 |
| Titel |
Quantifying the missing link between albedo and productivity of boreal
forests |
| VerfasserIn |
Aarne Hovi, Jingjing Liang, Lauri Korhonen, Hideki Kobayashi, Miina Rautiainen |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129127
|
| Publikation (Nr.) |
 EGU/EGU2016-9198.pdf |
|
|
|
|
|
| Zusammenfassung |
| Albedo and fraction of absorbed photosynthetically active radiation (FAPAR) determine the
shortwave radiation balance and productivity of forests. Several studies have examined the
relation between forest structure and albedo in the boreal zone. Studies regarding FAPAR are
fewer and the relations between albedo and FAPAR are still poorly understood. To study
these relations we simulated shortwave black sky albedo and canopy FAPAR, using the FRT
forest reflectance model. We used two sets of field plots as input data. The plots were located
in Alaska, USA (N = 584) and in Finland (N = 506) between Northern latitudes of 60˚ and
68˚ , and they represent naturally grown and more intensively managed (regularly thinned)
forests, respectively. The simulations were carried out with sun zenith angles (SZA)
typical to the biome, ranging from 40˚ to 80˚ . The simulated albedos in coniferous
plots decreased with increasing tree height, whereas canopy FAPAR showed an
opposite trend. The albedo of broadleaved plots was notably higher than that of
coniferous plots. No species differences in canopy FAPAR were seen, except for pine
forests in Finland that showed lowest FAPAR among species. Albedo and canopy
FAPAR were negatively correlated (r ranged from -0.93 to -0.69) in coniferous plots.
The correlations were notably weaker (r ranged from -0.64 to 0.05) if plots with
broadleaved trees were included. To show the influence of forest management, we further
examined the response of albedo and FAPAR to forest density (basal area) and
fraction of broadleaved trees. Plots with low basal area showed high albedos but also
low canopy FAPAR. When comparing the sparse plots to dense ones, the relative
decrease in canopy FAPAR was larger than the relative increase in albedo. However, at
large SZAs the basal area could be lowered to approx. 20 m2 ha−1 before FAPAR
was notably reduced. Increasing the proportion of broadleaved trees from 0% to
100% increased the albedos to approximately twofold, with only minor changes in
canopy FAPAR. The effect of broadleaved trees was largest in dense forest. The
results indicate that increasing the proportion of broadleaved trees in coniferous
forests is the most important means to maximize forest albedo without compromising
productivity. Because of SZA dependencies, studies that take into account seasonal and
diurnal courses of SZA will further explain which forest management practices
should be favored in order to maximize the climate cooling effects of boreal forests. |
|
|
|
|
|
|