Tropical Dry Forest Diversity, Climatic Response, and Resilience in a Changing Climate

High temperatures are associated with decreased immune system performance in a wild primate

Rising temperatures due to climate change are predicted to threaten the persistence of wild animals, but there is little evidence that climate change has pushed species beyond their thermal tolerance. The immune system is an ideal avenue to assess the effects of climate change because immune performance is sensitive to changes in temperature and immune competency can affect reproductive success. We investigate the effect of rising temperatures on a biomarker of nonspecific immune performance in a wild population of capuchin monkeys and provide compelling evidence that immune performance is associated with ambient temperature. Critically, we found that immune performance in young individuals is more sensitive to high temperatures compared to other age groups. Coupled with evidence of rising temperatures in the region, our results offer insight into how climate change will affect the immune system of wild mammals.

Natural and anthropogenic factors influence flowering synchrony and reproduction of a dominant plant in an inter-Andean scrub

PREMISE

Agriculture expansion, livestock, and global change have transformed biological communities and altered, through aerosols and direct deposition, N:P balance in soils of inter-Andean valleys, potentially affecting flowering phenology of many species and thereby flowering synchrony and plant reproduction.

METHODS

We evaluated the influence of variation in temperature and moisture along the local elevational gradient and treatments with the addition of N and P and grazing on flowering synchrony and reproduction of Croton, a dominant shrub of the inter-Andean dry scrub. Along the elevational gradient (300 m difference between the lowest and highest site), we set up plots with and without grazing nested with four nutrient treatments: control and addition of N or P alone or combined N + P. We recorded the number of female and male flowers in bloom monthly from September 2017 to August 2019 to calculate flowering synchrony. We assessed fruiting, seed mass, and pre-dispersal seed predation.

RESULTS

Higher growing-season soil temperatures, which were negatively associated with local elevation and higher nitrogen availability promoted flowering synchrony of Croton, particularly among larger plants. Greater flowering synchrony, high soil temperatures, and addition of N + P resulted in production of more fruits of Croton, but also intensified pre-dispersal seed predation.

CONCLUSIONS

Temperature, availability of moisture throughout the elevational gradient, and nutrient manipulation affected flowering synchrony, which subsequently affected production of fruits in Croton. These results emphasize the critical role of current anthropogenic changes in climate and nutrient availability on flowering synchrony and reproduction of Croton, a dominant plant of the inter-Andean scrub.

Tropical dry forests, water, biodiversity and the challenges of climate change in Nicaragua

The Tropical Dry Forests of Nicaragua located mainly in the Pacific and Central-North zones play an essential role in maintaining resources such as water and the special biodiversity of this vulnerable ecosystem now under pressure from land-use changes and climate change These resources are essential to the well-being of the population as the main aquifers of the country are located in this area along with ecosystem services of this now heavily fragmented forest ecosystem. The ongoing influence of climate change along with land-use changes have caused the growth of arid zones in all of Central America. These on-going land use changes are lowering the resilience to the present and future climate change. Individual efforts to sustainable management of the forests are mentioned but it is nonetheless urgent to introduce wider and more intensive sustainable forestry and watershed management under a well-planned strategy based on findings of scientific research. The importance of the interrelationship between water and forests in the management of sustainable forest ecosystems will be stressed.

Sustainable Development versus Extractivist Deforestation in Tropical, Subtropical, and Boreal Forest Ecosystems: Repercussions and Controversies about the Mother Tree and the Mycorrhizal Network Hypothesis

This research reviews the phenomenon of extractive deforestation as a possible trigger for cascade reactions that could affect part of the forest ecosystem and its biodiversity (surface, aerial, and underground) in tropical, subtropical, and boreal forests. The controversy and disparities in criteria generated in the international scientific community around the hypothesis of a possible link between "mother trees" and mycorrhizal networks in coopetition for nutrients, nitrogen, and carbon are analyzed. The objective is to promote awareness to generate more scientific knowledge about the eventual impacts of forest extraction. Public policies are emphasized as crucial mediators for balanced sustainable development. Currently, the effects of extractive deforestation on forest ecosystems are poorly understood, which requires caution and forest protection. Continued research to increase our knowledge in molecular biology is advocated to understand the adaptation of biological organisms to the new conditions of the ecosystem both in the face of extractive deforestation and reforestation. The environmental impacts of extractive deforestation, such as the loss of biodiversity, soil degradation, altered water cycles, and the contribution of climate change, remain largely unknown. Long-term and high-quality research is essential to ensure forest sustainability and the preservation of biodiversity for future generations.

