ak (Quercus) represents one of the most dominant species groups in the eastern deciduous forest of North America (Table 1). In certain eastern regions, oak dominance reflects the importance of this genus in presettlement forests (Abrams and Downs 1990, Spurr 1951, Whitney and Davis 1986). Yet, in other regions, the current distribution of oak greatly exceeds that of the original vegetation (Abrams 1986, Howell and Kucera 1956, Nowacki et al. 1990). Thus, the development of oak species has occurred through a variety of ecological pathways and disturbance conditions. The dominance of oak in presettlement forests is particularly interesting because most oaks are considered early to midsuccessional species. Indeed, most recent studies indicate the potential for widespread oak replacement by more shade-tolerant species in mature forests (Christensen 1977, Lorimer 1984, Nowacki et al. 1990). However, this phenomenon may vary with regional and edaphic factors and be more pronounced on mesic rather than on xeric sites (Abrams 1986, Host et al. 1987, McCune and Cottam 1985, Nowacki and Abrams 1991). These observations have led researchers to ask the following questions about oak ecology in eastern

https://www.jstor.org/stable/pdfplus/1311781.pdf

Fire and the Development of Oak Forests

Conservation genetic of endemic plant species

A novel dendroecological procedure was developed to elucidate canopy disturbances spanning a >300-yr period for oak (Quercus) forests of central Pennsylvania. Running comparisons of sequential 10-yr ring-width averages may effectively neutralize both short-term (i.e., drought) and long-term growth trends associated with climate while enhancing detection of abrupt and sustained radial-growth increases characteristic of canopy disturbance. Thinning-response studies revealed the conservative tendencies of overstory oak, with substantial basal area reductions (>1/3) required to attain moderate and consistently detectable growth increases. Based on empirical evidence, a minimum growth-response threshold of 25% was established to depict canopy disturbances. This is in contrast to the 50–100% sustained radial-growth release often used to detect disturbance using understory trees in closed forests. Our default threshold was adjusted higher as necessary for those trees highly correlated to climatic trends (as repr...

Radial-growth averaging criteria for reconstructing disturbance histories from presettlement-origin oaks

Desiccation-tolerance (DT), the ability to lose virtually all free intracellular water and then recover normal function upon rehydration, is one of the most remarkable features of bryophytes. The physiology of bryophytes differs in major respects from that of vascular plants by virtue of their smaller size; unlike vascular plants, the leafy shoots of bryophytes equilibrate rapidly with the water potential in their surroundings and tend to be either fully hydrated or desiccated and metabolically inactive. The time required to recover from desiccation increases and degree of recovery decreases with length of desiccation; both also depend upon temperature and intensity of desiccation. Tolerance in at least some species shows phenotypic plasticity. Recovery of respiration, photosynthesis and protein synthesis takes place within minutes or an hour or two; recovery of the cell cycle, food transport and the cytoskeleton may take 24 hours or more. Positive carbon balance is essential to survival of repea...

Desiccation-tolerance in bryophytes: a review

An attempt is made to compare bryophyte Ufe histories with recent models of life strategies of animals and phanerogams. Important life history traits in bryophytes include the balance between sexual and asexual reproduction, the reproductive effort spent on both kinds of reproduction, the size and number of the spores, and annual production and standing crop. Age of first reproduction is generally low for asexual reproduction, but low or high for sexual reproduction, depending on the species and the population included. Density-dependent mortality appears to be rare in bryophytes; in some groups of species mortality is for the greater part caused by abiotic environmental stress, whereas in other groups biotic factors such as competi tion and pr?dation are more prominent. Life expectancy varies from some weeks in extreme ephemerals to hundreds of years; in the longer lived species wide variation in life span of different individuals occurs. Tolerance and avoidance of environmental stress are two distinct alternative possibilities in bryophytes as well as in phanerogams. A preliminary system of six different bryophyte life strategies is pre sented. It is stressed that the choice of a fitness measure for a species or population should be made in accordance to its life strategy. Finally, some distinctive traits of bryophyte life histories are outlined.

https://www.jstor.org/stable/pdfplus/20149317.pdf

Life strategies of Bryophytes: a preliminary review

Chestnut blight, caused by the Ascomycete Endothia parasitic, was first discovered in the United States in 1904 in New York City and spread rapidly northeast, west, and southwest. By 1910 it had spread as far south as southeastern Pennsylvania and in 1920 the "80 per cent infection zone" extended along the Blue Ridge mountains to central Virginia. In 1926 local infections had been reported in western North Carolina, northern Georgia, and northwestern South Carolina. In 1930 Gravatt and Gill reported that infection in western North Carolina showed eighty to ninety-nine per cent. Owners of chestnut timber in the newly infected areas of the Carolinas and Georgia quickly cut as much of that lumber as possible. Most of the remaining chestnut (Castanea dentata)lt trees, dead or alive, have been gradually removed, until now, twenty years after the blight reached its peak, there are only a few scattered ghost trees left to indicate the once relatively great importance of the species. The removal of a species which made up more than 40 per cent of the overstory trees in the climax forests of an area would certainly be expected to produce changes in the composition of the vegetation of the region. It is possible that species co-dominant with chestnut would advance in rank and become the most important species in the new climax. It is also possible, as Braun (1950) suggests, that the opening of the canopy, the release of undergrowth trees, and the resulting changes in the humus layer may cause

Present Composition of Some Stands of the Former Oak-Chestnut Forest in the Southern Blue Ridge Mountains

SUMMARY 1. P. ponderosa seedlings, growing in sandy loam, reduced the moisture content of the soil to one percent below the permanent wilting point of the sunflower. When growing in clay loam this did not occur and the seedlings died when the moisture content was still one percent above the permanent wilting point. 2. Artificial dew (spray) at night prolonged the life of P. ponderosa seedlings by 3 months in the sandy loam and by 2 months in the clay loam after the soil moisture content had been reduced on the sandy loam to one percent below and in the clay loam to one percent above the permanent wilting point of the sunflower. 3. In both the presence and absence of artificial dew (spray) at night P. ponderosa seedlings grown in sandy loam reduced the soil moisture to below the ultimate wilting point of the sunflower. However, in the absence of artificial dew a lower moisture level was reached before the seedlings died.

Catherine Keever

Papers

Present Composition of Some Stands of the Former Oak-Chestnut Forest in the Southern Blue Ridge Mountains

Establishment of Grimmia Laevigata on Bare Granite

Heterotheca Latifolia, A New and Aggressive Exotic Dominant in Piedmont Old‐Field Succession