Tropical Montane Rain Forest Research Articles

Do leaf traits shape herbivory in tropical montane rainforests? A multispecies approach

AbstractThe co‐evolutionary arms race between herbivores and plants forces plants to evolve protection strategies that reduce the palatability of the plant modules attacked by the herbivores. These characteristics of traits have consequences for both the survival of plant individuals and the composition of plant communities. Thus, correlating traits of for instance leaves with herbivory is an important step toward understanding the dynamics of plant populations and communities. Traits can either be measured using conventional lab methods or recently developed spectral sensing techniques. We examined whether leaf traits of trees are related to herbivory in a multispecies approach. Furthermore, we explored whether leaf traits characterized by spectral sensing provide similar relations to herbivory as lab‐based leaf traits. We established nine 1‐ha square plots evenly distributed over three different forest types in Ecuadorian tropical montane rainforests where we estimated herbivory as the leaf area loss (in square centimeters) of 20 (±5) leaves sampled from the canopies of 380 tree individuals belonging to 51 tree species (7 ± 1 individuals/species) using lab‐ and spectral‐sensing‐based methods. For each methodological approach, we ran 100 linear mixed‐effects models with all respective leaf traits as predictor and herbivory as response variables for data subsets containing one randomly selected tree individual of each species to estimate the range of the regression coefficients for each trait. Automated stepwise backward selections determined the frequency of each trait having an important influence on herbivory. We found no clear relations between leaf traits and herbivory for neither lab‐ nor spectral‐sensing‐based traits. A nested variance component analysis demonstrated that the observed variability was mainly due to the variation in trait concentrations between tree individuals of a species. Our results suggest that snapshot data lead to a mismatch between herbivory and the concentrations of traits during the peak of herbivory. Another explanation could be that environmental conditions or processes along the food web are more important in structuring herbivory than leaf traits.

Carbon, nitrogen and phosphorus contents and their ecological stoichiometric characteristics in leaf litter from the Jianfengling Tropical Montane Rainforest.

Investigating carbon (C), nitrogen (N) and phosphorus (P) contents and ecological stoichiometric characteristics in leaf litter from tropical rainforests is crucial for elucidating nutrient cycling and energy flow in forest ecosystems. In this study, a 60-ha tropical montane rainforest dynamic monitoring plot in Jianfengling, was selected as the research site and 60 subplots were selected for detailed study. Leaf litter was collected monthly throughout 2016, branches of similar height were placed atthe four corners of each sample square to support a nylon cloth (1 m× 1 m) with 1 mm apertures. The collected plant leaves were sorted,placed into envelopes, labelled, and transported to the laboratory and samples from various plant species were identified, resulting in a total of 107 samples collected and analyzed. For the 31 dominant species, the leaf litter had C, N and P contents of 312.71 ± 28.42, 4.95 ± 0.46 and 0.40 ± 0.03 g/kg, respectively. The C:N, C:P and N:P ratios were 63.61 ± 7.50, 790.91 ± 82.30 and 12.49 ± 1.00, respectively, indicating moderate variability. The C, N and P contents exhibited greater variability among the plant groups, indicating significant heterogeneity among the samples. In contrast, the data from the subplots exhibited less variability, highlighting significant homogeneity. Overall, the mean carbon, nitrogen and phosphorus contents in the leaf litter from tropical montane rainforests were lower than those observed at national and global scales. The N:P ratios in leaf litter below 14 indicated that nitrogen limited litter decomposition in Jianfengling. However, no significant correlations were observed between the C, N and P contents and their stoichiometric ratios in leaf litter and those in soil. The above results provide important reference data and scientific basis for the nutrient cycling and energy flow processes, and in the future, we can explore the limiting role and mechanism of nitrogen in the decomposition process of leaf litter.

