City trees grow faster and die younger than trees in rural forestry, a new study finds. Over their lifetimes,then, urban trees will likely absorb less CO2 from the air thah forest trees.

As we all know, the earth would be freezing or burning hot without CO₂. However, CO2 is a greenhouse gas, meaning it traps energy from the sun as/heat. That makes temperatures near the ground rise. Human activities, especially the widespread burning-of fossil (化石) fuels, have been sending extra greenhouse gases into the air. This has led to a rise in average temperatures across the globe.

Studies had shown forests readily absorb CO₂, but there hadn’t been much data on whether city trees grow, die and absorb CO₂ at the same rate as forest trees do. So some researchers decided to find out.

To figure out how quickly trees were growing, researchers tracked their diameters (the width of their trunks) between 2005 and 2014. A tree’s diameter increases as it grows, just as a person’s waist size increases as they gain weight. About half the weight of a tree is carbon, research has shown. Most of the rest is water. Over the nine years’ tracking, the researchers found city trees absorbed four times as much carbon from the air as forest trees. However, they were twice as likely to die. So over the lifetime of each type of tree, forest trees actually absorbed more CO₂.

City trees grew faster because they had less competition for light from their neighbors. In a forest, trees tend to grow close together, shading their neighbors. Street trees also benefit from higher levels of nitrogen (氮) in rainwater. Nitrogen helps plants grow. Waste gases from gas-burning cars also contain nitrogen, thus enriching city air with nitrogen. Later, rainwater may wash much of it to the ground. Some street trees may also have better access to water than trees in the country because the underground water pipes can leak.

Dogs may appear to have selective hearing when it comes to commands (指令) but research suggests they are paying attention to human chitchat.

Researchers, who arranged for headphone-wearing dogs to listen to excerpts (节录) from the novel   The   Little   Prince,   revealed their brains can tell the difference between speech and non-speech when listening to human voices, and show different responses to speech in an unfamiliar language.

The research involved 18 dogs of various ages and breeds (品种) that were trained to lie in an MRI scanner with headphones on. They were then played recordings either of humans reading excerpts from The Little Prince or those same recordings cut up into small pieces and put back together in a different order so it sounded unnatural.

The results, published in the journal NeuroImage, revealed the dogs’ brains showed a different activity pattern in the primary auditory cortex (听觉皮层) for speech compared with non-speech, with the findings similar regardless of whether the language used — Hungarian or Spanish — was familiar. Curiously, the longer the dog’s head was, the better their brain could distinguish speech from non-speech.

The team also found the activity pattern was stronger for non-speech.In humans, we typically see stronger response to speech.

The research also revealed familiar and unfamiliar languages gave rise to different responses in the secondary auditory cortex —but only for speech. That was important, said Andics, senior author of the study at Eötvös Loránd University in Hungary,   as it suggested the ability to distinguish between languages was not simply down to the speakers being different.

Instead, the team said, the differences seen between languages for speech are probably down to exposure to the familiar language and a sensitivity to language-specific regularities.

“This is also supported by the observation that older dogs show the stronger discrimination between the two languages,” said Andics.

How to stay focused?

When you were at school, were you ever told to stop daydreaming and concentrate? 【小题1】Staying focused can still be a challenge in adult life, but understanding how to do it, and knowing what is distracting you, can help.

Scientists have looked at what makes us delay and found a number of ways to help us stay in the zone. One of the most obvious things is getting rid of noise.【小题2】 It also found turning off notifications on your phone, or switching it off altogether, removes a major distraction and helps us focus on the task at hand.

【小题3】 Psychologists and neuroscientists are increasingly interested in our ability to study and have looked at what we can change inside our head to make us concentrate. Attention Researcher Nilli Lavie of University College London has found that making a task of training takes up more processing power and leaves the brain nothing left to process distractions. So, keeping your mind busy might be the answer.

There are more practical tips to keeping your mind focused. 【小题4】 It’s possible the movement in your mouth occupies parts of the brain that might otherwise get distracted.

But according to Science Focus magazine, distraction isn’t all bad. “If we were always so focused that we never got distracted, we’d miss potential changes, such as threats, in our environment. 【小题5】”