Vegetation Gaps Research Articles

Application of remote sensing to understand the role of Galician feral horses in the biomass reduction of a shrub-grassland-dominated landscape

Galician forests in northwestern Spain are subject to frequent wildfires with high environmental and economic costs. In addition, due to the consequences of climate change, these fires are becoming more virulent, occurring throughout the year, and taking place in populated areas, in some cases involving the loss of human life. Therefore, forest fire prevention is even more relevant than mitigating its consequences. Given the costs involved in forestry work, alternative measures to reduce fuel load and create vegetation gaps are needed. One involves grazing by an endemic species of feral horses (Equus ferus atlanticus) that feed on thicket-forming gorse (Ulex europaeus). In a 100-ha forest fenced study area stocked with 11 horses, four 50 m2 enclosed plots prevented the access of these wild animals to the vegetation, with the aim of manipulating their impact on the reduction of forest biomass. The measurement of biomass volumes is an important method that can describe the assessment of wildfire risks, unfortunately, high-resolution data collection at the regional scale is very time-consuming. The best result can be using drones (unmanned aerial vehicles - UAVs) as a method of collecting remotely sensed data at low cost. From September 2018 to November 2020, we collected information about aboveground biomass from these four enclosed plots and their surrounding areas available for horses to forage, via UAV. These data, together with environmental variables from the study site, were used as input for a fire model to assess the differences in the surface rate of spread (SROS) among grazed and ungrazed areas. Our results indicated a consistent but small reduction in the SROS between 0.55 and 3.10 m/min in the ungrazed enclosured plots in comparison to their grazed surrounding areas (which have an SROS between 15 and 25 m/min). The research showed that radar remote sensing (UAV) can be used to map forest aboveground biomass, and emphasized the importance and role of feral horses in Galicia as a prevention tool against wildfires in gorse-dominated landscapes.

A Drone-Powered Deep Learning Methodology for High Precision Remote Sensing in California’s Coastal Shrubs

Wildland conservation efforts require accurate maps of plant species distribution across large spatial scales. High-resolution species mapping is difficult in diverse, dense plant communities, where extensive ground-based surveys are labor-intensive and risk damaging sensitive flora. High-resolution satellite imagery is available at scales needed for plant community conservation across large areas, but can be cost prohibitive and lack resolution to identify species. Deep learning analysis of drone-based imagery can aid in accurate classification of plant species in these communities across large regions. This study assessed whether drone-based imagery and deep learning modeling approaches could be used to map species in complex chaparral, coastal sage scrub, and oak woodland communities. We tested the effectiveness of random forest, support vector machine, and convolutional neural network (CNN) coupled with object-based image analysis (OBIA) for mapping in diverse shrublands. Our CNN + OBIA approach outperformed random forest and support vector machine methods to accurately identify tree and shrub species, vegetation gaps, and communities, even distinguishing two congeneric shrub species with similar morphological characteristics. Similar accuracies were attained when applied to neighboring sites. This work is key to the accurate species identification and large scale mapping needed for conservation research and monitoring in chaparral and other wildland plant communities. Uncertainty in model application is associated with less common species and intermixed canopies.

The contribution of seedbank to the green roof plant community dynamics analogous to semi-natural grasslands

Extensive green roofs have been shown to support native biodiversity and plant communities that are analogous to natural or semi-natural habitats such as grasslands. However, little is known about the role of soil seedbanks in the dynamic of extensive green roof plant communities. The purpose of this study was to analyze the seedbank that developed after 4 years of an extensive green roof analog to dry grassland plant community, seeded with 29 species. We aimed to understand the contribution of seedbank to the resilience of vegetation to harsh conditions of the roof and to colonization by surrounding spontaneous species. We monitored the plant species cover in 36 plots during 4 years in June (between 2018 and 2021), and sampled the seedbank in February 2021. Our results showed that the soil seedbank was dominated by transient spontaneous ruderals species, while the standing vegetation was still dominated by seeded grassland species. We found that seeded grassland species had poor seedbank stock, similar to their natural environments. The similarity index between the standing vegetation and the seedbank increased over time, and we measured a significant correlation between dominant species cover and their seedbank density. Spontaneous species cover was not correlated to the proportion of soil not colonized by seeded species cover, indicating that gaps in vegetation did not influence the development of spontaneous species. Our findings highlight the importance of seedbank in the dynamic of green roof vegetation and demonstrate that analogous habitat species exhibit similar behavior as in their natural environments.

Analytical assessment of street-level tree canopy in Austrian cities: Identification of re-naturalisation potentials of the urban fabric

