Regeneration in Manzanita

Abstract

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. (PI. I.) Arctostaphylos glandulosa. This is a rather low-growing species of the immediate coast region, occurring in formations of considerable extent on slopes of yellow shale. It is perhaps the most remarkable species in California in the matter of its behavior under repeated 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 characteristically 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