Bruce McCune

DISPERSAL LIMITATIONS OF EPIPHYTIC LICHENS RESULT IN SPECIES DEPENDENT ON OLD‐GROWTH FORESTS

Epiphytic lichen biomass accumulates slowly in forest canopies. We eval- uated three alternative hypotheses for the slow accumulation of epiphytic lichens, using two experiments in tree crowns from 15 Douglas-fir forest stands representing three age classes: old growth, young, and recent clearcuts. The first experiment evaluated whether forest age, bark roughness, or dispersal rate limits the establishment of the dominant old- growth-associated lichen, Lobaria oregana. Surface-sterilized branches with either rough or smooth bark were repeatedly inoculated with propagules and compared 1 yr after the last inoculation. Dispersal affected rates of establishment: inoculated branches had 27X more newly established thalli than controls. Establishment on smooth bark was highest in clearcuts, intermediate in young forests, and lowest in old growth. There was as much or more establishment of sown propagules on smooth-barked branches as on rough-barked branches in all age classes. In the second, transplant-performance experiment, Lobaria oregana grew as rapidly in young forests as in old growth but lost biomass and suffered more injuries in clearcuts. In contrast, L. pulmonaria performed at least as well in clearcuts as in young forests and old growth. Poor dispersal and establishment limit the development of L. oregana populations in Douglas-fir forests. Particular substrates and microenviron- ments found only in old growth are not essential for Lobaria establishment and growth. Maximizing the number and dispersion of remnant trees in cutting units should maximize the rate of accumulation of L. oregana biomass in the regenerating forest. The single most important action promoting the accumulation of old-growth-associated epiphytes will be the retention of propagule sources in and near all cutting units.

INFLUENCE OF NOISY ENVIRONMENTAL DATA ON CANONICAL CORRESPONDENCE ANALYSIS

Canonical Correspondence Analysis (CCA) is an increasingly popular method for multivariate analysis of ecological community data. It is, however, one of the most potentially misleading multivariate methods for community analysis. Inclusion of noisy or irrelevant environmental variables can distort the representation of gradients in community structure. These hazards are illustrated with simulated community data sets having a known, simple, underlying structure, then introducing different kinds and degrees of noise into the environmental data. Because of its sensitivity to even a modest amount of noise in the environmental data, CCA with site scores as linear combinations of environmental variables is inappropriate when the objective is to describe community structure. These problems can be avoided by using traditional indirect ordination methods, where pure community structure is expressed, without any constraint imposed by the environmental variables. CCA can be appropriate, however, when the objective is to describe how species respond to particular sets of observed environmental variables.

Repeatability of Community Data: Species Richness Versus Gradient Scores in Large-scale Lichen Studies

Repeated ecological assessments based on permanent plot data require sufficient data quality to detect a signal of change against a background of noise (sampling error of various kinds). We analyzed several components of error in the time-constrained method for sampling lichen communities used by the Forest Health Monitoring program: between-crew (Technicians), crew-to-expert, between-expert, and seasonal variation. Data were from the southeastern United States and Oregon. Two types of dependent variables were used: species richness and scores on lichen community gradients (responses to climatic and air quality gradients). Gradient scores were repeatable to within 2-10% for experts and technicians alike and did not differ between those groups. Species richness is much more difficult to estimate reliably. Despite relatively low species capture by technicians, the high repeatability in gradient scores demonstrates the statis- tical redundancy in information provided by various lichen species. These results imply that re- peated assessments of species richness will contain considerable observer error, but that shifts in community composition may nevertheless be detected reliably.

REMNANT TREES AND CANOPY LICHEN COMMUNITIES IN WESTERN OREGON: A RETROSPECTIVE APPROACH

The “New Forestry” practice of green-tree retention is becoming an important management tool for publicly owned lands, yet few data exist to demonstrate that this tool can succeed at enhancing biodiversity. We addressed this issue by using a retrospective approach to compare canopy lichen litter in adjacent, paired stands of rotation age (55–120 yr): one with and one without old-growth (>300 yr) remnant trees. We sampled three functional groups of lichens in 17 stands in western Oregon: alectorioid lichens, cyanolichens, and green-algal foliose lichens. Thirteen stands were low elevation (520–850 m) and four were mid-elevation (1220–1340 m). Biomass of cyanolichen and green-algal foliose lichen litter was greater in low-elevation sites, whereas alectorioid lichen litter biomass was greater in mid-elevation sites. Cyanolichens were absent from all mid-elevation sites. Biomass of alectorioid lichen and cyanolichen litter was greater in low-elevation sites with remnant trees than in those without remnant tre...

