Phytosociology of Ecological Transition Ecosystems in Anauá National Forest, Roraima State, Brazil

Cacao (Theobroma cacao) cultivation maintaining a high proportion of shade trees in a diverse composition (agroforestry) is currently being viewed as a sustainable land use practice. Our research hypothesis was that cacao agroforests (AF) can support relatively high tree diversity, as compared to surrounding primary and/or secondary forests. The objective of this study was to assess the impact of forest conversion on tree communities by comparing tree composition, community characteristics (richness and diversity) and spatial structure (density, canopy height, basal area) among primary forest, secondary forest, and cacao AF. In total, we collected data from 30 25 × 25 m plots on three land use systems (20 in cacao AF, five in secondary, and five in primary forests) in San Alejandro, Peruvian Amazon. All trees with DBH ≥ 10 cm were counted, identified to species, and their height and DBH were recorded. Our results support the hypothesis that cacao AF present a relatively high tree species richness and diversity, although they are no substitute for natural habitats. We identified most common species used for shading cacao. Tree species composition similarity was highest between cacao AF and secondary forest. Vegetation structure (density, height, DBH) was significantly lower compared to primary and secondary forest. Species richness and diversity were found to be highest in the primary forest, but cacao AF and secondary forests were fairly comparable. The tree species cultivated in cacao AF are very different from those found in primary forest, so we question whether the relatively high tree diversity and richness is able to support much of the diversity of original flora and fauna.

IntroductionForests play a pivotal role within the global carbon cycle. However, how to enhance carbon storage in existing forests remains unclear.MethodsIn this study, we conduct a comprehensive analysis of data from 2,948 forest sites across China. Utilizing structural equation modeling (SEM), we investigate the intricate relationship between climate, tree species diversity, stand structure, function traits, initial biomass carbon stocks (BCi), soil organic carbon stocks (Soil C content), and carbon accumulation in biomass (ΔBC) and soil organic carbon stocks (ΔSOC) within both natural forests (NF, n = 1,910) and planted forests (PF, n = 1,038).ResultsOur findings underscore the critical influence of tree species diversity and stand structure drivers of both direct and indirect carbon accumulation, with distinct drivers emerging based on the carbon pools in NF and PF. Specifically, increasing tree species diversity from its minimum to maximum value through management-results in a 14.798 tC/ha reduction in BC and 0.686 tC/ha in SOC in NF. Conversely, amplifies BC and SOC in PF by 0.338 tC/ha and 0.065 tC/ha, respectively. Enhancing stand structure-such as stand density-results in a 231.727 tC/ha reduction in BC and SOC in NF, and a 10.668 tC/ha in BC and 64.008 tC/ha increment in SOC in PF.DiscussionOverall, our results indicate that higher tree species diversity, stand density and age-group limits further carbon accumulation in BC and SOC in current NF. In contrast, low tree species diversity and stand density limits the development of carbon storage potential in planted forests. To enhance carbon sequestration capacity, China should change its current policy of completely banning logging of natural forests. Natural forests need thinning and reduced tree species diversity, while planted forests should increase tree species diversity and stand density.

The carbon storage in forest ecosystems is closely linked to biomass, and its dynamic changes are of significant importance for assessing forest structure and function, as well as their response to global climate change. Recently, the research on the influencing mechanism of forest carbon storage has been a hotpot in the field of forest ecology. However, it remains unclear on the relationships among stand structure, stand stability, and carbon storage. The issues needed to be answered are as follows: How are tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage correlated? Is there a direct or indirect effect between tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage? Do these factors have an impact on stand stability, and, subsequently, carbon storage? What is the crucial factor in the mechanism that influences carbon storage? Here, the natural Quercus mongolica forests in the Xiaolong Mountains were taken as the research object. Several methods, including Pearson’s correlation, the best-fitting SEM, and multiple regression, were used to examine the relationships among tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage. Our results show that there were correlations between tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage. Tree density not only directly affects stand stability but also indirectly influences it through the mediation of tree species diversity and stand structural characteristics. Meanwhile, tree density also indirectly influences carbon storage through the mediation of tree species diversity, stand structural characteristics, and stand stability. Crown volume exerts the greatest influence on stand stability, while carbon storage is mostly impacted by stand stability. Overall, the combination of tree density, tree species diversity, stand structural characteristics, and stand stability influences carbon storage (66.4%). Therefore, it is important to consider stand stability when assessing carbon sequestration potentials; furthermore, the importance of tree density, tree species composition, and stand structural characteristics should be emphasized. Our research provides a scientific basis for conservation and management decision-making in natural forests and offers novel insights as well as a scientific reference for future large-scale carbon storage investigations.

