Chapter 18 (HLTH-3): Abiotic Factors - Southern Research Station

25 Pages·2002·6.2 MB·English

Chapter 18: Abiotic Factors 429
Chapter 18:
How have abiotic factors,
Abiotic Factors
including environmental
stressors such as air
pollution, influenced
the overall health
of the South’s forests,
and what are future
Jennifer A. Moore, John G. Bartlett, Johnny L. Boggs,
effects likely to be?
Michael J. Gavazzi, Linda S. Heath, and Steven G. McNulty
USDA Forest Service, Southern Research Station
■ Continued increases in ozone specific and integrated broad-scale
Key Findings
concentrations will likely have stress responses at forest ecosystem,
significant negative impacts on community, and species levels.
■ Sulfur deposition will continue pine forests in the South.
to decrease and subsequently have ■ Forest area and growth rates Introduction
less of a negative impact on forest
could increase across the South
ecosystem nutrient cycling, whereas
with moderate increases in air
future nitrogen deposition will be The sustainability of southern
temperatures and carbon dioxide
beneficial to most southern forests, forests could be threatened by the
concentrations during the 21st century.
which are nitrogen limited. interactions of biotic and abiotic
Severe temperature increases could
■ High-elevation spruce-fir negatively affect forest productivity stressors (McLaughlin and Percy
1999). Environmental factors
forests in the Southern Appalachian and area, especially if precipitation
such as temperature, precipitation,
Mountains are the only forests rates do not increase to compensate H
atmospheric carbon dioxide (CO )
in which significant damage is for increased water demands. 2
and O concentrations, and acid
linked to acid deposition. ■ Carbon storage in southern forest deposi3tion affect forest processes such E
■ The overall health of hardwoods, ecosystems, including public, private, as carbon, water, and nutrient fluxes. A
oak-pine, and southern pine forests and industrial forests, could make These processes are the foundation
has not been shown to be adversely a significant contribution to carbon of forest ecosystems, and abnormally L
affected by acid deposition. sequestration. Future policies, large variability in their size, timing, T
■ Regionally, there is no evidence incentive programs, and forest or location may influence forest
H
that acid precipitation is causing management intensity will affect sustainability. Therefore, from an
significant damage to stream chem- carbon sequestration rates. ecosystem perspective, changes in
istry in the Southern United States. ■ Land use change, not climate forest processes may be indicators of
Water quality in some streams change or atmospheric chemistry, long-term forest function and health.
in the Southern Appalachian has been and probably will continue Sulfur and nitrogen deposition have
Mountains is decreasing. to be the most important determinant been indicted as contributors to forest
■ Ozone-related annual growth of carbon storage, uptake, and release degradation, especially in the high-
reductions for pine seedlings across in terrestrial ecosystems. elevation red spruce and Fraser fir
the South are probably between ■ Existing climate change models forests that occupy the ridges of the
2 and 5 percent. Tree-water stress do not provide adequate information Appalachian Mountains (McLaughlin
or forest drought is thought to to forecast changes in location, extent, and Kohut 1992). In an effort to
protect seedlings from the negative frequency, or intensity of extreme manage and sustain spruce-fir and
effects of ozone. Any protective weather events and their impacts hardwood forests in a way that does
benefits provided by drought stress on forest ecosystems. Potential not compromise the ability of future
for seedlings are likely offset by increases in air temperature and generations to meet their needs, the
growth and productivity reductions. changes in precipitation patterns current and future impacts of sulfur
■ Southern pines typically do not may contribute to increased freq- and nitrogen deposition on overall
show visible symptoms of ozone uency or intensity of some events. forest health in the Southern United
States must be addressed.
(O ) injury under ambient O ■ Detailed spatial and temporal
3 3
conditions, but growth of mature predictions of abiotic stressor Ground level (tropospheric) O is
3
southern yellow pines is being effects on forest sustainability are an air pollutant that affects U.S. forests
reduced by current ambient ozone not possible without long-term (U.S. Environmental Protection Agency
levels at annual rates that vary improvements in regional monitoring 1996). At current ambient levels, O
3
from 0 to 10 percent per year. and studies designed to understand can decrease tree growth, increase the
430 Southern Forest Resource Assessment
probability of mortality, cause visible potential to capture CO and
2
foliar damage, and alter forest store carbon. Acid Deposition
successional patterns (Flagler and Climate change also could generate
Chappelka 1996, McLaughlin and forest stress, and extreme weather
Downing 1995, Teskey 1996). For events can cause disturbances that Acid Deposition
these reasons, current and projected shape forest systems by influencing Methodology: Current
O impacts on southern forests are their composition, structure, and Conditions
3
addressed in this Assessment. functional processes. We discuss the
Acid deposition occurs when
Climate influences the establishment effects of these disturbances and their
emissions of sulfur dioxide (SO )
and growth of forest trees, affecting the relationship to changing temperature 2
and oxides of nitrogen (NO) react
extent and quality of forest ecosystems. and precipitation patterns. x
with atmospheric water, oxygen, and
The spatial and temporal distribution Biotic stressors such as insects and
oxidants to form acidic compounds.
of air temperature and precipitation pathogens have major negative impacts
Mild solutions of nitric and sulfuric
is the primary climatic factor shaping on forest ecosystems; in the United
acids are formed and fall as acid
forests. Human activities contribute States, they cause severe damage on
precipitation. Sulfur and nitrogen
significantly to current global climate an average of more than 50 million
deposition was first described as
change (Dale and others 2000), acres per year, costing $2 billion a
a problem in Europe in the early
predominantly due to the increasing year (Dale and others 2000). Biotic
19th century and has been studied
concentration of greenhouse gases stressors are the focus of chapter 17.
