme-rich fens. Habitat heterogeneity, plus pH or temperature in some peatland types, can be effectively used to predict site biodiversity. Patterns of species richness have long been of interest to biogeographers. Attempts to explain these patterns of species occurrence have been varied, ranging from those that are historically oriented (Fischer 1960) to those that are equilibrial and argue that richness patterns are attributable to current conditions (Rosenzweig 1975). Among processes that have been hypothesized to account for richness patterns are productivity, habitat harshness, climatic stability, interspecific competition, and habitat heterogeneity. Peatlands are unique ecosystems that accumulate carbon, as peat, due to unequal rates of plant production and decomposition. Peatlands can be easily separated from non-peat-forming ecosystems based on hydrological and physiographic criteria, and they posess a largely unique bryoflora. Within peatlands, there exist strong gradients in ecosystem age, productivity, stability, and habitat heterogeneity, and peatlands occur under a diversity of regional climates. Peatlands have been considered by many to be stressed ecosystems and in general have relatively low species richness when comparisons that utilize only vascular plants are made to other habitats. Based on hydrology, peatlands can be classified either as bogs ombrotrophic systems, or fens-minerotrophic systems. Wheeler (1993) has compared species richness between these two hydrological types in Britain and found 464 vascular plants and 189 bryophytes in fens, totalling 653 species, whereas in bogs he found only 109 vascular plants and 84 bryophytes with a total of 193 species. Clearly fens have more species than bogs; however, this is an unequal comparison. Fens and bogs are hydrological units, not vegetational units. When peatlands are classified on the basis of vegetation, four types have long been recognized (Sj6rs 1952; Vitt & Chee 1990). In western Canada, where permafrost can have a strong influence, bogs can be divided into two types based on vegetation, namely those largely underlain with permafrost, termed peat plateaus, and those without permafrost called continental bogs (Belland & Vitt 1995). Fens can be divided into three types, namely poor fens, moderate-rich fens (which some incorrectly term intermediate fens), and extreme-rich fens. Thus in continental western Canada, the comparisons of species richness need to be made using five vegetation types, not two peatland hydrological types. Three of the five vegetation types are Sphagnum-dominated (peat plateau, continental bogs, and poor fens) whereas the other two are brown-moss dominated (moderateand extreme-rich fens). When DuReitz (1949) originally proposed that fens can be divided into what he termed poor fens and rich fens, he based his terminology of poor and rich on the number of indicator species present in the fen. Poor fens have fewer indicator species than do rich fens. If this indicator species concept is continued along the bog-fen gradient to bogs, then sup0007-2745/95/218-227$1.15/0 This content downloaded from 157.55.39.100 on Wed, 06 Jul 2016 05:30:35 UTC All use subject to http://about.jstor.org/terms 1995] VITT ET AL.: PEATLAND DIVERSITY 219 posedly bogs have the least number of indicator species. These indicator species concepts have often been misapplied to chemical conditions and to overall species richness. Hence, many researchers have considered rich fens to have greater species richness than poor fens based on an incorrect interpretation of the concepts of rich and poor. Also, these apparent patterns in overall plant species richness are often based only on the vascular plant component, excluding bryophytes. Environmental factors important to bryophytes differ from those important to vascular plants. Vitt and Chee (1990) used multivariate methods to suggest that whereas bryophyte patterns largely follow the gradients of acidity and alkalinity, vascular plant patterns tend to follow nutrient gradients (especially nitrogen and phosphorus). It might be expected that species richness patterns of these two groups of plants also show different patterns. This is evident along gradients of elevation and latitude (Vitt 1991), wherein bryophyte diversity increased along elevation gradients and remained relatively stable along latitudinal ones. Although Glaser (1992) has recently examined vascular plant diversity in bogs at a regional scale in eastern North America, no one has examined the species diversity patterns of bryophytes along the bog-fen gradient using a comprehensive regional data set, and no one has suggested why patterns found in these peatlands might occur as they do. Our objectives here are to answer the following questions: 1) How does bryophyte species richness of a landscape (i.e., gamma diversity) vary along the bog-rich fen gradient? 2) Does bryophyte species richness correlate with environmental factors considered important in peatland classification? 3) How does bryophyte species richness at the site level (i.e., alpha diversity) vary when bogs, poor fens, and rich fens are compared? 4) Can bryophyte species richness be predicted using appropriate factors?