Forest-savanna Transition Research Articles

Woody and Herbaceous Species Diversity Respond Differently to Environmental Variables in Semiarid Areas in Ghana.

In the semiarid areas of Ghana, the interactive effects of various environmental drivers, their relative importance, and their direct and indirect effects on plant species composition and diversity are still poorly understood, hence affecting effective ecosystem management. Using a combined gradient approach, the study investigated the predictors of species diversity of both the woody and the herbaceous layers of a steep land-use and climatic gradient from the forest-savanna transition to the Sudan savanna of Ghana. Species richness and the Shannon-Weiner Index are the response variables. Two-way ANOVA was performed to test the interaction effects of climate and land-use on species diversity; linear mixed-effect models were used to test the relationships between multiple environmental variables, and structural equation modelling was used to determine the direct and indirect effects of climate and land-use on species diversity. We found significant effects of climate and land use, and their interactions on species diversity for both vegetation layers. We also found differential responses of the herbaceous and woody layers to environmental drivers. Land use (Grazing pressure) was the most important predictor of the woody layer while climatic aridity was the most important for the herbaceous layer. Climatic aridity and fire were only directly important for herbaceous vegetation but not the woody layer, although their indirect effects cannot be discounted. For soil properties, organic matter was important for both vegetation layers. Synthesis: The marked differences in species composition for various land uses along the climatic gradient imply that climate change will indeed affect vegetation. The observed importance of grazing for all response variables implies that land use could override climate effects and that appropriate land management strategies could mitigate potential negative effects of climate change.

Evaluating fertilizer effects on growth, yield, and nutritional value of Tiger Nut (Cyperus esculentus L.) in Ghana

This study assessed the effects of organic and inorganic fertilizers, both individually and in combination, on the mineral composition, yield, and soil chemical properties of Cyperus esculentus (tiger nut) tubers. The experiment was carried out over three growing seasons in the forest-savanna transition zone, where the soil is classified as Acrisol. A 2 x 4 factorial arrangement within a Randomized Complete Block Design (RCBD) was employed, comparing two varieties of tiger nut (brown and black) under four fertilization treatments: no fertilizer (control), 2,000 kg ha⁻¹ poultry manure, 300 kg ha⁻¹ NPK 15:15:15, and a combination of 1,000 kg ha⁻¹ poultry manure + 150 kg ha⁻¹ NPK 15:15:15. The findings indicated that the two tiger nut varieties responded similarly across all measured parameters. The application of poultry manure, both alone and in combination with NPK 15:15:15, significantly improved soil properties, particularly calcium, sodium, hydrogen, and aluminum levels, across all seasons. Additionally, the combined treatment of poultry manure and NPK 15:15:15 consistently enriched the tubers with essential nutrients such as phosphorus, potassium, iron, manganese, copper, and zinc throughout the study period. The sole use of poultry manure enhanced the levels of phosphorus and potassium in the nuts across all seasons. In conclusion, the combined application of poultry manure and NPK 15:15:15 significantly increased tiger nut yield, improved soil nutrient content, and enhanced the nutritional quality of the nuts compared to the control and other treatments. Therefore, this combined fertilization approach is recommended for farmers as it effectively boosts both the yield and quality of tiger nuts, providing a sustainable option for soil fertility management.

Identifying cassava production constraints, farmers preferences, and cassava mosaic disease perceptions in Togo: insights for a participatory breeding approach