Modern pollen assemblages in lake surface sediments and their relationships with vegetation, climate, and human activities in Yunnan, SW China

Modern pollen assemblages from moss polsters, topsoils, and lake surface sediments are crucial for interpreting palaeovegetational and palaeoclimatic conditions from fossil pollen records. While a large number of modern pollen assemblages exist from Yunnan Province, SW China, few are derived from lake surface sediments with depositional environments similar to those of fossil pollen records. In this study, we present modern pollen assemblages from lake surface sediments across 36 lakes in Yunnan, spanning spatially from the southeast to the northwest of the region. These lakes encompass a range of vegetation types, varying from alpine meadow grasslands to tropical seasonal and montane rainforests. Our findings demonstrate that modern pollen assemblages from lake surface sediments can effectively identify various vegetation zones. Redundancy analysis (RDA) reveals a strong correlation of pollen assemblages with climate factors (e.g., temperature and precipitation) but a weak correlation with human activities. This study suggests that modern pollen assemblages from lake surface sediments in Yunnan can be used not only to reflect changes in vegetation and climate, but also as reliable indicators for reconstructing the history of human activities to some extent.

Topography and life stage regulate species aboveground biomass distribution in combination in a tropical montane rainforest.

Understanding the correlation between topography, species biomass and species life stage would allow forest managers to better foster carbon storage in forests. Using census data from a 60-ha plot in south China, we first quantified aboveground biomass (AGB) and how much it varied among different topographies. Next, the specific contribution of 42 dominant species to total aboveground biomass was analyzed for each of the different topographies. We also explored whether these species-topography associations changed, in terms of species' AGB distribution, during each of the three life stages (sapling, juvenile, adult) for these 42 species. Our results showed that the average AGB was 368.79 Mg ha-1 and that it varied noticeably among the four topographies (Low valley, Slope, High valley and Ridge, which were classified by using fuzzy C-mean clustering based on elevation, convexity, and slope). AGB was significantly lower in the two valleys than in the two other topographies. Of the 42 species, 88.1% showed topographic preferences, and 78.6% appeared to exhibit topographic preferences that changed with life stage. Our work highlights the importance of topography and life stage in species biomass distribution and suggests that different combinations of species and life stages, based on species topographic preferences across life stages, may be better suited in different tropical rainforest topographies to maximize carbon storage overall.

Cell Wall Profiling of the Resurrection Plants Craterostigma plantagineum and Lindernia brevidens and Their Desiccation-Sensitive Relative, Lindernia subracemosa.

Vegetative desiccation tolerance has evolved within the genera Craterostigma and Lindernia. A centre of endemism and diversification for these plants appears to occur in ancient tropical montane rainforests of east Africa in Kenya and Tanzania. Lindernia subracemosa, a desiccation-sensitive relative of Craterostigma plantagineum, occurs in these rainforests and experiences adequate rainfall and thus does not require desiccation tolerance. However, sharing this inselberg habitat, another species, Lindernia brevidens, does retain vegetative desiccation tolerance and is also related to the resurrection plant C. plantagineum found in South Africa. Leaf material was collected from all three species at different stages of hydration: fully hydrated (ca. 90% relative water content), half-dry (ca. 45% relative water content) and fully desiccated (ca. 5% relative water content). Cell wall monosaccharide datasets were collected from all three species. Comprehensive microarray polymer profiling (CoMPP) was performed using ca. 27 plant cell-wall-specific antibodies and carbohydrate-binding module probes. Some differences in pectin, xyloglucan and extension epitopes were observed between the selected species. Overall, cell wall compositions were similar, suggesting that wall modifications in response to vegetative desiccation involve subtle cell wall remodelling that is not reflected by the compositional analysis and that the plants and their walls are constitutively protected against desiccation.

Laboratory and field measurements of water relations, photosynthetic parameters, and hydration traits in macrolichens in a tropical lower montane rainforest in Thailand.

