Mesic Areas Research Articles

Aridity drives the response of soil total and particulate organic carbon to drought in temperate grasslands and shrublands.

The increasing prevalence of drought events in grasslands and shrublands worldwide potentially has impacts on soil organic carbon (SOC). We leveraged the International Drought Experiment to study how SOC, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) concentrations, responds to extreme drought treatments (1-in-100-year) for 1 to 5 years at 19 sites worldwide. In more mesic areas (aridity index > 0.65), SOC and POC concentrations decreased by 7.9% (±3.9) and 15.9% (±6.2) with drought, respectively, but there were no impacts on MAOC concentrations. However, drought had no impact on SOC, POC, or MAOC concentrations in drylands (aridity index < 0.65). The response of SOC to drought varied along an aridity gradient, concomitant with interannual precipitation variability and standing SOC concentration gradients. These findings highlight the differing response magnitudes of POC and MAOC concentrations to drought and the key regulating role of aridity.

Non-systematic surveys reveal increases in areas occupied by endangered and data-deficient Nubian bustard

A large proportion of endangered species lack good-quality data for assessing population trends. Obtaining these data is especially challenging in remote arid ecosystems, in part because these desert environments have historically attracted less scientific attention and funding than more mesic areas. The Sahara-Sahel biome in northern Africa is home to over 1000 species of terrestrial vertebrates, of which 79 have been classified as threatened or near-threatened by the IUCN Red List. This includes the Nubian bustard (Neotis nuba), a species with deficient ecological information and unknown population trends. In this study we used non-systematic data collected over a 10-year period (2008–2017) across the Termit and Tin-Toumma National Nature Reserve in Niger to i) study the temporal trend in the proportion of areas occupied, ii) map occurrence, and iii) assess how vegetation productivity, elevation, and surface roughness affect species occupancy. We implemented a single-species, multi-year site-occupancy model with an intrinsic conditional autoregressive structure to account for detection probability and the spatial autocorrelation nature of the non-systematic patrolling dataset. Our results showed that birds were imperfectly detected, and detection probability increased for longer transects. Occupancy probability was higher in higher elevated areas and in smoother terrain. Contrary to expected, occupancy probability decreased with increasing vegetation productivity. However, all parameters presented high uncertainty. We found a small positive trend in the proportion of areas occupied by Nubian bustards across the study area and mapped the spatial distribution after accounting for the spatial autocorrelation. Our study provides a better understanding of the population status of Nubian bustards across the ecosystem and will serve as a guide to target and improve surveys for future conservation efforts. Systematic data collection is always advisable for monitoring biodiversity. However, our analysis demonstrates that combining advanced modeling with observations from non-systematic patrolling activities in protected areas can be used for assessing population trends of other endangered and data-deficient species across remote areas.

Effectiveness of forest density reduction treatments for increasing drought resistance of ponderosa pine growth.

As the climate changes, it is increasingly important to understand how forests will respond to drought and how forest management can influence those outcomes. In many forests that have become unnaturally dense, "restoration treatments," which decrease stand density using fire and/or mechanical thinning, are generally associated with reduced mortality during drought. However, the effects of such treatments on tree growth during drought are less clear. Previous studies have yielded apparently contradictory results, which may stem from differences in underlying aridity or drought intensity across studies. To address this uncertainty, we studied the growth of ponderosa pine (Pinus ponderosa) in paired treated and untreated areas before and during the extreme California drought of 2012-2016. Our study spanned gradients in climate and tree size and found that density reduction treatments could completely ameliorate drought-driven declines in growth under some contexts, specifically in more mesic areas and in medium-sized trees (i.e., normal annual precipitation > ca. 1100 mm and tree diameter at breast height < ca. 65 cm). Treatments were much less effective in ameliorating drought-associated growth declines in the most water-limited sites and largest trees, consistent with underlying ecophysiology. In medium-sized trees and wetter sites, growth of trees in untreated stands decreased by more than 15% during drought, while treatment-associated increases in growth of 25% or more persisted during the drought. Trees that ultimately died due to drought showed greater growth reductions during drought relative to trees that survived. Our results suggest that density reduction treatments can increase tree resistance to water stress, and they highlight an important pathway for treatments to influence carbon sequestration and other ecosystem services beyond mitigating tree mortality.

