GRAZING RANGES IN SOUTHERN ARIZONA. 15 
THE OAK BELT. 
About one section of the land in the MacBeath inclosure hes in 
the zone of the oaks (No. 5 in fig. 3). The forage in this area is 
composed mainly of the grasses of the needle-grass association (No. 
4 in fig. 3), with a diminution of the amount of perennial species 
of Aristida and an increase of Bouteloua chondrosioides, B. hirsuta, 
EKlonurus, Trachypogon, and others. The oak trees are distinctive 
of the zone, and the young ones afford considerable feed as browse, 
as do a number of the other shrubs and some perennial herbs (PI. 
IV, fig. 2). The precipitation of this belt is greater than that of 
any of the others, and there is no doubt that, including the browse 
and spring growth, the area produces more feed than the lower 
levels, though complete figures are not available to demonstrate how 
much more. This fact must be kept in mind in the comparison of 
the records of animal-days’ feed produced on the MacBeath inclosure. 
THE PLOWED AREAS. 
In the summer of 1912 it was decided to plow areas of an acre 
in extent in different parts of the reserve and determine as far as 
possible the sequence and rate of the return of the plants after they 
had been completely killed out. The effects of the change in the soil 
conditions were also considered. Late in September, areas were se- 
lected, measured, and plowed. One acre was chosen in the best of 
the crowfoot-grama area near the south gate (at H, fig. 2), and 
another in the six-weeks grass area where rayless goldenrod (/so- 
coma hartwegi) was very abundant, near the southwest corner of 
the reserve (at I, fig. 2). Collections as nearly representative as pos- 
sible were made on these areas (Nos. 15 and 16, fig. 2) .before the 
plowing was done, and the hay on the acre (near H, fig. 2) was cut 
and weighed.t| The plowing on the area (near I, fig. 2) was poorly 
done, so that the plants of Isocoma were not all killed, and it was 
plowed again more thoroughly and deeper (about 4 inches) in De- 
cember, 1913. At this later date another acre was plowed near the 
gate (at H, fig. 2), the intention being to get a larger number of 
collections for comparison. Collections have been made on each 
of these plowed areas each year, and other collections have also 
been made on the unplowed land beside the plowed area near the 
gate. These collections (Nos. 16, 25, and 48, fig. 2) indicate the pro- 
duction of forage on the unplowed land, the average total produc- 
tion for the three years being approximately 1,018 pounds of herb- 
age per acre, of which 601 pounds, or nearly 60 per cent, is grass. 
Of this grass 570 pounds, or 56 per cent of the total herbage, is 
perennial grass. Comparing these results with others derived from 
1See record in Table IV, for 1912: Felix, 1 acre=750 pounds. 
