canopy foliage (see sec. 9.1). It influences nutrient
cycles by altering ecosystem nutrient pools and path-
ways and rates of nutrient fluxes (Pike 1978, Coxson
and Nadkarni 1995). This material reaches its great-
est abundance and diversity in tropical montane
cloud forests (Madison 1977). Trunk cover is highly
variable and is dominated by climbers, scramblers,
and bryophytes, with little associated organic matter.
Outer branches support a low biomass of herbaceaous
plants and very little accumulated humus. Inner branch
surfaces and branch junctions are where most of the
EM occurs. Understory vegetation and herbaceous
plants support mainly bryophytes and very little dead
EM. The live components of EM determine the over-
all structure of canopy communities and contribute
to nutrient exchange by exudation and uptake by epi-
phyte roots, mycorrhizae, and host tree canopy roots
(Nadkarni 1981). Humus and other dead EM compo-
nents are important in nutrient cycling because they
represent a large pool of carbon and nutrients that is
microbially active (Vance and Nadkarni 1990).
In the leeward forest study area, all trees >10 cm
DBH were stratified to a quartile EM cover class. There
were 78 trees/ha with an epiphyte cover class of 3 or
4 (>50% cover). A random subsample of trees >50 cm
DBH were selected for intensive sampling of inner
branch surface and branch junction EM. Trees were
rigged with mountain-climbing ropes following Nad-
karni (1988). We stratified EM into seven types, based
on its substrate: (1) surfaces of trunks, (2) surfaces of
outer branches, (3) surfaces of inner branches, (4) junc-
tions of branch major branches and trunks, (5) branch
tips, (6) understory vegetation (2-10 cm DBH), and (7)
groundcover (plants <3 m in height).
Destructive sampling of other trees (six 10-30 cm
DBH, six >30 cm) involved rigging and climbing to
the top of the trunk. To assess trunk EM, all EM within
a 20-cm cylindrat encircling the trunk was taken every
3 m. For branch and branch tip EM samples, a pro-
fessional arborist climbed into the crown and cut
and lowered three randomly chosen branches to the
ground. The branch was measured and divided into
thirds. A 20-cm swatch of EM was collected from each
third and taken to the lab for processing. The remain-
ing EM was removed and weighed in the field. Sub-
samples of the branch, including branch tips, were
collected for dry weight determination and analyzed
for nutrients. To extrapolate to a larger spatial scale,
we counted the number of branches and estimated
their lengths on each sample tree, and all the sur-
rounding trees. For the understory and groundcover
biomass components, we established subplots (9 and
1 m^2 , respectively) from which all the plant material
was taken and separated into epiphytes, leaves, and
stems. To assess EM composition, branch samples
were separated into seven constituents: higher vascu-
lar plant leaves, stems, ferns, roots, reproductive parts,
cryptogams (bryophytes and lichens), and dead or-
ganic matter, which consisted of crown humus and
detritus.9.2.1. Biomass and Characteristics of
Forest Components
Biomass and composition of terrestrially rooted material.
Estimates of aboveground biomass of trees were made
by multiplying tree-level estimates of component
biomass by the density of trees of each size class. Sap-
ling and forest biomass was calculated by multiply-
ing sample plots to a per-hectare basis. Total above-
ground terrestrially rooted biomass was 490.1 tons/ha,
of which 85% was trunk wood and 12% was branch
wood; other constituents made up only 3% (Table
9.6). The nonwoody constituents (foliage, repro-
ductive parts, and parasites) contain the most labile
(readily decomposed) portions, and constituted 9.3
tons/ha (2%) of the terrestrially rooted aboveground
biomass. Nutrients followed the same trends as bio-
mass; the component with the greatest pool of nutri-
ents was trunk wood, followed by branch wood, tree
foliage, groundcover, understory wood, reproductive
parts, and parasites (Table 9.6).Biomass and composition of canopy EM. The biomass
of EM on inner branch surfaces was 2450 g/m^2 (branch
surface area basis). The mean volume of EM at branch
junctions in the sample trees was 115.8 dmVjunction
(SE = 40.1). The biomass of EM in branch junctions
varied considerably, ranging between 125.1 g/dm^3
and 6.3 g.dm^3 (mean = 56.2 g/dm^3 ). The greatest pro-
portion of EM was located in the branch junctions
(68%). Branch tips and ground cover vegetation
had very small amounts (0.34 g/tip and 0.02 ton/ha,
respectively), equivalent to less than 0.004% and
0.0001% of the total EM biomass (Table 9.6). Esti-
mates of whole system EM biomass were extrapolated
by multiplying single-tree estimates by the mean
density of trees in the same epiphyte cover and size
classes. Total EM ecosystem biomass was 33.1 tons/
ha (Table 9.6)
In general, the amounts of nutrients contained in
EM components followed the pattern of biomass.
However, disproportionately larger amounts of cal-
cium were found in trunk epiphytes. The majority of
nutrients were found in branch junctions, followed
by branch mats and on trunks, with smaller amounts
on branch tips, the understory, and ground cover
(Table 9.6).
The overwhelming majority of biomass was in
dead organic matter (DOM). Roots and bryophytes321 Ecosystem Ecology and Forest Dynamics