Vegetation Change in National Parks

From: "KD Weber"
Fw: Vegetation Change in National Parks

Vegetation Change in National Parks
(Note: It's quotes like these two, that make the intent to depopulate most
of
America of humans, crystal-clear: "Since the ultimate goal for the
management
of many areas is to mitigate settlement impacts and return the land to its
presettlement status, detailed knowledge of the effects of settlement is
imperative." "Land managers need to understand the nature and severity of
the effects
of settlement [, in order] to return the land to its presettlement
condition.")
no date given
By Kenneth L. Cole
National Biological Service
Natural ecosystems are always changing, but recent changes in the United
States have been startlingly rapid, driven by 200 years of disturbances
accompanying settlement by an industrialized society. Logging, grazing,
land clearing,
increased or decreased frequency of fire, hunting of predators, and other
changes have affected even the most remote corners of the continent.
Recent trends
can be better understood by comparisons with more natural past trends of
change, which can be reconstructed from fossil records. Conditions before
widespread impacts in a region are termed "presettlement"; conditions
after the impacts
are "postsettlement."
Fossil plant materials from the last few thousand years are used to study
past changes in many natural areas. Pollen buried in wetlands, for
example, can
reveal past changes in vegetation (Faegri and Iversen 1989), and larger
fossil
plant parts can be studied in deserts where the fossilized plant
collections
of packrats, called packrat middens, have been preserved (Betancourt et
al.
1990).
This article summarizes the rates of vegetation change in four national
park
areas over the last 5,000 years as reconstructed from fossil pollen and
packrat middens. These four national park areas from different ecological
regions
(Fig. 1) demonstrate the flexibility of these paleoecological techniques
and
display similar results.
Northern Indiana Prairie
A 4,500-year history of vegetation change was collected from Howes Prairie
Marsh, a small marsh surrounded by prairie and oak savanna in the Indiana
Dunes
National Lakeshore near the southern tip of Lake Michigan. Only 40 km (25
mi)
from Chicago, this area has been affected by numerous impacts from
settlements
but still supports comparably pristine tall-grass prairie vegetation as
well
as the endangered Karner blue butterfly (Lycaeides melissa samuelis).
Although this site has experienced more disturbances than any of the
others
described here, it is a most valuable site because of its many species
(Wilhelm
1990) and its tall-grass prairie vegetation that has been nearly
eliminated
elsewhere.
The many historical impacts to this area make it a good source for
studying
past changes. Past amounts of pollen from the primary plant taxa are
illustrated in Fig. 2. Many changes occurred before settlement, but more
rapid changes
occurred in the last 140 years.
Past rates of change in vegetation can be measured by summing the relative
change in each plant type between successive samples and then dividing by
the
number of years between samples. The technique is similar to that used by
Jacobson and Grimm (1986).
Although these changes had been occurring throughout the last 4,500 years,
the postsettlement rates of change are at least 10 times greater than the
presettlement rates of change (Fig. 3a). The rates of change have been
declining
over the last 50 years, but are still far greater than the presettlement
rates of
change.
Northern Michigan Forest
A similar analysis was carried out on pollen from a small bog (unofficial
name: 12-Mile Bog) surrounded by pine forest along the southern shore of
Lake
Superior (Fig. 3b). This site, within Pictured Rocks National Lakeshore,
was more
severely affected by logging and slash burning in the 1890's than by the
periodic wildfires that characterized this forest earlier, but it has been
protected for the last 80 years. The magnitude of change caused by the
crude logging
and slash burning of the logging era was far greater than any recorded
during
the 2,500 years since Lake Superior receded to create the forest of white
and
red pine (Pinus strobus and P. resinosa).
As in the Indiana Dunes, rates of change have declined during the last 60
years, and the forest is now very similar to the forest of 2,000 years
ago. Thus,
although the area is still changing at a rate far above normal, it has
begun
to recover through protection.
California Coastal Sage Scrub
Fossil pollen was analyzed from an estuary on Santa Rosa Island off the
coast
of southern California (Cole and Liu 1994). The semi-arid landscape around
the estuary is covered with coastal sage scrub, chaparral, and grassland.
This site, within Channel Islands National Park, is one of the least
affected
areas in this region of rapidly expanding urbanization, although the
island's
native plants and animals were not well adapted to withstand the grazing
of
the large animals introduced with the ranching era of the 1800s.
This island, which had no native large herbivores, became populated with
thousands of sheep, cattle, horses, goats, pigs, deer, and elk. The
National Park
Service is removing many of the large herbivores, although most of the
island
remains an active cattle ranch.
All pollen types from 33 samples spread over the last 4,600 years were
analyzed. The rates of change in the pollen were similar to those observed
from the
other sites.
