JeriLynn E. Peck

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.

Four Years of Epiphyte Colonization in Douglas-fir Forest Canopies

Abstract In 1995, we installed surface-sterilized, rough-barked and smooth-barked tree branches in clearcuts, young forests, and old growth. Half of the experimental branches were inoculated with propagules of the epiphytic cyanolichen, Lobaria oregana. In 1997, we concluded that L. oregana was associated with old-growth Douglas-fir forests because of dispersal limitation; addition of L. oregana propagules resulted in a marked increase in establishment rates. In 1999, we revisited the experiment to determine whether other epiphytes had colonized the tree branches. We also checked to see if the 1997 results of the experiment persisted. A total of 26 epiphyte genera (nine bryophytes and 17 lichens) had colonized the branches. Lichen colonization was generally fastest in clearcuts. Colonization by alectorioid lichens was rapid in both clearcuts and old growth but slow in young forests. In contrast, bryophyte colonization was relatively rapid in all age classes. Epiphyte colonization was generally more rapid on smooth bark than on rough bark, although Cladonia was more frequent on rough-barked branches. Bryophytes, cyanolichens, and Sphaerophorus globosus were more frequent on inoculated branches than on control branches, implying that the L. oregana propagule mixture used in 1995 was contaminated with other epiphytes. Like L. oregana, these species may also be dispersal-limited. The number of established L. oregana thalli in clearcuts and young stands decreased from 1997 to 1999, but the number of thalli remained relatively stable in old growth. After four years, established L. oregana thalli were larger in clearcuts than in either young stands or old growth. Overall, the fourth-year results of our experiment confirm the importance of dispersal limitation as the cause of old-growth association in L. oregana in western Oregon.

Diversity of Epiphytic Bryophytes on Three Host Tree Species, Thermal Meadow, Hotsprings Island, Queen Charlotte Islands, Canada

Three tree species (Picea sitchensis, Thuja plicata, and Tsuga heterophylla) near hot springs were examined for epiphytic bryophyte abundance and diversity on Queen Charlotte Islands. Cover was recorded at four heights up to 5 m, and on branches on the north and south sides of each tree. Eleven species of mosses and 25 species of hepatics were found. Cover was greater for mosses than hepatics but mosses had lower beta diversity. Bryophyte species composition differed by tree species, with species richness increasing in the order Tsuga, Picea, and Thuja. The similarity of mosses, and the dissimilarity of hepatics, on the north and south sides of trees, suggest relatively subtle diferences in moisture conditions. Ordinations indicate that epiphytic bryophytes followed a tree-position gradient that is closely related to a vertical gradient. Several species typical of log and forest floor habitats were found as branch epiphytes. Our findings support the previous observation that the vertical gradient in species composition parallels macroclimatic and successional gradients.

Harvestable Epiphytic Bryophytes and their Accumulation in Central Western Oregon

Abstract Methods for characterizing the composition, biomass, and accumulation rates of harvestable epiphytic bryophytes in the understory of temperate forests have recently been developed, but have yet to be implemented in a much wider geographical area and adapted to provide estimates at the individual mat level. In response to regulatory need, we modified and implemented these methods in 27 50+ yr-old upland and riparian forest stands below 915 m to: a) characterize the composition of harvestable epiphytic bryophytes in central western Oregon, b) evaluate the compositional changes immediately following harvest, and c) retrospectively estimate minimum simple accumulation rates for harvestable bryophyte mats. Twenty-two bryophyte species, two lichens, and one vascular plant were found in a total of 433 sampled mats, dominated by Isothecium myosuroides, Neckera douglasii, Antitrichia curtipendula, Frullania tamarisci subsp. nisquallensis, and Porella navicularis. Harvest brought on significant shifts in the relative abundance of species primarily through the disproportionate removal of these species, which are commonly found in harvestable bryophyte mats throughout western Oregon. The minimum simple accumulation rate for bryophyte mats from 13 of these stands, calculated as the oven-dried mat mass per unit surface area divided by the stem age, was 22.4 (std 15.5) g/m2/yr and is approximately comparable to that previously observed in the Coast and Cascade Ranges of northwestern Oregon. This accumulation rate translates into a commercial harvest rotation period of at least 21 (std. 12) yr. This long rotation time, coupled with the scarcity of sites supporting harvestable mats, leads to our recommendation that commercial bryophyte harvest be prohibited in the study region.