Ecophysiological studies of lichens in tropical Asia are rare, and additional studies can increase the understanding of lichen life in this region. The main aim of this study was to observe the relationships between water availability and photosynthetic parameters, as well as hydration trait parameters, in macrolichens during the rainy and dry seasons in a tropical forest. A total of 11 lichen species growing in a lower montane rainforest in Thailand were collected and studied. The results clearly showed that the specific thallus mass (STM), net photosynthetic rate (Pn), the potential quantum yield of primary photochemistry (Fv/Fm), chlorophyll content, and carotenoid content of almost all lichens were lower in the dry season than in the rainy season. Field measurements in the dry season revealed that only the foliose chlorolichen Parmotrema tinctorum was metabolically active and exhibited slight carbon assimilation. In the rainy season, all lichens started their photosynthesis in the early morning, reached maximal values, declined, and ceased when the thalli desiccated. The photosynthetically active period of the lichens was approximately 2-3h in the morning, and the activities of the cyanolichens ended approximately 30min after the chlorolichens. The hydration trait parameters, including the STM, maximal water content (WCmax), and water holding capacity (WHC), were greater in the cyanolichens. In addition, the maximal Pn (Pnmax) and optimal water content (WCopt) for Pn were also greater in the cyanolichens, but the maximal Fv/Fm (Fv/Fmmax) was lower. The cyanolichens compensated for their inability to use humid air to restore photosynthesis by having higher water content and storage, higher photosynthetic rates, and longer photosynthetically active periods. This study provides additional insights into lichen ecophysiology in tropical forests that can be useful for lichen conservation.

Spatial variation and controls of soil microbial necromass carbon in a tropical montane rainforest

Soil microbial necromass carbon is an important component of the soil organic carbon (SOC) pool which helps to improve soil fertility and texture. However, the spatial pattern and variation mechanisms of fungal- and bacterial-derived necromass carbon at local scales in tropical rainforests are uncertain. This study showed that microbial necromass carbon and its proportion in SOC in tropical montane rainforest exhibited large spatial variation and significant autocorrelation, with significant high-high and low-low clustering patterns. Microbial necromass carbon accounted for approximately one-third of SOC, and the fungal-derived microbial necromass carbon and its proportion in SOC were, on average, approximately five times greater than those of bacterial-derived necromass. Structural equation models indicated that soil properties (SOC, total nitrogen, total phosphorus) and topographic features (elevation, convexity, and aspect) had significant positive effects on microbial necromass carbon concentrations, but negative effects on its proportions in SOC (especially the carbon:nitrogen ratio). Plant biomass also had significant negative effects on the proportion of microbial necromass carbon in SOC, but was not correlated with its concentration. The different spatial variation mechanisms of microbial necromass carbon and their proportions in SOC are possibly related to a slower accumulation rate of microbial necromass carbon than of plant-derived organic carbon. Geographic spatial correlations can significantly improve the microbial necromass carbon model fit, and low sampling resolution may lead to large uncertainties in estimating soil carbon dynamics at specific sites. Our work will be valuable for understanding microbial necromass carbon variation in tropical forests and soil carbon prediction model construction with microbial participation.

Cross-scale spatial variability and associations of carbon pools provide insight into regulating carbon sequestration in tropical montane rainforests

The spatial distribution of plant, soil, and microbial carbon pools, along with their intricate interactions, presents a great challenge for the current carbon cycle research. However, it is not clear what are the characteristics of the spatial variability of these carbon pools, particularly their cross-scale relationships. We investigated the cross-scale spatial variability of microbial necromass carbon (MNC), soil organic carbon (SOC) and plant biomass (PB), as well as their correlation in a tropical montane rainforest using multifractal analysis. The results showed multifractal spatial variations of MNC, SOC, and PB, demonstrating their adherence to power-law scaling. MNC, especially low MNC, exhibited stronger spatial heterogeneity and weaker evenness compared with SOC and PB. The cross-scale correlation between MNC and SOC was stronger than their correlations at the measurement scale. Furthermore, the cross-scale spatial variability of MNC and SOC exhibited stronger and more stable correlations than those with PB. Additionally, this research suggests that when SOC and PB are both low, it is advisable for reforestations to potentiate MNC formation, whereas when both SOC and PB are high some thinning can be advisable to favour MNC formation. Thus, these results support the utilization of management measures such as reforestation or thinning as nature-based solutions to regulate carbon sequestration capacity of tropical forests by affecting the correlations among various carbon pools.

