New maps provide information on forest age and productivity

The maps have been created using digital methods and are based on two separate national airborne laser scanning campaigns conducted by the Swedish Mapping, Cadastral and Land Registration Authority (Lantmäteriet), combined with field plots containing measured tree attributes from the Swedish National Forest Inventory (Riksskogstaxeringen) at SLU.

The maps provide comprehensive, objective, and comparable information on forest conditions across Sweden and are openly available through the Swedish Forest Agency (Skogsstyrelsen). 

Long-awaited data for forest stakeholders 

Accurate and up-to-date information on forest age and productivity is essential for planning silvicultural operations and for forecasting forest condition and development over time.

“Many stakeholders in the forest sector have been requesting this for a long time, and it is gratifying that the maps are now available for the whole of Sweden,” says Jörgen Wallerman, who is responsible for the production of forest geodata at SLU. 

Site index, which describes forest productivity, influences the value of forest land, the choice of tree species, the timing and prioritization of forest management activities, and is also used as a statutory threshold for distinguishing between productive and unproductive forest land. 

The site index (SIS) maps make it easier to identify variation and gradients within forest stands and are useful for deriving information about forest land that has not been visited in the field. 

Forest stand age is a key variable for planning both forestry and conservation activities. The map performs well as a basis for field inventory and planning but should not be used to estimate forest area. 

The stand age map performs well for forests up to approximately 80 years of age, but it underestimates the age of older forests. This underestimation increases substantially with stand age, making age estimates for older forests uncertain. 

“The mapping of stand age is based on how much trees have grown between two different laser scanning campaigns. This makes it difficult to obtain reliable estimates in older forests where height growth has largely ceased,” says Mats Nilsson of SLU, who led the development of the models underlying the maps together with Alex Appiah Mensah. 

Tree species information needed

The stand age maps are available for five different tree-species categories, while the site index maps are available for Scots pine and Norway spruce. Additional information on species composition is required to select the appropriate map. 
Private forest owners and forestry companies can use tree-species information from forest management plans or stand registers. Other users can obtain species information from the National Land Cover Database (NMD), produced by the Swedish Environmental Protection Agency (Naturvårdsverket).

“Because Sweden is repeatedly scanned with airborne laser technology, we not only obtain an up-to-date picture of the forest but can also observe how it changes over time. This enables us to develop new types of forest information. The new maps of age and site index are excellent examples of this,” says Liselott Nilsson, Project Manager for Forest Geodata at the Swedish Forest Agency. 

Contacts

Jörgen Wallerman, SLU 
Mats Nilsson, SLU 
Alex Appiah Mensah, SLU 
Liselott Nilsson, Skogsstyrelsen