Climate Change and Managed Ecosystems - Chapter 10 pptx

201
10
Peatlands: Canada’s
Past and Future
Carbon Legacy
D.H. Vitt
CONTENTS
10.1 Introduction 201
10.2 Limitations on Carbon Sequestration in Boreal Peatlands 203
10.3 The Ecology of Boreal Peat Accumulation 204
10.3.1 Bog Accumulation 205
10.3.2 Poor Fen Accumulation 205
10.3.3 Rich Fen Accumulation 205
10.4 Northern Peatlands: Sinks or Sources of Carbon? 206
10.5 Potential Climatic Effects on Peatland Form and Vegetation 207
10.6 Permafrost Melting in the Boreal Forest 209
10.7 Global Climate Change vs. Cumulative Disturbance 210
10.8 Mitigation 211
Acknowledgments 213
References 213
10.1 INTRODUCTION
Peatland ecosystems are characterized by the accumulation of organic matter in soil
and, if following Joosten and Clark’s
1
definition of having at least 30 cm of peat
with a minimum organic content of 30%, then peatlands cover over 4 million km
2
— about 3% of the Earth’s land surface. Nearly 70% of this peatland area lies in
the boreal regions of Canada and Russia. Canada alone contains just over 1,200,000
km
2

of peat. Peatlands are significant in that they provide a wide diversity of
ecosystem services, not the least of which is the accumulation of large stores of
carbon. Joosten and Clark
1
estimated that since 1800, 10 to 20% of the world’s
peatlands have been lost, but it has been the view of many that Canada’s peatlands
remain in pristine condition, undisturbed by human activities.
2
However, as we will
see, this is certainly not the case.
Globally, wetlands (especially peatlands) represent a large carbon stock, with
estimates varying from 200 to 860 Pg (= Petagrams) of carbon (see for example
© 2006 by Taylor & Francis Group, LLC
202 Climate Change and Managed Ecosystems
Gorham,
2
Bohn,
3,4
Sjörs,
5
Post et al.,
6
Houghton et al.,
7
Armentano and Menges,
8
and Markov et al.
9
). Generally, carbon-rich peatland soils are thought to represent
about one third of the world’s soil carbon, yet cover only about 3% of the land

surface. Release of this store of carbon into the atmosphere would increase atmo-
spheric CO
2
concentrations by more than 50%. Canada’s peat inventory has been
estimated to contain up to 170 Pg of carbon
2
and is approximately 38% of the carbon
stock in northern peatlands. The western boreal forest region of Alberta,
Saskatchewan, and Manitoba contain 365,157 km
2
of peatlands and along with
British Columbia these four provinces have about 40% of Canada’s peatland area,
while eastern Canada (Ontario eastward) contains about 37%, and northern Canada
(the three territories) contains approximately 23%.
10
In terms of carbon, western and
northern Canada store at least 83 Pg, whereas eastern Canada has a minimum of 52
Pg. In Alberta, peatlands may contain as much as 70% of the province’s soil carbon
(13.5 Pg C in peatlands; 2.3 Pg C in lakes, 2.7 Pg C in forests, and 0.8 Pg C in
grasslands (data from J. Bhatti
11
). In general, the western Canadian peatlands have
sequestered about 48 Pg of carbon during the past 10,000 years, with about half of
this accumulated in the last 4000 years.
12
Peat accumulates on the landscape when annual net primary production exceeds
the sum of annual decomposition and the loss of carbon that is dissolved in the pore
water and exported from peatlands. The initiation, development, and succession of
ecosystems that sequester carbon, as well as the rate of peat accumulation in boreal
peatlands, are dependent on regional allogenic factors such as climate, substrate

chemistry, and landscape and hydrological position. These regional driving factors
in turn determine a suite of local factors that influence the form and function of
individual peatland sites (Figure 10.1). These local factors include water chemistry,
FIGURE 10.1 Diagrammatic representation of the interactions between regional, local, and
ecological factors that control function and form of peatlands.
Regional
Local
Disturbance
Function Form
Position
Climate
Autogenic
Processes
Vegetation
and Flora
Water Flow
Nutrients
Water
Chemistry
Water Level
Fluctuation
Production
Decomposition
Carbon Sequestration
Succession
Bog Development
Pattern Development
Landform Development
Substrate
© 2006 by Taylor & Francis Group, LLC

