Disease
In the wild, the species is seriously threatened by a root disease caused by the introduced fungal pathogen, Phytophthora lateralis. This disease is also a problem for horticultural plantings in some parts of North America. The tree is sometimes killed, though less often, by other species of Phytophthora.
Phytophthora lateralis infection begins when mycelium, from a germinated spore, invade the roots. The infection then spreads through the inner bark and cambium around the base of the tree. Spread up the trunk is generally limited. Infected tissue dies and effectively girdles the tree. Large trees are more likely to be infected than small trees due to larger root areas (although all trees at the edges of infected streams will eventually succumb). However, large trees can often live with the infections for a longer duration (up to several years).
Port Orford "Cedar" in streamside populations are highly susceptible to Phytophthora lateralis infection. However, the rate of Phytophthora spread through populations in dry upland areas appears to be slow. Phytophthora lateralis spreads through water via mobile spores (zoospores). The fungus also produces resting spores (chlamydospores) that can persist in soil for a long period of time. New infections generally begin when soil is transferred from an infected population to a non-infected population via human or animal movement. After initial infection in streamside populations, secondary spread via zoospores quickly infects all downstream individuals.
Human facilitated spread is thought to be responsible for most new, and all long-distance, infections. Soil on vehicle tires, especially logging trucks and other off road vehicles, is considered the most pressing problem due to the volume of soil that can be carried and the traffic rate in and between susceptible areas. Spread on boots and mountain bike tires has also been suggested and probably contributes to new infections locally. Animal facilitated spread is thought to occur, but is localized.
The Bureau of Land Management (BLM) and United States Forest Service (USFS) attempt to prevent Phytophthora spread through road closures, monitoring, research and education. Research has focused on determining the dynamics and mechanisms of spread, as well as attempts to breed resistant trees.
Read more about this topic: Chamaecyparis Lawsoniana
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