Fire History at the Treeline in Northern Quebec: a Paleoclimatic Tool 1 Serge Payette2
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This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Fire History at the Treeline in Northern Quebec: A Paleoclimatic Tool 1 Serge Payette2 Abstract.--The long term fire history at the treeline in Northern Quebec can be evaluated by ecological surveys of the major ecosystems. Available data suggest that fires are presently climate-controlled, and therefore may be used as paleoclimatic indicators. During a cold climatic interval, postfire tree regeneration is hindered, and a shift from forest to barren conditions is recorded. Examples from specific environments are provided in order to reconstruct significant ecological periods of the fire history since 3,000 years B.P. (Before Present). A pre liminary interpretation indicates that these periods of climatic cooling are centered around 2,800-2,500, 2,200- 2,000, 1,600-1,400, 1,100-900, 700 ? , 500-100 years B.P. and Present. INTRODUCTION Northern Quebec, and to emphasize their paleo climatic significance in ecological studies. The northernmost part of the boreal forest, called the forest-tundra ecotone, is particularly influenced by natural perturbations such as fires. FIRES IN FLUCTUATING ENVIRONMENTS Although of lower occurrence than in the boreal forest proper, fire has always been reported in A great diversity of habitats characterizes the forest-tundra of Northern Quebec (Hare 1969; the forest-tundra landscape. The northernmost Rousseau 1968; Low 1896; Hustich 1939, 1951; forests are selectively located in valleys and Payette 1976), and is far more frequent than in depressions protected from cold winds, and where the shrub tundra, either in Arctic Quebec or water is available from snowmelt. In upland elsewhere in the Arctic (Wein 1976). Fire occur locations, but also in many lowland sites, the rence seems to be related to the importance of forests are replaced by shrubby and lichenic vege shrub and forest covers, which are closely depen tation, including shrubby tree species stands dent on the cool subarctic or hemi-arctic climate. called krummholz. Black spruce (Picea mariana Fires are climate-controlled under certain conditions, (Mill.) BSP) is the most common krummholz-forming i.e., when weather initiates lightning, and when species. Krummholz are also found in the southern fuel is especially available through biomass shrub tundra (or Low Arctic) in depressions, on production. Additionally, postfire tree regeneration gentle slopes, and on low summits. A more detailed is strongly influenced by climatic conditions pre account of the vegetation pattern in both plant vailing during fire periods. Thus, fires may zones has been published elsewhere (Payette 1976). serve as climatic indicators of present and past It is generally assumed that the classical vege ecological conditions of the forest-tundra. Re tation pattern of the forest-tundra, the so-called constitution of the fire history in an area of forest-and-barren landscape, can be viewed as a adverse climatic conditions might help to detect response to a set of ecological gradients related paleoclimatic fluctuations, major changes of the to wind and snow conditions, and also to soil forest cover, and, ultimately, any relative dis properties. In fact, these ecological conditions placement of the treeline. The purpose of the are also expressing an underlying general climatic present paper is thus to stress the importance, on control, restricting tree populations to specific a space-time basis, of forest-tundra fires in and favourable sites. During a warm climatic in terval, it is presumed that forest transgression would occur, whereas under adverse conditions the 1Paper presented at the Fire History Workshop. reverse situation would prevail. This is a very (Laboratory of Tree-Ring Research, University of simple and quite general model of the evolution of Arizo~a, Tucson, October 20-24, 1980). the forest cover and the migration of the treeline Serge Payette is Director of the Centre in relation to Holocene climatic fluctuations. The d'etudes nordiques, Universit~ Laval, Quebec, reality is more complex, since forest cover changes Canada. derive also from conditions of plant succession, 126 of plant reproduction strategies, and also of a cold climatic period; as it was pointed out other environmental variables, where the time-lag (Payette and Gagnon 1979), the paleoclimatic sig in the vegetation response to climatic changes is nificance of the charcoal layer is strengthened poorly known. On the other hand, treeline dis if it belongs to a previous forest burn, but placements do not appear to be a mere expression to a less extent if it is related to a black spruce of major forest cover changes observed in southern krummholz burn. Identification of charcoal remains areas, because they are not always geographically is necessary to prevent any misinterpretation, and, and ecologically linked. The shift from one for example, the presence of charred cones of vegetation