Managed Zones Harbor Richer Forests Amid Widespread Degradation in Nigerian Reserve

Deep in southwestern Nigeria, a fragmented tropical forest reserve is telling a quietly dramatic story about what happens when conservation attention meets relentless human pressure. A new study of the Ise Forest Reserve, published in the journal Discover Forests, has found that the portion of the reserve managed under a dedicated conservation project supports markedly higher tree diversity and stronger forest structure than surrounding disturbed areas, even as satellite records reveal that land-cover degradation swept across the entire landscape between 2016 and 2023. The findings offer both encouragement and a warning: local management can coincide with healthier forest condition, but it has not stopped the wider erosion of one of Nigeria’s most important rainforest refuges.

Nigeria has lost more than 90 percent of its original forest cover, making it one of the countries with the highest deforestation rates in Africa. Between 2010 and 2015 alone, the country’s deforestation rate reached roughly five percent, driven by illegal logging, agricultural expansion, and infrastructure development. Ise Forest Reserve, located near the Uso community in Ondo State and spanning parts of Ekiti State, sits squarely within this crisis zone. The reserve is a critical stronghold for the critically endangered Nigeria-Cameroon chimpanzee and also harbors the African forest elephant, the yellow-casqued hornbill, Mona monkeys, and a rich assemblage of plant species including Gmelina arborea, Tectona grandis, and Khaya ivorensis. Despite its protected status, the reserve faces persistent encroachment from loggers and farmers, some of whom clear forestland to cultivate cannabis.

In 2021, the Ekiti State Government took a notable step by gazetting a portion of the reserve to the Southwest/Niger Delta Forest Project for conservation and restoration. The researchers behind the new study seized on this administrative boundary as a natural experiment. They designated the gazetted area as the managed zone and areas outside it as the disturbed zone, then asked a straightforward question: does the managed portion of the forest look ecologically different from the rest? Importantly, the team is careful to note that this division is administrative rather than a measure of true disturbance, and that the managed zone is by no means pristine, having also experienced logging and land-cover change.

To answer the question, the researchers combined painstaking fieldwork with satellite-based remote sensing. In the field, they established eleven sampling plots measuring 25 by 25 meters along transects spaced at least 200 meters apart, with eight plots in the larger managed zone and three in the smaller disturbed zone, allocated proportionally to the mapped area of each zone. Within each plot, they recorded every woody individual, measuring tree height, canopy cover, and diameter at breast height, the standard trunk measurement taken at 1.3 meters above the ground. In total, the survey documented 27 woody species from 17 families. The most frequently recorded species across the reserve was Ricinodendron heudelotii, appearing 55 times, while a single towering Diospyros lotus individual posted the most extreme structural values: a height of 12.20 meters, canopy cover of 18.60 meters, and a trunk diameter of 138.13 centimeters.

The structural comparison between zones was stark. Trees in the managed zone averaged 9.55 meters in height, 4.79 meters of canopy cover, and 21.92 centimeters in trunk diameter, compared with 7.64 meters, 3.35 meters, and 16.77 centimeters respectively in the disturbed zone. Using Welch’s independent t-tests with a Bonferroni-corrected significance threshold to guard against false positives across the three comparisons, the team found these differences were statistically robust: taller trees (p = 0.002), wider canopies (p < 0.001), and thicker trunks (p < 0.001) all favored the managed zone. Diversity metrics told the same story. The Shannon-Wiener index, which blends species richness with evenness; the Simpson concentration index, which reflects the probability that two randomly drawn individuals belong to the same species; and Margalef’s richness index all scored higher in the managed zone, which also contained 241 woody individuals across 19 families compared with 75 individuals across 14 families in the disturbed zone.

The satellite analysis painted a far grimmer picture of the wider landscape. Drawing on Landsat 7 and Landsat 9 imagery at 30-meter resolution from November 2016 and December 2023, the researchers classified land cover into secondary forest, degraded vegetation, and farmland, then computed transition rates between the two dates. In the managed zone, secondary forest collapsed from 31.40 square kilometers, or 97.65 percent of the zone, to just 14.10 square kilometers, or 43.85 percent, a net loss of 17.31 square kilometers. Degraded vegetation in the same zone exploded from a mere 0.14 square kilometers to 17.06 square kilometers. In the disturbed zone, farmland surged from 0.54 square kilometers to 7.24 square kilometers, more than a tenfold expansion, while degraded land shifted dramatically in extent. Across the landscape, conversions from secondary forest to degraded vegetation dominated the change matrix, and transitions back toward secondary forest were negligible, hovering around 0.01 percent in both zones.

The spatial contrasts were meaningful as well as the temporal ones. Farmland expanded more slowly in the managed zone than in the disturbed zone, and the loss of secondary forest proceeded at a lower rate there, suggesting that the conservation presence did dampen the most destructive forms of conversion. The species composition also shifted with disturbance. Ricinodendron heudelotii proved resilient and appeared in both zones, while economically valuable timber species such as Milicia excelsa were underrepresented in disturbed areas, consistent with overexploitation of high-value trees. These patterns echo findings from other Nigerian reserves, including Omo Biosphere Reserve, Ago-Owu, and Doma, where logging, fragmentation, and farming have been shown to strip out species diversity, stem density, and structural integrity.