Peatlands: Canada’s Past and Future Carbon Legacy 203
water level fluctuation, water flow rates, and nutrient inputs. Peatland form is deter-
mined by this interacting suite of local and regional factors through the development
of ombrotrophy wherein the peatland receives all water and nutrients from the
atmosphere, evolution of internal landforms and landscape pattern, and the direction
of succession. Additionally, once established, peatlands have strong autogenic con-
trols (acidification, eutrophication; Vitt
13
) that also help regulate form and function.
14
The functioning of peatland ecosystems centers on the process of peat accumu-
lation. Yu et al.
15
provided conceptual diagrams of carbon cycling in peatlands. Peat
accumulation is dependent on the rate of input of organic matter into the anaerobic
peat column (the catotelm) and on the rate of the slow decomposition of this material
over time.
16
Climate is the most important regional factor, mainly through its regu-
lation of local water regimes. Among climatic variables, Halsey et al.
17
demonstrated
for wetlands of Manitoba that temperature and aridity are the most critical limiting
factors at the landscape scale for peatland ecosystems.
Climate affects carbon sequestration by limiting photosynthesis and aerobic
(acrotelm) decomposition rates, thus influencing the amount and quality of the
organic material reaching the catotelm. Climate also affects carbon stocks within
the catotelm by limiting anaerobic processes (methenogenesis, sulfate reduction, and
N
2

O production), as well as controlling the position of the acrotelm–catotelm bound-
ary. Thus, climatic change can affect current peat accumulation as well as persistence
of the peat column itself.
10.2 LIMITATIONS ON CARBON SEQUESTRATION
IN BOREAL PEATLANDS
Four factors contribute to limiting carbon sequestration in pristine boreal peatlands:
(1) The formation of permafrost in boreal peatlands reduces the input of carbon to
the peatland. (2) Ground layer biomass contributes high-quality organic matter that
is resistant to decay to the peat column and, along with vascular plant roots and litter
from aboveground vascular plant biomass, compose the carbon inputs to peat-form-
ing ecosystems. These inputs are limited by net annual primary production (NPP).
(3) Rates of aerobic respiration (occurring in the acrotelm) limit peat accumulation.
Rates of aerobic decomposition may be determined by substrate quality and by
temperature. (4) The amount of time the decomposing plant material spends in
aerobic conditions. In summary, cold, dry climatic conditions favor permafrost aggra-
dation; warm, dry (arid) conditions limit ground-layer NPP and increase acrotelm
depth, while warm, wet conditions increase microbial respiration. Peat accumulation
decreases with aridity and increases under cool, moist conditions (Figure 10.2).
Corollaries to these relationships provide us with four mechanistic statements:
1. Increases in precipitation increase the ground layer production, and these,
coupled with a rise in water table, decrease residence time in the acrotelm
lowering initial catotelmic bulk densities: Carbon sequestration increases.
2. Decreases in precipitation decrease ground layer production and are cou-
pled to a lowering of the water table. These factors increase the residence
© 2006 by Taylor & Francis Group, LLC
204 Climate Change and Managed Ecosystems
time in the acrotelm, thus increasing the initial catotelmic bulk densities:
Carbon sequestration decreases.
3. Increases in temperatures increase acrotelmic respiration, hence increas-
ing initial catotelmic bulk densities: Carbon sequestration decreases.

4. Decreases in temperatures decrease acrotelmic respiration, hence decreas-
ing initial catotelmic bulk densities: Carbon sequestration increases.
10.3 THE ECOLOGY OF BOREAL PEAT ACCUMULATION
Accumulation of peat in the boreal region appears to occur under three somewhat
different ecological regimes.
FIGURE 10.2 Factors limiting carbon sequestration in boreal peatlands plotted over climatic
space represented by temperature (inverse on y axis) and precipitation (x axis). Shading of
central ellipse indicates increased rates of carbon accumulation. A = Direction of increase in
ground-layer NPP. B = Direction of bulk density decrease. White circle = Estimated peat
accumulation during Holocene wet period.
43
Black circle = Estimated peat accumulation
during Holocene dry period.
43
Details of long-term peatland dynamics are available in Yu et
al.
15,50
Dotted line is degrading permafrost.
A
B
Cold
Cool
Warm
Temperature
Precipitation
Acrotelm
Depth
Increase
Decreased
Ground layer

