The area of two clones of Populus tremuloides Michaux in the Fish Lake Basin, Sevier County, Utah, was determined using aerial photographs combined with ground delineation using leaf, bark, and stem characteristics. The clones occupied 24.9 acres (10.1 ha) and 106.8 acres (43.3 ha) and contained about 15 000 and 47 000 ramets, respectively. Other clones up to an estimated 200 acres (81.0 ha) were observed in the vicinity and in other areas of the central and southern Rocky Mountains. In contrast, the largest P. tremuloides clone in eastern North America whose boundary has been verified was 3.8 acres (1.5 ha). Populus tremuloides and P. grandidentata Michaux clones of eastern North America are generally small, typically less than 0.1 acres (0.04 ha) in size. The large size of many western clones is probably due to the establishment of few seedlings, periodic fires promoting suckering, expansion over a long time period, and little competition with conifers or other vegetation. Small size of most eastern North American clones and lack of large clones are probably due to establishment of many seedlings per unit area, competition among clones and with other more shade-tolerant vegetation, and their relatively young age.

Bigtooth and trembling aspens (Populus grandidentata and P. tremuloides) typically occur in Michigan and throughout much of their native range in natural clones of several to many genetically identical individuals. A clone is initiated by the establishment of a seedling (the ortet); suckers (ramets) arise from the root system of the ortet. Death of ramets and decay of root connections may result in formation of several independent root systems within the same clone. Average size of individual clones of both species on the research sites in Michigan was approximately 0.007 acre. Male and female clones did not differ in size. Clones are established, expand, intergrow, and coalesce depending upon the ease of seedling establishment, rapidity of root expansion, inherent suckering ability, and amount of disturbance. Although the aspens are typically recognized as pioneer species, they may be more permanently part of the habitat than most of their non—clonal associates. Recognition of the clonal structure of most aspen stands is important in many aspects of research.

Japanese red maple, Acer pycnanthum K. Koch, is the disjunct sister species of the red maple, Acer rubrum L. Whereas A. rubrum is one of the most widely distributed and abundant species in eastern North America, A. pycnanthum is rare in central Honshu, Japan. Although its morphological similarity to A. rubrum is well known, little is known about the sites and communities where it occurs, its natural history characteristics, sexual and asexual regeneration, and the reasons for its restricted occurrence. We located and described all known sites, totaling <18 ha, which supported populations of three or more clones. Twenty-seven of the 30 ecosystems described are remnant natural populations, which are confined to lower slopes of three river basins where wetlands have persisted and recurrently formed for millions of years due to unique geological, topographic, and soil properties. Acer pycnanthum, an obligate species of forested wetlands, occurs on diverse seepage and floodplain ecosystems that are characterized by poor drainage; acid, wet soils; high understory and ground-cover diversity, and associated rare species. The area occupied by each population is typically very small, usually <0.5 ha and often <0.2 ha. Regeneration is limited to sites with high light irradiance following disturbance. Because of the rarity of natural wetland sites, its inability to colonize upland sites occupied by dense natural vegetative cover or by planted conifers, and the encroachment of agriculture and urbanization, the occurrence of A. pycnanthum is increasingly limited. Using an ecosystem approach, conserving whole ecosystems, including their total vegetative diversity, is a high priority.Key words: biodiversity, disjunct species, landscape ecology, rare species, red maple (Acer pycnanthum, Acer rubrum), wetlands.

Aim We analysed variation in chloroplast DNA (cpDNA) in red maple (Acer rubrum L.) and silver maple (Acer saccharinum L.) across a large part of their geographic ranges. Acer rubrum is one of the most common and morphologically variable deciduous trees of eastern North America, while its sister species A. saccharinum has a more restricted habitat distribution and displays markedly less morphological variation. Our objective was to infer the impact of biogeographic history on cpDNA diversity and phylogeographic structure in both species.Location Deciduous forests of eastern North America.Methods We sequenced 1289 to 1645 bp of non-coding cpDNA from A. rubrum (n = 258) and A. saccharinum (n = 83). Maximum parsimony networks and spatial analysis of molecular variance (SAMOVA) were used to analyse phylogeographic structure. Rarefaction analyses were used to compare genetic diversity.Results A total of 40 cpDNA haplotypes were recovered from A. rubrum (38 haplotypes) and A. saccharinum (7 haplotypes). Five of the seven A. saccharinum haplotypes were shared with nearby samples of A. rubrum. SAMOVA recovered four phylogeographic groups for A. rubrum in: (1) south-eastern USA, (2) the Gulf and south-eastern Coastal Plain, (3) the lower Mississippi River Valley, and (4) the central and northern regions of eastern North America. Acer saccharinum had significantly lower haplotype diversity than A. rubrum, and novel haplotypes in post-glaciated northern limits of its range were shared with A. rubrum.Main conclusions This is the first study of A. rubrum to report a distinct phylogeographic group centred on the lower Mississippi River, and the first to examine data comparatively with A. saccharinum. We hypothesized that A. rubrum would display stronger phylogeographic structure and greater haplotype diversity than A. saccharinum because of its greater geographic range, and ecological and morphological variation. This hypothesis was supported by the cpDNA analysis. The sharing of cpDNA and chloroplast simple sequence repeat (cpSSR) haplotypes in areas of geographic overlap provides evidence of introgression, which led to an increase in haplotype diversity in both species, and to novel phylogeographic structure in A. rubrum. We recommend that introgression be considered, along with other potential causes, as an explanation for the phylogeographic structure of cpDNA in plants.

An ecological method of multifactor ecosystem classification was applied in the Sylvania Recreation Area, an 8500-ha tract of old-growth northern hardwood – conifer forests in upper Michigan. The uplands and wetlands were subjectively classified into 25 ecosystems by a method combining reconnaissance, plot sampling, data analysis, and ecosystem mapping. Each ecosystem was a characteristic combination of physiography, ecological species groups (ground vegetation), and soil. Discriminant analysis was used to evaluate the distinctness of the upland ecosystems and to compare the discriminating abilities of different ecosystem components (physiography, ground vegetation, and soil). The classification was corroborated in the multivariate analyses. The lowest estimated error rate (9.4%) in discriminant analysis was obtained by a model based on a combination of physiographic and soil characteristics and ecological species groups. The estimated error rates based on the species groups alone and physiography and soil alone were 42.2 and 25.0%, respectively. The discriminant analyses indicate that neither vegetation alone nor physiography and soil alone could be used with high reliability in classifying and mapping ecosystems. An additional discriminant analysis of the three ecosystem components indicated that the ecosystems could be distinguished by field characteristics without information from soil laboratory analyses. This analysis also demonstrated the particular value of the vegetation component as a readily observed, acceptable substitute for soil laboratory data in identifying and mapping ecosystem units.