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45 Extension Note
The Ecology of Wetland Ecosystems
Abstract Introduction
This extension note describes the Wetlands are an important element of
basic ecological features of wetland British Columbia’s biological diver-
ecosystems.It is a foundational docu- sity. From the extensive “muskeg”of
ment that provides important the outer north coast and boreal
Biodiversity concepts and background informa- northeast to the tiny “pothole
Management Concepts tion to be applied in future extension marshes”of the dry southern interior,
in Landscape Ecology notes on wetland management.Major wetland ecosystems perform essential
topics and concepts covered in this but varied ecological and hydrological
document are: functions.
Ministry contact: • definition of a wetland ecosystem Land managers,planners,and field
Allen Banner and and comparison of characteristics staff must recognize the functional
Will MacKenzie with other related ecosystems, diversity of wetland ecosystems in
B.C. Ministry of Forests • recognition of the different appli- order to manage wetlands sensibly
Research Branch cations of the term “wetland and sustainably.
Prince Rupert Forest Region
Bag 5000, 3726 Alfred Avenue ecosystem”at site and landscape Wetlands cover about % of the
Smithers, BC V0J 2N0 scales, province; this number varies region-
(250) 847-7500
• major environmental factors and ally from more than % (some
March 2000 their effects on wetland ecosystems, coastal and northern areas) to less
• classification of wetland than % (southern interior).These
ecosystems, ecosystems are transitional between
• successional patterns in wet- upland and open-water aquatic envi-
Wetland or riparian? land ecosystems, ronments.Wetlands provide essential
The term “wetland” refers to • natural disturbance regimes of habitats for many wildlife and plant
ecosystems dominated by wetlands, species, and are focal ecosystems for
water-loving plants and • role of reserves in protecting many others.
having wet or saturated soils. wetland ecosystems, Wetlands are often concentrated
The term “riparian” refers • regional variation in wetland abun- in valley bottoms and lowland
to any land adjacent to water dance and characteristics, and areas, where industrial, urban,
bodies or wetlands. These may
be upland sites or periodically • some important management andagricultural development pres-
flooded ecosystems. The ecology issues for wetland ecosystems in sures are highest. This has led to
of riparian areas is the subject British Columbia. significant wetland alteration and
of Research Branch Extension destruction,especially in the lower
Note 17. mainland and the semi-arid interior
of the province (Voller ).
Ministry of Forests Research Program
Hydrophytes Throughout British Columbia, mental and ecological attributes dis-
The water-saturated forestry activities have also had direct tinguishing major wetland types,and
environment of wetlands and indirect impacts on wetlands. then outline the dominant wetland
supports a unique group of Although only a small portion of the management issues in British
plants called “hydrophytes.” operable landbase consists of forested Columbia to be addressed in future
These plants are adapted to wetlands on which timber is being extension notes.
grow in waterlogged soils. harvested,many non-forested wet-
Excessive water and the low lands are adjacent to harvested areas. How are Wetlands Defined?
rate at which oxygen diffuses In , a wetland and riparian
under these conditions leads to classification program was initiated by Cattail marshes or peat bogs are com-
a complex of critical conditions the Research Branch of the Ministry mon images brought to mind by the
that require specialized of Forests to investigate these impor- term “wetland.”For many,this is self-
adaptations (Daubenmire
1959). Adaptations, such as tant ecosystems.This program was explanatory but for scientific,
leathery leaves (to reduce intended to extend the concepts of practical, and (more recently) legal
nutrient requirements and Biogeoclimatic Ecosystem purposes,we need to put some
combat “physiological Classification (bec) to wetlands and to descriptive bounds on the definition
drought”) or specialized provide an alternative classification of a wetland.
internal air compartments (to model that recognized the unique eco- Wetlands are:
transport oxygen to the roots), logical characteristics of these Areas where a water table is at, near,
are required for wetland plants. ecosystems (MacKenzie and Banner or just above the surface and where
Obligate hydrophytes (such as ).At this time,the recently soils are water-saturated for a suffi-
great bulrush) are restricted to released Riparian Management Area cient length of time such that excess
wetlands and semi-aquatic Guidebook (rmag) (B.C.Ministry of water and resulting low soil oxygen
sites. Facultative hydrophytes Forests ) of the Forest Practices levels are principal determinants of
(such as Labrador tea and
many other members of the Code (fpc) used a simple wetland vegetation and soil development.
Heather family) occur most classification system, based primarily Wetlands will have a relative abun-
commonly in wetlands but also on wetland size, to set widths for the dance of obligate hydrophytes in the
appear in some upland sites. riparian management areas around vegetation community and soils fea-
Wetland soils are subhydric or wetlands.However,this type of classi- turing “hydric” characteristics
hydric, having one or more of fication system,while administratively (see sidebars).
the following features easy to apply, does not reflect natural From an ecological perspective,
1. Peaty organic horizons variation in the sensitivity or ecologi- either an abundance of hydrophytes
greater than 40 cm thick. cal function of different wetland types or indicators of hydric soil conditions
2. Non-sandy soils with blue- that occur in British Columbia.A sys- is generally sufficient to indicate a
grey gleying within 30 cm tem that more explicitly addresses this wetland ecosystem.The boundary of
of the surface. variability would enable the develop- the wetland is identified by changes
3. Sandy soils with prominent ment of more site-specific best in vegetation structure, loss of
mottles within 30 cm of management practices as well as inter- hydrophytes,and wetland soil
the surface or blue-grey pretations for landscape planning,risk characteristics.
matrix.
