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Distribution of number of surveys per taxon for the 1,681 modelled taxa Of the taxa, 731 (44 %) were represented in a single survey, and the remaining 946 (56 %) were represented in multiple surveys.
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Logged and disturbed forests are often viewed as degraded and depauperate environments compared with primary forest. However, they are dynamic ecosystems¹ that provide refugia for large amounts of biodiversity2,3, so we cannot afford to underestimate their conservation value⁴. Here we present empirically defined thresholds for categorizing the cons...
Citations
... pnas.org from logging is too low to have zero impact on biodiversity, recent work in Southeast Asia suggests low intensity logging (<29% biomass removal) is associated with largely intact functional composition ( 32 ). Given logged structurally degraded forests under high human pressures can still harbor considerable biodiversity and maintain ecosystem functioning ( 33 -35 ), it would be worth restoring logged forests of lower integrity wherever feasible as opposed to converting them into agricultural lands or monoculture plantations. ...
Structurally intact native forests free from major human pressures are vitally important habitats for the persistence of forest biodiversity. However, the extent of such high-integrity forest habitats remaining for biodiversity is unknown. Here, we quantify the amount of high-integrity tropical rainforests, as a fraction of total forest cover, within the geographic ranges of 16,396 species of terrestrial vertebrates worldwide. We found up to 90% of the humid tropical ranges of forest-dependent vertebrates was encompassed by forest cover. Concerningly, however, merely 25% of these remaining rainforests are of high integrity. Forest-dependent species that are threatened and declining and species with small geographic ranges have disproportionately low proportions of high-integrity forest habitat left. Our work brings much needed attention to the poor quality of much of the forest estate remaining for biodiversity across the humid tropics. The targeted preservation of the world’s remaining high-integrity tropical rainforests that are currently unprotected is a critical conservation priority that may help alleviate the biodiversity crisis in these hyperdiverse and irreplaceable ecosystems. Enhanced efforts worldwide to preserve tropical rainforest integrity are essential to meet the targets of the Convention on Biological Diversity’s 2022 Kunming-Montreal Global Biodiversity Framework which aims to achieve near zero loss of high biodiversity importance areas (including ecosystems of high integrity) by 2030.
... For instance, passive rewilding has been shown to be an effective means of forest restoration when primary forests grow adjacently to secondary patches and seed dispersal networks are intact, while the absence of adjacent primary forests may restrict dispersal opportunities during regeneration (Mayhew et al., 2019). Assessment of tropical forest regeneration indicates that once forest clearance has surpassed a 60 % threshold, active replanting is needed to restore highly degraded landscapes (Ewers et al., 2024). Characterizing community assembly in regenerating secondary forests can provide an opportunity to identify such barriers to secondary succession, which can guide conservationists to optimize forest restoration in response to localized contexts and regional land use histories (Meli et al., 2017). ...
... Previous works investigating community phylogenetic structure in regenerating tropical and subtropical forests indicated opposing trends, with some exhibiting increasing phylogenetic overdispersion over time following the onset of secondary succession (Lososová et al., 2020;Padullés Cubino et al., 2021), while in other instances secondary succession was found to lead to increased levels of plant phylogenetic community clustering in young growth and even 200-year-old subtropical forests in Xishuangbanna, China (Mo et al., 2013). Further investigations of phylogenetic structural responses during secondary succession may help in consensus building, while regional investigations can help to evaluate the status of passive ecological restoration and indicate whether active conservation forestry is necessary (Ewers et al., 2024). ...
... Notwithstanding, our findings suggest that despite select dispersing fauna having been found to have returned to the region, the legacies of historical dispersal network degradation may still be influencing spatial phylogenetic turnover within the forest plant communities we investigated. Notably, even in the presence of intact dispersal networks, the lack of adjacent and widespread primary forest from which later successional tree species can disperse to secondary patches and the significantly low coverage of forest in Hong Kong following 1946 may continue to limit the scope for passive restoration without active planting (Corlett, 2011;Dudgeon and Corlett, 2011;Mayhew et al., 2019;Ewers et al., 2024). ...
... 3. Pitfalls of reverting to forest cover, at the expense of forest integrity 3.1. All forest cover is not equal Forest degradation from roads, selective logging, fire, and many other large-scale anthropogenic pressures can reduce the quality of forest cover and adversely affect biodiversity (Burivalova et al 2014, Barlow et al 2016, Feng et al 2021, Ewers et al 2024. In addition, degradation often alters the spatial configuration of remaining forest habitats for biodiversity which can lead to negative edge effects and also affect landscape-scale connectivity (Haddad et al 2015, Pfeifer et al 2017, Fletcher et al 2018. ...
... We acknowledge forests degraded by disturbances such as selective logging may retain much biodiversity and ecosystem functioning (Edwards et al 2011, Malhi et al 2022. Yet, an analysis of 1681 taxa across 126 functional groups in Bornean tropical forests showed adverse effects of logging, from the very onset of biomass removal, in nearly a quarter of the taxa and a third of the functional groups studied (Ewers et al 2024). Therefore, no amount of forest degradation appears to be too low to have zero impact on biodiversity, further validating the irreplaceability of high-integrity forests. ...
