Biodiversity Insurance of Forest Productivity Has Strengthened Under Recent Climate Change.

Diversity of trees and shrubs in agricultural systems contributes to provision of wood and non-wood products, and protects the environment, thereby, enhancing socioeconomic and ecological sustainability of the systems. This study characterizes the diversity, density and composition of trees in the agroforestry homegardens of Sidama Zone, Southern Ethiopia, and analyses physical and socioeconomic factors influencing diversity and composition of trees in the systems. A total of 144 homegardens were surveyed from 12 sites. In total, 120 species of trees and shrubs were recorded of which, 74.2 % were native to the area. The mean number of tree species per farm was 21. Density of trees varied between sites with mean values ranging from 86 to 1,082, and the overall average was 475 trees ha−1. Four different crop-based enset (Enset ventricosum (Welw.) Cheesman)-coffee homegarden types were recognized and they differed not only in the composition of major crops but also in the diversity, density and composition of trees. The composition, diversity and density of trees is influenced by physical and socioeconomic factors. The major physical factors were geographical distance between sites and differences in altitude of farms. The most important socioeconomic factors were farm size and access to roads. Tree species richness and density increased with farm size. Increased road access facilitated marketing opportunities to agricultural products including trees, and lead to a decline in the basic components of the system, enset, coffee and trees. In the road-access sites, the native trees have also been largely replaced with fast growing exotic species, mainly eucalypts. The decrease in diversity of trees and perennial components of the system, and its gradual replacement with new cash and annual food crops could jeopardize the integrity and complexity of the system, which has been responsible for its sustenance.

Tropical agroforestry systems have immense potential to sequester carbon both in aboveground and belowground biomass and soil. Homegarden agroforestry is a popular land-use system in the tropics, sequestrating more organic carbon in soil than crops, monoculture plantations and even than other agroforestry systems. Tree diversity and density are reported to affect soil organic carbon content in many of tropical agroforestry systems. Little evidence, however, exists for tropical homegardens. The present study has been conducted to investigate soil organic carbon content in relation to tree species diversity in the homegarden agroforestry system of north-eastern Bangladesh, to test the hypothesis that homegardens with high species diversity contain more organic carbon in soil than those with low species diversity. A multistage random sample of homegardens was selected and observations made in sample plots of tree density, species richness, soil pH and soil organic carbon content. Soil samples were collected at two depths (0–25, 26–50 cm) from each plot. Soil organic carbon content was found to be positively correlated with both tree density (r = 0.93, p < 0.01) and species richness (r = 0.79, p < 0.01). Soil pH was not found to differ significantly across soil depth (p = 0.67), except that more organic carbon content was found in the deeper soil layer than the upper layer (p < 0.05). The study demonstrates that species-rich homegarden with high tree density can sequester more carbon in soil than species-poor homegardens and thereby contribute more to climate change mitigation.

Tree species richness and density affect parasitoid diversity in cacao agroforestry

Climate and land use changes significantly endanger tree species’ structure and diversity in savanna woodlands. The destruction of these ecosystems hinders the achievement of several global environmental and development targets, notably SDGs 2, 13, and 15, which underscores the need for continuous tree monitoring to inform decision-making on biodiversity conservation. This study aims to characterize the relationships between tree diversity and structure across different land cover (LC) classes—Dense tree cover (D), Sparse tree cover (S), Grasslands (G), and Wetlands (W)—and altitudinal gradients (AGs) in Alain forest, located in Sudan’s savanna woodlands. A systematic sampling was used across varying AGs and LC types to collect data on tree species richness and structure in 926 circular plots. Tree diversity, measured using Shannon and Simpson indices, showed significant differences among LC classes (p &amp;lt; 0.05), with the highest diversity observed in D and the lowest in G. Both indices exhibited a significant negative correlation with AGs (Shannon: R = –0.33, p &amp;lt; 0.001; Simpson: R = –0.30, p &amp;lt; 0.001), indicating a decline in tree diversity with increasing elevation. Tree structural attributes also varied significantly across LC types: tree height and density were highest in D and lowest in G (p &amp;lt; 0.05). While tree height showed a weak but significant negative correlation with altitude (R = –0.106, p = 0.003), tree density did not (R = –0.048, p = 0.185). Principal Component Analysis (PCA) revealed distinct clustering of LC classes based on combined diversity and structural attributes, with tree height and diversity indices contributing strongly to the first two principal components. These findings highlight the influence of LC and AGs on tree community structure and biodiversity in Alain forest, offering valuable insights for conservation and land-use planning. Further research based on more comprehensive datasets is recommended to boost scientific knowledge for biodiversity conservation and sustainable management.

