Page 109 - Environment: The Science Behind the Stories

thE SCIENCE BEhINd thE StOry

Chronicling everything in their paths. Altogether, 4.1
3
3
Ecological recovery km (1.0 mi ) of material was ejected
from the mountain, severely altering
at Mount St. helens 1650 km (637 mi ), an area larger than
2
2
the entire city of Houston, Texas.
Step outside, look around, and you’ll In the aftermath of the blast, ecol-
likely find secondary succession ogists moved in to take advantage of
occurring somewhere nearby. The the natural experiment of a lifetime. For
nearest weedy lot or overgrown field them, the eruption provided an extraor-
will show how plants colonize a dis- dinary chance to study how primary
turbed area and begin building a new succession unfolds on a fresh volcanic dr. Virginia dale at Mount St. helens.
community from the foundations of the surface. Which organisms would arrive
old. But finding primary succession first? What kind of community would Instead, researchers discovered
is not as easy. It’s unusual to come emerge? How long it would take? that some plants and animals had
across a place where all life has been These researchers set up study plots to survived the blast. Some were pro-
extinguished and a brand new com- examine how populations, communi- tected by deep snowbanks. Others
munity is being built from scratch as ties, and ecosystems would respond. were sheltered on steep slopes facing
new organisms arrive from far away. Today, over 30 years later, the bar- away from the blast. Still others were
The eruption of Mount St. Helens ren gray moonscape that resulted from dormant underground when the erup-
offered ecologists a rare opportunity the blast is a vibrant green (Figure 1), tion occurred. These survivors, it turned
to study how communities recover carpeted with colorful flowers each sum- out, would play key roles in rebuilding
from catastrophic disturbance. On May mer. And what ecologists have learned the community.
18, 1980, this volcano in the state of has modified our view of primary suc- Many of the ecologists drawn
Washington erupted in sudden and cession and informed the entire study of to Mount St. Helens studied plants.
spectacular violence, with 500 times the disturbance ecology. Virginia Dale of Oak Ridge National
force of the atomic blast at Hiroshima. Given the ferocity and scale of Laboratory in Tennessee and her col-
The massive explosion oblit- the eruption, most scientists initially leagues examined the debris ava-
erated an entire landscape of forest presumed that life had been wiped out lanche, a landslide of rock and ash
as a scalding mix of gas, steam, ash, completely over a large area. Based as deep as a 15-story building. This
and rock was hurled outward for on traditional views of succession, they region appeared barren, yet small
miles. A pyroclastic flow (p. 59) sped expected that pioneer species would numbers of plants of 20 species had
downslope, along with the largest colonize the area gradually, spreading survived, growing from bits of root or
landslide in recorded history. Rock slowly from the outside margins inward, stem carried down in the avalanche.
and ash rained down for miles around, and that over many years a community However, most plant regrowth occurred
and mudslides and lahars (p. 60) would be rebuilt in a systematic and from seeds blown in from afar. Dale’s
raced down river valleys, devastating predictable way. team used sticky traps to sample these

(a) 1980 (b) 2012
Figure 1 Mount St. helens (a) after the eruption in 1980, and (b) in 2012.
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