1st SAPFLUXNET WORKSHOP

10-12 November 2021

CAN BALASC - BARCELONA

Meeting the Potential of SAPFLUXNET to Ground-Truth Tree Water Use and Drought Responses in Models and Remote Sensing Products at Regional to Global Scales

OVERVIEW

Predicting forest water use and drought responses under global warming is one of the biggest challenges of Terrestrial Biosphere Models (TBMs). These models now represent tree water and carbon fluxes using trait-based optimality approaches, whereby trees maximise profit (carbon gain) given a cost imposed by the risk of losing the capacity to transport water (hydraulic risk). Optimality-based, hydraulically explicit TBMs provide a unifying theory potentially linking physiological responses, ecosystem function and demography and leverage a rapidly growing availability of plant hydraulic traits. Likewise, remote sensing products of plant water fluxes and pools show promise in describing transpiration, plant water content and physiological strategies across large spatial scales. Multi-site assessment of models and data products have typically used ecosystem fluxes, which may obscure plant physiological responses. The availability of global sap flow data in the SAPFLUXNET database now makes it possible to benchmark models and data products against tree-measured water fluxes worldwide. Combining SAPFLUXNET data with co-located measurements of leaf water potentials can reveal how plant hydraulic conductance responds to repeated droughts across species. Drought legacy effects pervade forest water content and flux dynamics worldwide, and a temporally-resolved tree perspective is necessary to disentangle the ecohydrological and physiological mechanisms driving these legacy effects as well the influences of drought intensity, duration, timing and sequence.

QUESTIONS

(Q1) How can we use sap flow and other data streams to quantify transpiration regulation in response to drought at multiple timescales, including the response to repeated seasonal droughts (i.e., tree water use resilience)?

(Q2) To what extent are key models and remote sensing products capable of reproducing the hydrometeorological controls on transpiration and the physiological resilience patterns observed globally, including the impact and recovery from drought events?

(Q3) Can whole plant hydraulic conductance, estimated from sap flow and water potential time series, bridge the gap between empirical transpiration responses to drought and modelling results?

 Q3a How are in situ estimates of plant hydraulic conductance related to large-scale estimates obtained from model inversion?

LIST OF ATTENDEES

Workshop Participants:

Alexandra Konings (AK), Stanford University, USA

Diego Miralles (DM), Ghent University, Belgium

Jacob Nelson (JN), Max-Planck Institute for Biogeochemistry Jena, Germany

Kimberly Novick (KN), Indiana University,USA

Lucy Rowland (LR), University of Exeter, UK (Remote)

Maurizio Mencuccini (MM), CREAF, Spain

Mirco Migliavacca (MiM), European Commission, Joint Research Centre (JRC), Ispra, Italy (Remote)

Paulo Bittencourt (PB), University of Exeter, UK

Rosie Fisher (RF), Univ. Paul Sabatier III. Toulouse, France. (Remote)

Samuli Junttila (SJ), University of Eastern Finland, Finland

Weijie Zhang (WZ), Max-Planck Institute for Biogeochemistry Jena, Germany

William R.L. Anderegg (BA), University of Utah, USA

Organising committee:

Brenda Fatecha (BF), CREAF

Jordi Martínez-Vilalta (JMV), CREAF/UAB

Miquel de Cáceres (MC), CREAF

Rafael Poyatos (RP), CREAF

Víctor Flo (VF), CREAF

Víctor Granda (VG), CREAF

FACILITIES

Can Balasc Biological Station

Biological station near Barcelona. Located in the Serra de Collserola Natural Park, one of the metropolitan area of Barcelona’s largest and best preserved forest areas, Can Balasc has laboratories and greenhouses, a guest house with rooms for visiting researchers, and 100 ha of forests and experimental sites for research purposes. It is ideal for evaluating the effects of global change on Mediterranean metropolitan ecosystems, which provide essential ecosystem services and are especially affected by drivers of global change (land use changes, wildfires and invasive species). Several field experiments that have been running for more than 15 years and are part of the Spanish and European Long Term Ecological Research Networks (LTER-Spain and LTER-Europe) have been taking place at Can Balasc since 2012.