Cocoa (Theobroma cacao L.) growing systems in Ghana and West Africa consist of diverse tree species and densities. This study was conducted to determine factors that influence tree species configurations and how tree characteristics affect canopy cover in cocoa farms. Eighty-six farmers and corresponding farms were selected in a systematic approach in four districts across two agro-ecological zones in Ghana. Results show that men tend to have larger farm sizes, higher tree density and diversity than women. Tree density and canopy cover of shade trees were low on large farms, but diversity increased with increasing farm sizes. Even though there was a significant correlation between diameter at breast height and crown area for all species investigated, tree species differed considerably in their crown area and thus the amount of ground cover provided. Current recommendations for shade are usually expressed in number of trees per ha, and our results suggest that these should be refined to reflect the effects of species, the size of their diameter at breast height and the crown area.

The role of trees and livestock in ecosystem service provision and farm priorities on smallholder farms in the Rift Valley, Kenya

Tree diversity and density in agroforestry systems has been found to increase the diversity and density of soil macro-fauna. However, very little is known of the relationship between tree diversity and density in cocoa agroforests and soil macro-fauna diversity and density. This study was therefore undertaken to fill this knowledge gap. A mixed research approach was adopted and data analysis was done using descriptive and inferential statistics. From the findings, most cocoa farmers perceived that tree diversity in cocoa agroforests was either average, high or very high. Most cocoa farmers perceived that tree density on its part was either average or low. Concerning soil macro-fauna diversity in cocoa-based agroforestry systems, most of the cocoa farmers perceived that soil macro-fauna diversity was either average or high. For soil macro-fauna density in cocoa agroforests, most cocoa farmers perceived that soil macro-fauna density was either average, high or low. Through correlation and regression analyses, it was found that a statistically significant (p&lt;0.05) direct non-cause-effect and cause-effect relationship existed between the level of tree diversity and density in cocoa-based agroforestry systems (very high tree diversity, high tree diversity, average tree diversity, low tree diversity, very low tree diversity), and the level of soil macro-fauna diversity and density. This implies that increasing tree species diversity and density leads to increasing soil macro-fauna diversity and density in cocoa-based agroforestry systems. It is therefore recommended that policy makers take drastic measures to ensure greater tree diversity and density in cocoa agroforests in order to ensure higher soil macro-fauna diversity and density.

Natural regeneration after disturbances is a key phase of forest development, which determines the trajectory of successional changes in tree species composition and diversity. Regenerating trees can originate from either seeds or sprouts produced by disturbed trees with sprouting ability. Although both regeneration strategies often develop and co-occur after a disturbance, they tend to affect forest development differently due to significant functional differences. However, the origin of tree regeneration is rarely distinguished in post-disturbance forest surveys and ecological studies, and the differential roles of seed and sprout regeneration in forest productivity and diversity remain poorly understood. To address these research gaps, we explored the role of sprout and seed regeneration in the formation of woody species diversity and above-ground biomass (AGB) productivity in early-stage forest development. Data were collected in two experimental forest stands in the Czech Republic, where trees were cut with varying intensities with the density of residual (uncut) trees ranging from 0 to 275 trees per hectare. All trees were mapped and their sizes were measured before cutting and then, either as a stump with sprouts or a residual tree, remeasured 11 years later. In addition, all tree saplings were mapped and measured 11 years after logging, and their origin (sprout or seed) was identified. To assess abundances and productivity, we estimated AGB of all 2,685 sprouting stumps of 19 woody species and 504 generative (i.e., seed origin) individuals of 16 woody species, using allometric equations. Mixed-effects models were used to analyze the effects of each regeneration strategy on woody species diversity and the total AGB under varying densities of residual trees. Nonmetric multidimensional scaling was used to evaluate the effect of regeneration strategies on species composition. AGB and diversity of sprouts were significantly higher than those of seed regeneration. Sprouts formed on average 97.1% of the total regeneration AGB in Hády and 98.6% in Soběšice. The average species richness of sprouts was 4.7 in Hády and 2.2 in Soběšice, while the species richness of seed regeneration averaged 2.1 and 1.1 in Hády and Soběšice, respectively. Increasing density of residual trees reduced AGB and diversity of both sprouts and seed regeneration, but seed regeneration was affected to a greater extent. Residual trees had an especially strong inhibitory effect on the establishment of seed regeneration. Consequently, seed-originated saplings were nearly absent in plots with high residual tree density, and abundant sprouts accounted for most of the AGB and diversity. However, unlike sprouts whose species composition resembled that of the original stand, seed regeneration brought in new species, enriching the stand's overall species pool and beta diversity. Our results demonstrated differential roles of sprout and seed regeneration in the early stage of forest succession. Sprout regeneration was the main source of woody AGB productivity as well as species diversity, and its importance increased with the increasing density of standing mature trees. The results indicate the crucial yet previously underestimated role of sprout regeneration in post-disturbance forest dynamics. They suggest that the presence of residual mature trees, whether retained after partial cutting or undisturbed, can substantially suppress seed regeneration while the role of sprout regeneration in early succession becomes more distinctly evident.