Edge effects on ant diversity and functional composition in a forest fragment in the Central Amazon

The process of human-induced forest fragmentation increases the degree of isolation and causes biodiversity loss. Abrupt changes occur mainly near the edge of the fragment, where the average temperature is relatively higher and the humidity is lower. However, some natural environmental characteristics, such as higher air moisture in riparian areas, may buffer or minimize the edge effects. Here, we studied how the edge effect may affect ant species diversity and functional composition on valleys dissected by small streams (mesic areas). We categorized ant assemblages into the functional groups based on foraging, nesting habits, natural history information, and phylogeny. Ants were sampled using pitfalls and the Winkler extractor in ten riparian plots in a fragment of the Central Amazon. We individually fit the ant species richness, occurrence, and composition against two edge measures: forest edge distance and road-building distance. We recorded 99 species/morphospecies. Forest edge distance and road-building distance did not influence the occurrence and number of ant species per plot but were related to ant species composition. Moreover, there was not a clear pattern between functional groups distribution, except by leaf-cutters and generalist omnivorous species. Our results suggest a limited effect of forest edge distance and road-building distance on ant diversity

Changes in Forage Quality and Cattle Performance with Short-Duration Grazing of Mesic Meadows in the Intermountain West

Managers tasked with balancing livestock production and wildlife habitat in mesic meadows face a unique set of challenges. These challenges are compounded in the arid western United States because mesic areas comprise only a small portion of the landscape yet provide vital forage and water resources to livestock and wildlife and are essential to underlying ecosystem integrity and function. Our objectives were to compare the effects of short-duration grazing treatments that varied by season and intensity on the quantity and nutrient quality of pasture forage and average daily gains (ADG) of yearling cattle. We established pastures (n = 15 total pastures) in mesic meadows at the University of Idaho Rinker Rock Creek Ranch in south-central Idaho and stocked them with heifers during 2019 and 2020. Heifers grazed six pastures in June (early-season; 16 d) and six pastures in August (late-season; 16 d) at moderate (30−40%) and high (70-80%) relative utilization levels (n = 3 pastures per treatment). Three pastures were not grazed by cattle representing controls. Forage was collected and analyzed for nutrient quality at pregrazing, postgrazing, and after a period of regrowth in late September. Contrasted against all other treatments, early-season grazing at a high-intensity produced forages with the highest crude protein (P < 0.001) and lowest neutral-detergent fiber (P ≤ 0.04) after regrowth. ADGs of yearling heifers were greater (P ≤ 0.01) during the first year of the trial than the second year. Differences in ADG were not associated with grazing season (P = 0.08) or intensity (P = 0.12), despite numeric differences. Forage quantity and quality and heifer ADG responses varied between years, likely due to spring and annual precipitation differences. This study demonstrates the effectiveness of early-season grazing at a high intensity for improving forage quality and increasing ADG of livestock grazing mesic meadows.

Moisture abundance and proximity mediate seasonal use of mesic areas and survival of greater sage‐grouse broods