extensively in North America since
such as CO . Since the beginning of
2 Each of the abiotic stressors— the 1970s (Blancher 1991). Sulfur
the industrial revolution, CO levels
2 methods, data sources, results, and nitrogen deposition can impair
have been steadily increased by fossil
discussion, and conclusions—are tree growth in several ways. They can
fuel burning and land use changes
discussed separately. Current abiotic leach calcium and magnesium from
(Sarmiento and Wofsy 1999; U.S.
stressors have been described for soils where base cation stores are very
Department of Energy, Office of Sci-
different coarse-scale studies. Attempts low, and the ability of the ecosystems
ence, Office of Fossil Energy 1999).
at regional-scale characterizations to retain sulfur or nitrogen is minimal
Even if changes in CO concentration
2 and future predictions are underway (McLaughlin and others 1998). Acid
did not effect climate changes, they
and are highlighted when feasible. deposition may also involve the release
would affect plant growth.
of toxic elements such as aluminum
It is important to recognize the
Independently developed climate
from the soil, adversely affecting
H integrated nature of these abiotic
change scenarios are generated with
biological processes and living organ-
stressors and their cumulative effects
transient general circulation models
isms (Malmer 1976). Nutrient loss and
E on forest ecosystems. This integration
(GCMs) that simulate atmospheric
soil degradation have been observed
is referenced throughout the chapter.
Adynamics under a gradual doubling in some hardwood forests (Swank
It is imperative that readers consider
in greenhouse gas concentrations from
and Vose 1997). However, pine, hard-
Labout 1895 to 2100. Emissions of CO cumulative integrated effects when
wood, and mixed (oak-pine) forests
2 interpreting the results and conclu-
Tto the atmosphere are predicted to
experience slower losses of base cation
sions from this chapter.
increase from 7.4 gigatons per year in
H
1997 to 26 gigatons per year by 2100
(U.S. Department of Energy, Office of
Science, Office of Fossil Energy 1999).
For this Assessment, these scenarios are
used with ecological process models to
investigate the potential effects of
climate change on forest ecosystems.
Forest carbon sequestration, the
ability of forests to store and release
carbon, is currently an important issue
debated in the policy arena. Carbon
stored in forests affects the amount of
carbon contributing to the increasing
atmospheric CO concentration.
2
Reductions in carbon emissions have
been proposed as a mitigation strategy Pounds per acre
for rising atmospheric CO , which 1.88–6.28
2
may be causing global warming. Rising 6.28–9.74
atmospheric CO levels could also 9.74–12.87
be mitigated by i2ncreasing carbon 12.87–15.31
sequestration through forestry and 15.31–21.80
other land management activities.
Terrestrial ecosystems have enormous
Figure 18.1—Current (1999) distribution of sulfate deposition in pounds per
acre across the South (National Atmospheric Deposition Program 2000).
Chapter 18: Abiotic Factors 431
They are produced primarily in
industrialized States in the northern
part of the South.
Currently, forests in the South are
exposed to a wide range of nitrogen
deposition rates (National Atmospheric
Deposition Program 2000) (fig. 18.2).
The mean regional nitrogen deposition
for 1999 was 10 pounds per acre, a
10-percent decrease in nitrogen
deposition from 1994 (National
Atmospheric Deposition Program
2000). The highest regional nitrogen
values are generally located in the
Pounds per acre
northern part of the South (fig. 18.2).
2.06–5.94
5.94–7.97 Their sources are emissions from all
7.97–9.99 31 States east of the Mississippi River
9.99–12.40 (Nash and others 1992).
12.40–14.33
For this discussion, the South has
Figure 18.2—Current (1999) distribution of nitrogen deposition in
been divided into nine forest types
pounds per acre across the South (National Atmospheric Deposition
Program 2000). according to various factors that
include geographic location, precipi-
tation, minimum and maximum air
nutrients and degradation because (National Atmospheric Deposition
temperatures, and soil conditions (more
of their ability to buffer sulfur and Program 2000) (fig. 18.1). The mean
or less sensitive to acid precipitation).
nitrogen deposition. These forests regional sulfate deposition for 1999
Five of these forest types are shown in
generally have large calcium pools was 11 pounds per acre, which is a
fig. 18.3. Sensitive soils have low base
that increase their ability to buffer 13-percent decrease in sulfur deposi-
cation stores, and the ecosystem has a
acid deposition. tion from 1994 (National Atmospheric
low ability to retain sulfur or nitrogen,
There is a wide range of sulfate Deposition Program 2000). The highest or both. Less sensitive soils are ones
deposition rates across the South regional sulfur values are in North with high concentrations of base H
Carolina and Tennessee (fig. 18.1).
cations, high buffering capacity to
E
sulfur and nitrogen deposition, and,
normally, nitrogen deficiency. Within A
the region, the high-elevation spruce-fir
forests are most sensitive to sulfur and L
nitrogen deposition. The least sensitive T
ecoregions are those covered primarily
Spruce–fir H
by hardwood, pine, and oak-pine
Longleaf–slash pine
forests. The sensitivity of a given
Loblolly–shortleaf pine region to acid precipitation depends
Oak–pine on the ability of the rocks and soils
Oak–hickory to neutralize or buffer the acid. Soils
derived from granite, which are low
in calcium, are highly sensitive. Soils
VA
derived from limestone, which are
high in calcium, are much more
capable of buffering the acid.
Acid Deposition
Methodology:
TN
Future Predictions
Sulfur deposition is a primary
contributor to acid deposition that
indirectly affects forest decline by
NC
leaching base cations from the soil.
