The effects of logging last about three decades, leaving the next generation of rainforest trees at risk 30 years after logging.
New research shows that rainforest seedlings are more likely to survive in natural forests than in deforestation areas, even when tree restoration projects are implemented.
Scientists monitored more than 5,000 seedlings in northern Borneo for a year and a half. They examined a landscape that included both natural forests and areas deforested 30 years ago, some of which regenerated naturally and others that were restored through methods such as planting trees.
The drought had led to “fruit formation” throughout the region: At the same time, many trees dropped their fruit en masse and new seedlings emerged. Initially, there were similar numbers of seedlings in both natural and restored forests as in naturally regenerated forests, suggesting that restoration efforts improved fruit production.
However, these benefits did not last long: the low survival rate of seedlings in the recovering forest resulted in a small number of seedlings remaining in the recovering and naturally regenerating forest at the end of the study. In natural forests, the number of seedlings remained in greater numbers.
Taken together, these results suggest that regeneration ability may be affected by several factors depending on the restoration method: seed availability at natural regeneration sites and seedling survival at sites where trees have reached maturity. These differences may have long-term implications for how forests can provide important ecosystem services such as carbon sequestration.
The impact of logging on forest and jungle regeneration
Dr. Robin Hayward, who carried out the research while doing his PhD at the University of Stirling, said: “We were surprised that seedling survival rates were lower at restoration sites. After such a productive harvest in a restored forest, it is disappointing that so few were able to survive, and consider what this could mean for the long-term regeneration of many different tree species“.
Although restoration has been shown to increase biomass (overall growth) in these forests, research shows that it has not yet allowed the next generation of seedlings to become fully established.
Dr. David Bartholomew, who worked at the University of Exeter during research and now works at Conservation International Botanic Gardens, said of the impact of deforestation on the rainforest: “Our results show that seedlings in deforested forests are vulnerable to stress. This may be due to changes in canopy, microclimate, and soil structure, and current restoration efforts are insufficient to address these pressures. Highly specialized species in particular appear to be fighting for survival, so species diversity in the communities is lower compared to intact forests.“.
“Tropical forests are complex systems and there are many possible explanations for these discouraging results.said Daisy Dent from ETH Zurich in Switzerland and the Smithsonian Tropical Research Institute in Panama.”For example, seed-eating animals such as bearded pigs may be attracted to forest areas to eat as many seeds and saplings as possible, rather than moving to nearby low-quality forests. In natural forests, animals can move more freely and therefore do not deplete seed reserves to the same extent“.
Selective deforestation is common in the tropics, and long-term recovery is essential to maintaining high carbon stocks and biodiversity. Therefore, the low survival rate of seedlings three decades after tree felling raises concerns about possible failures in the regeneration of future generations of trees.
Dr. Lindsay F. Banin from the UK Center for Ecology and Hydrology said: “Taken together, these results suggest that there may be barriers to the regeneration of certain elements of plant communities.” We are now extending this research to different phases of the recovery process (fruiting, germination, establishment and mortality) to understand what mechanisms determine the patterns we observe and how we can promote and support the long-term development and sustainability of degraded forests.
Ecosystem restoration goals
The study highlights the importance of carefully planning, monitoring and managing restoration projects so that they can restore both biodiversity and carbon emissions from biomass in the long term. This is critical to restoring degraded landscapes and achieving global goals, such as those set out in the United Nations Kunming-Montreal Global Biodiversity Framework and the United Nations Decade for Ecosystem Restoration.
Local environmental conditions may be different in restored areas with higher biomass and number of trees than in degraded areas that have not been restored. Plant traits, or characteristics that determine their function, may be key to understanding low seedling survival rates: they may indicate resources that plants have difficulty accessing.
The study found differences in plant characteristics in deforested areas compared to intact forests, suggesting that some species may have difficulty surviving in disturbed areas and other species may need to adjust their growth patterns to adapt. This means that the effects of forest clearance must be taken into account in regeneration projects. The impacts of logging could lead to long-term differences in biodiversity and ecological function.
Further long-term research into the effects of logging is needed
This study only included the 18 months after fruiting. Long-term research is needed to fully understand the impact of historical crises and to improve seedling survival. The study was conducted in the Danum Valley Nature Reserve and around Ulu Segama in northern Borneo.
Here the intact forests are dominated by a single family of trees, the Dipterocarpaceae, which, along with many other tree families, bear fruit at large intervals between years, called mass events. These cyclical events have significant and persistent impacts on the availability of food for animals.
The study, published in the journal Biology of global changeThe title is: “Borneo’s rainforests are recovering from deforestation, but there is a risk that regeneration will fail“Current title:”Seedling responses to precipitation and recovery“.
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