16 Feb 2023
 | 16 Feb 2023
Status: this preprint is currently under review for the journal BG.

Coordination of rooting, xylem, and stoma strategies explains the response of conifer forest stands to multi-year drought in the Southern Sierra Nevada of California

Junyan Ding, Polly Buotte, Roger Bales, Bradley Christoffersen, Rosie A. Fisher, Michael Goulden, Ryan Knox, Lara Kueppers, Jacquelyn Shuman, Chonggang Xu, and Charles D. Koven

Abstract. Extreme droughts are a major determinant of ecosystem disturbance, which impact plant communities and feed back to climate change through changes in plant functioning. However, the complex relationships between above- and belowground plant hydraulic traits, and their role in governing plant responses to drought, are not fully understood. In this study, we use a plant hydraulics model, FATES-Hydro, to investigate ecosystem responses to the 2012–2015 California drought, in comparison with observations, for a site in the southern Sierra Nevada that experienced widespread tree mortality during this drought.

We conduct a sensitivity analysis to explore how different plant water sourcing and hydraulic strategies lead to differential responses during normal and drought conditions.

The analysis shows that:

1) deep roots that sustain productivity through the dry season are needed for the model to capture observed seasonal cycles of ET and GPP in normal years, and that deep-rooted strategies are nonetheless subject to large reductions in ET and GPP when the deep soil reservoir is depleted during extreme droughts, in agreement with observations.

2) risky stomatal strategies lead to greater productivity during normal years as compared to safer stomatal control, but lead to high risk of xylem embolism during the 2012–2015 drought.

3) for a given stand density, the stomatal and xylem traits have a stronger impact on plant water status than on ecosystem level fluxes.

Our study reveals the importance of resolving plant water sourcing strategies in order to represent drought impacts on plants, and consequent feedbacks, in models.

Junyan Ding et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-16', Anonymous Referee #1, 16 Mar 2023
  • RC2: 'Comment on bg-2023-16: "Coordination of rooting, xylem, and stomatal strategies explains the response of conifer forest stands to multi-year drought in the Southern Sierra Nevada of California" by Ding et al.', Anonymous Referee #2, 29 Mar 2023

Junyan Ding et al.

Junyan Ding et al.


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Short summary
We used a vegetation model to investigate how the different combination of plant rooting depths, and sensitivity of the leaves and stems to drying lead to differential responses of a pine forest to drought conditions in California, USA. We found that rooting depths are the strongest control in that ecosystem. Deep roots allow trees to fully utilize the soil water during a normal year, but result in prolonged depletion of soil moisture during a severe drought, hence high tree mortality risk.