Tree diversity and carbon storage cobenefits in tropical human‐dominated landscapes

Disentangling the response of species diversity, forest structure, and environmental drivers to aboveground biomass in the tropical forests of Western Ghats, India

Tropical forests are crucial to the global carbon cycle, but a significant knowledge gap in the precise distribution patterns of forest aboveground biomass (AGB) hinders our ability to formulate effective conservation efforts. A key unresolved issue is the lack of understanding of how forest AGB interacts with biotic and abiotic factors on large spatial scale. To address this, we used Structural Equation Modeling to disentangle the direct and indirect effects of environmental, anthropogenic, structural diversity species diversity and edaphic factors on AGB of trees, lianas and regenerating communities using the data from 96 1-ha plots in the central Western Ghats biodiversity hotspot, India. We hypothesized that the effect of structural attributes overrides AGB distribution, with relative contributions varying among plant communities. The landscape-level mean AGB was 245.12 ± 19.74 Mg ha-1, with SEM explaining 68-85 % of variations across the three vegetation communities. Structural diversity emerged as the primary mediator of the positive effects of taxonomic diversity on AGB in the regeneration community, whereas canopy cover and stem density linked diversity to AGB in adult tree and liana communities. Further, AGB showed a positive association with soil organic carbon in adult tree and regeneration communities, underscoring the significance of belowground resource availability on AGB. The results indicate that structural features were consistently the strongest AGB predictors at all levels of data aggregation, indicating the predominant role of niche complementarity and efficient space utilization in driving AGB, albeit differently across the plant communities. Our study emphasizes the importance of maintaining high structural features and managing taxonomic diversity while promoting soil fertility and minimizing disturbances to support AGB in tropical forests. We recommend testing the effects of predictor variables on biomass of vegetation communities independently to better understand the ecological principles of forest functioning.

Assessment of habitat features modulated carbon sequestration strategies for drought management in tropical dry forest fragments

Habitat features, such as species diversity, functional diversity, tree size, disturbances and fragment sizes have differential impacts on carbon (C) storage and C-sequestration in forest ecosystems. Present study attempted to understand the tree strategies for modulating C-sequestration capacity across tropical dry forest fragments with variable edge distances. We evaluated the differences between drought strategies (i.e., drought avoiding and drought tolerant) for variations in stem density, relative growth rate (RGR), C-storage and C-sequestration, species diversity, functional diversity, tree size and disturbance indicators along edge distance gradient, besides analyzed the differences between drought strategies for responses of C-storage and C-sequestration to variations in species diversity, functional diversity, tree size and disturbance indicators. Various traits and functional indices were analyzed using standard statistical techniques. For total trees and for the two drought strategies, generalized linear modeling results showed a significant decline in stem density, RGR, C-stock, C-sequestration, species diversity, functional diversity and tree size indicators, while a considerable increase in disturbance indicators, along decreasing edge distance across the fragments. The drought strategies exhibited a high degree of variation in the slope of associations for above variables with edge distance across fragments. For predicting C-sequestration, structural equation modeling results showed highly significant influence of functional diversity indicators for drought avoiding strategy, while species diversity indicators were strongly significant for drought tolerant strategy. Moreover, fire index and drought index were critical predictors for C-sequestration for drought avoiding and drought tolerant strategies, respectively. This study provide inputs to understand the largely ignored processes of C-storage and C-sequestration in fragmented forests, which are currently prevalent due to heavy anthropogenic pressures. Our findings are useful for forest managers to understand vegetation responses to interactions of species diversity, functional diversity, tree size and disturbance indicators, for predicting the stability of larger fragments and for planning restoration of smaller fragments.

Plant diversity drives soil carbon sequestration: evidence from 150 years of vegetation restoration in the temperate zone

Large-scale afforestation is considered a natural way to address climate challenges (e.g., the greenhouse effect). However, there is a paucity of evidence linking plant diversity to soil carbon sequestration pathways during long-term natural restoration of temperate vegetation. In particular, the carbon sequestration mechanisms and functions of woody plants require further study. Therefore, we conducted a comparative study of plant diversity and soil carbon sequestration characteristics during 150 years of natural vegetation restoration in the temperate zone to provide a comprehensive assessment of the effects of long-term natural vegetation restoration processes on soil organic carbon stocks. The results suggested positive effects of woody plant diversity on carbon sequestration. In addition, fine root biomass and deadfall accumulation were significantly positively correlated with soil organic carbon stocks, and carbon was stored in large grain size aggregates (1-5 mm). Meanwhile, the diversity of Fabaceae and Rosaceae was observed to be important for soil organic carbon accumulation, and the carbon sequestration function of shrubs should not be neglected during vegetation restoration. Finally, we identified three plants that showed high potential for carbon sequestration: Lespedeza bicolor, Sophora davidii, and Cotoneaster multiflorus, which should be considered for inclusion in the construction of local artificial vegetation. Among them, L. bicolor is probably the best choice.