BackgroundCassava is a crucial food security crop in Togo and the most significant root crop in terms of area under cultivation and production volume. However, its production is predominantly carried out by subsistence farmers using low-yielding landraces. Several constraints impede cassava production, threatening its sustainability in the country. The low adoption of improved varieties developed by the International Institute of Tropical Agriculture (IITA) underscores the need for a participatory approach to research and development. This study aimed to identify the cassava varieties grown, major production constraints, farmers' trait preferences, and perceptions of Cassava Mosaic Disease (CMD) through Participatory Rural Appraisal (PRA).MethodsThe study employed a multistage random sampling procedure to select regions, districts, and villages based on cassava production levels. The survey involved 83 men and 57 women in group interviews and 600 farmers in individual interviews: 200 in the forest–savanna transition, 180 in the rainforest, 120 in the wet savanna, and 100 in the dry savanna. Content analysis was used for qualitative data, and quantitative data were analyzed using descriptive statistics and comparative analyses, including Chi-square tests to assess differences in perceptions and preferences.ResultsThe PRA revealed key constraints to cassava production, including inadequate capital, CMD, post-harvest physiological deterioration (PPD), and the non-availability of clean planting materials. Traits such as high yield, pest and disease resistance, early maturity, high dry matter content, delayed root deterioration, poundability, and taste were highly valued by farmers. CMD was identified as a significant disease, causing yield losses, with various causes and management practices reported. The study highlighted the necessity for a sustainable cassava seed system, as farmers pointed out the lack of improved varieties and clean planting materials.ConclusionThis study provides essential insights into cassava farming practices, production constraints, and farmers' preferred traits, laying the groundwork for a participatory breeding program in Togo. Addressing low-yielding varieties and diseases, particularly CMD, is critical for enhancing cassava production and ensuring food security.

Indigenous agroecological knowledge and practices for climate change adaptation in the forest-savanna transition zone at Batchenga in the Centre Region of Cameroon

This study investigates the crucial role of the local community's agroecological knowledge in enhancing resilience and adaptability amidst changing climatic conditions. Employing a mixed-methods approach, researchers combined quantitative household questionnaires with qualitative interviews and focus groups. Through meticulous analysis of this diverse data, key themes emerged, facilitated by coding and indexing. Leveraging Excel’s pivot table function, they aggregated and computed monthly averages from daily temperature and rainfall data. Additionally, the logit model revealed factors influencing farmers’ perceptions of climate change. Among the sampled population, most were male (68.89%) and actively engaged in agriculture (82.22%). Most participants belonged to farmers’ organizations (55.56%) and managed an average farm size of 3.6 hectares. Gender played a significant role, with an inverse correlation between gender and the first perception factor (F1) (r = − 0.68). Conversely, household size was positively associated with F1 (r = 0.75). Community membership also impacted perception (p < 0.05), emphasizing context-specific approaches. In Cameroon’s Batchenga subdivision, indigenous communities possess a wealth of agroecological knowledge passed down through generations. Their finely tuned farming practices account for local conditions, including seasonal variations, specific soil types, and available resources, enhancing agricultural system resilience in the face of climate change. The Batchenga community has also developed sustainable resource management strategies, such as crop diversification, agroforestry, and local seed preservation. Collaboration among Indigenous communities, researchers, and decision-makers is crucial to integrating this Indigenous knowledge into climate change adaptation policies effectively.

Diversity, damage and pheromone specificity of fruit flies in the Forest-Savanna Transition zone of Ghana.

Mango is a delicious tropical fruit with high economic value worldwide. The Forest-Savanna Transition zone of Ghana contributes significantly to the production of mangoes for both local and international markets. The zone is plagued with the fruit fly 'menace' like all mango-producing areas in Ghana. Not much has been done in terms of species monitoring. A 24- month fruit fly monitoring survey was conducted in eight mango orchards, to assess the composition of fruit flies associated with Mango and their damage levels. Four para-pheromone attractants (Methyl Eugenol, Terpinyl Acetate, Trimedlure, and Cuelure) were used to monitor fruit flies. Eight improvised water bottle traps (two per lure) were purposefully deployed in each orchard. A total of 18 tephritid species belonging to five genera were recorded. Bactrocera (one species), Ceratitis (six species), Dacus (eight species), Zeugodacus (one species) and Xanthaciura (two species). Bactrocera dorsalis was the most abundant species (90% of the collected samples), while the native mango fly, C. cosyra constituted 0.5%. Dacus fuscovittatus and Dacus pleuralis were for the first time captured and identified in Ghana. Dacus langi, Dacus carnesi, Dacus (diastatus?), Ceratitis silvestrii and C. quinaria were recorded for the first time in the zone. The zone recorded a diversity index of 0.41. Damage levels ranged from 41-91%. Ten out of the 18 species, are of economic importance on mango and must be watched. Periodic updates on seasonal fluctuations, species composition and new arrivals are key to the successful implementation of any management strategy.

