stage when fast growing mosses, herbs, and tree
brief descriptions of types of human disturbances
seedlings become established after 310 years, (3)
and references to pertinent literature below.
tall shrubsapling stage occurring 330 years af-
The effects of roads on forest ecosystems has
ter fire, (4) dense tree stage of mostly birch, as-
been assessed briefly by Brown and Berg (1980),
pen, but also some white spruce after 1530 years,
but major studies on ecological effects are lacking.
(5) mature hardwood stage with quaking aspen
In addition to the direct impacts, the indirect im-
and paper birch after 50150 years, and (6) the
pact of dust also has significant ecological effects
spruce stage after 100200 years.
(Walker and Everett 1987).
The successional sequence on black spruce sites
Trails resulting from training exercises and rec-
is similar in structure but varies some in species
reational activities are common on both the YMA
composition, and includes (1) newly burned stage
and the Tanana Flats, but little is known about the
with resprouting ericaceous shrubs during 01
ecological changes and recovery potential for
years, (2) mossherb stage when fast growing
taiga ecosystems (Sparrow et al. 1978, Racine and
mosses, herbs, and tree seedling become estab-
Ahlstrand 1991). In addition, generalization of the
lished after 15 years, (3) tall shrubsapling stage
ecological effects and recovery potential is made
occurring 530 years after fire, (4) dense tree stage
more difficult by the complex interactions of eco-
of mostly birch, aspen, and black spruce after 30
system characteristics, season of impacts, number
55 years, (5) mixed hardwoodspruce stage with
of passes, type of vehicle or foot traffic, and soil
black spruce, paper birch and quaking aspen after
and permafrost conditions.
5590 years; and (6) the spruce stage with black
Contaminants have been identified at 81 known
spruce and Sphagnum mosses after 90200+ years.
or suspected areas at Ft. Wainwright and most of
Fire frequencies as high as every 3055 years has
these were located in the main cantonment area
been reported for some forest types in interior
(Kennedy et al. 1997). A wide range of con-
Alaska (Yarie 1981). Between 1940 and 1970,
taminants have been found including pesti-
nearly 1% of interior Alaska forest land burned
cides, dioxin/furans, heavy metals, petroleum
annually (Barney 1971), whereas, since 1970, 0.6%
products, and other organic compounds. Most of
of forested land has burned annually (Viereck and
this contamination was associated with leakage
Schandelmeier 1980). Based on fire occurrences
at buildings, tank farms, landfills, fire-training
recorded on Ft. Wainwright since 1950, 1% of the
pits, drum burial sites, and coal storage. Hydro-
area has burned annually.
carbon contamination of the Blair Lakes Target
Facility was evaluated by Chacho et al. (1995).
Humans
Little is known, however, about the nature and
Human disturbances include cut-and-fill asso-
extent of contamination associated with explo-
ciated with construction of roads and pads, land
sives used in the Stuart Creek Impact Area
clearing, excavation for impoundments, trail
(CEMML 1998). Contaminated areas were not
development, munitions testing and training, and
mapped by our study and the ecological effects
contaminants. Of these disturbances, only roads,
of contaminants are poorly understood.
pads, clearings, and excavations were large or dis-
In summary, thermokarst has had the largest
tinct enough to be mapped. Within the entire
overall effect (~30% of area over ~200 yr) on eco-
study area, human modified areas cover 0.2% of
logical changes. Recent fires have affected a simi-
the area. Most of this type was within the YMA
lar amount of area (27% of area over 47 yr) based
(531 ha) and was associated with roads. In con-
on mapping of fire occurrences. This measure-
trast, little human disturbance (44 ha) was evident
ment is similar to the extent of fires estimated by
on the Tanana Flats, and principally was associ-
summing areas of early and midsuccessional
ated with the Blair Lakes Target Facility.
ecotypes on uplands and lowlands that have
A companion study on ecological land evaluation
developed after fire are combined (~24% over
for Ft. Wainwright is assessing the nature and mag-
~100 years, general age of broadleaf and mixed
nitude of disturbance within the YMA and will pro-
forests). Some fire-affected areas, however, over-
vide a better analysis of disturbance regimes
lap with thermokarst-affected areas so the extent
(Jorgenson et al., in prep.). Although little is known
of fires is underestimated somewhat. Although
about the response of subarctic ecosystems to dis-
the extent of disturbance is similar, recovery after
turbance, because most research in Alaska has
fire usually ends in vegetation similar to the
focused on tundra ecosystems (Van Cleve 1977,
predisturbance condition, whereas thermokarst
Walker et al. 1987, Slaughter et al. 1989), we provide
leads to dramatically different ecosystems. Effects
61
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