PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

kg./m 2 . Both tables show, however, that
numerous sources of variation in litter fal l
occur in lodgepole pine forests. Variatio n
within plots is evident (table 3) . Generally
needle fall is less variable from microplot to
microplot (CV from 10 to 18 percent except
in low density stand 1 .3) than other components
of the annual litter production .
Branches and female cones exhibit very high
spatial variability, and the latter is furthe r
enhanced (beyond the values of table 3 )
through activities of the common pine squirrel ,
Tam ias c i u r u s h udsonicus . Generally th e
percentages of needles, branches, etc . are
rather uniform within and between stands ,
but marked departures from mean percent -
ages are found in the low density stands 1 . 3
and 4.3 . These departures probably resul t
from the lessened sloughing of branches a t
lower portions of the bole . Thus, branches
comprised only 2 percent of the annual litte r
fall in stand 4 .3, but 18 percent in high
density stand 2 .2. The very high cone accumulation
in stand 1 .3 is partially explained by
fire thinning around 1900 which remove d
many smaller, noncone-bearing trees, and
partly by the chance distribution of collectio n
sites near prominent cone-bearing trees . The
mean annual litter fall at the bottom of tabl e
2 indicates that stands with 'least canopy mas s
(2 .2 and 4 .3) have lowest litter fall, and thos e
with greatest canopy mass (1 .3 and LH2) have
the highest litter fall . This relationship is no t
clear, however, when only a single year ' s
annual litter fall is considered .
In all stands, 1969 was the maximum litter
fall year. Nevertheless, year-to-year differences
are not consistent from stand to stand .
Thus, 1970 was the year of least litter production
in stand 2 .2 but not LH2 . Seasonal variations
are also significant. The inclusive perio d
from early June to late August gave 38 per -
cent of the total annual litter production i n
1969, but only about 26 percent of the total
from the same stands the following year .
While some materials such as branches may b e
shed somewhat uniformly through the year ,
others such as needles showed weak seasonal
peaks from June through October . In only
one year was there a conspicuous "peak sea -
son" of needle fall in late August and September;
in general, each stand was shedding
needles continuously throughout the year .
Biomass and Net Growth Increment s
The live components of the abovegroun d
pine crop are given in table 4. From the data
the coefficients, k l and k 2 , of allometric
equations of the form, W = k l D k 2 , were computed
by regression (W is biomass in kg and D
is d .b.h. in cm from columns of table 4) .
These allometric equations and the entire
population of d .b.h. values in each of plots
4.3, 1 .1, and LH2 were used to compute th e
stand biomass values of table 5 . This biomas s
and the mean increments of table 4 were use d
to compute the "new growth" values of tabl e
6. The mean values of table 2 and the appropriate
percentages of litter constituents i n
table 3 were multiplied to give the litter fal l
results of table 6. Stand LH2 in the P.
contorta/V. myrtillus habitat is clearly th e
most productive . In this stand the proportion
of green needles to living shoot parts is very
high in average to dominant tree sizes, as
shown in the last column of table 4 . By contrast
stand 1 .1 in the P. contorta/G. fremonti i
habitat (Moir 1969) has in general a lowe r
ratio of green needles to living shoot parts i n
average to dominant trees . Current year
fascicles comprise a greater end-of-season proportion
of the green canopy (25 to 31 per -
cent) in stand 1 .1 than in stand LH2 (17 to
27 percent) . Most trees in the latter stand retain
fascicles for several years longer than
stand 1 .1 . Stand 4 .3 occurs in the same habitat
as stand 1 .1 but was thinned in 1934-3 5
to about 2 .5 x 2.5 m stem spacing . The consequence
was to reduce light competition an d
encourage lateral branch growth . Surviving
stems retained a high proportion of needle s
(11 to 17 percent of the shoot weight), an d
abscission would not occur until about th e
5th year. By 1969 this stand had age
reached a "closed" canopy condition ; exces s
needles were abscissing as suggested by th e
high needle percentage of table 5 and by th e
negative net needle production in table 6 .
Further discussion of foliage characteristics of
these stands is given by Moir and Franci s
(1972) .
193