NPP
Permafrost
Aggradation
Dry
Wet
Moist
© 2006 by Taylor & Francis Group, LLC
Peatlands: Canada’s Past and Future Carbon Legacy 205
10.3.1 B
OG
A
CCUMULATION
Bogs are ombrogenous, receiving their nutrients and water supply solely from the
atmosphere as precipitation. Bogs that occur in the boreal region are generally
treed and possess a continuous ground layer of Sphagnum (peat mosses). These
peat mosses develop an extensive, undulating microrelief of hummocks and hol-
lows. Hummocks attain heights of nearly 1 m above the water surface. Thus the
aerobic zone of decomposing peat (the acrotelm) is well developed and organic
matter spends a relatively large amount of time in this zone; however, rates of
decomposition are reduced here largely due to factors inherent in the Sphagnum
species themselves.
18–20
Furthermore, catotelmic bulk densities are relatively low
due to the fibrous nature of the hummock-occurring Sphagnum species and low
number of graminoid roots.
10.3.2 P
OOR
F
EN
A

CCUMULATION
Fens are geogenous, receiving waters and nutrients that have been in contact with
the surrounding uplands as well as from precipitation. Poor fens have ground layers
dominated by species of Sphagnum and are acidic ecosystems. The Sphagnum
species of poor fens occur in carpets and lawns forming extensive flat areas relatively
close to the water’s surface. Thus, the acrotelm is poorly developed and the residence
time of organic material in the aerobic zone is low, with the organic matter reaching
the catotelm rather quickly. Catotelmic bulk densities are higher than in bogs, but
due to the fibrous nature of Sphagnum and the low root biomass, are less than those
of the rich fens.
10.3.3 R
ICH
F
EN
A
CCUMULATION
Geogenous rich fens have ground layers dominated by true mosses (generally
referred to as “brown mosses”). These plants, like the sphagna of poor fens, form
lawns and carpets, water tables are high, and acrotelms are poorly developed.
Ground-layer canopies of rich fens differ from those of poor fens and bogs by the
difference between true moss and peat moss plant architectures. The rich fen
acrotelm has denser canopies because it is dominated by true mosses. As a result
of the high water table in rich fens, this relatively dense (carbon-rich) ground layer
spends little time in the acrotelm, and reaches the catotelm as high-quality peat
with high bulk densities. Additionally, rich fens have higher abundances of grami-
noids, and sedge roots also contribute to the high bulk densities.
All three peatland types effectively sequester carbon, each in a somewhat dif-
ferent manner. Fundamental differences in vegetation, hydrology, and chemistry
between these three peatland types
13,21

lead to three generalizations about how
climate change can affect the ecology of these peatland systems.
1. Bogs require a local positive climatic water balance. The large Sphagnum
hummocks and well-developed acrotelms must be maintained through
precipitation input. Nutrient supplies for these ombrogenous peatlands are
dependent on atmospheric influxes.
© 2006 by Taylor & Francis Group, LLC
206 Climate Change and Managed Ecosystems
2. Fens require a constant groundwater source, and the acrotelm–catotelm
boundary (so critical for peat accumulation in fens) must be maintained
at a relatively stable elevation. Lowering of water tables or changes in
annual water table fluctuations alter the boundary conditions.
3. Changes in upland and surrounding nutrient fluxes strongly affect fens,
whereas changes in atmospheric nutrient inputs strongly affect bogs.
In conclusion, peat accumulation and the sequestration of carbon from the
atmosphere (as CO
2
) to solid organic matter (as CHO) is determined and controlled
by a series of interacting processes. I argue that four of these processes are of
most importance (Figure 10.2) and that all of these are climatically controlled.
Two are more affected by temperature, while the other two are more affected by
precipitation. How these four factors interrelate and how they are individually
affected by climate change is still poorly understood and needs to be a priority
research goal.
10.4 NORTHERN PEATLANDS: SINKS OR SOURCES
OF CARBON?
Although I believe that it is generally acknowledged that northern peatlands are a
present-day sink for atmospheric CO
2
,