A Five-Year Study on Infestation and Abundance of Bat Flies (Hippoboscoidea: Streblidae) Under Severe Dry Season Conditions in the Tropical Dry Forest of Yucatan, Mexico

In Mexico, few studies have explored how environmental conditions in tropical dry forests (TDF) influence bat fly load even though, according to climate change scenarios, this ecosystem will experience a drier and warmer climate. Such an extension of the dry season in these ecosystems could have dramatic consequences for biodiversity, particularly in regions with plains where animals do not have elevational climate shifts. The present study therefore evaluates the effect of prevailing environmental conditions during 2015-2019, as well as host body conditions, on the infestation and abundance of bat-specific ectoparasites and the composition and bat fly load in the dry season of a TDF in Yucatan. Since Yucatan has an essentially flat and low-lying topography, organisms cannot escape from the predicted extreme conditions with elevational shifts. This region is therefore an excellent location for assessment of the potential effects of warming. We collected 270 bat flies from 12 species. Three streblid species (Nycterophilia parnelli Wenzel, Trichobius johnsonae Wenzel, and Trichobius sparsus Kessel) are new records for Yucatan. Our overview of the dry season bat ectoparasite loads reveals low values of richness and prevalence, but high aggregation. Our models detected significant differences in ectoparasite infestation and abundance over the years, but the environmental and body host condition variables were unrelated to these. We report that pregnant females are parasitized to a greater extent by bat flies during the dry season, which generally represents the season of most significant nutritional stress.

Climate and socioeconomic drivers of biomass burning and carbon emissions from fires in tropical dry forests: A Pantropical analysis

Global burned area has declined by nearly one quarter between 1998 and 2015. Drylands contain a large proportion of these global fires but there are important differences within the drylands, for example, savannas and tropical dry forests (TDF). Savannas, a biome fire-prone and fire-adapted, have reduced the burned area, while the fire in the TDF is one of the most critical factors impacting biodiversity and carbon emissions. Moreover, under climate change scenarios TDF is expected to increase its current extent and raise the risk of fires. Despite regional and global scale effects, and the influence of this ecosystem on the global carbon cycle, little effort has been dedicated to studying the influence of climate (seasonality and extreme events) and socioeconomic conditions of fire regimen in TDF. Here we use the Global Fire Emissions Database and, climate and socioeconomic metrics to better understand long-term factors explaining the variation in burned area and biomass in TDF at Pantropical scale. On average, fires affected 1.4% of the total TDF' area (60,208 km² ) and burned 24.4% (259.6 Tg) of the global burned biomass annually at Pantropical scales. Climate modulators largely influence local and regional fire regimes. Inter-annual variation in fire regime is shaped by El Niño and La Niña. During the El Niño and the forthcoming year of La Niña, there is an increment in extension (35.2% and 10.3%) and carbon emissions (42.9% and 10.6%). Socioeconomic indicators such as land-management and population were modulators of the size of both, burned area and carbon emissions. Moreover, fires may reduce the capability to reach the target of "half protected species" in the globe, that is, high-severity fires are recorded in ecoregions classified as nature could reach half protected. These observations may contribute to improving fire-management.

