Terrestrial Lab III


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1 TERRESTRIAL LAB III: FOREST FUNCTION In the second of the Terrestrial Labs you will examine a forest attribute called ecosystem function . Ecosystem function refers to the dynamic attributes of a forest. There are many dynamic components of a forest, but here we will be thinking about our forest from the perspective of ecosystem ecology, so will consider the carbon flux from a forest. Carbon flux from a forest ( respiration ) is one of many important processes that comprise ecosystem function. Carbon, in the form of carbon dioxide (CO 2 ), is an important greenhouse gas released to the atmosphere through both natural and human activity. The concentration of CO 2 in the atmosphere has increased since the start of the industrial revolution and a continued release of greenhouse gases threatens to alter global climatic patterns (Figure1). Ecosystem Methods : How do we estimate carbon cycling at a global scale? Scientists all around the world are studying net ecosystem carbon exchange and have constructed towers like the one pictured to the left. These towers take air samples and run them through an infrared gas analyzer (IRGA) to determine CO 2 concentrations. The theory behind the research is simple: plants take up CO 2 from the atmosphere by photosynthesis, thus, a decrease in air CO 2 is a direct result of net forest photosynthesis and plant growth. Offsetting this flux, CO 2 is released by plant and soil metabolic activity as respiration. Scientists can calculate ecosystem carbon flux by measuring changes in CO 2 above ecosystems. They compare the estimate of carbon flux with temperature, precipitation, light, and other factors to determine the controls over ecosystem carbon uptake, and how much carbon will be taken up, or released, from various terrestrial ecosystems. If you want to know more about these measurements, you should check out the following web site: http://public.ornl.gov/ameriflux/Participants/Sites/Map/index.cfm Figure 1. Atmospheric CO 2 levels measured in ice cores and in air from Mauna Loa, Hawaii. Neftel et al & Keeling
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2 Forest Flux : Forests are an important component of the global carbon cycle. Each year they withdraw carbon from the atmosphere through photosynthesis and release it to the atmosphere through soil respiration. The processes of photosynthesis and respiration are strongly affected by climatic conditions, particularly temperature and precipitation. Soil respiration is the loss of carbon (in the form of CO 2 ) from soils as a result of both microbial respiration and plant root respiration. Both temperature and moisture play an important part in determining soil respiration rates. Soil temperature plays a significant role in accounting for the seasonal and daily variations in respiration rates; however, moisture plays a more complicated role, often reducing respiration rates when soils are either very wet or very dry. As land uses change, so do
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