126 Botany 



No. 199. SHREVE, FORREST. A Montane Rain-forest: A Contribution to the Physi- 

 ological Plant Geography of Jamaica. Octavo, 110 pages, 29 plates, 

 18 figs. Published 1914. Price $1.50. 



The Blue Mountains of Jamaica are covered with a virgin rain-forest, in 

 which some of the habitats are among the most moist of the western hemisphere. 

 A description of the ecological and floristic characteristics of the rain-forest 

 above 4,500 feet elevation is given, and the various habitats of the region are 

 described. The climatic factors of environment are tabulated for the Blue Moun- 

 tain region as a whole, and particular attention is given to the measurement of 

 the differences of climatic conditions which underlie the dissimilarity of the condi- 

 tions on the floor of the rain-forest and in its canopy. The periodicity of growth 

 and flowering in the commonest trees and shrubs is described and detailed 

 measurements of the rate of growth are given. The influence of the low and 

 constant temperatures, the high percentages of cloudiness and fog, and of the 

 high and sustained humidities of the rain-forest are such as to retard both 

 photosynthetic and transpirational activity, an effect which is registered in the 

 slow rates of growth and is so pronounced as to make the montane rain-forest 

 a very unfavorable environment for plants as contrasted with tropical lowlands 

 and the moist temperate regions. Studies of the transpiration of plants from un- 

 like habitats within the rain-forest indicate that dissimilarities of transpiration 

 behavior with respect to moisture conditions underlie the localization of species 

 in the several habitats. 



No. 217. SHREVE, FORREST. The Vegetation of a Desert Mountain Range as Con- 

 ditioned by Climatic Factors. Octavo, 112 pages, 37 plates, 18 hgs. 

 Published 1915. Price $2.00. 



The principal aim of this work has been to correlate the climatic gradients of a 

 relatively isolated desert mountain range with the vertical differences of vegetation 

 which it exhibits. The Santa Catalina Mountains are characterized by desert on 

 their lower slopes, by encinal (evergreen oak forest) at their middle elevations, by 

 pine forest above 7,000 feet, and by fir forests on the highest summits. These types 

 of vegetation have been fully described and illustrated. Nearly all the species of 

 plants are distributed so definitely with relation to altitude and habitat as to indi- 

 cate that they are controlled in their movements and establishment by the oper- 

 ation of physical factors. The major differentiation of vegetation on the mountain 

 is controlled by the factors which are in turn due to differences of altitude. The 

 major influences of slope exposure and other topographic features cause local 

 departures from the normal altitudinal gradient of vegetation, but these departures 

 are merely such as to bring a given type of vegetation to an altitude higher or 

 lower than that in which it is commonly found. Rainfall, soil moisture, evaporation, 

 and temperature have been studied at a series of stations reaching from 3,000 to 

 9,000 feet, at 1,000-foot intervals. The influence of slope exposure on the condi- 

 tions of soil moisture and evaporation and the influence of topography in modifying 

 the theoretical conditions of temperature have been particularly emphasized. It 

 has been necessary to study the vertical gradient of temperature with special refer- 

 ence to the operation of cold-air drainage, which is very pronounced throughout 

 the lightly forested or unforested portions of the mountain. Comparisons have 

 been made between the climatic gradients of the Santa Catalinas and gradients 

 derived from the Weather Bureau stations of southern Arizona, situated at dif- 

 ferent elevations in the valleys of the adjacent region. These comparisons are 

 particularly significant with respect to the rainfall conditions, showing that the 

 isolated mountains have a greater rainfall at 4,000 and 5,000 feet than localities 

 in the valleys at the same elevations. The coldest temperatures of winter at 

 8,000 and 9,000 feet are much milder on an isolated mountain, surrounded by 

 desert, than they are at the same elevation on extensive plateaus. 



