Tree diversity and its ecological importance value in organic and conventional cocoa agroforests in Ghana

Nutrient addition alters plant community productivity but not the species diversity of a mountain meadow in Tajikistan

Introduction

Tajikistan is a typical mountainous country covered by different mountain grasslands that are important pasture resources. Recently, grassland degradation has become widespread due to climate change and human activities and fertilization has been used to improve grassland production. However, fertilizer inputs can substantially alter species diversity, but it is uncl\ear how productivity and species diversity respond to nutrient enrichment in the mountain meadows of Tajikistan.

Methods

Therefore, a 5-year (2018-2022) continuous in-situ mineral fertilizer experiment was conducted to examine the effects of three nitrogen (N) levels (0, 30, and 90 kg N ha-1 year-1), two phosphorus (P) levels (0 and 30 kg P ha-1 year-1), and their combinations on above-ground biomass (AGB) and species diversity in a mountain meadow grassland in Ziddi, Varzob region, Tajikistan. Five species diversity metrics-Margalef's species richness (Dma), the Shannon-Wiener index (H), the Simpson index (C), Pielou's equitability index (Epi), and the Evar Species Evenness index (Evar)-were used to measure species diversity.

Results and discussions

The results indicated that the addition of different N and P amounts and their various combinations considerably increased both total and dominant species AGB, with the highest increase occurring in the N90P30 (90 kg N ha-1 year-1 combined with 30 kg P ha-1 year-1) treatment in 2022; during the experiment, the importance value of Prangos pabularia (dominant species) first decreased and then increased, but its dominant status did not change or fluctuate among the years. Furthermore, N, P, and their different combinations had no significant effect on species diversity (Dma, H, C, Epi, and Evar). All the species diversity indexes fluctuated among years, but there was no interaction with mineral fertilizer addition. Total AGB had a negative relationship with species diversity and low concentration N fertilizer addition (N30; P30) strengthened this negative trend. However, this trend decreased under the high N fertilizer condition (N90P30). Overall, nutrient addition to the natural mountain grassland of the Varzob region improved AGB, which meant that there was more forage for local animals. Mineral fertilizers had no significant effect on species diversity, but may enhance P. pabularia dominance in the future, which will help maintain the stability of the plant community and improve the quality of the forage because P. pabularia is an excellent and important winter fodder. Our study suggests that scientific nutrient management could effectively promote grassland production, conserve plant variety, and regenerate degraded grassland, which will counteract the desertification process in northwest Tajikistan mountain meadows.

Allometric relationships between stem diameter, height and crown area of associated trees of cocoa agroforests of Ghana

Allometric models which are used to describe the structure of trees in agroforestry systems are usually extrapolated from models developed for trees in forest ecosystems. This makes quantitative assessment of the functions of shade trees in agroforestry systems challenging since increased availability of light and space in these systems may induce structural differences from those growing under forest conditions. We addressed this issue by providing species-specific allometric information on the structural characteristics of associated shade trees on cocoa agroforestry systems and assessed if allometries conformed to theoretical predictions. At the plot level, stand and soil characteristics affecting tree structural characteristics were assessed. The study was conducted in cocoa agroforestry systems at Suhum, Ghana. The height-diameter at breast height (H-DBH) allometry had the best fits (R2 = 53-89%), followed by the crown area (CA)-DBH allometry (R2 = 27-87%) and then the CA-H allometry (R2 = 22-73%). In general, the scaling exponents of the CA-DBH, H-CA and H-DBH allometries conformed to the metabolic scaling theory (MST). However, both the CA-DBH and H-DBH allometries diverged from the geometric similarity model. Though forest tree species had similar crown areas as fruit trees, they were slenderer than fruit trees. Tree slenderness coefficients were positively correlated with soil P, Ca, Cu and the ratios (Ca + Mg):K, (Ca + Mg):(K + Na) and Ca:Mg, but not C:N while DBH and H were correlated with soil P and C:N ratio. Our results show that critical soil nutrients and their ratios affects shade tree structural attributes (e.g. slenderness and CA), which possibly restrict variations in species-specific allometries to a narrow range on cocoa systems. Furthermore, shade tree species richness and density are better predictors of relative canopy projection area (a proxy for shade intensity) than tree species diversity. In conclusion, the results have implications for shade tree species selection, monitoring of woody biomass and maintenance of biodiversity.

