Ecological restoration success is higher for natural regeneration than for active restoration in tropical forests

A better understanding of the natural regeneration in tropical forests could help develop more effective restoration strategies. This study examined relationships in structural and diversity attributes of natural regeneration in five forest fallow ages after slash‐and‐burn agriculture (6 months, 2 years, 5 years, 10 years, and 15 years) in the Republic of Congo. For each fallow age, all stems with a diameter ≥1 cm and below 5 cm (height ≥ 130 cm), corresponding to natural forest regeneration, were identified to the species level, and measured (diameter and height) in 12 plots (10 m × 10 m). Three structural attributes (stem density, maximum diameter, and maximum height) and five diversity indices (species richness, Shannon diversity, Simpson diversity, Fisher's alpha and Pielou's evenness) were estimated at the plot level. Our results revealed an increase in structural and diversity attributes with fallow ages, except stem density. The young fallow (6 months, 2 years and 5 years) had greater stem density (61 ± 48 stems), while the old fallow (10 years and 15 years) had higher maximum height (5.39 ± 2.36 m) and Shannon's index (0.94 ± 0.18). These results provided new insights into natural regeneration between young and old secondary forests.

Tropical forest restoration initiatives are becoming more frequent worldwide in an effort to mitigate biodiversity loss and ecosystems degradation. However, there is little consensus on whether an active or a passive restoration strategy is more successful for recovering biodiversity because few studies make adequate comparisons. Furthermore, studies on animal responses to restoration are scarce compared to those on plants, and those that assess faunal recovery often focus on a single taxon, limiting the generalization of results. We assessed the success of active (native mixed-species plantations) and passive (natural regeneration) tropical cloud forest restoration strategies based on the responses of three animal taxa: amphibians, ants, and dung beetles. We compared community attributes of these three taxa in a 23-year-old active restoration forest, a 23-year-old passive restoration forest, a cattle pasture, and a mature forest, with emphasis on forest-specialist species. We also evaluated the relationship between faunal recovery and environmental variables. For all taxa, we found that recovery of species richness and composition were similar in active and passive restoration sites. However, recovery of forest specialists was enhanced through active restoration. For both forests under restoration, similarity in species composition of all faunal groups was 60–70% with respect to the reference ecosystem due to a replacement of generalist species by forest-specialist species. The recovery of faunal communities was mainly associated with canopy and leaf litter covers. We recommend implementing active restoration using mixed plantations of native tree species and, whenever possible, selecting sites close to mature forest to accelerate the recovery of tropical cloud forest biodiversity. As active restoration is more expensive than passive restoration, both strategies might be used in a complementary manner at the landscape level to compensate for high implementation costs.

Natural regeneration in tropical forests is considered an essential part of forest restoration efforts; however, it is often under-estimated where the main focus has traditionally been on tree planting. This study assessed natural regeneration and its potential for the conservation of native tree species in Sitapahar Forest Reserve, Bangladesh. We established 99 temporary plots (2 m × 2 m each) in three canopy classes, namely dense canopy (DC, 70–100% canopy coverage), moderate canopy (MC, 40–70%), and open canopy (OC, <40%). In each plot, regenerating tree species were counted, identified, and height (m), collar diameter (cm), and diameter at breast height (dbh, cm) were measured. We identified 79 regenerating tree species under 31 plant families of which 61 were found in DC areas followed by 56 and 36 in MC and OC areas, respectively. Most of the species in DC areas were late-successional, while the OC areas were dominated by early successional species. Diversity and density of regeneration were lowest in OC areas. Findings of this study suggest harnessing biodiversity conservation by promoting natural regeneration and identifying the areas with higher potential for assisted natural regeneration that will enable in situ conservation of rare and vulnerable species by protecting them from further erosion.