2
several complicating factors exist that may
severely limit their role in maintaining this large carbon sink.
Local temporal and spatial variation in carbon sequestration is high. Annual
changes from net carbon sinks to net carbon sources have been demonstrated for an
oligotrophic pine fen in Finland by Alm et al.,
22
a Minnesota peatland by Shurpali
et al.,
23
a Manitoba rich fen by Suyker et al.
24
and Lafleur et al.,
25
and a temperate
poor fen by Carroll and Crill.
26
Likewise, spatially local microhabitats may be either
net sinks or sources.
27
The concept of the Canadian peatlands and the boreal forest being of a pristine
nature is doubtful. Long-term carbon accumulation rates have been estimated at
between 19.4 g m
2
yr
–1
for western Canada
12
and 28.1 g m
2

yr
–1
for northern
peatlands in general.
2
These rates, however, are based on apparent long-term
accumulation in pristine peatlands (and as well may not be representative of current
net rates), and do not take into consideration peat lost from the direct and indirect
effects of fire and other natural disturbances. If peat losses due to the effects of
the historical fire regime are added back into the 19.4 g m
2
yr
–1
estimates of peat
accumulation the actual rate of peat accumulation is 24.5.
28
In the only cumulative
effects study of which I am aware, Turetsky et al.
28
estimated that 13% of western
Canada’s peatlands are disturbed. She estimated that of the 8940 Gg C yr
–1
of
carbon that should be sequestered annually under a no-disturbance regime, 48 Gg
C yr
–1
are lost to oil sands mining, 80 Gg C yr
–1
to flooding from hydro-electric
projects, 135 Gg C yr

–1
to peat extraction activities, 4704 Gg C yr
–1
from the direct
effects of fire (carbon released from the fire itself), and 1578 Gg C yr
–1
are lost
to the indirect effects of fire (due to decreased sequestration of carbon from
vegetation recovery, plus decomposition during recovery). On the positive side,
© 2006 by Taylor & Francis Group, LLC
Peatlands: Canada’s Past and Future Carbon Legacy 207
melting of boreal permafrost yields a return of +100 Gg C yr
–1
(see Turetsky et
al.
29
for explanation) and undisturbed peatlands sequester 7781 Gg yr
–1
of carbon.
Overall, disturbance and development across western Canada has reduced the
annual carbon sequestration to +1319 Gg C yr
–1
— only 14% of the long-term
carbon sink rate. Increases in any of the anthropogenic disturbances or in the
future fire regime, or a decrease of only 17% in the carbon sequestered in undis-
turbed peatlands because of drought and or temperature increases, will move
western Canadian peatlands from a sink to a source of CO
2
.
Additionally, peatland types differ in the forms of gaseous carbon release and

have different global warming potentials. Anaerobic respiration releases include
methane (among other gases). Methane is a greenhouse gas with different absorptive
properties and different atmospheric lifetimes from those of CO
2
. Boreal wetlands
release an estimated 34 Tg of CH
4
annually.
30,31
Joosten and Clark
1
provided global
warming potentials (GWP) for northern pristine bogs and fens that were calculated
for different time horizons into the future. Their data indicate that currently pristine
fens remove 250 kg C ha
–1
yr
–1
(as CO
2
) and release 297 kg C ha
–1
yr
–1
(as CH
4
),
while bogs currently remove 310 kg C ha
–1
yr

–1
and release 53 kg C ha
–1
yr
–1
. So,
even though a carbon sink is indicated by 560 kg C ha
–1
yr
–1
being sequestered and
only 350 kg C ha
–1
yr
–1
released, differences in atmospheric properties of CO
2
and
CH
4
produce a positive GWP when calculated per hectare for bogs and fens over
the next 20- and 100-year intervals, but a negative GWP at 500 years due to different
atmospheric residence times of the gases involved.
10.5 POTENTIAL CLIMATIC EFFECTS ON PEATLAND
FORM AND VEGETATION
Gignac et al.
32
established response surfaces for a number of the indicator and
keystone species of western Canadian peatlands for climate (using an aridity index),
pH, and height above the water surface table. Of the 31 indicator species that were

examined, all but 8 are climatically limited in western Canada. Using these response
surfaces, Gignac and Vitt
33
developed peatland indicator bryophyte communities and
constructed two peatland communities for contemporary climate; one at Athabasca,
Alberta and one at Wandering River, Alberta. These communities encompassed a
range of peatland types from bogs to rich fens. Then, by using the Canadian CCC
General Circulation model 2 × CO
2
scenario that predicted an increase of 4°C for
these southern boreal sites, an increase in the growing season of 19 days, and no
increase in precipitation, two future climate peatland bryophyte communities were
constructed. The resulting indicator communities for these two locations show the
complete absence of all peatland species at Athabasca and a reduction of cover at
Wandering River from 14 species with 77% cover to 5 species with less than 1%
cover. Essentially, peatland communities would cease to exist at both of these
southern boreal locations.
Nicholson and Gignac
34
and Nicholson et al.
35,36
examined the current and future
occurrences of fens and bogs in the Mackenzie River Basin. They constructed three-
dimensional response surfaces for 21 indicator species spanning the rich fen, poor
© 2006 by Taylor & Francis Group, LLC
208 Climate Change and Managed Ecosystems
fen, boreal bog, and peat plateau (ombrotrophic sites with extensive permafrost)
gradient. Under 2 × CO
2
climatic scenarios (using both the GFDL and CCC General

