? Importance of animals for natural regeneration of forests

In the climate crisis we are currently experiencing, the initiative to plant trees to compensate for our impact on the environment and thereby participate in the restoration of forest landscapes is becoming more and more widespread around the world. But according to a new scientific study, we should not forget that animals also play a key role in the natural regeneration of forests. However, as reminded by COP15 on biodiversity, in December 2022, more than one million species (animals and plants) are now threatened with extinction…

Forests are important to the climate, biodiversity and people, so why are they so degraded around the world? Climate change, intensive deforestation, land use change, extreme climate and meteorological events… This answer no longer surprises anyone because it is a problem that comes up often, very often.

According to FAO’s latest State of the World’s Forests report (2022 edition), forests are a resource of global importance and cover 31% of the land surface, but deforestation It caused 420 million hectares of forest to disappear between 1990 and 2020. “The rate of deforestation is decreasing, but between 2015 and 2020, 10 million hectares of forest were destroyed annually. From 2000 to 2020, 47 million hectares of primary forest have disappeared.– the report says.

An international team of researchers analyzed in a new scientific study published in the journal The Royal Society the crucial role of animals in reforestation. To do this, they based their research on a unique, long-term data set from the Barro Colorado Monumento Natural Forest in Panama, which is managed by the Smithsonian Tropical Research Institute (STRI).

The island of Barro Colorado and its five surrounding peninsulas provide easy access to the rainforests of the central Panamanian plains. The 1,560-hectare island was created in 1914 during the creation of Lake Gatun, the main corridor of the Panama Canal.

“Nearly 100 years of climate data, four decades of environmental monitoring, and the establishment of the first large-scale plan for long-term monitoring of tropical forests in 1980 provide important tools for understanding how tropical forests and their inhabitants change over time.”According to the website of the Smithsonian Tropical Research Institute.

Because this region has been specifically studied by STRI biologists for nearly a century, the team of scientists was able to deepen their research using data spanning several decades. Because this is an area with little hunting or logging, the study results provide accurate information on seed dispersal by animals over a range of regenerating forests over a period ranging from 20 to 100 years after abandonment.

We should not neglect the role of animals…

Global wildlife populations have declined by almost 70% over the past 50 years, and not surprisingly, humans are the main culprit.

COP15 on biodiversity, chaired by China in Montreal last December, concluded with the adoption of the Kunming-Montreal Global Biodiversity Framework (GBF) by the 196 Member States of the Convention on Biological Diversity. The latter is divided into four main goals and 23 action targets to be achieved by 2030, one of which is to protect 30% of the planet’s land and oceans.

“When we talk about reforestation, people usually think of going out and digging holes and planting seedlings.”Lisa Comita, Professor of Tropical Forest Ecology, explains. “It’s not really a very cost-effective or efficient way to restore natural forests. If you have an intact, protected forest nearby and animals to disperse the seeds, you can achieve natural regeneration, a less expensive and less labor-intensive approach. »

This study further revealed that animals are extremely important in the regeneration of tree species they carry different seeds in previously deforested areas. Indeed, a certain number of plants, known as zoochores, reproduce thanks to the transport of seeds by animals such as those caught in hair or left in feces.

The research team therefore closely analyzed the proportion of tree species scattered by four groups of animals: flightless mammals, large birds, small birds and bats.

Dispersal by flightless mammals and large birds is strong and increases as the forest ages, while dispersal by small birds tends to decrease as forests regenerate, the study found. The distribution of species dispersed by flightless mammals in forest ages contradicts the results of other studies. Indeed, researchers explain that flightless mammals generally exist in low numbers in forests due to habitat loss, fragmentation, or hunting…

It is true that Barro Colorado presents a particularly privileged situation, which explains why seed dispersal by flightless mammals and large birds is so important in this study. The presence of large protected forests adjacent to young secondary forests, low hunting and high functional reserve among dispersers constitute a favorable context for these animal species.

Redundancy corresponds to the probability of a plant species dispersing through several dispersal modes.

“We do not have data for the first two decades of reforestation, so we cannot confirm the importance of seed dispersal by flightless mammals and other dispersers during this period. However, given the well-preserved nature of our study area and the low level of disturbance after abandonment, species dispersed by flightless mammals may have already become widespread immediately after abandonment.say the researchers in the study.

Typically, small-seeded tree species dispersed by small birds, bats and wind colonize abandoned agricultural sites, the study found. The formation of the canopy then encourages the arrival of larger birds and mammals, which in turn bring larger seeded tree species.

However, when it comes to bat dispersal – important helpers – the results of the sample are not very conclusive. The researchers explain that the contribution of bats may have occurred during the first 20 years of regeneration, which could not be studied. Other studies show that seed dispersal by small birds and bats is critical.

And finally, the rate of natural forest regeneration depends on the landscape context. The latter has an interaction between dispersers and seed sources. For example, in completely deforested areas with few plant species, the recovery of interactions is slow and largely depends on the wind (especially for anemochorous plant species that reproduce by dispersing their seeds in the wind), …, but also bats and small birds. In contrast, in areas surrounded by large areas of forest, interactions are restored more rapidly, and seed movement is typically facilitated by larger birds and flightless mammals, but also by smaller birds and bats. .

… and rainforests

Tropical forests play an important role in regulating the global climate and support a great diversity of plants and animals. In these woods, more than 80% of tree species are spread by animals. Therefore, it is interesting and important to understand how different seed dispersers contribute to forest regeneration and which landscape variables determine the abundance of seed sources and seed dispersers.

“In these tropical environments, animals are critical to rapid forest regeneration”says Estrada-Villegas, a postdoctoral fellow at the Yale School of the Environment who recently joined the faculty at the Universidad del Rosario in Bogotá, Colombia.

Dispersal of seeds to animals is important when restoring tropical forests because it allows preservation of plant diversity and acceleration of regeneration.

In conclusion, the researchers suggest that aspects of seed dispersal should be monitored during restoration of forest ecosystems to assess the restoration of interactions between species. They assure that the results can serve as a road map for the natural regeneration of forests.