Work group 3 meetings were attended by 21 participants

I. Clarification of basic concepts

A. STRESS: Input from Armando Lenz: plant physiological concepts of „stress“ concepts on plants. Stress is a destructive form of limitation, can be abrupt or gradual.

Changes in site conditions may also be abrupt (e.g. flooding with nutrient input) or gradual (e.g. atmospheric N-input or acidification).

Physiological processes in plant can be transient (e.g. photosynthesis) or cumulative (growth). How to define thresholds for stress? Suggestion: Concept of „fitness“ (see graph below).


B. Genetics: Georg v. Wuehlisch reported about results from provenance trials (COST Aktion E52). At present, statistical effects of genes are week and genetically not well determined. Concerning the research gaps on genetics relevant for our cost action, the following suggestions are made:

  • for WG1: include a button ‚autochthonous‘ versus ‚allochthonous‘ tree populations in the data base
  • if ‚allochthonous‘ holds true for samples collected, try to find out provenance or source of origin (if managed forest)
  • Study of stress effects on trees at the source of the provenances vs. Plantation plots
  • Application of genetic markers (development in forthcoming ca. 2-3 years for several species) for proper characterization of genotypes
  • Calculation of genetic distances in trees of a population
  • Studies of adaptive capacity of genotypes
  • Adaptation potential of certain traits in different genotypes to environmental stress

General suggestion: include other woody plants (shrubs) into the perspective (WG1)


II. Stress indicators and stressors

A. Environmental stressors during short-term extreme climatic events (that should be regarded in our COST action)

Direct factors

  • Drought (include salinity?): severity, frequency, duration, seasonality
  • Heat waves: severity, frequency, duration, seasonality (incl. winter warming)
  • Frost: severity, frequency, duration, seasonality, phenology, frost hardening
  • Floods & hypoxia: severity, frequency, duration, seasonality
  • Storms (influencing tree mortality)

Indirect factors

  • Biotic agents (insect outbreaks, browsing impact) & related parameters
  • Forest fires: severity, frequency, seasonality
  • Additional aspects to be mentioned are long-term environmental changes (e.g. climate warming, atmospheric CO2-increase, remote fertilization) that may alter plant responses to short-term extreme events. Beside the individual stress factors, combinations of several factors have to be taken into account.

B. Stress response parameters (that should be regarded the WG1 database design)

Plant level

  • Tree Mortality (or survival), defoliation (%), tree morphology, plant / branch architecture,
  • Sapwood (conductive) area, root system (fine root biomass, fine root density, specific root length, specific root surface), shoot/root ratio


  • Chemical composition (N, P, Ca-concentrations)

Productivity (separated in earlywood and latewood)

  • Tree-ring width, wood density (also mechanical and quality parameter)

Wood anatomy

  • vessel /tracheid size, density, grouping, traumatic resin ducts, false rings, frost rings, flood rings, white rings, light rings, IADFs (intra-annual wood density fluctuations)

Wood chemistry

  • Stable isotopes (δ13C, δ18O, δD, δ15N)
  • Element composition
  • Lignin amount and composition

C. Time resolution of studied parameter: decadal, pentadal, annual, seasonal, intra-annual

D. Other relevant metadata (for database entries)

  • Species name (subspecies, provenance, genotype, source, progeny/clone)
  • Tree age, social status, tree height, DBH, health status (dead, alive)
  • Location, elevation, topography, aspect, inclination, soil characteristics
  • Forest management information
  • Growth form (single stem, multi-stem)
  • Organ (stem, branch, etc.)
  • Are tree-ring data cross-datable with a reference chronology or not?

III. Next steps until Napels

1. Clarification of threshold debate from environmental parameter‘s perspective

How do we define “extreme events” in the context of climatic differences over Europe (may be including other regions where data are collected)? E.g. what is drought in context of boreal or Mediterranean climate? Do we see this from event frequencies (100 year event, 1000-year event), from statistical thresholds or from the effects visible in the plants? For clarification, consultancy of colleagues (e.g. van der Schrier, local climatologists)

2. Organisation of review papers to summarize the state of the art and to identify research gaps

  • General review of palaeoclimatic stress indicators in wood (e.g. Progress in Physical Geography, Miklós Kázmér)
  • Review of anatomical stress indicators in woody plants (Hans Beeckman)
  • Subgroup on hydraulic failure / tree mortality (Andreas Bolte)