. Response of dwarf mistletoe-infested ponderosa pine to thinning. Arceuthobium Propagation; Ponderosa pine Diseases and pests; Ponderosa pine Thinning. r U ⢠Dominants y = - R = <r Codominantsy = - R2 = .97 ⢠Intermediates y = - R2 = .68. Years from 1950 2 4 6 8 10 12 14 I i i â ' â i i I 1 1 1 1 u 18 1950 52 54 56 58 60 62 64 66 68 Year of origin of supporting branch segment Figure 4 âNumber of dwarf mistletoe plants per meter of annual growth on branches comprising the crowns of 54 pole-
. Response of dwarf mistletoe-infested ponderosa pine to thinning. Arceuthobium Propagation; Ponderosa pine Diseases and pests; Ponderosa pine Thinning. r U ⢠Dominants y = - R = <r Codominantsy = - R2 = .97 ⢠Intermediates y = - R2 = .68. Years from 1950 2 4 6 8 10 12 14 I i i â ' â i i I 1 1 1 1 u 18 1950 52 54 56 58 60 62 64 66 68 Year of origin of supporting branch segment Figure 4 âNumber of dwarf mistletoe plants per meter of annual growth on branches comprising the crowns of 54 pole- size ponderosa pines. Dominants (14), codominants (14), and intermediates (26) are averaged separately and plotted. Figure 4, covering the period 1950 to 1968, shows the relationship between the increase in dwarf mistletoe and crown enlargement, expressed as the number of dwarf mistletoe plants per meter of branch. Prior to 1950 crown enlargement averaged only m of branchlet length per tree per year. On such slow grow- ing trees data are highly variable and even one dwarf mistletoe plant greatly in- fluences the plant to crown ratio. Data after 1968 underestimate the amount of mistletoe because of plant immaturity on the relatively new wood (fig. 2) and are excluded from figure 4. The number of plants per unit of stem declined from 1950 to 1968 on trees in all crown classes. This decline was slow in the dominants, fairly rapid in the codom- inants, and somewhat variable in the intermediates. Only in the latter was there a suggestion that fewer plants per unit of stem resulted from stand release. If thin- ning had influenced the ratio, the slope of lines in figure 4 would have changed after thinning in 1957-58. These changes in plant to branch ratio indicate a con- sistent improvement in stand condition but are not particularly convincing evi- dence that the treated stands have overcome their dwarf mistletoe problem. Between 1945 and 1970 the number of dwarf mistleto
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