# Girdling increases branch capacity to rehydrate in Juniperus thurifera and drought hampers bimodal growth

## TL;DR

Girdling affects how Spanish juniper branches respond to drought and rainfall, influencing growth and carbohydrate storage.

## Contribution

The study reveals how girdling and drought influence bimodal growth and carbohydrate dynamics in Juniperus thurifera.

## Key findings

- Girdled branches swelled more after rain pulses, indicating higher osmotic activity.
- Drought in 2022 reduced radial growth and IADF formation in both girdled and non-girdled branches.
- Starch concentrations in leaves suggest osmolytes may derive from starch hydrolysis.

## Abstract

Disentangling how forests respond to aridification in terms of carbon storage and use, including bimodal growth, is critical to forecast their mitigation potential. Bimodality, characteristic of Mediterranean trees, refers to the potential to produce a second growth peak after the dry summer, often accompanied by intra-annual wood density fluctuations (IADF). To induce IADF formation, we performed a girdling experiment on Spanish juniper (Juniperus thurifera) branches in a semi-arid site, and monitored changes in branch diameter, and measured non-structural carbohydrate (NSC) concentrations in sapwood and leaves. IADFs were formed in response to wet conditions in late summer in girdled and non-girdled branches. After girdling, the extraordinarily dry 2022 growing season hampered branch radial increment and IADF production. Girdled branches swelled more than control branches after rain pulses. This suggests girdled branches were osmotically more active. Girdled branches presented higher starch leaf concentrations, suggesting that osmolytes could proceed from starch hydrolysis upstream. Girdling did neither trigger bimodal growth nor IADF formation during a very dry year.