GEAZING EAIS^GES IN SOUTHEEX ARIZONA. 15 



THE OAK BELT. 



About one section of the land in the MacBeath inclosure lies 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. Mrsuta, 

 Elionurus, Trachjq^ogon, 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 (PL 

 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-daj^s' 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 {Iso- 

 coma hartioegil) was verj^ 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.^ 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 13, 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 



1 See record in Table IV, for 1912 : Felix, 1 acre=750 pounds. 