Figure 18.3—Distribution Therefore, in 1990, Title IV of the
of spruce-fir and other Clean Air Act set as its primary goal
southern forest types the reduction of annual SO emissions
in eastern Tennessee, 2
by 10 million tons below 1980 levels
western North Carolina,
(U.S. Environmental Protection Agency
and southern Virginia
(Eyre 1980). 1997a). To achieve these reductions by
432 Southern Forest Resource Assessment
2010, the law invoked a restriction on Currently, high-elevation spruce-fir competitive inhibition of calcium
power plants fired with fossil fuels. forests are the most susceptible to the uptake by aluminum. Dendroecolog-
By 1995, nationwide emissions of SO effects of sulfur deposition (McLaughlin ical- and plot-based data have shown
2
were reduced by almost 40 percent and Percy 1999) because they lack the declines in radial growth of red
below their required level. In addition, ability to buffer sulfur deposition and spruce (LeBlanc and others 1992)
monitoring sites throughout the United are low in base cation pools. Future and canopy-crown deterioration
States found statistically significant rates of sulfur deposition are expected during the mid-to-late 1980s in
reductions in precipitation acidity and to decrease, which could lead to the Southern Appalachian Mountains
sulfate concentrations (National Acid a reduction in the effects of sulfur (Peart and others 1992).
Precipitation Assessment Program deposition on base cations in high-
Whereas acid deposition has affected
1998). Attempts to reduce nitrogen elevation spruce-fir forests. Recent
tree growth in spruce-fir forests of the
deposition were initiated in 1996. evidence indicates that most Southern
Southern Appalachians (McLaughlin
Although Title IV initiated a reduction Appalachian soils supporting spruce-
and others 1998), damage to these
in annual nitrogen deposition, new fir ecosystems are poorly buffered, high
ecosystems is not limited to acid
concentrations are expected to have in aluminum, and nitrogen saturated
deposition. Reams and Van Deusen
potential impacts on forests across (Johnson and others 1991). Nitrogen
(1993) reported that stand disturbances
the South. Modeling future projections saturation occurs when ammonium
and changes in stand dynamics have
and impacts of nitrogen and sulfur (NH ) and nitrate (NO ) are present in
resulted in radial growth declines in
4 3
deposition on forested ecosystems in quantities that exceed total combined
spruce-fir forests. In addition, the
the Southern Appalachian Mountains plant and microbial demand. Excess
balsam woolly adelgid was introduced
is an ongoing research objective of levels of nitrogen have been found to
into North America at the beginning
the Southern Appalachian Mountains affect soil and plant calcium:aluminum
of the 20th century, and the exotic
Initiative (SAMI). The North Carolina ratios (Johnson and others 1991),
insect has been active in the Southern
General Assembly is reviewing a bill cause aluminum toxicity (Shortle and
Appalachians since the late 1950s
that would reduce nitrogen oxides Smith 1988), and decrease calcium
(McLaughlin and others 1998). The
and sulfur oxides generated by coal- uptake and leaching of base cations
damage to mature Fraser fir in the
powered utility plants by more than (McLaughlin and others 1998) in
Southern Appalachians by the woolly
70 percent (North Carolina General these sensitive forests. A lack of
adelgid has been extensive over
Assembly 2001). Governor Michael calcium changes the wood structure
the past 15 years (Dull and others
Easley supports this legislation and has of spruce and fir and may change
1988). Although heavy infestation
begun to discuss regional air pollution the ability of branches to withstand
H is unquestionable evidence that the
reduction initiatives with lawmakers stress (McLaughlin and others 1998).
adelgid plays a major role in killing
around the South (North Carolina Furthermore, excess levels of nitrogen
E these trees (see chapter 17 for more
Department of Environment and decrease the rates of some critical
details), it is also important to consider
ANatural Resources 2001). functions of soil microorganisms,
the influence of predisposing factors,
including decay of forest floor material
LAcid Deposition including abiotic stressors such as acid
(Drohan and Sharpe 1997). These
deposition, on the susceptibility of
TData Sources effects on forest soils are most dramatic
forests to pathogens (Manion 1981).
H Primary data sources for sulfur in the sensitive soils under spruce-fir Hardwood forests in the South are
forests. Conversely, in an oak-pine
and nitrogen deposition were the considered less sensitive to nitrogen
forest in the North Carolina Piedmont,
National Acid Deposition Program deposition than spruce-fir forests
Johnson and others (1995) predict
(National Acid Deposition Program because they still have adequate stores
that forest floor nutrient contents
2000) and cited literature. of base cation nutrients, and the soils
will be virtually unaffected by a 50-
still maintain considerable capacity to
Acid Deposition Results percent reduction in sulfur deposition
retain the deposited nitrogen (National
over the next 20 years.
Although sulfur is an essential Acid Precipitation Assessment Program
Effects of acid deposition on tree
nutrient for soil and plant metabolic 1998). In most hardwood forests,
growth have been associated with
processes, sulfur deposition can virtually all nitrogen deposition is
nutrient limitations caused by increases
contribute to degradation of soil either adsorbed in the soil or used by
in soil aluminum concentrations.
chemistry (Reuss and Johnson 1986). vegetation and microorganisms. Much
Studies of historical tree-ring chemistry
Long-term increases in soil acidity of this nitrogen may be removed later
(Bondietti and McLaughlin 1992) have
resulting from sulfur deposition by forest harvesting. These systems
shown that calcium concentrations
are believed to affect nutrient cycling therefore have not shown negative
in stemwood increased as growth
by leaching nutrients, such as calcium effects from increases in nitrogen
increased during the late 1940s and
and magnesium (Fenn and others deposition and may respond with
1950s. However, decreases in tree
1998). Research has also shown that increased growth. Research has shown
growth were associated with increases
sulfur deposition provides the stimulus that 22.8 pounds per acre per year
in aluminum:calcium ratios in the
to mobilize aluminum in soil solutions of nitrogen fertilizer increased basal
wood, suggesting that the availability
(Reuss and Johnson 1986). Dissolved area growth of trees by 67 percent
of calcium was reduced at the same
aluminum interferes with the uptake (McNulty and Aber 1993).
