title: A Changing Number of Alternative States in the Boreal Biome: Reproducibility Risks of Replacing Remote Sensing Products.
abstract: Publicly available remote sensing products have boosted science in many ways. The openness of these data sources suggests high reproducibility. However, as we show here, results may be specific to versions of the data products that can become unavailable as new versions are posted. We focus on remotely-sensed tree cover. Recent studies have used this public resource to detect multi-modality in tree cover in the tropical and boreal biomes. Such patterns suggest alternative stable states separated by critical tipping points. This has important implications for the potential response of these ecosystems to global climate change. For the boreal region, four distinct ecosystem states (i.e., treeless, sparse and dense woodland, and boreal forest) were previously identified by using the Collection 3 data of MODIS Vegetation Continuous Fields (VCF). Since then, the MODIS VCF product has been updated to Collection 5; and a Landsat VCF product of global tree cover at a fine spatial resolution of 30 meters has been developed. Here we compare these different remote-sensing products of tree cover to show that identification of alternative stable states in the boreal biome partly depends on the data source used. The updated MODIS data and the newer Landsat data consistently demonstrate three distinct modes around similar tree-cover values. Our analysis suggests that the boreal region has three modes: one sparsely vegetated state (treeless), one distinct 'savanna-like' state and one forest state, which could be alternative stable states. Our analysis illustrates that qualitative outcomes of studies may change fundamentally as new versions of remote sensing products are used. Scientific reproducibility thus requires that old versions remain publicly available.
authors.affiliation: School of Life Sciences, Nanjing University, Xianlin Road 163, Nanjing, 210023, P.R. China.|Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, The Netherlands.
authors.forename: Chi
authors.initials: C
authors.lastname: Xu
authors.affiliation: Resource Ecology Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, The Netherlands.
authors.forename: Milena
authors.initials: M
authors.lastname: Holmgren
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, The Netherlands.
authors.forename: Egbert H
authors.initials: EH
authors.lastname: Van Nes
authors.affiliation: Department of Physics, Federal University of Santa Catarina, P.O. Box 476, 88040-970, Florianópolis, Brazil.
authors.forename: Marina
authors.initials: M
authors.lastname: Hirota
authors.affiliation: Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska, 99775, United States of America.
authors.forename: F Stuart
authors.initials: FS
authors.lastname: Chapin
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, The Netherlands.
authors.forename: Marten
authors.initials: M
authors.lastname: Scheffer
mesh_terms: D057231:Climate Change; D017753:Ecosystem; D004784:Environmental Monitoring; D065928:Forests; D058998:Remote Sensing Technology; D015203:Reproducibility of Results; D012306:Risk; D014197:Trees