E249 - BAC: Biodiversity and Climate
Naturally-occurring greenhouse gasses are responsible for the hospitable climate of our planet. Of the light energy entering earth’s atmosphere, about 30% usually bounces back into the solar system. Greenhouse gasses trap a small percentage of this energy, warming global temperatures an average of 33 °C (59 °F). Without this greenhouse effect, the global average temperature on this planet would be below freezing. However, artificially large amounts of four of the longest-living greenhouse gasses (carbon dioxide, methane, nitrous oxide, and halocarbons) have been released into the atmosphere since 1750 as a result of technological advancements in industry and agriculture. This increased concentration of greenhouse gasses is trapping an increased amount of energy, contributing to the phenomenon known as global warming.
The Intergovernmental Panel on Climate Change (IPCC), an apolitical, nonprofit organization comprised of over 2500 scientists from over 130 countries, released their latest report in 2007 stating that “warming of the climate system is unequivocal”. Consensus of this magnitude among scholars is increasingly rare in today’s world of hot-button topics. The overwhelming evidence in support of global warming has convinced the vast majority of the scientific community, with dissenters few and far between.
While several global models exist to project future trends, no one is certain exactly what will happen as a result of climate change or precisely how much temperatures will rise. Long-term data shows that, in the past 65 years, the average daily minimum temperature at Cedar Creek has increased by 2.0 °C (3.6 °F) and the average daily maximum temperature has increased by 1.2 °C (2.2 °F). Best estimates suggest that within the next 70 years, Minnesota’s temperatures will rise another 2-7 °C (4-13 °F). Elevated temperatures affect many parts of an ecosystem, including soil moisture, plant phenology and distributions, biomass production, and decomposition processes. Initial conditions, such as biodiversity or nutrient availability, will influence the nature of any changes. Complex ecosystem interactions may lead to other unexpected effects.
The BAC (biodiversity and climate) experiment examines the interactive effects of global warming and biodiversity on prairie ecosystems. The experiment consists of 38 plots containing varying levels of biodiversity (1, 4, 16, or 32 prairie species). The plots are divided into three areas, each receiving a different warming treatment: a temperature increase of 1-3 °C (2-5 °F), a temperature increase of 3-5 °C (5-9 °F), and a control (no increase). Warming treatments occur from March to November.
Biotic factors to be monitored include any changes in plant phenology, such as budding time; and possibly an analysis of the microbial community. Abiotic factors to be tested include soil flux, which is the amount of CO2 being released from plant roots and underground microbial activity, and soil moisture. The results of this experiment will be analyzed in the hope of forming better models and management strategies about climate change in prairies.
In 2007, before any treatments were imposed, we sampled vegetation (species abundances, root mass, species diversity, aboveground plant biomass production) and soils (air dried and archived for C and N; fresh soils archived at -40°C for analyses of soil microbial communities). Lamps were installed and tested in summer and autumn of 2008 and have been in continuous operation from March 1 through November 30 each year since then. Soil temperatures (3 locations per subplot) are recorded continuously (~5 minutes between readings) in all subplots. Soil moisture (0-10 cm depth) is measured at >10 sites per subplot at weekly intervals, and at 2 sites per subplot at 5 depth intervals (0-20, 20-40, 40-60, 60-80 & 80-100 cm) every third week. Starting in 2012, humidity and air temperature will be measured at 2 locations within each subplot every 5 minutes throughout each growing season.
Funding for the BAC experiment was contributed by the National Science Foundation, with prior support from the Legislative-Citizen Commission on Minnesota Resources, and Conexus Energy.
The first three years of this experiment included a hot, dry (2009), a cool, wet (2010), and a warm, wet (2011) growing season. In all three years, warming had strong impacts on phenology, advancing all phases we monitored, especially flowering (Whittington et al. In Prep). Warming and plant diversity each had strong positive impacts on aboveground plant community biomass production, with a positive diversity x warming interaction in the cool, wet year (Cowles et al. In Prep). However, a strong positive early growing season diversity x warming interaction in 2010 (as observed via weekly Normalized Differential Vegetation Index (NDVI) measurements in each subplot) had dissipated by August (based on both NDVI and clipped plant mass measurements). Finally, by 2011, both warming treatments had caused significant reductions in plant species numbers in all subplots compared to 2009, but no decline had occurred in unwarmed control plots (Tilman et al. In Prep). In general, we could readily detect effects of the 3°C warming on measured responses, but detected effects of the 1.5°C treatment only on plant species number. We also have used BAC results to examine responses of consumers to temperature. Grass species differ in quality for aphid reproduction, but aphid reproductive rate is generally depressed in C3 grasses under elevated temperature (Schmidt et al. In Prep).
We will continue annual sampling in all subplots of primary productivity and plant species abundances; weekly measures of soil moisture and NDVI; hourly measurements of soil temperature, air temperature and humidity; and arthropod community composition and diversity from D-Vac samples from each plot each year. The results of the first three years of this experiment strongly suggest that the ecological impacts of elevated temperature depend on rainfall and possibly also on biodiversity. The proposed water manipulation to be implemented in 2012 will provide a direct test of this possibilityMethods for e249
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