Human disturbance in Nigerian forest reserve alters carbon storage dynamics

A new analysis from the Ise-Ekiti Forest Reserve in Southwestern Nigeria provides a nuanced look at how human activities affect the carbon-storing capabilities of tropical forests. Researchers from the Institute of Ecology and Environmental Studies and the Department of Botany at Obafemi Awolowo University investigated the intricate connection between biomass, carbon stock, and potential CO₂ emissions in woody plants. The work compares sections of the forest with minimal human interference to areas impacted by activities like logging and agricultural expansion, offering critical data for conservation and climate change mitigation strategies.

A Tale of Two Forests: Comparing Disturbed and Undisturbed Plots

To quantify the impact of human activity, the research team, including Adebowale D. Dada, Olaniran J. Matthew, and Anthony I. Odiwe, established ten 25x25 meter plots within the reserve. Five plots were located in undisturbed forest, while the other five were in areas showing clear signs of disturbance. Within each plot, every woody plant was identified, and its girth and height were meticulously measured. Using established allometric equations, the scientists calculated the above-ground and below-ground biomass for both trees and shrubs, which then allowed them to estimate the total carbon stock and the equivalent amount of sequestered carbon dioxide.

Trees Thrive in Tranquility, Shrubs Seize the Opportunity

The results confirmed the immense value of intact forests. The total carbon stock stored in trees was substantially higher in the undisturbed plots, registering 51.3 megagrams of carbon per hectare (Mg C ha-1) compared to 35.4 Mg C ha-1 in the disturbed plots. This disparity demonstrates that mature, undisturbed trees are powerhouses of carbon sequestration. The tree species Ceitis zenkeri, for instance, was identified as a particularly significant contributor to the carbon pool in the pristine sections of the forest, highlighting the importance of preserving specific keystone species.

An Unexpected Ecological Response

Conversely, the study revealed a surprising ecological shift in the disturbed areas. While the large trees suffered, the shrub layer flourished. With more sunlight reaching the forest floor due to a sparser tree canopy, shrubs in the disturbed plots exhibited higher total biomass, carbon stock, and potential CO₂ emissions than their counterparts in the undisturbed plots. This finding suggests that ecosystems respond to disturbance in complex ways; however, the small increase in carbon held by shrubs does not come close to offsetting the massive carbon losses from the decline of mature trees. The overall balance remains a net loss of stored carbon.

"Our findings reveal a dual reality. While undisturbed forests are immense carbon vaults, the data also shows that even within a designated reserve, human activities are subtly reshaping the ecosystem's function," states Adebowale D. Dada, the corresponding author. "The increase in shrub carbon in disturbed areas doesn't compensate for the loss from mature trees, signaling that the conservation goals for these reserves are challenged by ongoing pressures. It tells us that protection on paper is not enough; we need effective on-the-ground management to prevent degradation." The authors note the study is specific to this site and that a broader understanding would benefit from more extensive, long-term research.

Future Directions for Forest Carbon Accounting

The investigation concludes that the primary objective of forest reserves—to preserve ecosystems and their functions—is being compromised by human encroachment, contributing to the very climate change these forests should be mitigating. The authors call for future studies to incorporate the economic valuation of different woody species and the cost-effectiveness of various conservation strategies. Such information is essential for developing practical management plans that align with international frameworks like REDD+ (Reducing Emissions from Deforestation and Forest Degradation) and ensure the long-term health and carbon sequestration potential of Nigeria's vital forest ecosystems.

Corresponding Author: Adebowale D. Dada

Original Source: https://doi.org/10.1007/s44246-024-00115-2

 Contributions: Dada Adebowale analysed the data and wrote the article. Dada Adebowale and Olaniran Matthew revised the manuscript. Dada Adebowale and ODIWE Anthony collected the experiment data. Olaniran Matthew and Odiwe Anthony designed the whole experiment. Dada Adebowale submitted the manuscript. The author(s) read and approved the final manuscript.