Monitoring threats to Australian threatened birds: climate change was the biggest threat in 2020 with minimal progress on its management

ABSTRACT Most biodiversity monitoring globally tends to concentrate on trends in species’ populations and ranges rather than on threats and their management. Here we review the estimated impact of threats and the extent to which their management is understood and implemented for all threats to all Australian threatened bird taxa. The assessment reports the situation in 2020 and how this differs from 2010. The most marked finding was that the impact of climate change has increased greatly over the last decade, and now surpasses invasive species as the threat imposing the heaviest threat load. Climate change has driven recent massive population declines from increased temperatures in tropical montane rainforests and from fire. For both direct climate change impacts and fire management, progress in understanding how to relieve the threats has been slow and patchy. Consequently, little effective management has occurred. By comparison, our analysis showed that the single successful campaign to eradicate introduced mammals from Macquarie Island relieved the total threat load on Australian threatened birds by 5%, and more than halved the load on the birds from oceanic islands. Protection or rehabilitation of habitat, particularly on islands, has also delivered measurable benefit as have, in the longer term, controls on longline fishing. Our approach can be used with other taxonomic groups to understand progress in research and management and to allow quantification of potential benefits from proposed actions, such as the national threatened species plan.

Assessing the functional vulnerability of woody plant communities within a large scale tropical rainforest dynamics plot.

Tropical forests are characterized by intricate mosaics of species-rich and structurally complex forest communities. Evaluating the functional vulnerability of distinct community patches is of significant importance in establishing conservation priorities within tropical forests. However, previous assessments of functional vulnerability in tropical forests have often focused solely on isolated factors or individual disturbance events, with limited consideration for a broad spectrum of disturbances and the responses of diverse species. We assessed the functional vulnerability of woody plant communities in a 60-ha dynamic plot within a tropical montane rainforest by conducting in silico simulations of a wide range disturbances. These simulations combined plant functional traits and community properties, including the distribution of functional redundancy across the entire trait space, the distribution of abundance across species, and the relationship between species trait distinctiveness and species abundance. We also investigated the spatial distribution patterns of functional vulnerability and their scale effects, and employed a spatial autoregressive model to examine the relationships between both biotic and abiotic factors and functional vulnerability at different scales. The functional vulnerability of tropical montane rainforest woody plant communities was generally high (the functional vulnerability of observed communities was very close to that of the most vulnerable virtual community, with a value of 72.41% on average at the 20m×20m quadrat scale), and they exhibited significant spatial heterogeneity. Functional vulnerability decreased with increasing spatial scale and the influence of both biotic and abiotic factors on functional vulnerability was regulated by spatial scale, with soil properties playing a dominant role. Our study provides new specific insights into the comprehensive assessment of functional vulnerability in the tropical rainforest. We highlighted that functional vulnerabilities of woody plant communities and their sensitivity to environmental factors varied significantly within and across spatial scales in the tropical rainforest landscape. Preserving and maintaining the functionality of tropical ecosystems should take into consideration the variations in functional vulnerability among different plant communities and their sensitivity to environmental factors.

Biodiversity dynamics of terrestrial gastropods in the tropical montane rainforests of Nuwara Eliya, Sri Lanka

Sri Lanka is home to 253 terrestrial gastropod species, most of which are endemic. However, limited research has explored the diversity, distribution, and influencing variables of these gastropods. This study sampled gastropods in tropical montane rainforests by establishing 10-50 1m2 sampling plots across 60 randomly selected sites. Among the 46 recorded species, 79% were native, and 17% were exotic. Representative species of the five endemic genera to the island and two endemic semi-slug species were recorded from these forests. Native gastropod species were primarily found in forest interiors, while exotic species inhabited forest buffer regions. The distribution of most native species is influenced by elevation, air temperature, relative humidity, rainfall, and soil pH, while elevation and rainfall play a significant role in the distribution of most exotics. Exotics display broader environmental tolerance compared to natives, enabling exotics to invade the forests. The restricted habitat of many native species within deep canopy forests makes them highly vulnerable to habitat change, whereas exotics thrive under altered conditions.