Epiphyte Habitats in an Old Conifer Forest in Western Washington, U.S.A.

Abstract Old conifer forests in the Pacific Northwest have a wide range of microhabitats induced by canopy structure and substrate characteristics. We used the Wind River Canopy Crane to sample lichens and bryophytes throughout the spectrum of habitats available to epiphytes. Of the 111 species found in 72 sample units, 97 were lichens and 14 were bryophytes. Epiphyte communities showed marked variation with respect to height in the canopy, bark vs. wood, degree of sheltering, and stem diameter. Of these factors, height in the canopy was most strongly related to epiphyte communities. Furthermore, the top two meters of the tallest trees hosted a diverse assemblage of both rare species (Tholurna dissimilis) and weedy, nitrophilous species (Candelaria concolor, Hypogymnia tubulosa, Parmelia sulcata), presumably induced by birds delivering lichen propagules and nutrients. Ten species were more frequent on bare wood than bark, including Ophioparma rubricosa, Letharia vulpina, Placynthiella spp., Ptychographa xylographoides, Trapeliopsis flexuosa, and Xylographa parallela. Species richness was highly variable, even within habitats. The only factor found related to species richness was height in the canopy, the middle and upper layers each having about twice the species per sample unit as lower in the canopy.

Ecological diversity in North American pines

Ecological groups were identified from 34 North American species of pine using multivariate analysis of 18 ecological traits. Five adaptive modes are described: 1) fire‐resistant species that are large, thick‐barked, and have large cones and long needles; 2) tall, fast‐growing mesophytic species with moderately high shade tolerance; 3) stress‐tolerant species with animal‐dispersed seeds, occurring mainly on cold or dry sites where fire is infrequent; 4) fire‐resilient species that are precocious reproducers with small seeds, often in serotinous cones; and 5) species of southern mesic sites with fast growth, strong, heavy wood and short persistence of needles. Intermediates between these modes exist. Convergent evolution has occasionally occurred, as shown by high ecological similarity of species in different taxonomic sections within Pinus. However, the analogies between species are imperfect, suggesting the importance of constraint by shared ancestry and divergence produced by a diversity of environments.

Lichen Communities as Indicators of Forest Health

Abstract

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

. 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.

The successional status of a southern Wisconsin oak woods

We examined the applicability of concepts of succession to 27 yr of tree growth and demographic data from an oak woods. From 1956 to 1983 tree population dynamics in Noe Woods, a black oak—white oak woods in southern Wisconsin, were heavily influenced by oak wilt disease. Between 15 and 20% of the black oaks, many of them large, died in each 5—yr period; much of this mortality was due to wilt. White oak increased in basal area but declined slowly in numbers. Regeneration was dominated by black cherry, boxelder, and American elm; these species are either short—lived and small—statured or threatened by disease, and are, the therefore, unlikely to form a new canopy. None of the species in the woods seems capable of filling the role of a self—replacing climax species in the classical sense. We hypothesize that the absence of a climax species in Noe Woods and other areas of the prairie—forest transition is due to the changed disturbance regime. Decreased fire frequency has created an unprecedented opportunity for shade—tolerant species in dry woods. This opportunity has apparently been met by expansion of shade—tolerant native species from other habitats, invasion of exotic species, and increased abundance of some short—lived and small—statured native species.

Correlations Between Forest Layers in the Swan Valley, Montana

Compositional patterns of forest layers (tree, shrub, herb, bryoid, and epiphyte) are weakly correlated in the Swan Valley. While one can roughly predict the composition of one layer based upon the composition of another layer, different strata do not change composition across environmental gradients at the same rate or in the same pattern. The relative position of two or more stands in species space is different for different layers. Evidence in support of this conclusion was derived from: (1) correlation of dissimilarity matrices, (2) correlation of stand placement on ordination axes, and (3) comparison of stand groups defined by cluster analysis. See full-text article at JSTOR