Multiproxy Lake Sediment Records at the Northern and Southern Boundaries of the Aspen Parkland Region of Manitoba, Canada

Aspen parkland in central Canada may change substantially with increased warming and aridity as prairies replace forests, fire return intervals decrease and lake levels decline. We examined the relationships among vegetation, climate, fire and lake-ecosystem properties using lake sediment cores from the current northern and southern boundaries of the aspen parkland in southwestern Manitoba. We analyzed pollen, charcoal, sediment magnetics, biogenic silica, phosphorus, grain size and LOI, and dated the cores using 210Pb and 14C (AMS, calibrated). The Jones Lake record, from the southern edge of the parkland, began considerably earlier (~11 000 cal. BP) than the Mallard Pond record at the northern edge (~8600 cal. BP). These sites were characterized as prairie communities with low fire severity and relatively low lake productivity during the warm, dry period from 9000 to 6000 cal. BP. Beginning around 6500 cal. BP at Jones Lake and 3400 cal. BP at Mallard Pond, conditions appeared to get wetter as indicated by arboreal pollen percentage increases from ~30% to 40— 60%, concurrent with a rise in charcoal and proxies for lake productivity (biogenic silica and percent organic phosphorus). Similar to previous studies along the prairie—forest border, we found that charcoal increased during warmer, wetter periods with increased forest cover and fuel loading rather than during warmer, drier periods of prairie dominance. Our results underscore the importance of regional changes in moisture, and its effects on lake levels and forest biomass, as a dominant control of the aspen parkland dynamics

Multiproxy lake sediment records at the northern and southern boundaries of the Aspen Parkland region of Manitoba, Canada

Aspen parkland in central Canada may change substantially with increased warming and aridity as prairies replace forests, fire return intervals decrease and lake levels decline. We examined the relationships among vegetation, climate, fire and lake-ecosystem properties using lake sediment cores from the current northern and southern boundaries of the aspen parkland in southwestern Manitoba. We analyzed pollen, charcoal, sediment magnetics, biogenic silica, phosphorus, grain size and LOI, and dated the cores using Pb and C (AMS, calibrated). The Jones Lake record, from the southern edge of the parkland, began considerably earlier (~11 000 cal. BP) than the Mallard Pond record at the northern edge (~8600 cal. BP). These sites were characterized as prairie communities with low fire severity and relatively low lake productivity during the warm, dry period from 9000 to 6000 cal. BP. Beginning around 6500 cal. BP at Jones Lake and 3400 cal. BP at Mallard Pond, conditions appeared to get wetter as indicated by arboreal pollen percentage increases from ~30% to 40-60%, concurrent with a rise in charcoal and proxies for lake productivity (biogenic silica and percent organic phosphorus). Similar to previous studies along the prairie-forest border, we found that charcoal increased during warmer, wetter periods with increased forest cover and fuel loading rather than during warmer, drier periods of prairie dominance. Our results underscore the importance of regional changes in moisture, and its effects on lake levels and forest biomass, as a dominant control of the aspen parkland dynamics. © The Author(s), 2009. 210 1

Multiproxy Lake Sediment Records at the Northern and Southern Boundaries of the Aspen Parkland Region of Manitoba, Canada

Aspen parkland in central Canada may change substantially with increased warming and aridity as prairies replace forests, fire return intervals decrease and lake levels decline. We examined the relationships among vegetation, climate, fire and lake-ecosystem properties using lake sediment cores from the current northern and southern boundaries of the aspen parkland in southwestern Manitoba. We analyzed pollen, charcoal, sediment magnetics, biogenic silica, phosphorus, grain size and LOI, and dated the cores using 210Pb and 14C (AMS, calibrated). The Jones Lake record, from the southern edge of the parkland, began considerably earlier (~11 000 cal. BP) than the Mallard Pond record at the northern edge (~8600 cal. BP). These sites were characterized as prairie communities with low fire severity and relatively low lake productivity during the warm, dry period from 9000 to 6000 cal. BP. Beginning around 6500 cal. BP at Jones Lake and 3400 cal. BP at Mallard Pond, conditions appeared to get wetter as indicated by arboreal pollen percentage increases from ~30% to 40— 60%, concurrent with a rise in charcoal and proxies for lake productivity (biogenic silica and percent organic phosphorus). Similar to previous studies along the prairie—forest border, we found that charcoal increased during warmer, wetter periods with increased forest cover and fuel loading rather than during warmer, drier periods of prairie dominance. Our results underscore the importance of regional changes in moisture, and its effects on lake levels and forest biomass, as a dominant control of the aspen parkland dynamics

