188 



nearby; however, tlie number of ex- 

 tremely old Douglas-firs per unit area is 

 greater here than at any other site in 

 the Rockies thus far sampled by the 

 writer. 



On the basis of several hundred 

 sampled trees which were suitable for 

 chronologA' studies and which exceeded 

 the commonly assumed maximum age 

 of about 500 )ears for Rockv Mountain 

 conifers, certain characteristics of these 

 drought-site trees emerge as probably 

 very general in nature: (a) the abso- 

 lute maximum ages of Douglas-fir, 

 ponderosa-pine and pinyon pine in the 

 Rocky Mountains are of the order of 

 1,000 years, and for P. flexilis (limber 

 pine) in excess of 1,650 vears; (b) in 

 addition to the obsen'cd tendency for 

 maximum longevity on the most ad- 

 verse sites, there seems to be a syste- 

 matic though probably only indirect 

 relation to latitude in' the age hmits 

 of various stands of a given species; (c) 

 the median ring-width in the lower 

 stem is about 0.30 mm.; (d) this 

 growth rate is often approached by 

 early maturit}— two or three centuries 

 —after which the mean growth rate de- 

 creases very slowly; (e) the absolute 

 minimum in total mean radial growth 

 of the lower stem for an entire centur\^ 

 is about eight mm.; (f ) the number of 

 sapwood rings in over-age Douglas-fir 

 does not seem to be significantly re- 

 lated to either the number of heart- 

 wood rings or the thickness of heart- 

 wood (for relatively young trees a 

 systematic relation has been found by 

 Stallings when groups of five or more 

 trees are averaged); (g) false rings are 

 almost completely absent in these over- 

 age trees of all species except the scopu- 

 lorum juniper, and there is a marked 

 tendency to decreased incidence of 

 locally absent rings in higher lati- 

 tudes. 



FORESTRY 



CEOGRAPIIIC DISTRIBUTION OF 

 DROUGHT CONIFERS 



Do over-age conifers providing sig- 

 nificant rainfall chronologies exist on 

 other continents? It now seems quite 

 certain that they do. 



Along the foothills of the Patago- 

 nian Andes of Argentina, between lati- 

 tudes 38 S. and about 43 S., dry sites 

 comparable to the semi-arid Rocky 

 Mountain margins were sampled in 

 early 1950 by the writer. In two conif- 

 erous species, Araucaria imbricata 

 Prav. and Libocedrus chilensis Endl., 

 the ring records showed the characters 

 of sensitivity and crossdating which are 

 essential for the derivation of climatic 

 chronologies. Since these conifers are 

 developed only in scattered stands in 

 a ver)' thin and short belt between the 

 line of the Andes and the plains, little 

 area is available for development of 

 long-lived strains. Yet the same inverse 

 relation between mean growth rate and 

 age was found for the two Patagonian 

 species as for the conifers of the 

 Rockies. When the analvsis of these 

 collections and others 'in southern 

 Chile is completed, some hundreds 

 of years of climatic chronolog)' for 

 Patagonia should be available. 



Xerophytic conifers, and possibly 

 some hardwood species, exist in appar- 

 ently suitable environments in a num- 

 ber of other regions, particularh^ in 

 Asia, and will probabh- be found to 

 provide significant rainfall chronol- 

 ogies; little exploration seems yet to 

 ha\'e been made of the extensive Si- 

 berian forests as sources of temperature 

 chronologies. In the light of present 

 knowledge, however, it appears that 

 the combination of factors which 

 makes possible long tree-ring histories 

 of climate is particularh- favorable and 

 widespread in western North America. 



