ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

SILVICULTURE TREATMENT EFFECTS
Harvest-cutting and the fol lowup treatments substantially reduced the amount of
major shrub biomass, following the same pattern as that of shrub volume (fig. 15).
However, biomass recuperated more than its equivalent vol ume, wi th each uni t of shrub
volume weighing more after the shrubs had time to respond to their new environment of
increased light, water, and possibly nutrients. For example, if the biomass of maple
i n the mature forest averaged 1 000 kg/ha (892 pounds/acre) , the same volume of map1 e 4
years after cl earcutti ng and broadcast burni ng averaged 1 704 kg/hal~ounds/acre),
and 4 years after she1 terwood cutting and broadcast burning averaged 1 351 kg/ha (1,205
poundslacre) .
0 1 I I I
0 2 4
YEAR
Figure 15.--Shb biomass changes resuzting from siZvicuZture treaMents, in reZation
to preharvest vuZues in a Zarch/DougZas- fir forest.
Similar trends were noted for most other species. Some, such as Menziesk
ferruginea, more than doubled their biomass per unit of volume on the clearcut and
broadcast-burned treatment in relation to that of the mature forest. Some species such
as Ribes sp. tripled in biomass, and some such as Rosa quadrupled.
In general , clearcutting and group-selection cutting increased the ratio between
biomass and volume the most, followed by the shelterwood cutting. The ratio remained
the same during the same period in the mature forest.
Harvest cutting produced a decided shift in the leaf and stem composition of major
shrubs (fig. 16). Those shrubs such as maple, whose leaves accounted for very little
of the total biomass in the mature forest, showed a decided increase in the percentages
of leaves and small stems 4 years after harvesting. The same held true for those
shrubs such as ni nebark, whose leaves comprised a moderate percentage of biomass.
However, the release of thimbleberry resulted in a decrease in its percentage of leaves,
an increase in percentage of small stems, and almost no change in percentage of large
stems.