Asymmetric Vegetation Responses to Mid-Holocene Aridity at the Prairie–Forest Ecotone in South-Central Minnesota

The mid-Holocene (ca. 8000–4000 cal yr BP) was a time of marked aridity throughout much of Minnesota, and the changes due to mid-Holocene aridity are seen as an analog for future responses to global warming. In this study, we compare the transition into (ca. 9000–7000 yr ago) and out of (ca. 5000–2500 yr ago) the mid-Holocene (MH) period at Kimble Pond and Sharkey Lake, located along the prairie forest ecotone in south-central Minnesota, using high resolution (∼5–36yr) sampling of pollen, charcoal, sediment magnetic and loss-on-ignition properties. Changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland/forest-dominated landscape to a more open mix of grassland and woodland/savanna. In contrast, at the end of the MH, grassland remained an important component of the landscape despite increasing effective moisture, and high charcoal influxes (median 2.7–4.0 vs. 0.6–1.7mm2 cm−2 yr−1 at start of MH) suggest the role of fire in limiting woodland expansion. Asymmetric vegetation responses, variation among and within proxies, and the near-absence of fire today suggest caution in using changes associated with mid-Holocene aridity at the prairie forest boundary as an analog for future responses to global warming

Asymmetric Vegetation Responses to Mid-Holocene Aridity at the Prairie–Forest Ecotone in South-Central Minnesota

The mid-Holocene (ca. 8000–4000 cal yr BP) was a time of marked aridity throughout much of Minnesota, and the changes due to mid-Holocene aridity are seen as an analog for future responses to global warming. In this study, we compare the transition into (ca. 9000–7000 yr ago) and out of (ca. 5000–2500 yr ago) the mid-Holocene (MH) period at Kimble Pond and Sharkey Lake, located along the prairie forest ecotone in south-central Minnesota, using high resolution (∼5–36yr) sampling of pollen, charcoal, sediment magnetic and loss-on-ignition properties. Changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland/forest-dominated landscape to a more open mix of grassland and woodland/savanna. In contrast, at the end of the MH, grassland remained an important component of the landscape despite increasing effective moisture, and high charcoal influxes (median 2.7–4.0 vs. 0.6–1.7mm2 cm−2 yr−1 at start of MH) suggest the role of fire in limiting woodland expansion. Asymmetric vegetation responses, variation among and within proxies, and the near-absence of fire today suggest caution in using changes associated with mid-Holocene aridity at the prairie forest boundary as an analog for future responses to global warming

Impacts of the Interaction between Viral Pathogens and Mutualistic Fungi on Plant Performance

Background/Question/Methods Plant pathogens and mutualists can play an important role in plant performance. While previous studies indicated that the interaction between mycorrhizal fungi and plant enemies cause changes in overall plant performance, there have been no experimental studies explicitly studying the interactions between mutualistic mycorrhizal fungi and viral pathogens. Here we investigate the impact of arbuscular mycorrhizal fungi (AMF) and Barley Yellow Dwarf Virus (BYDV) on plant performance. While AMF provide a nutritional benefit to the host plant in the form of nitrogen and phosphorous, BYDV infection is systemic and localized to the phloem, where it causes necrosis and disruption of carbohydrate translocation.Using the invasive species Avena fatua (wild oats) we factorially manipulated AMF presence and BYDV infection in a greenhouse experiment using 72 plants. Plants were conditioned with a mixture of naturally occurring mycorrhizae. For plants which were conditioned with AMF, this mixture was mixed with a sterilized sandy loam soil while plants without AMF received a sterilized version of the natural inoculum. For pathogen infection, plants were infected via aphid vector (Rhopalosiphum padi) with an isolate of the PAV strain of BYDV. In order to control for herbivory effects, uninfected aphids fed on uninfected plants and infected aphids fed on infected plants. To assess plant performance, we measured germination rate, survivorship, above and belowground biomass, tiller number, BYDV infection, aphid reproduction, AMF colonization, seed production, photosynthetic capacity and longest leaf length. Results/Conclusions Two weeks after infection, infected plants had significantly higher aphid reproduction then uninfected plants. Plants infected with BYDV also had significantly shorter leaf lengths then compared to uninfected plants. Neither leaf length nor aphid reproduction was impacted by AMF colonization and BYDV infection. Tiller number was not significantly impacted by any of the treatments. Thus, BYDV infection decreased plant performance while AMF colonization did not have any impact on plant performance. This study explored the strength and nature of multiple, co-occurring interactions between viruses and mycorrhizal fungi and their overall impact on plant performance

