GLOBAL CHANGE AND BRITISH COLUMBIA NATIVE FLORA
Richard Hebda
Botany Unit
Royal British Columbia Museum
Victoria, B.C.   V8V 1X4
Presented at the "British Columbia Native Plants, their current Status and Future
Colloquium at Botany Dept., University of British Columbia, May 12, 1990
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Future of British Columbia's Flora and Vegetation
	Let us examine the possible consequences of global warming on 
British Columbia's  flora.  I cannot discuss all of the possible effects 
because we have little knowledge for many areas and because the analysis 
would be extremely lengthy.  I will focus on four broad vegetation 
assemblages where there will be significant impacts and where we can 
make predictions of what might happen with considerable degree of 
confidence.  The four categories are:  Alpine Tundra (= Alpine Tundra 
Biogeoclimatic Zone or AT), Ponderosa Pine and Bunchgrass 
Biogeoclimatic Zones (PPBG, these are combined in this paper even 
though recently separated from each other, Research Branch 1988), 
wetlands and shoreline vegetation.

Alpine Tundra
	The alpine zone and adjacent subalpine openings face serious 
changes in the near future.  Today alpine tundra occupies approximately 
150 000 km2 which represents 16 percent of the province's land area.  The 
alpine zone harbours many plant species, which grow in no other zone.  
Large areas of alpine tundra occur along the Coast Mountains, Rocky 
Mountains, and in the northern half of the province.  In the north, where 
the treeline is low enough, and in the highest mountains, alpine habitats 
may be continuous or nearly so.  However, many alpine areas, especially 
in the south are discontinuous and cover small isolated areas. This 
component of the alpine tundra is most at risk from global warming.
	Let us turn to paleoecological studies as predictive tools for 
changes in the extent of the alpine.  Several studies (see Clague and 
Mathewes 1989) in British Columbia identified that timberlines were 
significantly higher during the first half of the Holocene than today.  I 
estimate the potential rise in timberline to have been in the range of 100 - 
200 m, (see also Clague and Mathewes 1989).  Since Alpine zones are 
topographically top-limited even a slight climb of the timberline 
dramatically reduces the area for alpine habitats.  This "cone" effect would 
work as follows.  Suppose you have an ideal conical peak 2300 m high 
with 25 slopes and suppose the alpine zone begins today at about 2000 m. 
A rise of timberline by 100 m would reduce the alpine area by 56%.
(surface area of a cone = r x  r2 + h2; r is radius of cone base, h is height of 
cone).  Proportionately small increases in timberline reduce alpine habitat 
dramatically.
	What impact might we expect at the species level?  For many 
species there will only be a reduction in area of distribution and perhaps 
isolation of 
populations leading to potential increases in speciation.  Notably, many 
species survived the xerothermic interval intact to give us the alpine flora 
that we know today.  Unfortunately, because there have been few 
paleoecologic studies in
alpine sites we do not know in any detail how the alpine flora and zone 
were affected by the warmer and presumbably drier xerothermic climate.  
On the Brooks Peninsula, in one of the most moist and equable climatic 
regimes in British.
Columbia, alpine and subalpine species did survive (Hebda in press).  
Their survival was likely the result of unique microclimatic conditions.  
Indeed plants of alpine settings may survive by clinging to unforested 
cliffs or exposed outcrops below timberline.  
	However, we must expect some loss of populations and perhaps 
some species if global warming occurs.  B.C.'s  Alpine Tundra 
Biogeoclimatic Zone contains 106 taxa listed as rare by Straley et al. (1988).  
Many of these also occur in other zones, but many grow only in the AT.  
Often the taxa listed for other zones occur only in openings.  These taxa, 
especially those of southern B.C. alpine habitats, are at greatest risk.  Their 
populations should be identified and monitored for non-climatic 
disturbances to assist them to survive until, and perhaps persist through, 
the predicted climatic maximum.
	Further, we must double our efforts to document species 
occurrence in the alpine and understand the factors controlling their 
distribution.  We must examine our parks, reserves, and other "set-asides" 
and assess whether we have protected areas large enough, especially in 
the southern part of the province, so that some AT will survive.  
Fortunately, the human impact on alpine habitats remains relatively low, 
but it is increasing.