Intact native forests under negligible large-scale human pressures (i.e. high-integrity forests) are critical for biodiversity conservation. However, high-integrity forests are declining worldwide due to deforestation and forest degradation. Recognizing the importance of high-integrity ecosystems (including forests), the Kunming-Montreal Global Biodiversity Framework (GBF) has directly included the maintenance and restoration of ecosystem integrity, in addition to ecosystem extent, in its goals and targets. Yet, the headline indicators identified to help nations monitor forest ecosystems and their integrity can currently track changes only in (1) forest cover or extent, and (2) the risk of ecosystem collapse using the IUCN Red List of Ecosystems (RLE). These headline indicators are unlikely to facilitate the monitoring of forest integrity for two reasons. First, focusing on forest cover not only misses the impacts of anthropogenic degradation on forests but can also fail to detect the effect of positive management actions in enhancing forest integrity. Second, the risk of ecosystem collapse as measured by the ordinal RLE index (from Least Concern to Critically Endangered) makes it unlikely that changes to the continuum of forest integrity over space and time would be reported by nations. Importantly, forest ecosystems in many biodiverse African and Asian nations remain unassessed with the RLE. As such, many nations will likely resort to monitoring forest cover alone and therefore inadequately report progress against forest integrity goals and targets. We concur that monitoring changes in forest cover and the risk of ecosystem collapse are indeed vital aspects of conservation monitoring. Yet, they are insufficient for the specific purpose of tracking progress against crucial ecosystem integrity components of the GBF’s goals. We discuss the pitfalls of merely monitoring forest cover, a likely outcome with the current headline indicators. Augmenting forest cover monitoring with indicators that capture change in absolute area along the continuum of forest integrity would help monitor progress toward achieving area-based targets related to both integrity and extent of global forests.
... Conversely, secondary forests regenerate following the clearance of primary forest by either human or natural disturbances, and secondary succession proceeds from extremely small remnants, dispersal or seed bank (Chokkalingam & De Jong, 2001). Disturbed forests are distinct from secondary forests due to their sustained exposure to anthropogenic influences, such as selective logging in Malaysian Dipterocarp forests, or rubber plantation in South China, which continue to impact the forest plant community structure and composition (Ewers et al., 2024;Ma et al., 2019;Saiful & Latiff, 2014). ...
... Within the Southern Chinese provinces of Guizhou, Guangxi and Yunnan alone, secondary forests undergoing succession may represent as much as 70% of total forest cover, while in Hong Kong secondary forests dominate forest cover alongside scattered remnant patches and Feng Shui woodlands (Dudgeon & Corlett, 1994;Zhuang & Corlett, 1997;Lee et al., 2023). With secondary forests now representing a major share of regional forest cover, determining the time frames for secondary succession to form plant communities comparable to primary forests, or evaluating whether this is possible without human intervention, represents a major conservation priority for the 21st century (Ewers et al., 2024). ...
Secondary forests represent a significant proportion of global forest cover, with over 70% of forests in East Asia classified as regenerating. While succession has been studied extensively in temperate systems, trajectories of subtropical succession remain poorly characterized in highly disturbed, urban‐adjacent forests. Investigating the additive beta diversity components of turnover and nestedness may reveal community assembly mechanisms driving secondary succession. The present study investigates plant community assembly along a successional gradient from 7 to 70 years following the onset of succession in secondary subtropical forests in Hong Kong, China. Plant survey data for 28 plots were analysed, generating additive Simpsons turnover and nestedness beta diversity metrics. Dissimilarity matrices were generated and modelled as a function of environmental matrices including forest plant community age (years following onset of secondary succession), inter‐community distance (metres), and soil moisture saturation (%) across three elevational bands using generalized dissimilarity models. Nonmetric multidimensional scaling of plant communities was conducted with Bray–Curtis dissimilarity matrices. Inter‐community distance and successional age differentially influenced plant species turnover between lowland and Montane forest types. Models of nestedness found that plot age and soil moisture saturation were significant drivers of nestedness patterns in plant communities across elevational classes. Turnover represented a higher proportion of Sorensen beta diversity than nestedness, while ANOSIM found significant differentiation between plant communities at different successional stages. Turnover patterns suggest a deterministic model of community assembly, with strong patterns of species replacement between communities at fine spatial scales and successional stages, as well as clear compositional shifts between lowland and montane forest types. NMDS analysis and functional compositional assessments suggested a transition from early successional communities with a high proportion of shrub species, to later successional communities with a higher proportion of tree species, with an increase in species turnover with greater age dissimilarity.
... Conversely, secondary forests regenerate following the clearance of primary forest by either human or natural disturbances, and secondary succession proceeds from extremely small remnants, dispersal or seed bank (Chokkalingam & De Jong, 2001). Disturbed forests are distinct from secondary forests due to their sustained exposure to anthropogenic influences, such as selective logging in Malaysian Dipterocarp forests, or rubber plantation in South China, which continue to impact the forest plant community structure and composition (Ewers et al., 2024;Ma et al., 2019;Saiful & Latiff, 2014). ...
