A remarkable remnant mesic deciduous forest stand: are composition and structure of old-growth retained?

Old-growth forests are declining throughout eastern North America, especially toward the northern limit of the deciduous formation where gently undulating topography and milder climate especially encourage human activity. Remnants exist, but do they retain the defining characteristics of the original vegetation? The objective was tomarshal information required to answer this question, and toward this objective we assessed vegetation in a small 1 ha remnant of maple-beech forest with no history of past logging and compared it to well known and larger old-growth areas in the region. We used Curtis. s (1959) Point Quarter method to provide full quantitative data for trees, saplings, shrub and herbs. Size class distribution of trees and successional status of the stand were assessed. As a general conclusion, we found that tree species richness of our remnant was higher than most recognized large old-growth forests and, while the herbaceous understorey was poorer in species than larger tracts, it exhibited three provincially rare species. Furthermore, the successional status and structural complexity of the remnant were typical of old-growth forests. In overall comparative terms, the remnant was found not be an outlier when ordinated with larger forests. It thus is safe to conclude that this remnant constitutes an ecological benchmark well worth protection, despite its limited size

CHROMOSOME NUMBERS OF SOME NORTH AMERICAN SPECIES OF ASTRAGALUS (LEGUMINOSAE)

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Growth of crustose lichens : a review

Crustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (lichenometry). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development; 2) radial growth rates (RGR, mm yr−1); 3) the growth rate–size curve; and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenized fungal hypothallus. Recent data suggest that 'primary' areolae may develop from free-living algal cells on the substratum while 'secondary' areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the 'asymptotic' type of curve recorded in foliose and placodioid species; the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature 'reproductive' areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments