. Journal of forestry . fty and the most rapidly growing trees in a habit of selecting the best trees sometimes retards the process ofnatural thinning by reducing the height growth of the tallest trees and 198 JOURNAI, OF FORESTRY giving the backward trees the opportunity of overtaking the in this way trees which would normally have been forced 8000 7000 3000 \ SOOO \ \ w B 4 4000 \ M \ w 3090 \ H \ N ^ \ ^ \, \ 1000 \ ^ \^ 10 20 30 40 SO 60 70 80 90 104 PERCENT INJURED PER ACRE Fig. 4.—Relation of density to the per cent of trees injured per acre out by natural se
. Journal of forestry . fty and the most rapidly growing trees in a habit of selecting the best trees sometimes retards the process ofnatural thinning by reducing the height growth of the tallest trees and 198 JOURNAI, OF FORESTRY giving the backward trees the opportunity of overtaking the in this way trees which would normally have been forced 8000 7000 3000 \ SOOO \ \ w B 4 4000 \ M \ w 3090 \ H \ N ^ \ ^ \, \ 1000 \ ^ \^ 10 20 30 40 SO 60 70 80 90 104 PERCENT INJURED PER ACRE Fig. 4.—Relation of density to the per cent of trees injured per acre out by natural selection succeed in establishing themselves as dominanttrees. This interference with normal development reduces the rate ofgrowth for the stand as a whole. THE WHITE-PINE WEEVIL 199 Influence of Density on the Extent of Weevil Injury In open stands where the crowns are all free the trees are all equallysubject to attack, but in the denser stands the percentage of trees suit- 9000 80O0 7000 6000 5000 4000 3000 2000 1000. LOSS KR TUCK IN FCKT FiC. 5.—Relation of the loss per tree in height growth to the density of the stand able for the development of the weevil becomes smaller, while in verydense stands the injury may be reduced to practically nothing. 300 JOURNAL OF FORESTRY The curve* shown in figure 4 illustrates this point. This curvewas constructed from counts on sample plots made near Grande, innorthern Isanti County, Minnesota. Up to a density of 400 trees peracre, 100 per cent are infested. Above that point the percentage in-fested constantly diminishes until at 4,500 per acre the infestation isslightly less than 10 per cent, while at 9,000 trees per acre the infesta-tion is reduced to less than i per cent. One plot, where the trees stood11,200 to the acre, only per cent were infested. This plot waswithin 100 feet of another more open plot of the same age which hadan infestation of over 50 per cent. With this decrease in weevil attack the density increases, and wi
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectforestsandforestry
