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)