Document Type

Article

Publication Date

2024

DOI

10.1002/ecs2.4762

Publication Title

Ecosphere

Volume

15

Issue

2

Pages

e4762 (1-16)

Abstract

Savannas are water-limited ecosystems characterized by two dominant plant types: trees and an understory primarily made up grass. Different phenology and root structures of these plant types complicate how savanna primary productivity responds to changes in water availability. We tested the hypothesis that productivity in savannas is controlled by the temporal and vertical distribution of soil water content (SWC) and differences in growing season length of understory and tree plant functional types. To quantify the relationship between tree, understory, and savanna-wide phenology and productivity, we used PhenoCam and satellite observations surrounding an eddy covariance tower at a semiarid savanna site in Arizona, USA. We distinguished between SWC across two different depth intervals (shallow, <0–30 cm and deep, >30–100 cm). We found that tree greenness increased with SWC at both depths, while understory greenness was only sensitive to the shallower SWC measurements. Onset of ecosystem dormancy, estimated from satellite observations close to the eddy covariance tower, explained more variability in annual gross primary productivity (GPP) than in other phenometrics. Higher SWC led to an extended growing season, caused by delayed dormancy in trees, but the understory showed no evidence of delayed dormancy in wetter periods. We infer that the timing of ecosystem scale dormancy, driven by trees, is important in understanding changes in a savanna's GPP. These findings highlight the important effects of rainfall during the winter. These findings suggest that savanna GPP is conditional on different responses to moisture availability in each of the dominant vegetation components.

Rights

© 2024 The Authors.

This is an open access article under the terms of the Creative Commons Attribution 4.0 International License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Data Availability

Article States: "MODIS data for this research were collected from Google Earth Engine (GEE) and filtered between years 2004 and 2020; these data were created by Schaaf and Wang (2015) (https://doi.org/10.5067/MODIS/MCD43A4.006). PhenoCam imagery was retrieved from the PhenoCam Network (https://phenocam.nau.edu/webcam/) at site “srm,” daily (when possible from 2015 to 2020), between 10:00 AM and 2:00 PM local time. Flux tower data (including ancillary meteorological and soil moisture data) can be found at Ameriflux (https://ameriflux.lbl.gov/sites/site-search/#all_metadata=US-SRM). The flux tower site was “US-SRM,” 30-min gap-filled and partitioned, from 2004 to 2020. While the code is not novel, scripts (both R and GEE) and processed datasets used to make the figures and tables (Steiner, 2023) are available from Zenodo: https://doi.org/10.5281/zenodo.10136688."

Original Publication Citation

Steiner, B., Scott, R. L., Hu, J., MacBean, N., Richardson, A., & Moore, D. J. P. (2024). Using phenology to unravel differential soil water use and productivity in a semiarid savanna. Ecosphere, 15(2), 1-16, Article e4762. https://doi.org/10.1002/ecs2.4762

ORCID

0000-0002-4403-7687 (Steiner)

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