Vegetation,environmental characteristics and ideas on the maintenance of alvars on the Bruce Peninsula,Canada

Abstract. Despite international recognition that alvar habitats are important reservoirs of biodiversity, they remain little studied in North America. In this paper, the results are reported on an investigation of alvars in the central portion of their known distribution on this continent. 210 plots were distributed among seven sites and were quantitatively sampled for vascular plants, lichens, bryophytes and a suite of environmental variables. Detrended and Canonical Correspondence Analyses and other methods were used to investigate differences among alvars, within alvars and between alvars and adjacent forested habitats. The plant communities and environmental conditions were highly similar among sites in the study region, yet very different from surrounding habitats. There were abrupt changes in vegetation and environmental conditions from alvar to forest, without the presence of transition zones in the vegetation or environmental gradients as the forest was approached. The environmental factors associated with the change from alvar to forest and with variation within alvar habitat were examined. Some alvars in the study were found to contain stunted, slow-growing trees reaching ages of 524 yr. These same sites appear to have remained unburned for several centuries, while other sites likely burned 90 yr ago. The plant communities were very similar between the alvars that lacked a major, biomass-removing disturbance in centuries and alvars that had experienced catastrophic fire relatively recently. Maintenance of the plant communities and open nature of alvars appears site-specific rather than habitat specific.     

Phytogeographical and community similarities of alpine tundras of Changbaishan Summit,China, and Indian Peaks,USA

Abstract. We compared the diversity, phytogeography, and plant communities in two mid-latitude alpine tundras with comparable aerial and elevational extents: Changbaishan Summit in eastern Asia and Indian Peaks in western North America. Despite wide separation, the two areas shared 72 species. In all, 43% of the species on Changbaishan Summit are also distributed in the alpine zones of western North America, while 22% of the species on Indian Peaks are also distributed in the alpine zones of eastern Asia. Almost all the shared species also occur in the Beringian region. Phytogeographical profiles of species and genera showed that 69% of species and over 90% of genera in both alpine tundras belong to the three phytogeographical categories: cosmopolitan, circumpolar, and Asian-North American. We attributed the current floristic relationship between these widely separated areas to the periodic past land connection between the two continents during the Tertiary and Pleistocene. Indian Peaks has a closer floristic relationship with the Arctic tundra than does Changbaishan Summit. Indian Peaks also has 45% higher species richness and lower vegetation cover than Changbaishan Summit. Plant communities from the two areas were completely separated in the two-way indicator species analysis and non-metric multidimensional scaling on floristic data at both species and generic levels, whereas ordination of communities by soil data produced a greater overlap. The plant communities on Changbaishan Summit in general have lower alpha diversity, higher beta diversity (lower between-community floristic similarity), and more rare species than does Indian Peaks. Mosaic diversity does not differ in the two alpine tundras, although the analysis suggests that Changbaishan Summit communities are more widely spaced on gradients than the Indian Peaks communities.     

Cryptogam communities on fallen logs in the Duke Forest,North Carolina

Abstract. I studied cryptogam (i.e. bryophyte and lichen) communities on fallen logs in the Duke Forest, Durham and Orange Counties, North Carolina, USA, to determine the relationship of log characteristics and microsite to community composition. Species composition and abundance were estimated for 111 randomly selected fallen logs. Interior wood samples were used to identify the tree species. I determined physical and chemical characteristics for each log, and described the log microsite. Canonical Correspondence Analysis (CCA) detected a clear gradient in cryptogam species composition which is correlated with the species of log and the presence of bark. Communities on hardwood bark, hardwood wood, and pine substrates were the most distinct. CCA also revealed that the microsite is not as closely related to species composition as are substrate pH and density. The majority of the cryptogam species encountered on the fallen logs are commonly reported from other substrates in the forest. However, within the habitat type of fallen logs, several species were apparently restricted to certain substrate types.     

Neighbour diversity in lichen-dominated communities

Abstract. In this study, we examined two sets of contact neighbour data from lichen-dominated communities (one saxicolous, the other epiphytic) to determine whether the diversity of contact neighbours is significantly less than expected, indicating segregation of species. We also wanted to test whether the observed neighbour diversity changed with the species' own frequency. Using two measures of diversity, we found that in both saxicolous and epiphytic communities, there was a significant tendency for neighbour diversity to be lower than expected. The results are consistent with Pacala's spatial segregation hypothesis but may indicate that the plants’responses to environmental variables act at very small scales in these communities.     

