Abstract. We present an exploratory study examining the use of airborne
remote-sensing observations to detect ecological responses to elevated
CO2 emissions from active volcanic systems. To evaluate these
ecosystem responses, existing spectroscopic, thermal, and lidar data acquired
over forest ecosystems on Mammoth Mountain volcano, California, were
exploited, along with in situ measurements of persistent volcanic soil
CO2 fluxes. The elevated CO2 response was used to
statistically model ecosystem structure, composition, and function, evaluated
via data products including biomass, plant foliar traits and vegetation
indices, and evapotranspiration (ET). Using regression ensemble models, we
found that soil CO2 flux was a significant predictor for ecological
variables, including canopy greenness (normalized vegetation difference
index, NDVI), canopy nitrogen, ET, and biomass. With increasing CO2,
we found a decrease in ET and an increase in canopy nitrogen, both consistent
with theory, suggesting more water- and nutrient-use-efficient canopies.
However, we also observed a decrease in NDVI with increasing CO2 (a
mean NDVI of 0.27 at 200 g m−2 d−1 CO2 reduced to a mean
NDVI of 0.10 at 800 g m−2 d−1 CO2). This is inconsistent
with theory though consistent with increased efficiency of fewer leaves. We
found a decrease in above-ground biomass with increasing CO2, also
inconsistent with theory, but we did also find a decrease in biomass
variance, pointing to a long-term homogenization of structure with elevated
CO2. Additionally, the relationships between ecological variables
changed with elevated CO2, suggesting a shift in coupling/decoupling
among ecosystem structure, composition, and function synergies. For example,
ET and biomass were significantly correlated for areas without elevated
CO2 flux but decoupled with elevated CO2 flux. This study
demonstrates that (a) volcanic systems show great potential as a means to
study the properties of ecosystems and their responses to elevated
CO2 emissions and (b) these ecosystem responses are measurable using a
suite of airborne remotely sensed data.
Effects of elevated CO2 on fine root biomass are reduced by aridity but enhanced by soil nitrogen: A global assessment