Katherine A. Frego

Propagule sources of forest floor bryophytes: Spatiotemporal compositional patterns

Abstract The roles of bryophyte propagule sources in community composition and structure are poorly understood, but regeneration processes may be critical to the conservation of severely disturbed communities such as those in Acadian forests managed for timber production. Our research objectives were to 1) describe the compositions of the aerial diaspore rain and the buried propagule bank at two locations, 2) compare compositional turnover (β-diversity) among assemblages (i.e., changes in composition across sample units), and 3) investigate potential temporal variability across a growing season within the aerial diaspore rain. A case study approach was used to 4) determine the potential recovery of two extant communities based on available propagules. Compositions of propagule sources were determined by emergence and compared to that of the extant community sampled intensively, i.e., within two grids (1 m2 and 1.69 m2) of contiguous 100 cm2 cells established on the forest floor of mature mixed forests in southeastern New Brunswick, Canada. Overall, 51 taxa (0–12 taxa per 100 cm2) were found in the aerial diaspore rain and buried propagule banks, 36 taxa (0–9 taxa per 100 cm2) in the extant community. High degree of turnover among sample units and seasonal variability within the aerial diaspore rain indicate that a very intensive sampling protocol is necessary for accurate description of bryophyte propagule sources. We also argue that the emergence method is essential, given the taxonomic richness of these propagule sources. Of the two sources of propagules, the aerial diaspore rain across the growing season was more similar to the composition of the extant community than was the buried propagule bank.

Microsite Tolerance of Four Bryophytes in a Mature Black Spruce Stand: Reciprocal Transplants

In the feather moss community under mature upland Picea mariana in northern Ontario, four bryophyte species coexist over periods of decades. The bryophytes comprise a thick, dense carpet with more or less discrete patches of Ptilium crista-castrensis, Dicranum polysetum, and Ptilidium ciliare in a matrix of Pleurozium schreberi. A previous study showed that the four species occupy microsites which overlap in temperature, light, moisture, and litter input. We used three experiments to determine whether spatial pattern was attributable to microhabitat in existing microsites. 1) Individual shoots and 10 cm diameter colonies of the four species within one stand were transplanted reciprocally and grown for one and three years, respectively. Shoot growth was evaluated as elongation; colony growth was assessed as a ratio of final:starting biomass. 2) Colonies of Ptilidium from one stand were transplanted to three microsites in a stand from which the species was absent, and growth assessed as above. 3) A thick layer of spruce needle litter was applied to one of each pair of preweighed colonies, and growth assessed as above. All four species were cabable of surviving in all microsites currently occupied by others in their community, at least over three growing seasons. A single episode ofheavy needle deposition enhanced growth ofallfour species. This suggests that spatial pattern is not due to habitat partitioning, but does not rule out slow competitive exclusion by vigorous/invasive growers.

Calypogeia suecica (Arnell & J. Perss.) Müll. Frib., a New Liverwort Record for New Brunswick, Canada

Abstract. Calypogeia suecica is reported for the first time for New Brunswick, Canada. It occupies microhabitats consistent with previous records in adjacent jurisdictions (Nova Scotia, Ontario, Quebec, and Maine): rotting wood in conifer-dominated forests.

Synthetic Logs for Controlled Culture of Epixylic Bryophytes: Log Physical Properties, Surface Moisture, and Dicranum flagellare Growth

Abstract. Experimental studies of epixylic bryophytes require stable, biologically inactive substrata with physical properties that mimic those of coarse decayed wood. In two preliminary tests, we compared three synthetic logs (made from upholstery wadding, mattress foam, and floral foam) to decayed natural logs, in terms of their physical properties, moisture transmission, and ability to support growth of Dicranum flagellare in the laboratory. We also tested the effects of clumped vs. smeared propagule application on growth response. Vegetative moss propagules (flagellae and dried gametophore fragments) were applied as clumps or smears with nutrient agar gel, and evaluated as to horizontal expansion, vertical growth and dry weight of new growth over 6 months. Synthetic logs had higher porosity and lower density than natural logs, but showed similar moisture transmission capabilities to each other and to natural logs when moisture was supplied from the base. Nevertheless, surficial water potentials were consistently less than -5 MPa, and were therefore incapable of supporting bryophyte growth without applying liquid water from above. Horizontal expansion of D. flagellare was greatest with a smear application on floral foam logs, but vertical growth was greatest on upholstery wadding logs with a clumped application. Although floral foam (substratum) and smear (application) produced the greatest new shoot growth, observations suggest that the moss may allocate more growth to rhizoids on more penetrable substrata (those with a larger mean pore size). Future studies must modify the structure of synthetic substrate units to more closely mimic the moisture-related characteristics of rotting wood of target species, and further isolate the components of bryophyte growth.

Log moisture capacity does not predict epixylic bryophyte growth under thinned and unthinned forest canopies

Summary 1.Coarse woody debris (CWD) serves as habitat for diverse and rare taxa in forest systems. Because the abundance of mosses appears to be correlated with log size and stage of decay, many have suggested that CWD serves as a moisture reservoir, ensuring a humid microclimate and facilitating moss growth, but no one has tested this connection. Intact forest canopies are also thought to maintain humid conditions that benefit moss growth. If microclimatic regulation is the primary mechanism contributing to high moss abundance on CWD, then epixylic moss growth should increase with the capacity of the log moisture reservoir, and the importance of the reservoir size should increase with canopy opening. 2.Three types of synthetic logs, identical in size and shape but differing in moisture capacity, and two natural substrates, well-decayed birch and cedar logs, were used to test the effects of log moisture capacity on growth of Dicranum flagellare under thinned and intact canopies of a spruce plantation over 20 months. 3.Surface humidity was positively associated with moisture capacity, but did not reach the water compensation point outside of precipitation events. Under a closed forest canopy, moss growth was negligible across all log types. Under an open forest canopy, moss growth was greater on natural substrates than synthetic ones, and negatively related to moisture capacity. CWD facilitates a sufficiently humid surface for only a short time after precipitation, presumably when a film of liquid water is maintained near the surface. 4.For Dicranum flagellare, canopy condition is a more accurate predictor of growth than CWD-moisture capacity; any beneficial properties of CWD appear to be lessened by a dense forest canopy (as in silvicultural plantations), probably because it reduces access to liquid water from precipitation. 5.We propose that the surface moisture availability of CWD depends on optimal depth of a “resisting layer” below the log surface, representing a tradeoff between water retention and loss (via percolation or runoff at extremely deep vs. shallow resisting layer depth). CWD may possess microclimate-regulating traits that benefit moss growth, but it does not appear to act as a moisture capacitor. This article is protected by copyright. All rights reserved.