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Tropical forests are incredibly diverse in structure and function. Despite, or perhaps because of, this diversity, tropical biologists often conduct research exclusively in one or perhaps a few forest types. Rarely do we study the ecotone—the interstitial region between forest types. Ecotones are hyper-diverse, dynamic systems that control the flow of energy and organisms between adjacent ecosystems, with their locations determined by species' physiological limits. In this review, we describe how studying ecotones can provide key indicators for monitoring the state of Neotropical forests from organisms to ecosystems. We first describe how ecotones have been studied in the past and summarize our current understanding of tropical ecotones. Next, we provide three example lines of research focusing on the ecological and evolutionary dynamics of the ecotone between tropical dry forests and desert; between tropical dry and rainforests; and between Cerrado and Atlantic rainforests, with the latter being a particularly well-studied ecotone. Lastly, we outline methods and tools for studying ecotones that combine remote sensing, new statistical techniques, and field-based forest dynamics plot data, among others, for understanding these important systems. [ABSTRACT FROM AUTHOR]

New World monkeys (NWM) comprise a group of extant and extinct taxa exclusive to the Neotropics. Lineage dispersal modeling was employed to test the validity of previously reported biogeographic patterns in NWM. Specifically, this research sought to confirm whether the dispersal timings of these patterns were supported by the modeling results. Species geographic distributions of extant platyrrhines were used to obtain a bioregionalization scheme. A lineage dispersal model was constructed based on multiple-area range, likelihood inference of rate, and stochastic mapping under likelihood. Based on published phylogenies, ten trees were randomly sampled and, for each tree, ten stochastic mappings were simulated. Results were presented as event counts and averages across the 100 stochastic mappings, and the timings of the inferred dispersal routes were compared to the timings of 12 biogeographic pattern hypotheses gathered from the literature. The modeling analysis provided directional and temporal support for eleven of the twelve patterns. Lineages most frequently dispersed from Western Amazonia towards other bioregions. For four dispersal routes, events initiated earlier than previously reported. The Western Amazonia bioregion served as both the ancestral area and primary source of platyrrhine lineages. Analyses revealed a novel biogeographic pattern, namely the “Amazonian eastward” dispersal route, which started in the Miocene epoch, during the establishment of the transcontinental Amazon River system, and lasted until recently in an increasing trend of dispersal rate. This route showed the greatest number of dispersal events during the macroevolution of NWM. [ABSTRACT FROM AUTHOR]

Tropical forests are incredibly diverse in structure and function. Despite, or perhaps because of, this diversity, tropical biologists often conduct research exclusively in one or perhaps a few forest types. Rarely do we study the ecotone—the interstitial region between forest types. Ecotones are hyper-diverse, dynamic systems that control the flow of energy and organisms between adjacent ecosystems, with their locations determined by species’ physiological limits. In this review, we describe how studying ecotones can provide key indicators for monitoring the state of Neotropical forests from organisms to ecosystems. We first describe how ecotones have been studied in the past and summarize our current understanding of tropical ecotones. Next, we provide three example lines of research focusing on the ecological and evolutionary dynamics of the ecotone between tropical dry forests and desert; between tropical dry and rainforests; and between Cerrado and Atlantic rainforests, with the latter being a particularly well-studied ecotone. Lastly, we outline methods and tools for studying ecotones that combine remote sensing, new statistical techniques, and field-based forest dynamics plot data, among others, for understanding these important systems.

Observations of the annual cycle of atmospheric CO2 in high northern latitudes provide evidence for an increase in terrestrial metabolism in Arctic tundra and boreal forest ecosystems. However, the mechanisms driving these changes are not yet fully understood. One proposed hypothesis is that ecological change from disturbance, such as wildfire, could increase the magnitude and change the phase of net ecosystem exchange through shifts in plant community composition. Yet, little quantitative work has evaluated this potential mechanism at a regional scale. Here we investigate how fire disturbance influences landscape‐level patterns of photosynthesis across western boreal North America. We use Alaska and Canadian large fire databases to identify the perimeters of wildfires, a Landsat‐derived land cover time series to characterize plant functional types (PFTs), and solar‐induced fluorescence (SIF) from the Orbiting Carbon Observatory‐2 (OCO‐2) as a proxy for photosynthesis. We analyze these datasets to characterize post‐fire changes in plant succession and photosynthetic activity using a space‐for‐time approach. We find that increases in herbaceous and sparse vegetation, shrub, and deciduous broadleaf forest PFTs during mid‐succession yield enhancements in SIF by 8–40% during June and July for 2‐ to 59‐year stands relative to pre‐fire controls. From the analysis of post‐fire land cover changes within individual ecoregions and modeling, we identify two mechanisms by which fires contribute to long‐term trends in SIF. First, increases in annual burning are shifting the stand age distribution, leading to increases in the abundance of shrubs and deciduous broadleaf forests that have considerably higher SIF during early‐ and mid‐summer. Second, fire appears to facilitate a long‐term shift from evergreen conifer to broadleaf deciduous forest in the Boreal Plain ecoregion. These findings suggest that increasing fire can contribute substantially to positive trends in seasonal CO2 exchange without a close coupling to long‐term increases in carbon storage. [ABSTRACT FROM AUTHOR]