High diversity mixed plantations of Eucalyptus and native trees: An interface between production and restoration for the tropics

Ecological and socio-economic factors influence stand biodiversity

The relationship between satellite-derived indices and species diversity across African savanna ecosystems

Invasions are one of main drivers transforming the functions of forest ecosystems. The invasion of alien fungus Hymenoscyphus fraxineus is still reducing the abundance of Fraxinus excelsior throughout temperate Europe. F. excelsior is a tree species belonging to the group of foundation species for numerous epiphytic species. We studied the effects of F. excelsior decline on epiphytic bryophytes in the Białowieża Primeval Forest. In this forest human interference is limited, allowing us to register the natural dynamics of ash-dependent bryophyte communities. F. excelsior decline was discovered in the Białowieża Primeval Forest in 1998, and in 2016 we resurveyed a historical survey of epiphytic bryophytes, i.e. shortly before the dieback process started. Using ordination methods and mixed-effect models we assessed shifts in epiphyte bryophytes composition over time and amongst the plots with (i) historical and recent presence of F. excelsior, (ii) with recent extinction of F. excelsior, and (iii) absence of F. excelsior both historically and recently, as well as at the level of alternative tree hosts employing the paired Mann-Whitney and t-tests. F. excelsior dieback did not influence the species composition of bryophytes associated with this tree host. Despite the drastic reduction in living F. excelsior trees (85%), overall the species composition, species richness and Shannon index of F. excelsior-dwelling bryophytes did not shift significantly between two sampling periods. Similarly weak changes over time we reported for the bryophytes’ community weighted means of ecological indicator values. Equally subtle temporal shifts in epiphytes’ biodiversity were observed amongst the plots with the presence, absence, and extinction of ash, likely due to the relatively high diversity of available alternative hosts. F. excelsior-associated epiphytic bryophytes were able to exploit other niches in the microhabitat-heterogeneous Białowieża Forest ecosystem, and thus far have not suffered a reduction in biodiversity parameters at the scale of our survey. High diversity of alternative host tree species, with particular emphasis on the occurrence of pioneer trees (i.e. B. pendula and P. tremula), may maintain the epiphytic bryophyte communities, which themselves may be able to act as a source for the recovery of F. excelsior-affiliated epiphyte populations.

Large areas of primary mixed broadleaf-Korean pine forests on Changbai Mt., on the border between China and North Korean have been replaced by secondary forests through clearcuting since the 1950s. How clearcutting impacts the mixed forest ecosystem still remains unclear. We compared the tree species composition, structure, and diversity of a primary and a secondary forest that had suffered clearcutting, 30 yr. previously. Results showed that the mean basal area of trees (≥10 cm diameter at breast height (DBH)) was markedly lower in the secondary forest than in the primary forest, whereas the density of seedlings (＜2 cm DBH, ≥50 cm tall), saplings (2~9.9 cm DBH), and trees were all significantly higher in the former. Values for the species richness and both Simpson's and Shannon's diversity indices for seedlings and saplings were greater in the secondary forest than in the primary forest, but the values of these 3 indices for trees were significantly lower in the former. These results indicate that clearcutting altered the forest structure by significantly decreasing the basal area of trees and increasing the numbers of seedlings and saplings. It also altered the species composition with the secondary forest having more pioneer species than the primary forest. The secondary forest has higher species diversity and abundant climax species of seedlings and saplings, and this potentially favorable situation offers an opportunity to develop restoration plans.

Successional development of wood-inhabiting fungi associated with dominant tree species in a natural temperate floodplain forest

Tree species composition and diversity were investigated in the riparian forest around Lake Barombi Kotto, Cameroon. This study aimed at determining the tree species composition, population structure, and providing evidence of anthropogenic disturbances in the riparian forest of Lake Barombi Kotto. The objectives were to determine the tree species composition and diversity in the riparian forest around Lake Barombi Kotto, to elucidate the forest structure and to document the anthropogenic disturbances in this forest. Five plots were laid within which the tree enumeration and measurement of dbh were carried out. Trees were identified using scientific identification keys in the Flora of West Africa. Disturbance scores were given to each site by qualitatively assessing various disturbances. A total of 340 trees belonging to 70 plant species, 63 genera and 28 plant families were enumerated. Shannon-Wiener diversity varied across sites, with the highest value (H = 3.45) recorded in Tung and the lowest (H = 2.21) in Malenda. Population structure differed across sites, the largest stand basal area of 43.78 m2/ha was recorded in Bondokombo while the smallest (2.15 m2/ha) was recorded in the Sacred Island. Cecropia peltata L., Pseudospondias macrocarpa Oliv. Pierre and Ceiba pentandra (L.) Gaertn had the largest basal areas across the different sites. Species rich families were Malvaceae (9 species), Fabaceae (9 species), Annonaceae (4 species), and Anacardiaceae (4). This study shows that, there is a high tree species diversity in the protected forest (Tung) but the other unprotected sites are highly disturbed by anthropogenic activities. There is need to develop and enhance existing management policies for this riparian forest, especially by replanting the cut trees and creating a protected riparian buffer to conserve its floristic diversity and ecological functions.

