17 June 2024

Mixed forests are less vulnerable to soil acidification


The Chinese study: in larch and broad-leaf forests, nitrogen deposition has no significant impact on soil chemistry. Therefore, in the fight against acidification, the creation of mixed forests could be effective

by Matteo Cavallito


Mixed forests would be more resistant to soil acidification, a problematic phenomenon that can be affected by several factors. This was reported in a study by a group of researchers from the Chinese Academy of Sciences. The investigation, published in the journal Plant and Soil, highlights in particular how larch and broad-leaf forests are less prone to the phenomenon in comparison with forests composed exclusively of larches. According to the authors, protecting tree biodiversity could therefore be an effective strategy for managing forest ecosystems and tackling acidification.

The key role of nitrogen

The study first emphasises the key role of nitrogen, which is an ambivalent element. Nitrogen is valuable for crops, in fact, but also dangerous to the environment when it is dispersed in excessive quantities, thereby favouring various phenomena. These include eutrophication, or excessive nutrient enrichment, as well as acidification itself.

“Human activities such as burning fossil fuels and using chemical fertilizers have led to high levels of nitrogen deposition, the transfer of nitrogen from the atmosphere to the Earth’s surface, across many regions globally,” according to a statement from the Chinese Academy of Sciences.

“While air pollution control measures are implemented, overall levels of nitrogen deposition remain relatively high in some parts of China.” In this scenario, however, the response of forest ecosystems and the role of tree species composition are still unclear.

The impact of the element varies between different trees

To better understand these phenomena, scientists from the Academy’s Institute of Applied Ecology conducted an investigation using simulated nitrogen deposition experiments in larch and mixed larch and deciduous forests in Qingyuan County, located in Liaoning Province in north-east China. The study of the effects of element dispersion on soil and tree leaves lasted four years.

“We conducted N addition experiments (…) and examined whether soil N availability, soil acid–base chemistry, leaf nutrients and stoichiometry of these two forests responded differently to four-year N addition,” the researchers explain.

“We found that N addition increased soil nitrate concentrations and resulted in soil acidification in the larch forest,” the study continues. At the same time, “N addition did not significantly affect soil inorganic N concentration, soil acid–base chemistry, and tree leaf nutrients in the larch-broadleaf mixed forest.”

A better forest management

The study, in short, provides valuable insights into the management of forest ecosystems. By understanding the characteristics of different forest tree species, the scientists point out, a significant environmental problem in the north-eastern regions of China can be better addressed. “The establishment of conifer-broadleaf mixed forests,” the researchers conclude, “is an important silvicultural practice to alleviate soil acidification induced by N deposition.”