Showing papers on "Tree canopy published in 1971"

Wind profiles in and above a forest canopy

Abstract: Using an on-line computer, measurements were made of wind speeds in and above a pine forest together with accurate potential temperature profiles over a wide range of stability conditions. It was found that between values of Richardson number of approximately –0.05 and +0.10 the wind profile above the canopy followed a pure log form with the measured roughness length increasing linearly from 0.75 to 1.23 m respectively. Outside this stability range a log-linear profile could be fitted. The shape of the wind profile within the canopy was determined, and an increase of wind speed within the trunk space was noted. A preliminary experiment to determine the effect of the anemometer tower structure upon wind speed readings is also described.

Savanna in central Wisconsin, U.S.A.

Abstract: A black oak savanna in central Wisconsin was analyzed in detail, including canopy trees, understory and tree seedlings. Although many authors have held that savanna in this region is a subclimax maintained by fire, this stand, unburned for many years, shows a high degree of stability and very little trend toward the postulated increase in trees. Of the 25 most frequent understory species, 80% have higher affinity for prairie or other very open habitats than for forest. Although oak seedlings had 72% frequency in 1 m2 quadrats, their growth is exceedingly slow, while dieback and mortality are very high; few survive to 1 m in height and saplings are nearly absent. The tree canopy at 40% is low in relation to B. A., probably due to frequent wind and lightning damage. The inhibition of oak seedlings which prevents succession toward forest appears to be caused by a combination of frost, drouth, sandy soil of low water retaining capacity, interspecific competition and allelopathy; seedlings in an adjacent old field grow approximately 3 times faster, with little injury or mortality. Light grazing in early years of settlement may have allowed a temporary increase in tree establishment, since over 2/3 of the present canopy trees appear to be in one age group of 105–110 years. On the basis of this evidence we propose that at least some savanna sites in this region are naturally stable communities maintained by a complex interaction of the local climate, edaphic factors, and the existing community; fire is not an essential factor.

The Rate of Forest Tree Growth and a Forest Ordination at Xumeni, Natal

Abstract: The rate of increment in circumference at breast height of canopy tree species in the southern temperate, Mist-belt forest at Xumeni, Natal, South Africa, is very slow. The mean for all trees calculated from measurements in 1929 and 1966 is 0.201 ± 0.015 inches per year. Results from an ordination analysis of 39 plots were interpreted in terms of a successional gradient from serai sites on steep ground, characterized by Kiggelaria africana, Xymalos monospora and Fagara davyi , to climax sites on flatter ground with Podocarpus spp. Two climax types are indicated, with P. henkelli on moist soil and P. falcatus on drier soils.

An Investigation of Flow over High Roughness. Task I: Study of Airflow in Simulated Temperature and Tropical Forest Canopies, Fort Huachuca.

Abstract: : An experimental investigation of the atmospheric boundary-layer flow on high roughness was conducted by simulating the flow over a forest canopy in a meteorological wind tunnel. The model forest canopy used consisted of plastic simulated-evergreen trees. The measurements were carried out at constant free-stream velocity and under thermally neutral conditions. Two canopy densities were tested to explore the effects of the roughness density on the flow. (Author)