ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

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YEAR
Mature Forest
Clearcut
Shelterwood
Group Selection
Figure 5.--Effect of three siZvicuTtura2 harvest-cutting systems on understory shrub
voZwne 2 and 4 years after harvesting a Zarch/fir forest.
As shown in figure 5, the volumes measured at year two are ranked as one would
expect for the three harves t-cutting sys tems . The group-selection cutting areas, at 10
percent of their preharvest level, had been subjected to highly concentrated falling
and cable-skidding activities because of their small sizes (averaging < 0.3 ha [0.8
acre]). The same was true to a lesser extent on the clearcuts where activity was not
necessarily as confined, and where no internal trees, such as those in the shel terwood,
were left to protect the understory vegetation during logging. Conversely, shrubs
averaged 23 percent of their preharves t 1 eve1 on the shel terwoods . She1 terwoods retained
about one-half their original tree volume. As a result, there was not only less falling
and skidding, but reserve trees provided some protection from the logging activities.
Shrub volume recovered rapidly on a1 1 three harves t-cutting systems (fig. 5).
However, differences in recovery slopes follow expectations--the greater the release
from the overstory trees, the greater the percentage shrub recovery. Clearcuts were
recovering the fastest, fol 1 owed by the group selections and shel terwoods . As shown in
figure 5, shrub volume in clearcuts had returned from 14 percent of preharvest volume
at 2 years to 37 percent in 4 years. Shrubs on the group-selection cuttings went from
18 percent of preharvest volume at year two to 28 percent at year four. Although
shrubs on the shelterwoads had a higher base value at 2 years--23 percent of preharvest
volume--than those on the other cuttings, their recovery rate was slower. The mature
forest showed no detectable change in shrub volume during the 4-year study period.