Role of The Forest-Savanna Transition Zones in Mitigating Climate Change at Lamto Scientific Reserve, Côte d’Ivoire

In the context of global climate change, forests play a crucial role as carbon sinks, contributing to regulating greenhouse gases and stabilising the climate. This study evaluates the role of forest-savanna transition zones in mitigating climate change at Lamto Scientific Reserve, Côte d’Ivoire, by assessing their carbon sequestration capacity and economic value. The study employed a combination of field surveys, remote sensing and statistical analysis to gather and analyse the data. The floristic inventory recorded 4,018 individuals, distributed among 142 species, 92 genus, and 37 families. The stem density ranges from 510 stems/ha (shrub savanna) to 758 stems/ha (moist semi-deciduous forest), with a basal area varying from 5.65 m²/ha (open forest) to 11.79 m²/ha (gallery forest). The vegetation structure, characterised by a “bell-shaped” vertical stratification and an “inverted J” horizontal distribution, reflects active regeneration. In terms of biomass and carbon sequestration, the gallery forest dominates with 287.37 ± 201.68 t/ha of biomass, 143.69 ± 100.84 tC/ha of carbon, and an exceptional capacity to sequester 526.856 tCO₂/ha, accounting for 57.6% of the total carbon sequestered. Its economic value, supported by mechanisms such as REDD+ High, reaches 13,171 EUR/ha (8,639,880 FCFA). In contrast, the shrub savanna, with a biomass of 9.38 ± 8.41 t/ha and limited sequestration of 17.203 tCO₂/ha, offers a maximum value of 430 EUR/ha (282,111 FCFA). The results highlight the key role of the gallery forest as the primary carbon sink and the economic potential of Lamto’s ecosystems. They underscore sustainable management’s importance in maximising climate regulation, preserving biodiversity, and enhancing ecological resilience.

Decoupling the Effects of Fire and Dry Season Drought on Seedling Establishment Success of Tree Functional Types in Humid Savannas

Background: In the seasonal tropics, fire generally occurs in the dry season. Consequently, the effects of fire and dry season drought on seedling establishment of different tree functional types are correlated. Therefore, factors that are more important for tree recruitment in forest-savanna ecotones are still poorly understood. Methods: We studied seedling establishment success of seven tropical tree species (of forest and forest-savanna transition origins) in a common garden experiment using combinations of dry season (irrigation vs no-irrigation) and fire (burning vs no-burning). Results: We found that burning caused a significant decline in survival of forest species, but not of forest-savanna transition species. The combination of burning without dry season irrigation (which typifies dry season fire) had the largest overall effect on survival, mass and height of plants. The separate effect of burning was larger than that of dry season drought. Seedling size at the onset of the dry season significantly predicted root starch content and, hence, dry season survival probability of forest-savanna transition species, but not of forest species. Dry season irrigation increased post-fire survival of forest-savanna transition species, but not of forest species, possibly linked to differences in resprout capacity and root starch reserves. Conclusion: Our work shows that fire and dry season drought produce a stronger negative effect together, than their separate effects on seedling establishment particularly of forest species. This provides a mechanistic explanation for the existence of forest-savanna transition species in fire-prone humid savannas. Implications for Conservation: The mosaic of forest, transitional and savanna vegetation within the forest-savanna ecotone reflects the influences of fire and dry season drought. Any changes in these elements will influence vegetation dynamics within the forest-savanna ecotone.