Natural regeneration is an essential component of forest dynamics and the recovery of ecosystem functions. Therefore, understanding regeneration status, and how abiotic and biotic factors affect it, is important for ecological studies. This study discovered different regeneration statuses of tropical forests in response to differences in rainfall in Myanmar, and the environmental and overstory factors that had the most influence on understory regeneration. Study sites were set up in regions with 625 to 2035 mm of annual rainfall, and ecological characteristics were measured. According to the results, natural regeneration increased with rainfall, showing a good regeneration status at all sites. Forests within a range of 1411–2035 mm of annual rainfall had a significantly higher density and species diversity at specific natural regeneration stages than those with 625–1029 mm. Not only abiotic but also overstory structure affected the natural regeneration of forests. However, not all factors influenced natural regeneration status. Overstory size distribution parameters did not show a significant influence on natural regeneration. Average annual rainfall (abiotic), as well as ecosystem complexity, density, species richness, and diversity (overstory), were found to be the most influential factors for the density and diversity of natural regeneration. The results of this study will support silviculture and the management of tropical forests.

Recently, several important papers have been published dealing with the recovery of tropical forests by natural regeneration (van Breugel et al. 2025; Bousfield and Edwards 2025; Williams et al. 2024). We appreciated the results about the high potential for natural regeneration of forests throughout the tropics reported by some of the studies (Bousfield and Edwards 2025; Williams et al. 2024) and we completely agree that natural regeneration (spontaneous succession, passive restoration) is often more suitable and a cheaper approach to restore degraded or destroyed ecosystems. However, we stress that this approach does not always lead to species composition similar to that of undisturbed reference sites, especially in tropical forests. Tropical rain forests exhibit the lowest chance for recovery of natural species composition among all forest biomes of the world (Table 1). This pattern can be best explained by Hubbell's neutral theory (Hubbell 2001) based on stochasticity because natural vegetation in the tropics is composed of a high number of species. In contrast, the number of late successional (climax) species decreases with latitude (Ellis et al. 2012). For example, in northern Europe they are importantly represented by only two species (Picea abies, and Pinus sylvestris) and both readily establish in young successional stages. Consequently, the probability of reaching a natural species composition by natural regeneration increases with latitude. Moreover, in the tropics, alien invasive species have the highest probability of dominating late successional stages (Table 1) despite their highest total frequency in the middle latitudes (Ellis et al. 2012). Bousfield and Edwards (2025) and Williams et al. (2024) do not consider species composition but only cover. The authors derived their figures from remote sensing analyses with 30 m resolution, which naturally show only the total cover of woody species but not species composition. Despite the limitations, the analyses made by the authors are valuable and demonstrate the regeneration of tropical forests from the point of view of carbon sequestration but not from the point of view of biodiversity recovery. Carbon pools generally recover more easily than biodiversity in tropical forests (Martin et al. 2013). For the evaluation of biodiversity recovery we need thorough surface investigations (Viani and Reid 2025, etc.) and not only of disturbed sites themselves but also of the broader landscape context, which may substantially influence the recovery process (van Breugel et al. 2025, etc.). More such studies will enable more detailed and reliable global meta-analyses of the potential of natural regeneration than have been done till now. Both authors equally contributed to the paper. The authors declare no conflicts of interest. This article is a Letter to the Editor regarding Breugel et al., https://doi.org/10.1111/gcb.70037. See also the Response to the Letter by Breugel et al., https://doi.org/10.1111/gcb.70578. The data that support the findings of this study are openly available in Dryad at https://doi.org/10.5061/dryad.7m0cfxq8g.

Several recent meta-analyses have aimed to determine whether natural regeneration is more effective at recovering tropical forests than active restoration (for example, tree planting). We reviewed this literature and found that comparisons between strategies are biased by positive site selection. Studies of natural forest regeneration are generally conducted at sites where a secondary forest was already present, whereas tree planting studies are done in a broad range of site conditions, including non-forested sites that may not have regenerated in the absence of planting. Thus, a level of success in forest regeneration is guaranteed for many studies representing natural regeneration, but not for those representing active restoration. The complexity of optimizing forest restoration is best addressed by paired experimentation at the same site, replicated across landscapes. Studies that have taken this approach reach different conclusions than those arising from meta-analyses; the results of paired experimental comparisons emphasize that natural regeneration is a highly variable process and that active restoration and natural regeneration are complementary strategies.