Abstract Water is a critical and limited resource, particularly in the arid West, but water availability is projected to decline even while demand increases due to growing human populations and increases in duration and severity of drought. Mesic areas provide important water resources for numerous wildlife species, including the greater sage‐grouse (Centrocercus urophasianus; hereafter, sage‐grouse), an indicator for the health of sagebrush ecosystems. Understanding how wildlife use these crucial areas is necessary to inform management and conservation of sensitive species. Specifically, the influence of anthropogenic water subsidies such as irrigated pastures is not well‐studied. We evaluated brood‐rearing habitat selection and brood survival of sage‐grouse in Long Valley, California, an area where the water rights are primarily owned by the city of Los Angeles and water is used locally to irrigate for livestock. This area thus represents a unique balance between the needs of wildlife and people that could increasingly define future water management. In this study, sage‐grouse broods moved closer to the edge of mesic areas and used more interior areas during the late brood‐rearing period, selecting for greener areas after 1 July. Mesic areas were particularly important during dry years, with broods using areas farther interior than in wet years. Brood survival was also positively influenced by the availability and condition of mesic resources, as indicated by variation in values of normalized difference vegetation index (NDVI), with survival peaking at moderate values of NDVI and just outside the edge but decreasing inside the mesic areas. Our results highlight the importance of quality edge habitat of large mesic areas for sage‐grouse to balance habitat selection and survival, particularly during drier years and during the late brood‐rearing period, which is a critical period because chick survival has been shown to influence population growth. This study highlights the implications of large‐scale anthropogenic water manipulation, and the balance between local irrigation and water distribution to benefit other regions, from the context of a species of high conservation concern in North American sagebrush ecosystems.

Grazing lawns and overgrazing in frequently grazed grass communities.

Frequent grazing can establish high forage value grazing lawns supporting high grazer densities, but can also produce overgrazed grass communities with unpalatable or low grass basal cover, supporting few grazers. Attempts to create grazing lawns via concentrated grazing, with a goal to increase grazer numbers, are thus risky without knowing how environmental conditions influence the likelihood of each outcome. We collected grass species and trait data from 33 frequently grazed grass communities across eastern South Africa (28 sites) and the Serengeti National Park, Tanzania (five sites), covering wide rainfall (336–987 mm year−1) and soil (e.g., 44%–93% sand) gradients. We identified four grass growth forms using hierarchical clustering on principal components analyses of trait data and assessed trait–environment and growth form–environment relationships using fourth corner and principal components analyses. We distinguished two palatable grass growth forms that both attract yet resist grazers and comprise grazing lawns: (1) “lateral attractors” that spread vegetatively via stolons and rhizomes, and (2) “tufted attractors” that form isolated tufts and may have alternate tall growth forms. By contrast, (3) tough, upright, tufted “resisters,” and (4) “avoiders” with sparse architectures or that grow appressed to the soil surface, are of little forage value and avoided by grazers. Grazing lawns occurred across a wide range of conditions, typically comprising lateral attractor grasses in drier, sandy environments, and tufted attractor grasses in wetter, low‐sand environments. Resisters occurred on clay‐rich soils in mesic areas, while avoiders were widespread but scarce. While grazing lawns can be established under most conditions, monitoring their composition and cover is important, as the potential for overgrazing seems as widely relevant. Tufted attractor‐dominated lawns appear somewhat more vulnerable to degradation than lateral attractor‐dominated lawns. Increased avoider and resister abundance both reduce forage value, although resisters may provide better soil protection.

A global meta‐analysis of grazing effects on soil seed banks

AbstractLivestock grazing is a major disturbance affecting plant diversity and abundance in terrestrial ecosystems. The intermediate disturbance hypothesis (IDH) predicts that moderate‐intensity grazing should produce the highest species diversity, while the Milchunas‐Sala‐Lauenroth (MSL) model posits that the IDH is valid only for mesic areas. However, it remains unclear how grazing affects soil seed bank and whether or not the IDH or MSL models are valid for soil seed bank communities. Here, we presented a global meta‐analysis synthesizing 483 observations: we found that grazing had a negative effect on soil seed bank abundance, but did not alter seed bank richness or the compositional similarity between the soil seed bank and the aboveground vegetation. Further refining the analysis, light‐intensity grazing was found to increase seed bank richness, while moderate‐intensity grazing had no effect, and heavy‐intensity grazing had a negative effect. Additionally, for both arid and mesic areas, soil seed bank richness declined with grazing intensity increased. Overall, grazing effects on soil seed banks differed from expectations set by studies of aboveground vegetation. Our study provides key insights for policy‐makers managing livestock grazing and grassland conservation.