Impacts of the Interaction between Viral Pathogens and Mutualistic Fungi on Plant Performance

Background/Question/Methods Plant pathogens and mutualists can play an important role in plant performance. While previous studies indicated that the interaction between mycorrhizal fungi and plant enemies cause changes in overall plant performance, there have been no experimental studies explicitly studying the interactions between mutualistic mycorrhizal fungi and viral pathogens. Here we investigate the impact of arbuscular mycorrhizal fungi (AMF) and Barley Yellow Dwarf Virus (BYDV) on plant performance. While AMF provide a nutritional benefit to the host plant in the form of nitrogen and phosphorous, BYDV infection is systemic and localized to the phloem, where it causes necrosis and disruption of carbohydrate translocation.Using the invasive species Avena fatua (wild oats) we factorially manipulated AMF presence and BYDV infection in a greenhouse experiment using 72 plants. Plants were conditioned with a mixture of naturally occurring mycorrhizae. For plants which were conditioned with AMF, this mixture was mixed with a sterilized sandy loam soil while plants without AMF received a sterilized version of the natural inoculum. For pathogen infection, plants were infected via aphid vector (Rhopalosiphum padi) with an isolate of the PAV strain of BYDV. In order to control for herbivory effects, uninfected aphids fed on uninfected plants and infected aphids fed on infected plants. To assess plant performance, we measured germination rate, survivorship, above and belowground biomass, tiller number, BYDV infection, aphid reproduction, AMF colonization, seed production, photosynthetic capacity and longest leaf length. Results/Conclusions Two weeks after infection, infected plants had significantly higher aphid reproduction then uninfected plants. Plants infected with BYDV also had significantly shorter leaf lengths then compared to uninfected plants. Neither leaf length nor aphid reproduction was impacted by AMF colonization and BYDV infection. Tiller number was not significantly impacted by any of the treatments. Thus, BYDV infection decreased plant performance while AMF colonization did not have any impact on plant performance. This study explored the strength and nature of multiple, co-occurring interactions between viruses and mycorrhizal fungi and their overall impact on plant performance

Multiproxy, Cross-Biome Analysis Of Ecosystem Dynamics During Late-Glacial And Holocene Climatic Change In North-Central North America

Vegetation ecotones and lake ecosystem dynamics have the potential to change dramatically with rapid climate warming. We present data for 15 proxies from eight well-dated lake sediment cores documenting late glacial and Holocene changes in both terrestrial and lake processes across a latitudinal gradient in central North America spanning grassland, aspen parkland, boreal, and tundra biomes. Our goal was to examine the timing and magnitude of terrestrial and aquatic ecosystem proxies across known climatic gradients in space and time. Results indicate that fire and vegetation dynamics were influenced by how climate controlled the relative abundance of arboreal vs. herbaceous taxa. Fire severity was greatest during the Holocene Thermal Maximum (HTM, 8500-5000 BP) only in forest-dominated boreal and northern parkland landscapes. At the grassland-woodland border and tundra-woodland ecotones, fire severity peaked after the HTM, presumably during more mesic conditions that supported greater landscape productivity. Lake ecosystems differed across the latitudinal gradient, with warmer grassland lakes showing a potential shift from diatoms to cyanobacteria following HTM aridity, P inputs, N:P (molar) declines to \u3c 5-15, and N limitation, leading to poor or negative overall correlations among biogenic silica, nutrients, and organic matter. At the northernmost parkland and boreal and tundra sites, there was no indication from the pollen, magnetics, grain size, TP, or N:P data of significant mineral transport to these lakes or shifts in lake stoichiometry at or following the HTM, suggesting that aridity was less severe in higher latitudes. Unlike the grassland sites, which may have experienced a state change in the plankton community from diatoms to cyanobacteria as a result of HTM mineral inputs, cyanobacteria probably played a smaller role in the northernmost parkland, boreal, and tundra sites because the strong positive correlations between organic matter and bSi (P \u3c 0.05) as well as low molar C:N ratios (9-12) suggest that lake organic matter is primarily derived from plankton and that diatoms have been the dominant primary producers over the Holocene. Our work shows that the magnitude of climate-driven changes in catchment processes varies latitudinally, with more southerly lakes subject to greater past aridity and nutrient-driven state changes compared to higher-latitude lakes. If precipitation and temperature increase to a greater extent at higher latitudes with climate warming, we may see differential changes in fire severity, terrestrial material export to lakes, and shifts in stoichiometry and nutrient limitation, thereby strengthening geographic differences in ecosystem function