Impacts of climate variability on the spatio-temporal dynamics of plant formations in the forest-savannah transition zone: the case of the Lamto Scientific Reserve, Central Côte d’Ivoire

Understanding climatic variability’s effects on land and biodiversity is vital for guiding sustainability, conservation, and climate impact predictions in fragile ecosystems like Côte d’Ivoire’s forest-savanna transition zone. This study aims to analyse the impact of climate variability on the spatio-temporal dynamics of land use in the Lamto Scientific Reserve. To do this, a set of monthly climate data covering the period from 1990 to 2022 was used, including indicators such as rainfall, maximum, minimum and average temperatures, drought and standardised rainfall indices. The study also involved the classification of Landsat images dating from 1990, 2002, 2012 and 2022, enabling changes in land use to be observed. The corresponding areas were correlated with the climatic variables using a Spearman correlation test. The results show a transition from savannah to denser tree cover in the reserve. In addition, an increase in rainfall, varying between 900 and 1687 mm, suggests that Lamto could be classified as a humid region. The analysis highlights the complex interactions between climate change, particularly high temperatures, and land-use dynamics. Gallery and semi-deciduous forests show resilience in the face of rising temperatures, favouring their expansion. On the other hand, pre-forest formations, such as open forests and wooded savannahs, are more affected by these temperatures, which hinders their development. Tree savannahs also show a certain resilience, while shrub savannahs and bare land are often associated with ecological degradation processes in response to high temperatures. Finally, although rainfall plays a role, its influence seems minor, suggesting that other environmental or climatic factors, such as watercourses or microclimate, play a more significant role in land use/land cover dynamics.

Multi-fold increase in rainforest tipping risk beyond 1.5–2 °C warming

Abstract. Tropical rainforests rely on their root systems to access moisture stored in soil during wet periods for use during dry periods. When this root zone soil moisture is inadequate to sustain a forest ecosystem, they transition to a savanna-like state, losing their native structure and functions. Yet the influence of climate change on ecosystem's root zone soil moisture storage and the impact on rainforest ecosystems remain uncertain. This study assesses the future state of rainforests and the risk of forest-to-savanna transitions in South America and Africa under four Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5). Using a mass-balance-based empirical understanding of root zone storage capacity (Sr), defined as the maximum volume of root zone soil moisture per unit area accessible to vegetation's roots for transpiration, we project how rainforest ecosystems will respond to future climate changes. We find that under the end-of-the-21st-century climate, nearly one-third of the total forest area will be influenced by climate change. As the climate warms, forests will require a larger Sr than they do under the current climate to sustain their ecosystem structure and functions, making them more susceptible to water limitations. Furthermore, warming beyond 1.5–2 °C will significantly elevate the risk of a forest–savanna transition. In the Amazon, the forest area at risk of such a transition grows by about 1.7–5.8 times in size compared to the immediate lower-warming scenario (e.g. SSP2-4.5 compared to SSP1-2.6). In contrast, the risk growth in the Congo is less substantial, ranging from 0.7–1.7 times. These insights underscore the urgent need to limit the rise in global surface temperature below the Paris Agreement to conserve rainforest ecosystems and associated ecosystem services.

Phenotypic Variation in a Panel of 149 varieties of Cassava (Manihot esculenta Crantz): A Pre-Breeding Investigation in Togo

Evaluating the genetic diversity within a plant species is crucial for identifying genes that control important biological functions, facilitating the rationale for developing new varieties. The genetic diversity in a panel of 149 cassava varieties was explored to assess its nature, pattern, and differentiation. The experiment was conducted at the Breeding Station of Davié in the forest-savanna transition zone characterized by a bimodal rainfall pattern. One hundred and fourty nine varieties were planted in an augmented block design, with five improved and released varieties as check genotypes. Data on sixteen phenotypic traits were collected based on cassava traits ontology. A high diversity coefficient of 0.78 was observed among varieties. Multivariate analysis revealed all assessed traits as discriminative for cassava varieties. Principal Component Analysis identified traits such as fresh root yield, plant vigour, number of roots per plant, Cassava Mosaic Disease (CMD) severity, aboveground biomass, leaf lobe dimensions, Cassava Bacterial Blight (CBB) severity, plant height, height to first branching, petiole length, harvest index as major contributors to the variability of the germplasm. Cluster and canonical analyses delineated seven significant groups, characterized by traits like CMD and CBB resistance, vigorous growth, high canopy and fresh root yield, high harvest index and root dry matter content.The findings provide a foundation for informed selection of parental lines in developing new high-yielding and CMD-resistant cassava varieties.

