VEGETATIONAL ANALYSIS 43 



considerable time and labor. Also certain types of materials may 

 be surprisingly expensive, especially if plots are replicated. If the 

 effects of grazing are to be studied, a barbed-wire fence will keep 

 out cattle, but rabbits must also be considered. They may be at- 

 tracted by the very things that nourish within the exclosure after 

 the cattle are kept out. Again, small plots may be fenced for rab- 

 bits and yet permit squirrels or birds to come in over the top. 

 Then the entire plot must be covered. Lesser rodents may go 

 through or tunnel under the wire, and suitable precautions must 

 be taken to check them. 



The effects of the exclosure itself upon the vegetation should 

 not be ignored since it may serve as a windbreak, which may re- 

 duce transpiration and intercept snow, soil, and seeds. Small plots 

 completely screened over will have quite a different micro-climate 

 from unscreened areas. To hold constant a single variable within 

 an exclosure is difficult, but it can be approached by having ex- 

 closures as large as possible, by insuring a liberal transition or isola- 

 tion strip around the margin, which will not be used in sampling, 

 and by having the barriers as low and as open as possible within 

 the limitations of the experiment. 



Quadrat Methods —Actually the unit sampling area can be any 

 shape or size, and any number can be used in a variety of ways, 

 depending upon circumstances and objectives. As one soon learns, 

 the major concern is to get adequate data with a minimum of 

 effort. Because vegetation is so variable, generalizations cannot be 

 made to fit all situations. Because objectives are rarely the same, 

 methods quite satisfactory in one instance may not be so in another. 

 Set rules are not advisable for sampling, but certain generalizations 

 may well be considered in the light of experience. 



Shape of Quadrat.— The term, quadrat, implies a square, and 

 this shape is undoubtedly more commonly used by ecoloo-ists than 

 any other. This is probably a matter of habit, for other shapes are 

 just as usable and sometimes more efficient. When Raunkiaer 202 

 was making his pioneer studies of frequency, he at first used a 

 square frame for marking his sample areas but later used a circle 

 exclusively because of its convenience. He wished to have data 

 from many small quadrats that were randomly distributed. For 

 marking, he used a rod to which a stick was attached at right angles 