... Within the Southern Chinese provinces of Guizhou, Guangxi and Yunnan alone, secondary forests undergoing succession may represent as much as 70% of total forest cover, while in Hong Kong secondary forests dominate forest cover alongside scattered remnant patches and Feng Shui woodlands (Dudgeon & Corlett, 1994;Zhuang & Corlett, 1997;Lee et al., 2023). With secondary forests now representing a major share of regional forest cover, determining the time frames for secondary succession to form plant communities comparable to primary forests, or evaluating whether this is possible without human intervention, represents a major conservation priority for the 21st century (Ewers et al., 2024). ...
Secondary forests represent significant proportions of global forest cover, with over 65% of forests in Asia classified as regenerating. While succession has been studied extensively in temperate systems, trajectories of sub-tropical forest succession remain poorly characterized in highly disturbed, urban-adjacent forests. Investigating the additive beta diversity subcomponents of Turnover and Nestedness may reveal community assembly mechanisms driving secondary succession. The present study investigated plant community assembly along a successional gradient from 7 to 70 years following the onset of succession in secondary sub-tropical forests in Hong Kong. Plant survey data for 28 plots were analysed, generating additive Simpsons and Nestedness beta diversity metrics as subcomponents of Sorenson Beta Diversity. Dissimilarity matrices were generated and modelled as a function of transformed environmental matrices of forest plant community age (years following onset of secondary succession), elevation (metres), inter-community distance (metres), soil moisture saturation (%) and soil organic carbon (g kg-1). Generalized dissimilarity models were generated for plant species Turnover and Nestedness. Nonmetric Multidimensional Scaling of plant communities was conducted with Bray-Curtis dissimilarity matrices. Our findings indicate that elevation was the primary driver of plant species Turnover, while age and inter-community distance played less prominent roles. Models of Nestedness found that plot age and soil moisture saturation were the sole drivers of Nestedness patterns in plant communities. While models of Turnover were robust, the low explanatory power of Nestedness models suggest additional unobserved factors driving patterns of plant community Nestedness during secondary succession. Turnover patterns suggest a deterministic model of community assembly, with strong patterns of species replacement between Lowland and Montaine forest types, as well as between successional age classes.
Insects are crucial for the functioning of ecosystems and might be facing declines globally, although data are biased away from the tropics where insect diversity and abundance are highest. In this Review, we assess the current status of insect populations in the tropics and discuss the prevailing threats to tropical insect biodiversity. Burgeoning human populations, increasing urbanization and land-use changes are leading to habitat loss and fragmentation, as well as increased pollution, including both light and pesticides. Insects on tropical islands are particularly sensitive to invasive species, which have already led to the extinction of multiple unique endemic species. Climate change further threatens insect populations across the tropics and might be disrupting crucial weather cycles such as El Niño and La Niña, which are important drivers of phenology and synchrony at these latitudes. Tropical insect declines might alter fundamental ecosystem processes such as nutrient cycling, carbon sequestration and herbivory. Disruption of food webs could lead to increased outbreaks of pests and of insect-vectored diseases in humans and livestock, affecting human health and reducing food security. Methodological advances — including artificial intelligence and computer vision, remote sensing and meta-barcoding — are facilitating taxonomy, speeding up identification of diverse samples and improving the monitoring of tropical insect biodiversity to guide future conservation efforts.
The Amazon rainforest, a vital global ecosystem, is facing significant threats from the loss of intact forest through deforestation and degradation. This report provides an overview of recent forest changes in the Amazon, focusing on Brazil, the country with the largest portion of the Amazon. Based on the JRC cloud-computed, remote sensing – based, large-scale tropical forest monitoring approach, maps and statistical estimates on forest cover changes from 1990 – 2023 are provided in this report for the whole region as well as for the different Amazon countries. The report contains a discussion about the drivers of deforestation, such as agricultural expansion, and forest degradation (e.g. illegal or unsustainable selective logging, forest fires). These activities have severe consequences for biodiversity, climate regulation, and the livelihoods of millions of people. In addition, a dedicated chapter on forest regrowth in the Amazon biome shows its spatial distribution and its changes over time, and provides a detailed analysis of its growth dynamics and their value regarding biodiversity and carbon storage. Understanding the changes in the forest is crucial for developing effective strategies to protect the Amazon. By identifying vulnerable areas and understanding the underlying drivers of deforestation, forest degradation and regrowth, informed and targeted interventions can be planned and implemented to mitigate these threats.
The impacts of degradation and deforestation on tropical forests are poorly understood, particularly at landscape scales. We present an extensive ecosystem analysis of the impacts of logging and conversion of tropical forest to oil palm from a large-scale study in Borneo, synthesizing responses from 82 variables categorized into four ecological levels spanning a broad suite of ecosystem properties: (i) structure and environment, (ii) species traits, (iii) biodiversity, and (iv) ecosystem functions. Responses were highly heterogeneous and often complex and nonlinear. Variables that were directly impacted by the physical process of timber extraction, such as soil structure, were sensitive to even moderate amounts of logging, whereas measures of biodiversity and ecosystem functioning were generally resilient to logging but more affected by conversion to oil palm plantation.