time aluminum concentrations
of calcium and other root functions
Impacts of nitrogen deposition on
increased. McLaughlin and Kohut
(Johnson and others 1991).
forest health have not been detected
(1992) have shown evidence for the
Chapter 18: Abiotic Factors 433
in the pine and oak-pine forests of
Table 18.1—Acid neutralizing capacity (ANC) categories for brook
the South (National Acid Precipitation
trout response
Assessment Program 1998). However,
nitrogen is a major contributor to
the depletion of base cations in many meq/L Classification Biological response
buffered soils supporting southern
pine and oak-pine forests. Therefore, >50 Not acidic Reproducing brook trout populations
over the course of decades, nitrogen expected where habitat is suitable
deposition is likely to reduce pine
20-50 Transitional Extremely sensitive to acidification;
forest productivity (National Acid
brook trout response variable
Precipitation Assessment Program
1998). Increases in growth are expected
0-20 Episodically acidic Sublethal and/or lethal effects on
for some nitrogen deficient soils,
brook trout likely
whereas negative effects are expected
to be limited to the most acidic soils. <0 Chronically acidic Lethal effects on brook trout likely
In the future, nitrogen deposition will
Source: Bulger and others 1998.
continue to impact the structure and
function of high-elevation spruce-fir
forests. In addition, some hardwood, of brook trout can be altered by ANC drought, loss of foliage, insects, and
pine, and oak-pine forests that are (table 18.1). Furthermore, the Southern diseases. Hardwood, pine, and mixed
sensitive to nitrogen deposition could Appalachian Assessment has shown oak-pine forests are less sensitive than
respond with reduced growth rates and that 70 percent of sampled streams spruce-fir for several reasons, including
accelerated tree mortality over the long have suffered moderate to severe fish biological nitrogen demand, higher soil
term. However, research has predicted community degradation, and about cation exchange capacity, and faster
that in oak-pine forests in the North 50 percent of the stream miles in West nitrogen cycling.
Carolina Piedmont, vegetation will Virginia and Virginia show habitat Since most hardwood, pine, and
respond positively to a 200-percent disruption (Southern Appalachian mixed forests are nitrogen deficient,
increase in nitrogen deposition over Man and the Biosphere 1996). they may experience increased growth
the next 20 years. A 3- to 9-percent However, streams targeted by the rates in response to continued elevated
increase in vegetation nutrient content NSS in the southeastern highlands, nitrogen deposition. Conversely,
and a 10- to 30-percent increase (which includes the Ozarks/Ouachita, nitrogen deposition can significantly H
in forest floor nutrient content are Piedmont, Southern Appalachians, degrade some of these forests over
expected (Johnson and others 1995). Southern Blue Ridge, and ecological time (years to decades), especially E
subregions in the States of Arkansas,
Currently, the SAMI Class I in areas where nitrogen levels may A
Georgia, North Carolina, and
Wilderness Areas are much more be high and the soil has reached
Tennessee) appear to be buffered
sensitive to acid precipitation than any or is approaching saturation. L
from sulfur deposition by a substantial
other areas surveyed by the National Sulfate and nitrate concentrations T
amount of sulfate adsorption in
Stream Survey (NSS) in the Southern have increased in streams throughout
watershed soils (Rochelle and Church H
Appalachians (Herlihy and others the South, but not to levels that are
1987). As a result, sulfate concen-
1996). The wilderness areas of greatest considered regionally problematic.
trations in these streams are low.
concern are Otter Creek and Dolly Furthermore, sulfate and nitrate in
Sods in West Virginia. There, the Acid Deposition Discussion some streams are low or near detec-
percentage of acidic stream length and Conclusions tion limits (Swank and Vose 1997).
is high, pH is low, and sulfate and
inorganic aluminum concentrations Emissions of SO2 and NOx are Acid Deposition Needs
are high. Additionally, stream nitrate decreasing. However, plant species for Additional Research
concentrations, an indicator of acid structure and compositon, soil
To address the indirect impacts of
deposition effects, have been shown chemistry, and microbial activities
nitrogen and sulfur deposition that
to have a strong correlation with forest continue to change. Currently, the
lead to soil and vegetation degradation
age. The highest concentrations occur mortality and decline of Fraser fir
in high-elevation spruce-fir and
in old-growth forests, where biological and red spruce at high elevations in
hardwood forests, continued intensive
demand for nitrogen is lowest. The the Southern Appalachians are the only
monitoring, modeling, and validating
wilderness area of least concern is cases of significant ecosystem damage.
of acid deposition and nutrient cycling
the Sipsey in Alabama because sulfate Thus, less than 5 percent of the South is
processes must occur across local
concentrations are not increasing, currently being negatively impacted by
and regional scales. Monitoring efforts
and acid neutralizing capacity (ANC) elevated sulfur and nitrogen deposition
should be supplemented with long-
of streams in this area is high. (Fenn and others 1998). In addition,
term regional experiments (greater
atmospheric deposition reduces the
ANC has been used to determine than 5 years) in which realistic acid
number of microorganisms important
stream quality because stream deposition effects on soil chemical
to nutrient cycling and removes
acidification affects fish and other properties and stream quality are
important nutrients from the soil,
aquatic species. Research in the South evaluated (McNulty and others 1996).