Circulation Models), peatland ecosystems of all types were displaced northward
approximately 780 km (Figure 10.3). The southern limit of peat-forming ecosystems
was predicted to be at about 60° N latitude. Bryophyte species are especially sensitive
indicators of water level changes, and Nicholson et al.
36
utilized these sensitivities
to predict projected changes in depth to the water table relative to the peat surface.
Predictions of changes ranged from –7 dm in northeastern Alberta, to –5 dm in north
central Alberta, decreasing to a –3 to –1 dm change north of 60˚ N latitude (Figure
10.4). The use of plant indicators to predict water table position is a site-specific
modeled response that has much more ecosystem relevance than predictions made
from landscape-scale hydrology. Present-day vegetation response for drawdown is
clearly evident in fens of the Athabasca area, which is situated north of central
Alberta. Furthermore, the latitudinal position of the parkland–boreal forest boundary
may react to increasing temperature through a parallel northward migration.
FIGURE 10.3 Geographical locations of extant peatlands (left) and projected distributions
(right) by peatland type of sites in the Mackenzie River Basin as a result of global warming.
Climatic data that were used by the model to generate the projected distribution of peatlands
were obtained from the Geophysics Fluid Dynamics Laboratory (GFDL) Model for 2 × present
CO
2
concentrations. (From Nicholson, B.J. et al., in Mackenzie Basin Impact Study (MBIS),
Final Report, Cohen, S.J., Ed., Environment Canada, Downsview, Ontario, 1997, 295. With
permission.)
© 2006 by Taylor & Francis Group, LLC
Peatlands: Canada’s Past and Future Carbon Legacy 209
10.6 PERMAFROST MELTING IN THE BOREAL FOREST
In 1994, Vitt et al.
37
described a series of landforms associated with permafrost

features (frost mounds) found in boreal peatlands. When these frost mounds melt,
they collapse and form melt features termed internal lawns. Boreal permafrost melt
is in disequilibrium with present-day climate,
38
owing to the insulative features of
peat and of living Sphagnum, as well as the local microclimatic variation due to tree
and shrub cover. Over the last millennium, permafrost distribution in the boreal
forest has fluctuated in a sensitive zone that is 672,000 km
2
in extent across western
continental Canada. During the Little Ice Age, about 28,800 km
2
of permafrost were
present.
39
With the climate warming over the past 100 to 150 years, 9% (or 2627
km
2
) of this permafrost has degraded. Additionally, 22% (5813 km
2
) is currently in
disequilibrium and actively degrading. Only 69% of boreal permafrost exists today
in an equilibrium undegraded state.
Collapse of a frost mound is followed by extremely rapid recolonization of the
resulting internal lawn by sedges and species of Sphagnum that form wet carpets
and lawns.
37,40,41
Over the subsequent 100 to 200 years, vegetation of the internal
FIGURE 10.4 Projected minimum mean changes in depth of water table relative to peat
surface (dm) for peatlands in the Mackenzie Basin based on climatic data obtained from the

Canadian Climate Centre (CCC) Model for 1 × and 2 × present CO
2
concentrations. (From
Nicholson, B.J. et al., in Mackenzie Basin Impact Study (MBIS), Final Report, Cohen, S.J.,
Ed., Environment Canada, Downsview, Ontario, 1997, 295. With permission.)
© 2006 by Taylor & Francis Group, LLC
210 Climate Change and Managed Ecosystems
lawn gradually increases in height and the system regenerates to the hummocky
microrelief of a continental bog. For at least the first 100 years, carbon sequestration
in internal lawns is greater than that of both nonpermafrost boreal bogs and perma-
frost mounds,
29
and the melting of permafrost results in an increase in the storage
of organic matter. Turetsky et al.
29
reported organic matter accumulation in internal
lawns (formed when permafrost melts) are 1.6 times higher than the close-by frost
mounds and boreal bogs. Organic matter accumulation in boreal western Canada
(where at least 90% of the permafrost has melted) has increased by 5% (or 2 × 10
–11
g yr
–1
) when compared to Little Ice Age amounts.
12
10.7 GLOBAL CLIMATE CHANGE VS. CUMULATIVE
DISTURBANCE
Across the boreal and subarctic regions of the world large amounts of carbon are
sequestered in different places in our natural ecosystems. Carbon can be sequestered
in lakes and buried in lake sediments where it is effectively permanently removed
from the global carbon cycle. In Alberta, Campbell et al.

