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Clear-cuts and carbon fluxes: observing change at Harvard Forest


Monday, July 28, 2014, by Alayna Johnson
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[Plant identification is an important aspect of understanding the successional changes within a forest, following a clear-cut]I came to Harvard Forest with only a vague idea as to just how expansive and diverse the forests of New England are and with the intention of studying a scene that would have been commonplace here just over a hundred years ago – regenerating forests. With both climate change and deforestation being pressing global ecological issues, my lab group is utilizing a tiny fraction of New England forest to help piece together the overall relationship between climate and deforestation.

In recent years, much attention has been given to the role forests may play as "carbon sinks" – helping mop up some of the excess carbon dioxide in the atmosphere as they grow and integrate carbon dioxide into stored carbon in biomass and forest soils. However, in order for a forest to be a carbon sink, this rate of integration and storage must exceed the competing influence of carbon dioxide release from processes such as decay and soil respiration. Since deforestation typically results in lots of dead and decaying biomass, it is important to pinpoint when a forest begins to uptake more carbon dioxide than it releases as the forest regenerates.

[The new eddy flux tower REU students Alayna Johnson and Josh Alaniz helped Dr. Chris Williams install at one of the research sites]One way the Williams lab group is monitoring carbon flux is by measuring carbon dioxide levels below and above the canopy with sensors along an eddy flux tower, and with equipment that allows us to measure just how busy the soil microbes and plant roots of the forest are as they respire and release carbon dioxide. Such processes may give us an idea of the amount of carbon dioxide entering and leaving the forest, but it is also useful to estimate how much carbon is currently being stored within the forest in the years following the clear-cut. This is where my field partner Josh and I come in, battling brambles and bugs to acquire data directly from the trees themselves.

Gathering data on the tree size, diameter, and number of tree stems at each of our sites allows us to determine how productive our regenerating forests sites are, and therefore how much carbon is being stored within biomass as the years go by. In addition to this, these measurements tell us important information about the succession of plant species as they compete for light, moisture, and nutrients over time following the clear-cut.

[REU student Alayna Johnson, holding a stadia rod, which is used to measure trees, in order to understand how productive the regenerating forest at a research site is]

I also came to Harvard Forest with a strong interest in learning more about what specific attributes can enable a forest to become a carbon sink. Fortunately, the research program at Harvard Forest has provided us with the resources and freedom to follow our own interests within the context of our broader research projects. Through this, I have been able to dive further into my interest on the effects of nutrient availability on productivity, to see if this can give us any valuable insight into what site-specific conditions may be impacting carbon storage in biomass and whether or not the abundance of soil nutrients – like nitrogen – can explain some of the variability seen at our sites.

[Soil samples being prepared for nutrient analysis]

As the summer starts to wind down and data and results are coming in, we've all been reflecting back on a summer full of hard work, but also many opportunities to explore the changes occurring within the forest throughout the summer and the many sights of New England. While many of our projects are long-term, it's been a very rewarding experience to not only get a glimpse of the research going on at Harvard Forest, but actually contribute to it by following our own interests. 

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