making spruce-fir forests more
has shown that the biological response
susceptible to canopy deterioration,
434 Southern Forest Resource Assessment
Ozone Methodology: Ozone Data Sources
Ozone
Future Predictions
Ozone monitoring studies have
identified different O exposure profiles
Over the past century, industrial
3
Ozone Methodology: at high elevations (greater than 4,900
activity and automobile emissions
Current Conditions have increased the atmospheric con- feet) than at lower elevations (less than
1,600 feet) and near sea level (Aneja
centrations of O precursors. As a
Ground level O is created through 3 and others 1994). Levels of O in
a complex series o3f atmospheric result, typical ambient O3 concen- mountains are lower than in lo3wlands
trations have increased from 0.02-
chemical reactions involving NO during the daytime. Near sea level,
x 0.04 to 0.04-0.06 ppm—a trend that
and volatile organic compounds O levels are very high during the
is expected to continue into the 21st
(VOC) in the presence of specific da3y , often exhibiting a distribution
century (National Academy of Science
climatic and weather conditions characteristic of the peak hours for
1992). Assuming a 1- to 2-percent
(Chameides and Lodge 1992). Ozone automobile traffic. The concentrations
annual increase in tropospheric O ,
exposure levels are influenced by 3 in the mountainous areas of the South
as estimated by Fishman (1991), the
factors such as temperature, time of have important implications for forest
United States would achieve a 50-
day, relative humidity, wind speed, health. The ambient O concentrations
percent increase in ambient O in
wind direction, and spatial proximity 3 are sufficiently high to 3induce injury
21 (base 1990) years and a doubling
of anthropogenic and biogenic emission to sensitive native vegetation in the
of O concentrations in 35 years. The
sources (Schichtel and Husar 1999). 3 Blue Ridge Mountains (Skelly and
National Academy of Science (1992)
Ozone can reduce foliage, stem, and Hildebrand 1995). In addition, some
estimated an increase of 40 percent
root growth in trees by impacting leaf- areas in the region are downwind of
by the year 2020. Thompson (1992)
cell photosynthesis and gas exchange. significant NO and VOC emission
used several computer models to
x
Allen and Gholz (1996) revealed predict that O concentrations will rise sources. For example, regionally high
extensive spatial and temporal variation by 0.5 percent3 per year for the next 50 O levels found in the Blue Ridge
3
in O concentrations across the region. years, whereas Chameides and others Mountains and Shenandoah Valley of
3
For at least two reasons, accurate (1994) suggested that the frequency Virginia result from a combination of
prediction of annual variability in of O events with concentrations high upwind emission sources located in the
O levels for forested areas has not enou3gh to damage plants will triple industrial Midwest and specific weather
3
yet been achieved: (1) monitoring over the next 30 years. However, patterns (Wolff and others 1977). These
sites in rural, forested areas are lacking; more recent ozone modeling efforts weather-related O episodes may be
Hand (2) modeling O exposure is by SAMI predicted a 10- to 15-percent attributed to a com3bination of local-
3
very difficult because of weather reduction in maximum daily ozone and regional-scale factors: (1) higher
Eand human-related conditions that levels between 1995 and 2010 for than normal ambient temperatures, (2)
Acontribute to its annual variability the Southern Appalachians based wind speeds and directions associated
(Allen and Gholz 1996). However, on current emissions controls with stationary high-pressure systems
Lannual variation in O at select (Southern Appalachian Mountains that produce local air stagnation, and
3
Tmonitoring sites has been analyzed. Initiative 2001). (3) lower than normal relative humidity
(Aneja and Li 1990).
H Annual O variability for the United
3
States can be seen in figure 18.4,
which shows 3-month maximum
daily SUM06 O exposure levels for
3
1988 through 1992. A SUM06 value
is the sum of all mean hourly daytime
O concentrations that are at least
3
0.06 parts per million (ppm) over a
continuous 3-month period (92 days)
during the summer. The SUM06
exposure index represents the threshold
ambient O level (0.06 ppm-hours)
3
below which many forms of vegetation
can resist harmful cumulative O
3
effects. The SUM06 index may be
particularly useful because negative
effects of O exposure, especially
3
on tree photosynthetic capacity
(Richardson and others 1992)
and foliage production and retention
(Kress and others 1992), may be
Figure 18.4—Three-month maximum daily SUM06 ozone exposure
cumulative and linear, extending
grid for 1990 showing spatial variability in ozone concentrations. The
over multiple growing seasons. exposure grid was calculated by U.S. Environmental Protection Agency
using NHEERL-WED’s Geographic Information System model to spatially
interpolate SUM06 values calculated from the AIRS monitoring network
(Schichtel and others 1996).
Chapter 18: Abiotic Factors 435
Ozone Results reductions for pine seedlings in the the location of a burn, and substantial
South were between 2 and 5 percent. increases in O concentrations (greater
To cause tree damage, O must 3
3 For mature loblolly pines, Dougherty than 50 percent above ambient) have
be absorbed by the plant through
and others (1992) used a process model been detected downwind of burned
the stomatal openings found on the
to estimate annual growth reductions areas and at the top of burn plumes.
surface of leaves in a process known
of about 3 percent under ambient
as stomatal conductance. Stomates The important relationship between
O concentrations.
open during daylight hours to permit 3 soil moisture, stomatal conductance,
the exchange of gaseous compounds Hogsett and others (1997) found that and tree sensitivity to O levels high-
3
(CO , O and water vapor) necessary black cherry has strong O sensitivity, lights the importance of climate in
for p2hoto2,synthesis. At night, stomates and tulip poplar has mode3 rate O predicting future impacts of O on
3 3
close, preventing the transpiration sensitivity. Southern yellow pine species forest health. Under future climate
of water. Because stomates are open showed little response to changes in scenarios, trees in areas of the South
during the day, daytime O concen- SUM06 O concentrations, and sugar characterized by periods of persistent
trations are most likely to 3d amage maple exh3ibited a threshold response drought and poor soil water storage
trees. Rates of stomatal conductance in which annual biomass increased capacity will be more sensitive to
vary by species and age, and these rates dramatically between 26 and 38 O pollution and will likely incur
3
directly determine both the quantity ppm-hour per year SUM06. substantial visible foliar damage
of O uptake and the plant’s response Overall, it appears that the growth of (Maier-Maercker 1999) and growth
to a g3iven concentration of O (Kelly mature southern yellow pines is being reductions (Southern Appalachian
and others 1995). In general, 3ozone- reduced by current typical ambient O Mountains Initiative 2001).