Ecological importance and sociological characters of fourteen widespread weeds and their contribution to the observed (dis)similarity between weed communities

Widespread weeds are a serious nuisance to farmers in any country whether they are growing agricultural or horticultural crops for the great damage they cause to the economy, human health and environment loss. Thus, it is important to measure their ecological importance, sociological characters, their contribution to the observed (dis)similarity between weed communities associated with agronomic and horticulture crops, as well as performing time series analysis and forecasting for their cumulative records. Hopefully with the aforementioned information available, it will be possible to determine the most detrimental which deserve resistance priority within a successful weed control plan, which is the aim of the current study. Depending on species records 2018-2020, fourteen weeds assigned widespread out of the 537-species recorded. Their values in the Importance Value Index (IVI) suggested that Sonchus oleraceus had the highest ecological importance among winter weeds (IVI = 50.5), whereas Bassia indica had the highest IVI among summer weeds (IVI = 42.7) and Cynodon dactylon showed the highest value in the observed competition throughout the year (IVI = 46.2). Analysis of Similarities (ANOSIM) indicates that the weed community structure is significantly affected by widespread weeds and the mean of ranked dissimilarities in floristic composition between groups (weed communities associated with crop categories) is greater than within groups. Similarity Percentage analysis (SIMPER) based on Bray-Curtis as a distance dissimilarity measure, revealed that Cyperus rotundus, Melilotus indicus and Beta vulgaris were the most discriminant species in creating the observed pattern of (dis)similarity between the weed community structure associated with agronomic and horticultural crops during the winter half of the year, while Aster squamatus and Echinochloa colona were the most discriminant during the summer half. It is prominent from the results of the current study and the implemented time-series analysis and forecasting that no-decline is expected in the cumulative records of the 14-widespread weeds when the same current weed management strategy is applied.

A review of agroforestry ecosystem services and its enlightenment on the ecosystem improvement of rocky desertification control

Agroforestry (AF) has become an important strategy in reconciling the contradictory requirements of environmental protection and economic development in ecologically fragile areas, and whose multiple ecosystem services provide effective ways to promote the restoration of degraded ecosystems in the region. However, agroforestry ecosystem services (AFES) are usually constrained by their generative elements (vulnerability, structure, function, and ecological assets) and service management-both crucial for informed decision-making which enhances AFES supply capacity and AF sustainable management. Karst rocky desertification (KRD) is a typical case in an ecologically fragile area, and within the KRD region greatly relevant for promoting AFES as a strategy for restoring degraded regional ecosystems and for achieving sustainable development goals. In this study, a total of 164 publications related to AFES that met a set of inclusion criteria were obtained through the Scopus database using the literature review method of searching, appraisal, synthesis, and analysis. From the systematic literature review results, (i) we found that the number of relevant publications generally exhibited a year-on-year growth trend, with AFES generation elements being the most common topic (68.11 % of publications), and service management research being the second most common (31.89 % of publications); (ii) we summarised the main progress and landmark results of AFES generation elements and service management research and explored the relevant key scientific questions; and (iii) the above information enlightened the key improvement areas of KRD control ecosystem within three aspects: natural environment, agricultural development, and human-environment relationship. This study provides agroforestry practitioners and relevant decision-makers with information for improving and managing the supply capacity of AFES, and also presents important insights on the KRD control ecosystem to land degradation restoration technicians.

Tree diversity in agroforestry systems of native fine-aroma cacao, Amazonas, Peru

Cocoa cultivation is of considerable economic and social importance to the Amazonas region and is commonly associated with forest species in the region. However, the diversification level and composition of cacao agroforestry systems in Peru are poorly understood. The objective of this study is, therefore, to describe the diversity of tree species in cocoa AFS by plantation age. Accordingly, the number of species of 15 plots covering a total of 1.5 hectares was recorded. Moderately low levels of tree species diversity were reported (H´ ranged 0.89-1.45). In total 17 species were reported throughout the study area. The most abundant botanical family was represented by a single Musa sp. species. The dissimilarity indices show a moderate similarity between the age ranges evaluated (over 62%). Additionally, the IVI indicates that the most important species are used for food and timber apart from providing shade, additionally major of this species are introduced intentionally for the farmers. Based on the observations, it may be concluded that the farmer's interest in obtaining further benefits from the plot, mostly economic benefits affect the diversification of cocoa agroforestry systems.