42
estimated that about 2.3
Pg of carbon are stored in this long-term sink.
Forests and croplands, on the other hand, sequester new carbon that is released
and recirculated to the atmosphere within a short-term time range of decades to a
few hundred years and have current soil carbon stocks estimated at 3.5 Pg C.
11
These
two ecosystem types have carbon stored largely in living biomass and in the upper-
most relatively shallow soil profile. These systems are generally intensively managed
with harvest and planting cycles planned and implemented following tight manage-
ment schedules.
Northern peatlands contain one third of the world’s soil carbon. In Alberta, they
contain about 13.5 Pg of carbon, while in continental western Canada they store 48
Pg of carbon of which only 0.1 Pg is found in living vascular plant aboveground
biomass.
12
Of this large carbon stock, 50% was developed in the last 4000 years.
Vitt et al.
12
estimated that in the last 1000 years, the western Canadian carbon store
increased by 7.1 Pg or 14.8%. Both rates of peat accumulation and peatland initiation
apparently are highly sensitive to natural Holocene climatic changes. In western
Canada, carbon sequestration has been highly sensitive to millennial wet climate
cycles.
43,44
These periods of increased moisture, rapid organic matter accumulation,
and increased peatland initiation in western Canada appear to be related to warm
periods in the North Atlantic,
45

as well as to global atmospheric CO
2
concentrations
in the past.
43
Peat accumulation rates at one rich fen in western Alberta varied from
means of about 183 g m
2
yr
–1
during wet periods to a low of 7 g m
2
yr
–1
during dry
periods (with the long-term time-weighted mean of 31.3).
43
These data suggest that
even minor climatic fluctuations in the past have had strong affects on peatland
function and they may alter the rates of peat accumulation considerably. Furthermore,
northern peatlands appear to be strongly coupled to natural global climatic changes.
From these data it is apparent that boreal peatlands have been strongly affected
by climate change in the past; however, it is also important to realize that the
cumulative effects of disturbance may actually have more of an impact on these
© 2006 by Taylor & Francis Group, LLC
Peatlands: Canada’s Past and Future Carbon Legacy 211
carbon-rich ecosystems. Given current disturbance in the western boreal forest,
28
reduction in carbon sequestration rates by only 17% will convert these northern
peatlands to a net CO

2
source to the atmosphere. This reduction in carbon seques-
tration is closer to reality then one might expect. Currently, it appears that much
of the area in boreal western Canada is too dry for new peatland initiation, and
current peatlands are largely relicts of a once wetter (and perhaps cooler) climatic
regime.
46,47
Increased atmospheric CO
2
concentrations are predicted to increase
temperatures and perhaps decrease precipitation, or at least increase drought across
the boreal zone, where peatlands are abundant. This global climate change will
potentially reduce carbon sequestration through a series of progressively more
severe mechanisms.
• Net primary production of the ground layer will decrease, thus new high
quality (= highly recalcitrant) carbon input to the ecosystem will be
reduced.
• Belowground net primary production (vascular plant roots) will increase
in some peatland types, thus new low-quality (= easily decomposed)
carbon input to the ecosystem will be increased and may increase methane
production.
• Rates of microbial respiration will be increased; thus existing carbon will
be released to the atmosphere at an increased rate. This assumes that
decreased moisture availability in the acrotelm will not be so severe as to
decrease microbial respiration.
• Initially, acrotelms will increase in depth; thus the residence time of young
peat in an aerobic atmosphere will increase the amount of CO
2
released
to the atmosphere, but will also serve to oxidize the methane produced