Seasonal and interannual variation on social wasps’ assemblages in two habitats of a seasonally dry tropical forest region

AbstractThe patterns of the spatial distribution of insects in seasonally dry tropical forests (SDTFs) are strongly influenced by marked seasonal fluctuations. Tropical arthropod seasonality has been linked to multiple factors, ranging from microclimate changes to large‐scale environmental processes. The group of social wasps includes eusocial organisms that play essential roles in ecosystems, acting as pollinators and predators. This study examines the variation in abundance and species richness according to season, rainfall, and temperature in an area of the Caatinga biome in northeastern Brazil, which has distinct vegetation characteristics. Four years of continuous sampling with Malaise traps constituted the medium‐term data used in our study. During dry seasons, populations of xerophytic vegetation experienced significant decreases in abundance, which were associated with decreased rainfall; however, we did not observe the same effect in evergreen vegetation. Mesic habitats have less variation in food resources, which may have kept populations active during droughts. However, during wet periods, especially after heavy rainfall, more individuals were recorded in the xeric area compared with the mesic area. Using results from social wasp populations, we conclude that the spatio‐temporal dynamics of insects in forest areas with seasonal characteristics are greatly affected by factors such as the landscape composition and mainly by the distribution of rainfall.Abstract in Spanish is available with online material.

Occurrence of Australian woody species is driven by soil moisture and available phosphorus across a climatic gradient

AbstractQuestionsWoody species are crucial biotic components in many of Earth’s terrestrial ecosystems because they support multiple ecosystem functions. The occurrence of woody species (i.e. their likelihood of being present at a single position) is driven by both climate and soil properties. However, empirical evidence is lacking on how multiple environmental factors regulate woody species occurrence across various climate regimes, limiting our ability to predict woody species distribution under different climate change scenarios.LocationWoody plant species in eastern Australia; 1,500 km gradient.MethodsWe surveyed 6,353 mature (height &gt;4 m) woody plants from 62 woody species at 150 sites along a 1,500 km climatic (i.e. aridity) gradient in eastern Australia, and used a generalized linear mixed model to explore the impact of summer rainfall, available soil phosphorus in the surface layer (0–10 cm), subsurface (100–200 cm) soil moisture and clay content, and interactions between aridity and the three soil variables on woody species occurrence (presence/absence).ResultsThe overall occurrence of Australian woody species declined as the concentration of available soil phosphorus in the surface layer increased, with the impacts varying with increasing aridity. Subsurface soil moisture had strong positive effects on woody species occurrence in mesic areas, but the effect was attenuated with increasing aridity. Subsurface soil clay regulated the distribution of woody species, with finer soils promoting the likelihood of species occurrence in the dry subhumid zone, whereas coarser soils supported more woody species in the arid zone.ConclusionsOur study provides empirical evidence that the distribution of Australian woody species is regulated by large‐scale shifts in soil moisture and available soil phosphorus, and local‐scale heterogeneity in soil texture. Our results suggest that forecasted climate change may restrict the distribution of woody species preferring particular soils, but expand the range of woody species that occur on dry or infertile soils.

Remotely-sensed water budgets for agriculture in the upper midwestern United States

Process based hydrological models are often the most accurate and comprehensive tools available for answering hydrological questions. However, the resources needed to parameterize and calibrate them can be problematic for small organizations with limited resources or for management questions where emerging problems require rapid investigation. To address this need, this study calculates a simplified monthly water balance using gridded remote sensing actual evapotranspiration (ETa) data and PRISM precipitation data for 223,355 agricultural parcels in Wisconsin totaling 2,966,250 ha of agricultural land. Agricultural management features such as crop rotation and irrigation as well as physical features such as soil drainage and hillslope gradient were compared to identify differences in monthly water budgets. Results showed that Wisconsin was energy limited in most years such that additional precipitation was more likely to suppress ETa. Significant differences were identified with dairy and pasture rotations having the highest annual ETa and the potato/vegetable rotation having the lowest annual ETa rates. Growing season length was identified as a likely predictor of annual ETa. Surprisingly, results also showed that there were no appreciable differences in ETa between rainfed cropland and irrigated cropland. Lastly, results indicated that across all rotations, the months most susceptible to infiltration and runoff were April, May, October, and December. This research demonstrates that cropland management plays a significant role in mitigating or accentuating potential infiltration and runoff relative to variability in precipitation in mesic areas. Without accommodating hydrological variability in mesic, energy-limited areas, water or nutrient conservation policy strategies designed to target average weather conditions may be regularly under-protective or over-restrictive.

