ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

In the lower clearcut (block 13), dispersal of sound seed from 1974 through
1977 decreased rapidly for a distance of 300 feet (91 m) upslope from the lower
timber edge, then decreased slowly to 500 feet (153 m) from the bottom (about 100
feet, 30 m, below the up er timber edge) (fig. 6). Much less seed fell within the
upper clearcut (block 23 7 , but it followed a similar, though less distinct, pattern
(fig. 6). This pattern indicated most seed was dispersed by thermal winds with
upslope motion--the same as has been recorded on other clearcuts at Corarn (Shearer
1959). However, in 1976, seed was dispersed by erratic winds associated with a dry,
cold front in October that interacted with the upslope winds, An average of 146,000
and 17,000 sound seed per acre (361,000 and 42,000 per hectare) fell within the
lower and upper clearcuts from the 1974, 1975, and 1976 seed crops. This ranged
from an average of 396,000 and 26,000 sound seeds per acre (979,000 and 64,000 per
hectare) along the bottom row of seed traps, to 51,000 and 14,000 sound seeds per
acre (126,000 and 35,000 per hectare) along the top row of seed traps within the two
clearcuts. An estimate of variation in total sound-seed dispersed over the lower
clearcut (block 13) through three seed years can be seen by the iso-seed lines in a
map of the clearcut (fig. 7).
Bottom
Timber
Edge
DISTANCE FROM BOTTOM TIMBER EDGE (FT)
Figure 7. --DispersaZ of sound seed
into the Zower cZearcut (Block 131,
l974-lg77, Corn EqerimentaZ Forest.
Dashed Zines indicate iso-seed Zines
separating riders fthousandsl of
sound seeds, Dots represent pema-
nen-b sample poin-bs where seed traps
were Zocated.
Upper
Timber
Edge
Figure 6. --Average number of sound
seeds f~housands) dispersed {nto
two cZearcut blocks from 1974-1977,
from bot-tom to top, Coram EqerimentaZ
Forest.