PARENT SESSION
Contributed Oral Session 29: Climate Dynamics: Arid Land Responses to Variability in Rainfall
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal

Assessing the response of common ragweed (Ambrosia artemissiifolia L.) to climate change at multiple scales: a six year study.

Ziska, Lewis^*,1, ¹ Crop Systems and Global Change Laboratory, Beltsville, Maryland, USA

ABSTRACT- Indoor experiments using environmental growth chambers were begun in 1999 to assess the growth and pollen production of common ragweed in response to increasing concentrations of atmospheric carbon dioxide [CO₂] above pre-industrial levels. Although these initial data suggested increased sensitivity to [CO₂], the utility of such a study to an in situ response was unclear. To evaluate the impact of climatic change under realistic conditions, an existing temperature/[CO₂] gradient between urban and rural areas was used to quantify changes in growth, flowering times and pollen production in ragweed monocultures. Although these data confirmed that ragweed growth and pollen productivity are likely to be affected by concurrent increases in CO₂ and temperature, the use of monocultures did not address questions related to the establishment and persistence of ragweed following anthropogenic disturbance. To address temporal questions related to longevity of ragweed in a plant community during secondary succession, fallow agricultural soil with a common seed bank that included ragweed was exposed to a CO₂/temperature gradient along the same urban-rural gradient from 2002 through 2004. Measurements over this period demonstrated that ragweed biomass along the transect was initially greatest at the urban site, peaking in 2003. However, by the Fall of 2004, urban ragweed populations had dwindled to a single plant, while the suburban ragweed community now demonstrated maximum biomass. Parallel changes in pollen production as a function of urbanization were also inferred over this time period (2002-2004) based on previously established relationships between pollen release and ragweed biomass. The decline in urban ragweed populations was associated with a demographic shift in plant types from annuals to perennials, indicating an accelerated rate of succession for this location. Overall, these data suggest that macro-climatic differences in [CO₂] and temperature associated with the urban heat-island effect, while initially increasing ragweed productivity, may reduce the longevity of ragweed during secondary succession and its subsequent growth and pollen production.

Key words: ragweed, climate change, scale