Multiproxy, Cross-Biome Analysis Of Ecosystem Dynamics During Late-Glacial And Holocene Climatic Change In North-Central North America

Vegetation ecotones and lake ecosystem dynamics have the potential to change dramatically with rapid climate warming. We present data for 15 proxies from eight well-dated lake sediment cores documenting late glacial and Holocene changes in both terrestrial and lake processes across a latitudinal gradient in central North America spanning grassland, aspen parkland, boreal, and tundra biomes. Our goal was to examine the timing and magnitude of terrestrial and aquatic ecosystem proxies across known climatic gradients in space and time. Results indicate that fire and vegetation dynamics were influenced by how climate controlled the relative abundance of arboreal vs. herbaceous taxa. Fire severity was greatest during the Holocene Thermal Maximum (HTM, 8500-5000 BP) only in forest-dominated boreal and northern parkland landscapes. At the grassland-woodland border and tundra-woodland ecotones, fire severity peaked after the HTM, presumably during more mesic conditions that supported greater landscape productivity. Lake ecosystems differed across the latitudinal gradient, with warmer grassland lakes showing a potential shift from diatoms to cyanobacteria following HTM aridity, P inputs, N:P (molar) declines to \u3c 5-15, and N limitation, leading to poor or negative overall correlations among biogenic silica, nutrients, and organic matter. At the northernmost parkland and boreal and tundra sites, there was no indication from the pollen, magnetics, grain size, TP, or N:P data of significant mineral transport to these lakes or shifts in lake stoichiometry at or following the HTM, suggesting that aridity was less severe in higher latitudes. Unlike the grassland sites, which may have experienced a state change in the plankton community from diatoms to cyanobacteria as a result of HTM mineral inputs, cyanobacteria probably played a smaller role in the northernmost parkland, boreal, and tundra sites because the strong positive correlations between organic matter and bSi (P \u3c 0.05) as well as low molar C:N ratios (9-12) suggest that lake organic matter is primarily derived from plankton and that diatoms have been the dominant primary producers over the Holocene. Our work shows that the magnitude of climate-driven changes in catchment processes varies latitudinally, with more southerly lakes subject to greater past aridity and nutrient-driven state changes compared to higher-latitude lakes. If precipitation and temperature increase to a greater extent at higher latitudes with climate warming, we may see differential changes in fire severity, terrestrial material export to lakes, and shifts in stoichiometry and nutrient limitation, thereby strengthening geographic differences in ecosystem function

Late-Glacial and Holocene Climatic Effects on Fire and Vegetation Dynamics at the Prairie–Forest Ecotone in South-Central Minnesota

1. Treeline ecotones, such as the prairie–forest boundary, represent climatically sensitive regions where the relative abundance of vegetation types is controlled by complex interactions between climate and local factors. Responses of vegetation and fire to climate change may be tightly linked as a result of strong feedbacks among fuel production, vegetation structure and fire frequency/severity, but the importance of these feedbacks for controlling the stability of this ecotone is unclear. 2. In this study, we examined the prairie–forest ecotone in south-central Minnesota using two lake sediment cores to reconstruct independent records of climate, vegetation and fire over the past 12 500 years. Using pollen, charcoal, sediment magnetic analyses and LOI properties, we investigated whether fires were controlled directly by climate or indirectly by fuel production. 3. Sediment magnetic and LOI data suggest four broad climatic periods occurring c. 11 350–8250 BP (cool/humid), c. 8250–4250 BP (warm/dry), c. 4250–2450 BP (warm/humid), and c. 2450–0 BP (cool/humid), indicating that, since the mid-Holocene, climate has shifted towards wetter conditions favouring greater in-lake production and fuel production on the landscape. 4. The area surrounding both lakes was characterized by boreal forest c. 12 500–10 000 BP, changing to an Ulmus-Ostrya forest c. 10 000–9000 BP, changing to a community dominated by prairie (Poaceae-Ambrosia-Artemisia) and deciduous forest taxa c. 8000–4250 BP, and finally shifting to a Quercus-dominated woodland/savanna beginning c. 4250–3000 BP. 5. Charcoal influx increased from an average of 0.11–0.62 mm2 cm−2 year−1 during the early Holocene forest period (c. 11 350–8250 BP) to 1.71–3.36 mm2 cm−2 year−1 during the period of prairie expansion (c. 8250–4250 BP) and again increased to 4.18–4.90 mm2 cm−2 year−1 at the start of the woodland/savanna period (c. 4250 BP). 6. As a result of the influence of climate on community composition and fuel productivity, changes in fire severity may be the result and not the cause of shifts in vegetation