Phenotypic variability of some varieties of pepper (&lt;i&gt;Capsicum&lt;/i&gt; spp) in the forest-savanna transition zone of Edo State, Nigeria

Description of the subject. The phenotypic variability of some varieties of pepper (Capsicum spp) was carried out in Research Farm, Ambrose Alli University Ekpoma. This is to determine the different growth performance of varieties of pepper in south- south geopolitical zone in Nigeria.Objectives. The study aims to evaluate the phenotypic variability of certain improved varieties of pepper (Atarodo “scotch bonnet”, Atawewe “bird eye”, Tatashe “red pepper” and Shombo “cayenne pepper”.) in the Edo State region of Nigeria.Methods. The experiment was Randomized Complete Block Design replicated four times. Data collected were subjected to Analysis of Variance at P˂0.05. The genetic variability were analyzed using Genetic model (Heritability), Genetic gain and Genetic advance.Results. Plant height and number of leaves at 3, 6 and 9 WAP differed significantly. However at 6 WAP there was no significant difference for number of leaves. There was no significant difference for the number of branches/plant. Petiole length, leaf area and stem girth varied significantly. Days to 50% flowering, 50% maturity, fruit length, fruit width, fruit weight and fruit yield were significantly different. Days to 50 % flowering and maturity, fruit length, fruit width and fruit yield (96.09 % and 4.02), (97.56 % and 3.08), (61.83% and 9.53), (75.32 % and 5.13) and (71.46 % and 2.41) recorded high values for heritability and genetic gain.Conclusion. The Atawewe variety had the highest yield/ha and it is recommended for farmers in the locality.

Variability of soil organic carbon and nutrient content across land uses and agriculturally induced land use changes in the forest-savanna transition zone of Cameroon

Variability of soil organic carbon and nutrient content across land uses and agriculturally induced land use changes in the forest-savanna transition zone of Cameroon

Soil organic carbon and nutrient characteristics of Anogeissus groves in old Opara forest reserve, Nigeria.

Forest-savanna transition zones of West Africa are uniquely characterized by forest groves, forest patches, or forest islands, the importance of which for sustainable resource management and their potential for carbon sequestration and nutrient cycling is often underrated. Our study conducted a comparative analysis of the soil organic carbon and nutrient characteristics of the Anogeissus groves in the old Opara forest reserve and their adjoining arable lands. We established 30 sampling frames of 100m × 100m plots with 15 frames per land use type. For each sampling frame, six observation points were randomly selected, and composite soil samples were collected at soil depths of 0-20cm and 20-50cm per observation point. Our results showed Anogeissus groves and their adjoining arable lands to exist on similar landscapes while the groves have enriched soil morphological characteristics (e.g., soil color), higher soil organic carbon (SOC), and better nutrient characteristics. There were strong positive relationships between SOC, effective cation exchange capacity, total nitrogen, calcium, magnesium and calcium, zinc, electrical conductivity, and copper. The significant soil organic matter accumulation in the groves accounts for the overall improved soil characteristics over the adjoining arable lands. Preserving the groves and similar Africanecosystems may be important in climate regulation, resources and biodiversity conservation, and ethnopharmacology for rural communities. Thus, a question arises: should more land be set aside for ecological conservation or for agricultural productivity?

The role of environmental gradients and microclimates in structuring communities and functional groups of lizards in a rainforest-savanna transition area.

