Larch

Larix spp.

1. Identification and origin

The larch (Larix spp.), belonging to the Pinaceae family, is a genus of deciduous conifers native to the cold regions of the Northern Hemisphere. The most common species include Larix decidua Mill. (European larch), Larix kaempferi (Lamb.) Carrière (Japanese larch) and Larix sibirica Ledeb. (Siberian larch). They are trees adapted to cold climates, with great resistance to frost and the ability to colonise poor and mountainous soils.

2. Economic importance

The larch is valued for its wood of high natural durability, resistant to moisture and rot, being used in construction, exterior carpentry, posts, rustic furniture and the production of paper pulp. It is also used in reforestation, slope protection and ornamental tree planting. In Portugal, the Japanese larch is occasionally used in mountain plantations and parks.

3. Botanical characterisation

Medium to large trees, capable of reaching 25–45 m in height, with a pyramidal crown. The leaves are needle-like, soft, grouped on short shoots, falling in autumn — a rare characteristic among conifers. The cones are ovoid, small, persistent and vary between species. The bark is thick and fissured. The root system is deep and well adapted to cold and stony soils.

4. Soil and climate requirements

It prefers cold or temperate mountain climates, with harsh winters and cool summers. It tolerates intense frosts and poor soils, provided they are well drained. It develops best in slightly acidic soils, with a pH between 5.0 and 6.5. It is sensitive to hot and dry climates, where it shows lower vigour and greater susceptibility to pests and diseases.

5. Main pests

• Larch budmoth (Zeiraphera diniana): severe defoliation in population cycles.
• Aphids (Cinara spp.): sap sucking and decline in vigour.
• Weevils (Curculionidae): damage to seedlings and young bark.
• Pine processionary (Thaumetopoea pityocampa): may attack larches in mixed areas.
• Nematodes (Bursaphelenchus spp.): risk in areas with infested pines.

6. Main diseases

• Larch canker (Lachnellula willkommii): cankers on branches and trunk, causing death of young plants.
• Rust (Melampsora spp.): leaf spots and premature drop of the needles.
• Root rots (Armillaria spp.): decline and death of trees.
• Trunk rots (Heterobasidion annosum): internal rotting and structural instability.
• Mildew and opportunistic fungi in nurseries: damping-off and root necrosis.

7. General crop management

It includes the choice of species adapted to the local climate (e.g.: L. kaempferi for temperate areas), planting in well-drained soils, control of competing vegetation, monitoring of defoliating pests and soil fungi, and maintenance of adequate densities to reduce excessive moisture. In reforestation, it is recommended to avoid areas with a history of Heterobasidion or Armillaria. Timber harvesting should take into account the high natural durability, doing away with intensive treatments.

Bibliographic references

• EPPO Global Database. Larix spp. – pests and diseases.
• CABI Invasive Species Compendium. Larix spp. – datasheets.
• Schweingruber, F. H. (1993). Trees and Wood in Dendrochronology. In: Springer Series in Wood Science.
• Farjon, A. (2017). A Handbook of the World’s Conifers. In: Brill.
• Kim, Y. S., et al. (2010). Larch species and wood properties. In: Forest Products Research. Springer.