Estimation of leaf area index and canopy openness in broad-leaved forest using an airborne laser scanner in comparison with high-resolution near-infrared digital photography

We estimated leaf area index (LAI) and canopy openness of broad-leaved forest using discrete return and small-footprint airborne laser scanner (ALS) data. We tested four ALS variables, including two newly proposed ones, using three echo types (first, last, and only) and three classes (ground, vegetation, and upper vegetation), and compared the accuracy by means of correlation and regression analysis with seven conventional vegetation indices derived from simultaneously acquired high-resolution near-infrared digital photographs. Among the ALS variables, the ratio of the “only-and-ground” pulse to “only” pulse (OGF) was the best estimator of both LAI (adjusted R ² = 0.797) and canopy openness (adjusted R ² = 0.832), followed by the ratio of the pulses that reached the ground to projected lasers (GF). Among the vegetation indices, the normalized differential vegetation index (NDVI) was the best estimator of both LAI (adjusted R ² = 0.791) and canopy openness (adjusted R ² = 0.764). Resampling analysis on ALS data to examine whether the estimation of LAI and canopy openness was possible with lower point densities revealed that GF maintained a high adjusted R ² until a fairly low density of about 0.226 points/m², while OGF performed marginally when the point density was reduced to about 1 point/m², the standard density of high-density products on the market as of February 2008. Consequently, the ALS variables proposed in the present study, GF and OGF, seemed to have great potential to estimate LAI and canopy openness of broad-leaved forest, with accuracy comparable to NDVI, from high-resolution near-infrared imagery.     

Response of female beetles to LIDAR derived topographic variables in Eastern boreal mixedwood forests (Coleoptera, Carabidae)

Biodiversity monitoring is increasingly being bolstered with high resolution data derived from remote sensing such as LIDAR (Light Detection and Ranging). We derived a series of topographical variables, including slope, azimuth, ground curvature and flow accumulation from LIDAR images and compared these to captures of female carabids in pitfall traps in Eastern boreal mixedwood forests. We developed a series of species-specific logistic models predicting the proportion of females for eight dominant species, including Agonum retractum, Calathus ingratus, Platynus decentis, Pterostichus adstrictus, Pterostichus coracinus, Pterostichus pensylvanicus, Sphaeroderus nitidicollis and Synuchus impunctatus. We used these models to test three hypotheses related to how the modest topography in boreal forests could influence the availability of microhabitats and possibly potential sites for oviposition and larval development. In general, topographic features such as north facing slopes and high flow accumulation were important predictors of the proportion of females. Models derived from larger scale topography, such as hillsides or small watersheds on the order of ¼-1 ha were better predictors of the proportion of females than were models derived from finer scale topography such as hummocks and small depressions. We conclude that topography likely influences the distribution of carabids based on hydrological mechanisms rather than factors related to temperature. We further suggest based on the scale of responses that these hydrological mechanisms may be linked to the attenuation of past disturbances by wildfire and the propensity of unburned forest patches and fire skips.     

Densities of Bornean orang‐utans (Pongo pygmaeus morio) in heavily degraded forest and oil palm plantations in Sabah,Borneo

The conversion of forest to agriculture continues to contribute to the loss and fragmentation of remaining orang‐utan habitat. There are still few published estimates of orang‐utan densities in these heavily modified agricultural areas to inform range‐wide population assessments and conservation strategies. In addition, little is known about what landscape features promote orang‐utan habitat use. Using indirect nest count methods, we implemented surveys and estimated population densities of the Northeast Bornean orang‐utan (Pongo pygmaeus morio) across the continuous logged forest and forest remnants in a recently salvage‐logged area and oil palm plantations in Sabah, Malaysian Borneo. We then assessed the influence of landscape features and forest structural metrics obtained from LiDAR data on estimates of orang‐utan density. Recent salvage logging appeared to have a little short‐term effect on orang‐utan density (2.35 ind/km ²), which remained similar to recovering logged forest nearby (2.32 ind/km ²). Orang‐utans were also present in remnant forest patches in oil palm plantations, but at significantly lower numbers (0.82 ind/km ²) than nearby logged forest and salvage‐logged areas. Densities were strongly influenced by variation in canopy height but were not associated with other potential covariates. Our findings suggest that orang‐utans currently exist, at least in the short‐term, within human‐modified landscapes, providing that remnant forest patches remain. We urge greater recognition of the role that these degraded habitats can have in supporting orang‐utan populations, and that future range‐wide analyses and conservation strategies better incorporate data from human‐modified landscapes.     

Airborne test of laser pump-and-probe technique for assessment of phytoplankton photochemical characteristics

Initial results of the airborne LIDAR measurement of photochemical quantum yield, Φ_Po, and functional absorption cross-section, σ_{PS II}, of Photosystem II (PS II) are reported. NASA's AOL3 LIDAR was modified to implement short-pulse pump-and-probe (SP-P&P) LIDAR measurement protocol. The prototype system is capable of measuring a pump-induced increase in probe-stimulated chlorophyll fluorescence, ΔF/F_sat, along with the acquisition of `conventional' LIDAR-fluorosensor products from an operational altitude of 150 m. The use of a PS II sub-saturating probe pulse increases the response signal but also results in excessive energy quenching (EEQ) affecting the ΔF/F_sat magnitude. The airborne data indicated up to a 3-fold EEQ-caused decline in ΔF/F_sat, and 2-fold variability in the EEQ rate constant over a spatial scale a few hundred kilometers. Therefore, continuous monitoring of EEQ parameters must be incorporated in the operational SP-P&P protocol to provide data correction for the EEQ effect. Simultaneous airborne LIDAR measurements of Φ_Po and σ_{PS II} with EEQ correction were shown to be feasible and optimal laser excitation parameters were determined. Strong daytime ΔF/F_sat decline under ambient light was found in the near-surface water layer over large aquatic areas. An example of SP-P&P LIDAR measurement of phytoplankton photochemical and fluorescent characteristics in the Chesapeake Bay mouth is presented. Prospects for future SP-P&P development and related problems are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.