Changes in the parkland-boreal forest boundary in northwestern Ontario over the Holocene
TL;DR: In this paper, changes in vegetation were tracked from a well-dated sediment core from a boreal lake, Lake 239, at ∼200-year resolution over the Holocene.
About: This article is published in Quaternary Science Reviews.The article was published on 2011-05-01. It has received 20 citations till now. The article focuses on the topics: Boreal & Holocene.
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TL;DR: In this paper, the authors simulated changes in tree growth and disturbances at the southern edge of Canada's boreal zone and projected changes in forest landscapes resulting from four climate scenarios (baseline RCP 2.6, RCP 4.5 and RCP 8.5).
Abstract: Forest landscapes at the southern boreal forest transition zone are likely to undergo great alterations due to projected changes in regional climate. We projected changes in forest landscapes resulting from four climate scenarios (baseline, RCP 2.6, RCP 4.5 and RCP 8.5), by simulating changes in tree growth and disturbances at the southern edge of Canada’s boreal zone. Projections were performed for four regions located on an east–west gradient using a forest landscape model (LANDIS-II) parameterized using a forest patch model (PICUS). Climate-induced changes in the competitiveness of dominant tree species due to changes in potential growth, and substantial intensification of the fire regime, appear likely to combine in driving major changes in boreal forest landscapes. Resulting cumulative impacts on forest ecosystems would be manifold but key changes would include (i) a strong decrease in the biomass of the dominant boreal species, especially mid- to late-successional conifers; (ii) increases in abundance of some temperate species able to colonize disturbed areas in a warmer climate; (iii) increases in the proportions of pioneer and fire-adapted species in these landscapes and (iv) an overall decrease in productivity and total biomass. The greatest changes would occur under the RCP 8.5 radiative forcing scenario, but some impacts can be expected even with RCP 2.6. Western boreal forests, i.e., those bordering the prairies, are the most vulnerable because of a lack of species adapted to warmer climates and major increases in areas burned. Conservation and forest management planning within the southern boreal transition zone should consider both disturbance- and climate-induced changes in forest communities.
109 citations
Cites background from "Changes in the parkland-boreal fore..."
...2003; Frelich and Reich 2010), meaning a transition to forest conditions closer to those that prevailed during the Holocene (*4500–8000 cal year BP) in this area (Williams et al. 2009; Moos and Cumming 2011)....
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...…activity suggest a strong decrease in forest productivity and density (De Groot et al. 2003; Frelich and Reich 2010), meaning a transition to forest conditions closer to those that prevailed during the Holocene (*4500–8000 cal year BP) in this area (Williams et al. 2009; Moos and Cumming 2011)....
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01 Jan 1969
TL;DR: A pollen diagram from a lake in the former bed of the eastern arm of Lake Agassiz in northern Minnesota records a vegetation of spruce forest followed by immigration successively of Pinus banksiana and (or) P.P. resinosa, resulting in a gradual decline of pollen of deciduous forest types.
Abstract: A pollen diagram from a lake in the former bed of the eastern arm of Lake Agassiz in northern Minnesota records a vegetation of spruce forest followed by immigration successively of Pinus banksiana and (or) P. resinosa at 10 000 B.P., then Abies and Pteridium, and still later Alnus. Between 8000 and 7000 B.P. prairie and (or) Quercus savanna prevailed on the uplands, followed by deciduous forests of mainly Quercus, Ostrya virginiana, Fraxinus pennsylvanica, and possibly Populus sp. Slightly later, Pinus strobus migrated into the area, resulting in a gradual decline of pollen of deciduous forest types. Betula pollen, however, rises, and there is an indication of a return to prairie conditions prior to 3000 B.P. During the 8000-7000 B.P. dry interval the lowland vegetation consisted of fens of Typha latifolia, Dryopteris thelypteris, and Cyperaceae. Later paludification and lateral expansion of the peatland gave rise to rather rich swamps of Picea mariana, Larix laricina, Alnus rugosa, and Thuja occidentalis. There are some conspicuous peaks of Myrica in the pollen diagram. The time after 3000 B.P. is characterized by much Pinus strobus pollen and minima of deciduous trees and herbs. In the lowlands, formation of raised bogs and poor swamps and fens began, indicating a shift in climate towards wetter conditions. The arrival of white man in the area is reflected by the rise of Ambrosia. The shifts in overall peatland types are clearly accompanied by changes in the species composition of Pediastrum in Myrtle Lake, indicating corresponding changes in the lake waters.
58 citations
TL;DR: In this article, the analysis of diatom assemblages in sediment cores from two additional lakes, which span a distance of over 200 km across the present-day boreal forest, from 80 km west of ELA Lake 239 to ~150 km to the northeast.