Restoring formerly degraded ecosystems is a promising nature-based solution to mitigate climate change and ensure the provisioning of ecosystem services. Consequently, ecosystem restoration is prominent on both governmental and private agendas (e.g., the Bonn Challenge, airline carbon off-sets by planting trees). Two opposing strategies are employed to promote forest restoration: active versus passive (e.g. natural regeneration) restoration. Assessing how these two approaches influence biodiversity hot spots such as tropical rainforests is uniquely important, but the benefits and limitations of these two techniques have not been thoroughly compared.Among all tropical moist forests globally, forests of Asia-Oceania have experienced the highest disturbance rates in the past three decades, among which Sabah, Malaysian Borneo, contains forests with past managements to strategically assess long-term forest recovery following active and passive restoration strategies.How overall forest carbon balance, including carbon storage in the soil, is affected by active versus passive restoration, remains a blind spot not only at this site, but also globally. Given that up to half of the total carbon stored in secondary tropical rainforests can be stored belowground, and that this carbon has slower turn-over rates than above-ground vegetation, Sabah is a perfect testing ground to examine how common forest restoration influences below-ground carbon dynamics and total forest carbon balance.To address this, we collected soil samples in 15 actively restored and 15 naturally regenerating forest plots in INFAPRO, a restoration project in Sabah. This site was severely, selectively logged for two decades and then actively restored by planting (mainly) Dipterocarpacaea (i.e., diptertocarps) seedlings more than 20 years ago. These trees associate with ectomycorrhizal fungi that mediate important soil biochemical cycles as root-inhabiting tree symbionts.At this restoration site, active restoration enhanced tree diversity, promoted rare species, and increased above-ground carbon density in living vegetation in comparison to natural regeneration. We hypothesize that active restoration, including the planting of diptertocarps, further enhances the presence of ectomycorrhizal fungi, leading to a suppression of free-living microbial decomposition of plant litter inputs (i.e., the Gadgil effect), and an increase in total soil carbon storage. While this may increase total soil carbon storage, the more persistent fraction that is mineral-associated may decrease. This is due to slowed plant litter decomposition and thus less production of compounds that absorb onto mineral surfaces in addition to less microbial necromass inputs sticking to minerals due to the lower growth efficiency by ectomycorrhizal fungi compared to free-living microbes.This knowledge on soil carbon storage and its persistence is a much needed contribution to holistic assessments of active restoration compared to natural regeneration. Empirical results on soil carbon analyses will be generated by the time of the EGU conference.

Apresenta um modelo matemático para expressar a taxa de regeneração natural em florestas tropicais, através dos valores de abundância. 0 modelo proposto e. o seguinte-.tr = { (A1/A0)- 1 }. 100, onde:tr = taxa de regeneração natural em percentagem;A = abundância absoluta = número de indivíduos por unidade de área;A1 = A0 + ne - ns = abundância absoluta final;ne = número de indivíduos que ingressaram no estudo, por germinação ou mudança de categoria de tamanho (in-put)) ;ns = número de indivíduos que saíram do estudo, por morte ou mudança de categoria de tamanho (out-put).-1 = constante que indica a mortalidade.Os resultados demonstram que a floresta está em equilíbrio dinâmico, uma vez que, apresentou um valor de + 0,10% para a taxa de regeneração natural, a qual pode ser utilizada para espécies, grupos de espécies ou para o total da floresta.