in the catotelm.
• With lowered water tables, hummock-growing plant species will die in
place and recolonize the previous hollow/lawn — the result will be
enhanced decomposition (and loss of) the uppermost peat column until
equilibrium with the new water table is established.
• Continued aridity will limit keystone bog species. Peatlands will only
continue to serve as a carbon sink in discharge sites served with stable
groundwater flows; however, these peatlands will be at risk or reduced
due to increased decomposition.
• It remains unclear whether new peatland initiation and development north
of 60˚ N latitude will be as extensive as the loss of peatlands to the south
and whether the peatland carbon stock will remain intact.
• Altered disturbance regimes, especially increases in fire frequency, may
lead to catastrophic carbon losses from peatlands, especially bogs.
10.8 MITIGATION
It is my opinion that even under current climate conditions of the western Canadian
boreal region, most boreal Canadian peatlands may not be able to continue to
sequester carbon. What their ultimate fate will be is currently unknown and should
© 2006 by Taylor & Francis Group, LLC
212 Climate Change and Managed Ecosystems
be a high research priority. The worst-case scenario is clearly shown in predictions
by Nicholson et al.
35,36
The best-case scenario may be a “resetting” of the peat surface
at some distance below the present surface, with recolonization and continued carbon
sequestration. What is not known is how much, and in what gaseous form, the
uppermost peat column will be lost.
Clearly, mitigation for these loosely managed boreal peatlands is difficult. How-
ever, several priorities are suggested here:
• Develop a long-range plan of corridors and reserves that includes pre-

dicted future occurrences of peatlands. Since our future peatlands may
only exist in a fully functional condition north of 60˚ N latitude, we
should begin now to incorporate a reserve system that examines these
northern sites.
• Restoration of wetlands after oil sands extraction may only be possible
by examining wetlands that currently exist under our future predicted
climatic regime. Examination of how these wetlands have initiated and
continue to exist may provide valuable insights into our wetland environ-
ments. For example, a key indicator species of rich fens is Meesia trique-
tra. Examination of herbarium specimens and distribution maps
48
of the
occurrence of M. triquetra in southern Saskatchewan and the midwestern
states may be useful in developing landscapes for rich fen development
under future climatic regimes.
• Maintain our peatlands in as pristine condition as possible. Use of peat-
lands for agriculture increases GWP (global warming potential) of fens
and bogs substantially. Whereas the GWP of pristine bogs is negative and
of fens is only slightly positive (less than 100 kg CO
2
-C equiv ha
–1
yr
–1
),
when peatlands are drained for pasture or tilled the GWP increases to
4000 to 5000 kg CO
2
-C equiv. ha
–1

yr
–1
for the former and more than
10,000 for the latter for fens.
49
• Disturbance in peatlands has two effects: direct effects of the disturbance
itself (peat removal by the peat harvesting industry, clearing areas for
oil exploration vehicles) and indirect effects (the effect of returning to
the pre-disturbance condition). Mitigation for indirect effects can be as
follows:
Do not remove the actively growing top few centimeters of the ground lay-
er when grading access lines.
Keep the time from the end of peat harvesting activity to revegetation as
short as possible. In western Canada, develop a clear management plan
for restoration of cut over bogs back to fens.
Avoid nutrient inputs to peatlands during construction activities; these
include keeping to a minimum the introduction of mineral soil to peat-
land areas.
Adequate buffer zones should be maintained around peatland complexes.
Higher water tables from increased upland runoff after forest harvest or
wildfire increase nutrients and decrease acrotelms resulting in complete
© 2006 by Taylor & Francis Group, LLC
Peatlands: Canada’s Past and Future Carbon Legacy 213
successional turnover of keystone species and this may be as devastat-
ing for peatlands as lowered water tables due to climate change. Buffer
zones should be designed relative to peatland size, runoff amount, and
watershed extent in order to protect small, sensitive peatlands as well as
larger, less sensitive peatland complexes.
Road construction engineering should endeavor to understand peatland
hydrology in order to avoid changes in water levels.

ACKNOWLEDGMENTS
Many of the ideas and data presented here were developed and collected during
periods of funding from The Natural Sciences and Engineering Research Council
of Canada and from The National Science Foundation (U.S.), for which I am grateful.
In particular, I thank Ilka Bauer, Jagtar Bhatti, Suzanne Bayley, Kevin Devito, Dennis
Gignac, Linda Halsey, Barbara Nicholson, Merritt Turetsky, R. Kelman Wieder, and
Zicheng Yu for providing data and stimulating discussions, for offering many ideas
that I have liberally used, and for friendship over the years. Portions of the text were
extracted from joint manuscripts of R. Kelman Wieder and myself. Sandi Vitt
prepared the graphics, for which I am grateful.
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