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Trees and people suffer together

Trees and people suffer together

Tree dying leads to health problems for the population

Tree extinction has a massive impact on human health. On behalf of the U.S. Forestry Agency, scientists have investigated possible relationships between the deaths of millions of ash trees and deaths in just under 1,300 counties in 15 U.S. states. The study shows a significant correlation between the condition of the trees and deaths from respiratory and cardiovascular diseases, said lead author Geoffrey Donovan of the Forest Service at Pacific Northwest Research Station. The study was published.

From previous studies, it was known that "exposure to the natural environment can improve human health", but the findings to date have always been controversial due to structural weaknesses in the studies, the US scientists justify their research approach. The observation of the biological invasion by the Asian ash beetle (Agrilus planipennis) and the associated tree extinction offered a unique opportunity to examine effects on human health, Donovan and colleagues continue.

100 million trees died from imported beetles The imported ash tree beetle "was first discovered near Detroit, Michigan, in 2002," the researchers report. The beetle attacks all 22 species of ash found in North America and kills almost all the trees it infests, Donovan and colleagues write. Tree pests are now also common in other neighboring US states and in southeastern Canada. According to experts, the beetle invasion has so far resulted in the death of around 100 million trees in the affected North American regions. In their current study, the scientists have now compared this tree extinction with the medical population data from the past 18 years from 1,296 counties in 15 states. In order to avoid bias from other factors as much as possible, the researchers also took into account the demographic data from 1990 to 2007 as part of their study. The influence of variables such as income, race or educational level on health could thus be largely excluded.

21,000 additional deaths from tree deaths In both regression models used for the calculation, according to the US researchers, there was a clear statistical connection between tree deaths from the ash tree beetles and the deaths from cardiovascular and respiratory diseases. Between 2002 and 2007, "15,000 additional deaths due to cardiovascular diseases and 6,000 additional deaths due to respiratory diseases suffered" were recorded in the affected regions. The presence of the Asian ash beetle in the states is associated with an increase of almost seven deaths per 100,000 inhabitants per year in cardiovascular diseases and an increase in annual deaths in respiratory diseases by around 17 per 100,000 inhabitants, Donovan and colleagues write .

Causal relationship between nature and human health "Of course, when looking at the results, there is a tendency to find that higher mortality is variable due to some disruptive factors, such as income or education, and not the loss of trees", Donovan explained. But the pattern had to be demonstrated "in districts with very different demographic starting conditions". The statistical connection between tree extinction and the increased number of deaths was also confirmed as significant, taking demographic factors into account. The current study provides clear evidence of a causal relationship, but further studies are needed to clearly prove this. The “results do not provide direct insight into how trees reduce mortality associated with cardiovascular and respiratory diseases,” but the researchers believe there are several plausible explanations. Improving air quality, reducing stress, increasing physical activity or the influence of trees on the microclimate and temperature could play a role here, Donovan and colleagues report. It is clear that the presence of the trees has a positive effect on the health of the population, and that the death of the trees also has a lasting impact on human health. (fp)

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