Study highlights impact on rainforest regeneration

By Isobel Williams via SWNS

Tropical rainforest areas that are replanted after logging do not fare as well as natural forests, a new study has found.

Even when the wood is harvested "sustainably" and new seedlings replanted, they are less likely to survive.

And this held true even when they used areas where tree restoration projects had taken place.

Scientists from the University of Exeter monitored over 5,000 seedlings for a year and a half in North Borneo to see if the harvesting process impacts the future of the forests.

They studied a landscape containing both natural forest and areas logged 30 years ago – some of which were recovering naturally, while some had been restored by methods including tree planting.

A drought had triggered “mast fruiting” across the region, with trees simultaneously dropping masses of fruit and new seedlings emerging.

At first, both natural forest and restored forest had similarly high numbers of seedlings, compared to naturally recovering forest – suggesting restoration activities enhanced fruit production.

But these benefits did not last as low seedling survival in the restored forest meant that, by the end of the study, similarly low numbers of seedlings remained in restored and naturally recovering forest.

Seedling populations remained higher in natural forest.

Therefore, the team think that regeneration may be challenged by different factors depending on the restoration approach – seed availability in naturally recovering sites and seedling survival in sites where planted trees have matured.

Dr. Robin Hayward, who undertook this research during their PhD at the University of Stirling, said: “We were surprised to see restoration sites having lower seedling survival.

“After such a productive fruiting event in the restored forest, it’s disappointing that so few were able to survive – and to think what this might mean for the long-term recovery of different tree species.”

Local environmental conditions may differ between restored areas with higher biomass and canopy cover than in degraded areas with no restoration.

The study, published in the journal Global Change Biology, observed differences in traits of the plants in logged areas compared to intact forest, showing that some species may be struggling to survive in disturbed areas, and some have to adapt how they grow to accommodate.

This could lead to differences in biodiversity and ecological functioning in the long-term.

Dr. David Bartholomew, based at the University of Exeter during the study and now at Botanic Gardens Conservation International, said: “Our findings suggest that seedlings are experiencing stress in logged forests.

“This could be due to changes to the canopy structure, microclimate and soil, with current restoration treatments insufficient to eliminate this stress.

“In particular, highly specialized species seem to struggle to survive, leaving communities with reduced species diversity compared to intact forest.”

The research team say that there could be a number of explanations for their findings, such as animals being more drawn to certain areas.

Daisy Dent of ETH Zürich, Switzerland and the Smithsonian Tropical Research Institute, Panama added: “Rainforests are complex systems and there are many possible explanations for our results.

“For example, animals that eat seeds – like bearded pigs – may be drawn into restored forest patches to eat the more abundant seeds and seedlings, rather than moving into adjacent poor-quality logged forest.

“In natural forests, animals potentially move more freely and so do not exhaust seed supplies in the same way.”

Selective logging of forests is prevalent throughout the tropics, and long-term recovery is crucial to maintaining carbon stocks and high biodiversity.

The researchers say that low rates of survival among seedlings three decades after logging therefore raises concerns about potential regeneration failure in future generations of trees.

They believe that their results highlight the importance of carefully designing, monitoring and adaptively managing restoration projects so that they can recover both biodiversity and carbon.

Dr. Lindsay F Banin of the UK Centre for Ecology & Hydrology concluded: “Together, these results reveal there may be bottlenecks in recovery of particular elements of the plant community.

“We are now progressing this research into the various stages of the regeneration process – fruiting, germination, establishment and causes of mortality – to help understand which mechanisms are driving the patterns we have observed and how we can better assist forest regeneration and support the long-term sustainability of degraded forests.”