Richard Hebda
Botany Unit
Royal British Columbia Museum
Victoria, B.C.   V8V 1X4
Presented at the "British Columbia Native Plants, their current Status and 
Colloquium at Botany Dept., University of British Columbia, May 12, 1990
Future of British Columbia's Flora and Vegetation
	The greatest effects of global warming will likely be on wetland 
taxa and and wetland ecosystems including lakes, ponds, swamps, bogs, 
fens, marshes and related entities.  There are at least four reasons for this.  
First, any change in moisture availability results in a change in wetland 
hydrology and hence character of the wetland.  Wetlands, unlike the 
alpine habitat, cannot "migrate" along the climatic gradient, - they are 
physiographically limited.  A change in hydrologic regime often results in 
wholesale changes in plant community structure and complete 
elimination of certain habitats and species.  In some cases, a sufficient 
hydrologic change leads to disappearance of the wetland.   Second, even a 
small decline in moisture supply at the margins results in proportionately 
large loss or change in wetland habitat.  For example, in a circular wetland 
with a radius of 2 km, a decline of moisture sufficient to maintain a 
wetland in a zone of only 0.4 km from today's margin, results in a loss of 
64% (ır2) of the original wetland surface and hence habitat.  Third, many 
if not most, wetland species have very narrow, physical requirements with 
respect to moisture (duration of inundation), nutrient flux and water 
quality (nutrient concentration indirectly measurable by pH).  We observe 
this in the wild by the concentric pattern of species distribution around 
wet zones.  These species exist on an environmental tightrope, unable to 
compete in the terrestrial realm, squeezed against an inhospitable  aquatic 
environment.  Changes in any of the elements of the wetland gradient and 
indeed changes in the steepness of the gradient could easily eliminate 
their niche along the gradient.  Further, the species cannot easily escape 
because habitat opportunities are not continuous.
	 Fourth, of all the habitat systems, wetlands may be the most 
directly affected by human activity because there will likely be increased 
demands for water.  Water will be the critical natural resource in the 
coming decades.  At the local/rural level, people will demand more from 
their small neighbouring wetlands, lowering their water table or digging 
them out.  Also, drying wetlands will be seen as excellent sites to expand 
agriculture under droughty conditions. On a community or regional scale, 
water consumption may drastically reduce water levels in large wetland 
reservoir sources or reduce the ground water table.  The latter effect has 
already been noticed in places such as Grand Forks in the southern 
interior, where, according to local residents, water levels in wells are 
lower than ever in living memory.  A further concern is that many water 
sources are already polluted beyond health standards.  Hence, people and 
municipalities must look for alternate sources of clean water:  Look out 
	What kinds of changes can we expect in wetland systems as a result 
of warming?  First, the area covered by wetland and aquatic environments 
will shrink.  My work (Hebda 1982) and that of Rolf Mathewes and 
students (Mathewes and King 1989) at Simon Fraser University reveals 
that, especially in southern and central interior B.C., lakes, ponds and 
wetland systems shrunk or dried-up completely during the warmest part 
of the early Holocene about 10 000 - 8 000 years ago.  Finney Lake in the 
Hat Creek Valley provides an excellent example. Today the lake covers 
about 15 hectares, and, has a mean depth of 3 m and a maximum depth of 
5 m.  During the early Holocene there was little or no water in the lake - a 
decline of 10 m (Holocene sediments included) in lake level and a decrease 
of 95-100% of lake volume.  This aquatic body obviously could not 
support the aquatic flora it does today.  At best it might have harbored 
alkaline or salt-tolerant taxa in the bottom of the basin, like much smaller 
and shallower basins do today.
	Even a small climatic change resulting in a net moisture loss can 
create dramatic changes in a lake and in dependent plant species and 
habitats.  It is my experience that many interior lakes have a wide, 
shallow, littoral platform. At the lakeward edge of the platform the bottom 
drops off.  Finney Lake exhibits such morphology.  During the winter 
season the lake is full to the limits of the landward edge of the platform.  
As the lake level drops during the summer, ephemeral species grow along 
a marginal community gradient forming typical concentric vegetation 
zones.  Many uncommon species thrive in this setting. Under slightly drier 
conditions this zone may revert largely to a terrestrial setting and the 
peculiar ephemeral habitat disappear or be greatly reduced.
	Furthermore, it is just in such a marginal zone that cattle in the 
interior trod the soil into mush and weedy species thrive.  With changing 
climate the natural native species of this zone may be decimated or 
extirpated and weeds such as Taraxacum officinale Weber and 
Tragopogon spp will thrive.  Species such as the rare fern Marsilea vestita 
Hook. and Grev. would possibly disappear.  Ammania coccinea Rottb. 
and Rotalla ramosior (L.) Kuehne could likewise be extirpated from British 
	Organic wetlands will experience great changes.  The types of 
changes possible are recorded in wetland deposits along the coast of B.C.  