No‐analogue associations in the fossil record of southern conifers reveal conservatism in precipitation, but not temperature axes

AbstractAimSouthern conifers have evolved under different evolutionary pressures compared with northern lineages, but in both regions these plants have undergone extensive extinction and range alteration over the Cenozoic (the last 66 Myr). It is not possible to observe the ecology of fossils directly, but indirect evidence of changes in bioclimatic envelopes can be derived from no‐analogue assemblages (i.e., groups of co‐occurring fossils that have climatically incongruous living relatives). We identify and examine the specific pairs of no‐analogue fossils within assemblages to disentangle the effects of climatic factors on past conifer extinctions and suggest which of these factors are likely to threaten southern conifer biodiversity in the future.LocationSouthern Hemisphere.Time periodCenozoic.Major taxa studiedConifers.MethodsWe use a recently developed method, “hyperoverlap”, to identify no‐analogue pairs of southern conifers. We characterize each pair in terms of temperature and precipitation and evaluate temporal patterns in no‐analogue pairs. These analyses represent a novel approach to studying both no‐analogue fossils and past changes in bioclimatic envelopes.ResultsWe identified 240 no‐analogue pairs in the Cenozoic record of southern conifers. Most (75.4%) observations of no‐analogue pairs are likely to result from a change in the thermal (rather than hydrological) distribution between the fossil taxa and their extant counterparts, regardless of region or assemblage age. Thus, the fossil record shows some thermal lability, but strong hydrological stability in the tolerances of these plants. This implies that most southern conifers have inhabited wet climates through the Cenozoic, which is consistent with physiological evidence suggesting strong conservatism in drought tolerance.Main conclusionsSouthern conifers have adapted successfully to a wide range of temperatures, but future changes in rainfall are likely to pose the greatest threat to these plants, either directly or indirectly (e.g., through increased incidence of fire in mesic areas).

The effects of herbivore aggregations at water sources on savanna plants differ across soil and climate gradients.

Water sources in arid and semiarid ecosystems support humans, wildlife, and domestic animals, forming nodes of activity that sculpt surrounding plant communities and impact critical grazing and soil systems. However, global aridification and changing surface water supply threaten to disrupt these water resources, with strong implications for conservation and management of these ecosystems. To understand how effects of herbivore aggregation at water impact plant communities across contexts, we measured herbivore activity, plant height, cover (trees, grasses, forbs, and bare ground), diversity, and composition at 17 paired water sources and matrix sites across a range of abiotic factors in a semiarid savanna in Kenya. The effects of proximity to surface water and herbivore aggregation on plant communities varied substantially depending on soil and rainfall. In arid areas with nutrient-poor sandy soils, forb and tree cover were 50% lower at water sources compared to neighboring matrix sites, bare ground was 20% higher, species richness was 15% lower, and a single globally important grazing grass (Cynodon dactylon) dominated 60% of transects. However, in mesic areas with nutrient-rich finely textured soils, species richness was 25% higher, despite a 40% increase in bare ground, concurrent with the decline of a dominant tall grass (Themeda triandra) and increase in C.dactylon and other grass species near water sources. Recent rainfall was important for grasses; cover was higher relative to matrix sites only during wet periods, a potential indication of compensatory grazing. These findings suggest that effects of herbivore aggregation on vegetation diversity and composition will vary in magnitude, and in some cases direction, depending on other factors at the site. Where moisture and nutrient resources are high and promote the dominance of few plant species, herbivore aggregations may maintain diversity by promoting grazing lawns and increasing nondominant species cover. However, in arid conditions and sites with low nutrient availability, diversity can be substantially reduced by these aggregations. Our results highlight the importance of considering abiotic conditions when managing for effects of herbivore aggregations near water. This will be particularly important for future managers in light of growing global aridification and surface water changes.