Summary Despite growing evidence that, on average, diverse forests tend to be more productive than species‐poor ones, individual studies often report strongly contrasting relationships between tree species richness and above‐ground wood production (AWP). In the attempt to reconcile these apparently inconsistent results, we explored whether the strength and shape of AWP–diversity relationships shifts along spatial and temporal environmental gradients in forests across Europe. We used tree ring data from a network of permanent forest plots distributed at six sites across Europe to estimate annual AWP over a 15‐year period (1997–2011). We then tested whether the relationship between tree species richness and AWP changes (i) across sites as a function of large‐scale gradients in climatic productivity and tree packing density and (ii) among years within each sites as a result of fluctuating climatic conditions. AWP–species richness relationships varied markedly among sites. As predicted by theory, the relationship shifted from strongly positive at sites where climate imposed a strong limitation on wood production and tree packing densities were low, to weakly negative at sites where climatic conditions for growth were most suitable. In contrast, we found no consistent effect of interannual fluctuations in climate on the strength of AWP–species richness relationships within sites. Synthesis. Our results indicate that the shape and strength of the relationship between tree diversity and forest productivity depends critically on environmental context. Across Europe, tree diversity shows the greatest potential to positively influence forest productivity at either end of the latitudinal gradient, where adverse climatic conditions limit productivity and lead to the development of less densely packed stands.

ABSTRACTRecent studies have highlighted the significant role of tree species' mycorrhizal traits on forest soil microbial communities and their associated ecosystem functions. However, our understanding of how tree species richness in mono‐mycorrhizal (arbuscular mycorrhiza [AM] or ectomycorrhiza [EcM]) or mixed‐mycorrhizal (AM and EcM = AE) stands affects the rooting zone microbial community assembly processes remains limited. We investigated this knowledge gap using the MyDiv tree diversity experiment, which comprises plantings of AM and EcM tree species and their mixture in one‐, two‐, and four‐species plots. Soil microbiomes in the target tree rooting zone were analyzed using meta‐barcoding of the fungal ITS2 and bacterial 16S V4 rRNA regions. We examined the effects of plot mycorrhizal type, tree species identity and richness on microbial diversity, community composition, and microbial community assembly processes. We found that AM plots exhibited higher fungal richness compared to EcM and mixed mycorrhizal type (AE) plots, whereas tree species identity and diversity showed no significant impact on fungal and bacterial alpha diversity within mono and mixed mycorrhizal type plots. The soil fungal community composition was shaped by tree species identity, tree diversity, and plot mycorrhizal type, while bacterial community composition was only affected by tree species identity. EcM tree species significantly impacted both soil fungal and bacterial community compositions. Plot mycorrhizal type and tree species richness displayed interactive effects on the fungal and bacterial community composition, with AM and EcM plots displaying contrasting patterns as tree diversity increased. Our results suggest that both stochastic and deterministic processes shape microbial community assemblage in mono and mixed mycorrhizal type tree communities. The importance of deterministic processes decreases from AM to EcM plots primarily due to homogeneous selection, while stochastic processes increase, mainly due to dispersal limitation. Stochastic processes affected fungal and bacterial community assembly differently, through dispersal limitation and homogenous dispersal, respectively. In fungi, the core, intermediate and rare abundance fungal taxa were mainly controlled by both stochastic and deterministic processes whereas bacterial communities were dominantly shaped by stochastic processes. These findings provide valuable insights into the role of tree species identity, diversity and mycorrhizal type mixture on the soil microbiome community composition and assembly processes, highlighting the differential impacts on core and rare microbial taxa. Understanding the balance between deterministic and stochastic processes can help forest ecosystem management by predicting microbial community responses to land‐use and environmental changes and influencing ecosystem functions critical for ecosystem health and productivity.

