The cedar of Lebanon - a drought-tolerant tree species for dry sites

The question of where to obtain seed of suitable provenances for Bavarian forests has not been investigated so far. As part of the “CorCed” project funded by the Federal Ministry of Agriculture and Food, several seed crop stands of Lebanon cedar in Turkey were viewed. The aim was to cover different climatic conditions and altitudes in order to be able to assess the potential of this drought-tolerant tree species in provenance trials in Bavaria and Baden-Württemberg. Provenance plays a key role with the Lebanon cedar, as it does with other tree species both native and non-native. As well as growth-relevant traits, the genetic make-up of the individual populations is important, so that its potential to adapt can be assessed.

In spring 2020, four cedar provenance trials were set up in Bavaria and Baden-Württemberg as part of the CorCed project. They include six to seven provenances of Atlas and Lebanon cedar. In addition, more than 20 practical cultivation trials were established throughout Bavaria using selected provenances of these two tree species under different site and environmental conditions, in order to gather initial experience with this species in cooperation with forestry practitioners.

The natural range of the Lebanon cedar is fragmented and split into two larger areas. One area consists of individual pockets of remnant populations in Lebanon and Syria. The species has been overused in both countries. In Lebanon, only 1,700 ha of the original 500,000 ha still exist; the size of the Syrian populations of Lebanon cedar is not known. The largest population of the Lebanon cedar (Turkish: Toros sediri) is to be found in Turkey. It is divided between forests in the East and West Taurus Mountains. The cedars that occur here are known as Cedrus libani subsp. stenocoma. The area in Turkey (463,500 ha) covers a large part of the western and central Taurus mountains and the Amanus mountain range. As a result of centuries of overuse, the population is fragmented and divided into many island-like individual clusters. Turkey is a world leader in the afforestation of open landscapes and has restocked 400,000 to 500,000 ha of forest over the last 30 years by sowing and planting different tree species. The potential of the forestry sector in Turkey will increase in future as a result.

In its natural range, the Lebanon cedar colonises areas at altitudes between 800 and 2,100 m above sea level. In many places it forms the timberline. Larger and contiguous cedar forests are still to be found in the West Taurus Mountains. Individual clusters grow here at altitudes of 500 to 800 m a.s.l. In times of climate change, our Turkish colleagues are counting on Lebanon cedar in their afforestation programmes, along with black pine. Turkey is currently afforesting more than 10,000 ha annually with Lebanon cedars. In Europe, Lebanese cedar stands are being established in France, Italy and Bulgaria. In Germany and other central European countries, the Lebanon cedar is only known as a park tree; there are few forest areas where it is cultivated.

The Lebanon cedar will grow in calcareous and siliceous soils. In France, its cultivation is particularly recommended on calcareous soils. As it develops a 2 to 3 m long taproot, it can access deeper and therefore fresher layers as well as rocky locations. Because it does not compete well with other tree species, it is often relegated to marginal sites (poor, shallow, rocky and structurally rich ground) in its natural range.

The climatic conditions in the natural range of the Lebanon cedar can vary widely. The Turkish Lebanon cedar thrives in four climate types: “arid”, “semi-arid”, “humid” and “semi-humid”. The average annual precipitation ranges from 600 to 1,300 mm, and at higher altitudes may also exceed 2,000 mm. The natural populations on the south Anatolian coast are in the Mediterranean winter rainfall area. The sub-areas in the Amanus and Aluite Mountains (Syria) and in Lebanon have a lot of rainfall (up to 1,300 mm/year). Higher altitudes have a Mediterranean mountain climate, transitioning in places to a steppe climate. Only about 5 % to 25 % of the annual rainfall usually falls during the growing season from May to September in the area of natural range. The Lebanese cedar copes well with dry periods in the summer months, with precipitation of just 50 to 100 mm. At higher altitudes, the extreme summer drought can be mitigated by the occurrence of fog. From around 1,000 m above sea level, winter precipitation often falls as snow. The snow cover can be up to two metres thick and remain until April. The Lebanon cedar copes well with snow pressure. However, independently of dry periods, it requires at least 500 to 600 mm of precipitation per year for growth. Average annual temperatures range from 6.0 to 15.7 °C. The temperatures in stands in the eastern Taurus mountains can drop to -32 °C in January and rise to 36.8 °C in July. The Lebanon cedar is considered to be less frost-resistant than the Atlas cedar.

As with native tree species, the choice of provenance of a tree species and the quality and sustainable production of the seed and planting material are important for the selection of the alternative tree species. The Lebanon cedar is subject to the [German] law on forest reproductive material (FoVG). The production, import, export and bringing to market of the reproductive material must be carried out in compliance with the legal requirements as set out in the FoVG. Because of the low economic importance in Germany of this tree species, no areas of provenance have been designated so far in Germany. The production (e.g. plant breeding from foreign seeds) and marketing of forest reproductive material are clearly regulated and the regulations must be complied with. The requirements for the approval and harvesting of such stands are defined by the respective states. Where the seed is produced in third countries that have joined the OECD scheme, its production must be subject to the same conditions as seed production in an EU member state. For the importing of seed from third countries, an import notification must be submitted to the Federal Agency for Agriculture and Food (BLE).

In Turkey, 22 seed crop stands covering an area of 3,437 ha have been selected and approved. In addition, eight seed orchards have been established. For this, plus trees from different regions of Turkey were selected between 1990 and 1995. Since the Lebanon cedar can form its first cones at the relatively young age of 30, these seed orchards will soon be ready for harvesting. Propagation material from non-approved stands of the “source-identified” category is not permitted for use in forests in Germany, and nor is harvesting in individual arboretums, parks, or plantations of exotic species.

The aim of the CorCed project is to investigate and evaluate the suitability and viability of different provenances of Atlas cedar (Cedrus atlantica) and Lebanon cedar (Cedrus libani) for cultivation in Bavaria and Baden-Württemberg. For this purpose, provenance trials have been set up in Kelheim, Kipfenberg, Wüstenrot and Kandern in cooperation with the Forest Research Institute (FVA) of Freiburg. Six to seven provenances are being grown per cedar species, all of which are being genetically characterised. Just a few years after planting, traits such as their growth behaviour, frost-tolerance and drought-tolerance can be evaluated.

The provenance trials can be used as a basis for the development of provenance recommendations. The climate data of the selected stands show that the cedar species are already adapted to extreme drought and heat and can certainly be considered as an alternative species in times of climate change. It is known from other European trials that the average height growth of the Lebanon cedar is lower than that of the Atlas cedar. A few particularly vigorous provenances from eastern Turkey reach a comparable height. Four Turkish provenances of Lebanon cedar from the species’ eastern range (Anti-Taurus) are being recommended for afforestation in France. It remains to be seen how the individual provenances develop in southern Germany, and which are the most suitable for Bavaria and Baden-Württemberg.