Leaf traits and canopy structure together explain canopy functional diversity: an airborne remote sensing approach

Abstract

Plant functional diversity is strongly connected to photosynthetic carbon assimilation in terrestrial ecosystems. However, many of the plant functional traits that regulate photosynthetic capacity, including foliar nitrogen concentration and leaf mass per area, vary significantly between and within plant functional types and vertically through forest canopies, resulting in considerable landscape‐scale heterogeneity in three dimensions. Hyperspectral imagery has been used extensively to quantify functional traits across a range of ecosystems but is generally limited to providing information for top of canopy leaves only. On the other hand, lidar data can be used to retrieve the vertical structure of forest canopies. Because these data are rarely collected at the same time, there are unanswered questions about the effect of forest structure on the three ‐dimensional spatial patterns of functional traits across ecosystems. In the United States, the National Ecological Observatory Network's Airborne Observation Platform (NEON AOP) provides an opportunity to address this structure‐function relationship by collecting lidar and hyperspectral data together across a variety of ecoregions. With a fusion of hyperspectral and lidar data from the NEON AOP and field‐collected foliar trait data, we assessed the impacts of forest structure on spatial patterns of N. In addition, we examine the influence of abiotic gradients and management regimes on top‐of‐canopy percent N and total canopy N (i.e., the total amount of N [g/m2] within a forest canopy) at a NEON site consisting of a mosaic of open longleaf pine and dense broadleaf deciduous forests. Our resulting maps suggest that, in contrast to top of canopy values, total canopy N variation is dampened across this landscape resulting in relatively homogeneous spatial patterns. At the same time, we found that leaf functional diversity and canopy structural diversity showed distinct dendritic patterns related to the spatial distribution of plant functional types.

Unraveling Forest Complexity: Resource Use Efficiency, Disturbance, and the Structure‐Function Relationship

“…The ability of UAS LiDAR systems to capture three-dimensional profiles of stand structure is particularly useful in the mixed temperate forests of the upper Midwest USA, where once even-aged forests are undergoing a transition to more complex systems as they approach advanced stages of successional development following a long history of intensive disturbance (Bogdanovich et al, 2021;Frelich, 1995;Hardiman et al, 2011). In addition, three-dimensional profiles from LiDAR provide important information about the distribution of foliar traits that drive photosynthesis at the leaf level (Chlus et al, 2020;Kamoske et al, 2021). The impact of human management and disturbance on structure-function relationships varies depending on the severity, frequency, spatial scale, and intensity of the event (Ehbrecht et al, 2021;Ford & Keeton, 2017).…”

Poor relationships between NEON Airborne Observation Platform data and field‐based vegetation traits at a mesic grassland

“…2020, Kamoske et al. 2021), we focused on a different suite of traits that correspond directly to NEON’s products. Additionally, other NEON studies have leveraged greater variability in trait values across sites and biomes.…”

Towards mapping biodiversity from above: Can fusing lidar and hyperspectral remote sensing predict taxonomic, functional, and phylogenetic tree diversity in temperate forests?

“…We processed the atmospherically corrected hyperspectral imagery from the NEON AOP before analysis using our hypRspec R package on GitHub (Kamoske et al, 2020; http://github.com/ akamo ske/hypRspec). After removing all flight lines re-flown due to cloudiness, we visually identified noisy bands in the data (e.g., moisture and atmospheric absorption) and removed all wavelengths that were below 500 nm, between 1,350 and 1,450 nm, between 1,800 and 2,000 nm, and above 2,400 nm.…”