106 CLIMATIC CYCLES AND TREE-GROWTH 



surroundings. This has been sought by comparative analyses of basin 

 and ridge trees. A lag of 3 years or more could have been detected, 

 but none was found. There may, of course, be a shorter one. 



PIKE'S PEAK TOPOGRAPHY 



Pike's Peak contours — In collecting 47 specimens from the vicinity 

 of the Cog Road on Pike's Peak in 1920, locations of test trees were 

 selected with reference to contour and water-supply. The region 

 lends itself exceedingly well to such tests. The valley bottoms are 

 v-shaped rather than rounded, as in the sequoia basins. The sides of 

 the valleys extend for great distances at a somewhat even slope. 

 Water is far less abundant and the trees are left more to their own 

 resources, as it were. The trees are scattered generally and one can 

 get north and south exposures, stream contact, and other features. 

 The soil material is relatively homogeneous compared to the Flag- 

 staff region, where transition is abrupt from limestone to lava or the 

 reverse, and hence tests are impeded on this account. However, on 

 Pike's Peak the same tree does not cover all the conditions tested, and 

 so each must be taken separately. 



Yellow pines — Four groups had yellow pines in them, as follows, 

 in order from north to south : Upper North Transect, 5 ; Lower North 

 Transect, 2; Brook, 2; South Transect, 2. The mean ring-sizes in 

 order were, 1.26, 1.60 (variable), 1.74, and 0.81 mm. The first and 

 second of these showed considerable internal variation. The trees 

 on gentler slopes or in small side-gullies had the larger mean growth, 

 while trees on the very steep slopes toward Ruxton Creek had very 

 slow growth. The largest growth was near Jack Brook, the two yellow 

 pines there being some 20 feet above the water (and near the dendro- 

 graph tree). The smallest growth was on the South Transect, with 

 its ridge topography, very steep slope, and sand areas indicating 

 dryness. 



The south-exposed North Transect, near the foot of a long moun- 

 tain slope, has growth 75 per cent greater, and the brook has growth 

 100 per cent greater than the South Transect, which extends nearly 

 to the top of a low, dry ridge. The extra brook growth is obviously 

 a question of water-supply. So we infer that the added growth on the 

 North Transect is due to moisture-supply also, and from the simi- 

 larity to the Flagstaff area in some prominent features of the tree 

 record, this better moisture-supply comes in the snows of winter. This 

 has been considered in some detail, because the Douglas firs next con- 

 sidered give similar results. 



Douglas firs — Douglas firs occur also in the same four groups: 

 Upper North Transect, 3; Lower North Transect, 3; Brook, 4; and 

 South Transect, 6. The respective mean growths are 1.09, 0.99, 1.20, 