Los bosques estacionalmente secos del Perú

Los bosques estacionalmente secos en el Perú constituyen un conjunto de ecosistemas que incluye tres grandes grupos florísticos: bosques costeros, interandinos y orientales. Con la excepción de los bosques estacionalmente secos de las llanuras costeras del norte del país, hasta hace poco la ausencia de datos hacía difícil describir adecuadamente estos grupos en base a su florística. En los últimos 20 años, en estos bosques se han generado diversos estudios florísticos e inventarios botánicos enfocados en plantas leñosas, que han llenado vacíos de conocimiento en áreas críticas. Con estos estudios hemos generado la base de datos DRYFLOR Perú que a la fecha incluye 526 inventarios cuantitativos (listas de especies en áreas discretas incluyendo registros de sus abundancias) y que nos permiten confirmar la distinción florística de los tres grandes grupos. Adicionalmente logramos reconocer claramente dos subgrupos de bosques estacionalmente secos costeros (de llanura y de montaña), dos subgrupos interandinos (valles del Marañón-Mantaro y del Pampas) y tres subgrupos orientales (valles del Huallaga, Tambo y Urubamba). Todos los subgrupos tienen un ensamblaje de especies de plantas leñosas que los distingue y caracteriza en términos de abundancia, frecuencia, riqueza de especies y niveles de endemismo. Si bien ahora podemos describir mejor la heterogeneidad florística de los bosques estacionalmente secos en el Perú, hemos identificado vacíos de conocimiento importantes que requieren de atención prioritaria: i) requerimos de esfuerzos de inventario adicionales en los bosques orientales, ii) necesitamos resolver las afinidades florísticas de los bosques del valle del Apurímac, iii) nuestros datos coinciden en poco más del 75% con las definiciones y distribución de bosques secos del reciente Mapa Nacional de Ecosistemas del Perú, y será necesario revisar el concepto de bosque estacionalmente seco para lograr capturar adecuadamente su distribución en este instrumento de gestión.

Surface temperature behavior in view of the conversion of tropical dry forest into anthropic uses, northern Minas Gerais-Brazil

Tropical dry forests (TDFs) are essential for environmental dynamics, especially in terms of climate variations. However, several anthropic factors have threatened the integrity of TDFs, and consequently the surface temperature (ST), which is a proxy variable for several environmental processes in TDFs. So, understanding their behavior is crucial. The objective was to analyze the behavior of surface temperature owing to conversion of TDFs into anthropic uses in northern Minas Gerais between 2007 and 2016. In 9 years, dry forests decreased by 22.9%, with pastures as the central driver (counted 93% of change). Between 2007 and 2016, there was an increase in ST by 1.55 K ± 1.15 K. When TDFs were converted to pastureland, the increase in ST was 2.21 K ± 1.39 K and for crops by 0.57 K ± 1.24 K. The remaining TDFs (2016) had an increase in their thermal average of 1.41 K ± 1.02 K. This analysis is essential for the adoption of conservation actions for the maintenance of ecological corridors in TDFs, considering their importance in the ecosystem context.

The impacts of seasonal variation and climate on food utilization in a population of critically endangered cotton-top tamarins (Saguinus oedipus) in Colombia: A 22-year longitudinal study

To examine how precipitation patterns and climate change impact feeding choices made by a population of critically endangered cotton-top tamarins (Saguinus oedipus), we examined 22 years of feeding data (1999-2020) from 21 groups collected at Parque Natural Regional Bosque Seco El Ceibal Mono Tití in Santa Catalina, Colombia. We describe the diet and examine the role of seasonal rainfall and annual variation in rainfall on diet. Rainfall is highly seasonal (mean annual rainfall 1562 mm [range 940-2680 mm]) with a dry, early rainy, and late rainy season in each year. Over 80 species of plants formed part of the fruit, nectar, and exudate components of the diet. Fruits, although available year-round, were more commonly available and consumed during the late rainy seasons (August-November). Exudates were consumed more frequently in the dry season (December-March) and invertebrate consumption was stable across the year. Nectar feeding from a single species (Combretum fruticosum) peaked in November. Rainfall varied over the years, with 13 years exceeding the 99% confidence intervals for mean rainfall. Ten of these extreme years (both drought and extremely wet) occurred in the last 11 years. Fruit consumption did not vary between extreme and average years, but cotton-top tamarins consumed more invertebrates and exudates in wet years. Presently, cotton-top tamarins appear to be able to cope with these extreme variations in rainfall due to their highly varied diet. However, the forests that these primates depend upon for survival are threatened by human exploitation making it critically important to maintain a generalist feeding strategy for survival as many fruiting trees that compose a large proportion of the diet are removed. As conservation efforts continue, plant species consumed by cotton-top tamarins provide useful data when selecting species for habitat restoration programs.

