New York, Jan 8 (PTI) When blocks of forests lose half of their cover, the deforestation in the remaining half happens very quickly, according to a study which may lead to a much deeper understanding of global landscape change.
Researchers, including those from the University of Cincinnati in the US, have identified a series of deforestation events that may lead to a domino-effect of more rapid, catastrophic forest loss.
The geographers used high-resolution satellite images from the European Space Agency (ESA) to study landscapes in nine-kilometer-wide blocks across every inch of the planet between 1992 and 2015.
According to the study, published in the journal Geophysical Research Letters, deforestation occurs comparatively slowly in these blocks until about half of the forest is gone, after which the remaining forest disappears very quickly.
The study showed that mixed landscapes -- like agricultural land and forest -- are comparatively few, and do not stay this way for long.
These mixed blocks, the researchers noted, tend to become homogeneous over time, regardless of the landscape type.
Based on the findings, the scientists believe that nature has in-built mechanisms to steer away from mixed landscapes, at least on a scale of 81 square kilometers.
'I think it's very intuitive. It corresponds to the different climatic zones. The Earth before people was certainly like that. You had forests and mountains and wetlands and deserts,' study co-author Tomasz Stepinski said.
'You would expect people would create more fragmentation, but as it turns out, people never stop. They convert the entire block on a large scale,' he said.
Landscapes across the world are always changing through natural or human-induced causes.
Human causes could be both direct -- like clear-cutting -- or indirect like climate change, the study noted.
Citing an example of human induced change, the researchers said from one of their earlier studies that 22 per cent of the Earth's habitable surface was altered in measurable ways between 1992 and 2015 with the biggest change coming from forest to agricultural land transition.
In the current study, Stepinski and his team examined nearly 1.8 million blocks covering the Earth's seven continents, which were categorized by 64 landscape combinations.
The geographers observed transitions from predominantly one type of landscape to mainly another in about 15 per cent of the blocks between 1992 and 2015.
'The data we have covers 23 years. That's a relatively short period of time. But from that we can calculate change in the future,' Stepinski said.
The scientists found that deforestation was the most significant type of human-caused landscape change.
Using statistical methods, they determined the likelihood of different types of landscape change over time -- in this case for hundreds of years.
According to the scientists, the most likely trajectory of change was from one homogeneous type to another.
'Planet Earth wants to be homogeneous. The land wants to be the same in all these patches. And when they start to change, they don't stop until they convert everything into another homogeneous block,' Stepinski said.
While the researchers did not examine the causes for blocks to change quickly when a transition begins, they speculated that developments like logging roads, or drainage required to clear forest makes continued change much easier.
'If you are cutting forest, you have the infrastructure to finish it. It's so much easier to cut the rest. Second, the forest is more vulnerable to change when there has been a disturbance,' Stepinski explained.
Jakub Nowosad, another co-author of the study, said the findings provide a data-driven model of long-term landscape change.
While in the current study, the researchers only looked at changes between forest and agriculture, Nowosad said future research can help understand whether such critical tipping points exist for other landscape transitions.
'This model can be used to help understand how landscapes evolved, and are going to evolve in the future,' Nowosad said. PTI VIS VIS VIS