Southern Utah Desert
Because fossil pollen is usually preserved in accumulating sediments of
wetlands, different paleoecological techniques are necessary in arid
areas. In
western North America, fossil deposits left by packrats (Neotoma spp.)
have proven
a useful source of paleoecological data (Betancourt et al. 1990).
Past desert vegetation can be reconstructed by analyzing bits of leaves,
twigs, and seeds collected by these small rodents and incorporated into
debris
piles in rock shelters or caves. These debris piles can be collected,
analyzed,
and radiocarbon dated.
The vegetation history of a remote portion of Capitol Reef National Park
(Hartnett Draw) was reconstructed through the analysis of eight packrat
middens
ranging in age from 0 to 5,450 years (Cole 1995).
The vegetation remained fairly stable throughout this period -- until the
last few hundred years. The most recent deposits contain many plants
associated
with overgrazed areas such as whitebark rabbitbrush (Chrysothamnus
visidiflorus), snakeweed (Gutterezia sarothrae), and greasewood
(Sarcobatus vermiculatus),
which were not recorded at the site before settlement.
Conversely, other plants that are extremely palatable to grazing animals
were
present throughout the last 5,450 years, only to disappear since
settlement.
Plant species preferred by sheep and cattle, such as winterfat (Ceratoides
lanata) and rice grass (Stipa hymenoides), disappeared entirely, while
many other
palatable plant species declined in abundance after 5,000 years of
comparative stability.
The past rates of vegetation change for this site were calculated in a
manner
similar to the fossil pollen records (Fig. 3d). Although the rate of
change
calculation is less precise than the fossil pollen records because there
were
fewer samples, the results show a similar pattern.
The rate of vegetation change is highest between the two most recent
records.
Although this area is still grazed by cattle today through grazing leases
to
private ranchers from the National Park Service, much of the severe damage
was
probably done by intensive sheep grazing during the late 1800s when the
entire region was negatively affected by open-land sheep ranching.
We cannot yet demonstrate whether the grazing effects are continuing or if
the site is improving, although reinvasion of palatable species is
unlikely in
the face of even light grazing.
Severe overgrazing is required to eliminate abundant palatable species,
but
once they are eliminated, even light grazing can prevent their
restoration.
Implications
Wise land management decisions are more likely to be made if land managers
understand a site and are able to place the status quo into a historical
perspective.
Because most of the damage to these four sites occurred before the 20th
century, land managers might not even be aware of the tremendous changes
that have
occurred were it not for these fossil records.
Since the ultimate goal for the management of many areas is to mitigate
settlement impacts and return the land to its presettlement status,
detailed
knowledge of the effects of settlement is imperative.
In all study areas, postsettlement rates of change were at least 10 times
higher than the presettlement rates of change.
Thus, the changes now being observed in even remote natural ecosystems are
unlike former natural changes.
Some areas are continuing to change at rapid rates, while other areas,
which
have not been disturbed as recently, are stabilizing. The climatic warming
projected for the next 50 years may exacerbate these ongoing changes, but
will be
only one of many variables operating in the unplanned redesign of our
natural
ecosystems.
Land managers need to understand the nature and severity of the effects of
settlement [, in order] to return the land to its presettlement condition.
For further information:
Kenneth L. Cole
National Biological Service
Cooperative Park Studies Unit
University of Minnesota
Department of Forest Resources
115 Green Hall
St. Paul, MN 55108
References
Betancourt, J.L., T.R. Van Devender, and P.S. Martin, eds. 1990. Packrat
middens: the last 40,000 years of biotic change. The University of Arizona
Press,
Tucson. 467 pp.
Cole, K.L. 1995. A survey of the fossil packrat middens and reconstruction
of
the pregrazing vegetation of Capitol Reef National Park. National Park
Service Res. Rep. In press.
Cole, K.L., D.R. Engstrom, R.P. Futyma, and R. Stottlemyer. 1990. Past
atmospheric deposition of metals in northern Indiana measured in a peat
core from
Cowles Bog. Environmental Science and Technology 24:543-549.
Cole, K.L., and G. Liu. 1994. Holocene paleoecology of an estuary on Santa
Rosa Island, California. Quaternary Res. 41:326-335
Faegri, K., and J. Iversen. 1989. Textbook of pollen analysis. Wiley and
Sons, New York. 328 pp.
Jacobson, G.L., Jr., and E.C. Grimm. 1986. A numerical analysis of
Holocene
forest and prairie vegetation in central Minnesota. Ecology 67:958-966.
Wilhelm, G.S. 1990. Special vegetation of the Indiana Dunes National
Lakeshore. Indiana Dunes National Lakeshore Research Program, Rep. 90-02,
Porter, IN.
http://biology.usgs.gov/s+t/noframe/m1109.htm