Given accelerated dryland expansion, studies on aridity‐driven desertification are of great importance for advancing our understanding of land degradation mechanisms and developing possible mitigation measures. However, the mechanism by which increased aridity drives ecosystems toward desertification and the impacts of aridity on desertification vulnerability both in space and over time remain unclear. Here, we collected eight key ecosystem structure/functioning data (including soil, vegetation, and animal) for threshold identification using piecewise linear models, and then linked them to biome shifts to explore the process of aridity‐driven desertification. The results show that ecosystems along aridity index (AI, 1 − precipitation/potential evapotranspiration) gradients experience three vulnerable stages featuring different threshold and biome responses: a low vulnerability stage (AI: 0.5–0.65; mainly featuring a soil fertility loss and a forest decline), a moderate vulnerability stage (AI: 0.65–0.75; mainly featuring accelerated non‐forest vegetation degradation) and a high vulnerability stage (AI: 0.75–1; mainly featuring rapid overall land degradation). According to further simulations, areas with low to high vulnerability account for 31% of the global terrestrial area, which is projected to increase by 18.8% (21.2%) by the end of the 21st century under the greenhouse gas emission scenario SSP2‐4.5 (SSP3‐7.0). Given increased vulnerability and population growth, Africa and East Asia are exposed to great desertification risk and ensuing contradiction between humans and land. These findings can provide a theoretical and practical reference for ecosystem management and policy development, which are critical for dryland ecological security and human welfare in areas threatened by desertification. [ABSTRACT FROM AUTHOR]

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The persistent spread of shrublands is a global phenomenon observed across semiarid grassland-shrubland boundaries. Observations in South Africa, however, have detected a contrasting trend of increasing grass cover across the transition between the Nama-Karoo and Grassland Biomes over the last few decades. A west-to-east gradient of increasing mean annual rainfall, and underlying geology, controls the natural transition of Karoo dwarf shrublands to semiarid grasslands. The availability of historical vegetation surveys and landscape photographs, weather, and livestock census records, made it possible to assess the nature, extent, and drivers of vegetation change across this biome transition. Rainfall has been generally higher over the last four decades compared to the years prior to the original surveys. This, together with a reduction in livestock numbers, is the main driver of the westward expansion by ∼100 km of perennial grasses, and a general increase in dwarf shrub and total vegetation cover. Rangeland condition, as indexed by estimates of grazing capacity, has improved significantly. Despite a structural shift towards grassland-dominance, the original species complement has persisted. The rainfall-driven increase in grass fuel loads in the region, however, places these rangelands at risk of becoming altered by increasing fire frequency. [ABSTRACT FROM AUTHOR]

Where each species actually lives is distinct from where it could potentially survive and persist. This suggests that it may be important to distinguish established from enabled biome affinities when considering how ancestral species moved and evolved among major habitat types. We introduce a new phylogenetic method, called RFBS, to model how anagenetic and cladogenetic events cause established and enabled biome affinities (or, more generally, other discrete realized versus fundamental niche states) to shift over evolutionary timescale. We provide practical guidelines for how to assign established and enabled biome affinity states to extant taxa, using the flowering plant clade Viburnum as a case study. Through a battery of simulation experiments, we show that RFBS performs well, even when we have realistically imperfect knowledge of enabled biome affinities for most analyzed species. We also show that RFBS reliably discerns established from enabled affinities, with similar accuracy to standard competing models that ignore the existence of enabled biome affinities. Lastly, we apply RFBS to Viburnum to infer ancestral biomes throughout the tree and to highlight instances where repeated shifts between established affinities for warm and cold temperate forest biomes were enabled by a stable and slowly-evolving enabled affinity for both temperate biomes.

Rhytiphora Audinet-Serville, 1835 is the most speciose longhorn beetle (Cerambycidae Latreille, 1802) genus in Australia, with ~200 species (from nearly 40 former genera, now synonymised into one) distributed across the entire continent. We used mitochondrial genome data from whole genome shotgun sequencing and COI barcoding of museum specimens to reconstruct the phylogeny of 68 Rhytiphora species, and analysed the morphological diversity and biogeographic history. We recovered a monophyletic Rhytiphora containing two distinct clades, within which all of the former genera (except Achriotypa Pascoe, 1875) are paraphyletic. Nine morphological traits (including body size and the male setose 'sex patches') show strong phylogenetic signal and can be used to differentiate between the two clades. One clade is mainly restricted to Australia's tropical north, whereas the other, larger clade has many species along the mesic east coast. Both clades have experienced multiple biome shifts, displaying a remarkable flexibility in habitat occupancy. [ABSTRACT FROM AUTHOR]

