title: Estimating and Analyzing Savannah Phenology with a Lagged Time Series Model.
abstract: Savannah regions are predicted to undergo changes in precipitation patterns according to current climate change projections. This change will affect leaf phenology, which controls net primary productivity. It is of importance to study this since savannahs play an important role in the global carbon cycle due to their areal coverage and can have an effect on the food security in regions that depend on subsistence farming. In this study we investigate how soil moisture, mean annual precipitation, and day length control savannah phenology by developing a lagged time series model. The model uses climate data for 15 flux tower sites across four continents, and normalized difference vegetation index from satellite to optimize a statistical phenological model. We show that all three variables can be used to estimate savannah phenology on a global scale. However, it was not possible to create a simplified savannah model that works equally well for all sites on the global scale without inclusion of more site specific parameters. The simplified model showed no bias towards tree cover or between continents and resulted in a cross-validated r2 of 0.6 and root mean squared error of 0.1. We therefore expect similar average results when applying the model to other savannah areas and further expect that it could be used to estimate the productivity of savannah regions.
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
authors.forename: Niklas
authors.initials: N
authors.lastname: Boke-Olén
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
authors.forename: Veiko
authors.initials: V
authors.lastname: Lehsten
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Ardö
authors.affiliation: School of Earth and Environment (SEE), The University of Western Australia, Crawley, Australia.
authors.forename: Jason
authors.initials: J
authors.lastname: Beringer
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Eklundh
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Holst
authors.affiliation: Centre for Ecosystem Studies, University of Wageningen, Wageningen, the Netherlands.
authors.forename: Elmar
authors.initials: E
authors.lastname: Veenendaal
authors.affiliation: Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Torbern
authors.initials: T
authors.lastname: Tagesson
mesh_terms: D057486:Carbon Cycle; D057231:Climate Change; D017753:Ecosystem; D065948:Grassland; D006801:Humans; D008954:Models, Biological; D018515:Plant Leaves / Q000254:growth & development* / Q000378:metabolism; D011891:Rain; D012621:Seasons