7. Biodiversity Patterns in Relation to Climate
115
seasonal rainforests on Vancouver Island and on the adjacent mainland
coast of British Columbia, Thuja achieves its most extensive distribution,
particularly in riparian and moist to wet sites (Pojar et al., 1987). In the
perhumid zone , Thuja is mostly restricted to wet, nutrient-poor sites
(DeMeo et al. , 1992; Ver Hoef, 1985).
Chamaecyparis nootkatensis, a native of the seasonal and perhumid
rainforest types, also appears to have a relatively low level of genetic
diversity (Russell and Cartwright, 1991)~ Its highly fragmented and
scattered populations may reflect effects of recent glacial events on the
northern Pacific coast. In the perhumid rainforest zone, Chamaecyparis
has very inconsistent seed output and often fails to regenerate naturally.
In old-growth forests, it may maintain itself through layering. It appears
that seed is often shed when immature (Colangeli, 1991; Owens & Molder,
1975). Seeds are produced in warm climates within one season, whereas
in cool climates it may take two more seasons, with more variability in
quality. Physiological studies of Chamaecyparis also suggest a narrow
environmental tolerance. Photosynthesis appears to be very sensitive to
moisture stress , with a 50% reduction occurring from 1 kPa to 2 kPa
(Grossnickle & Russell, 1991). Chamaecyparis is also extremely sensitive
to root temperature (more so than other native conifers in the Pacific
Northwest region), so it may benefit significantly from higher temperatures,
as predicted under a global-warming scenario (Grossnickle, 1991).
Only limited information is available on the genetic architecture of
Chamaecyparis. Preliminary provenance studies in British Columbia
suggest that Chamaecyparis may have more potential for genetic improvement than Thuja, but not as much as Pseudotsuga , Tsuga, or Picea
(Akasi & Kawamura, 1977; Russell & Cartwright, 1991). A weak relationship exists between seedling frost tolerance and latitude of provenance . Seedling height growth appears to have a significant additive
genetic component, mostly at the family level, rather than the provenance
level. The closely related analog for this species in Japan, C. obtusa, also
appears to have low levels of genetic diversity and has a limited natural
distribution (Shiraishi, Kaminaka, & Ohyama, 1987). In addition, tree
plantations appear to have significantly less diversity than natural ones (as
contrasted with those of Pseudotsuga and Picea, where this relationship
does not appear to exist). C. lawsoniana appears to be significantly more
diverse than the other Chamaecyparis species but is still only half or less
the expected heterozygosity of dominant widespread conifers such as
Picea and Pseudotsuga. C. Lawsoniana occurs only in the warm temperate
rainforest zone and nearby mesophytic climatic zones. Moderate levels of
variation occur in the coastal zone, and low diversity exists in interior
populations (Millar & Marshall, 1991).
Several major native forest trees from Tasmania and New Zealand also
appear to have relatively low levels of genetic diversity and limited
distributions (Hawkins & Sweet, 1989b, 1889c), perhaps because of
115
seasonal rainforests on Vancouver Island and on the adjacent mainland
coast of British Columbia, Thuja achieves its most extensive distribution,
particularly in riparian and moist to wet sites (Pojar et al., 1987). In the
perhumid zone , Thuja is mostly restricted to wet, nutrient-poor sites
(DeMeo et al. , 1992; Ver Hoef, 1985).
Chamaecyparis nootkatensis, a native of the seasonal and perhumid
rainforest types, also appears to have a relatively low level of genetic
diversity (Russell and Cartwright, 1991)~ Its highly fragmented and
scattered populations may reflect effects of recent glacial events on the
northern Pacific coast. In the perhumid rainforest zone, Chamaecyparis
has very inconsistent seed output and often fails to regenerate naturally.
In old-growth forests, it may maintain itself through layering. It appears
that seed is often shed when immature (Colangeli, 1991; Owens & Molder,
1975). Seeds are produced in warm climates within one season, whereas
in cool climates it may take two more seasons, with more variability in
quality. Physiological studies of Chamaecyparis also suggest a narrow
environmental tolerance. Photosynthesis appears to be very sensitive to
moisture stress , with a 50% reduction occurring from 1 kPa to 2 kPa
(Grossnickle & Russell, 1991). Chamaecyparis is also extremely sensitive
to root temperature (more so than other native conifers in the Pacific
Northwest region), so it may benefit significantly from higher temperatures,
as predicted under a global-warming scenario (Grossnickle, 1991).
Only limited information is available on the genetic architecture of
Chamaecyparis. Preliminary provenance studies in British Columbia
suggest that Chamaecyparis may have more potential for genetic improvement than Thuja, but not as much as Pseudotsuga , Tsuga, or Picea
(Akasi & Kawamura, 1977; Russell & Cartwright, 1991). A weak relationship exists between seedling frost tolerance and latitude of provenance . Seedling height growth appears to have a significant additive
genetic component, mostly at the family level, rather than the provenance
level. The closely related analog for this species in Japan, C. obtusa, also
appears to have low levels of genetic diversity and has a limited natural
distribution (Shiraishi, Kaminaka, & Ohyama, 1987). In addition, tree
plantations appear to have significantly less diversity than natural ones (as
contrasted with those of Pseudotsuga and Picea, where this relationship
does not appear to exist). C. lawsoniana appears to be significantly more
diverse than the other Chamaecyparis species but is still only half or less
the expected heterozygosity of dominant widespread conifers such as
Picea and Pseudotsuga. C. Lawsoniana occurs only in the warm temperate
rainforest zone and nearby mesophytic climatic zones. Moderate levels of
variation occur in the coastal zone, and low diversity exists in interior
populations (Millar & Marshall, 1991).
Several major native forest trees from Tasmania and New Zealand also
appear to have relatively low levels of genetic diversity and limited
distributions (Hawkins & Sweet, 1989b, 1889c), perhaps because of