Tracking tree demography and forest dynamics at scale using remote sensing

Area of Science:

• Ecology
• Forest Science
• Remote Sensing

Background:

• Understanding tree demography is crucial for ecosystem dynamics.
• Characterizing large-scale tree population processes is challenging due to slow growth and vast areas.

Purpose of the Study:

• To track individual tree height growth, crown expansion, and mortality over nine years.
• To investigate the influence of tree size, competition, and topography on demographic rates.
• To assess the carbon sequestration potential of old-growth woodlands.

Main Methods:

• Utilized repeat airborne laser scanning (ALS) data over 25 km² of semi-arid woodland.
• Monitored 42,213 individual trees to quantify growth and survival.
• Analyzed spatial patterns in relation to topographic wetness.

Main Results:

• Demographic rates were constrained by tree size, competition, and topography.
• Trees shifted from height growth to crown expansion with increasing size; mortality risk decreased with size.
• Tree growth and survival increased with topographic wetness, creating spatially structured vegetation patterns.

Conclusions:

• Old-growth woodlands in Western Australia function as a net carbon sink, with biomass gains exceeding mortality losses.
• Topographic wetness is a key driver of spatial patterns in tree demography.
• Airborne laser scanning provides a scalable method for monitoring tree demography in complex ecosystems.