November 19, 1909] 



SCIENCE 



721 



outposts of the tall coniferous forest, which 

 through the Canadian and Iludsonian zones 

 envelops all the remainder of the range with 

 a mantle of needle-leaf evergreen differing 

 only in its much deeper hue from the light 

 green, of the largely sclerophyllous broadleaf 

 brush-woods of the lower slopes. 



The larger species most characteristic of the 

 several zones are as follows : Lower Sonoran or 

 Desert Zone — Acacia constricta Benth., A. 

 greggii A. Gray, Prosopis velutina Wooton.^ 

 Upper Sonoran or Oak Zone — Quercus ohlongi- 

 folia Torr., Q. emoryi Torr., Q. toumeyi Sarg., 

 Juniperus monosperma Engelm., Prosopis 

 glandulosa Torr.' Transition or Pine Zone — 

 Pinus chihuahuana Engelm., P. mayriana 

 Sudw., P. cemhroides Zucc, Quercus hypoleuca 

 Engelm., Q. reticulata H. B. K. Canadian or 

 Fir Zone — Abies concolor (Gord.) Parry, 

 Pinus arizonica Engelm. Iludsonian or 

 Spruce Zone — Picea Engelmannii (Parry) 

 Engelm. 



Other prominent species are Quercus ari- 

 zonica Sarg. and Juniperus pachyphloea 

 Torr., which are practically coextensive 

 throughout the Upper Sonoran and Transition 

 zones. In like manner, Pinus strohiformis 

 Engelm. links and extends over the Canadian 

 and Hudsonian zones, becoming increasingly 

 abundant toward the summits, while Pseudo- 

 tsuga taxifolia (Lam.) Britton is present here 

 and downward, reaching the remarkably low 

 altitude of 6,500 feet on residual north slopes 

 in several instances. 



If three maps were to be drawn of this 

 mountain range, to show the three chief fea- 

 tures of its floral geography, the first would 

 give the several altitudinal zones, both in suc- 

 cession and relative limits somewhat as out- 

 lined by Merriam for San Francisco Peak 

 in northern Arizona.' The chief differences 

 between the two mountain masses are : (1) 

 The absence of the two uppermost zones of 

 Merriam from the Chirieahuas, due to insuffi- 

 cient elevation. (2) The absence in the San 

 Francisco Mountains of the evergreen oaks, 



•Often considered varieties of Prosopis Jiili/lora 

 (Sw.) DC. 



' Xorth American Fauna No. .3, U. S. Dept. Agr., 

 pp. 7-17, 1890. 



whereas in the Chirieahuas the pinyon of the 

 former is to a great extent replaced by oak, 

 and should be designated the oak zone or oak- 

 pinyon zone. 



TABLE OF ALTITUDES 

 Zones of San Francisco Mts. (Merriam) 



Desert Area 

 Pinyon Zone 

 Pine Zone 

 Balsam Fir Zone 

 Spruce Zone 

 Timber-Line Zone 

 Alpine Zone 



4,000-6,000 feet 



6,000-7,000 feet 



7,000-8,200 feet 



8,200-9,200 feet 



9,200-10,500 feet 



10,.500-11..';00 feet 



Above 11, .500 feet 



Zones of Chiricahua His. 

 Deseft Area Below 4,500 feet 



Oak Zone 4,500-6,000 feet 



Pine Zone 6,000-7,900 feet 



Fir Zone 7,900-8,900 feet 



Spruce Zone Above 8,900 feet 



The San Francisco altitudes represent mean 

 elevations of the limits of the several zones. 

 The lower limits of the Chiricahua zones are 

 approximate averages of the lowest points of 

 extension on residual slopes of the species or 

 groups of species for which the respective 

 zones are named." The upper limits, as given, 

 merely coincide with the lower limits of the 

 next higher zones. This will partly account 

 for the lower elevation of the Chiricahua 

 zones, while in part it may be due to lower 

 base level (smaller land mass)' despite the 

 counteractive effect of lower latitude. The 

 zones in reality overlap, but on paper we have 

 thus at least their true lower limits. Their 

 upper limits fall into other zones or else are 

 not reached. For example, the four or five 

 larger pines extend from a limit of 6,000 feet 

 to the ultimate summits of the range, on 

 sunny aspects covering both the fir and the 

 spruce zones completely. In order to admit 

 the latter two, the former must be restricted. 

 Similarly the oak zone, equivalent to the 

 lower portion of the total oak area and devoid 



' Tliese altitudes were obtained by aneroid 

 loaned by the Desert Laboratorj' of the Carnegie 

 Institution, frequently checked by the new bench 

 marks of the U. S. Geological Survey. 



° See Lowell, Century Magazine, March, 1908. 



