Douglas C Anderson 
of the hypothesis that the recovery 
rate on a site from which vegetation 
has been totally obliterated depends 
on the proximity to a pool of colonists. 
According to this hypothesis, recovery 
should proceed much more rapidly on 
the South Fork than on the North 
Fork. 
Experimental manipulations of 
plots established on the debris flows 
during the next several years may also 
help answer some general questions 
about succession. Is there a definitive 
sequence to the recovery pattern or 
do chance and local seed availability 
dominate the process? Are the activi- 
ties of specific colonizing plant species 
required to facilitate the subsequent 
success of other species? One way to 
test such hypotheses is by determining 
whether, after a number of years, plots 
In many places, trees that withstood 
the blast were scorched by heat and 
noxious gases and covered with ash. 
Where this occurred, the mountain 
shows a line between brown, dead 
trees and green, living ones. 
(Populus trichocarpa) seedlings colo- 
nizing the lower North Fork of the 
Toutle. Because they float through the 
air, cottonwood seeds were among the 
few seeds available shortly after the 
May eruption. Unfortunately, subse- 
quent erosion from minor summer 
rains washed these seedlings away. 
Bob Zasoski of the University of 
Washington has estimated that more 
than ten years will pass before the 
first trees are established on these 
mudflows and more than a century 
before a more or less normal forest 
can develop. 
While mudflows devastated the 
lower river valleys, a huge debris flow 
— a turbulent, water-driven, hot mass 
of rocks, boulders, and uprooted trees 
— ravaged the upper valley of the Tou- 
tle’s North Fork. A few plants mi- 
raculously survived the vast jumble, 
and an occasional fireweed or bracken 
fern rhizome sprouted, but recovery 
on this debris flow will depend pri- 
marily on seeds invading from less 
damaged areas. 
Comparisons between the broad de- 
bris flow on the North Fork of the 
Toutle River and the much narrower 
mudflow, close to intact vegetation, 
on the South Fork will provide a test 
42 
