Tropical Forest Floor Research Articles

Application of Infrared Spectroscopy in the Identification of Fallen Trees from the Amazon Rainforest (Myristicaceae)

Abstract The infrared spectrum carries the so-called fingerprint of a plant, a characteristic that can help the identification of wood from an integrative perspective. Fourier-transform near-infrared spectroscopy (FT-NIRS) was evaluated for its potential use in the taxonomic identification of natural fallen trees from the Amazon rainforest (Myristicaceae). Trees found on the forest floor (Amazonas, Brazil) were surveyed, and eight individuals were selected for the study. The material was removed from the trunk for anatomical identification based on xylem structure and obtaining NIR spectra (10,000 to 4,000 cm-1). A total of 1,080 spectra were collected and used in the multivariate analysis. Absorption bands in the NIR region and chemometrics (calibration models) were used to interpret the spectra, which indicated similarity trends at the genus and species levels. Linear discriminant analysis (LDA) was able to differentiate Iryanthera ulei and Virola (five species), which were misclassified in the field as a single species (Virola sp.). The accuracy of the results obtained by chemometric models (LDA 7 and 14) indicates the robustness of NIR spectroscopy, which can be used as a new tool in the integrative taxonomy of plant material from tropical forests that are difficult to identify and can analyzing many tests quickly and securely. Study Implications: The taxonomic identification of natural fallen trees found on the floor of tropical forests is quite complex given the lack of flowers, fruits, and leaves in field collection. Fourier-transform near-infrared spectroscopy demonstrated its capability to distinguish between wood samples from fallen trees belonging to the Myristicaceae family. The chemometric model successfully discriminated the samples, which had been erroneously lumped together in the field under the single species designation of Virola sp. This technique has been previously overlooked for providing differentiation. Our study highlights its efficacy to address misclassifications and allow taxonomic identification.

Tropical forest mammal occupancy and functional diversity increase with microhabitat surface area.

Many animal-environment interactions are mediated by the physical forms of the environment, especially in tropical forests, where habitats are structurally complex and highly diverse. Higher structural complexity, measured as habitat surface area, may provide increased resource availability for animals, leading to higher animal diversity. Greater habitat surface area supports increased animal diversity in other systems, such as coral reefs and forest canopies, but it is uncertain how this relationship translates to communities of highly mobile, terrestrial mammal species inhabiting forest floors. We tested the relative importance of forest floor habitat structure, encompassing vegetation and topographic structure, in determining species occupancy and functional diversity of medium to large mammals using data from a tropical forest in the Udzungwa Mountains of Tanzania. We related species occupancies and diversity obtained from a multispecies occupancy model with ground-level habitat structure measurements obtained from a novel head-mounted active remote sensing device, the Microsoft HoloLens. We found that habitat surface area was a significant predictor of mean species occupancy and had a significant positive relationship with functional dispersion. The positive relationships indicate that surface area of tropical forest floors may play an important role in promoting mammal occupancy and functional diversity at the microhabitat scale. In particular, habitat surface area had higher mean effects on occupancy for carnivorous and social species. These results support a habitat surface area-diversity relationship on tropical forest floors for mammals.

Deposition and Re-Emission of Atmospheric Elemental Mercury over the Tropical Forest Floor.

Significant knowledge gaps exist regarding the emission of elemental mercury (Hg0) from the tropical forest floor, which limit our understanding of the Hg mass budget in forest ecosystems. In this study, biogeochemical processes of Hg0 deposition to and evasion from soil in a Chinese tropical rainforest were investigated using Hg stable isotopic techniques. Our results showed a mean air-soil flux as deposition of -4.5 ± 2.1 ng m-2 h-1 in the dry season and as emission of +7.4 ± 1.2 ng m-2 h-1 in the rainy season. Hg re-emission, i.e., soil legacy Hg evasion, induces negative transitions of Δ199Hg and δ202Hg in the evaded Hg0 vapor, while direct atmospheric Hg0 deposition does not exhibit isotopic fractionation. Using an isotopic mass balance model, direct atmospheric Hg0 deposition to soil was estimated to be 48.6 ± 13.0 μg m-2 year-1. Soil Hg0 re-emission was estimated to be 69.5 ± 10.6 μg m-2 year-1, of which 63.0 ± 9.3 μg m-2 year-1 is from surface soil evasion and 6.5 ± 5.0 μg m-2 year-1 from soil pore gas diffusion. Combined with litterfall Hg deposition (∼34 μg m-2 year-1), we estimated a ∼12.6 μg m-2 year-1 net Hg0 sink in the tropical forest. The fast nutrient cycles in the tropical rainforests lead to a strong Hg0 re-emission and therefore a relatively weaker atmospheric Hg0 sink.

