6 research outputs found
Airborne laser scanning of natural forests in New Zealand reveals the influences of wind on forest carbon
Abstract
Background
Forests are a key component of the global carbon cycle, and research is needed
into the effects of human-driven and natural processes on their carbon pools.
Airborne laser scanning (ALS) produces detailed 3D maps of forest canopy structure
from which aboveground carbon density can be estimated. Working with a ALS dataset
collected over the 8049-km2 Wellington Region of New
Zealand we create maps of indigenous forest carbon and evaluate the influence of
wind by examining how carbon storage varies with aspect. Storms flowing from the
west are a common cause of disturbance in this region, and we hypothesised that
west-facing forests exposed to these winds would be shorter than those in
sheltered east-facing sites.
Methods
The aboveground carbon density of 31 forest inventory plots located within the
ALS survey region were used to develop estimation models relating carbon density
to ALS information. Power-law models using rasters of top-of-the-canopy height
were compared with models using tree-level information extracted from the ALS
dataset. A forest carbon map with spatial resolution of 25 m was generated from
ALS maps of forest height and the estimation models. The map was used to evaluate
the influences of wind on forests.
Results
Power-law models were slightly less accurate than tree-centric models (RMSE
35% vs 32%) but were selected for map generation for computational efficiency. The
carbon map comprised 4.5 million natural forest pixels within which canopy height
had been measured by ALS, providing an unprecedented dataset with which to examine
drivers of carbon density. Forests facing in the direction of westerly storms
stored less carbon, as hypothesised. They had much greater above-ground carbon
density for a given height than any of 14 tropical forests previously analysed by
the same approach, and had exceptionally high basal areas for their height. We
speculate that strong winds have kept forests short without impeding basal area
growth.
Conclusion
Simple estimation models based on top-of-the canopy height are almost as
accurate as state-of-the-art tree-centric approaches, which require more computing
power. High-resolution carbon maps produced by ALS provide powerful datasets for
evaluating the environmental drivers of forest structure, such as wind.
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