title: Estimating the onset of spring from a complex phenology database: trade-offs across geographic scales.
abstract: Phenology is an important indicator of ecological response to climate change. Yet, phenological responses are highly variable among species and biogeographic regions. Recent monitoring initiatives have generated large phenological datasets comprised of observations from both professionals and volunteers. Because the observation frequency is often variable, there is uncertainty associated with estimating the timing of phenological activity. "Status monitoring" is an approach that focuses on recording observations throughout the full development of life cycle stages rather than only first dates in order to quantify uncertainty in generating phenological metrics, such as onset dates or duration. However, methods for using status data and calculating phenological metrics are not standardized. To understand how data selection criteria affect onset estimates of springtime leaf-out, we used status-based monitoring data curated by the USA National Phenology Network for 11 deciduous tree species in the eastern USA between 2009 and 2013. We asked, (1) How are estimates of the date of leaf-out onset, at the site and regional levels, influenced by different data selection criteria and methods for calculating onset, and (2) at the regional level, how does the timing of leaf-out relate to springtime minimum temperatures across latitudes and species? Results indicate that, to answer research questions at site to landscape levels, data users may need to apply more restrictive data selection criteria to increase confidence in calculating phenological metrics. However, when answering questions at the regional level, such as when investigating spatiotemporal patterns across a latitudinal gradient, there is low risk of acquiring erroneous results by maximizing sample size when using status-derived phenological data.
authors.affiliation: National Coordinating Office, USA National Phenology Network, Tucson, AZ, 85719, USA. katgerst@email.arizona.edu.|School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85719, USA. katgerst@email.arizona.edu.
authors.forename: Katharine L
authors.initials: KL
authors.lastname: Gerst
authors.affiliation: National Coordinating Office, USA National Phenology Network, Tucson, AZ, 85719, USA.|School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85719, USA.|Natural Sciences Department, Oregon Institute of Technology, Klamath Falls, OR, 97601, USA.
authors.forename: Jherime L
authors.initials: JL
authors.lastname: Kellermann
authors.affiliation: National Coordinating Office, USA National Phenology Network, Tucson, AZ, 85719, USA.|School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85719, USA.|Southwest Climate Science Center, U.S. Geological Survey, Tucson, AZ, 85719, USA.
authors.forename: Carolyn A F
authors.initials: CA
authors.lastname: Enquist
authors.affiliation: National Coordinating Office, USA National Phenology Network, Tucson, AZ, 85719, USA.|School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85719, USA.
authors.forename: Alyssa H
authors.initials: AH
authors.lastname: Rosemartin
authors.affiliation: National Coordinating Office, USA National Phenology Network, Tucson, AZ, 85719, USA.|School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85719, USA.
authors.forename: Ellen G
authors.initials: EG
authors.lastname: Denny
mesh_terms: D016208:Databases, Factual; D005843:Geography; D016014:Linear Models; D019684:Magnoliopsida / Q000254:growth & development; D018515:Plant Leaves / Q000254:growth & development; D012107:Research Design; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000254:growth & development*; D014481:United States
keywords: Data selection; Leaf-out; Onset; Phenological metrics; Phenology; Sampling frequency