3
sensitive tree species under high levels at annual rates that vary from 0
Ozone Needs for
O stress experience reduced leaf to 10 percent per year. Annual growth
3 Additional Research
area, slower growth during drought reductions for pine seedlings in the
conditions, and lower vertical South are probably between 2 and 5 Because expert predictions identify
growth rates (Southern Appalachian percent (Teskey 1996). However, at O as a significant forest stressor well
Mountains Initiative 2001). present there are no indications of in3to the 21st century (Heck and others
It appears that O affects growth and community level changes (competi- 1998), scientists and policy experts
vitality indirectly b3y predisposing trees tion dynamics, community structure, have jointly assessed critical research
to injury from other biotic and abiotic and function, etc.) attributable to needs pertaining to effects on forested
stressors (Chappelka and Freer-Smith O (McLaughlin and Percy 1999). systems. The Ecological Research
3 H
1995). For example, ponderosa pine Although O may be reducing annual Needs Workshop (U.S. Environmental
3
exhibits increased sensitivity to bark growth of trees in the South, other Protection Agency 1998) developed
E
beetle attack in the San Bernardino air-borne chemicals such as CO and one such set of research priorities.
2
Mountains following O damage (Cobb nitrogen and sulfur compounds may A summary of those priorities for A
and others 1968). In th3e South, pines be simultaneously increasing growth forests and natural areas is provided
typically do not show visible symptoms (Teskey 1996), thereby effectively here (Heck and others 1998): L
odfi tOio3n isn (jBueryrr uanngd earn adm obthieenrst O193 9c6o)n- omna sokvienrga ltlh feo rneesgt ahteivaelt hef.fects of O3 1to. Cscoanlisnigd erreastuioltns ionf gfarcotwortsh rcehlaatmedbers TH
except during extended periods of high Ozone Discussion to mature trees, stands, communities,
O levels when injury is readily visible. and landscapes.
3 and Conclusions
The amount and way that O affects 2. Measurement of selected endpoints
trees depend on the age of the3 trees The growth impacts of ambient (growth, mortality, foliage injury, etc.)
and the species. Given similar amounts O levels on southern pines appear in managed and natural ecosystems
3
of O exposure, immature hardwoods to be statistically significant at this such as loblolly pine plantations or
gene3rally exhibit more growth loss than time (McLaughlin and Percy 1999, bottomland hardwood ecosystems
softwoods (table 18.2) (McLaughlin Teskey 1996). Additional increases in across selected O gradients throughout
and Percy 1999). Based on the limited tropospheric O will almost certainly the South, using r3esults to support
3
number of studies available, mature have negative impacts on the growth development of empirical and process-
hardwood growth rates appear to be of pine species in the South (Southern based models designed to understand
more sensitive to O exposure than Appalachian Mountains Initiative the mechanisms of plant response
mature softwood gr3owth rates (table 2001, Teskey 1996). to O .
18.2). According to Dougherty and Another important consideration 3
3. Determination of utility of using
others (1992), an average mature for future forest health is the frequency
visible foliar injury and other biological
loblolly pine tree growing in a plan- and intensity of forest fires. Forest
indicators to interpret effects of O on
tation experiences a 3-percent annual fires produce carbon monoxide (NO) 3
specific indices of ecosystem health.
loss of gross primary production under and gaseous hydrocarbons that are x
ambient O conditions in the South. the precursors of atmospheric O 4. Development of economic
In a review3 of 19 studies measuring the (Bohm 1992). Therefore, forest f3ires techniques that measure changes
influence of O exposure on growth of may contribute to O production in the value of managed and natural
slash pine, sho3rtleaf pine, and loblolly in wilderness and ru3ral areas (Bohm ecosystems affected by O3.
pine seedlings and saplings, Teskey 1992). Bohm (1992) observed that 5. Development of a reasonable O
(1996) concluded that annual growth O has been found to accumulate near exposure index via defined relation3ship
3
436 Southern Forest Resource Assessment
Table 18.2— Estimates of ambient O effects on growth of forest tree species occurring in the South
3
Growth
Species reduction Conditions Source
Percent
Seedling/sapling studies
Multiple species 0-10 Shoot growth Chappelka and
Samuelson 1998
Southern pines 2- 5 Summary estimate of 19 field-chamber Teskey 1996
studies
Loblolly pine 0- 3 Mean response to 50-200 ppm-hr Taylor 1994
1-10 Sensitive family response to 50-200 ppm-hr (synthesis-whole tree
biomass)
Hardwoods 13 Values derived from response Reich and others 1988
Conifers 3 surface at 20 ppm-hr
Black cherry 10-24 Hogsett and others 1997
Yellow-poplar 5-13 Values derived from O exposure-
3
Sugar maple 0- 9 response functions and model-
Red maple 0- 1 simulated tree and stand
Loblolly pine 2- 5 responsea
Eastern white pine 4- 8
Virginia pine 0- 1
Mature tree studies
Loblolly pine 2- 9 Whole tree carbon model using branch Dougherty and others
H
chamber data (GA) 1992
E 3 Mean response
0-13 Mean annual weekly responses to O and McLaughlin and
A 3
interactions of O and moisture stress, Downing 1996
3
L 5 years (TN)
T 0- 5 Annual O effect—no water stress
3
0-30 Annual O effect—moderate water stress
H 3
Hardwoods 3-16 Regional simulation with canopy-stand Ollinger and others 1997
model across moisture gradients. Highest
reductions occurred in areas with highest
O levels and on soils with high water holding
3
capacity where drought stress was absent.
a Percent reduction in annual net primary production.
