A flock of drones is lifting off, carrying thousands of seeds. They're on a mission to plant trees and help save the climate. In July 2019, researchers at the Swiss Federal Institute of Technology, ETH Zurich, made global headlines. Planting trees could help mitigate（减轻） climate change, they said, but it would require a huge number of trees to be planted worldwide. Reforestation covering an area about the size of the United States, a massive undertaking（工作）, but the idea was an appealing（吸引人的） one, a promise to save the climate with a simple act, planting trees. But the initial euphoria（精神欢快） soon began to ebb（衰退）.

  Critics included scientists who called the idea unrealistic. In Germany, the University of Bonn's Eike Lüdeling was one of the first scientists to speak out. There are a number of questions the authors of that study need to address. Is all of that land actually suited to planting trees? They see a lot of potential in the tiger, in the tundra（[生态] 苔原）, in regions that are too cold for trees. They want to plant trees in the savannah（(南美)大草原）, which is nothing like a forest.

  A savannah has lots of grassland（草原）, and just a few trees. And you have to be realistic. The trees would need watering, tending to. With millions or even billions of new trees, who's going to do that work? In Western Australia, a huge tree-planting project is already underway. It's a landscape that isn't exactly welcoming for young saplings.

  The soil is dry. The terrain（地形） is uneven. Salinity（盐度） can be a problem. For staff members of the environmental tech startup, Lord of the Trees, the work here is a challenge. Planting trees by hand here would be extremely time-consuming. That's why David Kennet and Mahmoud Hussein are using drone technology.

  A drone can distribute seeds evenly from the air, quickly. When it comes to planting trees, Kennet believes drones are the future. It's a great big balancing act. You know, can we replace the trees faster than people are destroying them? This technology that we've developed is going to be fantastic in doing that. This is really the future for saving the planet.

  For each patch（片） of land, Kennet creates a special mix of seeds. But distributing these seeds is just one step towards planting a forest. Technology is going to play a big role. And just for instance in drones, not only do we map the area, we sow the seeds, we monitor. But we can actually plant seeds where the human person can't go. It's always dangerous for that person to do.

  A drone can sow almost 7,000 seeds an hour, a job that would take a human six days. David Kennet first planted trees here 20 years ago. Now he's testing various planting methods on different plots of land. Like many countries, Australia has been felling woodland to make way for agriculture. Kennet says that's a mistake. Groundwater（地下水） levels have plummeted（垂直落下）.

  A problem for young trees. I mowed（割草） this as one of hundreds of varieties of eucalyptus that I've got growing on the property. And I choose them specifically to be salt tolerant, which is important because salinity is such a big problem in this area. And also I like them with large leaves, because with the larger the leaves, the more carbon sequestration takes place to address climate change. So it's a double whammy. David Kennet only plants trees that are native to Australia.

  They're suited to the local land and climate. Non-native species and monocultures would further damage the soil. But even local species don't have it easy here. This is a bit of a sad specimen, as you can see in my wood. It has died. It could have died for a variety of reasons, unsuitable for the soil type, or it could be being completed for nutrient etc.

  from this tree. But when we're sowing the seeds that you'll be sowing with your drones, we'll be sowing varieties which are particularly suited to the soil type. The other good thing with drones is that we can monitor. So two months later, three months later, we fly the same flight path, and we can tell how they're progressing. And we will be able to give you a report which says that particular tree is healthy. This one down the road is not.

  This drone is taking off with seeds from a type of acacia tree native to the region. This technology could help plant millions of new trees. If all goes well, a new forest will soon take root here. In Ireland, new forests have already been planted. But climate protection isn't the only goal here. Landowners（地主） such as Brendan Lynch and County Leitrim want to harvest（收割） their trees.

  Back in the day, Lynch's father was able to earn a living from cattle（牛） farming. But those times are long gone. It's not possible to make full-time living out of beef production anymore. It's just income has dropped so much over the past three or four years that it's just not possible without a job. You need to have a job as well as farming. Lynch has placed his hopes in the fast-growing Sitka Spruce（云杉）.

  He's planted five hectares（公顷） of them on his land. The moist, rich soil is well suited to the evergreen（常绿树） species. The Sitka Spruce is the bread and butter of the plantations. You have to look at the economics of it as well. There's no point in planting something that you can't sell down the line. In years to come, when it's cut down, I hope to get anything from eight or nine thousand euros an acre（英亩(=607亩)） for the timber（木材）, which is tax-free.

  Like Brendan Lynch, thousands of Irish farmers have planted spruce trees for harvest. The Irish government says these plantations are also a boon（恩惠） to the climate. But many environmental activists（积极分子） say that's not the case. And a Leitrim Citizens' Initiative agrees. They say the monoculture plantations do more harm than good. Not too long ago, Adrian Kelly's farm was surrounded by spruce trees.

  Then the entire plantation was clear-cut, practically overnight. It was a disaster for the soil ecology, and the land now lies fallow. But there were problems even before the plantation was clear-cut. It was a shadow on my land because we were at the northern side of the shore and said, "Well out the field there, a good 30, 40 meters out the field." So this had become useless. If I wanted to expand the hold, and I can't expand because, as you can see, I can't go south and I can't go east either.

  Soon, new spruce trees will be planted here. For the local activists, monoculture plantations are nothing but greenwashing. They're moneymakers, yes, but the health of the soil, biodiversity（生物多样性）, and even the beauty of the natural landscape, don't factor into the equation（方程式）.