32 CIRCULAR 3 3 3, U.S. DEPARTMENT OE AGRICULTURE 



more liable to loss than a plot within an area reserved for research 

 purposes. 



The question of whether plots should be protected against insects 

 and diseases cannot be settled arbitrarily. If an insect or disease 

 common to the region threatens plot trees, possibly the attack should 

 be considered normal and any resulting loss accepted as part of the 

 history. If an insect or disease is epidemic, then efforts should un- 

 doubtedly be made to control it. In the case of blister rust of white 

 pine, the problem is complicated by the question whether removal 

 of Ribes, as by digging up the roots, will affect the experiment. 

 The investigator must decide which is the lesser of the two evils. 



Unfortunately, agencies conducting forest research often find it 

 necessary to protect sample plots from other agencies, and even from 

 forest administrators. All too often a busy forest administrator fails 

 to recognize the value of plots, regarding them as something outside 

 his range of interest or even as something that intrudes on his activi- 

 ties, rather than as an opportunity to understand more fully the con- 

 ditions existing on the forest under his care and the possibilities of 

 its development. The investigator should recognize this situation 

 and endeavor to meet it. This involves an effort to acquaint the 

 administrator with the purpose of the plot, its value in management 

 work, its value in time, and its cost of replacement. Having made 

 this effort, the investigator should aggressively follow up any need- 

 less or wanton damage so as to prevent repetition of the offense. 



PLOT TREATMENT 



Specific methods for treating sample plots will not be described in 

 this publication. Some general features of treatment that are of con- 

 cern in most plot work will, however, be outlined. 



Amy cultural treatment accorded a plot should be completed within 

 the shortest possible time, in order that the experiment may not be 

 unduly complicated by variations corresponding to change of season. 

 If an experimental cutting or thinning operation, for example, is 

 allowed to drag out over a period of weeks or months, unseen or 

 unrecorded seasonal changes in the stand during that period may 

 greatly alter the dependability of the results. A considerable lapse 

 of time between a cutting operation and subsequent measurements, 

 although it sometimes does no harm, in most instances introduces 

 errors that may cause confusion when the data are analyzed. 



So far as possible, all cultural work should be carried out during 

 the season of slowest change, i.e., during the dormant period. This 

 principle calls for concentration of such work in the coldest season, 

 normallv from November to February, inclusive, the period being 

 shorter in the South or at low elevations and longer in the North 

 or at high elevations. For many of our forest tree species, data as 

 to the actual time of year during which growth either in diameter or 

 in height stands still or is greatly retarded are not available. 

 Enough such data are available, however, to show that in mixed 

 stands the growth of different species is not uniform. A season's 

 diameter growth may be practically completed by one species before 

 it is begun by another species in the same stand. Such variation 