Tree composition and diversity in relation to urban park history in Hong Kong, China

Effects of the forests-agriculture conversion on the availability and diversity of forest products in a neotropical rainforest region

Tree density and diversity in Hong Kong’s public housing estates: From provision injustice to socio-ecological inclusiveness

Background. Structural and floristic characteristics are a crucial aspect in proposing technical solutions for forest ecosystem restoration. The study was conducted in Kon Chu Rang Natural Reserve, Gia Lai, Vietnam. The differences in structure (such as density, tree size, abundance, diversity, species composition, etc.) between secondary and old-growth forests were shown in the several previous researches. However, within secondary forests, different histories of disturbance have resulted in very different stages of forest succession, despite the same length of time since human influence ceased and the same protection conditions. Secondary forests recovering after shifting cultivation, with directly light and fast-growing species, have higher density and abundance, while tree size indices and the number of dominant species are lower compared to secondary forests recovering after logging, which are mainly composed of shade-tolerant species. The research results provided a basis for group classification and the application of silvicultural measures to effectively promote forest recovery processes. Purpose. To study the potential for natural successional recovery as a basis for proposing the application of silvicultural measures to rehebilitate the evergreen closed tropical rain forest in the Kon Ha Nung Biosphere Reserve. Materials and methods. The subject of the study was the tropical evergreen broadleaf forest types in Kon Chu Rang Nature Reserve. In this study, satellite imagery (Landsat 8) was collected in the same season from 2013 to 2022 and Normalized Difference Vegetation Index was calculated to determine the forest successional stages of tropical evergreen broadleaf rainforest in Kon Chu Rang Nature Reserve. The results of classification combined with field survey based on the establishment of 09 permanent sample plots (50×50 m, 2,500 m²) to ensure the forest successional stages. These plots were established in each typical successional stage (secondary forest after logging, secondary forest after shifting cultivation, and old-growth forest). In each plot, all live woody stems with a diameter at breast height greater than 10 cm were measured, including tree diameter at breast height and tree species. All data collected in each plot were then used for data analysis using SPSS software. This research conducted an ANOVA (Analysis of Variance) with a Fisher's Least Significant Difference post hoc test to explore differences between multiple group means of tree density, number of trees distribution in each group of tree diameter, tree diameter, basal area and tree diversity. In addition, to investigate forest structure and diversity, the Impotance Value Index, Shannon-Wiener Index (He') and Simpson Index, and Jaccard's coefficient of similarity were calculated in this study. Results. Tree density ranged from 347 to 763 stems per hectare and total basal area from 15.5 to 42.8 m² per hectare. No significant difference was observed among the three forest types for tree diameter classes from 10 to 25 cm, while for tree diameter classes greater than 25 cm, old growth forest had the highest tree density, significantly different from the others. A decrease in tree density was observed in all forest types except old growth, which had the highest tree density and basal area for tree diameter classes greater than 25 cm. Diversity was found to be significantly higher in the old-growth forest compared to the secondary forest, which may be due to the duration of the restoration process and the initial stage of disturbance cessation. A total of 31 to 43 tree species were identified in 28-38 genera and 19-22 families, with the lowest species richness observed in the secondary forest after logging and only 3-7 tree species calculated in the tree composition. The dominant species in the post-logging secondary forest were heliophilous and fast-growing tree species such as Machilus parviflora, Macaranga tanarius, Litsea elongata, Clausena sp. and Prunus arborea, whereas in the post-shifting secondary forest they were shade-tolerant such as Rehderodendron truongsonense, Cinnamomum mairei, Castanopsis pseudoserrata, Litsea elongata, Syzygium wightianum. In particular, the associations of Clusiaceae and Myrtaceae species in old-growth forests were a novel finding. Conclusions. It can be concluded that the structure and diversity characteristics of these successional stages exhibited remarkable variation. The old-growth forest had greater tree density, basal area, tree diversity and evenness than those of in secondary forest, along with the differences in number tree distribution, tree composition and diversity. These differences may come from the regeneration time and site condition. These results suggest that long-term monitoring and research are essential to assess restoration success over time.

The effects of tree density on the distribution of tree and pasture roots under an agroforestry experiment were investigated. Trees were planted in a Nelder fan design, and three planting densities of 2150,304 and 82 stems per hectare were chosen for this study. Proximity to trees and increase in tree density reduced pasture root growth, with lowest concentrations of pasture roots occurring under the highest tree density. Tree root systems were deeper and denser at high tree densities, although total length and mass of roots produced per tree decreased with increasing tree density. Tree root:shoot ratios increased as tree density decreased owing to greater root production at low tree densities.