Forests worldwide at risk of dying due to drought
Forests worldwide are at increased risk of death from drought, which is occurring more frequently and are more severe, according to researchers at the University of Stirling in Scotland.
Sarah Greenwood, a postdoctoral researcher in the University of Stirling’s Faculty of Natural Sciences, said:
We can see that the death of trees caused by drought is consistent across different environments around the world. So, a thirsty tree growing in a tropical forest and one in a temperate forest, such as those we find throughout Europe, will have largely the same response to drought and will inevitably suffer as a result of rising temperatures and changes in rainfall patterns on Earth.
That said, there are features specific to some tree types that affect its drought resistance. For example, species with denser wood and smaller, thicker leaves tend to fare better during prolonged, unusually dry periods, according to the researchers.
California Drought’s Effects on Trees
In November 2016, the United States Forest Service estimated that 62 million trees in California had died in 2016, with a total of more than 100 million over the drought’s six years. The agency called this “unprecedented in our modern history.”
Drought also affects forests by causing conditions that increase both wildfires and damaging erosion, and it places trees at greater risk for damage and death from beetles and other organisms. Humans are endangered by weaker trees, which fall more easily than healthy trees, and the effects of wildfires, which fueled by dying and dead trees.
Even when the water picture in California changes, experts expect tree die-off to continue for a year or two.
Water Reuse and Tree Irrigation
Some areas are turning to water reuse to irrigate forests or tree plantations. Water must be treated to levels viable for irrigation, whether the trees are for commercial or environmental use. Several U.S. cities, including Woodburn, Oregon, and Missoula, Montana, are using treated wastewater to provide for poplar plantations. The Missoula site is expected to have 96,000 trees fed by 20 percent of the Missoula Wastewater Treatment Plant’s average daily discharge.
Water reuse has helped cultivate dates in Israel. Drip irrigation, in combination with water reuse and desalination, continues to aid Medjool date growers. Since this method of irrigation began in the 1980s, Israel has captured a 60 percent share of the global date market.
Trees Beneficial to Water
Trees and other vegetation can serve several other roles in water treatment. For instance, contamination of groundwater and other water sources can be reduced with vegetation. In urban areas, trees provide natural water filtration systems.
Forest health is essential in protecting water resources, too. Former United Nations Secretary-General Ban Ki-moon called them “an insurance policy for the planet.” Forests are “central to our future prosperity and the stability of the global climate.”
The U.N. estimates 7 million hectares of natural forests are lost and 50 million hectares of forest land are burned each year, affect about 1.6 billion people who depend on forests for their livelihoods, shelter, jobs, and a range of other economic benefits. The U.N. Food and Agriculture Organization has launched a program to improve water security in eight West African countries by promoting forest restoration.
Forest Health and Groundwater Depletion
In 2013, Australian researchers found a link between forest health and groundwater depletion. Derek Eamus, professor at the University of Technology Sydney Plant Functional Biology and Climate Change Cluster, called establishing this relationship between groundwater depth and forest health “one of the ‘holy grails’ in groundwater science.”
Alastair Jump, a co-author on the new research and a professor of ecology at University of Stirling, added:
As the temperature of the planet continues to climb, mass tree mortality will hit more forests than ever before. Forests store a substantial amount of the world’s carbon and increased tree death will only propel future global warming. This has very significant implications for fully understanding the impact of climate change on our planet.
The results — “Tree Mortality Across Biomes Is Promoted by Drought Intensity, Lower Wood Density and Higher Specific Leaf Area” — were published in Ecology Letters.
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