Mixed Forests Are Healthier, But Can They Survive Climate Change?
By Tim Radford
German researchers have confirmed once again that a good forest is a mixed forest, a natural one, with a diversity of species. The more diverse the forest, the better it becomes at doing what forests do.
Forests with a greater number of species grow at a faster rate, store more carbon, and are more resistant to pests and diseases, according to a six-nation study of European woodlands.
But this safety-in-species-numbers approach may not offer quite the protection against climate change and its consequences that such a finding should predict. A second study by European researchers suggests that when conditions become extremely wet, or extremely dry, diversity may not confer automatic resilience.
The message is that healthy, diverse, natural forest systems remain important buffers against climate change—but also that climate extremes could diminish the capacity of the forest to absorb carbon and limit global warming.
At the heart of both studies is a deeper concern about the response of the natural world to human-induced change, in the destruction of habitat, the loss of the plants, birds, insects, mammals, amphibians and reptiles that depend on habitat, and in the steady increase in atmospheric levels of greenhouse gases, as a consequence of profligate combustion of fossil fuels.
Repeated studies have confirmed that the world's forests are under threat. Repeated studies have confirmed that in overall rewards for humanity, undisturbed natural forests deliver a greater economic return. And repeated studies have confirmed that rising global temperatures offer a threat to plant diversity around the planet in general and to Europe in particular.
Researchers at the Centre for Integrative Biodiversity Research in Germany reported in the journal Ecology Letters that they selected plots of forest in Germany, Finland, Poland, Romania, Italy and Spain.
Within these plots the numbers of species varied: there might be one species, or five. The German plot, for example was home to beech, oak, Norway spruce, birch and hornbeam.
The scientists then measured 26 functions in these plots that could answer questions about nutrients, carbon cycles, growth and resilience and forest regeneration. Those stands of timber with more species grew faster and withstood pests and disease assault better than those with fewer.
"Our summers will be drier and longer as a result of climate change," said Christian Wirth, who directs the Cenre for Integrative Biodiversity Research and heads the department for systematic botany at Leipzig University. "We are therefore presuming that in future, it will be even more important to manage forests in a way that they have a high diversity of tree species."
But a study in the Journal of Ecology suggests that the answer may not be so simple.
Researchers led by Hans de Boeck from the University of Antwerp reported that they looked at a wide range of studies of what scientists call ecosystem stability and biodiversity during climate extremes—that is, unusual heat, drought or flooding.
The answer, they found, was mixed. A greater range of diversity in an ecosystem seemed to speed up recovery after an extreme climatic event, but if the event was extreme enough biodiversity alone might not offer much protection.
The relationship between diversity and resistance wasn't always obvious. Researchers, the scientists suggested, have more questions to resolve.
In the stilted language of sciencespeak, the researchers concluded that "there are numerous and non-trivial exceptions to the purported general rule that biodiversity increases stability. This raises the question of whether existing concepts of biodiversity-stability derived from the context of mild fluctuations are readily transposable to extreme events."
Reposted with permission from our media associate Climate News Network.
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Where Does the Deficiency Begin?<p>Nobody knows exactly how much vitamin D a person actually needs. The question of when a deficiency starts is correspondingly controversial. However, vitamin D is becoming increasingly popular.Not only is the pseudo-scientific literature on the "sun vitamin" experiencing an upswing, but the number of published studies has also increased enormously in recent years. For example, in 2019 <a href="https://academic.oup.com/edrv/article/40/4/1109/5126915" target="_blank">a study found that</a> Vitamin D is responsible for keeping the skeleton functional and is associated with cardiovascular diseases, type 2 diabetes and various types of cancer. <br></p>
An All-Rounder<p>Vitamin D levels in the body rise and fall according to sun exposure. If sufficient UV rays reach the skin, the body is able to produce the vitamin itself. However, the human body only derives an estimated 10 to 20 percent of its daily requirement from food.</p><p>The vitamin D that we synthesize from sunlight or food is not biologically active at first. Before the kidneys can produce the biologically active form of the vitamin, known as calcitriol, and release it into the blood, some metabolic processes must take place beforehand.</p><p>In addition, many organs have receptors to which the precursor of calcitriol binds. Further, this substance is also present in blood.</p><p>From this precursor, the organs then produce calcitriol themselves, which the body then uses for countless other processes in the body. This form of vitamin D thus regulates insulin secretion, inhibits tumor growth, and promotes the formation of red blood cells as well as the survival and activity of macrophages, which are important for the <a href="https://www.mdpi.com/2072-6643/5/7/2502/htm" target="_blank">immune system.</a></p>
Low Vitamin D, Severe COVID-19 Disease?<p>A research study carried out <a href="https://www.sciencedirect.com/science/article/pii/S2352364620300067?via%3Dihub" target="_blank">at the University of Hohenheim</a> has now established a link between vitamin D deficiency, certain previous diseases, and severe cases of COVID-19.</p><p>According to the study, "there is a lot of evidence that several non-communicable diseases (high blood pressure, diabetes, cardiovascular diseases, metabolic syndrome) are associated with low vitamin D plasma levels. These comorbidities, together with the often accompanying vitamin D deficiency, increase the risk of severe COVID-19 events."</p><p>"This statement is completely correct," said Martin Fassnacht, head of endocrinology at the University Hospital of Würzburg. However, he qualifies that it is a pure association, "i.e. a mere observation that these events occur together.</p><p>Dr. Fassnacht is very critical of the hype surrounding vitamin D, but not because he denies the vitamin serves important functions. However, studies on humans have not been able to show that vitamin D has the healing powers many often propagate.</p><p>Fassnacht says, "If you take a closer look, the hopes that the administration of vitamin D has a healing effect have not been confirmed so far."</p>
Association Versus Intervention Studies<p>Many studies on the vitamin are association or observational studies. "By definition, these studies cannot prove the causal relationship, but only point to mere correlations," said Fassnacht. The physician tries to illustrate this with an example:</p><p>"Imagine two groups of 80-year-olds. One group is spry, active and does sports. If you compare them with another group living in nursing homes, the difference in vitamin D levels will be dramatic. Life expectancy would also be extremely different."</p><p>But to try to explain the difference in fitness by vitamin D status alone is far too simplistic. "Vitamin D levels are a good measure of how sick someone is. But not more," says Fassnacht. </p><p>According to Fassnacht, none of the intervention studies carried out to date -- that specifically examined the effect of vitamin D on various diseases -- has been able to confirm the previous association and laboratory studies or the presumed positive effect of vitamin D.</p>
Further Research Is Needed<p>"If a coronavirus infection is suspected, it is therefore absolutely necessary to check the vitamin D status and quickly correct any possible deficit," said the recommendation of the paper published by the University of Hohenheim.</p><p>"Studies are underway to see whether vitamin D helps in COVID-19 infection, but I personally do not believe that this is really the case," says endocrinologist Fassnacht. Nevertheless, he says it is of course useful to carry out these studies.<br></p><p>"I don't want to rule out that there are actually subgroups of people who benefit from an additional vitamin D dose," he says. After all, this has been proven to be the case with a severe deficit.</p><p>In view of the study situation, Fassnacht does not think much of preventive, nationwide vitamin D substitutes. "My belief that the vitamin helps somewhere is very low. But, of course, I can be wrong."</p>
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