Structure and Stability of Agroforestry Ecosystems: Insights into the Improvement of Service Supply Capacity of Agroforestry Ecosystems under the Karst Rocky Desertification Control

Agroforestry provides essential ecosystem services; its structure and stability directly determine ecosystem function and service provision. Sustaining agroforestry ecosystem functions and services in the long term is necessary to meet the needs of people. This study conducted a literature search and statistical analysis based on WOS and CNKI literature databases. We reviewed 136 literature reports on studies of agroforestry ecosystem structure and stability. The landmark results are summarized in five aspects of agroforestry ecosystems: structure characteristics, structure optimization, structure design, stability research, and influence factors. On this basis, the key scientific issues that need to be solved are summarized, and their insights for improving the supply capacity of agroforestry ecosystem services under the rocky desertification control are discussed.

Temporal changes in litterfall and potential nutrient return in cocoa agroforestry systems under organic and conventional management, Ghana

Litterfall is a critical link between vegetation and soils by which nutrients are returned to the soils, thus the amount and pattern of litterfall regulates nutrient cycling, soil fertility and primary productivity for most terrestrial ecosystems. We quantified, analyzed and compared macro- and micro-nutrients return through litterfall in organic and conventional cocoa agroforestry systems in Suhum, Ghana. We further assessed the contribution of shade tree species to litterfall and nutrient dynamics. The annual pattern of litterfall was affected by seasonality, with a major peak in the dry season and minor peaks during the rainy season. In terms of annual fractional litterfall, mean leaf litter from shade tree species was significantly higher (50 %) in organic systems (5.0 ± 0.5 Mg ha⁻¹ yr⁻¹) compared to conventional systems (3.3 ± 0.6 Mg ha⁻¹ yr⁻¹). Whereas cocoa leaves (45.0 %) were the predominant fraction of annual litterfall from conventional farms, both shade leaves (40.0 %) and cocoa leaves (39.4 %) dominated litterfall from organic farms. The return of primary macro-nutrients (P and K), secondary macro-nutrients (Ca, Mg and S) and micro-nutrients (Mn, B, Cu, Zn and Mo) via litterfall varied significantly with season, and annual return of nutrients were similar in organic and conventional cocoa systems. Shade tree leaf litter accounted for 30–47 % of annual macro- and micro-nutrient return (except Ni and Zn) in organic cocoa systems versus 20–35 % in conventional cocoa systems. The results emphasize the complementary role of the different shade tree species which compose organic and conventional cocoa systems in nutrient recycling. We conclude that organic management of cocoa agroforestry systems ensure nutrients return similar to those receiving synthetic fertilizer inputs, highlighting its potential to support cocoa production.

Impact of exclosures on woody species diversity in degraded lands: the case of Lemo in Southwestern Ethiopia

Exclosures are popularly applied to rehabilitate degraded lands and to gradually restore the productive potential of the land in the long term. This study was conducted to examine the impact of removing human and livestock interference from a degraded land to allow natural recuperation for extended period of years. The aim was to assess the trend of changes in the composition, diversity and structure of the woody component of the vegetation within the exclosures. Degraded lands with different years of exclosure were compared with adjacent open grazing lands under similar environmental conditions. A Systematic transect sampling method was employed to collect vegetation data in sampling quadrat plots, each with a size of 20 m × 20 m, evenly distributed along parallel transect lines. All the woody plant species in each plot were identified and measured for DBH and height. The species diversity and density were analyzed using standard indices. The structural pattern and regeneration status of the woody vegetation was described using size class distribution plots. The findings showed that the woody vegetation composition significantly varied between exclosures and open grazing land. There was significantly (P < 0.05) higher diversity, richness and stand density of the woody species in the exclosures than in the open grazing lands. The size class distribution of the DBH and height of the recorded species exhibited an inverted "J" shape pattern suggesting a healthy regeneration status of the important species, while the distribution pattern in the open grazing lands revealed irregular and less interpretable pattern. This study evidently showed exclosures can successfully contribute to biodiversity restoration in highly degraded lands, perhaps due to improvements in the important micro-climate conditions such as moisture and organic matter.