Monoterpenes from tropical forest and oil palm plantation floor in Malaysian Borneo/Sabah: emission and composition.

Regional estimates of VOC fluxes focus largely on emissions from the canopy and omit potential contributions from the forest floor including soil, litter and understorey vegetation. Here, we measured monoterpene emissions every 2 months over 2 years from logged tropical forest and oil palm plantation floor in Malaysian Borneo using static flux chambers. The main emitted monoterpenes were α-pinene, β-pinene and d-limonene. The amount of litter present was the strongest indicator for higher monoterpene fluxes. Mean α-pinene fluxes were around 2.5-3.5 μg C m-2 h-1 from the forest floor with occasional fluxes exceeding 100 μg C m-2 h-1. Fluxes from the oil palm plantation, where hardly any litter was present, were lower (on average 0.5-2.9 μg C m-2 h-1) and only higher when litter was present. All other measured monoterpenes were emitted at lower rates. No seasonal trends could be identified for all monoterpenes and mean fluxes from both forest and plantation floor were ~ 100 times smaller than canopy emission rates reported in the literature. Occasional spikes of higher emissions from the forest floor, however, warrant further investigation in terms of underlying processes and their contribution to regional scale atmospheric fluxes.

Increase in abundance and decrease in richness of soil microbes following Hurricane Otto in three primary forest types in the Northern Zone of Costa Rica.

Little is known of how hurricane-induced deposition of canopy material onto tropical forest floors influences the soil microbial communities involved in decomposition of these materials. In this study, to identify how soil bacterial and fungal communities might change after a hurricane, and their possible roles in the C and N cycles, soils were collected from five 2000 m2 permanent plots in Lowland, Upland and Riparian primary forests in Costa Rica 3 months before and 7 months after Hurricane Otto damaged the forests. The soil Water, inorganic N and Biomass C increased and total organic C decreased Post-Hurricane, all of which best predicted the changes in the Post-Hurricane soil microbial communities. Post-Hurricane soils from all forest types showed significant changes in community composition of total bacteria, total fungi, and five functional groups of microbes (i.e., degrading/lignin degrading, NH4+-producing, and ammonium oxidizing bacteria, and the complex C degrading/wood rot/lignin degrading and ectomycorrhizal fungi), along with a decrease in richness in genera of all groups. As well, the mean proportion of DNA sequences (MPS) of all five functional groups increased. There were also significant changes in the MPS values of 7 different fungal and 7 different bacterial genera that were part of these functional groups. This is the first evidence that hurricane-induced deposition of canopy material is stimulating changes in the soil microbial communities after the hurricane, involving changes in specific taxonomic and functional group genera, and reduction in the community richness while selecting for dominant genera possibly better suited to process the canopy material. These changes may represent examples of taxonomic switching of functionally redundant microbial genera in response to dramatic changes in resource input. It is possible that differences in these microbial communities and genera may serve as indicators of disturbed and recovering regional soil ecosystems, and should be evaluated in the future.

Tropical understory herbaceous community responds more strongly to hurricane disturbance than to experimental warming.

The effects of climate change on tropical forests may have global consequences due to the forests’ high biodiversity and major role in the global carbon cycle. In this study, we document the effects of experimental warming on the abundance and composition of a tropical forest floor herbaceous plant community in the Luquillo Experimental Forest, Puerto Rico. This study was conducted within Tropical Responses to Altered Climate Experiment (TRACE) plots, which use infrared heaters under free‐air, open‐field conditions, to warm understory vegetation and soils + 4°C above nearby control plots. Hurricanes Irma and María damaged the heating infrastructure in the second year of warming, therefore, the study included one pretreatment year, one year of warming, and one year of hurricane response with no warming. We measured percent leaf cover of individual herbaceous species, fern population dynamics, and species richness and diversity within three warmed and three control plots. Results showed that one year of experimental warming did not significantly affect the cover of individual herbaceous species, fern population dynamics, species richness, or species diversity. In contrast, herbaceous cover increased from 20% to 70%, bare ground decreased from 70% to 6%, and species composition shifted pre to posthurricane. The negligible effects of warming may have been due to the short duration of the warming treatment or an understory that is somewhat resistant to higher temperatures. Our results suggest that climate extremes that are predicted to increase with climate change, such as hurricanes and droughts, may cause more abrupt changes in tropical forest understories than longer‐term sustained warming.

