Back to monitoring outcomes

Tree age

  • Biodiversity

  • Structure


Tree age provides an insight into the overall status of the forest ecosystem: seedling regeneration and establishment to maturity determines ongoing survival of the forest and senescent trees often support important specialist biodiversity (Gao et al. 2014, Rainey and Holmes 2023).

Numbers of large living trees are correlated with species richness of multiple taxa, from birds to fungi (Zeller et al. 2022). Highest species richness overall across 29 taxonomic groups was found in old forest stands in a study using National Forest Inventory plots in Germany (Storch et al. 2023).

Methodology summary

Tree age data can be collected at the same time as assessing Vegetation biomass, Vegetation structure, Seedling regeneration, and Tree diversity.

The UK National Forest Inventory (NFI) provides a standardised methodology to establish fixed area survey plots and record tree growth categories (Forestry Commission 2020). Young trees (seedlings and saplings), diameter at breast height (DBH) < 4 cm and mature trees, DBH > 4 cm, are recorded.

  • Forest is defined as having >20% canopy cover.
  • 0.01 ha plots (5.64m radius) are established, the number of plots is determined by the size of the forest area
  • Within each plot DBH is recorded for all mature trees (DBH > 4 cm)
  • Saplings (height > 50 cm, DBH < 4 cm) are recorded in a 2.52 m radius plot at the centre of each 0.01 ha plot
  • Seedlings (height < 50 cm, DBH < 4 cm) are recorded in a 1.78 m radius plot at the centre of each 0.01 ha plot • All dead stems with DBH > 4 cm are recorded in the 2.52 m radius plot at the centre of each 0.01 ha plot

The NFI Survey Manual provides the methodology:

  • How to allocate plots – Chapter 12 Plot Assessments
  • Recording mature trees – Chapter 13 Tree Assessment Procedures
  • Recording young trees – Chapter 15 Young Tree Assessments
  • Recording standing deadwood – Chapter 18 Decay Classes

A methodology for categorising trees by growth stage (dependent on species) is given in Appendix 2: Field Survey Methodology of the Caledonian Pinewood Recovery Project.

Metric threshold or direction of change

A healthy forest ecosystem will have a diverse age structure, with trees represented from seedlings through to senescent trees.

Technological innovations

LiDAR can measure 3D vegetation structure and cluster analysis of lidar-derived habitat variables can be used to classify vegetation structure into different classes (Guo et al. 2017, Bradbury 2005).


  • Forest


  • Community


  • Low


  • Tier 2

Technical expertise

  • Medium

Standardised methodology

  • Yes