Abstract: Boreal regions and their freshwater ecosystems may be susceptible to future climate change under projected warmer conditions. Northwest Ontario is a boreal region adjacent to the climatically sensitive prairie-forest ecotone (PFE). Pollen records spanning the Holocene from near the Manitoba/Ontario border to lakes up to ~300 km east of the PFE indicate a warmer and possibly wetter mid-Holocene period across northwest Ontario from ~8000 to 4500 cal. yr BP. To date, only one Holocene-scale record of changes in effective moisture, as indicated through diatom-inferred changes in lake level (Experimental Lakes Area (ELA) Lake 239), is available from this region. Our study expands the regional context of Holocene climate changes, with the analysis of diatom assemblages in sediment cores from two additional lakes, which span a distance of over 200 km across the present-day boreal forest, from 80 km west of ELA Lake 239 to ~150 km to the northeast. In cores from both lakes, benthic taxa predominate in the early-to-mid-Holocene period, with a low abundance of planktonic taxa, suggesting lower lake levels by ~2–5 m. Increases in the abundance of planktonic taxa to >50% occurred in both lakes beginning ~4500–4000 cal. yr BP suggesting positive water balance over the last 4000 years in comparison with the mid-Holocene period. This new evidence supports a regional mid-Holocene period of aridity, with reduced water levels across the boreal region of northwest Ontario. If future climate change results in lower effective moisture, then conditions could become similar to the mid-Holocene period aridity, leading to real challenges for the management of water resources across the region.
20 citations
Cites background from "Changes in the parkland-boreal fore..."
...A synthesis of available pollen-based records from the North American Pollen Database, which span the Canadian prairieboreal forest ecotone, indicate changes in vegetation at eight sites (Moos and Cumming, 2011)....
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...Influences of lake-level changes are mainly known from various proxies on one lake sediment record, ELA Lake 239, in northwest Ontario (Laird and Cumming, 2008; Moos and Cumming, 2011, 2012; Moos et al., 2009)....
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...However, the few sites in this region indicate changes to a more open forest (parkland) during the early-to-mid-Holocene period (Björck, 1985; Lewis et al., 2001; McAndrews, 1982; Moos and Cumming, 2011)....
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TL;DR: In this paper, total and morphotype analysis showed a two-to-three fold increase in accumulation rates in the early to mid Holocene (range: 1 to 6 pieces cm-2 year-1) compared with the early and late Holocene, whereas fire-return interval and fire frequency based on total charcoal did not show patterns consistent with climate.
Abstract: Charcoal accumulation rates and fire-return intervals were calculated from total charcoal and charcoal morphotypes over the Holocene, from a well-dated sediment core from Lake 239 located in north-western Ontario, and compared with previously published independent climate reconstructions. Both total and morphotype analysis show a two-to-three fold increase in accumulation rates in the early-to-mid Holocene (range: 1 to 6 pieces cm–2 year–1) compared with the early and late Holocene (range: 0 to 2 pieces cm–2 year–1). Fire-return intervals and fire frequencies calculated during these periods, based on peak analysis, showed very different trends. The fire-return interval based on Type M charcoal, a morphotype associated with primary charcoal deposition, was high during the early and late Holocene, and low from ~7500 to 4000 cal year BP, with high inferred fire frequency during the warm mid-Holocene (~12.5 fires per 1000 years), compared with <5 fires per 1000 years over the rest of the Holocene, whereas fire-return interval and fire frequency based on total charcoal did not show patterns consistent with climate. These results suggest that a two- to three-fold increase in fire frequency would not be unexpected in the future under a predicted warmer climate.
15 citations
TL;DR: The authors investigated changes in diatoms, scaled chrysophytes, and sedimentary pigments in two nearshore cores from Gall Lake to infer limnological and water-level changes over the last two millennia.
Abstract: Lack of long-term studies on drought in the boreal region of northwest Ontario limits our ability to assess the vulnerability of this region to climate change. We investigated changes in diatoms, scaled chrysophytes, and sedimentary pigments in two near-shore cores from Gall Lake to infer limnological and water-level changes over the last two millennia. The two coring locations, at modern water depths of 7.5 and 11.5 m, were selected to contrast inferences for past lake level based on distance from the modern water-depth boundary between predominantly benthic and planktonic diatom assemblages in surface sediments (6.0 m). Diatom-inferred depth inferences were more variable in the core from 7.5-m water depth, consistent with the hypothesis that the greatest changes occurred at water depths closest to the benthic:planktonic boundary. Both sites revealed a pronounced drought from ~AD 950 to 1300, synchronous with the medieval climate anomaly (MCA). This finding suggests a northeast expansion of the arid MCA into northwest Ontario, extending the known spatial extent of this megadrought. Scaled chrysophytes and sedimentary pigments suggest a recent increase in thermal stratification. Our findings indicate this region is more susceptible to changes in moisture than was previously suspected based on the instrumental record for the past century.
13 citations
Cites background from "Changes in the parkland-boreal fore..."
...More arid conditions than present have been inferred for the mid-Holocene using pollen analysis (Moos and Cumming 2011), but not at a sufficiently fine sampling interval to examine changes at bi-decadal resolution....
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References
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TL;DR: The first volume of the IPCC's Fourth Assessment Report as mentioned in this paper was published in 2007 and covers several topics including the extensive range of observations now available for the atmosphere and surface, changes in sea level, assesses the paleoclimatic perspective, climate change causes both natural and anthropogenic, and climate models for projections of global climate.
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