274 JOURNAL OF FORESTRY 



with such studies in this region is that reproduction is normally so 

 slow and uncertain, even under the most favorable conditions afforded 

 by Nature, that it is often impossible without authentic records to es- 

 tablish any definite relation between cause and effect. 



The shortcomings of the early investigations were quickly rec- 

 ognized, and steps were taken to solve the problems in a thorough 

 manner. One of the methods of study adopted as particularly suitable 

 for conditions in this region is the permanent sample-plot method. 

 The principle is known to all foresters. In brief, the procedure is to 

 establish plots on typical areas and maintain complete records of what 

 takes place during a period of years. It involves more, however, than 

 merely passive observation of results ; it also involves painstaking in- 

 quiry into causes. 



During the period from 1909 to 191 5, 19 permanent sample plots 

 aggregating about 2,000 acres were established mainly in pure west- 

 ern yellow-pine stands in Arizona and New Mexico. One of the plots 

 is in a virgin forest, two are on private cuttings, and the remainder 

 are on areas logged under Forest Service supervision. About 90 per 

 cent of the acreage is in the form of "extensive" plots and 10 per cent 

 in the form of "intensive" plots. On the "extensive" plots the trees 

 are merely recorded by i-inch diameters and classified as to "yellow 

 pine" ^ or "black jack," "healthy" or "unhealthy." Supplementary rec- 

 ords are kept for windfalls, trees struck by lightning, and attacked by 

 mistletoe, porcupine, and other common enemies. The "intensive" 

 plots, which are usually selected to represent large areas, rarely ex- 

 ceed 10 acres. In these the studies are much more detailed than is 

 possible on "extensive" plots. Each tree is numbered and recorded 

 separately, , giving diameter, height, clear length, crown description, 

 and full notes regarding the condition of the tree, particularly with 

 respect to disease and injuries. A map on the scale of i inch or more 

 to the chain gives the exact location of each tree down to 4 inches 

 d. b. h., scattered seedlings and groups of reproduction i foot or over 

 in height, stumps, brush piles, logs, tree-tops, logging roads, and in 

 fact every feature which may be expected to affect the stand. On ad- 

 ditional small plots, all seedlings over one year old are staked and 

 numbered. On a few plots all vegetation, including herbaceous plants, 

 is charted with a view toward determining its effect upon forest repro- 

 duction. 



* The older, or j^ellow-barked, trees are commonly designated as "yellow pine," 

 while the younger, or dark -barked, trees are called "black jack." 