Yet the authors are refreshingly candid about the limits of what their study can claim. Because no vegetation inventory was conducted before the conservation project began in 2021, the study could not use a before-after-control-impact design. The observed differences between zones represent a spatial snapshot, and pre-existing environmental, historical, or accessibility differences between the zones could partly explain them. The researchers explicitly state that the results cannot be attributed solely to the 2021 project and remain subject to review in a long-term evaluation. The two-date satellite comparison, meanwhile, captures net change over seven years but cannot resolve annual fluctuations, seasonal dynamics, fires, or short disturbance pulses that may have occurred in between. Unequal plot replication, dictated by the zones’ different sizes, also means the species counts should be read as field summaries rather than precise estimates of true richness.

Those caveats do not diminish the study’s central significance. It provides one of the first quantitative baselines for Ise Forest Reserve, coupling ground-truthed structural measurements with remote sensing in a data-scarce landscape, and it demonstrates a replicable template for monitoring restoration efforts across West Africa’s embattled forest reserves. The picture that emerges is of a landscape under siege but not yet lost: management appears to coincide with taller, thicker, more diverse forest and slower farmland encroachment, even as degraded land expands relentlessly across both zones. The researchers call for intensified patrolling, effective buffer-zone management, community livelihood programs, and rehabilitation of degraded patches. Most critically, they recommend permanent monitoring plots and annual dry-season Landsat or Sentinel-2 imagery to track whether the conservation trajectory truly diverges from the region’s grim baseline. For the chimpanzees, elephants, and hornbills that depend on Ise, the answer to that question may determine whether the reserve’s remaining forest endures.

The study’s methodological choices reflect broader trends in tropical forest monitoring. By pairing ground-based plot inventories with freely available Landsat imagery, the researchers worked within the constraints common to conservation science in data-scarce regions, where funding for extensive field campaigns is limited and historical vegetation records are often absent. Satellite indices such as the Normalized Difference Vegetation Index and the Enhanced Vegetation Index, which track photosynthetic activity from orbit, have become standard tools for detecting vegetation condition across large or inaccessible landscapes, and recent Nigerian studies have shown that machine learning classifiers applied to satellite data can produce usable land-cover maps even where ground information is sparse.

The ecological indicators used in the study each capture a different dimension of forest condition. Species richness counts how many distinct woody species occur in a sample, while the Shannon-Wiener index weighs both richness and the evenness with which individuals are distributed among species, and the Simpson concentration index estimates the probability that two individuals drawn at random belong to the same species. Structural measures such as diameter at breast height, height, and canopy cover complement these diversity metrics because they relate directly to carbon storage, habitat complexity, and the capacity of a forest to support wildlife such as primates that depend on layered canopy and mature fruiting trees.

The reserve’s setting also matters for interpreting the results. At roughly 366 meters above sea level, with mean annual rainfall of about 1,380 millimeters concentrated in an eight-month wet season from April to October and temperatures ranging between 19 and 30 degrees Celsius, the forest lies within the humid zone of southwestern Nigeria. Its fragmentation, noted by the authors, is itself ecologically significant, since smaller and more isolated forest patches generally support fewer species than large contiguous tracts. A stream near the eastern boundary and the Ogbese River to the west shape the local landscape, while proximity to the Akure-Benin expressway facilitates both access and encroachment.

Finally, the study underscores a persistent challenge for protected-area governance in Nigeria: legal designation alone has not prevented logging, farming, or hunting within reserve boundaries. The authors’ recommendation for permanent monitoring plots and regular dry-season satellite imagery reflects a growing consensus that restoration success must be measured against quantitative baselines rather than assumed from management status, particularly when interventions begin after degradation is already well advanced.

Subject of Research: Vegetation diversity, forest structure, and land-cover degradation in a managed versus disturbed Nigerian forest reserve

Article Title: Higher vegetation diversity and stronger forest structure occur in managed zones despite widespread land cover degradation in Ise Forest Reserve Nigeria

Article References: Olaniyi, O., Ogunsakin, E., Ogunjemite, B., Rafiu, K., & Anozie, E. (2026). Higher vegetation diversity and stronger forest structure occur in managed zones despite widespread land cover degradation in Ise Forest Reserve Nigeria. Discover Forests, 2(1), Article 67. https://doi.org/10.1007/s44415-026-00129-1

Image Credits: AI Generated

DOI: 10.1007/s44415-026-00129-1

Keywords: forest degradation, vegetation diversity, Ise Forest Reserve, land-cover change, forest structure, remote sensing, conservation management, Nigeria, tropical forest, Landsat imagery, secondary forest, restoration ecology