<p><strong>Six new species of<em> Tetrapyrgos</em> (Basidiomycota, Agaricales, Marasmiaceae) from the Brazilian Amazon</strong></p>

Tetrapyrgos is characterized by small basidiomata which have a mostly whitish pileus, a well-defined central or eccentric, mostly dark greyish stipe, a non- or very weakly gelatinous pileipellis and pileus tramal tissues; the pileipellis is composed of Rameales-like structures, and the basidiospores are distinctly tetrahedral. Members of this genus are commonly found on dead leaves and woody debris on the floor of tropical and subtropical forests. Recent studies suggest changes in the circumscription of Tetrapyrgos and Campanella Still poorly documented, to date, only about 18 species have been assigned to Tetrapyrgos. Through integrative taxonomy, we describe six new species from the Brazilian Amazon, based on evidence from morphological and ITS data. Tetrapyrgos longicystidiata is formally synonymized in T. atrocyanea.

Activity patterns of terrestrial frugivorous mammals in a Mexican Neotropical forest

Fruits reaching the floor of tropical forests constitute an attractive resource for a variety of mammals. Study of the characteristics of the frugivory interaction can help to advance in the understanding of the mechanisms favoring animal’s coexistence. However, there are few studies focused on analyzing patterns of activity of mammals feeding on fruits in the forest floor. Camera traps were used to record consumption of Licania platypus and Pouteria sapota fruits by Cuniculus paca, Dasyprocta punctata, Nasua narica, Dycotiles crassus and Tapirella bairdii. Patterns of mammal activity were characterized based on the day, time and tree in which they were recorded. Overlap in daily (delta coefficient) and spatial occurrence (same tree and day, Jaccard, Ochiai indices and V ratio) was assessed. High segregation in the activity of frugivores occurred during the day (mean 0.291 and 0.191 for L. platypus and P. sapota, respectively) and among trees/days (max. Jaccard = 0.14 and 0.19 for L. platypus and P. sapota, respectively). Our results suggest that activity overlap among mammalian frugivores feeding in the forest floor is lower than expected. This likely relates to the fact we conducted our analysis at a finer detail than previous studies (for example those focusing exclusively on dietary overlap). Thus, our study increases our understanding of the possible factor that can favor coexistence of tropical frugivorous mammals.

Automated tracking and analysis of ant trajectories shows variation in forager exploration

Determining how ant colonies optimize foraging while mitigating pathogen and predator risks provides insight into how the ants have achieved ecological success. Ants must respond to changing resource conditions, but exploration comes at a cost of higher potential exposure to threats. Fungal infected cadavers surround the main foraging trails of the carpenter ant Camponotus rufipes, offering a system to study how foragers behave given the persistent occurrence of disease threats. Studies on social insect foraging behavior typically require many hours of human labor due to the high density of individuals. To overcome this, we developed deep learning based computer vision algorithms to track foraging ants, frame-by-frame, from video footage shot under the natural conditions of a tropical forest floor at night. We found that most foragers walk in straight lines overlapping the same areas as other ants, but there is a subset of foragers with greater exploration. Consistency in walking behavior may protect most ants from infection, while foragers that explore unique portions of the trail may be more likely to encounter fungal spores implying a trade-off between resource discovery and risk avoidance.

Discovery of a specialist Copelatinae fauna on Madagascar: highly ephemeral tropical forest floor depressions as an overlooked habitat for diving beetles (Coleoptera, Dytiscidae).