Natural regeneration in tropical forests along a disturbance gradient in South-East Cameroon

When compared to planted reforestation, natural unassisted regeneration is often reported to result in slow recovery of biomass and biodiversity, especially early in succession. In some cases, naturally regenerating forests are not comparable to the community structure of primary forests after many decades. However, direct comparison of the outcomes of tropical forest restoration and natural regeneration is hindered by differences in metrics of forest recovery, inconsistency in land use histories, and dissimilarities in experimental design. We present the results of a replicated reforestation experiment comparing natural regeneration and polyculture tree planting at multiple diversity levels (3, 6, 9, or 12 native tree species), with uniform land use history and initial edaphic conditions. We compare the recovery of basal area and floristic diversity in these treatments after 5 yr of succession. Total basal area was higher in planted plots than in naturally regenerating plots, but it but did not vary among the different planted diversity levels. The basal area of woody recruits did not differ among treatments. The diversity of woody recruits increased substantially over time but did not vary among planting treatments. Species composition trajectories showed directional turnover over time, with no consistent differences among treatments. The convergence of restoration trajectories and similarity of floristic community diversity and composition across all treatments, after only 5 yr, provides evidence of the viability of natural regeneration for rapid restoration of forest biodiversity.

A major global effort to enable cost‐effective natural regeneration is needed to achieve ambitious forest and landscape restoration goals. Natural forest regeneration can potentially play a major role in large‐scale landscape restoration in tropical regions. Here, we focus on the conditions that favor natural regeneration within tropical forest landscapes. We illustrate cases where large‐scale natural regeneration followed forest clearing and non‐forest land use, and describe the social and ecological factors that drove these local forest transitions. The self‐organizing processes that create naturally regenerating forests and natural regeneration in planted forests promote local genetic adaptation, foster native species with known traditional uses, create spatial and temporal heterogeneity, and sustain local biodiversity and biotic interactions. These features confer greater ecosystem resilience in the face of future shocks and disturbances. We discuss economic, social, and legal issues that challenge natural regeneration in tropical landscapes. We conclude by suggesting ways to enable natural regeneration to become an effective tool for implementing large‐scale forest and landscape restoration. Major research and policy priorities include: identifying and modeling the ecological and economic conditions where natural regeneration is a viable and favorable land‐use option, developing monitoring protocols for natural regeneration that can be carried out by local communities, and developing enabling incentives, governance structures, and regulatory conditions that promote the stewardship of naturally regenerating forests. Aligning restoration goals and practices with natural regeneration can achieve the best possible outcome for achieving multiple social and environmental benefits at minimal cost.

The knowledge of the nutritional aspects of native species, mainly in natural regeneration, may be important for understanding their establishment, particularly in areas with low nutrient availability soils, such as tropical soils. This study aimed to determine the biological utilization efficiency (BUE) of the nutrients N, P, K, Ca, and Mg of forest species of natural regeneration in a Lowlands Dense Ombrophilous forest fragment in Pernambuco, Brazil. A phytosociological study of the fragment was carried out and were defined the ten species with the highest absolute density (AD). Three individuals per species were selected. The N, P, K, Ca, and Mg contents were determined in the sample leaves of the species, and the foliar biomass was determined “in loco”. Nine individuals of each species were collected according to the following diameter intervals at the base (DBs): DBs&amp;lt;5 cm; 5≤DBs&amp;lt;10 cm and 10≤DBs&amp;lt;15 cm. The content, stock and BUE of nutrients were calculated per species. The BUE of nutrients by species varied according to the following decreasing order: P&amp;gt;Mg&amp;gt;K&amp;gt;Ca&amp;gt;N. The highest BUE of nutrients was of the species Protium heptaphyllum. In tropical soils of low natural fertility, the use of these species can be recommended in environmental reforestation projects. The difference in the nutritional demand of the forest species can indicate the planting of those with greater capacity of absorption and BUE of nutrients, being more efficient in areas of soils with low natural fertility like in the tropical forests.