4. Hydrogen sulphide (rotten ranking,and wildlife habitat evalua- This wetland definition encom-
egg smell) in upper 30 cm. tion.An ecological classification of the passes a wide range of ecosystems,
province’s wetlands could provide a from semi-terrestrial fens, bogs, and
knowledge base to incorporate ecolog- swamps to semi-aquatic marshes and
ical principles into wetland shallow open water.
management. Excluded from the definition are
This extension note provides basic deep water and flowing aquatic
ecological information as a technical ecosystems and transitional ecosys-
contribution to the evolution of wet- tems such as shrub-carrs,riparian low
land management practices.We define benches,and graminoid “wet”mead-
and describe the primary environ- ows,which have at various times been
considered wetland ecosystems. An interaction of hydrological fac-
Transitional sites are not saturated for tors manifests itself in the biotic and
long enough to be considered true abiotic features of a wetland. The eco-
wetland ecosystems and generally lack logical features that reflect these
an abundance of hydrophytes. hydrological gradients are vegetation
However,these types of ecosystems composition,species richness,pro-
are frequently associated with wet- ductivity, soil characteristics, organic
lands. From an ecological perspective, matter accumulation rates,and nutri-
it often makes sense to include them ent cycling and availability.
(and the surrounding riparian forest) Annual soil moisture regime,water
with wetland sites and treat them as a table pH,and magnitude of lateral
larger ecological unit or wetland and vertical water table movements
mosaic in the landscape (Figure ). (hydrodynamics) are the primary
Ata broad spatial scale, this complex hydrological features distinguishing
of sites acts as a single ecological unit biological communities.The relation-
in terms of wildlife habitat. ship between wetland classes and
these major environmental factors is
The Wetland Environment diagrammatically represented in
Figure .
Wetlands can form wherever soil Soil moisture regime (smr): smr
water is excessive. Climate, internal describes the annual “average”water
soil drainage, and topography all regime (Klinka et al. ).A Wet or
interact to create the hydrological Very Wet smr is the prerequisite to
template for wetland formation.Other wetland formation.Wet sites have a
factors (such as bedrock geology, soil water table within cm of the surface
characteristics, and hydrological sys- but for a least some of the year have
tem) influence specific wetland an aerated surface layer.Very Wet sites
characteristics (such as plant commu- remain saturated at the surface
nity composition and productivity).
Bog Fen
Riparian Water
forest
Shrub-carr
Wetland sites
Transitional site
Riparian forest
Boundary of the wetland mosaic or landscape unit
A comparison between the boundary of wetland ecosystem sites and
a wetland mosaic
Soil Nutrient Regime
Alkaline
Very Poor Poor Medium Rich Very Rich /Saline
Wet BOGS SWAMPS
Ve le
Acidic
ry ariab
v
M FENS MARSHES
oderatel
Very Acidic
Wet y x
Soil Moisture Regime pH/Base Slightl nde
Acidic y ic I
cations am
N dyn
eutral ydro
Alkaline H
gnant
sta
Major environmental gradients affecting wetland ecosystems. Modified
from Vitt (1994) in MacKenzie and Banner (2000).
throughout the year and often have a take up nutrients. In peatlands, very
water table above the soil surface. low mineral content reflects isolation
Hydrodynamics:The degree of verti- from groundwater sources and is often
“Hydrology, the way in which a cal water table fluctuation and rate of indicated by an abundance of
wetland is supplied with water, lateral groundwater flow (hydrody- Sphagnummosses.Sphagnumactively
is one of the most important namics) describe much of the removes basic minerals from the soil
factors in determining the way functional variation in wetlands. Sites water, exchanging them with hydro-
in which a wetland will with relatively stable water regimes gen ions, thereby increasing acidity.
function, what plants and (bogs and fens) are peat-accumulating On other sites, soil water chemistry is
animals will occur within it and sites. With more active hydrodynamics a function of degree of groundwater
how the wetland should be (marshes and swamps),organic mat- influence and mineralogy of the adja-
managed” ter is more likely to decompose, cent terrain.
(Welsh et al. 1995). aeration improves,and nutrients The soil nutrient regime (SNR) is
become more available. mainly a function of the two gradients
Some interior marshes have signifi- of base cation availability (as indicated
cant drawdown during the summer by pH) and hydrodynamics.
and this contributes to the concentra- Soils
tion of salts in soil horizons.
Soil acidity/alkalinity:The abun- While all wetlands share some com-
dance of base cations, such as calcium, monsoil attributes,such as saturation
has a strong influence on wetland and anaerobic (no oxygen) condi-
characteristics, especially species com- tions, the physical, chemical, and
position and productivity.Low biological properties of wetland soils
mineral content yields fewer nutrients are highly variable. This variability is
as well as lower pH.Acidic conditions due primarily to the hydrological gra-
inhibit the ability of most plants to dients mentioned above.
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