Thermophilisation of Afromontane forest stands demonstrated in an elevation gradient experiment

Abstract. The response of tropical trees and tree communities to climate change is crucial for the carbon storage and biodiversity of the terrestrial biosphere. Trees in tropical montane rain forests (TMFs) are considered particularly vulnerable to climate change, but this hypothesis remains poorly evaluated due to data scarcity. To reduce the knowledge gap in the response of TMF trees to warming, we established a field experiment along a 1300–2400 m elevation gradient as a proxy for warming in Rwanda. Seedling-size trees of 20 species native to montane forests in eastern and central Africa were planted in multi-species plots at three sites along the gradient. They have overlapping distributions but primarily occur in either transitional rain forests (∼ 1600–2000 ma.s.l.) or mid-elevation TMFs (∼ 2000–3000 ma.s.l.), with both early- (ES) and late-successional (LS) species represented in each elevation origin group. Tree growth (diameter and height) and survival were monitored regularly over 2 years. We found that ES species, especially from lower elevations, grew faster at warmer sites, while several of the LS species, especially from higher elevations, did not respond or grew slower. Moreover, a warmer climate increased tree mortality in LS species, but not much in ES species. ES species with transitional rain forest origin strongly increased proportional to stand basal area at warmer sites, while TMF species declined, suggesting that lower-elevation ES species will have an advantage over higher-elevation species in a warming climate. The risk of higher-elevation and LS species of becoming outcompeted by lower-elevation and ES species due to a thermophilisation response in a warmer climate has important implications for biodiversity and carbon storage of Afromontane forests.

Long-Term Effects of Ecological Restoration Projects on Ecosystem Services and Their Spatial Interactions: A Case Study of Hainan Tropical Forest Park in China.

Ecological restoration projects aim to comprehensively intervene in damaged or deteriorating ecosystems, restore them, improve the provision of ecosystem services, and achieve harmonious coexistence between humans and nature. Implementing ecological restoration projects leads to continuous changes in land use/land cover. Studying the long-term changes in land use/land cover and their impacts on ecosystem services, as well as the trade-off and synergy between these services, helps evaluate the long-term effectiveness of ecological restoration projects in restoring ecosystems. Therefore, this study analyzes the land use/land cover, and ecosystem services of the Hainan Tropical Forest Park in China to address this. Since 2000, the area has undergone multiple ecological restoration projects, divided roughly into two stages: 2003-2013 and 2013-2021. The InVEST model is used to quantify three essential ecosystem services in mountainous regions (water yield, carbon storage, and soil conservation), and redundancy analysis identifies the primary driving factors influencing their changes. We conducted spatial autocorrelation analysis to examine the interplay among ecosystem services under long-term land use/land cover change. The results indicate a decrease in the total supply of water yield (-5.14%) and carbon storage (-3.21%) in the first phase. However, the second phase shows an improvement in ecosystem services, with an increase in the total supply of water yield (11.45%), carbon storage (27.58%), and soil conservation (21.95%). The redundancy analysis results reveal that land use/land cover are the primary driving factors influencing the changes in ecosystem services. Furthermore, there is a shift in the trade-off and synergy between ecosystem services at different stages, with significant differences in spatial distribution. The findings of this study provide more spatially targeted suggestions for the restoration and management of tropical montane rainforests in the future.

Response of protists to nitrogen addition, arbuscular mycorrhizal fungi manipulation, and mesofauna reduction in a tropical montane rainforest in southern Ecuador.