Using ion-exchange resins to monitor nitrate fluxes in remote semiarid stream beds

Monitoring in remote areas can represent a real challenge in environmental studies. Numerous techniques have been developed over the last decades to monitor nutrients and other elements in different systems. However, not all of them are suitable for field applications, particularly when the locations are difficult to access or its accessibility depends on seasonal climate conditions. This study was aimed to test the applicability and efficiency of resin samplers and resin bags to monitor nitrates fluxes (NO₃-N) in two small semi-arid catchments in Northwestern Mexico. Resin samplers were installed in the hyporheic zone below the river bed in order to monitor the vertical fluxes of NO₃-N and remained there for 5 months (during the summer rains). Resin bags were anchored in rock outcrops upstream of the resin samplers before the onset of the summer rainfall season and replaced every 2 weeks during 4 months to capture pulses of NO₃-N in ephemeral streams. NO₃-N pulses in the stream are a potential source of NO₃-N that can infiltrate into the soil. Results of the resin samplers found a difference of up to 12 kg ha^-1 season^-1 between the two catchments. The resin bags showed a higher accumulation of NO₃-N in the catchment with lower vegetation cover (160.3 mg L^-1 season^-1) compared to the one with higher vegetation (67.8 mg L^-1 season^-1). Measured nitrate fluxes at both sites responded to rainfall pulses recorded during the monitoring period. Resin samplers and resin bags can be used together, to assess nutrient fluxes on the surface and in the soil and can be tested in any type of ecosystem. In this particular case, these methods demonstrated an efficient way of determining spatio-temporal nitrate fluxes in semi-arid ecosystems in remote areas that are difficult to access, monitor, and collect data.

Biogeographic regionalization by spatial and environmental components: Numerical proposal

Regionalization through the analysis of species groups offers important advantages in conservation biology, compared to the single taxon approach in areas of high species richness. We use a systematic framework for biogeographic regionalization at a regional scale based on species turnover and environmental drivers (climate variables and soil properties) mainly of herbaceous plant species richness. To identify phytogeographic regions in the Balsas Depression (BD), we use Asteraceae species, a family widely distributed in Seasonally Dry Tropical Forest (SDTF) and the most diverse of the vascular plants in Mexico. Occurrence records of 571 species were used to apply a quantitative analysis based on the species turnover, the rate of changes in their composition between sites (β-Simpson index) and the analysis of the identified environmental drivers. Also, the environmental predictors that influence species richness in the SDTF were determined with a redundancy analysis. We identified and named two phytogeographic districts within the SDTF of the BD (Upper Balsas and Lower Balsas). According to the multi-response permutation procedure, floristic composition of the two districts differs significantly, and the richness of exclusive species in Upper Balsas was higher (292 species) than in the Lower Balsas (32 species). The proportion of Mg and Ca in the soil and the precipitation of the driest three-month period were the environmental factors with greatest positive influence on species richness. The division of geographic districts subordinated to the province level, based on diverse families such as Asteraceae, proved to be appropriate to set up strategies for the conservation of the regional flora, since at this scale, variation in species richness is more evident. Our findings are consistent with a growing body of biogeographic literature that indicates that the identification of smaller biotic districts is more efficient for the conservation of biodiversity, particularly of endemic or rare plants, whose distribution responds more to microhabitats variation.

Canopy Density and Roughness Differentiate Resistance of a Tropical Dry Forest to Major Hurricane Damage

Tropical dry forest is vulnerable to increased climate variability with more frequent and severe storms. Studies of hurricane impact on tropical dry forest often focused on individual tree traits. How trees in tropical dry forests work together to combat wind damage is still unclear. To address this, we integrated ground-observed ecosystem structure from National Ecological Observation Network (NEON) with airborne-LiDAR images and analyzed resistance in forest structure of Guánica dry forest in Puerto Rico to major hurricanes in 2017 at the forest-stand level. Using each plot instead of the individual tree as the base unit, we regressed mean changes in stem height and fractions of lost or damaged stems at 15 plots on mean stem diameter, mean and standard deviation of stem height, stem density, and topography. Meanwhile, using the LiDAR-derived canopy heights, we compared the changes in canopy height before and after the hurricanes and regressed spatially the canopy height change on prior-hurricane tree cover, canopy height, and rugosity. We found that the damage was small in places with high stem density or high tree cover. Ground-observed damage in terms of height reduction significantly increased with the standard deviation of stem height, an index of roughness, but decreased with the mean stem diameter of the plots. LiDAR-detected damage in terms of reduction in canopy height was also found to decrease with tree cover and mean canopy height when the canopy height was small or moderate but increase with the rugosity. The fraction of lost stems significantly decreased with the stem density, and the fraction of damaged stems significantly increased with the roughness and the plot elevation. The collective parameters of forest stand quantified from ground-observation and LiDAR, such as stem density, tree cover, and canopy roughness or rugosity, highlighted mutual supports of trees and played important roles in resisting damages to the tropical dry forest during major hurricanes.

