196
T.T . Veblen and P.B. Alaback
Another native herbivore affecting some Nothofagus forests is the
defoliating caterpillar, Ormiscodes cinnamomea (Gentili & Gentili, 1988)
which periodically defoliates areas of many square kilometers in northern
Patagonia. Although outbreaks result in relatively little tree mortality,
but incomplete recovery has led to an increases in trees with partial
"crown dieback." Thus, periodic insect defoliation followed by incomplete
recovery may contribute to the abundance throughout Patagonia of
Nothfagus with partially dead crowns, which formerly was attributed to
recent climate change (Auer, 1939, 1958; Kalela, 1941). In the Punta
Arenas region wood borers (Chilecomadia sp .) attack Nothofagus pumilio,
but the extent of the damage has not been investigated. In northern
Patagonia we have also observed that N. pumilio with partial crown
dieback which has been attacked by wood-boring insects.
In North America, in the outer coastal environment, where mild winters
prevail high native deer (Odocoileus hemonius var, sitkensis and var.
columbiana) populations persist and result in reduced shrub and tree
seedling populations. In mainland and more protected island regions
within the perhumid zone, deer seldom reach sufficient population levels
to significantly alter successional pathways (Klein, 1985; Lewis, 1992). In
the seasonal rainforest region logging and fire have created abundant deer
habitat. Parks and preserves, such as the Olympic rainforest, develop a
park-like structure from the heavy browsing of deer and elk (Cervus
elaphus). Thuja and Tsuga generally decline in seedling recruitment compared to Picea under heavy browsing pressure, but reductions in elk
populations do not necessarily correspond to increases in Tsuga seedling
recruitment (Harmon & Franklin, 1983). Highl y palatable shrubs such as
Vaccinium parvifolium and Ribes spp. may also decline in heavily browsed
sites. Planted tree seedlings generally have to be protected from deer
until they reach above their browsing height. Porcupines (Erethixon
dorsatum) can also significantly affect forest structure by killing dominant
trees especially in young even-aged forests thereby creating small canopy
gaps. Mountain beaver (Alpodontia rufa) may also play an important role
in limiting tree regeneration in the seasonal rainforest zone.
Insect outbreaks can also have important localized effects in temperate
rainforest especially during successive warm or dry years in which overwinter survival is unusually high. In the perhumid zone black-headed
budworm (Acleris gloverana) and the hemlock sawfly (Neodiprion tsugae)
are considered the most serious defoliating insects. Outbreaks are infrequent, and tend to be of greatest consequence in even-aged or managed
forests (Ruth & Harris, 1979). In the seasonal zone Sitka spruce weevil
(Pissodes sitchensis) is one of the key factors limiting the growth of Picea
sitchensis inland from the coastal fog belt (Ruth & Harris, 1979). The
spruce budworm (Choristoneura spp.) can also cause significant defoliation
during warm or dry years or after a large accumulation of organic debris
from fire or windthrow. In comparison with interior forests , however,
T.T . Veblen and P.B. Alaback
Another native herbivore affecting some Nothofagus forests is the
defoliating caterpillar, Ormiscodes cinnamomea (Gentili & Gentili, 1988)
which periodically defoliates areas of many square kilometers in northern
Patagonia. Although outbreaks result in relatively little tree mortality,
but incomplete recovery has led to an increases in trees with partial
"crown dieback." Thus, periodic insect defoliation followed by incomplete
recovery may contribute to the abundance throughout Patagonia of
Nothfagus with partially dead crowns, which formerly was attributed to
recent climate change (Auer, 1939, 1958; Kalela, 1941). In the Punta
Arenas region wood borers (Chilecomadia sp .) attack Nothofagus pumilio,
but the extent of the damage has not been investigated. In northern
Patagonia we have also observed that N. pumilio with partial crown
dieback which has been attacked by wood-boring insects.
In North America, in the outer coastal environment, where mild winters
prevail high native deer (Odocoileus hemonius var, sitkensis and var.
columbiana) populations persist and result in reduced shrub and tree
seedling populations. In mainland and more protected island regions
within the perhumid zone, deer seldom reach sufficient population levels
to significantly alter successional pathways (Klein, 1985; Lewis, 1992). In
the seasonal rainforest region logging and fire have created abundant deer
habitat. Parks and preserves, such as the Olympic rainforest, develop a
park-like structure from the heavy browsing of deer and elk (Cervus
elaphus). Thuja and Tsuga generally decline in seedling recruitment compared to Picea under heavy browsing pressure, but reductions in elk
populations do not necessarily correspond to increases in Tsuga seedling
recruitment (Harmon & Franklin, 1983). Highl y palatable shrubs such as
Vaccinium parvifolium and Ribes spp. may also decline in heavily browsed
sites. Planted tree seedlings generally have to be protected from deer
until they reach above their browsing height. Porcupines (Erethixon
dorsatum) can also significantly affect forest structure by killing dominant
trees especially in young even-aged forests thereby creating small canopy
gaps. Mountain beaver (Alpodontia rufa) may also play an important role
in limiting tree regeneration in the seasonal rainforest zone.
Insect outbreaks can also have important localized effects in temperate
rainforest especially during successive warm or dry years in which overwinter survival is unusually high. In the perhumid zone black-headed
budworm (Acleris gloverana) and the hemlock sawfly (Neodiprion tsugae)
are considered the most serious defoliating insects. Outbreaks are infrequent, and tend to be of greatest consequence in even-aged or managed
forests (Ruth & Harris, 1979). In the seasonal zone Sitka spruce weevil
(Pissodes sitchensis) is one of the key factors limiting the growth of Picea
sitchensis inland from the coastal fog belt (Ruth & Harris, 1979). The
spruce budworm (Choristoneura spp.) can also cause significant defoliation
during warm or dry years or after a large accumulation of organic debris
from fire or windthrow. In comparison with interior forests , however,