Appendix 7. Structural stage codes

Structural stage	Definition	Age criteriaa
1 Non-vegetated/ Sparse	Initial stages in primary or secondary succession. Little or no residual vegetation except for bryophytes and lichens. Less than 10% cover of vascular plants. This stage may be prolonged (50-100+ yr) where there is little or no soil development (bedrock, boulder fields).	<20 yr for normal forest succession. Up to 100+ yr for rocky or bouldery sites, and other severe sites.
1a Non-vegetated	Less than 5% total cover of vegetation.
1b Sparse	Less than 10% cover of vascular plants. Up to 100% cover of bryophytes and lichens. This stage may be prolonged (50-100+ yr) where there is no soil development (bedrock, boulder fields).
2 Herba	Early successional stage or disclimax/climax communities (e.g., avalanche tracks, wetlands and grasslands) dominated by herbaceous vegetation; some invading or residual shrubs and trees may be present. Tree cover less than 10%, shrub cover less than 25%, and herbaceous cover greater than 25%, or greater than or equal to 33% of total cover.	<20 yr for normal forest succession. Up to 100+ yr for disclimax/climax communities.
3 Shrub/Herbb	Early successional stage or disclimax/climax communities dominated by shrubby vegetation less than 10 m tall. Seedlings and advance regeneration may be abundant. Tree cover less than 10%, shrub cover greater than 25%, or greater than or equal to 33% of total cover.	<20 yr for normal forest succession. Up to 100+ yr for disclimax/climax communities.
3a Low Shrubc	Early successional stage or disclimax/climax communities dominated by shrubby vegetation less than 2 m tall. Seedlings and advance regeneration may be abundant. Tree cover less than 10%, shrub cover greater than 25% or greater than or equal to 33% of total cover.	<20 yr for normal forest succession. Up to 100+ yr for disclimax/climax communities.
3b Tall Shrubc	Early successional stage or disclimax/climax communities dominated by shrubby vegetation greater than 2 m tall but less than 10 m tall. Seedlings and advance regeneration may be abundant. Tree cover less than 10%, shrub cover greater than 25%, or greater than or equal to 50% of total cover.	<20 yr for normal forest succession. Up to 100+ yr for disclimax/climax communities.
4 Pole/Saplingd	Trees greater than 10 m tall, have overtopped shrub and herb layers and stands are typically dense; younger stands are vigorous, usually greater than 10-15 yr old; older pole-sapling stages, composed of dense, stagnated stands (up to 100 yr old) are also included in this stage. The pole-sapling stage persists until self-thinning and canopy differentiation becomes evident (often by 30 yr in vigorous stands).	20-40 yr for normal succession. Up to 100+ yr for dense (>2000 stems per ha) stagnant stands.
5 Young Forestd	Self-thinning has become evident and the forest canopy has begun differentiation into distinct layers (dominant, co-dominant and suppressed); vigorous growth and a more open stand than in the pole-sapling stage characterizes forest at this phase of development; this stage begins as early as age 30 and extends to 50-80 yr depending on tree species.	40-80 yr
6 Mature Forestd	Trees that were established after the last disturbance have matured and a second cycle of shade tolerant trees may have become established; understories become well developed as the canopy opens up.	80-140 yr for Subzone Group Ae 80-240 yr for subzone Group Be
7 Old Forestd	Old, structurally complex stands comprised mainly of climax tree species, although older seral remnants may still be present in the upper canopy; standing snags and rotting logs on the ground are typical and understories are patchy.	¬ 140 yr for Subzone Ae ¬ >250 yr for Subzone Group Be

a Age ranges reflect "normal" rates of succession on forested sites. When determining structural stage, stand structure should be emphasized rather than stand age; deciduous stands will generally be younger than coniferous stands belonging to the same structural stage.
b Stages 2 and 3 may represent disclimax or climax communities (e.g., avalanche tracks, wetlands) that may be much older than indicated here.
c Stage 3a and 3b may include very old krummholz less than 2 m tall and very old, low productivity stands (e.g., bog woodlands) less than 10 m tall. Stage 3 should be used for successional communities that will become forested at climax. Stages 2, 3a and 3b should be used for communities that are permanent herb, low shrub and tall shrub communities, respectively.
d Structural stages 4-7 will typically be estimated from forest inventory maps and aerial photography. In addition to structural stage designation actual age for forested units can be estimated and included as an attribute in the database if required.
e Group A includes the following subzones (which follow the Biodiversity Guidelines NDTs):

BWBSdk1, BWBSdk2, BWBSmw1, BWBSmw2, BWBSvk, BWBSwk1, BWBSwk2, BWBSwk3;
ESSFdc , ESSFdk, ESSFdv, ESSFxc;
ICHdk, ICHdw, ICHmk1, ICHmk2, ICHmv1, ICHmw3;
MSdc, MSdk, MSdm1, Msdm2, MSxk, MSxv;
SBPSdc, SBPSmc, SBPSmk, SBPSxc;
SBSdh1, SBSdh2, SBSdk, SBSdw1, SBSdw2, SBSdw3, SBSmc1, SBSmc2, SBSmc3, SBSmh, SBSmk1, SBSmk2, SBSmm, SBSmw, SBSwk1 (plateau), SBSwk3.
Group B includes all other subzones.
Appendix L of the Terrestrial Ecosystems Mapping Methodology lists all subzones in Group A and Group B.