REPRODUCTION OF WESTERN YELLOW PINE. 



53 



1914 and 1919. A comparison of present conditions inside and out- 

 side the fenced areas also gives a good idea of the effects of grazing. 

 The present composition inside the fence is indicated by Table 12. 

 It will be seen from this that the dominants in the subclimax as- 

 sociations are the two bunch grasses, Festuca arizonica and MuhJm- 

 beryla nwntana. 



The following stages 11 of development in plant cover are recog- 

 nized. No. 1 representing the lowest and No. 4 the highest. 



STAGE OF DEVELOPMENT. 



1. First weed stage : 



Completely denuded and packed 

 areas such as roads and severely 

 overgrazed areas. ( PI. IX, Fig. 1. ) 



2. Second weed stage: 



Cultivated plots, and stump 

 patches. (PI. IX, Fig. 2.) 



3. Subclimax stage: 



Normal openings unaffected by 

 overgrazing or other disturbing 

 factors. (PI. III.) In some 

 localities the subclimax stage is 

 represented by bunch grasses, in 

 others by turf forming grasses 

 such as grama or wheat grass. 

 Since these grasses are associated 

 with the pine and are essentially 

 a part of the forest, they might, 

 from this point of view, be placed 

 in the climax stage. But the fact 

 that they are always shaded out 

 where the pine is dense seems to 

 justify the classification here 

 used. 



4. Climax stage: 



Areas occupied by western yel- 

 low pine. (PL XIV, Fig. 2.) 



CHARACTERISTIC SPECIES. 



Polygonum douglasii. 

 Erigeron d i vergens. 

 Bouteloua procumbens (annual) 

 Sporobolus ramulosus (annual). 



Vicia americana. 

 Lotus wrightii. 

 Sitanion sp. 

 Hymenoxys floribunda. 

 Sen ecio spartioides. 

 Koeleria cristata. 

 Artemisia mexicana. 

 Artemisia dracunculoides. 



Festuca arizonica. 

 Muhlenbergia montand. 

 Blepharoneuron tricholepis. 

 Lupinus hilUi. 

 Sporobolus interruptus. 

 Agropyron smithii. 

 Bouteloua gracilis. 

 A ) i dropogon scopa ri u s. 



Pin us ponderosa scopulorum. 



A characteristic difference between the vegetation inside and that 

 outside the inclosure is the absence outside of vetch ( Vicia americana) 

 and the red-and-yellow pea (Lotus wrightii) . Both of these plants 

 are considered excellent sheep feed and are therefore very closely 

 grazed outside the fence. Although casual observations suggest com- 

 plete extermination, it is more probable that the perennial roots 

 still persist, but that the stems are repeatedly eaten off before they 

 attain sufficient height to become noticeable. These species became 

 prominent on the fenced plots within five years after the exclusion 



11 Adapted from Sampson's Plant Succession in Relation to Range Management (85), 