Source: McLaughlin and Percy (1999), with additions provided.
Chapter 18: Abiotic Factors 437
between O exposure concentration, smoke can impair road visibility and in coastal and floodplain areas. On
3
uptake dose, and selected endpoints breathing in sensitive individuals. average, floods cause almost $4
(growth, mortality, foliar injury). billion dollars in damage each year
Wildfire can substantially influence
(National Oceanic and Atmospheric
6. Study of the interactions between forest structure and function. Ecological
Administration 2000). Upland forest
O and other abiotic or biotic stressors. effects of forest fires include mortality
3 ecosystems that experience flooding
of individual trees, shifts in successional
respond with reduced photosynthetic
Climate Change and direction, induced seed germination,
rates; over extended periods, changes
acceleration of nutrient cycling, death
Extreme Weather- in tree species composition are possible,
of seeds stored in the soil, changes
Related Events in surface soil organic layers and as some species are more flood tolerant
that others (Burke and others 1999,
underground plant root and
Iles 1993). Most trees can withstand
reproductive tissues, volatilization of
1 to 4 months of flooding duration
Extreme Weather-Related soil nutrients, and increased landscape
without significant injury (Bratkovich
Event Methodology: heterogeneity (Whelan 1995). As a
and others 1993). In extreme situations,
result of these effects, the capacity of
Current Conditions higher mortality rates may occur (Iles
forests to provide wildlife habitat,
1993). Anaerobic soil conditions in
Climate effects on forest conditions timber, and recreation may be
flooded areas cause physiological
are most strongly expressed by diminished (Flannigan and
stress and influence nutrient availability
extreme events such as fire, hurricanes, others 2000).
(Burke and others 1999). Secondary
tornadoes, floods, drought, and ice Hurricanes—Hurricanes disturb
effects of flooding include elevated
storms (Dale and others 2000). Each forests along the coastlines of the
soil erosion and sedimentation rates
type of event affects forests differently; South. Ocean temperatures and
(Iles 1993). At the regional scale,
some cause large-scale tree mortality, regional weather influence the path,
there is high variability in the spatial
whereas others, such as ice storms, size, frequency, and intensity of
location and amount of disturbance
impact community structure and hurricanes (Emanuel 1987). An average
associated with floods.
organization without causing of two hurricanes strike land every
massive mortality. 3 years in the United States (Hebert Drought—Droughts occur in most
forest ecosystems in the South. Occur-
Wildfire—The frequency, seasonality, and others 1997). Some scientists have
rence is irregular in forests east of the
size, intensity, and type of wildfires hypothesized that hurricane impacts
Mississippi River, occasional across
depend on weather phenomena and on forests, including mortality, may
most of the South, and more common H
forest structure and composition. be related to soil characteristics
in late summer on the Coastal Plain
Fire initiation and spread also depend (Duever and McCollum 1993).
(Hanson and Weltzin 2000). Conse- E
on fuel availability, the presence of Tornadoes—Tornadoes are one
quences of long-term drought or
ignition agents, and topography. of the most important agents of abiotic A
flooding are generally proportional
Across the southern Coastal Plain, disturbance in eastern deciduous to the area affected; during the past L
forest shrub and brush species can forests. Nearly 1,000 tornadoes occur few decades, an increasing portion
T
create highly flammable fuel conditions each year in the conterminous United of the United States has experienced
in just 5 years under the right climatic States (Peterson 2000). In the South, either severe drought or flooding H
conditions if fuel loads are not tornadoes are very common in (Karl and others 1995c). Drought
managed. Therefore, fuel management Oklahoma and Texas and frequent effects are influenced by soil texture
is necessary. Each year, across all land in Alabama, Florida, Louisiana, and and depth, exposure, species compo-
ownership classes, 5.4 million acres Mississippi. Tornadoes can cause severe sition, life stage, and the frequency,
are managed with prescribed fire. mortality, reduce tree density, alter duration, and severity of drought.
Seventy-five percent of the prescribed stand-size structure, and modify local The immediate response of forests
burning occurs in the States of environmental conditions via soil to drought is to reduce water use
Alabama, Florida, and Georgia. All erosion or nutrient loss (Dale and and growth. Small plants, including
34 national forests in the region have others 2000). The resulting disturbance seedlings and saplings, are usually the
prescribed fire programs, and, since may bring about the release of advance first to succumb to moderate drought
1944, approximately 21 million acres regeneration, seed germination, or conditions. Deep rooting and stored
have been treated to minimize wildfire accelerated seedling growth (Peterson carbohydrates and nutrients make
risk (Forest Health Protection Program and Pickett 1995). These effects can large trees susceptible only to severe
2000). Fire management would be change gap dynamics, successional droughts (Dale and others 2001).
more prevalent were it not for smoke patterns, and other ecosystem level
Ice Storms—Ice storms occur
problems associated with controlled processes such as water use. The rela-
throughout the South. They are
burns. Criteria included in the U.S. tionship between wind strength and
produced when rain falls through
Environmental Protection Agency’s severity of disturbance varies by tree
subfreezing air masses, freezing when
National Ambient Air Quality species and forest type. Shallow-rooted
contact is made with objects on the
Standards for Particulate Matter (U.S. species and thinned stands tend to be
ground. Ice accumulation varies with
Environmental Protection Agency more vulnerable, but multiple factors
topography, elevation, and area of
1997b) limit the amount and extent influence tree response to windstorms.