The tropical Andes are a species-rich and nitrogen-limited system, susceptible to increased nitrogen (N) inputs from the atmosphere. However, our understanding of the impacts of increased N input on belowground systems, in particular on protists and their role in nutrient cycling, remains limited. We explored how increased N affects protists in tropical montane rainforests in Ecuador using high-throughput sequencing (HTS) of environmental DNA from two litter layers. In addition, we manipulated the amount of arbuscular mycorrhizal fungi (AMF) and mesofauna, both playing a significant role in N cycling and interacting in complex ways with protist communities. We found that N strongly affected protist community composition in both layers, while mesofauna reduction had a stronger effect on the lower layer. Changes in concentration of the AMF marker lipid had little effect on protists. In both layers, the addition of N increased phagotrophs and animal parasites and decreased plant parasites, while mixotrophs decreased in the upper layer but increased in the lower layer. In the upper layer with higher AMF concentration, mixotrophs decreased, while in the lower layer, photoautotrophs increased and plant parasites decreased. With reduced mesofauna, phagotrophs increased and animal parasites decreased in both layers, while plant parasites increased only in the upper layer. The findings indicate that to understand the intricate response of protist communities to environmental changes, it is critical to thoroughly analyze these communities across litter and soil layers, and to include HTS.

Burn severity and proximity to undisturbed forest drive post-fire recovery in the tropical montane forests of northern Vietnam

BackgroundIn recent decades, fire has increasingly occurred in the tropical montane rainforests of northern Vietnam. However, there are few studies of the effects of fire on forest composition and recovery in this region, and understanding these effects is critical for effective forest fire management and conservation. Forest plant species richness, structure (density, basal area), and composition were quantified for 133 forest plots randomly located in unburned (> 20 years since last fire) and recently burned (3–9 years since fire) vegetation associated with ten selected wildfires in three provinces of northern Vietnam where fires since 2000 were most frequent. Linear mixed effect models and nonmetric multidimensional scaling (NMDS) ordination were used to explore the structure, richness, and composition of burned and unburned forests and their environmental drivers, and to explore the key drivers of regeneration patterns in burned forest, including time since fire occurrence, fire severity, and distance to unburned forest edge.ResultsTotal species richness and diversity, tree species richness, tree density, and basal area were higher in unburned (vs. burned) forest plots, low (vs. high) severity burn areas, near (vs. far) from the closest unburned forest edge, and longer (vs. shorter) time since last fire. Results suggest that while burned forests were recovering on a trajectory back towards unburned forest composition, recovery was likely to be markedly slowed where fires were large (distance from edge effects) and/or of high severity, and forests may shift towards a different state (i.e., composition and structure) where more than one fire affects the same area over short time intervals.ConclusionsThis study provides insights into the effects of fire and other environmental factors on forest composition and recovery in the tropical montane forests of northern Vietnam, crucial for informing policymakers involved in forest conservation and management.

Nitrogen-Fixing Plants Enhance and Stabilize Rhizospheric Soil Organic Carbon in Tropical Rainforests, Hainan Island, China

