2.2.2 Microclimate and microhabitat structure
The air temperature (˚C) and relative humidity (%) were measured at 0.5
h intervals over 24 hours using Hobo Pro RH/Temperature Data Logger
(Onset Computer Corporation, Pocassest, MA, USA) during our sampling
period. Data loggers were placed at 3 m intervals along each vertical
transect, starting 1 m above the ground. At each sampling point, the
photosynthetic photon flux density (PPFD) was recorded using a handheld
light meter (Quantum Lightmeter, Spectrum Technologies, Plainfield, 1L,
USA), and was further normalized by dividing by maximum light value
within each vertical transect to account for between-day variation in
lighting; the intent was to identify the relative (not absolute) light
environment of the forest canopy (Dial et al 2006). As microclimate was
only measured over a single 24-hour period for each transect, the
dataset does not capture daily microclimate variation at any single
vertical transect, but rather is a reflection of the spatial variation
in microclimate across the vertical plane sampled. Although we measured
microclimate over a relatively short time, the daily variation and
vertical pattern in air temperature and relative humidity presented was
consistent with microclimate patterns from a nearby lowland primary
forest site over a longer time period (128 consecutive days measure in
Maliau Basin Conservation Area (4˚49’N, 116˚54’E), Hardwick et al.
2015).
We estimated one-sided total leaf area between sampling trays as a
measure of microhabitat structure at different sampling points for
transects 1 to 6. The leaf area within a sampling interval was
calculated by multiplying the number of leaf intersections by the size
of the base area of the interval which was 1 m2 (the
area of the sample tray). We then used these data to estimate leaf area
index (LAI) over vertical intervals (sampling methods described in Dial
et al. 2004, 2006, and 2011; estimation methods in Dial et al. 2006 and
2011). Conceptually, LAI refers to the number of leaf layers above the
ground surface that would be pierced by a vertical line. For example, if
LAI = 7, then there are, on average seven leaf layers above a random
point on the ground within that height range; or 7 m2of leaf area per m2 of ground surface. We assumed
(following MacArthur and Horn 1969) that at any sample point in the
canopy located at height z above the ground, the foliage density
was approximately equal in all directions. Following this assumption at
each height z , we systematically measured horizontal distances
(di ) with a laser range finder to the nearest
canopy element (foliage and stems) in 12 uniformly distributed azimuths
every 2 m vertically from the ground to the height of the horizontal
traverse line supporting the vertical transect. Using the n ≤ 12
distances to foliage at each sample point, we found the mean distance
(\(\overset{\overline{}}{d}\)) to foliage, doubled the mean (assuming
that the observer was on average midway between foliage elements), then
inverted it to find leaf intersections per vertical meter at heightz as LAIz = 1/(2\(\overset{\overline{}}{d}\)). By
multiplying the LAIz by collection area
(1m2) we estimated the leaf area sampled within the
interval.
Data analysesAll statistical analyses were conducted in R version 4.0.0 (R Core
Team, 2013)