In the southern Great Lakes Region, North America, between 19,000 and 8,000 years ago, temperatures rose by 2.5–6.5°C and spruce The role of rising temperatures in driving the regional demise of The decline of At the other three sites, there was no statistical relationship between charcoal accumulation and vegetation composition change rates, though fire frequency was a significant predictor of rates of vegetation change at Appleman Lake and Triangle Lake Bog. At these sites,
Rising temperatures, increasing hydroclimate variability and intensifying disturbance regimes increase the risk of rapid ecosystem conversions. We can leverage multi‐proxy records of past ecosystem transformations to understand their causes and ecosystem vulnerability to rapid change. Prior to Euro‐American settlement, northern Indiana was a mosaic of prairie, oak‐dominated forests/woodlands and beech‐dominated hardwood forests. This heterogeneity, combined with well‐documented but poorly understood past beech population declines, make this region ideal for studying the drivers of ecosystem transformations. Here, we present a new record from Story Lake, IN, with proxies for vegetation composition (pollen), fire (charcoal) and beech intrinsic water use efficiency (δ13C of beech pollen; δ13Cbeech). Multiple proxies from the same core enable clear establishment of lead–lag relationships. Additionally, δ13Cbeechenables direct comparisons between beech population abundance and physiological responses to changing environments. We compare Story Lake to a nearby lake‐level reconstruction and to pollen records from nearby Pretty and Appleman Lakes and the distal Spicer Lake, to test hypotheses about synchrony and the spatial scale of governing processes. The 11.7 ka sediment record from Story Lake indicates multiple conversions between beech‐hardwood forest and oak forest/woodland. Beech pollen abundances rapidly increased between 7.5 and 7.1 ka, while oak declined. Oak abundances increased after 4.6 ka and remained high until 2.8 ka, indicating replacement of mesic forests by oak forest/woodland. At 2.8 ka, beech abundances rapidly increased, indicating mesic forest reestablishment. Beech and oak abundances correlate with charcoal accumulation rates but beech abundance is not correlated with δ13Cbeech. Fluctuations in beech abundances are synchronous among Story, Appleman and Pretty Lakes, but asynchronous between Story and Spicer Lakes, suggesting regulation by local‐scale vegetation‐fire‐climate feedbacks and secondarily by regional‐scale drivers. Holocene forest composition and fire dynamics appear to be closely co‐regulated and may be affected by local to regional climate variations. The importance of extrinsic drivers and positive/negative feedbacks changes over time, with higher ecoclimate sensitivity before 2.8 ka and greater resilience afterwards.
- PAR ID:
- 10539551
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 112
- Issue:
- 5
- ISSN:
- 0022-0477
- Format(s):
- Medium: X Size: p. 1101-1122
- Size(s):
- p. 1101-1122
- Sponsoring Org:
- National Science Foundation
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Summary Extinct hippopotamuses (
Hippopotamus spp.) were part of Madagascar's megaherbivore guild. Stable carbon (δ13C) and nitrogen (δ15N) isotopes in radiometrically dated bone collagen track spatial and temporal variation in diet and habitat. If hippos helped maintain C4grassy biomes, then they should have regularly consumed C4grasses, which have high δ13C values. However, if expansive C4grassy biomes are anthropogenic, then forests would have been more extensive in the past, and hippos would have predominantly consumed C3plants with low δ13C values. Nitrogen isotopes can clarify foraging habitat (moist or dry).We assessed δ13C and δ15N values for hippos from different ecoregions of Madagascar and compared these with data for extinct herbivorous lemurs from the same ecoregions. We further explored the effects of wet/dry transitions on isotopic trends for hippos from the central highlands and spiny thicket ecoregions.
Carbon isotopes suggest (1) limited C4consumption by hippos in the central highlands, dry deciduous forest, and succulent woodland ecoregions; and (2) moderate consumption of C4resources in the spiny thicket. Nitrogen data indicate that hippos foraged in wetter habitats than sympatric lemurs in all regions.
Malagasy hippos did not regularly graze C4grasses in dry, open habitats, even in regions blanketed by C4grassy biomes today. Malagasy grasses are adapted to grazing and fire, but these are likely ancient adaptations that accompanied grasses when they initially spread to Madagascar. C4grassy biomes were spatially limited in extent in the past and only expanded after the Late Holocene introduction of domesticated ungulates.
