occidentalis – west (Latin)

Native range: Western North America

Leaves:

• needle-like leaves
• deciduous
• 1–2” long
• dense, short shoots
• white stomatal bands on lower surface

Cones:

• monoecious
• male cones:
  • small
  • oblong
  • solitary and terminal
  • often yellow
  • many spirally arranged anthers
  • stalked or sessile
• female cones:
  • subglobose
  • solitary
  • rounded scales
  • persistent scales
  • new cones are often red/purple or green
  • long-winged seeds
    • distributed generally within 328 ft. (100 m.) of the parent, though some travel much further

Other characteristics:

• trees up to 210 ft.
• pyramidal form when young
• bark in mature trees is thick and furrowed into large, flaky or scaly plates
• fall color is yellow to orange
• short shoots resemble Cedrus but is deciduous, so leaves are soft

Relevant info:

• may live up to 900 years
• L. lyallii – NW native
• L. decidua – common ornamental species
• important timber-producing species in W. North America
  • densest wood of the northwestern conifers
  • durable and decay-resistant

Ecology & Adaptations:

• native to region east of the Cascades, southeastern British Columbia to Oregon, east to Montana and Alberta
• found in alpine and subalpine forests, mountain valleys and lower slopes, often in swampy areas
• occupies relatively cool, moist climatic zones
• upper elevational range is limited by low temperatures, while the lower extreme is limited by low precipitation.
• long-lived early successional species – grows rapidly in disturbed environments and maintains dominance over other species
• efficient light capture:
  • leaf configuration maximizes light availability and limits self-shading within the canopy
  • lower cost of producing leaves than associated conifers, which incorporate lignin and compounds used for herbivory defense
• pollinated by wind
• fire-resistance:
  • most resistant species in its range
  • needles are less flammable than other species’ due to their small size and high water content (due to being less than 5 months old)
  • since tree replaces its needles annually anyway, it is better adapted to defoliation than other conifers
  • after defoliation early in the season western larch trees often will produce a 2nd set of needles from heat-resistant woody buds and epicormic branches
  • small needles also minimize accumulation of surface litter at tree bases that would serve as fuel for fire
  • seeds are very light and long- winged, and can reach, germinate and grow readily on recently burned soils
  • sapwood (xylem) has greater water storage capacity than other conifers of comparable diameter
• low nutrient conditions:
  • adapted to medium and coarse textured soils, which tend to be low in nutrients
  • leaf nitrogen content and leaf area indicate high photosynthetic capacity in comparison with associated conifers
  • uses nitrogen efficiently during the growing season and reabsorbs nitrogen from leaves at the end of the growing season
  • uses nitrogen more efficiently than evergreen trees
• herbivory, insect & pathogen defense:
  • volatile compounds in oleoresin (pitch) interfere with insect larvae production and protect against some pathogens
  • many insects and diseases can affect western larch, but damage is usually less severe than in associated species
  • deciduous habit helps with resistance to pests
  • if trees are defoliated, they produce a 2nd set of needles later in the season
  • epicormic branching (from inactive buds under the bark that become active) appears to offer protection against disease by replacing older, potentially infected branches
• wildlife:
  • provides habitat for variety of species:
    • pileated woodpeckers, a sensitive species, are dependent on old-growth western larch forests and forage for insects
    • though generally unpalatable to deer, elk, etc., may be eaten as emergency food
    • seeds are palatable to small birds and mammals
    • several species of grouse rely on large needles
    • flying squirrels, woodpeckers, owls, and various songbirds nest in rotting western larch cavities