Various facets of global changes and related problems and challenges are asking for sound impact assessments and corresponding coping strategies. The human impact on nature is a major driver of biodiversity loss and restricted ecosystem functioning and services. Assessing such global changes is often done by using biomes as benchmarks. However, even if the wording and terminology seem common sense ('tropical rain forest', 'steppe', 'boreal forest') global biome units and maps deviate in many ways. This is well justified by their individual intention, expert opinions, disciplinary background, and methodology of creation. A closer look reveals linkages between spatial accordance and common origin in climate classifications and maps. Their original influence, however, is rarely evident. In consequence, it is difficult if not impossible for users to realize and understand differences in these global maps. Furthermore, it is difficult to accept the fact that there is no common standard for global biomes. Even more surprising is the fact that some approaches are uncritically taken for common sense and are perpetuated over decades. This study aims to review established global biome concepts. Regions that are consistently assigned to comparable types of biomes shall be detected and also regions where ambiguity exists. For this purpose, we shortly review the history of existing concepts and the generic relations between them. Biomes, ecozones and climate classifications are considered. We digitized the most prominent biome classifications. Spatial match and mismatch between concepts were analyzed globally. We detect areas of spatial agreement and regions with ambiguous classifications. A clustering approach including 287 individual biomes originating from 12 established global biome concepts and their classifications/units revealed 12 terrestrial biome clusters among which 8 can be assigned to terrestrial ecological units. One cluster on ice caps adds to this. And finally, 3 clusters represent rather transition zones (ecotones), high mountain plateaus or are of minor areal extent. The spatial arrangement of these emerging clusters is displayed on a global map. Additionally, regions of uncertainty related to class assignment were identified. Those primarily occur in the vicinity of mountainous regions. The findings of this study should be seen as a work in progress and as a basis for further optimization of global biome concepts. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems respond to climate change in various ways, making it crucial to improve our understanding of these dynamics and uncertainty in projections. Here, we investigate how the species composition in a temperate-subtropical mixed forest on Jeju Island, South Korea, would change by 2099 and analysed the resultant effects on phenological timings and carbon flux using an individual cohort-based model—the ecosystem demography biosphere model version 2. We use the analyses of variance to decompose the contribution of model parameters (four sets) and climate inputs (four global climate models under four representative concentration pathway (RCP) scenarios) to the total uncertainty in the leaf area index (LAI) and net ecosystem productivity (NEP) projections. We find that with increases in temperature, photosynthetically active radiation, and vapour pressure deficit, the dominance of subtropical species will gradually increase by approximately 11%, from 30.2% in 2013 to 41.1% by the end of this century, yet there was a large variation in the projections depending on the model parameter and climate inputs. We also show the increases in the LAI and length of growing season by the end of this century, resulting in an increased NEP at the rate of up to 62.7 gC m ^−2 yr ^−1 per decade under the RCP8.5. The uncertainty in the LAI projection was largely due to the model parameter (and its interaction with climate inputs); however, the uncertainty contribution of climate models is as large as the emission scenario in the NEP projection. This study highlights the importance of identifying uncertainty sources for a robust projection of terrestrial ecosystem and carbon cycle.

Nama-Karoo vegetation is fire naïve and therefore vulnerable to transformation by fire. This study investigated the effect of fire, a novel disturbance, on the composition and structure of shrub communities in semi-arid Eastern Upper Karoo rangelands. Nine sites across a rainfall gradient had been burnt between eight years and six months before time of sampling, whose grazing history ranged from heavy or lenient to no grazing. Fire markedly changed the composition and structure of Karoo shrublands, the nature and extent of which depended on climate regime. Non-sprouting species, including some dominant species, were extirpated by fire and replaced by previously non-dominant sprouter species. Replacement of non-sprouter by sprouter species was conspicuous for palatable and unpalatable dwarf shrubs. Under conditions that closely resemble climate change forecasts for the region, fire transformed Nama-karoo shrublands. The possibility of larger more frequent fires in the Nama-Karoo threatens to transform the vegetation, ecosystem functioning, and economy of the region. Fire has emerged as a novel agent of vegetation change in the eastern Nama-Karoo owing to a directional increase in annual rainfall over the past three decades, that may cement a state change from shrubland to grassland in an ampliative, positive feedback manner. • Fire changes the composition of Nama-Karoo shrub communities. • The effect of Fire on Karoo shrub communities depends on mean annual rainfall which increases from East to West. • Abundant, non-sprouting species are eliminated by fire leading to drastic changes in shrub community composition. • The potential of fire to change Nama-Karoo vegetation has management implications for livestock production. • A positive feedback between rainfall and fire may lead to biome-shift from Nama-Karoo shrubland to grassland. [ABSTRACT FROM AUTHOR]