Abstract Nitrogen (N)-fixing plants play an important role in stimulating soil nitrogen supply, but the effect of N-fixing plants on soil organic carbon (SOC) sequestration has not been well documented. In this study, we measured rhizospheric carbon components and N content of first to second (1–2)-order and third to fifth (3–5)-order roots of N-fixing and non-N-fixing plants in a montane tropical rainforest in Hainan Island, China, to examine the effects of N-fixing plants on SOC and soil heavy fraction carbon (HFC), and to ascertain the main regulating factors. The results showed that rhizospheric SOC between (1–2) and (3–5)-order roots was 14.2% and 10.5% greater, respectively, for N-fixing plants compared with non-N-fixing plants. Similarly, the HFC was 0.9% (1–2) and 3.6% (3–5) greater for N-fixing plants than non-N-fixing plants. Redundancy analysis showed that spatial variance in rhizospheric SOC and HFC associated with 1–2-order roots was explained by specific root length (SRL) of second-order roots (55.8%) and specific leaf area (SLA) (14.6%), whereas spatial variance was better explained for 3–5 roots by total soil N (44.6%), diameter of fifth-order roots (16.4%), and leaf C (17.9%), respectively. Within the rhizospheric soil of 1–2 roots, N-fixing plants with smaller SRL of second-order roots presented greater SOC and HFC, whereas smaller SLA was associated with greater HFC. By contrast, rhizospheric soil of 3–5 roots under N-fixing plants had greater SOC and HFC levels in environments with higher total soil N and smaller diameters of fifth-order roots. Our study revealed that N-fixing plants enhanced rhizospheric SOC and HFC compared with non-N-fixing plants. The rhizospheric SOC and HFC were correlated strongly by root morphology traits, leaf morphology, and soil properties. Study Implications: In this article, we compared rhizospheric soil of N-fixing and non-N-fixing species in a montane tropical rainforest in Hainan Island, China, to examine the effects of N-fixing plants on SOC and HFC. Our results suggest the N-fixing plants enhance and stabilize rhizospheric SOC and HFC; rhizospheric SOC and HFC for first- to second-order roots of N-fixing plants were mostly negatively regulated by SRL of second-order roots; and N-fixing plants had positive effects on rhizospheric SOC and HFC for third- to fifth-order roots through increased soil N. Understanding these mechanisms could improve and accumulation of soil C sink in tropical areas.

Coffee Leaf Rust: Wreaking Havoc in Coffee Production Areas Across the Tropics

Abstract Coffee ( Coffea spp.) originates from the tropical montane rainforest understorey. In this shaded environment, the coffee plant has co-evolved with a wide array of pests and diseases. The fungal pathogen Hemileia vastatrix is the most notorious of all known coffee plant diseases. With a rich history rooted in colonial trade and power struggles, H. vastatrix has had its lion’s share of research and scrutiny by the plant pathology community. Though this disease was discovered more than 150 years ago, many unknowns concerning its spread and persistence across the tropics still exist today. Despite its relevance to coffee production, there is little global data that synthesizes the impact of this disease on coffee yield and plant health. Best practices for control of coffee leaf rust are contentious. Genetic resistance has been breaking down in cultivars across the coffee belt over the past decade. How can farmers best control outbreaks of the disease? Are these practices at odds with new trends and challenges in coffee farming (e.g. organic, biodiversity-friendly, agroforestry etc.). What are the future prospects of our global coffee supply under pressure from this rampant disease? All these questions are examined in this case study using pertinent literature sources and supplemented by coffee farmers or extension service providers in Latin America and Africa. Information © The Author 2023 Cover photo courtesy of the author.

Shaping of topography by topographically-controlled vegetation in tropical montane rainforest.

Topography is commonly viewed as a passive backdrop on which vegetation grows. Yet, in certain circumstances, a bidirectional feedback may develop between the control of topography and the spatial distribution of vegetation and landform development, because vegetation modulates the erosion of the land surface. Therefore, if reinforcing feedbacks are established between erosion and land cover distribution over timescales relevant to landform development, then the interactions between vegetation and topography may create distinctive landforms, shaped by vegetation. We expose here a strong correlation between the spatial distribution of vegetation, erosion rates, and topography at a characteristic length scale of 102-103m (mesoscale topography) in the Luquillo Experimental forest (LEF) of Puerto Rico. We use high-resolution LiDAR topography to characterize landforms, satellite images to classify the vegetation into forest types, and in-situ produced cosmogenic 10Be in the quartz extracted from soils and stream sediments to document spatial variations in soil erosion. The data document a strong correlation between forest type and topographic position (hilltop vs. valleys), and a correlation between topographic position and 10Be-derived erosion rates over 103-104 years. Erosion is faster in valleys, which are mostly covered by monocot Palm Forest, and slower on surrounding hills mostly covered by the dicot Palo Colorado Forest. Transition from one forest type to the next occurs across a break-in-slope that separates shallowly convex hilltops from deeply concave valleys (coves). The break-in-slope is the consequence of a longer-lasting erosional imbalance whereby coves erode faster than hills over landscape-shaping timescales. Such a deepening of the coves is usually spurred by external drivers, but such drivers are here absent. This implies that cove erosion is driven by a process originating within the coves themselves. We propose that vegetation is the primary driver of this imbalance, soil erosion being faster under Palm forest than under Palo Colorado forest. Concentration of the Palm forest in the deepening coves is reinforced by the better adaptation of Palm trees to the erosive processes that take place in the coves, once these develop steep slopes. At the current rate of landscape development, we find that the imbalance started within the past 0.1-1.5 My. The initiation of the process could correspond to time of settlement of these mountain slopes by the Palm and Palo Colorado forests.