Moisture availability and ecological restoration limit fine fuels and modelled wildfire intensity following non‐native ungulate removal in Hawaii

Abstract The removal and exclusion of non‐native ungulates for conservation of biodiversity is common globally, including on tropical Pacific Islands. However, the poorly quantified effects of ungulate exclusion on fuels and wildfire may represent an important conservation trade‐off. We measured fuels (live and dead fuel loads, type, height and continuity) and modelled potential wildfire behaviour (flame height and rate of spread) inside and outside of 13 ungulate exclosures, three of which received active ecological restoration (e.g. planting of native shrubs and trees), across a 2,740 mm mean annual rainfall (MAR) gradient on the Island of Hawaii. Differences in fuel characteristics and modelled wildfire behaviour inside versus outside of ungulate exclosures were assessed using linear mixed effects analyses. Non‐native ungulate removal, in general, increased fine fuel loading (average change ranged from −0.7 to 11.3 Mg/ha), shrub fuel loading (−0.1 to 5.6 Mg/ha) and modelled flame lengths (−0.2 to 1.9 m). Post‐removal fine fuel loading and modelled flame lengths increased linearly and positively with moisture availability, by as much as 56% in the wettest sites. Dead fine fuels, a key driver of fire intensity and combustion rates, also increased with ungulate removal. Sites undergoing active ecological restoration exhibited reductions in fuel loading, with greater reductions over time since ungulate removal; by the 10th year following ungulate removal, fine fuel loading was reduced at restoration sites by 41%. Synthesis and applications. Dry and mesic environments where wildfire occurrence is more frequent are of particular concern following non‐native ungulate removal, but with drought even typically wet environments can be at high risk of wildfire following ungulate removal. Given limited resources, managers in mesic and wet forests might focus first non‐native ungulates in non‐native grass‐dominated areas that contribute disproportionately to wildfire spread and are adjacent to fenced higher value areas, while managers in dry to mesic areas might focus on removing non‐native ungulates. Where possible, land managers in all situations should invest in long‐term fuel management strategies such as active ecological restoration to reduce fuel loads and the occurrence and intensity of wildfires.

Fe-Mn concentrations in upland loess soils in mid-continental north America: A step towards dynamic soil survey

Iron-manganese (Fe-Mn) concentrations are common morphological indicators of soil oxidation-reduction reactions and are widely used to infer soil hydrology. The factors determining occurrence and distribution of Fe-Mn concentrations at the continental scale have been rarely studied. The objective of this study was to explore the distribution of Fe-Mn concentrations in upland loess soils and identify their favorable environment conditions in the mid-continental North America. A total of 3966 soil profiles were collected from the National Soil Information System database (NASIS). A decision tree (DT) model was used to analyze the spatial relationships between Fe-Mn concentration formation and its relevant environmental factors (climate, soil properties, and land use/land cover), and to identify key factors of Fe-Mn concentrations distribution and occurrence in upland loess soils. The DT model was evaluated with 25% validation dataset with an accuracy of 79%. Results showed that Fe-Mn concentrations were more likely to occur in mesic areas with large precipitation and low internal soil drainage rates, compared to frigid and thermic areas with low precipitation and large internal soil drainage rates. Annual precipitation and temperature were identified as the most important climatic factors influencing the occurrence of Fe-Mn concentrations and showed a complex interaction with soil properties at multiple scales. Soil properties related to potential wet to saturated soil conditions were also important for the occurrence of Fe-Mn concentrations. Results demonstrated the importance of using knowledge of pedogenesis in the selection of environmental covariates and the interpretation of DT model results. Understanding where Fe-Mn concentrations tend to form in the landscape will contribute to improving decisions about proper use of soil that may be limited by wetness and possible inferences about climate influences.

