Bazant, V. | Search bioRxiv

bioRxiv2026

Fast and Reliable: Evaluating Smartphone LiDAR App for Stem Diameter Measurement and Tree Mapping

Tree inventories require rapid, accurate measurements of stem diameter at breast height (DBH) and precise tree locations to support monitoring, planning, and informed decision-making. We evaluated a smartphone-based LiDAR app (SBLA), Forest Scanner, against (i) a diameter tape for DBH and (ii) a Vertex ultrasonic device for spatial coordinates. Across DBH of 725 trees, the LiDAR closely matched diameter tape measurements: discrepancies >5 cm occurred in 10.5% and > 10 cm in 3.5% of trees. Errors were concentrated in trees with smaller DBH, where occasional overestimation by SBLA arose from point-cloud misfitting. For medium and large trees, agreement was consistently high. Tree coordinates from SBLA and the ultrasonic device were broadly comparable at fine scales. Field efficiency was substantially improved: a 1,000 m2 plot with 70-80 trees required [~]2 hours using an ultrasonic device and diameter tape versus [~]20 minutes (one person) with SBLA, an [~]85-90% reduction in person-hours. Current limitations of SBLA are primarily software-related (stability, data handling, low-light performance). Overall, SBLA offers an efficient, auditable, and operationally relevant tool for tree inventories, with utility for rapidly updating DBH and spatial data used in management, planning, and asset databases.

ecology↗

bioRxiv2025

Elevational Shifts in Tropical Tree Leaf Traits: Interactions Between Soil, Climate, Light, and Phylogeny

Understanding how tropical trees respond to complex environmental gradients is essential for predicting forest resilience under climate change. We examined variation in key leaf traits, including specific leaf area (SLA), foliar nitrogen (N) and phosphorus (P), C:N and N:P ratios, and stable isotope composition ({delta}13C, {delta}15N), in 160 tree species along a 3,200-m elevational transect on Mount Cameroon. This gradient spans hyper-humid coastal rainforests to arid Afroalpine savannas, capturing sharp transitions in climate, soils, and forest structure. Leaf traits shifted nonlinearly with elevation, from acquisitive strategies at mid-elevations to conservative syndromes in lowlands and highlands. Mid-elevation forests ([~]1,000-1,500 m), characterized by moderate climate and canopy disturbance by elephants, supported nutrient-rich, high-SLA foliage. In contrast, high-elevation forests (>2,000 m) exhibited low SLA, high C:N, and enriched {delta}13C, consistent with stress tolerance under cold, dry, and fire-prone conditions. The strongest phosphorus limitation occurred in hyper-humid lowlands, where extreme rainfall (>12,000 mm/year) drives leaching losses. Foliar {delta}15N declined markedly with elevation (from +5{per thousand} to -5{per thousand}), indicating a shift from mineral N uptake and N-fixation in lowland Fabaceae to ecto- and ericoid mycorrhizal associations in montane Ericaceae. A bimodal {delta}15N pattern, with enrichment in both lowland and upper montane forests, reflects N-fixation under leaching and fire-driven N scarcity, respectively. Phylogenetic analyses showed that climate, soils, forest structure, and lineage jointly shaped trait-environment relationships. Traits related to {delta}13C, C:N, and {delta}15N exhibited strong phylogenetic signal, highlighting evolutionary constraints. These findings underscore the value of integrating functional traits, isotopes, and phylogeny to predict tropical forest responses to global change.

plant biology↗