Diving beetles are generally aquatic and live submerged in water during larval and adult stages. A few groups have colonised hygropetric habitats and fewer species still can possibly be referred to as terrestrial. Here we describe six new Copelatine species that were mainly found in dry shallow forest floor depressions in the eastern and northeastern lowland humid forests of Madagascar. Three new species are described in each of the two genera Copelatus and Madaglymbus: Copelatus amphibiussp. nov., Copelatus betamponasp. nov., Copelatus zanatanensissp. nov., Madaglymbus kelimasosp. nov., Madaglymbus menalambasp. nov., and Madaglymbus semifactussp. nov. Diagnosis, description, known distribution, ecology, and conservation notes are provided for each species. All species are illustrated with a dorsal habitus image, ventral and lateral views of the male penis, and parameres. Photographs of the unusual terrestrial habitats where the species were found are provided. Madaglymbus menalambasp. nov. is also documented with macrophotos and videorecordings of the terrestrial locomotion and behaviour in the field. Although these species should not be classified as terrestrial, or even semi-terrestrial Dytiscidae, they seem to be specialists of very ephemeral aquatic habitats and stay put instead of disperse when the habitat dries up. It is hypothesised that this lifestyle and behaviour on Madagascar is restricted to the high-precipitation humid forest regions mainly in the east. It may also represent a transition step, or stepping-stone, towards becoming fully terrestrial, a step that the few known terrestrial Dytiscid taxa once passed through. It is very likely that this type of habitat is overlooked for aquatic beetles, not only in Madagascar, and the six species herein described may be just the “tip of the iceberg”.

Singing mice take turns talking

![Graphic][1] As the northern winter silence melts, spring greets us with its familiar choir of birds chirruping in the tree tops. Yet, beneath the trees on the floor of Costa Rica's tropical cloud forests, the year-round sound of animal chatter never dies down. Alston's singing mice (

Convergence of ecophysiological traits drives floristic composition of early lineage vascular plants in a tropical forest floor.

Tropical understorey plant communities are highly diverse and characterized by variable resource availability, especially light. Plants in these competitive environments must carefully partition resources to ensure ecological and evolutionary success. One mechanism of effective resource partitioning is the optimization of functional traits to enhance competition in highly heterogeneous habitats. Here, we surveyed the ecophysiology of two early lineage vascular plant groups from a tropical forest understorey: Selaginella (a diverse lineage of lycophytes) and ferns. In a lowland rain forest in Costa Rica, we measured a suite of functional traits from seven species of Selaginella and six fern species. We evaluated species microclimate and habitat; several photosynthetic parameters; carbon, nitrogen and phosphorus content; chlorophyll concentration; leaf mass per area (LMA); and stomatal size and density. We then compare these two plant lineages and search for relationships between key functional parameters that already exist on a global scale for angiosperms. Convergence of trait function filtered Selaginella species into different habitats, with species in heavily shaded environments having higher chlorophyll concentrations and lower light compensation points compared with open habitats. Alternatively, lower foliar nitrogen and higher stomatal densities were detected in species occupying these open habitats. Selaginella species had denser and smaller stomata, lower LMA and lower foliar nutrient content than ferns, revealing how these plant groups optimize ecophysiological function differently in tropical forest floors. Our findings add key pieces of missing evidence to global explorations of trait patterns that define vascular plant form and function, which largely focus on seed plants. Broadly predictable functional trait relationships were detected across both Selaginella and ferns, similar to those of seed plants. However, evolutionary canalization of microphyll leaf development appears to have driven contrasting, yet successful, ecophysiological strategies for two coexisting lineages of extant homosporous vascular plants.

Review: Diversity of soil organisms and their relationship with diversity of plant species in tropical rainforest of Pinang-Pinang Padang, Indonesia

Marsandi F, Hermansah, Agustian, Yasin S. 2017. Review: Diversity of soil organisms and their relationship with diversity of plant species in tropical rainforest of Pinang-Pinang Padang, Indonesia. Pros Sem Nas Masy Biodiv Indon 3: 309-318. Tropical rain forests are the Earth's richest biological community as holder of an important role in maintaining the proportion of global biodiversity. These forests provide many ecosystem services in order fulfillment of human well-being. Land as a tropical rain forest floor also has an important role in maintaining ecological sustainability in the forest, where many living creatures that have direct or indirect dependency on the ground. This causes the soil is a medium that can provide nutrients for living things in it. The tropical rain forest of PinanangPinang (Padang, West Sumatra, Indonesia) has high diversity of tree and varied so that it becomes an attraction for scientists to conduct research. Researchers have grouped of Pinang-Pinang plots into three categories according to the degree of diversity of tree species, namely the high diversity, middle diversity and low diversity. The results of previous research on the plot state that Pinang-Pinang plot with a high degree of diversity of trees has the infertile soil and vice versa. Such phenomena are affected by plant group hyperaccumulator. So as to ensure the necessary study of soil organisms (microbes and soil fauna) as well as its relation to the diversity of species of tropical rainforest tree at Pinang-Pinang plot, West Sumatra, Indonesia.