Spatial patterns of tree cover change at a dry forest margin are driven by initial conditions, water balance and wildfire

Increases in tree cover at dry forest margins are a global phenomenon. Yet, how pre-existing tree cover interacts with terrain and water balance to influence tree cover change is not well-understood, nor whether subsequent disturbances restore prior tree cover patterns or create novel patterns. To assess how terrain, water balance and pre-existing patterns of tree cover influenced late twentieth century tree cover change, and how subsequent wildfires altered tree cover patterns. We analyzed tree canopy cover at four sites at the forest-steppe ecotone on the eastern side of the Sierra Nevada, California, U.S.A., using aerial photographs from 1953/1955, 1999/2002 and 2016. Influences on tree cover change were assessed using statistical modeling, and tree cover in 1953/1955 was compared with post-wildfire tree cover in 2016. From 1953 to 2002, area with > 25% canopy cover increased by 1.5 to 5-fold and treeless area decreased by 17–111%. Mesic areas and areas of sparse tree cover close to existing forest tended to gain more canopy cover. Subsequent wildfires caused a mix of net tree cover loss, little change and gain relative to 1953/1955, but at all sites areas with > 25% cover and < 10% cover in 1953/55 experienced net losses and gains respectively by 2016. Accounting for initial tree cover and its configuration are crucial to assessing water balance and terrain effects on tree cover change. Our work highlights how wildfires can generate novel patterns of tree cover relative to historical baselines, especially following decades of fire exclusion.

Biological Soil Crusts of the Great Plains: A Review

Biological soil crusts (BSCs), or biocrusts, are composed of fungi, bacteria, algae, and bryophytes (mosses, etc.) that occupy bare soil, entwining soil particles with filaments or rootlike structures and/or gluing them together with polysaccharide exudates to form a consolidated surface crust that stabilizes the soil against erosion. BSCs are common in arid and semiarid regions where vascular plant cover is naturally sparse, maximizing the exposure of surface-dwelling organisms to direct sunlight. Although less prominent and less studied there, BSC organisms are also present in more mesic areas such as the Great Plains where they can be found in shortgrass and mixed-grass prairie, in the badlands of several states, where burrowing animals have created patches of bare soil, on damaged road-cuts, strip-mines, gas and oil drill pads, military training areas, heavily grazed areas, and burn scars. Even where BSCs are not readily visible to the naked eye, many of the organisms are still present. BSC organisms are passively dispersed to the Great Plains as airborne organismal fragments, asexual diaspores, or sexual spores that accompany wind-blown dust from as far away as northern China and Mongolia. BSCs can best be studied and managed by 1) acknowledging their presence; 2) documenting their diversity, abundance, and functional roles; and 3) minimizing unnecessary disturbance, particularly when the soils are dry. This paper describes the current knowledge of Great Plains BSCs in an effort to heighten awareness of these cryptic but crucial ecosystem components and to encourage new research initiatives to better understand and manage them in this biome. Some specific actions may include refined taxonomic and ecologic studies of BSC organisms in underexplored areas, particularly those previously less or not recognized as BSC habitat, and incorporation of techniques to sample airborne organisms.

Changes in plant functional composition of wetland vegetation along an aridity gradient on the Highveld plateau of South Africa

AbstractQuestionPlant communities will change along environmental gradients, even in “azonal” vegetation such as wetlands. It is hypothesized that functional community composition of wetland vegetation changes along a natural gradient from dry low‐lying areas to wet high‐lying areas. We wanted to know how the functional groups that make up wetland plant communities change along such aridity and altitudinal gradients.LocationHighveld area of Central South Africa, covering four provinces of the country: Northern Cape, Free State, North West and Mpumalanga.MethodsThe community composition of 201 vegetation plots was obtained from a compilation of South African wetland vegetation types of the study area. Functional traits were collected for the dominant plant species and community‐weighted means of plant functional traits were calculated for wetland vegetation plots. Redundancy analysis was performed to plot these against environmental and climatic gradients.ResultsThe ordination results showed that the community‐weighted plant functional traits were correlated with environmental and climatic variables. For example, specific correlations reveal that root/shoot biomass ratio, leaf nitrogen and specific leaf area are associated with high temperature and evaporation, conditions that prevail in the driest end of the gradient. On the opposite end, wetland vegetation in mesic areas has adaptations for fast growth and high productivity, as it is composed of tall plants with wide stems and deep roots. A hierarchical cluster analysis (HCA) resulted in nine plant functional groups, with different representation along the aridity gradient in the Highveld Plateau of South Africa.ConclusionsWetlands in dry areas have plant functional groups different from those in mesic areas. Changes in community composition show how wetlands are responding to climatic variability and environmental change. Thus, the study of changes in plant functional groups can be useful for detecting the impacts of climate change on wetland vegetation.