exposure. Ice storms may sever twigs
of prescribed fire programs because Floods—Floods occur throughout
and bend or break stems, causing
the South but are most concentrated
438 Southern Forest Resource Assessment
moderate crown loss. Damage to forest and environmental scenarios. The For the continental United States, the
stands can range from light and patchy several biogeography models used HadCM2Sul scenario includes a
to the breaking of all mature stems, for this Assessment included the relatively modest 2.8∞ average increase
depending on stand composition, past Mapped Atmosphere Plant Soil System in air temperature, a 20-percent average
disturbances, and the amount of ice (MAPSS), BIOME3, and MC1 (Bachelet increase in precipitation, and effects
accumulation (Irland 2000). Effects and Neilson 2000, Bachelet and others of doubled CO and altered sulfate
2
of ice storms on forest stands include 2001). Input datasets include latitude, aerosol concentrations (based on IPCC
stem damage, loss of growth until leaf mean monthly temperature, wind projections of future greenhouse gases)
area is restored, and possible shifts in speed, solar radiation, and soil by 2100 (Bachelet and others 2001).
tree species composition toward trees properties such as texture and depth. The mean temperature increase for the
more resistant to ice damage. All of these models project vegetation South is about 1.0∞ by 2030 and 2.3∞
responses to changes in CO but by 2100; this degree of warming is
Recently thinned stands may have
2
through different mechanisms. smaller than that of any other region
increased vulnerability to ice storm
(National Assessment Synthesis Team
damage because tree crowns have Climate Change and
2001). This scenario predicts that the
spread into openings, but branch
Extreme Weather-Related South will remain the wettest region
strength has not yet increased.
Potentially, there are several secondary Event Data Sources for the next century; mean annual
precipitation increase will be about
consequences of ice damage. Sus-
To date, it is generally believed 3 percent by 2030 and 20 percent
ceptibility to insects and diseases
that hotter and more variable air by 2100. Other regions in the
may be increased, and fuel loads
temperatures will occur across the Eastern United States are predicted
may accrue, heightening wildfire
United States in the future (National to experience similar increases in
risk in some areas (Irland 2000).
Assessment Synthesis Team 2001). precipitation (National Assessment
Climate Change However, the timing and distribution Synthesis Team 2001).
of precipitation or other weather
Methodology: Future Predictions of forest area, distribution,
phenomena are much less certain
Predictions and biodiversity used four equilibrium
(Dale and others 2000). The transient
(UKMO, GISS, GFDL-R30, OSU)
climate change scenarios used for this
The effects of climate change on and three transient (HadCM2Sul,
Assessment do not adequately represent
southern forest productivity and HadCM2GHG, CGCM1) climate
extreme events because of their coarse
hydrology across a range of climate scenarios as input for the MAPSS
spatial and temporal resolution
Hand site conditions were assessed biogeography and MC1 dynamic
(monthly time step, approximately
with the well-validated, physiologically global vegetation models. The range
1,000 square miles) (National
Ebased forest process model PnET-II Assessment Synthesis Team 2001). in temperature increase is 2.8 to 6.6∞
(McNulty and others 2000). PnET-II for all scenarios, with changes in
A Extreme events may last only minutes
used four monthly climate variables precipitation varying greatly between
or days, and their extents may range
L(amir itneimmpuemra tauirr et,e mprpeecripatiutartei,o nm, aaxnimdum from local to small regional scales. tthraen sscieennta r(iaoss w, aitnhd HchadanCgMes2 Sinu lC) Oor2
T When the effects of extreme events
solar radiation), forest-type-specific instantaneously doubling in the case
are averaged over large periods of time
Hvegetation parameters, and site-specific of the equilibrium scenarios. MC1 used
and space, much information is lost.
soil water holding capacity to predict only HadCM2Sul and CGCM1, whereas
Therefore, very little quantitative data
forest growth and drainage across MAPSS used all equilibrium scenarios
on extreme weather events are available
the South at a 0.5- by 0.5-degree and averaged the last 30 years of the
to predict future forest impacts. Instead,
(approximately 30- by 30-mile) spatial transient scenarios so they could be
we will discuss the potential impact
resolution. Atmospheric CO increases treated as equilibria. The BIOME3
2 of projected general trends in extreme
were incorporated into PnET-II by model used only the transient climate
weather events on forest structure
entering the relationship between water scenarios (Bachelet and Neilson 2000).
and function.
use efficiency (WUE) and CO level.
PnET-II results for pine and ha2rdwood Two climate datasets developed by Climate Change and
forest types have been validated for the Vegetation/Ecosystem Modeling and Extreme Weather-Related
the South (McNulty and others 2000). Analysis Project (VEMAP) were used
Event Results
with the PnET-II model to assess future
Impacts of climate change on forest
climate impacts on southern forest Wildfire—Because climate change
area, distribution, and biodiversity were
growth. The Historical Climate Series may alter the frequency, intensity,
studied with biogeography models.
includes monthly and daily climate distribution, or extent of wildfires,
This type of model uses resource and
data with interannual variability for the species regeneration patterns may be
ecophysiological constraints such as
conterminous United States from 1895 disturbed with species or communities
available soil water and minimum
to 1993 (National Assessment Synthesis at the edges of their natural range
winter temperatures to simulate climate
Team 2001). The Hadley Centre experiencing potentially severe effects.
change impacts on forest ecosystems
HadCM2Sul transient climate change
at regional, continental, and global Model results from the fire
scenario was used to represent climate
scales (Bachelet and Neilson 2000). distribution module of MC1 predict
variables from 1994 to 2100; other
The biogeography models used here great variation in future fire-weather
climate scenarios exist but were not
predict the dominance of different patterns for the northern portion of
available at the time of this analysis.
plant species under different climatic North America (Bachelet and Neilson