Nitrogen dynamics during ecosystem development in tropical forest restoration

Although large scale analyses of foliar N:P ratios suggest and overall pattern of P limitation in tropical forests, analyses within the biome are less indicative of a consistent pattern of nutrient limitation. High tree species diversity and soil heterogeneity are important factors driving the variability of foliar chemistry in the tropics; however, this variability could be reduced at the level of the functional characteristics of the species present at a site. In this study it is hypothesized that foliar N:P ratios would be more constrained when the species are grouped according to functional characteristics, and would reveal patterns of nutrient limitation. The study was conducted in a tropical forest landscape of the Porce region in Colombia, which consists of patches of primary and secondary forests of different ages. The functional groupings revealed consistent patterns of conservative N cycling in species present at young secondary sites, as well as conservative P cycling of the species present later in succession and in primary forests. Although the observed data have limitations in terms of capturing the overall variability for each functional group, the classification used here provided support for the proposed hypotheses. It is concluded that functional composition, rather than taxonomic composition, can potentially improve our understanding of nutrient cycling in tropical forests.

Illegal selective logging and forest fires occur on a large scale in the northern Brazilian Amazon, contributing to an increase in tree mortality and a reduction in forest carbon stock. A total of 120 plots of 0.25 ha (30 ha) were installed in transitional ecosystems or ecotones (LOt) between the forested shade-loving campinarana (Ld) and dense-canopy rainforest, submontane (Ds), in the National Forest (Flona) of Anauá, southern Roraima. Measuring the diameters at breast height (DBH ≥ 10 cm) and the heights of 171 dead trees (fallen naturally, illegally exploited, and affected by forest fires), enabled the estimation of carbon content from the application of a biomass equation developed at Manaus, and the calculation of a correction factor, using the average height of the largest trees. From 2015–2017, we mapped the real extent of illegal selective logging and forest fires across the region with CLASlite and INPE/Queimadas. From measurements of 14,730 live and dead trees across 30 hectares (491 ± 15 trees·ha−1), the illegal selective logging and associated forest fires, and aggravation by severe El Niño droughts resulted in an 8.2% mortality of trees (40 ± 9 dead trees·ha−1) and a 3.5% reduction in forest carbon stock (6 ± 3 Mg·ha−1) in the short-term. The surface area or influence of forest fires of very high density were estimated in the south-central region of Roraima (8374 km²) and the eastern region of the Flona Anauá (37 km²). Illegal selective logging and forest fires in forest areas totaled 357 km² in the mosaic area, and 6 km² within Flona Anaua. Illegal selective logging and forest fires in the years of severe El Niño droughts threatened the maintenance of environmental services provided by Amazonian forests.

Trees are important components of agricultural landscapes in different parts of Ethiopia, and information on their type, diversity and distribution in sub-humid agroecologies is essential for designing interventions. A study was conducted to evaluate tree diversity and their spatial patterns in agricultural landscapes under different land use categories in four selected sub-humid sites in Western Oromia, Ethiopia. Tree inventory was conducted on 100 homesteads (19 ha), 18 crop lands (35 ha) and 11 grazing lands (5.5 ha) belonging to 100 randomly selected households. A total of 82 tree species were identified: 67 in the homesteads, 52 in the crop lands and 29 in the grazing lands. The density of trees varied from 68 trees per ha in crop lands to 801 trees per ha in homesteads. Diversity indices revealed that homestead was the most diverse with Shannon index of 2.42, and Simpson index of 0.84. The density of trees among the tree communities in the four sites varied from 133 in Bako Tibe to 476 in Jima Arjo, but not any one of the sites had more diverse tree community as revealed by the Renyi diversity profiles analysis. The three dominant tree species in the agricultural landscapes were Eucalyptus camaldulensis, Vernonia amygdalina and Cordia africana. Pearson correlation analysis showed that high tree species density, richness and diversity had high association with homesteads than with crop lands and grazing lands. It also revealed significant positive correlations between land size and evenness, and latitude and evenness whereas there were significant negative correlations between family size and Shannon diversity index, and land size and tree density. The majority (81.6%) of the trees were established through plantation and only 18.4% were regenerated naturally. The proportion of planted trees varied from 68% in Gobu Seyo to 94.1% in Guto Gida. The study showed that agricultural landscapes harbour high diversity of tree species with a spatial pattern, and increasing the tree cover with focus in the crop lands is essential for improved resilience of the agricultural systems and for circa-situm conservation of biodiversity.

Mixed plantations composed of Eucalyptus intercropped with a high diversity of native tree species are a promising option for combining biodiversity recovery with wood production during forest landscape restoration. The viability of this approach relies not only on its potential to offset implementation costs but also on the capacity of native trees to perform well when intercropped with Eucalyptus. We investigated competition for light and nutrients in these mixed plantations in the Atlantic Forest of Brazil. We compared (1) Eucalyptus monocultures, (2) plantations composed of native species for restoration, and (3) mixed plantations intercropping Eucalyptus with native tree species, in which Eucalyptus replaced native pioneers. We found no evidence of competition for nutrients or facilitation. Native species plots intercepted more Photosynthetically Active Radiation than Eucalyptus monocultures or mixtures. Our results add to the previous studies on these experiments and altogether suggest that well-managed mixed plantations of Eucalyptus and a high diversity of native tree species are a viable silvicultural solution for offsetting the costs of forest landscape restoration in the tropics.