Forests are disappearing at an alarming rate, with human activities such as logging being a major cause of this loss. One way China is addressing this problem is through so-called mountain closure, that is, by stopping all anthropogenic activity within degraded forests. But precisely how mountain closure affects ecosystem renewal isn’t well known. To answer this question, researchers have turned their attention underground, to fine roots. By following the status of these structures, they’ve shed light on how forests renew themselves over the decades after human activity is stopped.
Plants use fine roots to acquire water and nutrients from soil, which gives them a crucial role in terrestrial carbon and nutrient cycling. Because soil composition is key to ecosystem productivity, changes in fine root abundance are one indicator of a forest’s health. This prompted the researchers to use fine roots to assess how forests fare after closure.
The team collected soil from subtropical forest stands in China that had either never been closed or had been closed for 6, 11, 21, or 31 years. All stands experienced similar levels of degradation prior to closure. The fine roots were carefully removed from each sample and weighed. The team also noted the average tree size and density in each stand.
The results showed that fine root biomass spiked 0 to 6 years after forest closure. This corresponded to an uptick in tree density, particularly of smaller trees. Fine root mortality and turnover were also high in this period. Interestingly, turnover was the greatest in deeper levels of soil about 11 years after closure. Around this time, the tree density per stand also decreased. But this wasn’t a sign that the forest wasn’t thriving. Rather, the forest’s composition was shifting, with smaller plants like bamboo dying off, providing space for larger trees to thrive.
These findings show that closure indeed supports rapid recovery in highly degraded forestland. With the key role that roots play in soil carbon retention, the carbon-lowering effects of China’s large-scale closure efforts might just extend to the global scale.