Busy Nights: High Seed Dispersal by Crickets in a Neotropical Forest.

Among invertebrates, ants are the most abundant and probably most important seed dispersers in both temperate and tropical environments. Crickets, also abundant in tropical forests, are omnivores and commonly attracted to fruits on the forest floor. However, their capability to remove seeds has been reported only once. We compared Marantaceae seed removal by crickets and ants to assess the role of crickets as secondary seed dispersers in Amazonia. Compared with ants, crickets dispersed an equivalent number of seeds and tended to disperse larger seeds farther. However, seed removal by crickets occurs mostly at night, suggesting that removal of arillate seeds by crickets on the tropical forest floor is probably being overlooked or wrongly attributed to other invertebrate groups. One potential consequence of seed dispersal by crickets may be a change in the local spatial distribution of arillate-seed species, due to lower aggregation around ant nests.

Functional redundancy dampens the trophic cascade effect of a web-building spider in a tropical forest floor

The trophic cascade effect of predators on ecosystem functioning is generally believed to be less frequent and weaker in detritus-based than primary producer-based food webs, in part because of functional redundancy among soil fauna. Despite this view, no empirical studies have explicitly examined roles of different soil fauna within trophic levels in mediating cascading effects of predators in detritus food webs. Here we manipulated the density of a dominant funnel-web building spider Macrothele yunnanica in permanent plots (1 m2) for one year. Three spider treatments were applied: 0 spiders, 6 spiders (natural density) and 10 spiders (high density). We found that although changes in spider densities caused large shifts in litter-dwelling Collembola community composition on average, modifying spider densities did not generate a trophic cascade effect and alter litter decomposition in litter bags with coarse mesh (2 mm). Our data supports the hypothesis that functional redundancy among Collembola species may weaken the strength of spider-initiated cascading effects. Consequently, changes in Collembola diversity occupying the same trophic level may not significantly alter ecosystem function in tropical forest-floor ecosystems.

Cascading effects of spiders on a forest-floor food web in the face of environmental change

Spiders have cascading effects on forest-floor food webs and ecosystem processes by depressing soil fauna densities and altering species composition. However, it remains unclear how spiders with different foraging strategies influence cascading effects on decomposition. In addition, prolonged droughts would likely have important consequences for trophic interactions in detritus-based food webs. In the present study, we evaluated how interactions between spider predation and drought affect litter decomposition in a tropical forest floor. We manipulated densities of dominant spiders with actively hunting or sit-and-wait foraging strategies in microcosms which mimicked the tropical-forest floor. We found a positive trophic cascade on litter decomposition rates triggered by actively hunting spiders under ambient and reduced moisture. However, sit-and-wait spiders showed no cascading effects on litter decomposition under ambient and drought conditions. Our findings suggest that trophic interactions in detritus-based food webs should be considered to better understand litter decomposition in the face of environmental change.

Spider foraging strategy affects trophic cascades under natural and drought conditions.

Spiders can cause trophic cascades affecting litter decomposition rates. However, it remains unclear how spiders with different foraging strategies influence faunal communities, or present cascading effects on decomposition. Furthermore, increased dry periods predicted in future climates will likely have important consequences for trophic interactions in detritus-based food webs. We investigated independent and interactive effects of spider predation and drought on litter decomposition in a tropical forest floor. We manipulated densities of dominant spiders with actively hunting or sit-and-wait foraging strategies in microcosms which mimicked the tropical-forest floor. We found a positive trophic cascade on litter decomposition was triggered by actively hunting spiders under ambient rainfall, but sit-and-wait spiders did not cause this. The drought treatment reversed the effect of actively hunting spiders on litter decomposition. Under drought conditions, we observed negative trophic cascade effects on litter decomposition in all three spider treatments. Thus, reduced rainfall can alter predator-induced indirect effects on lower trophic levels and ecosystem processes, and is an example of how such changes may alter trophic cascades in detritus-based webs of tropical forests.

