Epicormic shoots in plant architecture

epiphenomenon or general habit ?

Yves Caraglio, Eric Nicolini, Claude Edelin, Claire Atger, Tristan Charles-Dominique

Tree epicormics and related aspects Importance to ecology, forest management and tree care

September 14th - 17th, 2017 Nancy

AMAP joint research unit botAny and Modelling of Plant Architecture and vegetation

Epicormic branch => traumatic event ?

• Kozlowski, 1971 “Sudden and excessive exposure of trees often results in stimulation of dormant buds on the main stem or branches to produce epicormic shoots…”

• Traumatic reiteration: delayed reiteration

• Particular branching process ?

Plant Architecture

Bud activation during plant development – Immediate and/or delayed branching

• « Expected events » – Sequential branching – Contribution to 3D spatial occupancy

Plant Architecture

• Epicormic potential – Where ?

• Mainly waiting zones ! – Limit of growth unit – Base of delayed branches

» not on immediate branching – Accessory meristems

?

Plant Architecture

• Epicormic potential – When ?

• A great delay, » sometimes infinite…

– On old stem

• Unpredictable… – Lack of knowledge

» secondary growth, » hormonal signal, » carbohydrates content…

epicormics

height

ring width

Photo Sabatier

Nicolini, 1997

Particular Growth model • Activation of meristems after 4-7 years

– Prévost’s model • Paulownia imperialis

Nozeran’s model

Theobroma cacao (Malvaceae)

Orthotropic epicormic shoots

Epicormic branches expression

• During plant life cycle – Establishment growth

– Branching system bigger and more and more complex according time

– Epicormic buds at the basal part of successive stem

1

2 3

Rosa spp. (Rosaceae)

Epicormic branches expression

• During plant life cycle – Bush growth form

• Axis basitony – Epicormic buds – Life-long expression

15y 7y

3y

1y

Epicormic branches expression

• During plant life cycle – Scandent growth form

• Stack of bending axes – Epicormic buds mobilized on

external part of the curvature

Maclura cochinensis (Moraceae)

Picea excelsa (Pinaceae)

Platanus hybrida (Platanaceae)

Branch and crown die back

• Partial delayed reiteration – Spatial exploitation

Araucaria spp. (Araucariaceae)

Abies balsamea (Pinaceae)

Branch mortality

• Lateral axis senescence – Location – Origin

Epicormics from resting meristems of winter bud scars scale

Epicormics from resting meristem on lateral bud scar scales sequential branches epicormics

Senescence

• On old trees – sequential crown branching ceases… – branching still occurs through epicormics – we don’t predict when, but we know where

Pinus nigra (Pinaceae)

Chestnut tree

Pinus aristata

Tree resilience!

• Long life cycle,…eternity – A specific strategy – Low growth rate

– Avoiding individual mortality

• New individual, root autonomy

Photo Barthélémy

What should be considered as epicormics ?

• Do we consider only preventitious buds ? – Adventitious buds are considered in main papers – Epicormic bud : extension to all dormant buds (Meier,

Busgen)

• If we refer to « epicormic » term – Only localisation : on leafy axes…

• So what about root expression

– Accessory roots (monocot) – Root sucker…

Sequential Roots – Lateral roots

• Pericycle activation • Meristem initiation • Emergence or not… dormant root ?

Epicormic roots

• Jenik uses this term • What kind of reality ?

– New lateral root on old root • Traumatic response… • Included in plant architecture

– i.e. Platanus spp.

X

Dormant root ?

Photos Atger Epicormic roots

Origin of epicormic branches • Great diversity

– Actual groups • Monocot, Cycads

– Fossil groups • Progymnosperms

• Mecanism

– Bud survival

• Evolution – First expression – Radiation

Archaeopteris (Progymnospermes, Archaeopteridales) Dévonien Supérieur -365 MA

Epicormic trace Branch trace

Meyer-Berthaud et al. 2000

Cordyline sp.

Encephalarctos sp..

Epicormic branches for ever !

• In plant architecture – sequential branching (immediate or delayed) – differed branching (epicormics)

• All along plant life epicormic expression contribute to plant architecture – Not only a stress response – great contribution during senescence

• Branch level • Tree level

Research topics

• Epicormic life – How long can survive a meristem (some studies) – How can it survive (well documented on stem)

• Dynamics of such epicormic during plant development – How plant with immediate branch can react ? – Distribution of bud banks

• Proventitious , accessory, adventitious – Diversity and Ecological significance

Thank you for your attention