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Hybrid larch production in Iceland – in search for the optimal provenances and seed sources

Date: 2018.03.21

In Iceland, with practically no forests until recently and only one native forest-forming tree species, obtaining seed of the right species and provenances has long been and still is the most important issue affecting progress in forestry.

The one native forest-forming tree, a species complex of birch, is not productive and it sequesters much less carbon than forests of larger species. Emphasis has therefor been on finding exotic species that are adapted to the climate and soils of Iceland, which can also be economically productive.

But even more important than finding a promising species, is locating the best provenances and available seed sources.

Establishment of the hybrid larch seed production program
Provenance trails are used to indicate which exotic seed sources would be best. Most of the trees planted however end up being of the best available seed source, not the best possible seed source. To address this problem, breeding programmes are ongoing and seed orchards have established in Iceland as in most other countries with organised forestry.

One that is particularly worth mentioning is an accelerated breeding and seed production programme for hybrid larch.

It started in 1993 with the aim of breeding Siberian larch (Larix sibirica / Larix sukaczewii) to be better adapted to Icelandic conditions. Included in the original selections was a clone of European larch, and controlled crosses were made between that clone and several Siberian larch clones. Progeny trials soon revealed that the hybrid outgrew all Siberian larch families, especially in volume, and had much better form than European larch generally shows in Iceland. The advantage of the hybrid over both parental species in growth and adaptation to Icelandic conditions has since become increasingly obvious over the years. Since the mid-1990s, the climate has been warming, which in Iceland mostly means milder winters, exactly the climatic factor that Siberian larch has limited adaptation to deal with.

Hrymur, the giant from the east
The decision was made in 2006 to change direction in larch breeding in Iceland. Emphasis was placed on producing the European x Siberian larch hybrid using parents selected in Iceland. The hybrid was given the name Hrymur, the name of a giant who comes from the east during Ragnarrök according to Völuspá (part of the Poetic Edda).

The greenhouse built for use in tree breeding was reassigned to house an indoor seed production orchard.

Having an indoor seed orchard addresses several problems in production of hybrid seed:

flower induction is more effective,
low pollen viability outdoors due to variable winter weather is not a problem,
flowering of the two species can be synchronised by heating the greenhouse,
no pollen comes from other sources since flowering takes place earlier than outdoors,
crosses are made by hand so that pollen of one species pollinates the other,
good seed development and ripening.

Several issues have been solved but several remain, and things can always be improved. The main goals now are to increase seed production and improve germination. The seed crop in 2017 was enough to produce well over 100,000 seedlings, but the aim is for the greenhouse to produce 5-10 times that much every other year in the near future. When that goal is reached, it will be time to build more greenhouses.

Text: Throstur Eysteinsson, General Manager at the Icelandic Forest Service

The next NordGen Forest thematic day will take place in Akureyri, Iceland on 11 April 2018. The theme of the day is “Seed supply and tree breeding”, including a presentation about the hybrid larch seed production and an excursion to the hybrid larch seed orchard in Vaglir.