Tree biomass, carbon stock characteristics and ground beetles (Coleoptera: Carabidae) diversity in the Uzungwa Scarp Forest Nature Reserve, Tanzania

Reducing carbon emission from Deforestation and forest Degradation (REDD+) has drawn attention and remain one of the main options for climate change mitigation. However, the extent to which conservation for carbon may enhance biodiversity conservation in both disturbed and relatively undisturbed (control) environment remain unclear in most forest types. The extent to which anthropogenic disturbances affect carbon stock and ground beetle diversity is also far from clear. This paper addressed these knowledge gaps using data based on ground beetles, carbon stock in live trees and tree species sampled in Uzungwa Scarp Nature Forest Reserve (USNFR). All trees with a diameter at breast height (DBH) ≥ 5 cm were measured for height and DBH in twelve clusters of 1 ha in size. In the same clusters, ground beetles were sampled using pitfall traps, active night search and active day search. The species diversity of ground beetles differed significantly between control sites and disturbed sites (p < 0.05). The mean total biomass and carbon stock in live trees were high in disturbed sites (323.72 t/ha) when compared to control sites (289.72 t/ha) but the difference was not statistically significant (U = 14, p > 0.05). Carbon in live trees and ground beetle diversity showed a weak positive correlation, while richness and abundance showed weak negative in control sites. Results show that REDD+ related activities in a tropical forest may enhance ground beetle diversity and carbon stock if ground beetles conservation is explicitly taken into account. Thus forest conservation planning that pursues both carbon storage and ground-dwelling invertebrate diversity is recommended.

Ten facts about land systems for sustainability

Land use is central to addressing sustainability issues, including biodiversity conservation, climate change, food security, poverty alleviation, and sustainable energy. In this paper, we synthesize knowledge accumulated in land system science, the integrated study of terrestrial social-ecological systems, into 10 hard truths that have strong, general, empirical support. These facts help to explain the challenges of achieving sustainability in land use and thus also point toward solutions. The 10 facts are as follows: 1) Meanings and values of land are socially constructed and contested; 2) land systems exhibit complex behaviors with abrupt, hard-to-predict changes; 3) irreversible changes and path dependence are common features of land systems; 4) some land uses have a small footprint but very large impacts; 5) drivers and impacts of land-use change are globally interconnected and spill over to distant locations; 6) humanity lives on a used planet where all land provides benefits to societies; 7) land-use change usually entails trade-offs between different benefits-"win-wins" are thus rare; 8) land tenure and land-use claims are often unclear, overlapping, and contested; 9) the benefits and burdens from land are unequally distributed; and 10) land users have multiple, sometimes conflicting, ideas of what social and environmental justice entails. The facts have implications for governance, but do not provide fixed answers. Instead they constitute a set of core principles which can guide scientists, policy makers, and practitioners toward meeting sustainability challenges in land use.

Tropical forest dung beetle-mammal dung interaction networks remain similar across an environmental disturbance gradient

Conservation outcomes could be greatly enhanced if strategies addressing anthropogenic land-use change considered the impacts of these changes on entire communities as well as on individual species. Examining how species interactions change across gradients of habitat disturbance allows us to predict the cascading consequences of species extinctions and the response of ecological networks to environmental change. We conducted the first detailed study of changes in a commensalist network of mammals and dung beetles across an environmental disturbance gradient, from primary tropical forest to plantations, which varied in above-ground carbon density (ACD) and mammal communities. Mammal diversity changed only slightly across the gradient, remaining high even in oil palm plantations and fragmented forest. Dung beetle species richness, however, declined in response to lower ACD and was particularly low in plantations and the most disturbed forest sites. Three of the five network metrics (nestedness, network specialization, and functionality) were significantly affected by changes in dung beetle species richness and ACD, but mammal diversity was not an important predictor of network structure. Overall, the interaction networks remained structurally and functionally similar across the gradient, only becoming simplified (i.e., with fewer dung beetle species and fewer interactions) in the most disturbed sites. We suggest that the high diversity of mammals, even in disturbed forests, combined with the generalist feeding patterns of dung beetles, confer resilience to the commensalist dung beetle-mammal networks. This study highlights the importance of protecting logged and fragmented forests to maintain interaction networks and potentially prevent extinction cascades in human-modified systems.

Drivers of Bornean Orangutan Distribution across a Multiple-Use Tropical Landscape

Logging and conversion of tropical forests in Southeast Asia have resulted in the expansion of landscapes containing a mosaic of habitats that may vary in their ability to sustain local biodiversity. However, the complexity of these landscapes makes it difficult to assess abundance and distribution of some species using ground-based surveys alone. Here, we deployed a combination of ground-transects and aerial surveys to determine drivers of the critically endangered Bornean Orangutan (Pongo pygmaeus morio) distribution across a large multiple-use landscape in Sabah, Malaysian Borneo. Ground-transects and aerial surveys using drones were conducted for orangutan nests and hemi-epiphytic strangler fig trees (Ficus spp.) (an important food resource) in 48 survey areas across 76 km2, within a study landscape of 261 km2. Orangutan nest count data were fitted to models accounting for variation in land use, above-ground carbon density (ACD, a surrogate for forest quality), strangler fig density, and elevation (between 117 and 675 m). Orangutan nest counts were significantly higher in all land uses possessing natural forest cover, regardless of degradation status, than in monoculture plantations. Within these natural forests, nest counts increased with higher ACD and strangler fig density, but not with elevation. In logged forest (ACD 14–150 Mg ha−1), strangler fig density had a significant, positive relationship with orangutan nest counts, but this relationship disappeared in a forest with higher carbon content (ACD 150–209 Mg ha−1). Based on an area-to-area comparison, orangutan nest counts from ground transects were higher than from counts derived from aerial surveys, but this did not constitute a statistically significant difference. Although the difference in nest counts was not significantly different, this analysis indicates that both methods under-sample the total number of nests present within a given area. Aerial surveys are, therefore, a useful method for assessing the orangutan habitat use over large areas. However, the under-estimation of nest counts by both methods suggests that a small number of ground surveys should be retained in future surveys using this technique, particularly in areas with dense understory vegetation. This study shows that even highly degraded forests may be a suitable orangutan habitat as long as strangler fig trees remain intact after areas of forest are logged. Enrichment planting of strangler figs may, therefore, be a valuable tool for orangutan conservation in these landscapes.