The Future of Afrotropical Rainforests: Logging and Regrowth

Afrotropical rainforests are super important places in the world. They are famous for having a lot of plant species and for providing essential services like clean air and habitat for animals. The rainforests host over 30,000 types of plants, and they have many species of flowering plants. However, these forests have fewer plant types compared to the tropical rainforests found in places like South America. This difference comes down to geology, climate, and not enough researchers working here.

#Roles in Ecosystem Function

These rainforests do a great job of producing oxygen and storing carbon, which helps reduce climate change. The Congo Basin, which is part of these forests, stores a huge amount of carbon-way more than the Amazon! Unfortunately, human activities, like farming and Logging, are putting these crucial forests at risk. About four million hectares of African rainforest vanish every year, making it disappear faster than many other places in the world.

#Threats from Human Activities

We often hear about clear-cutting, but another sneaky danger is forest degradation. This is when people mess with the forest without completely cutting it down, which can be just as harmful. Selective logging is a main problem, especially in Afrotropical forests. This involves taking some trees while leaving others, and it’s mostly driven by the need for charcoal and construction wood. Due to this, about one-third of the Afrotropical rainforests are now heavily damaged.

#Regrowth of Tropical Rainforests

Despite high rates of deforestation, there’s a silver lining: abandoned rainforests are growing back! Many African countries are working to restore their forests through projects like the African Forest Landscape Restoration Initiative. Between 2000 and 2019, nearly a million hectares of forest were either actively or passively restored in sub-Saharan Africa. Some studies suggest that biodiversity in these regrowth forests can bounce back pretty quickly, but it takes longer for the mix of species to get back to what it was before.

#Measuring Biodiversity Effects

Traditionally, people looked at biodiversity by counting different species. But, as Darwin pointed out a long time ago, species aren’t just random. They have shared histories and can perform different ecological roles. Counting species misses a lot of the richness found in nature. So, researchers now try to include Phylogenetic (evolutionary relationships) and Functional (how species interact and their roles) Diversity too.

Understanding these relationships better helps researchers see how logging and regrowth affect the structure and make-up of rainforest communities. This is vital for creating smart conservation strategies.

#Lack of Data in the Tropics

Despite knowing how important these aspects are, there are still not enough studies that combine phylogenetic and functional dimensions, especially in tropical areas. In Asia and South America, studies hint at a common theme: as disturbances increase, diversity tends to decrease. However, when it comes to the Afrotropics, particularly the Congo Basin, research is scarce.

#Study Objectives

To fill this gap, we used data from previous studies to look at how logging and regrowth affect the tree communities in the Congo Basin. We set out to see how selective logging impacts the phylogenetic and functional diversity compared to untouched forests.

#Study Area

Our study focused on the Yangambi region in northeastern DR Congo. This area represents typical rainforest landscapes in the Congo Basin, combining different types of land use. Unfortunately, no management plan has been implemented, which adds to the challenges faced by this ecosystem.

#Vegetation Sampling

In this region, scientists set up 25 forest plots to study the vegetation. They took samples from these areas and gathered data on over 7,000 trees, identifying them to species level. This included gathering information on their traits, such as wood density and leaf area.

#Phylogeny Construction

To understand the evolutionary relationships among tree species, researchers built a phylogenetic tree. They matched species names to help ensure accuracy and included missing species by connecting them to their closest relatives.

#Data Analysis: Phylogenetic Diversity

Researchers calculated several metrics to assess phylogenetic diversity based on the phylogenetic tree constructed earlier. This included looking at how many different lineages are present and how closely related species are to each other. They compared diversity among the three types of forests: undisturbed old-growth, disturbed old-growth, and regrowth forests.

#Data Analysis: Functional Diversity

Similar to phylogenetic diversity, researchers also assessed functional diversity by looking at how different species interact with their environment and what roles they play. They measured various aspects of the community related to functional traits to see how these vary between different forest types.

#Results: Phylogenetic Diversity

The forests that had been logged showed higher phylogenetic diversity in certain areas compared to untouched forests. This suggests that while logging removes some trees, others still remain and help maintain some diversity. Regrowth forests showed a higher amount of terminal phylogenetic diversity, meaning they had more newer or younger species coming in.

#Results: Functional Diversity

When looking at functional diversity measures, the logged forest displayed a higher functional divergence compared to untouched forests. However, overall, researchers didn't find major differences in functional metrics across the forest types, suggesting that the basic functions of the ecosystem still exist.

#Comparing Forest Categories

Through a range of tests, researchers found significant differences in both phylogenetic and functional community compositions among the different forest types. The changes were driven largely by wood density and trunk size, which are influenced by human activities such as logging.

#Drivers of Change

The removal of trees with high wood density due to selective logging has altered the diversity in both phylogenetic and functional terms. The changes in wood density and trunk size highlight how logging affects the remaining trees and their capabilities within the ecosystem. This also impacts how forests store carbon, with lower wood density trees being less effective at sequestering carbon.

#Forest Regrowth Impact

Looking at regrowth after farming was abandoned, the results suggest that regrowth forests are recovering. However, they have not fully returned to the diversity levels found in untouched old-growth forests. The presence of younger and late-successional species points to a recovery process that is still ongoing.

#Limitations of the Study

While this research provides valuable insights, there are some limitations, such as the availability of data on certain species and traits. This could lead to less accurate estimates of diversity, but these limitations apply equally across all forest types in the study.

#Conclusion

Incorporating both phylogenetic and functional aspects of diversity is crucial for assessing the impacts of logging and regrowth in these rainforests. The study found that while community compositions were significantly changed in logged and regrowth forests, the basic functions of these ecosystems have managed to persist. We can say that undisturbed old-growth forests are irreplaceable and need protection, while regrowth forests play a significant role in supporting biodiversity and recovering ecosystem functions.

#Supporting Information

A wealth of additional data and information supports the findings, helping to build a clearer picture of the changes occurring in these important ecosystems.