HEATH FAMILY 



31 



shrubs, retaining all their foliage, but with the leaves bro\™ and dead, stand after conflagrations 

 on the margin of fire-swept bands in the chaparral as if suddenly struck dead, without any visible 

 sign of tissue injury to the plant as a whole (Fig. 293). The shallowness of the root system in- 

 creases distinctly the chances of mortality in running fires. On Mt. Tamalpais the species tends 

 to colonize exclusively small areas on the slopes. After fires seedlings appear promptly on burns 

 and fruit at the age of five or six years. This species thus adapts itself to short fije intervals and 

 is a true fire-type shrub (Fig. 295). 



It is next desirable to consider the Napa Eange for further illustrations of reaction of Arcto- 

 staphyli to chaparral fires. In this range Arctostaphylos manzanita is locally common. It is a 



shrub 5 to 8 feet high or sometimes a small tree up to 22 

 feet high, generally with a distinct trunk in either case. 

 Under chaparral fires an individual of this species is 

 killed completely. Commonly heavy crops of berries are 

 set, and seedlings appear in large numbers on its own 

 territory in the area of burns. These seedlings produce 

 fruits in the juvenile stage and thus provide a safeguard 

 against destructive fires of short time intervals. In ad- 

 dition seeds hibernate in the soil for long periods and 

 provide an additional resource for a new stand. Arcto- 

 staphylos manzanita is a fire-type shrub as evidenced by 

 the following summary: (a) the trunk develops no en- 

 largement at the ground level; (b) the shrub is killed 

 completely by chaparral fires and does not sprout from 

 the root-crown; (c) it is shallow-rooted, thus increasing 

 its sensitivity to intense chaparral fires; (d) seed pro- 

 duction is abundant; (e) seedlings appear on burns in 

 large numbers and tend to repossess the territory of the 

 species; (f ) seedlings fruit at an early age, often in 10 

 or 12 years, a period usually shorter than the interval 

 between severely destructive chaparral fires; (g) seeds 

 hibernate in the soil and have the capacity to develop 

 seedlings in response to heat shock following very long 

 hibernation periods, as shown by successive germinations 

 of seed after short-period repetition of fire on a burn. 

 In the Napa Range Arctostaphylos stanfordiana is often 

 associated with Arctostaphylos manzanita and displays 

 similar characteristics in response to destruction of indi- 

 viduals by fire. Both of these species are typical fire- 

 type .shrubs. 



Factual matter thus far accumulated indicates that 

 root-crown sprouting on the one hand or fire destruction 

 on the other characterize a given species. In other words 

 a given species is wholly a root-crown shrub or a fire-type 

 shrub. This fact is thus of importance in species differ- 

 entiation ; all the more in that reaction to fire does not 

 run parallel to small species groups but cuts across thera. 

 It will be profitable to cite illustrations. A closely related group of species which may be noted 

 is that of Arctostaphylos patula, A. manzanita and A. stanfordiana. It must be remembered that 

 our species of Arctostaphylos are as a whole only slightly differentiated by definitely marked 

 characters; distinct species, or what are believed to be such, often have very similar bark, leaves, 

 flowers and berries. The ordinary taxonomie marks which are so commonly associated with such 

 organs are in this genus either deficient or largely lacking. In the above group, material of one 

 of these species may sometimes be mistaken as belonging to one of the other two. The distinction 

 as to fire reaction between Arctostaphylos patula on the one hand and A. manzanita and A. stan- 

 fordiana on the other is, however, decisive. It is a criterion of certainty. As to distinction be- 

 tween Arctostaphj'los manzanita and A. stanfordiana, both of which are fire-types, the situation 

 as to sound criteria between species is saved by the fact that these two are distinguishable by 

 many points of difference. If any one point fail, the sum total of the differentiae operate and so 

 make clear two specific units. 



A like text can be derived from consideration of another group consisting of Arctostaphylos 

 glandulosa and A. canescens. The.se two species are sometimes difficult to distinguish on the basis 

 of ordinary herbarium specimens, not in their typical form, but in view of their variables, especi- 

 ally when there are brought into view the variables of Arctostaphylos glandulosa. The former 

 species is a root-crown shrub of remarkable habits and regenerates by sprouting after fire with 

 unusual vitality; the latter is a fire-type shrub, since according to its author, Alice Eastwood, it 

 is killed completely by fire and does not crown-sprout. It is thus evident that reaction to fire 

 provides a species criterion of value; it is indeed of outstanding value in a group where distinc- 

 tive characters of the reproductive organs or of the leaves are weakly developed or are hopelessly 

 obscure. 



Fig. 292. Arctostaphylos num- 

 MTJLAKIA Gray. Mt. Tamalpais, south 

 slope, showing the shallow root system 

 of a shrub. 