Maintaining a pine legacy in Itasca State Park.

ABSTRACT: Itasca State Park, located in the northern central portion of Minnesota, is challenged with maintaining a pine forest covertype, yet regeneration failures may allow much of the park to succeed to northern hardwoods. Efforts to improve pine regeneration and growth have included deer exclosures and prescribed burning to reduce competing vegetation. We revisited Itascas Mary Lake deer exclosure 66 years after establishment to compare stand development, structure, and white pine (Pinus strobus L.) regeneration and growth with that of adjacent plots that have been: (1) untreated and (2) recently repeatedly under-burned. Overstory structure and composition was similar among all three treatments, and mid- and understory structures were similar in the treatments subject to deer browse. Sapling and midstory white pine were only present in the exclosure. White pine regeneration was present in all treatments and most abundant in the burned treatment, but was restricted to the smallest height class and consistently overtopped by the shrub layer. Regeneration, sapling, and midstory layer tree densities were highest within the deer exclosure, as was white pine height growth. The untreated plot lacked young pine and will likely succeed to northern hardwoods with a shrub understory. The three-fire sequence of the burned treatment increased the abundance of white pine regeneration at this site, but may require additional measures to control competing vegetation to allow that regeneration to ascend into the sapling layer.

Microhabitat affinities of Missouri Ozarks lichens

Abstract The lichen communities of nine mixed-hardwood sites in the southeastern Missouri Ozarks were characterized from sampling of the ground layer, tree-bases, midboles, and canopy branches. Of the 181 lichen taxa documented, the majority were crustose (55%) or foliose (32%) lichens. Only a quarter (26%) of all species occurred across all four microhabitats, with the majority of dominant taxa demonstrating apparent preferences for a single (38%) or multiple (27%) microhabitat, a given host tree species (17%), or a particular ground substrate (12%). High diversity of ground substrates and a large amount of presumed litterfall in the ground layer were of particular note. Relative species composition and abundance of lichen communities differed in stands with overstories dominated by red oak species as opposed to white oak species, but showed only suggestive variation with aspect class, geology, bedrock, landform, and soil type. Lichen diversity measures were also weakly associated with the presence of individual white or red oak species in the overstory, but no clear patterns appeared with respect to white or red oak subgroups. Stratification by microhabitat and host species would be necessary in future experimental studies in this region.

Tree size distribution and abundance explain structural complexity differentially within stands of even-aged and uneven-aged structure types

Abstract Characterizations of physical structural complexity are an important surrogate for the potential of forested stands to provide desired ecosystem services such as biodiversity. Distinguishing between stands with different structural conditions is not only a necessary feature of useful structural metrics and indices, but how such measures vary among stands can reveal clues to the ecological processes driving structure. We used stand inventory metrics and indices of structural complexity to differentiate between even-aged and uneven-aged structure types using 10 stem-mapped coniferous stands of each type distributed across Switzerland. Within each structure type, we further explored relationships among stand inventory metrics and structural indices over a roughly 10-year period of management intervention. The even-aged and uneven-aged structure types were clearly differentiated using both stand inventory metrics and spatially explicit structural complexity indices. Overall, structural complexity within even-aged stands was strongly related to, and best predicted by, metrics including the distribution of basal area among canopy layers, while complexity in the uneven-aged stands was most strongly related to, and best predicted by, metrics including measures of abundance. Although predictive models could be developed for canopy position mixture, diameter differentiation, and small-scale structural complexity (but not spatial aggregation) using only stand inventory metrics, the prediction success after only a single management intervention was lower than expected. These results indicate that research to explore small-scale structural complexity requires detailed spatially explicit inventory data and that management to enhance structural complexity may require the manipulation of different attributes in stands of even-aged (diameter distribution) and uneven-aged (total abundance) structure types.

