Defoliating insects damage trees by eating leaves or needles, removing the photosynthetic tissue critical for plant maintenance and growth. A significant loss of leaves or needles results in growth loss, increased susceptibility to attack by other insects and pathogens, and sometimes tree mortality.
The impact of defoliation on individual trees is dependent on a variety of factors. Tree species vary in their tolerance to defoliation. In most cases, hardwood species can sustain repeated defoliation over several years because they store large food supplies and can re-foliate in the same year. The timing of the defoliation relative to seasonal growth benchmarks is also important. For example, late season defoliation of hardwoods has a lesser impact than does late season defoliation of conifers; even a single late season defoliation of pines often results in tree mortality. As a general rule, trees that are healthy and growing vigorously will survive defoliation better than stressed trees.
Historically, the two most destructive defoliators in the Southwestern Region were the western spruce budworm and the Douglas-fir tussock moth. Both of these defoliators can cause severe growth loss, top-kill, increased susceptibility to bark beetles, and cause outright tree mortality. More recently, three other defoliators have been causing heavy defoliation in higher elevation forests. Since the early 1990s, the exotic spruce aphid and a native looper, Nepytia janetae, have caused high levels of mortality in the spruce-fir forest type in the White Mountains and Pinaleño Mountains of Arizona. More recently, a New Mexico fir looper outbreak began in 2002 in the Sacramento Mountains of southeastern New Mexico, causing elevated levels of fir mortality.
7
Based on the passage, which of the following would probably be LEAST susceptible to mortality from defoliation?
A
A growing fir tree in the White Mountains of Arizona
B
A healthy hardwood tree in a low elevation forest
C
A healthy pine tree late in the growth season
D
A hardwood tree still recovering from a previous defoliation
E
A pine tree early in the growth season that is free of bark beetles
The impact of defoliation on individual trees is dependent on a variety of factors. Tree species vary in their tolerance to defoliation. In most cases, hardwood species can sustain repeated defoliation over several years because they store large food supplies and can re-foliate in the same year. The timing of the defoliation relative to seasonal growth benchmarks is also important. For example, late season defoliation of hardwoods has a lesser impact than does late season defoliation of conifers; even a single late season defoliation of pines often results in tree mortality. As a general rule, trees that are healthy and growing vigorously will survive defoliation better than stressed trees.
Historically, the two most destructive defoliators in the Southwestern Region were the western spruce budworm and the Douglas-fir tussock moth. Both of these defoliators can cause severe growth loss, top-kill, increased susceptibility to bark beetles, and cause outright tree mortality. More recently, three other defoliators have been causing heavy defoliation in higher elevation forests. Since the early 1990s, the exotic spruce aphid and a native looper, Nepytia janetae, have caused high levels of mortality in the spruce-fir forest type in the White Mountains and Pinaleño Mountains of Arizona. More recently, a New Mexico fir looper outbreak began in 2002 in the Sacramento Mountains of southeastern New Mexico, causing elevated levels of fir mortality.
7
Based on the passage, which of the following would probably be LEAST susceptible to mortality from defoliation?
A
A growing fir tree in the White Mountains of Arizona
B
A healthy hardwood tree in a low elevation forest
C
A healthy pine tree late in the growth season
D
A hardwood tree still recovering from a previous defoliation
E
A pine tree early in the growth season that is free of bark beetles
A SMALL TOWN GUY