Diversity and succession of epiphytic macrolichen communities in low‐elevation managed conifer forests in Western Oregon

Abstract. We examined epiphytic macrolichen communities in Pseudotsuga menziesii (Douglas‐fir) forests across the western Oregon landscape for relationships to environmental gradients, stand age and structure, and commercial thinning. We used a retrospective, blocked design through the Coast and the western Cascade ranges of Oregon. Each of our 17 blocks consisted of a young, unthinned stand (age 50–110 yr); an adjacent, thinned stand of equivalent age; and an old‐growth stand (age > 200 yr). We found 110 epiphytic macrolichen taxa in the stands. Forage‐providing alectorioid lichens and the nitrogen‐fixing cyanolichen Lobaria oregana associated strongly with old‐growth stands and remnant old trees in younger stands (unthinned + thinned). Relative to unthinned stands, thinned stands had a slightly higher abundance of alectorioid lichens and a greater presence of Hypogymnia imshaugii. However, thinned stands hosted a lower landscape‐level (γ) diversity, lacking many species that occurred infrequently in the unthinned stands. Patterns in the lichen community composition correlated strongly with climatic gradients; the greatest variation in composition was between the Coast and Cascade ranges. The difference in communities between mountain ranges was greatest among stands 70–110 yr old, suggesting a difference in lichen successional dynamics between the ranges.     

Plant communities and landscape diversity along a Canadian Arctic river

Abstract. We analysed the structure and diversity of the vegetation along an Arctic river to determine the relationship between species richness and plant community structure. We examined whether variation in species richness along the corridor is structured as (1) an increase in the number of communities due to increasing landscape heterogeneity, (2) an increase in the floristic distinctiveness (β-diversity) of communities, or (3) an increase in within-community richness (α-diversity) as species-poor communities are replaced by species-rich communities. We described 24 community types and analysed the relationship between site vascular species richness (γ-diversity) and β-diversity, α-diversity, site environmental heterogeneity, and the number of distinct plant communities. We also measured diversity patterns of vascular, bryophyte, and lichen species within communities and examined their relationship to community-level estimates of environmental factors. We found that an increase in site species richness correlated with an increase in the number of communities (r²= 0.323, P= 0.0173) and β-diversity (r²= 0.388, P= 0.0075), rather than an increase in the α-diversity of individual communities. Moisture and pH controlled most of the differences in composition between communities. Measures of species richness and correlations with moisture and pH within communities differed among vascular, bryophyte, and lichen species. Bryophyte richness was positively correlated with moisture (r²= 0.862, P= 0.0010) and lichen richness was negatively correlated with moisture (r²= 0.809, P= 0.0031). Vascular plants had a peak in richness at pH 6.5 (r²= 0.214, P < 0.0001). We conclude that site variation in vascular richness in this region is controlled by landscape heterogeneity, and structured as variation in the number and distinctiveness of recognizable plant communities.     

Conservation of bog plant species assemblages: Assessing the role of natural remnants in mined sites

Abstract. Bogs, economically valuable wetlands, are subjected to exploitation in southern Canada. We addressed plant conservation within bogs mined for peat, in which small undisturbed remnants are left, mostly at the margins of the mined areas. The main goal of the study was to test whether these remnants act as refuges for plants which could recolonize areas that are planned for restoration after mining is completed. Mosses, lichens and vascular plants were sampled in remnants of 24 mined bogs in southeastern Canada during the summer of 1997. The vegetation was also sampled at the margins and centres of 24 nearby natural bogs in plots similar in size to these remnants. Using similarity analysis and ordination techniques, we found that plant species assemblages in remnants of mined bogs differ from those near the margins of natural bogs, and that certain species are associated with the centre of natural bogs, due to the presence of pools. We also showed that water conditions of remnants are affected by drainage due to peat mining. Sphagnum moss showed itself to be a key indicator of mining effects on vegetation. Implications for peat resource management and bog conservation are discussed.     

中国绿绒蒿属新资料

吉隆沟是喜马拉雅西部最大的水汽通道,水热条件好,地形地貌多样,孕育了丰富的植物多样性。该文报道了在西藏吉隆县发现的中国绿绒蒿属2个中国新记录种——秋花绿绒蒿(Meconopsis autumnalis P. Egan)、美花绿绒蒿(Meconopsis bella Prain)以及1个发表后再次记录到的物种——心叶绿绒蒿［Meconopsis polygonoides (Prain) Prain］。文中提供了形态特征描述、分布及生境,并简要说明了与近似种的区别。该发现丰富了中国西藏植物区系,为中国绿绒蒿属研究提供了新资料。结合过往的调查,作者认为吉隆县的植物多样性调查应减少传统吉隆县沿吉隆藏布到吉隆镇的过度采集,建议向吉隆口岸及两侧深入采集。