Lawson’s cypress (Chamaecyparis lawsoniana)
|Also known as:||Port Orford Cedar|
|Size||Height: 30 - 60 m (2)|
Lawson's cypress is classified as Near Threatened (NT) on the IUCN Red List (1).
While a popular and widespread garden conifer, natural populations of Lawson’s cypress are restricted to a small range and have declined significantly over the past 150 years (3) (4). Lawson’s cypress is a tall, conical tree with short branches and flattened twigs, bearing blue-green, scale-like leaves that form a dense crown (3) (5). The thick, furrowed bark of mature trees, which enables this species to survive moderate fires, is red-brown to silver-brown (2) (5) (6). Male and female cones are borne on the same branches but are very different in appearance; male cones are small, red-brown and oblong, whilst female cones are relatively large and spherical, and begin green but turn red-brown at maturity (5) (6). Under cultivation this species mutates very easily and consequently occurs in a remarkable variety of forms, often barely resembling the appearance of naturally occurring individuals (4) (7).
The native range of Lawson’s cypress is limited to coastal northern California and southern Oregon (2).
Lawson’s cypress occurs naturally where soil water is abundant during the summer, as is the case with the moisture-laden climes of its native range (2) (3). It grows on a wide variety of soil types and often with several other conifer species (2) (5).
Lawson’s cypress is fairly tolerant of shading, growing in both full sunlight and partial shade (2) (5). It can therefore act as both a pioneer, rapidly occupying disturbed areas in a stand, or as a climax species, gradually replacing other pioneer species in a process of succession (2). With a moderate growth rate, Lawson’s cypress reaches maturity after 250 to 300 years, living for as long as 560 years, but first begins reproducing after just five to nine years (2) (5). The male and female cones begin to develop in the spring but do not become reproductively active until the following spring (2). As is the case with all conifers, pollination occurs when a small but crucial fraction of the abundant pollen produced by the male cones is transferred by wind to ovules within the female cones (8). The winged seeds reach maturity in October but are released from the cones throughout the year and are dispersed by both wind and water (2).
Historically, Lawson’s cypress has been heavily exploited and international trade for its commercially valuable wood continues to put enormous pressure on the remaining old-growth stands (2) (9). Nonetheless, it is the spread of a root rot, Phytopthora lateralis, that presents the biggest threat to the future of the species. Originating from an unknown source in the mid-20th century, this root rot, which only affects Lawson’s cypress, has spread throughout most of its native range (2) (5). It spreads via aquatic spores in mud and water and can be transported by people, animals and machinery (2). Numerous stands have been eliminated by this lethal disease and it is preventing successful regeneration in many areas (2) (9). As of yet, very few naturally resistant trees have been identified and there are no effective chemical controls (2) (5) (10).
The priority for Lawson’s cypress conservation is to control the spread of the root rot. As the fungal spores require moist conditions to survive, existing control methods are focused around restricting human and vehicle movements through Lawson’s cypress habitat during the wet season (2) (10). There is also a program to cultivate trees that are resistant to the disease, but it will take hundreds of years before resistant seedlings will grow large enough to replace old-growth stands. Consequently the fate of surviving stands is for now completely dependent on the effective control of the spread of the disease (10).
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- Mutates: when the structure or amount of genetic material of an organism changes. This change is the source of variation in subsequent generations.
- Old-growth: forest that has remained undisturbed for a long time and has reached a mature condition.
- Ovules: structures within the female reproductive organs of plants that contains eggs and when fertilized by pollen, develops into seeds.
- Pollination: the transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
- Succession: the progressive sequence of changes in vegetation types and animal life within a community that, if allowed to continue, result in the formation of a ‘climaxcommunity’ (the last stage in a succession where the vegetation reaches equilibrium with the environment).
IUCN Red List (July, 2013)
- Zobel, D.B., Roth, L.F. and Hawk, G.M. (1985) Ecology, Pathology, and Management of Port-Orford-cedar (Chamaecyparis lawsoniana). Gen. Tech. Rep. PNW-184. U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station, Portland, Oregon.
Royal Botanic Gardens, Kew (November, 2008)
- Peattie, D.C. (2007) A Natural History of North American Trees. HMCo Field Guides, Boston.
- Preston, R.J. and Braham, R.R. (2003) North American Trees. Blackwell Publishing, Oxford.
- Brockman, F., Merrilees, R.A., Latimer, J.P., Nolting, K.S. and Challinor, D. (2001) Trees of North America: A Field Guide to the Major Native and Introduced Species North of Mexico. Macmillan, New York.
- Farjon, A. (2008) A Natural History of Conifers. Timber Press, Portland, Oregon.
- Owens, J.N., Takaso, T. and Runions, C.J. (1998) Pollination in conifers. Trends in Plant Science, 3(12): 479 - 485.
- Oldfield, S., Lusty, C. and MacKinven, A. (1998) The World List of Threatened Trees. World Conservation Press, Cambridge, UK.
- Hansen, E.M., Goheen, D.J., Jules, E.S. and Ullian, B. (2000) Managing Port-Orford-Cedar and the introduced pathogen Phytophthora lateralis. Plant Disease, 84: 4 - 13.