. Twenty-year growth of ponderosa pine saplings thinned to five spacings in central Oregon. Ponderosa pine Oregon; Forest thinning Oregon. Height Growth Both stand density and understory vegetation had significant effects on height growth throughout the 20 years of observation (table 1). Trees at the widest spacing are growing about feet per year where vegetation was con- trolled and only about foot at the narrowest spacing (fig. 10). Understory vegetation is having the greatest effect at the wider spacings, reducing growth as much as 15 to 20 percent during some periods. The reader sh
. Twenty-year growth of ponderosa pine saplings thinned to five spacings in central Oregon. Ponderosa pine Oregon; Forest thinning Oregon. Height Growth Both stand density and understory vegetation had significant effects on height growth throughout the 20 years of observation (table 1). Trees at the widest spacing are growing about feet per year where vegetation was con- trolled and only about foot at the narrowest spacing (fig. 10). Understory vegetation is having the greatest effect at the wider spacings, reducing growth as much as 15 to 20 percent during some periods. The reader should keep in mind that before thinning these trees were heavily suppressed by high density and overstory, and height growth was only a few inches per year. After thinning, roots needed time to grow and expand into space formerly occupied by those of cut trees. From figure 10 one might be tempted to conclude that trees in the two lowest densities (62 and 125 trees per acre) have reached maximum capacity for annual height growth. Reaching this growth rate capability apparently took about 12 years. Trees at higher densities may still be in- creasing in annual rate of growth, but additional time is needed to see if these denser spacings have reached maxi- mum rate or will ever reach the rate attained by wider-spaced trees. Because of the uneven pattern of past height growth (fig. 11), no attempt was made to project future height growth. Thus, volume growth could not be pro- jected an additonal 8 years. o> 0) ^ 4-1 5 2 _ (0 3 C c ra 0> O) (0 ra 0 u H5 o 1 2 3 4 5 12 4 5 Period 2 3 4-5- 1 2 3 4 5 3 4 jUnderstory vegetation left j Understory vegetation controlled i 1000 0) a 500 250 Trees per acre Spacing (feet) 125 62 Figure 10.—Periodic average annual height growth during five 4-year measurement periods. Increment is based on the average growth of individual trees living through each period. 38 36 34 32 30 1 28 H- — 26
Size: 1343px × 1861px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, bookleafnumber15