Seasonal and successional dynamics of size-dependent plant demographic rates in a tropical dry forest

Tropical forests are globally important for biodiversity conservation and climate change mitigation but are being converted to other land uses. Conversion of seasonally dry tropical forests (SDTF) is particularly high while their protection is low. Secondary succession allows forests to recover their structure, diversity and composition after conversion and subsequent abandonment and is influenced by demographic rates of the constituent species. However, how these rates vary between seasons for different plant sizes at different successional stages in SDTF is not known. The effect of seasonal drought may be more severe early in succession, when temperature and radiation are high, while competition and density-dependent processes may be more important at later stages, when vegetation is tall and dense. Besides, the effects of seasonality and successional stage may vary with plant size. Large plants can better compete with small plants for limiting resources and may also have a greater capacity to withstand stress. We asked how size-dependent density, species density, recruitment and mortality varied between seasons and successional stages in a SDTF. We monitored a chronosequence in Yucatan, Mexico, over six years in three 0.1 ha plots in each of three successional stages: early (3–5 years-old), intermediate (18–20 years-old) and advanced (>50 years-old). Recruitment, mortality and species gain and loss rates were calculated from wet and dry season censuses separately for large (diameter > 5 cm) and small (1–5 cm in diameter) plants. We used linear mixed-effects models to assess the effects of successional stage, seasonality and their changes through time on demographic rates and on plant and species density. Seasonality affected demographic rates and density of large plants, which exhibited high wet-season recruitment and species gain rates at the early stage and high wet-season mortality at the intermediate stage, resulting in an increase in plant and species density early in succession followed by a subsequent stabilization. Small plant density decreased steadily after only 5 years of land abandonment, whereas species density increased with successional stage. A decline in species dominance may be responsible for these contrasting patterns. Seasonality, successional stage and their changes through time had a stronger influence on large plants, likely because of large among-plot variation of small plants. Notwithstanding the short duration of our study, our results suggest that climate-change driven decreases in rainy season precipitation may have an influence on successional dynamics in our study forest as strong as, or even stronger than, prolonged or severe droughts during the dry season.

Climate Perspectives in the Intra–Americas Seas

The Intra–Americas Seas region is known for its relevance to air–sea interaction processes, the contrast between large water masses and a relatively small continental area, and the occurrence of extreme events. The differing weather systems and the influence of variability at different spatio–temporal scales is a characteristic feature of the region. The impact of hydro–meteorological extreme events has played a huge importance for regional livelihood, having a mostly negative impact on socioeconomics. The frequency and intensity of heavy rainfall events and droughts are often discussed in terms of their impact on economic activities and access to water. Furthermore, future climate projections suggest that warming scenarios are likely to increase the frequency and intensity of extreme events, which poses a major threat to vulnerable communities. In a region where the economy is largely dependent on agriculture and the population is exposed to the impact of extremes, understanding the climate system is key to informed policymaking and management plans. A wealth of knowledge has been published on regional weather and climate, with a majority of studies focusing on specific components of the system. This study aims to provide an integral overview of regional weather and climate suitable for a wider community. Following the presentation of the general features of the region, a large scale is introduced outlining the main structures that affect regional climate. The most relevant climate features are briefly described, focusing on sea surface temperature, low–level circulation, and rainfall patterns. The impact of climate variability at the intra–seasonal, inter–annual, decadal, and multi–decadal scales is discussed. Climate change is considered in the regional context, based on current knowledge for natural and anthropogenic climate change. The present challenges in regional weather and climate studies have also been included in the concluding sections of this review. The overarching aim of this work is to leverage information that may be transferred efficiently to support decision–making processes and provide a solid foundation on regional weather and climate for professionals from different backgrounds.

