SAMPLE PLOTS IX SILVICULTUEAL KESEAKCH 31 



Where difference in species is a factor, the normal reforestation 

 spacing of 6 by 6 feet should be used. On plots where growth 

 and development of plantations are to be followed, a 6- by 6-foot 

 spacing is preferable to closer or wider spacing unless variation in 

 spacing is one of the factors in the experiment. 



When the initial research project is completed, adjoining plots 

 can be combined into a larger block to be used in further studies, if 

 the stands are similar as to species, age, etc., and if the survival in 

 individual blocks is sufficient to justify it. The initial plan of plot 

 distribution and establishment should, when possible, be framed 

 with a view to obtaining in the future, through such combination, 

 good-sized blocks of stands approximately uniform as to age, seed 

 source, species composition, and spacing. 



Trees used in planting experiments should be set out in uniform 

 rows regularly spaced. This will eliminate the need of marking 

 each tree with a numbered pin or stake, as the individual tree can 

 be identified by the number of the row and its position in the row. 

 For identification in later years, however, it may be highly advan- 

 tageous to number the individual plants. 



In plantation studies a splendid opportunity is afforded to reduce 

 error and increase the reliability of results through replication. 

 Plot replications may be established in the form of the Latin square, 

 or may follow any one of many other such schemes. Most planting 

 research involves replication of plots over periods varying, accord- 

 ing to local conditions, from 5 to 20 years. The more variable 

 the climatic conditions, especially during the most critical growth 

 period, the more time the experiment requires. 



Control plots should be established to provide adequate basic 

 comparison. On these plots, when species or seed-source compari- 

 sons are involved, normal-sized stock representing a local strain of a 

 commonly planted species should be planted by identical methods. 



In dealing with species that produce seed only intermittently, an 

 effort should be made to obtain in advance sufficient seed of a single 

 crop to provide for the project to its end, and to use only stock 

 grown from this seed. This procedure is all the more desirable 

 if selected individual trees are being used as a seed source. 



PROTECTION OF PLOTS 



Areas containing sample plots should be carefully protected from 

 anything that would alter ecological conditions, such as cutting, 

 grazing, fire, and camping, and from any other form of disturbance 

 that conflicts with the experimental requirements. Since sample plots 

 increase in value with age, even greater watchfulness is needed as 

 plots become older. 



Protection needs vary with local conditions. Experimental for- 

 ests should be posted against all trespass and protected in every 

 possible way against unauthorized use. Circumstances on each such 

 area dictate whether there is need of firebreaks, or of a patrol dur- 

 ing the fire or camping season, and whether there is need of com- 

 plete fencing against livestock. 



For isolated plots, woven-wire fencing and warning signs may 

 be required. It should be realized that any isolated plot is much 



