Tracking the Rhythms of the Forest with Lidar Phenology Monitoring
Today we are looking at an interesting application of lidar in forestry. Lidar is used in forestry for many applications, including wildfire risk (such as, detecting fire risk associated with forest structure from GEDI), calculating timber volume with lidar, and carbon accounting. Lidar’s precision and ability to penetrate forest canopies make it a versatile tool across a variety of forest management and research challenges.
Today’s focus is on a lesser-known but vitally important topic: phenology – the study of the timing of natural events in plants and animals, such as when trees leaf out in the spring or shed leaves in the fall. Lidar phenology monitoring allows researchers to study these seasonal changes with exceptional spatial and temporal detail. Understanding phenology is essential for modeling forest productivity, tracking responses to climate change, and managing tree health across landscapes.
A Breakthrough in Lidar Phenology Monitoring at SMEAR II
In a new study published in Agricultural and Forest Meteorology, researchers from the University of Helsinki and the Finnish Geospatial Institute used lidar to monitor individual trees’ phenological cycles with centimeter-level precision. The study took place at the SMEAR II research station in Hyytiälä, Southern Finland—an internationally recognized hub for long-term ecosystem research.
Rather than relying on aerial lidar or drone surveys, the team deployed a permanent laser scanning system (PLS) to monitor changes over time.
The LiPhe Station: Hourly 3D Scanning of Tree Phenology
Installed at a 30-meter height on a 35-meter observation tower, the LiDAR Phenological Station (LiPhe) used a Riegl VZ-2000i time-of-flight scanner (operating at 1550 nm) to collect hourly scans of a fixed forest scene. The scanner captured data with a fine angular resolution of 0.006°, resulting in 10 mm point spacing at 100 meters, and a scan frequency of 1200 kHz.
This high-frequency scanning approach allowed researchers to collect detailed structural data on the phenological and growth dynamics of silver birch trees from an above-canopy perspective—a unique setup that ensures continuity, accuracy, and non-invasive data collection.
What They Found: Trees Don’t Wake Up All at Once
The continuous lidar phenology monitoring revealed that trees in the same forest, and even the same species, do not leaf out or senesce in unison. The team found up to 12-day variation in spring leaf-out among individual silver birches. Light availability was a major driver of spring timing, while soil moisture levels influenced when trees began shedding leaves in autumn.
This level of insight highlights how local environmental conditions—such as shading or microtopography—can significantly affect a tree’s internal biological rhythms.
Why Lidar Phenology Monitoring Matters
The implications of this research go beyond academic curiosity. Monitoring phenological change is key to understanding how forests respond to climate stressors, managing biodiversity, and refining models of carbon dynamics. The use of a permanent lidar system like LiPhe opens the door to long-term, automated phenological datasets that are both spatially rich and temporally dense.
For practitioners and researchers, this study demonstrates the incredible potential of lidar phenology monitoring to capture the fine-scale dynamics that traditional field methods miss.
For more information, please visit the publication in Agricultural and Forest Meteorology.
Image credit: Morsdorf, F., et al. (2024). Monitoring spring and autumn phenology of individual silver birches with hourly terrestrial laser scanning. Agricultural and Forest Meteorology, 346, 110800. CC BY 4.0. Source: ScienceDirect
