SoylentNews is people
SoylentNews
Local water availability is permanently reduced after planting forests:
River flow is reduced in areas where forests have been planted and does not recover over time, a new study has shown. Rivers in some regions can completely disappear within a decade. This highlights the need to consider the impact on regional water availability, as well as the wider climate benefit, of tree-planting plans.
"Reforestation is an important part of tackling climate change, but we need to carefully consider the best places for it. In some places, changes to water availability will completely change the local cost-benefits of tree-planting programmes," said Laura Bentley, a plant scientist in the University of Cambridge Conservation Research Institute, and first author of the report.
Planting large areas of trees has been suggested as one of the best ways of reducing atmospheric carbon dioxide levels, since trees absorb and store this greenhouse gas as they grow. While it has long been known that planting trees reduces the amount of water flowing into nearby rivers, there has previously been no understanding of how this effect changes as forests age.
The study looked at 43 sites across the world where forests have been established, and used river flow as a measure of water availability in the region. It found that within five years of planting trees, river flow had reduced by an average of 25%. By 25 years, rivers had gone down by an average of 40% and in a few cases had dried up entirely. The biggest percentage reductions in water availability were in regions in Australia and South Africa.
Partial river flow recovery with forest age is rare in the decades following establishment (open, DOI: 10.1111/gcb.14954) (DX)
(Score: 4, Informative) by JoeMerchant on Friday January 31 2020, @03:54AM
One of the features of natural forests is ... well, I can't remember the word, but basically the organic "waste" on the forest floor acts as a slow-release sponge, so water that falls as rain spends a lot more time near the surface and runs down into rivers both more slowly, and importantly, more consistently over longer periods of time.
In Florida, most of the "riparian zones" have been stripped, cleared, turned to agriculture or residential / recreational use. The swamps have been mostly drained, so now when it rains that rainwater heads to the rivers quickly, and runs out to the sea quickly. They call it a "pulse" ecosystem - short deep floods followed by long periods of low flow, where the pre-settlement pattern had deeper water in the rivers most of the time, for many reasons including modern clearing of waterways to make them navigable...
Not only have people drained the aquifer through direct usage, the changes in surface permeability and water retention mean the aquifer recharges more slowly than in the past. Modern planning calls for retention ponds (gator pits), which is a step back in the right direction, but it's not at all the same as having a pine forest with a natural bed of fallen needles over a foot thick above the mineral soil. And some navigable rivers have locks installed, which does indeed keep their water levels up, but a locked river is usually a less than wonderful ecological system as compared to its pre-settlement state.
All in all, bring back the trees - although you might choose them carefully, some trees like the imported tea tree or melaleuca respire ridiculous quantities of water into the air. Some genius thought they could dry the everglades by air-dropping melaleuca cuttings. The cuttings did sprout, and the exotic trees did indeed respire a lot of water into the air (as if Miami needed MORE humidity), but they were far from drying out the ground or making it in any way useful.
Also, if the managers of the forests can refrain from raking the organic matter off the ground to make a buck or two in the short term, the trees will grow faster and earn them more money per year in the long run, as well as being better behaved in the water cycle and somewhat more friendly to forest dwellers.
🌻🌻 [google.com]