Environmental heterogeneity poses a significant influence on the functional characteristics of species and communities at local scales. Environmental transition zones, such as at the savanna-forest borders, can act as regions of ecological tension when subjected to sharp variations in the microclimate. For ectothermic organisms, such as lizards, environmental temperatures directly influence physiological capabilities, and some species use different thermoregulation strategies that produce varied responses to local climatic conditions, which in turn affect species occurrence and community dynamics. In the context of global warming, these various strategies confer different types of vulnerability as well as risks of extinction. To assess the vulnerability of a species and understand the relationships between environmental variations, thermal tolerance of a species and community structure, lizard communities in forest-savanna transition areas of two national parks in the southwestern Amazon were sampled and their thermal functional traits were characterized. Then, we investigated how community structure and functional thermal variation were shaped by two environmental predictors (i.e., microclimates estimated locally and vegetation structure estimated from remote sensing). It was found that the community structure was more strongly predicted by the canopy surface reflectance values obtained via remote sensing than by microclimate variables. Environmental temperatures were not the most important factor affecting the occurrence of species, and the variations in ecothermal traits demonstrated a pattern within the taxonomic hierarchy at the family level. This pattern may indicate a tendency for evolutionary history to indirectly influence these functional features. Considering the estimates of the thermal tolerance range and warming tolerance, thermoconformer lizards are likely to be more vulnerable and at greater risk of extinction due to global warming than thermoregulators. The latter, more associated with open environments, seem to take advantage of their lower vulnerability and occur in both habitat types across the transition, potentially out-competing and further increasing the risk of extinction and vulnerability of forest-adapted thermoconformer lizards in these transitional areas.

Response of mango ginger (Curcuma amada) to plant population and different weed control methods in the forest-savanna transition zone of south-western Nigeria

Field trials were conducted in the early cropping seasons of 2016 and 2017 at the Teaching and Research Farm of Federal University of Agriculture, Abeokuta (07? 20? N, 3? 23? E 159 m above sea level) in the forest-savanna transition zone of south-western Nigeria to evaluate the response of mango ginger to plant population and different weed control methods. Treatments were laid out in a randomized complete block design with a split-plot arrangement and replicated three times. The main plot consisted of two plant populations: 444,444 plants/ha and 250,000 plants/ha, while the sub-plots consisted of ten weed control methods. The collected data on growth and yield of mango ginger plant, and weed biomass were subjected to analysis of variance (ANOVA) and the means of the treatments were separated using the least significant difference (LSD at p ? 0.05). Planting mango ginger at 444,444 plants/ha resulted in a 43.1% increase in rhizome yield compared to 250,000 plants/ha. Different weed control methods gave significantly higher crop vigor score, yield and yield components than the weedy check. Relative to the highest value in both years, uncontrolled weed infestation resulted in a 91.4% reduction in rhizome yield. There was a 60.7% increase in mango ginger rhizome yield when post-emergence weed control followed pre-emergence weed control. Our study has revealed that mango ginger, as a perennial crop with initially slow growth, requires a weed-free period beyond the first 12 weeks after planting (WAP) for acceptable weed control and optimum rhizome yield. Hence, a pre-emergence application of oxyfluorfen at a dosage of 0.24 kg a.iha-1 and a post-emergence hoe weeding are recommended.

Drivers of integrated crop–livestock farming system’s efficiency for smallholder farmers in the forest-savanna transition agro-ecological zone of Ghana

Drivers of integrated crop–livestock farming system’s efficiency for smallholder farmers in the forest-savanna transition agro-ecological zone of Ghana

Soil carbon stock and nutrient characteristics of forest–savanna transition: Estimates from four land use systems in Ghana

Soil carbon stock and nutrient characteristics of forest–savanna transition: Estimates from four land use systems in Ghana

Evaluation and Mapping of Evapotranspiration in Forest-Savanna Transition Zone of Ogun State, South-Western Nigeria

Evapotranspiration's impact on crop production, determined by water consumption in plants, varies across locations due to surface and climate differences. Traditional ground-based methods for measurement fall short in capturing these variations. In order to address this, the study evaluated and mapped the evapotranspiration in the forest-savanna transition zone of Ogun State, South-western Nigeria using a geo-informatics approach. Over six years, 12 Landsat images were collected, representing dry and wet seasons. These images were used to estimate the Normalized Difference Vegetative Index (NDVI), indicating vegetation density, and compute evapotranspiration values across the area. During the dry season, NDVI ranged from -0.326 to 0.376, and during the wet season, it ranged from -0.435 to 0.780, showing higher vegetation cover in the wet season. Evapotranspiration values varied across different regions. In Abeokuta South, Abeokuta North, and Odeda Local Government Areas, values ranged from 2.83 to 6.37 mm/day, 0.12 to 2.64 mm/day, and 3.12 to 5.44 mm/day, respectively, influenced by varying vegetation characteristics. The geo-informatics approach offered a realistic representation and spatial understanding of evapotranspiration, proving cost-effective and accessible. In conclusion, the study recommends the geo-informatics approach for evapotranspiration measurement due to its ability to consider spatial characteristics. This understanding is essential for effective water resource management and crop planning in the Forest-Savanna transition zone of Nigeria.

