388 



THE STUDY OF PLANT COMMUNITIES 



Tree-ring studies, 308-310 

 Trenched plots and shade tolerance, 



134, 135 

 Tropical formations, 298-299 



factors, 298 



growth forms, 298 



listed, 299 



rain forest, 298 

 Tsuga canadensis, 248, 249, 250 



heterophylla, 277, 279 



mertensiana, 70, 261, 272, 276, 279 

 Tundra formation, 236-240 



alpine tundra, 236, 239 



arctic tundra, 238 



U 



Ulmus, 255, 269 

 a?nericana, 249 

 Umbellularia calif ornica, 281 

 Uniola paniculata, 51, 52 



V 



Vaccinium spp., 242, 278 

 Vapor pressure deficit, 78-80 



application, 79 



nomogram, 83 



relation to relative humidity, 80 



significance, 79 

 Vegetational analysis 



basis for other work, 34 



methods, 33-54 



objectives, 55-74 



quantitative data a necessity, 34 



sampling, 35 

 Vegetational changes, historical, 301- 

 314 



climatic parallels, 301-302 



modern evidences, 301 



relations to glaciation, 301 

 Vegetation girdles 



aquatic, 216 



rock succession, 219-220 

 Vegetation type 



and climate, 29 



local variations, 29, 30 



variation of species, 30 

 Vegetation types, North America, 



235 

 Vegetation zones, disrupted 



by angle of slope, 124, 133 



by exposure, 124, 125 

 Vegetation zones, Rockies, 260 



extent, 260 



factors involved, 259 



foothills (woodland), 267-269 



montane, 263-267 



subalpine, 261-263 



tundra, 239-240 

 Viburnum alnifolium, 241 



cassinoides, 241 

 Virgin forest, need for study, 321 

 Vitality, 64 



classes, 65 



indicator significance, 65 



W 



Warm front (air masses), 87 

 Water 



capillary, 162 

 gravitational, 161 

 hygroscopic, 162 

 of the atmosphere, 77-97 

 of the soil, 161-174 

 solvent in soil formation, 145 

 Water absorption and movement 



modified by temperature, 128 

 Water balance and temperature, 128 

 Water holding capacity, 168 

 ■ Water conservation, 341 -342-343-344 

 pollution, 344 

 trends, 344 

 Water supply, and snow, 68 

 Water table 



and evaporation from soil, 165-166 

 hydrarch succession, 219 

 Weathering 

 biological, 144 

 chemical, 144 

 hydration, 145 

 oxidation, 145 

 physical, 144 

 soil acids, 145 

 Wildlife conservation, 345-347 

 ecological problems, 345-346 

 management, 345 

 refuges, 346 

 Wilting coefficient, 169 

 Wilting percentage, 169-170 

 Wind, 97-115 

 and atmospheric pressure, 97-98 

 anemometers, 99 

 daily and seasonal variation, 98 

 effects on plants, 99-105 

 general pattern, 97-98 

 Krummholz, 101, 102 

 measurement, 99 

 physiological-anatomical effects, 



99-100 

 salt spray, 102-103 

 Wind and soil, 109-115 



