Oxygen. Clean air. Shade. Trees provide people with all sorts of benefits. A major one: removing carbon dioxide (CO2) from the air and storing it. That makes trees an important part of the fight against climate change. But they only hold onto carbon as long as they’re alive. Once they die, trees release that CO2 back into the atmosphere. This movement of carbon between forests and the atmosphere is called a carbon flux, notes Roel Brienen, a forest ecologist at the University of Leeds.
“These fluxes affect the amount of carbon a forest can store,” he explains. It’s like the way a bank account works. Forests store carbon the way a bank account stores money. If you spend more than you make, your bank account will shrink. And it will grow if you put more money into the account than you take out. Which direction a forest’s “carbon account ” goes has a huge influence on climate.
Recent studies have found that trees around the world are growing faster than ever. Rising atmospheric CO2 is probably driving that rapid growth, Brienen says. High levels of this gas are boosting temperatures, which speed tree growth. Brienen also found that fast-growing tree species, in general, live shorter lives. That quickens their release of carbon back into the air which is disappointing news for global warming. Brienen then examined what factors might influence tree growth, including rainfall, soil type and how crowded a forest was. None was linked to early tree death.
Levels of carbon in our forests could return to those from before the increases in growth, Brienen says. That does not mean planting trees won’t help fight climate change, but which trees are used could have a big impact. A forest of mostly fast-growing trees would store less carbon over the long term. It would therefore have less value for carbon storage projects.
“We must understand, however, that the only way to bring down CO2 levels is to stop emitting (排放)it into the atmosphere,” says Brienen.
【小题1】How does the author explain “a carbon flux”?| A．By giving examples. | B．By making a comparison. |
| C．By describing the process. | D．By analyzing cause and effect. |
| A．An increase in CO2 levels. | B．Crowdedness of a forest. |
| C．Rich carbon in the soil. | D．The long rainy season. |
| A．Plant as many trees as possible. |
| B．Remove dead trees from forests. |
| C．Plant trees with a long growth cycle. |
| D．Ban the emission of gases into the atmosphere. |
| A．Fast-growing trees may add to climate crisis |
| B．Climate change is cutting the number of trees |
| C．Is planting trees the answer to climate change? |
| D．What are the best carbon-trapping trees to plant? |
