Biomedical subjects

M J Lechowicz

Publications and source records attributed to M J Lechowicz.

6 recordsLinked to original sources

PubMed2000

Environmental distribution of four Carex species (Cyperaceae) in an old-growth forest.

We conducted an in-depth characterization of the range of micro-environments (1 m) in which four Carex species (C. backii, C. communis, C. plantaginea, and C. platyphylla) grow in the understory of an old-growth, deciduous forest in southern Québec, Canada. All four species occurred in significantly different micro-environments. Carex plantaginea was found at the wet end of a moisture gradient, in soils with high nitrate availability. Carex backii and C. platyphylla were found at the dry end of the moisture gradient, with C. backii occupying soils with higher phosphorus availability than C. platyphylla. Carex communis, the only ant-dispersed species studied, was found in the broadest range of environmental conditions. Our results suggest that environmental heterogeneity and interspecific microhabitat preferences are important for the maintenance of local species diversity in the forest understory, not only for common species as demonstrated in previous studies, but for infrequent species, and those within a functional group (upland Carex species). However, there was some evidence that the distributions of C. backii and C. communis were not in equilibrium with current environmental conditions, indicating that historical factors, such as dispersal and colonization events, may also have important effects on the distributions of these species and the maintenance of species diversity in old-growth forest.

Journal Article↗

PubMed2000

Germination and establishment of forest sedges (Carex, Cyperaceae): tests for home-site advantage and effects of leaf litter.

We investigated aspects of germination and seedling establishment that might influence the distribution and diversity of Carex species growing in the forest understory. We tested the ability of Carex communis and C. platyphylla to germinate and establish at plots where adult individuals of one of these two species, or one of two other Carex species (C. backii and C. plantaginea), occurred in an old-growth forest in southern Québec, Canada. We also tested for effects of leaf litter on germination and establishment of these sedges. From a series of experiments in the field and in a lath house, we found no evidence of home-site advantage with respect to germination or seedling establishment. Leaf litter had a negative effect on germination and establishment. The results emphasize the importance of dispersal and colonization events in determining local diversity and distribution of Carex species in upland forests. High frequency of occurrence of C. communis at our study site may result from relatively wide dispersal provided by ants, and a suite of traits associated with ant dispersal in some understory Carex species.

Journal Article↗

PubMed1998

Rugby injuries.

Explore the source record for details and available documents.

Adult↗

PubMed1987

Losses of Polyol through Leaching in Subarctic Lichens.

Upon rewetting, lichens lose polyols through leaching. We quantified leaching losses for 21 species under simulated rainfall. Polyol concentrations in these lichens range from 1.0 to 8.8%, with a mean of 2.8%. Leaching losses range up to about 7.5 mg (polyol)/g (lichen dry weight) in a typical rain event. The rate of polyol leaching declines exponentially, becoming negligible within 1 hour of continuous rain. The response of polyol leaching rate to rainfall intensity and amount varies between species-six species showed no response, one had increased leaching with increased rainfall intensity, four had increased leaching with increased amount of rainfall, and one had decreased leaching with increased total amount of rainfall. Polyol leaching rates are positively correlated with polyol concentration for 20 species. Literature values of average daily growth rates for subarctic lichens are of the same order of magnitude as leaching rates, suggesting that polyol leaching is an important part of the carbon budget of lichens.

Journal Article↗

PubMed1983

Age Dependence of Photosynthesis in the Caribou Lichen Cladina stellaris.

The fruticose thallus of the lichen Cladina stellaris (Opiz.) Brodo can be subdivided into individual whorls of branches of known age. Photosynthesis declines steadily with age from a maximum rate of 0.76 milligram CO(2) per gram dry weight per hour in 1-year-old whorls to 0.02 milligram CO(2) per gram dry weight per hour after 15 years. Conversely, the dry biomass of the whorls increases up to age 9 years and then approximately levels off. Photosynthesis in whorls older than 15 years is less than 0.01 milligram per gram per hour. Progressive changes in thallus color with age are associated with the observed photosynthetic decline. Whorls aged 6 years and younger together account for 18% of thallus biomass but 50% of photosynthetic activity. The implications of these results for the idea that the lichen symbiosis results in truly integrated organisms with senescence phenomena akin to those in higher plants is discussed.

Journal Article↗

PubMedDate not supplied

Ice storm damage and early recovery in an old-growth forest.

We quantified the damage caused by a major ice storm to individual trees in two 1-ha permanent plots located at Mont St. Hilaire in southwestern Québec, Canada. The storm, which occurred in January 1998, is the worst on record in eastern North America; glaze ice on the order of 80-100 mm accumulated at our study site. All but 3% of the trees (DBH > or = 10 cm) lost at least some crown branches, and 35% lost more than half their crown. Damage to trees increased in the order: Tsuga canadensis, Betula alleghaniensis, Ostrya virginiana, Acer saccharum, Fagus grandifolia, Quercus rubra, Betula papyrifera, Acer rubrum, Tilia americana, and Fraxinus americana. Only 22% of the saplings and small trees (4 cm < DBH < 10 cm) escaped being broken or pinned to the ground by falling material. Levels of damage generally were greater in an exposed ridge top forest than in a cove protected from wind. By August 1999 only 53% of the trees had new shoots developing from the trunk or broken branches; among the more dominant canopy trees, Fagus grandifolia had the least sprouting and Acer saccharum and Quercus rubra the most. We anticipate and will monitor both significant turnover in the tree community and some shift in composition of the canopy dominants.

Disasters↗