EAM, Ndakidemi PA, Treydte AC. Anthropogenic Pressure on Tree Species Diversity, Composition, and Growth of Balanites aegyptiaca in Dinder Biosphere Reserve, Sudan

Anthropogenic disturbances, such as illegal harvesting and livestock browsing, often affect natural forests. However, the resulting tree species diversity, composition, and population structure have rarely been quantified. We assessed tree species diversity and importance value indices and, in particular, Balanites aegyptiaca (L.) Del. population structure, across 100 sample plots of 25 m × 40 m in disturbed and non-disturbed sites at the Dinder Biosphere Reserve, Sudan, from April 2019 to April 2020. We found that the tree species diversity in non-disturbed sites was more than double that of disturbed sites (p < 0.001, T = 32.6), and seedlings and saplings comprised more than 72% of the entire tree population (F_2,48 = 116.4, p = 0.034; F_2,48 = 163.2, p = 0.021, respectively). The tree density of B. aegyptiaca in the disturbed site was less than half that of the non-disturbed site (p = 0.018, T = 2.6). Balanites aegyptiaca was seven times more aggregated in disturbed sites compared to more regularly spaced trees in non-disturbed sites (T = 39.3 and p < 0.001). The poor B. aegyptiaca population status of the disturbed site shows that the conservation of this vulnerable species is essential for a sustainable management and utilization scheme.

Rebuilding Tree Cover in Deforested Cocoa Landscapes in Côte d’Ivoire: Factors Affecting the Choice of Species Planted

Intensive cocoa production in Côte d’Ivoire, the world’s leading cocoa producer, has grown at the expense of forest cover. To reverse this trend, the country has adopted a “zero deforestation” agricultural policy and committed to rehabilitating its forest cover through the planting of high-value tree species in cocoa landscapes using a participatory approach. However, little is known regarding the factors influencing farmers’ introduction of high-value tree species to cocoa landscapes. We tested the hypothesis that ten previously reported factors to influence agroforestry system adoption to predict the number and choice of tree species that farmers introduce to cocoa farms. We interviewed 683 households in the cocoa-producing zone of Côte d’Ivoire and counted tree species on their cocoa farms. On average, two tree species were recorded per surveyed farm. Generalized Poisson regression models revealed that, in the cocoa production area, experience in tree planting and expected benefits, including income and food, influence tree species introduction through planting or “retention” when clearing land for cocoa establishment. The age of the farmer also influenced (p = 0.017) farmers’ tree species planting on cocoa farms. Fewer tree species were introduced into current intensive cocoa-production areas than in “old cocoa-loops” and forested areas. The number of tree species introduced to cocoa farms increased with expected benefits and experience in tree planting. The number of planted tree species also increased with farmers’ age. Tree species were mostly selected for the provision of shade to cocoa, production of useful tree products (38%), and income from the sale of these products (7%). Fruit tree species were the most planted, while timber tree species were mostly spared when clearing land for cocoa production.

Biodiversity of the Cocoa Agroforests of the Bengamisa-Yangambi Forest Landscape in the Democratic Republic of the Congo (DRC)

Cocoa agroforestry has evolved into an accepted natural resource conservation strategy in the tropics. It is regularly proposed as one of the main uses for REDD+ projects (Reducing Emissions from Deforestation and forest Degradation and the role of conservation, sustainable management of forests, and enhancement of forest carbon stocks in developing countries) in the Democratic Republic of the Congo. However, few studies have characterized the cocoa agroforestry systems in this country. Hence, this research proposes to determine the impact of distance from Kisangani (the unique city in the landscape) and land-use intensity on the floristic composition of cocoa agroforests in Bengamisa-Yangambi forest landscape in the Congo Basin. The results revealed that species diversity and density of plants associated with cocoa are influenced by the distance from Kisangani (the main city in the landscape and province). Farmers maintain/introduce trees that play one or more of several roles. They may host caterpillars, provide food, medicine, or timber, or deliver other functions such as providing shade to the cocoa tree. Farmers maintain plants with edible products (mainly oil palms) in their agroforests more than other plants. Thus, these agroforests play key roles in conserving the floristic diversity of degraded areas. As cocoa agroforestry has greater potential for production, biodiversity conservation, and environmental protection, it should be used to slow down or even stop deforestation and forest degradation.