Trees ‘grow faster, store more carbon’

In a press release, issued via Newswise, Mitchigan Technological University researcher Dr Andrew Burton suggested that moderate climate change was beneficial for northern hardwood trees.

In a very brief notice of the findings, reproduced in its entirety below, it offers a very basic explanation of how a slight warming changes the growth dynamics of the trees:

More than 20 continuous years of research into the effects of climate and atmospheric pollution on forest productivity in the Great Lakes region indicate that moderate increases in temperature with sufficient moisture and increased nitrogen deposition have extended the growing season in northern hardwood forests, causing the trees to grow faster and to store more carbon.

Dr. Andrew Burton, director of the Midwestern Regional Center of the National Institute for Climatic Change Research, can talk about his NSF-funded Michigan Gradient Study referenced above and the effects of temperature, moisture and acid rain on northern hardwood forests.

Tree Cover decided to attempt to find out more about this project and found an abstract for the project on the University’s website:

We will assess the degree to which temperature acclimation occurs in root systems of a variety of woody plants and determine if such acclimation is a short-term, direct physiological adjustment to warmer temperatures (days to months) or a longer term response to changes in nutrient, moisture and C availability and mycorrhizal status as the ecosystem adjusts to long-term warming (years).

Specific questions we will address include: Does rapid temperature acclimation occur in roots of large perennial woody plants? How do root biomass, root N concentration, and root respiration rates adjust to long-term changes in soil temperature and moisture and concomitant changes in N availability? How are rates of mycorrhizal infection influenced by the effects of warmer soil temperatures on host C balance and soil N availability? How do the short- and long-term responses of roots and mycorrhizae to warming and associated changes in soil nutrient cycling affect soil CO2 efflux and C availability for aboveground NPP? Are the interrelationships between warmer soil temperature regimes and C fluxes to and from roots and mycorrhizae adequately described by current ecophysiological models?

To understand both immediate and long-term effects, plots with 0 to 16 years of warming will be utilized. These include northern hardwood forests in Michigan, with warming to be initiated after a year of pre-treatment measurements; willow and alder in the shrub layer of a fen peatland in Michigan, with warming to be initiated in 2008; and mixed hardwoods at Harvard Forest that have been warmed since 1991, 2003 and 2006.

We will measure specific root respiration, root N concentration, root biomass, N mineralization, root N uptake, litter inputs, biomass increment, soil C content and mycorrhizal abundance, community composition and respiration. Treatments at the two Michigan locations include both soil warming and moisture manipulations, allowing us to examine the interaction of these two important global change factors.

We will know in the first year if rapid, physiological acclimation of root respiration occurs or if warming immediately alters mycorrhizal abundance. What may be of more importance are the amounts of C allocated to root respiration and mycorrhizal symbiosis that will exist in an ecosystem after N cycling, aboveground productivity, litter quantity, quality and decomposition, and microbial community composition and function have equilibrated to the altered climatic regimes. We will assess the interrelationships that exist between such processes and determine the factors that will ultimately control soil CO2 efflux and NPP in an altered climate.

However, there are no further details about the study’s findings, making it hard to know whether the project has completed gathering field data or whether this part of the research was ongoing. The abstract appears to have been uploaded on to the website in 2008.

It seems strange to release a statement saying “moderate climate change” was beneficial, especially when previous research papers have highlighted that forests are projected to responsed differently to a warming world, depending on what latitude they are located.

While there could be benefits to the region’s timber sector, it is seems bereft of key parameters – such as what extent of warming constitutes “moderate” warming, and to what degree is this warming projected to alter other factors, such as precipitation.

Also, in the context of the global carbon cycle, how does this degree of warming alter other carbon sinks – tropical forests, oceans etc – in  terms of sequestration; do we see a net increase or net decrease in the amount of atmospheric carbon being absorbed?

Looking forward to see more data on this interesting project being made available.

Source: MTU press release

Date: 17/10/2008

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