Quantifying the missing link between forest albedo and productivity in the boreal zone
Albedo and fraction of absorbed photosynthetically active radiation (FAPAR) determine the shortwave radiation balance and productivity of forests. Currently, the physical link between forest albedo and productivity is poorly understood, yet it is crucial for designing optimal forest management strat...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-11-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/6015/2016/bg-13-6015-2016.pdf |
| Summary: | Albedo and fraction of absorbed photosynthetically active radiation (FAPAR)
determine the shortwave radiation balance and productivity of forests.
Currently, the physical link between forest albedo and productivity is poorly
understood, yet it is crucial for designing optimal forest management
strategies for mitigating climate change. We investigated the relationships
between boreal forest structure, albedo and FAPAR using a radiative transfer
model called Forest Reflectance and Transmittance model FRT and extensive forest inventory data sets ranging from southern
boreal forests to the northern tree line in Finland and Alaska
(<i>N</i> = 1086 plots). The forests in the study areas vary widely in
structure, species composition, and human interference, from intensively
managed in Finland to natural growth in Alaska. We show that FAPAR of tree
canopies (FAPAR<sub>CAN</sub>) and albedo are tightly linked in boreal
coniferous forests, but the relationship is weaker if the forest has
broadleaved admixture, or if canopies have low leaf area and the composition
of forest floor varies. Furthermore, the functional shape of the relationship
between albedo and FAPAR<sub>CAN</sub> depends on the angular distribution of
incoming solar irradiance. We also show that forest floor can contribute to
over 50 % of albedo or total ecosystem FAPAR. Based on our simulations,
forest albedos can vary notably across the biome. Because of larger
proportions of broadleaved trees, the studied plots in Alaska had higher
albedo (0.141–0.184) than those in Finland (0.136–0.171) even though the
albedo of pure coniferous forests was lower in Alaska. Our results reveal
that variation in solar angle will need to be accounted for when evaluating
climate effects of forest management in different latitudes. Furthermore,
increasing the proportion of broadleaved trees in coniferous forests is the
most important means of maximizing albedo without compromising productivity:
based on our findings the potential of controlling forest density (i.e.,
basal area) to increase albedo may be limited compared to the effect of
favoring broadleaved species. |
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| ISSN: | 1726-4170 1726-4189 |