Local Shelter Research Articles

An analysis of six simultaneous wind records taken near Vancouver

Abstract Hourly wind speeds and directions taken at six sites near Vancouver, Canada over a period of one year during 1971–1972 have been analyzed. Mean magnitude ratios obtained for different wind directions under high wind conditions vary from about 0.3 to 1.4 and can be explained qualitatively by local shelter effects, local terrain effects or anemometer heights. The mean magnitude ratio is in every case shown to be essentially identical to the ratio of mean wind magnitudes, for high wind conditions; this is justified by simple analysis. The standard deviation of the magnitude ratio lies between 0.24 and 0.69 of the mean ratio. Uncertainty in this mean ratio, which is an important link in wind engineering design, may have to be incorporated into statistical design procedures to avoid taking unknown risks in the estimation of design wind speeds.

Shell form and niche occupation in Nucella lapillus (L.) (Gastropoda)

Collections of Nucella lapillus (L.) from various eastern Atlantic areas have been measured, and shell shape has been analysed by D'Arcy Thompson's method in terms of whorl ratio, apical angle, and spiral angle. In southwestern Ireland N. lapillus varies greatly from tall and narrow in sheltered situations to short and wide at very wave-exposed sites. A local population is described for a bay near Crookhaven, County Cork. In northwestern Spain the open-sea form is developed only weakly. In southwestern Ireland N. lapillus effectively populates mussel beds in the lower littoral on open coasts, whereas in Spain it is sparse or absent from such situations but plentiful high up on the shore on barnacles in places where there is some local shelter from rocks or crevices. It is suggested that failure to develop the open-sea type in Spain is responsible for this difference in niche. Both in Spain and at a site in Scotland N. lapillus feeding on mussels in sheltered situations is of the tall narrow type, so that a diet of mussels cannot alone be responsible for the development of the open sea type, although it still might be a necessary condition. It is to be expected that the genetic composition of populations will vary regionally and will contribute to variation in shell form, but the part which it plays on a purely local scale remains uncertain.

Distribution and changes in shell form of Thais SPP. (Gastropoda) near Bamfield, B.C.

The distribution and shell form of the three species of Thais present have been investigated along the southeast shore of Barkley Sound (Vancouver Island) along a gradient of decreasing exposure to waves, from Pachena Point (open Pacific) to Grappler Inlet (extreme shelter). The 20 stations comprised rocky promontories and adjacent boulder beaches, the latter giving some local shelter. Thais emarginata (Deshayes), which has the lowest shell weight per unit of shell capacity, was found to range (mainly in the upper littoral) from full exposure to waves to considerable shelter. It corresponds most nearly in range of wave-exposure to the North Atlantic Nucella (= Thais) lapillus (L.) and the New Zealand Lepsiella Iredale, but is probably more tolerant of wave-exposure and less of shelter than these. Its shell was found to be lighter per unit of capacity. T. canaliculata (Duclos) was normally confined to low levels on the shore and to wave-exposed situations; it is somewhat better armoured. T. lamellosa (Gmelin) was found to occupy low levels from moderate to extreme shelter. It is very heavily armoured, no doubt in relation to the greater risk of predation inherent in its habitat. In laboratory tests it was found to be much more resistant than T. emarginata to crabs. Measurements of 477 Thais emarginata, divided between 9 stations, showed that the shell form changed from short and broad on the open coast to tall and narrow on sheltered promontories and on boulder beaches. With increasing shelter the whorl ratio ( R) and apical angle decreased and spiral angle (as defined by D'Arcy Thompson) increased. The ratio of increase of the tubular cavity of the shell per turn of the spiral (proportional to R 2) may reflect the growth rate of the animal.

Wind and Exposure as Limiting Factors in the Establishment of Forest Plantations

The influence of air in motion, or wind, upon the distribution of tree species is a climatic factor that has received but passing notice. Major attention seems rather to have been centered upon the factor of transpiration, and upon the mechanical effects of wind on tree form and structure. It has also been recognized that wind, combined with low temperatures, plays an important part in the geographic distribution of a given species. Wind in particular seems to definitely limit the extension of forests on the high arctic tundras. It is only in the valleys sheltered from the winds that tree growth persists in the far northern extension of their ranges. But the influence of the wind in the local distribution of a species, particularly in its establishment, or rather as affecting its ability to establish itself on a given site, has received little attention. It has been noted that forests usually cease on hilly regions when the mountain structures commence to break into isolated peaks. Above this point tree growth is only found where there is local shelter from the wind. Specifically was this called to the attention of the writer in the examination of some plantations established on the campus of Syracuse University. The site of the plantations was a high hill directly south of the University buildings, perhaps one of the highest hills in the vicinity. The top of this hill marks the break of the northern escarpment of the Great Northern Appalachian Plateau. Its elevation is some 400 feet above Onondaga Lake, to the level of which it drops in less than a mile. From the base of the hill the land stretches north and west with no other features than the gentle undulations of the Great Lake Plains of which it is a part, to the shore of Lake Ontario forty miles away. The general slope of the hill is toward the northwest and west, with a degree of slope on the site of the plantations of about 6o degrees. This combination of factors has presented a site particularly exposed to winds from this quarter, winds that have an uninterrupted sweep clear from the northern shores of the Great Lakes. The intensity of the exposure and susceptibility of the trees to damage is further aggravated by heavy clay glacial soil rather impervious to water and susceptible to loss or the intragranular frozen moisture by drying. The plantation was established in the spring of I920. Red pine and white were set out 6 ft. x 6 ft. in alternate rows. Failures were filled in the