302 



GRAZING INDICATORS. 



completely replaced by them. This is usually only when the disturbance 

 has been long continued and the supply of ruderals maintained by the presence 

 of man. In the case of complete replacement, such as by Avena or Bromus, 

 fire has often played an effective part. When more palatable species have 

 disappeared, annuals often furnish considerable grazing, though it is usually 

 inferior in all respects to that afforded by the climax dominants displaced. 

 Avena fatua is an exception to some extent, while in the Southwest the winter 

 annuals are extremely important in tiding over the cattle until the summer 

 grasses appear. 



There are several hundred annuals which serve in some degree as over- 

 grazing indicators. The most important ones are found chiefly in the grass- 

 land climax and its contacts with the scrub formations. Some of these extend 

 upward into the grasslands of the montane zone, while the indicators of over- 

 grazing in the higher zones usually belong to the same or similar genera. A 

 few of the annual indicators extend more or less throughout the grassland 

 formation, but most of them occur in their particular region. Hence, it seems 

 most convenient to group them under the three heads, namely, prairies and 

 plains, desert plains, and bunch-grass prairies. 



Prairie and plains indicators. WTiile different species of annuals indicate 

 small differences in the degree of overgrazing, the abundance and height of 

 the plants is usually of greater importance. In addition, annual indicators 

 have received little quantitative study, and hence it is possible only to list 

 them in the general order of their importance. Some of those listed are either 

 annual or biennial, and a few are typically biennial (plate 78, a). 



Plantago patagonica. 

 Festuca octoflora. 

 Hedeoma hispida. 

 Lepidium intermedium. 

 Lepidiimi alyssoidea. 

 Lepidium ramosum. 

 Lappula texana. 

 Verbena bracteosa. 

 Helianthua petiolaria. 

 Helianthus annuus. 

 Erigeron canadensis. 

 Erigeron divergens. 

 Erigeron ramoaus. 

 Chenopodium leptophyllum. 

 Chenopodium album. 

 Eriogonum annuum. 

 Eriogonum cemuum. 



Desert plains indicators. These fall into two groups, depending upon their 

 time of appearance. The sunmier annuals correspond to those listed above. 

 They occur with the grasses, and hence are a more exact measure of over- 

 grazing than the winter annuals. Most of them are distributed throughout 

 the region, but are more typical in New Mexico. The winter annuals de- 

 velop most abundantly in overgrazed areas also, but they finish their growth 

 before the grasses appear and hence indicate conditions of the previous year. 

 They are characteristic of southern Arizona and adjacent Mexico. The most 

 important ones, such as Plantago fastigiata, EschschoUzia mexicana, Lesquerella 

 gordoni, Lejyidium lasiocarpum, Pectocarya linearis, etc., often form a dense 

 cover and are invaluable for spring grazing (plate 78, b). 



Eragrostia pilosa. 

 Eragroatis major. 

 Ambrosia artemisifolia. 

 Salsola kali. 

 Solaniun roatratum. 

 Argemone platyceraa. 

 Dysaodia pappoaa. 

 Hordeum jubatum. 

 Schedonnardus texanus. 

 Munroa aquarroaa. 

 Euphorbia marginata. 

 Croton texensia. 

 CoUomia linearis. 

 Verbesina encelioidea. 

 Orthocarpus luteus. 

 Polygonum aviculare. 

 Polygonum ramosiasimum. 



Aater tanacetifolius. 

 Aster canescens. 

 Phacelia heterophylla. 

 Allionia linearis. 

 Cassia chamaecriata. 

 Coreopsis tinctoria. 

 Salvia lanceolata. 

 Lupinus pusillus. 

 Lotus americanus. 

 Draba caroliniana. 

 Myosurus minimus. 

 Androsace occidentalis. 

 Pectis angustifolia. 

 Sophia pinnata. 

 Phyaalia lobata. 

 Solanimi triflortun. 