type to another is more frequently tamarack (Larix laricina (DuRoi) K. Koch) in the achieved by a major perturbation of the environ charcoal layer suggests more strongly that it is ment. Forest-tundra fires therefore appear to be in fact a forest burn, since this species does not important catalysts of ecological change operating produce numerous and extensive eroded growth-forms through time, under the control of fluctuating like krummholz. We will briefly outline fire climate. The forest-tundra of Northern Quebec influence in the long term with examples from might be defined as an assemblage of postfire specific habitats whose development is thought to plant communities where forest regeneration generally be primarily controlled by the present climate: varied on a space-time basis. In other words, the the forest-and-barren system, the snowpatch system, forest-tundra appears to be a vegetation zone the peatland system, and the sand dune system. composed of a fire ecological mosaic, where the rotation period varies strongly between different ecosystems and geographic areas. It is worthwhile, The Forest-and-Barren System in this context, to study the fire history in distinct parts and habitats of the forest-tundra, Virtually all forest and krummholz stands in whose makeup is tightly associated with Holocene Northern Quebec are of postfire origin. Forest climatic fluctuations. fires in presently wooded stands are generally younger than 300 years old, and range between 50 As pointed out by Wright and Heinselman (1973) and 250 years old. The oldest foi%st fires yet and by Weinand Moore (1979), one can reconstruct recorded in the forest-tundra by C dating and the fire history of a particular region within the age structure studies are about 45Q-500 years old short term by historical document analyses, fire in the white spruce (Picea glauca (MOench) Voss) scar and tree population age studies. Many pub fog belt along the Hudson Bay coast, and it is lished works concern this time perspective, for highly probable that older white spruce stands example, in mixed hardwood-coniferous forest might be eventually found. Very small tamarack regions (Heinselman 1973, Cwynar 1977), and in groves 400-500 years old have also been located in boreal forest and forest-tundra regions (Rowe et al. continental Northern Quebec (Payette and Gagnon 1974, 1975; Johnson and Rowe 1975; Zackrisson 1977). 1979) and some of them appear to be older (Godmaire A second perspective emphasized by Wright and in prep.)". As a general rule, charcoals found in Heinselman (1973) and by Wein and MOore (1979) is forested soils of the forest-tundra are younger related to the long term environmental history, as than 500-600 14c years B.P. revealed by pollen analysis (Swain 1973, Terasmae and Weeks 1979, Cwynar 1978) and where fire occur The fire history is quite different in krum rence. is traced back to early Holocene forest bio mholz stands of the forest-tundra and the shrub climates. In the forest-tundra and in the shrub tundra. It is important to distinguish the Cladonia tundra, the long term fire history can also be krummholz sites of the southern forest-tundra from achieved by another approach related to ecological those of the northern forest-tundra and the south surveys based on soil-plant investigations of the ern shrub tundra. In the southern forest-tundra, major ecosystems. fire frequency in Cladonia-krummholz stands seems to be related more or less closely to the fire Paleoecological studies were conducted north frequency in forest stands found nearby. These and south of the modern treeline in Keewatin krummholz are characterized by scattered eroded (Northwest Territories) by Bryson et al. (1965), black spruces established from seeds. Their age Nichols (1967, 1975) and Sorenson et al. (1971); may range from 10 to 250 years old. The wide Fossil charcoals were found in paleosols, radio occurrence of Cladonia-krummholz sites suggests carbon dated, and assigned to previous displacements that wildfires, since the onset of the Little Ice of the treeline. In Northern Quebec, studies on Age, are restricting forest regeneration to the treeline dynamics related to paleoecological con most favourable habitats, and therefore causing a ditions have been undertaken recently (Payette and shift in the forest-barren cover ratio. The Gagnon 1979), and research is focused on the evolu present landscape of the southern forest-tundra, tion of terrestrial and peatland systems, where with rather disjunct forests and widely distributed fire is most influential. Cladonia-isolated black spruce trees, and Cladonia krummholz stands, is a response to fire influence One of the main hypotheses that underlies prevailing during a cold interval. these studies is that major periods of fire are climate-controlled, and depending on their occur The extent of the Cladonia-krummholz habitat rence during warm or cold climatic intervals, act increases significantly in the northern forest selectively on tree or forest regeneration. There tundra and in the southern shrub tundra.