Trophic cascade of a web-building spider decreases litter decomposition in a tropical forest floor

Trophic cascade effects on detritus-based food webs of forest floor have the potential to alter ecosystem functioning, but due to the complexity of detrital food web no general pattern of cascading effects has emerged. The goal of this study was to evaluate trophic cascade effects of a dominant funnel-web building spider on leaf-litter decomposition rate and microbial biomass in a tropical forest floor. We manipulated the density of a dominant funnel-web building spider Macrothele yunnanica in permanent plots (1 m2) for one year. Three spider treatments were applied: 0 spider, 6 spiders (natural density) and 10 spiders (high density). We found that the high density of M. yunnanica led to significant negative cascading effects on litter decomposition rate, which is probably due to decreased density of one dominant collembolan, Entomobrya, in the litter layer. We detected no cascading effects from the natural density of M. yunnanica, and changes in spider densities had no cascading effects on microbial biomass. Modifying spider densities can generate a trophic cascade effect and alter leaf litter decomposition, with a potential to influence ecosystem function in tropical forest floors. This study suggests that trophic interactions in detritus-based food webs should be considered to better understand soil organic matter dynamics in tropical forests.

Free-living nitrogen fixation responds to elevated nutrient inputs in tropical montane forest floor and canopy soils of southern Ecuador

Although often overlooked in forest research, the canopy can play an important role in forest nutrient cycling. Since the canopy is spatially isolated from the forest floor, nutrient cycling in the two areas may differ as terrestrial nutrients accumulate. We measured rates of free-living N2 fixation along an elevation gradient (1,000, 2,000 and 3,000 m) of tropical montane canopy soils, compared these to rates measured in the top 5 cm of forest floor soils (excluding fresh litter), and assessed the effects of elevated nutrient inputs to the forest floor. N2 fixation was measured using the acetylene reduction assay. Measurements occurred in the field, in the wet and dry seasons, using intact cores of soil. The forest floor had been fertilized biannually with moderate amounts of nitrogen (N) and phosphorus (P) for 4 years; treatments included control, N, P and N + P. N2 fixation rates exhibited little variation with elevation but were higher in the dry season than the wet season. Fixation was inhibited in forest floor N plots compared to control and P plots, and stimulated in canopy P plots compared to control. At 2,000 m, the canopy contributed 12 % of measured canopy and forest floor N2 fixation (1.2 kg N ha−1 year−1). Results suggest that N2 fixation is an active process in canopy soils, which is variable across seasons and sensitive to changes in terrestrial nutrient availability. Long-term terrestrial accumulation of N and/or P has the potential to significantly change the dynamics of soil N cycling in these canopies.

Phylogenomics, molecular evolution, and estimated ages of lineages from the deep phylogeny of Poaceae

The deeply diverging subfamilies of grasses: Anomochlooideae, Pharoideae, and Puelioideae, today inhabit tropical forest floors as sparsely distributed depauperate lineages. The BEP/PACMAD grasses, which make up the majority of the family, are the result of a more recent radiation. Species in the deeply diverging subfamilies were here investigated to better understand molecular evolutionary processes and ages of divergence. Complete chloroplast genomes (plastomes) of Pharus latifolius L., P. lappulaceus Aubl., and Puelia olyriformis (Franch.) Clayton were determined. Four plastome loci from seven species of the deep subfamilies were also sequenced. Phylogenetic and mutation analyses and divergence estimations were conducted on all sequences together with homologous sequences from other Poaceae. Mutation analyses surveyed insertion/deletion mutations across the plastomes, clarified a trend in the molecular evolution of the rpoC2 locus, and indicated unique pseudogenizations in the plastomes of Pharus and Puelia. Phylogenetic analyses largely confirmed earlier multi-gene phylogenies. Phylogenomic and divergence analyses produced estimated origins of the crown nodes of Anomochlooideae at 65–104 Ma, Pharoideae at 44–71 Ma, and Puelioideae at 62–96 Ma. The upper ends of our estimated ranges are in general agreement with previous estimates. However, the lower ends of our ranges are considerably older than previous estimates, reflecting the influence of the less commonly used oldest fossil calibration point. The deeply diverging subfamilies exhibited the accumulation of numerous substitution and indel mutations consistent with a long evolutionary history that predated the radiation of the BEP/PACMAD grasses. We hypothesize that relatively rapid warming and drying in Africa at 55–56.5 Ma may have acted as selective forces stimulating adaptive radiations of grasses from the African tropical forests into diverse habitats.