Hygric Niches for Tropical Endotherms

Biotic selective pressures dominate explanations for the evolutionary ecology of tropical endotherms. Yet, abiotic factors, principally precipitation regimes, shape biogeographical and phenological patterns in tropical regions. Despite its importance, we lack a framework for understanding when, why, and how rain affects endotherms. Here, we review how tropical birds and mammals respond to rain at individual, population, and community levels, and propose a conceptual framework to interpret divergent responses. Diverse direct and indirect mechanisms underlie responses to rainfall, including physiological, top-down, and food-related drivers. Our framework constitutes a roadmap for the empirical studies required to understand the consequences of rainfall variability. Identifying the patterns and mechanisms underpinning responses to temporal variation in precipitation is crucial to anticipate consequences of anthropogenic climate change.

Disentangling the influence of ecological and historical factors on seed germination and seedling types in a Neotropical dry forest

In tropical dry forests, although seed germination and seedling establishment are in general limited by the seasonal availability of water, high interspecific variability, nonetheless, exists in terms of seedling traits and germination dynamics. Differences among species in seed germination and seedling traits may be related to other plant life-history traits, such that assessing these relationships may increase our understanding of factors influencing plant establishment, which would affect the regeneration pathways of tropical dry forest communities. In this study, taking into consideration the effect species’ phylogeny, we evaluated the relationships of seed germination metrics (percentage, lag time, and rate of germination) and seedling types (i.e. cotyledons functional morphology), with plant life-history traits (growth form, seed mass, dispersal syndrome and dispersal phenology) for 110 species in a Neotropical dry forest in Mexico. A total of 92% of the species studied disperse their seeds during the dry season, mainly at the beginning of this season (66%), a strategy mostly associated with autochorous herbs. Seed germination was more frequent in species that dispersed seeds at the end of the dry season. Germination percentage was not related to any of the traits studied. However, germination lag time and rate were negatively related to seed mass, a trait that in turn depended on growth form and dispersal syndrome. The dominant seedling type in the community was phanerocotylar epigeal with foliaceous cotyledons (56%), which was mostly associated with small seed mass and herbaceous growth form. Our results provide evidence that several plant life-history traits explain an important part of the variation in seed germination and seedling characteristics observed among species. Therefore, these plant life-history traits may be useful for grouping species in terms of their establishment strategies and roles on the regeneration of tropical dry communities.

Shifts of the Mean Centers of Potential Vegetation Ecosystems under future climate change in Eurasia

Climate change dominantly controls the spatial distributions of potential vegetation ecosystems; the shift trends in the mean centers of potential vegetation ecosystems could be used to explain their responses to climate change. In terms of the climate observation data of Eurasia for the period from 1981 to 2010 and the climate scenario data for the period from 2011 to 2100 under the three Representative Concentration Pathways (RCPs) scenarios of RCP2.6, RCP4.5 and, RCP8.5, which were released by the Coupled Model Intercomparison Project Phase 5 (CMIP5), the Holdridge Life Zone (HLZ) ecosystem model was improved to quantitatively classify the potential vegetation types, and the shift model of mean center was adopted to compute the trends in the spatiotemporal shifts of potential vegetation types in Eurasia. The results showed that the mean centers of the major potential vegetation ecosystems would be distributed in the central and southern parts of Eurasia. Under the RCP2.6, RCP4.5, and RCP8.5 scenarios, the potential shift distances of the mean centers of the vegetation types under the RCP8.5 scenario would be the largest, and those of the polar/nival area, subpolar/alpine moist tundra, warm temperate dry forest, subtropical moist forest, cool temperate moist forest, cool temperate wet forest, subtropical wet forest, subtropical thorn woodland, warm temperate moist forest and subtropical dry forest would be larger than those in the other potential vegetation types in Eurasia. Moreover, the shift directions of the mean centers of the major potential vegetation types would generally shift northward, and subtropical dry forest, warm temperate moist forest and subpolar/alpine moist tundra would be the most sensitive to change among all vegetation types under the three scenarios for the period from 2011 to 2100.