Forest genetic resources

The Natural Resources Institute Finland (Luke) is responsible for the conservation of genetic resources in agriculture, forestry and fisheries. The purpose of conserving forest genetic resources is to maintain the genetic diversity of species and their local adaptations far into the future. Genetic diversity increases the potential of tree species to adapt to changing conditions, such as climate change.

The Finnish National Genetic Resources Programme for Agriculture, Forestry and Fishery, coordinated and executed by Luke, defines goals and plans for the management of genetic resources in agriculture, forestry and fisheries. The programme promotes the conservation and sustainable use of genetic resources and defines conservation measures for a total of 14 tree species.

In conserving forest genetic resources, the main focus is not on the preservation of individual genotypes, but on the conservation of genetic diversity and processes that maintain it.

The primary methods in forest genetic conservation are in situ and ex situ conservation. In situ conservation means the preservation of genetic resources in the original growth location. In practice, it means the establishment of gene reserve forests. This is how common and widely spread tree species are usually conserved. Ex situ conservation takes place outside the original growth location by planting tree collections or by storing seeds, pollen or cells. This usually applies to rare species. Luke is responsible both for the identification and selection of gene reserve forests and the establishment of genetic resource collections.

A gene reserve forest is an area in which the genetic pool of a specific tree species is preserved as diversely as possible in natural conditions in the original growth location. The more diverse the genetic pool of a species is, the better it can adapt to changing environmental conditions, such as climate change.

Finland has 44 gene reserve forests with a total surface area of roughly 7,200 hectares (2020). They are located in different climate zones so as to preserve as many different adaptations as possible.

The goal is to build a comprehensive network of gene reserve forests for Scots pine (Pinus silvestris) and Norway spruce (Picea abies), as well as downy (Betula pubescence) and silver birch (Belula pendula).

The most important requirement for a gene reserve forest is that the forest is natural, meaning that trees have grown from seeds of a local origin and have preferably regenerated naturally. Generally, forests are selected as reserves for a specific target species, but mixed tree species are also permitted. Reserves of wind-pollinated species, such as spruce, pine and birches, must be sufficiently extensive to ensure pollination inside a forest. The targeted surface area of a forest is 100 hectares. The forest may also be smaller if it can later be expanded by using seeds from the forest in question. Areas of a few hectares are also accepted as gene reserves for rarer temperate deciduous trees, such as European white oak (Quercus robur), common ash (Fraxinus excelsior), Norway maple (Acer platanoides), small-leaved linden (Tilia cordata), wych elm (Ulmus glabra) and European white elm (Ulmus leavis).

To ensure continuity, gene reserve forests should be constituted of different age cohorts. Natural regeneration is used whenever possible. If regeneration needs to be based on seeding or planting, seed and seedlings must originate from the same forest. Seed is stocked from forests should storms or forest fires occur and is used as reference material in forest tree breeding and in research. 

As a rule, gene reserve forests are managed according to normal silvicultural practices so that thinning and other fellings are carried out when necessary. Luke prepares their management plans together with landowners to ensures that management practices promote ample regeneration and maintains genetic diversity.

Owners of gene reserve forests have full ownership of their forests. They have allowed to dedicate their forest to the conservation of genetic resources free of charge, and they have made a long-term commitment to always using natural regeneration or seeds and seedlings originating from the same forest. Roughly three quarters (33) of all gene reserve forests are under state ownership and managed by Metsähallitus. Other owners are Oy Fiskars Ab, Finsilva Oyj, Tornator Oyj, UPM Metsä, one investment company and one private forest owner.

Ex situ conservation is necessary for rare tree species that only grow in small stands where the natural regeneration of the species is uncertain. For forest trees, the most important method in ex situ conservation is the establishment of tree collections for which individual trees are reproduced either by grafting or as seedlings and will eventually crossbreed and produce a new, diverse tree generation. Collections produce highly adaptable, genetically diverse seed that can be used in forest regeneration or landscaping.

Ex situ collections have been established for temperate deciduous trees, common juniper (Juniperus communis), mountain-ash (Sorbus aucuparia) and bird cherry (Prunus padus). The material has been collected from several (20–90) forests by selecting 5–10 trees from each stand so as to cover the natural distribution area of each species in Finland. Linden and elm collections have been established by means of grafting, common juniper collections from cuttings, and maple, ash, mountain-ash and oak collections from seedlings.

The trees selected for the collections of genetic resources are not selected for commercial traits, since the collections for each species should include a sample of the hereditary variation as random and comprehensive as possible.

Many tree species have natural special forms resulting from hereditary factors, such as golden Norway spruce and curly birch. These special forms are rare and, apart from curly birch, they are mainly used for decorative purposes. However, they are valuable expressions of diversity, which is why they have also been included in collections.