Linking Vegetation-Climate-Fire Relationships in Sub-Saharan Africa to Key Ecological Processes in Two Dynamic Global Vegetation Models

Africa is largely influenced by fires, which play an important ecological role influencing the distribution and structure of grassland, savanna and forest biomes. Here vegetation strongly interacts with climate and other environmental factors, such as herbivory and humans. Fire-enabled Dynamic Global Vegetation Models (DGVMs) display high uncertainty in predicting the distribution of current tropical biomes and the associated transitions, mainly due to the way they represent the main ecological processes and feedbacks related to water and fire. The aim of this study is to evaluate the outcomes of two state-of-the–art DGVMs, LPJ-GUESS and JSBACH, also currently used in two Earth System Models (ESMs), in order to assess which key ecological processes need to be included or improved to represent realistic interactions between vegetation cover, precipitation and fires in sub-Saharan Africa. To this end, we compare models and remote-sensing data, analyzing the relationships between tree and grass cover, mean annual rainfall, average rainfall seasonality and average fire intervals, using generalized linear models, and we compare the patterns of grasslands, savannas, and forests in sub-Saharan Africa. Our analysis suggests that LPJ-GUESS (with a simple fire-model and complex vegetation description) performs well in regions of low precipitation, while in humid and mesic areas the representation of the fire process should probably be improved to obtain more open savannas. JSBACH (with a complex fire-model and a simple vegetation description) can simulate a vegetation-fire feedback that can maintain open savannas at intermediate and high precipitation, although this feedback seems to have stronger effects than observed, while at low precipitation JSBACH needs improvements in the representation of tree-grass competition and drought effects. This comparative process-based analysis permits to highlight the main factors that determine the tropical vegetation distribution in models and observations in sub-Saharan Africa, suggesting possible improvements in DGVMs and, consequently, in ESM simulations for future projections. Given the need to use carbon storage in vegetation as a climate mitigation measure, these models represent a valuable tool to improve our understanding of the sustainability of vegetation carbon pools as a carbon sink and the vulnerability to disturbances such as fire. (Less)

Easternmost record of the Cuban Broad-banded Trope, Tropidophis feicki (Squamata: Tropidophiidae)

Tropidophis feicki Schwartz, 1957 is restricted to densely forested limestone mesic areas in western Cuba (Schwartz &amp; Henderson 1991; Henderson &amp; Powell 2009). This species has been reported from about 20 localities distributed from near Guane, in Pinar del Río Province, to Ciénaga de Zapata, in Matanzas Province Rivalta et al., 2013; GBIF 2020; Fig. 1). On 30 June 2009 and on 22 December 2011 we found an adult male and an adult female Tropidophis feicki (ca. 400 mm SVL; Fig. 2), respectively, at the entrance of the “Cueva de la Virgen” hot cave (22.8201, -80.1384; 30 m a.s.l.; WGS 84; point 14 in Fig. 1). The cave is located within “Mogotes de Jumagua” Ecological Reserve, Sagua La Grande Municipality, Villa Clara Province. This locality represents the first record of this species for central Cuba, particularly for Villa Clara Province. This new record is about 123 km northeast (airline distance) of the nearest previous record at Playa Máquina, Ciénaga de Zapata, Matanzas Province (Rodríguez &amp; Rivalta 2007).