Spatial heterogeneity and influence mechanisms on soil respiration in an old-growth tropical montane rainforest with complex terrain

IntroductionAlthough numerous studies have investigated ecosystem-scale soil respiration (SR) at different ecosystem, our understanding of spatial heterogeneity of SR at plot scale is still incomplete, especially in tropical rainforests with complex topography. Further, the ecological factors that drive the variability of SR in tropical rainforests is also poorly understood.MethodsHere, we investigated the spatial variations and control mechanisms of SR in a 60-ha plot of old-growth tropical rainforest with complex topography. Specifically, we sampled a 60-ha plot in intervals of 20 m to measure SR with LI-8100, used semi-variogram of geostatistical tools to examine spatial heterogeneity of SR.ResultsThe mean SR rate in this plot was 4.312 ± 0.0410 (SE) μmol m−2 s−1. Geostatistical analysis indicated that the SR rate at this plot had a moderate spatial dependence, with a nugget-to-sill ratio of 68.1%. The coefficients variance of SR was 36.2% and the patch size was approximately 112 m. Stepwise linear regression analysis (involving a multiple regression tree) revealed that the independent factors regulated different types of SR’s. Liner mix-effect models showed that SR was significantly positively related to soil phosphorus and negatively to the slope in the 60-ha plot. Spatial disturbance of SR along multidimensional habitats that an increase in elevation of the multidimensional habitat, which was accompanied by enhanced SOC and soil phosphorous, also increased its SR in the 60-ha plot.DiscussionThis study would be helpful in designing future field experiments for a better understanding of SR at plot scale.

Does Forest Soil Fungal Community Respond to Short-Term Simulated Nitrogen Deposition in Different Forests in Eastern China?

Nitrogen (N) deposition has changed plants and soil microbes remarkably, which deeply alters the structures and functions of terrestrial ecosystems. However, how forest fungal diversity, community compositions, and their potential functions respond to N deposition is still lacking in exploration at a large scale. In this study, we conducted a short-term (4-5 years) experiment of artificial N addition to simulated N deposition in five typical forest ecosystems across eastern China, which includes tropical montane rainforest, subtropical evergreen broadleaved forest, temperate deciduous broadleaved forest, temperate broadleaved and conifer mixed forest, and boreal forest along a latitudinal gradient from tropical to cold temperature zones. Fungal compositions were identified using high-throughput sequencing at the topsoil layer. The results showed that fungal diversity and fungal community compositions among forests varied apparently for both unfertilized and fertilized soils. Generally, soil fungal diversity, communities, and their potential functions responded sluggishly to short-term N addition, whereas the fungal Shannon index was increased in the tropical forest. In addition, environmental heterogeneity explained most of the variation among fungal communities along the latitudinal gradient. Specifically, soil C: N ratio and soil water content were the most important factors driving fungal diversity, whereas mean annual temperature and microbial nutrient limitation mainly shaped fungal community structure and functional compositions. Topsoil fungal communities in eastern forest ecosystems in China were more sensitive to environmental heterogeneity rather than short-term N addition. Our study further emphasized the importance of simultaneously evaluating soil fungal communities in different forest types in response to atmospheric N deposition.