Lichen-based indices to quantify responses to climate and air pollution across northeastern U.S.A

Abstract Lichens are known to be indicators for air quality; they also respond to climate. We developed indices for lichen response to climate and air quality in forests across the northeastern United States of America (U.S.A.), using 218–250 plot surveys with 145–161 macrolichen taxa from the Forest Inventory and Analysis (FIA) Program of the U.S. Department of Agriculture, Forest Service. Lichen indicator species for response to climate and air quality were selected using Indicator Species Analysis, correlations with environmental variables, and published literature. Ordinations were used to evaluate the strength and relationships of the final indices. The Pollution Index was calculated for a plot from abundances of 12 tolerant and 45 sensitive indicator species standardized by abundance of all lichen species. The Index was correlated with modeled deposition of acidifying sulfur and oxidized nitrogen and with lichen community ordination pollution axes. Analyses suggested separate response of lichens to fertilizing N (weak statistical support). The Climate Index, from abundances of 19 warmer and 47 cooler climate indicator species, was correlated with modeled minimum January and annual maximum temperatures, and with ordination climate axes. The two indices are statistically independent. Repeat sample variability for each index was 7–14.5% (lower with higher quality data), supporting detection of consistent trends of 16–20% change over time or variation across space. Variability of the Climate Index was more affected by data quality than that of the Pollution Index. The continuous gradient of Pollution Index values suggests the cleanest areas may have air pollution above a critical load to fully protect lichen communities. These Indices can be applied to track lichen responses using other data from our study regions; suitability should be tested before use outside of the study area.

Reconstructing the competitive dynamics of mixed-oak neighborhoods

The disparity between the potential for latent oak dominance within a stand and their region-wide decline in importance value raises questions about the competitiveness of oaks in early stand dynamics. We reconstructed tree height growth dynamics in mixed-species neighborhoods to determine if currently dominant oaks were ever shorter than their competitors and at what age currently subordinate oaks fell behind. In 23-36 year old mixed-oak stands in two physiographic provinces of Pennsylvania, we identified dominant and subordinate northern red oaks (Quercus rubra L.) and chestnut oaks (Quercus prinus L.) competing with adjacent non-oaks (red maple (Acer rubrum L.), sweet birch (Betula lenta L.), and black cherry (Prunus serotina Ehrh.)) of equal crown class. In each stand, we randomly selected 20 tree neighborhoods and collected stem cross sections every metre from the base to the tip of each tree. In the Allegheny Plateau province, dominant northern red oaks never averaged more than 2 m shorter than their competitors, while by age 20, subordinate oaks were commonly more than 2 m behind. Dominant chestnut oaks in the Ridge and Valley province were never more than 1 m shorter than their competitors; subordinate oaks, however, were generally always at least a metre behind. In both regions, growth dynamics of currently subordinate trees were indistinguishable from those of currently dominant trees during their first decade. Because oaks that were considerably behind at age 15 were likely to be subordinate by age 30, the window of opportunity for release to prevent oaks from becoming permanently overtopped and unable to recover may thus be relatively early (age 10-20).

Extensive Green Roofs and Mosses: Reflections from a Pilot Study in Terra Alta, West Virginia

Abstract. Bryophytes are increasingly used in “green roofs” (especially in Europe), usually mixed with Sedum in prevegetated mats rolled onto roofs. In this paper, we briefly review the roof moss literature and also report our preliminary findings on voluntarily established roof moss communities near Terra Alta, West Virginia. We found 11 bryophyte species (including one liverwort) on four partly shaded roofs (differing in material, aspect, and pitch) that had apparently been relatively undisturbed for over 40 years. Species richness and composition varied considerably among roofs. The most frequent and abundant taxa were Hedwigia ciliata, Plagiomnium cuspidatum, Brachythecium laetum, and Platygyrium repens, each of which dominated a different roof. We suggest that Hedwigia merits further investigation as a candidate for extensive green roofs, based on drought-tolerance and a growth-form similar to that of Racomitrium -- which is used for green roofs in Japan. We hope that our review and preliminary data will encourage others to study roof mosses, which could potentially play an important role in the worldwide greening of cities.