whereas removal of herbage after seed matu- 
rity does not interfere with plant growth—the 
basis for recommending grazing deferment sys- 
tems. Sampson (1914, 1917) also studied the 
life history and growth requirements of sev- 
eral important range plants, both under graz- 
ing and under protection. 
In the Great Plains regions, Briggs and 
Shantz (1913, 1914) determined the water re- 
quirements of some native grasses and forbs. 
Weaver (1914, 1919) reported on important 
ecological studies concerning grasslands, par- 
ticularly with regard to root relations. 
The text on plant ecology by Weaver and 
Clements (1929) stressed developmental taxon- 
omy of plant communities and provided elabor- 
ate descriptions of plant formations in North 
America. In animal ecology, texts by Pearse 
(1926) from the United States and Elton 
(1927) from the United Kingdom, probably 
had the greatest impact upon ecological think- 
ing. Primary interest of both plant and animal 
ecologists was the distribution of the animal 
community, its structure and organization, and 
its temporal development and change. 
RANGE ECOLOGY: 1929-45 
Range ecology was given impetus by the 
McSweeney-McNary Forest Research Act of 
1928, which extended and intensified the USDA 
Forest Service research program. Also, during 
the Great Depression, establishment of such 
agencies as the Civilian Conservation Corps, 
Works Projects Administration, and National 
Recovery Administration brought conservation 
research and action to national attention. Also, 
a number of additional experimental ranges 
were established. Agricultural Experiment Sta- 
tions at State Colleges expanded their studies 
in range ecology: Linney et al. (1930) in New 
Mexico, Hanson et al. (1931) in Colorado, and 
Brinegar and Keim (1942) in Nebraska (Chap- 
line et al. 1944). 
Illustrative of fundamental range ecology 
studies during this period are those in: Envi- 
ronmental relations—Nelson (1934), Lister 
and Schumacher (19387), Humphrey (1937), 
Craddock and Forsling (1938), and McGinnies 
and Arnold (1939) ; succession, indicators, and 
conditions—Campbell (1931), Talbot (1937), 
Sampson (1939), McGinnies et al. (1941), 
Pickford and Reid (1942), and Ellison (1949) ; 
woody plant invasion—Parker (1939), and 
Young et al. (1948); and range and wildlife re- 
lations—Vorhies and Taylor (1933, 1940), Ni- 
chols (1988), and Arnold (1942). 
In general, ecological research during this 
period was exceedingly active, both in quantity 
and quality of studies. Ecological theory began 
to mature as a result of development and coor- 
200 
dination of biological principles. Moreover, 
theory was based upon sound empirical evi- 
dence rather than upon speculation (Allee et 
al. 1949). 
In range ecology, workers were now aware 
that: (1) Ecology was a state of mind, i.e., an 
ability to relate biological facts correctly; (2) 
life processes operated on a revolving basis and 
that ecological systems were interdependent; 
(3) life processes were subject to natural laws, 
and man could manipulate some but not all of 
the forces involved; and (4) ecological think- 
ing could not be applied exclusively to either 
plants or animals; instead, the entire biotic 
complex had to be considered as the basic oper- 
ating unit. 
POST WORLD WAR II CONTRIBUTIONS 
After World War II, grazing studies based 
upon range ecology were reported for a diver- 
sity of range plant communities from experi- 
mental ranges previously established. High- 
lights of these studies are summarized in table 
1. Other research centered on life history stud- 
ies of major range plants, invasion processes of 
rangelands by woody shrubs and trees, range 
condition classification, and timber-livestock- 
wildlife relations. Many of the latter studies 
were closely related to applied research involv- 
ing various aspects of management on the 
western ranges. 
Life history studies —A number of life his- 
tory studies of range vegetation were reported 
during the postwar period: Reproduction of 
southwestern grasses (Canfield 1957); growth 
habits, habitat requirements, phenology, root 
systems, soil relations, and diseases of cheat- 
grass (Klemmedson and Smith 1964) ; seasonal 
development and annual yield of individual 
forage species in relation to climatic factors 
for the sagebrush-perennial grass association 
of southern Idaho (Blaisdell 1958); root sys- 
tems, growth and development, reproduction, 
genetics physiology, and enemies of bitter- 
brush (Hall 1964; Nord 1965) ; growth habits, 
geographic distribution, poisonous properties, 
invasion and its causes, and relation to grazing 
and competition with forage plants of burro- 
weed (Tschirley and Martin 1961) ; ecological 
studies of pinyon and juniper (Arnold et al. 
1964); and intensive studies of the root sys- 
tems of range plants (Weaver 1958). 
Woody plant ecology.—On the invasion of 
grazing lands by woody plants, Humphrey 
(1958) reported that mesquite, creosote bush, 
cactus, burroweed, and snakeweed were among 
the principal invaders in the Southwest. He 
concluded that since the introduction of live- 
stock, reduced plant competition, fire suppres- 
sion, and rodents have favored woody plants at 
the expense of perennial grasses. Glendening 
Me 