Banner et al. (1988) illustrate organic sediment records from several 
wetlands in the Pacific Temperate Wetland Region and the Pacific Oceanic 
Wetland Region.  These sequences reveal major changes in organic 
sediment type, hence environment of deposition and hence plant habitat 
and community composition since deglaciation.  Notable is the occurrence 
of a slimy, humic horizon, usually in the mid to lower part of the sequence 
which at "Bear Cove Bog" near Port Hardy occurs during the early 
Holocene Xerothermic Interval (Hebda 1983).  It is also notable that the 
development of Sphagnum- dominated wetland is a mid to late Holocene 
phenomenon. I believe that many, if not most, of the changes in organic 
wetland sequences on the coast are primarily the result of climatic change 
and related hydrological and hence community changes.  Hydrosere 
succession is an ongoing and important element too.  But, the last 5000 
years has seen paludification (wetland expansion into non-wetland areas) 
rather than loss of wetlands due to forest encroachment on the coast of 
British Columbia (Quickfall 1987).
	These observations imply that we may well experience the decline 
of the paludification process with the predicted climatic change.  Certainly 
the conditions favourable to Sphagnum growth and peat accumulation 
will be reduced. In the long run, this may result in a major reduction of 
acidic bog and bog forest presently so typical of the Pacific Oceanic 
Wetland Region.  With this will come a major reduction in appropriate 
habitat for acid-requiring species.
	In general, I would expect a shift from acidic, rain-water fed 
systems to less acidic and even alkaline ground-water fed wetland 
systems, resulting in a shift from bogs and bog woodlands to fens, 
swamps and marshes.  The changes would be most profound in regions 
with greatest summer moisture deficits such as the Coastal Douglas-fir 
Biogeoclimatic Zone of southwest British Columbia.  In the interior, fens 
and boggy fens may shift to alklaline marshes especially at low to mid 
elevations.  Species most seriously affected would be those of hyperacid 
bog environments or boreal species surviving in southern bog enclaves, 
such as cloudberry (Rubus chamaemorus) L.) in Burns Bog, Fraser Delta.  
	Species of hypermaritime acidic habitats would be most at risk.  
However, even with major net reduction in moisture availability, the 
settings may remain moist and cool enough for these species to survive.  
Studies on the Brooks Peninsula (Hebda in press) reveal that moist acidic 
subalpine-alpine communities survived during the Xerothermic interval.  
Within those were preserved several of our rarest species such as 
Ligusticum calderi Math. and Const., Geum schofieldii Calder and Taylor.  
If temperature increases and moisture decreases more than that during the 
Xerothermic, then we may loose these botanical treasures forever.
	What do we need to do to help plan for and mitigate possible 
changes in our wetland flora?  First, we must develop a functional 
classification system and a model for wetlands that accommodates 
principles of succession and predictability. I briefly mentioned such an 
approach in Banner et al. (1988) where wetlands could be viewed within 
three interdependent aspects of the associated water supply: 1)  water 
source;  2)  water flow rate; and 3)  water table depth.  I called this the 
"hydrologic gradient" approach. 
	Water source determines the nutrient levels of the water supply to 
the wetland.  Ground-water dominated wetlands, such as springs, have a 
rich supply of nutrients, especially bases, because the water has flowed 
through the ground 
of the watershed, dissolved nutrients, and brought them to the wetland 
plants. At the other extreme of the spectrum is nutrient-poor rain water 
such as feeds raised bogs.  A simple, although perhaps not ideal way to 
measure nutrient availability could be along a ground water ph scale.
	Water flow, where combined with nutrient measurement in soil 
water, provides a measure of nutrient flux.  Thus stagnant water, even if 
rich in 
nutrients, supplies less nutrients for plant consumption per unit time than 
moderately flowing low nutrient water.  Basin bogs show the results of 
effect clearly.  The centre of the bog will be occupied by species and 
communities typical of nutrient poor circumstances.  The lagg or margin, 
where water flows relatively quickly, is occupied by nutrient-requiring 
species such as willows and red osier dogwood (Cornus sericea L.)
	Water table depth establishes the degree of inundation of a 
wetland.  This parameter influences how much organic matter 
accumulates or breaks down above the water table.  One way of 
measuring it is by an estimate of the number of centimeter-days per year 
above or below the ground surface.  Water table depth or some measure of 
inundation would likely be the parameter most affected by global change.
	Today's wetland communities and indeed species distributions 
could be plotted on a multi-dimensional coordinate axis system according 
to the measure of quantitative parameters which reflect the three factors of 
the hydrologic gradient.  By inspecting the arrangement of communities 
or species on the gradient it should be possible to predict in which 
direction a wetland would change given a change in one of the hydrologic 
gradient variables.  Of greatest interest with respect to global warming 
would be the water table axis.
	Another step we must take to develop an understanding of 
wetlands is to study and classify interior wetlands.  One of the great 
omissions of National Wetlands Working Group (1988) The Wetlands of 
Canada was the absence of a description of Montane Wetlands.   These 
wetlands are most important in southern British Columbia.  We know 
very little about these habitats yet it is these that are most likely to suffer 
the greatest change.  These wetlands need to be described, classified and 
the occurrence of species noted.