tree from an estimate of the proportion of trees 

 that are infested. 



Working with 6- to 8-foot tall trees, we found 

 it difficult to count egg clusters accurately. 

 Sawfly eggs are laid in the fall in loose clusters 

 on the current year's needles. Foliage must be 

 examined thoroughly and systematically to 

 make sure none of the clusters is missed or 

 counted more than once. Examination of whole 

 trees is expensive unless the trees are quite 

 small. The sampling pole was used to overcome 

 these problems by delineating a volume of 

 known size and position. 



The sampling device 



In field situations it is very difficult to locate 

 the boundaries of vertical sampling units. To 

 overcome this problem, a hardwood pole, 1 inch 

 in diameter and 6 feet long, was fitted with 3/8- 

 inch hardwood dowels at 1-foot intervals from 

 the base to the top (Fig. 1). Each dowel is at a 

 right angle to the one below. Near each end of 

 each dowel, a 3/16-inch vertical hole was drilled; 

 the two holes being 8.478 inches apart. A 1/8- 

 inch sighting wire can be inserted vertically 

 through the holes. The dowels and sighting 

 wires delineate a 0.25 cubic foot (0.5 x 0.5 x 1.0 

 ft) space (Fig. 2). For trees taller than 6 feet, two 

 poles can be joined with an aluminum sleeve to 

 provide a stack of 11 cubes. Larger or smaller 

 volumes can be sampled by using different dis- 

 tances between the dowels and sighting wires. 

 Each cube is a vertical sampling unit. Numbers 

 of egg clusters and the presence or absence of 

 vegetation can be recorded for each vertical 

 unit. 



During the preliminary field trials, it became 

 apparent that the convenient size of sample unit 

 depends on stand conditions. In open stands, 

 cubes as large as 2 feet on a side are convenient. 

 Smaller cubes are easier to use when the foliage 

 is dense. In our judgement a 0.25 cubic foot unit 

 is satisfactory in such conditions. The sampling 

 pole should be as long as the tallest tree ex- 

 pected to be encountered. 



Field test 



To gain experience with the sampling pole, we 

 sampled a 20-acre Scotch pine plantation at Pine 

 Plains, Dutchess County, New York, that was 

 infested with the European pine sawfly. The 

 plantation was established in 1958. Data were 

 collected during the winters of 1969 and 1970. 



Four 208- by 208-ft blocks were selected at 

 random in the plantation. A map of each block 

 was divided into quarters five times in succes- 

 sion, producing 1024 squares 6.5 by 6.5 feet. 



Figure 1.— General view of the 

 sampling pole being used to 

 delineate vertical sampling 

 units. 



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