Human-induced land use changes and phosphorus limitation affect soil microbial biomass and ecosystem stoichiometry.

Soil and microbial biomass carbon (C), nitrogen (N), and phosphorus (P) play an important role in soil nutrient dynamics in biogeochemical cycles of terrestrial ecosystems. However, increased human activities as a result of agricultural intensification on soil nutrients and microbial C:N:P stoichiometry are poorly understood in this fragile forest-savanna transition agroecosystem. This study aimed to (i) assess soil and microbial C, N, and P stoichiometry in different land use systems, and (ii) examine the effect of soil and microbial C, N, and P stoichiometry on soils susceptible to human-induced land use changes. A total of 82 composite soil samples at a depth of 0-20 cm were sampled from forest, savanna, grassland, fallow and cropland for laboratory analysis. The results revealed that the concentrations of C, N, and P were low in Fallow and Cropland compared to other land use systems. Analysis of variance in microbial C, N, and P stoichiometric ratios revealed a significant decreasing tendency compared to soil C:N, C:P and N:P ratios with no statistical significance (p < 0.05). The C:P and N:P ratios were low compared to the C:N ratio in land uses. A significant positive correlation was observed between MBC and MBN (0.95; p < 0.01), and with C and N (0.69; p < 0.01). There were significant interactive effects of land use on soil and microbial variables. The estimated microbial C:N:P stoichiometric ratios (21:2:1) were well constrained in the study area. The transition from Forest to Cropland resulted in 64%, 52%, and 71% reduction in C, N, and P, respectively. This implies that phosphorus is the main factor limiting productivity. The low availability of phosphorus in these tropical soils may have resulted in low C:P and N:P ratios. Therefore, we conclude that our results highlight the importance of phosphorus limitation on ratios of microbial C:P and N:P in landuse systems. Nutrient inputs such as fertilizers, manure and crop residues should be applied to croplands to improve soil and microbial C, N and P levels. Further, effects of land use on soil nutrient status and stoichiometry at 1-meter depth will be considered in our future work.

Current Forest–Savanna Transition in Northern South America Departs from Typical Climatic Thresholds

The forest–savanna transition is the most widespread ecotone in the tropics, with important ecological, climatic, and biogeochemical implications at local to global scales. However, the factors and mechanisms that control this transition vary among continents and regions. Here, we analyzed which factors best explain the transition in northern South America (Llanos ecoregion and northwestern Amazon), where common thresholds on typical environmental factors (for example, mean annual precipitation (MAP), wet season precipitation) fail to predict it. For instance, savannas in the Llanos occur at MAP levels (> 1500 mm) which are typical of forests in other tropical regions. We examined the transition’s climate features, soils, and disturbance (fire frequency) spaces using remotely sensed data. We used logistic generalized linear models to assess the effect of seasonal (season length) and intra-seasonal (daily precipitation frequency and intensity) precipitation metrics during the dry season, soil silt content, and fire frequency, on the transition using canopy cover, tree cover, and the maximum Plant Area Volume Density as vegetation structure descriptor variables. Fire frequency and precipitation frequency were the most important variables explaining the transition. Although most fires occur in savannas, we found that a significant percentage of savanna pixels (46%) had no fires. This study indicates that the transition should be characterized regionally in response to biogeographic differences (for example, climatic space) among regions and continents. Our results highlight the importance of fire frequency and intra-seasonal precipitation in determining the transition in northern South America. Furthermore, future studies should consider regional differences in the climatic space of forest and savanna to improve projections of global change impacts on these highly diverse ecosystems.