Rainforests replanted with seedlings after logging don't recover well

In a recent research project, scientists made a significant discovery regarding the survival of rainforest seedlings in various environmental conditions.

This study, which meticulously monitored over 5,000 seedlings for 18 months, has revealed a stark contrast in the survival rates of seedlings between natural forests and areas affected by logging — even after restoration efforts have been implemented.

Natural restoration vs. active restoration

The research took place within a diverse landscape that includes untouched natural forests alongside areas that were logged three decades ago. Some of these logged areas have been left to recover naturally, while others have undergone active restoration, including tree planting.

A noteworthy phenomenon observed during this period was the occurrence of “mast fruiting,” a process where trees drop their fruit simultaneously in massive quantities, leading to a surge in seedling emergence.

Initial observations suggested that both natural and restored rainforests boasted high numbers of seedlings, ostensibly indicating that restoration efforts might enhance fruit production.

However, as the study progressed, it became evident that the survival rate of seedlings in restored rainforests was significantly lower compared to their counterparts in natural forests.

The struggle of restored rainforest seedlings

By the study’s conclusion, the number of surviving seedlings in restored and naturally recovering rainforests was similarly low, whereas natural rainforests maintained higher populations of seedlings.

Dr. Robin Hayward, a key researcher in this study, expressed disappointment at the lower survival rates in restoration sites, highlighting the potential implications for the long-term recovery of diverse tree species.

“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,” explained Dr. Hayward.

This observation suggests that while restoration can boost biomass accumulation, it does not necessarily facilitate the establishment of the next generation of seedlings.

Dr David Bartholomew, based at the University of Exeter during the study and now at Botanic Gardens Conservation International, gave his thoughts.

“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,” Bartholomew explained.

Rainforest seedlings survival in the food chain

This research underscores the complexity of rainforest ecosystems and the multitude of factors affecting seedling survival.

Daisy Dent of ETH Zürich, Switzerland and the Smithsonian Tropical Research Institute, Panama, commented on how the interaction between animals and seedlings in these environments plays a crucial role.

“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,” Dent explained.

The findings of this study raise concerns about the potential for regeneration failure in future generations of trees, especially considering the widespread practice of selective logging in the tropics.

Dr. Lindsay F. Banin from the UK Centre for Ecology & Hydrology emphasized the importance of understanding the bottlenecks in plant community recovery to improve forest regeneration and ensure the sustainability of degraded forests.

“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,” Banin concluded.

Biodiversity and restoration in the balance

This research highlights the critical need for carefully designed, monitored, and adaptively managed restoration projects to recover biodiversity and carbon storage effectively. It points to the importance of understanding plant traits and local environmental conditions to enhance seedling survival rates.

Conducted in the Danum Valley Conservation Area and the surrounding Ulu Segama landscape, the study emphasizes the significance of intact forests and their role in supporting biodiversity through masting events.

These findings, although preliminary, suggest that long-term research is necessary to fully comprehend the impacts of historic disturbances and devise strategies to improve seedling survival, thereby supporting the goals of the UN Kunming-Montreal Global Biodiversity Framework and the UN Decade on Ecosystem Restoration.

More about rainforest restoration and seedlings

As discussed above, rainforest restoration involves actively participating in the recovery of deforested or degraded rainforest areas to regain their ecological integrity and biodiversity.

This process helps in combating climate change by absorbing carbon dioxide and restores habitats for countless species and maintains the water cycle vital for our planet.

Methods of rainforest restoration

Natural regeneration without seedlings

Natural regeneration is the most cost-effective method, where the forest is allowed to heal itself over time. This approach relies on the natural seed bank present in the soil and the nearby intact forests as sources for species dispersal.

Assisted rainforest regeneration with seedlings

In areas where natural regeneration is slow or unlikely, assisted regeneration steps in. This method involves human intervention to remove barriers to natural forest recovery, such as planting native tree species, controlling invasive species, and protecting young saplings from predation.

Reforestation

Reforestation is the process of planting trees in areas where forests have been completely removed. The choice of species is critical, with a preference for indigenous trees to ensure the restoration of the natural ecosystem. This method is labor-intensive but provides a faster way to restore forest cover.

Impact of rainforest restoration

Biodiversity conservation

By restoring rainforests, we create habitats for a vast array of species, many of which are endangered. This not only helps in preserving biodiversity but also in maintaining ecological balance.

Climate change mitigation

Rainforests are excellent carbon sinks. Restoring these forests plays a crucial role in mitigating climate change by absorbing carbon dioxide from the atmosphere. This contributes significantly to global efforts to reduce greenhouse gas emissions.

Community benefits

Rainforest restoration often involves local communities, providing them with sustainable livelihood options. From agroforestry to ecotourism, these activities help in creating economic opportunities while promoting conservation.

Challenges and solutions

Restoring rainforests is not without its challenges. These include land tenure issues, funding constraints, and the risk of introducing non-native species.

Addressing these challenges requires a multi-faceted approach, including policy support, community engagement, and scientific research to guide restoration efforts effectively.

In summary, rainforest restoration is a vital endeavor for the health of our planet. Through collective efforts and sustainable practices, we can recover these critical ecosystems, ensuring they continue to thrive for future generations.

The journey is complex and challenging, but the benefits of a restored rainforest are immeasurable, making it a mission worth pursuing.

The full study was published in the journal Global Change Biology.

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