March 15, 2012

Impacts of logging on nitrogen

whitemountainlforest_150.jpgLogging impacts on the amount of nitrogen in soils for decades

According to a recent report published in the Proceedings of the National Academy of Sciences, activities or events that disturb natural ecosystems – such as the logging of forests – can have long term impacts on the soil.  Furthermore, the report says, disturbances like cutting down trees can obscure other effects on forest ecosystems.  The effects of climate change, for instance, are difficult to unravel from other factors, like logging or even hurricanes.

whitemountainlforest_425.jpgOne of the authors, Dr. Likens of the Cary Institute of Ecosystem Studies, said that: “Understanding how climate change is shaping forests is critical.  Our paper underscores the complexity if forest ecosystems, the legacy left by disturbance, and the difficulty in isolating climate impacts from the legacies of past disturbances.”

The core of their research revolved around the rates of nitrate drainage from a forested watershed.  Nitrogen is a useful indicator of changes to a forest ecosystem since it is essential for plant growth.  It is also a pollutant in water.

Basing their research on the Hubbard Brook Experimental Forest, New Hampshire, the records showed that nitrate levels in the streams were at a 46-year low.  In fact, eco-system-wide loss of nitrate from the watershed had dropped by 90%.  Assuming that this could be because climate change had increased growing periods and therefore might be generating greater demand from plants for nitrates, the scientists were surprised to discover that despite five warmer decades there was no evidence of increased plant growth.  There was, however, a relationship between a decline in snowmelt events and the lower levels of waterborne nitrate losses. 

The study drew two conclusions.  Firstly, 40% of the nitrate loss could be put down to higher soil temperatures and changing soil water flow pattern.  And, secondly, 50-60% could be explained by extensive logging that occurred here some decades ago.

Source: Science Daily


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