ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Dispersal of sound seed on the upper shelterwood area (block 21) was extremely
variable from 1974 - 1977, averaging 160,000 seeds per acre (395,000 per hectare),
but ranging from 8,000 to 550,000 seeds per acre (20,000 to 1,359,000 per hectare)
at the 20 sampling points. Heaviest seedfall (averaging 204,000 sound seeds per
acre, or 504,000 per hectare) occurred on the south half of the area. An average of
117,000 sound seeds per acre (289,000 per hectare) fell on the north ha1 f of the
area. Because the heavier seedfall in 1974 was on the area that was prescribed
burned in September 1975, many of the seedlings that germinated in the spring of
1975 were killed by the fire.
During the period September 23 - October 17, 1974, seed dispersal followed a
characteristic pattern on the study units. Greatest seedfall occurred during the
windy portions of the day (fig. 8).
NOON
HOUR (M. 5. T. I
Figure 8.--Average number of seed caught per hour in four seed coZZectors
and average uind veZocity fm.p. h, ) by hour of day, Corm ExperimentaZ
Forest. CoZZections of seed were made during 20 days of the period
September 23 through October 17, 1974; wind measurements were taken
each day of the period.
Temperature, humidity and probably other factors influenced the amount of seed
dispersed. Figure 8 shows averages only; periods of high seedfall usually were
associated with ups1 ope (easterly) winds of greater than average el oci ty, lower
than average humidity and warmer than average temperature, Because seed counts were
not made during the hours of 1600 through 0700, an average of overnight seedfall is
shown in figure 8. Seedfall probably increased during the hours of 2000 through
2200, instead of remaining constant as shown in figure 8.
Seed Loss
The amount of seed eaten or otherwise removed from the seedbed between the time
of seedfall in 1974 and germination in May 1975 was estimated by counting the seed
in seed traps and in adjacent duff samples at the time of emination in the spring.
The data show that only about 9 percent of the sound seed 9 mostly western larch)
dispersed in 1974 was available for germination in May 1975; the amounts ranged from
3 percent on clearcuts to 16 percent in uncut timber.