In degraded tropical landscapes, lack of seed dispersal can strongly limit recovery, and restoration interventions can overcome this barrier by attracting dispersers. However, seed dispersal patterns are typically studied over short time periods, thus the influences of temporal and spatial variability on seed arrival cannot be teased apart. The choice of management approach can have important implications for restoration‐mediated community reassembly. Accordingly, we used a 3.5‐year record of seed deposition in pre‐montane tropical wet forest in southern Costa Rica to examine how seed arrival differed between passive (natural regeneration) and active (applied nucleation, plantation) restoration after a decade of recovery, compared to remnant forest. We investigated: (a) how restoration treatments affected seed deposition rates and community composition; (b) how within‐plot heterogeneity of animal‐dispersed seed deposition varied by intervention; and (c) how interannual variation influenced animal‐dispersed seed arrival across treatments. Overall seed rain composition and diversity in restoration treatments was converging towards, but still differed substantially from, remnant forest (89.7%, 86.6% and 76.3% Shannon diversity recovered in applied nucleation, plantation and natural regeneration respectively). Within‐plot animal‐dispersed seed heterogeneity was similar in applied nucleation and remnant forest, 27.0% more heterogeneous in applied nucleation than plantation, and equivalent when comparing natural regeneration to either applied nucleation or plantation. In contrast to active interventions, animal‐dispersed tree and shrub communities did not differ year to year in natural regeneration, which may promote the assembly of relatively homogeneous plant communities at this successional stage. Synthesis and applications. Compared to natural regeneration, active restoration interventions: (a) catalysed the recovery of seed diversity (overall Shannon diversity 17.5% and 13.4% higher in applied nucleation and plantation respectively), (b) shifted seed community composition towards remnant forest more rapidly (overall Shannon diversity 13.4% and 10.2% closer), (c) almost doubled the proportion of later‐successional tree species arriving, and (d) had seed communities that differed year to year—a pattern not observed in natural regeneration. Finally, applied nucleation was the only intervention where seed arrival was as spatially heterogeneous as remnant forest, highlighting that this approach may facilitate the recovery of specific natural dispersal processes.

Given the importance of species diversity as a tool for assessing recovery during forest regeneration and active restoration, robust approaches for assessing changes in tree species diversity over time are urgently needed. We assessed changes in tree species diversity during natural regeneration over 12-20 years in eight 1-ha monitoring plots in NE Costa Rica, six second-growth forests and two old-growth reference forests. We used diversity profiles to show successional trajectories in measures of observed, asymptotic and standardized tree diversity and evenness as well as sample completeness. We randomly subsampled 1-ha plot data to evaluate how well smaller spatial subsamples would have captured temporal trajectories. Annual surveys in eight 1-ha plots were missing substantial numbers of rare or infrequent species. Older second-growth sites showed consistent declines in tree diversity, whereas younger sites showed fluctuating patterns or increases. Subsample areas of 0.5 ha or greater were sufficient to infer the diversity of abundant species, but smaller subsamples failed to capture temporal trajectories of species richness and yielded positively biased estimates of evenness. In tropical forest regions with high levels of diversity, species diversity from small sample plots should be assessed using methods that incorporate abundance information and that standardize for sample coverage. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Restoration of degraded forests and landscapes is emerging as a global conservation priority. Opinion is divided, however, whether active restoration is a better approach than passive intervention in forest ecosystem rehabilitation. We assessed the variation in woody species composition and stand structure during the first five years of both active and passive restoration interventions in a degraded humid forest in western Kenya. Passive restoration entailed natural regeneration, while active restoration comprised planting at 5m, 1m and 0.3m spacing. The plots were protected from repeat incidences of disturbance using enclosures. Natural regeneration registered a significantly higher woody species richness (36.75±6.97) than active restoration (12.75±1.75). It had a higher Shannon-Wiener diversity index (3.05) than active restoration (2.32). Despite up to 10,000 seedlings per ha being planted under active restoration, woody stem density was significantly higher under natural regeneration (21,789±7,087 stems ha-1) than active restoration (13,118±1,857 stems ha-1). Mean sapling height was higher under natural regeneration (2.60±0.31 m) than active restoration (1.38±0.30 m). The results suggest that passive restoration interventions may be superior to active restoration approaches in rehabilitating degraded forest landscapes in the humid tropics if repeat incidences of disturbance are controlled. The long-held view that active restoration leads to greater woody species diversity and stand structure may have been spurred by the fact that ecological restoration interventions are often carried out in open sites that are exposed to continual incidences of disturbance, which tends to hamper the recruitment and survival of natural regrowth.