1916 -] JEPSON: REGENERATION IN MANZANITA 3 



REGENERATION IN MANZANITA. 



Willis L. Jepson. 



In the Oakland Hills there may be found two manzanitas that are 

 species of Arctostaphylos growing in localized areas. Arctostaphylos 

 andersonii Gray grows on the main ridge a mile south of the summit 

 of the Snake Road which leads into the headwater basin of San 

 Leandro Creek. Arctostaphylos glandulosa Eastw. grows on the 

 same ridge on yellow shale, and also abundantly on Moraga Ridge 

 on the same formation. A number of years ago while making field 

 studies of these shrubs, my attention was directed to the rather 

 striking fact that individuals of Arctostaphylos andersonii had been 

 killed outright by fire, and that Arctostaphylos glandulosa was 

 stump-sprouting abundantly from heavy root-crowns. No root-crown 

 or tabular development at base of the stem could be found in the 

 former species, nor even any attempts at root sprouting at all, while 

 in the case of the latter species the root-crowns became very heavy, 

 globose, or turnip-shaped, or even eventually forming broad tabular 

 areas of irregular shape at the surface of the ground. Since then 

 many further observations have been made upon the species of this 

 genus in various parts of the state to determine if reaction to fire 

 ran parallel with the specific limitations. 



Arctostaphylos andersonii is a larger shrub, eight to twelve feet 

 high. One individual within a few feet of the bridle-path along the 

 eastern brow of the Oakland Hills, and about half-mile south of 

 Snake Road summit, is sixteen feet high, with a trunk circumference 

 of three feet nine inches, at six inches above the ground. As said 

 above, this species is killed by fire. Trunks decapitated four feet 

 high failed to regenerate. This species may be recognized by its 

 densely set leaves, which are heart-shaped at base, and by its very 

 close flower-clusters. (PL I.) 



Arctostaphylos glandulosa. This is a rather low-growing species 

 of the immediate coast region, occurring in formations of consider- 

 able extent on slopes of yellow shale. It is perhaps the most remark- 

 able species in California in the matter of its behavior under re- 

 peated fire devastation. After the stems are fire-killed, young plants 

 begin to form a root-crown which becomes turnip-shaped or globose 

 (Fig. 1) and lies immediately at or below the surface of the ground. 

 As the plants increase in age and fires continue to run, as character- 

 istically in chaparral, the root-crowns increase in size (PL II, A) 

 and give rise to many stems. While at first small, root-crowns often 

 become two to five, or indeed ten to thirteen, feet broad. 



The very large ones form irregular circles or crescent-shaped 

 areas, and are truly remarkable structures. (Fig. 2) Such crowns 

 can be studied to advantage upon the southeastern slopes of Mt. 

 Tamalpais or in the Oakland Hills just south of the low wagon pass 



