SAMPLE PLOTS IN SILVICULTURAL RESEARCH H 



ISOLATION STRIPS 



In order that conditions may be the same at the edges of a plot as 

 in its interior, an area surrounding the plot on all sides should re- 

 ceive the same treatment as the plot. This area is then called the 

 isolation strip. In general the chief factors to be considered in thus 

 isolating plots are light and soil moisture; in many regions, equal 

 weight must be given to evaporation, wind, and temperature. 



The isolation strip should be so wide that any treatment accorded 

 the stand outside the strip will not affect the plot. In studies in- 

 volving treatment of young stands, such as weeding, thinning, or 

 pruning, it is desirable that the width of this strip at least equal the 

 height to which the dominant trees on the plot may be expected to 

 grow during the course of the experiment. In studies involving nat- 

 ural seeding, it may be necessary to make the isolation strip so wide 

 that seed from trees outside cannot blow across it to the plot. (In 

 many cases, particularly where light-seeded species are involved or 

 in regions of strong winds, a requirement that plots used in studies 

 of natural seeding be absolutely protected from outside seeding could 

 not be met.) 



Xeighboring plots that are to be treated differently should be sep- 

 arated by a double isolation strip, each plot having its own full- 

 width strip. 



The outside boundary of the isolation strip should be marked so 

 that treatment of the stand outside will not encroach upon the strip 

 and so that any subsequent plot treatment may cover the whole of the 

 strip. The markings should be distinct from those used on the plot 

 boundary. 



Often it is advantageous that an extra area surrounding both 

 plot and isolation strip be treated uniformly with them. This makes 

 it possible, without disturbing the plot or the isolation strip, to sup- 

 plement plot data through detailed study of changes in wood struc- 

 ture and quality, form, etc., that have taken place in trees treated 

 uniformly with those on the plot. 



In some studies, such as those of fire damage or natural reproduc- 

 tion of light-seeded species, it is highly advantageous to use a large 

 area in order to obtain natural conditions. Thus an area to be 

 burned experimentally must be large enough to develop typical 

 forest-fire conditions, and the area cut over must be sufficiently large 

 to eliminate marginal effects. 



PLOT ESTABLISHMENT 6 



SELECTING THE STAND 



The stand selected for the establishment of permanent sample 

 plots must be representative of those to which the results of the 

 plot study are to be applied; and its location, etc., must be such that 

 the plots will be readily accessible, both at the time of establishment 

 and throughout the study period, and will be assured of protection 

 from all disturbing influences throughout that period. 



6 Instruments, tools, etc.. needed in plot establishment and in other plot work are 

 listed in the appendix (p. 72). 



