Multi-scale Drivers of Spatial Variation in Old-Growth Forest Carbon Density Disentangled with Lidar and an Individual-Based Landscape Model

Forest ecosystems are the most important terrestrial
carbon (C) storage globally, and presently mitigate
anthropogenic climate change by acting as a large
and persistent sink for atmosphericCO2. Yet, forest C
density varies greatly in space, both globally and at
stand and landscape levels. Understanding the
multi-scale drivers of this variation is a prerequisite
for robust and effective climate change mitigation in
ecosystem management. Here, we used airborne
light detection and ranging (Lidar) and a novel highresolution
simulation model of landscape dynamics
(iLand) to identify the drivers of variation in C
density for an old-growth forest landscape in Oregon, USA. With total ecosystem C in excess of
1 Gt ha-1 these ecosystems are among the most
C-rich globally. Our findings revealed considerable
spatial variability in stand-level C density across the
landscape. Notwithstanding the distinct environmental
gradients in our mountainous study area
only 55.3% of this variation was explained by
environmental drivers, with radiation and soil
physical properties having a stronger influence than
temperature and precipitation. The remaining variation
in C stockswas largely attributable to emerging
properties of stand dynamics (that is, stand structure
and composition). Not only were density- and sizerelated
indicators positively associated with C stocks
but also diversity in composition and structure,
documenting a close link between biodiversity and
ecosystem functioning. We conclude that the complexity
of old-growth forests contributes to their
sustained high C levels, a finding that is relevant to
managing forests for climate change mitigation.

Key words: forest carbon storage; old-growth
forests; climate change mitigation; ecosystem
structure and functioning; functional diversity;
forest stand dynamics; airborne Lidar; individualbased
modeling; iLand.