Climate change-related impacts such as heat stress, extreme weather events, and their consequences are particularly felt within densely built-up urban areas. Urban re-naturalisation is recognised as a promising cost-effective strategy for improving urban resilience to these environmental and societal issues. In this respect, the present contribution focuses on a comprehensive city-wide assessment of street-level urban tree canopy to detect the existing vegetation gaps and identify re-naturalisation potentials within the urban fabric for the three largest cities in Austria (Vienna, Graz, and Linz). The study relies on QGIS and R software environments to carry out spatial data analytics on georeferenced tree cadastre data and the global map of Local Climate Zones (LCZ) to compute spatial density maps and urban structure parameters. The results suggest a rather random distribution of tree clusters and highly fragmented instances within the city. This fragmentation is predominantly observed within central densely built urban fabric for all three cities, with the absence of street trees in peripheral urbanised areas being more prominent in Graz and Linz. The computed percentage of potentially disconnected areas in terms of the tree canopy for Vienna, Graz, and Linz amounts to 45%, 54%, and 37%, respectively. The analysis of urban structure revealed a homogeneous densely built-up character over central districts and a dominantly heterogeneous character across non-central and peripheral districts with a more openly built fabric (this heterogeneity is, generally more prominent in the case of Graz and Linz). In general, there are numerous opportunities for urban re-naturalisation, focusing on urban trees within such openly arranged buildings. Due to the evident physical constraints of the urban space within central districts, the consideration of building-level greening (e.g. green roofs, green facades) may be a better approach to urban re-naturalisation in these cases. Given the further constraints imposed by the abundance of historic buildings, such measures may not be feasible in every event. Hence, this calls for consideration of novel, innovative and emerging greening systems with the proposition of movable vertical green screens and vertical gardens.

Size-biased compositional impacts of small mammal herbivores in an old-field plant community

Plant species height (mature height), which strongly correlates with other measures of size, is widely considered an important functional trait. Taller species contribute greatly to ecosystem function and are frequently identified as strong competitors. Additionally, important ecological processes like self-thinning scale with plant species size. In spite of the clear functional importance of species size, evidence for size-based plant community assembly rules has been scant. While herbivory can be species specific and there are reasons why herbivores may target larger plant species, it is unknown whether herbivory has size-biased impacts on species composition. In an old-field plant community, we compared plant species composition in herbivore exclusion (caged) and control plots over five years to test whether herbivore activity favors species at one end of the size spectrum. Across 5 years, smaller species were modestly, but consistently, underrepresented in caged plots compared to control plots. This underrepresentation of relatively smaller plant species in caged plots, where seedling herbivory was greatly diminished, was driven by lower small plant species richness and abundance in those plots; the abundance and richness of tall species did not differ across treatments. Our findings demonstrate that reducing herbivore activity in our study community modestly but consistently altered plant species composition, slightly favoring larger species. There was no evidence that larger species are preferentially targeted by herbivores. Some research suggests, although it will require further investigation, that seedling herbivory, regardless of the species eaten, produces vegetation gaps that small plant species are more successful in colonizing.

Distribution Quality of Agrochemicals for the Revamping of a Sprayer System Based on Lidar Technology and Grapevine Disease Management

Grapevines are one of the most intensely treated crops with a high potential risk to health and biodiversity. Thus, the distribution control of agrochemicals is crucial to obtain a high quality and sustainable product for intensive viticulture. Although the search for systems to reduce the waste of chemical products is consistent in some countries, such as Italy, the machinery used are obsolete. The development of an upgrading system for sprayers can be a good compromise to achieve the pollution reduction without requiring huge investments. Field tests were conducted using a LIDAR-based prototype coupled to a commercial sprayer. This study tested the distribution performance using water-sensitive papers and evaluated the infections of grapevine downy and powdery mildews. The results showed a distribution in the vegetation gaps with a higher frequency in the coverage classes >20% in the standard treatment and 10–15% in the LIDAR treatment. Treatments performed with LiDAR reduced the incidence of downy mildew and severity of powdery mildew. The innovative sprayer reduces the distribution of agrochemicals thanks to the on/off control of the nozzles in the voids of vegetation and, meanwhile, controls vineyard fungal disease, so it can be a good way to meet the sustainability and quality of the production.

Fire-released seed dormancy - a global synthesis.

ABSTRACTSeed dormancy varies greatly between species, clades, communities, and regions. We propose that fireprone ecosystems create ideal conditions for the selection of seed dormancy as fire provides a mechanism for dormancy release and postfire conditions are optimal for germination. Thus, fire‐released seed dormancy should vary in type and abundance under different fire regimes. To test these predictions, we compiled data from a wide range of fire‐related germination experiments for species in different ecosystems across the globe. We identified four dormancy syndromes: heat‐released (physical) dormancy, smoke‐released (physiological) dormancy, non‐fire‐released dormancy, and non‐dormancy. In fireprone ecosystems, fire, in the form of heat and/or chemical by‐products (collectively termed ‘smoke’), are the predominant stimuli for dormancy release and subsequent germination, with climate (cold or warm stratification) and light sometimes playing important secondary roles. Fire (heat or smoke)‐released dormancy is best expressed where woody vegetation is dense and fires are intense, i.e. in crown‐fire ecosystems. In such environments, seed dormancy allows shade‐intolerant species to take advantage of vegetation gaps created by fire and synchronize germination with optimal recruitment conditions. In grassy fireprone ecosystems (e.g. savannas), where fires are less intense but more frequent, seed dormancy is less common and dormancy release is often not directly related to fire (non‐fire‐released dormancy). Rates of germination, whether controls or postfire, are twice as fast in savannas than in mediterranean ecosystems. Fire‐released dormancy is rare to absent in arid ecosystems and rainforests. The seeds of many species with fire‐released dormancy also possess elaiosomes that promote ant dispersal. Burial by ants increases insulation of seeds from fires and places them in a suitable location for fire‐released dormancy. The distribution of these dormancy syndromes across seed plants is not random – certain dormancy types are associated with particular lineages (phylogenetic conservatism). Heat‐released dormancy can be traced back to fireprone floras in the ‘fiery’ mid‐Cretaceous, followed by smoke‐released dormancy, with loss of fire‐related dormancy among recent events associated with the advent of open savannas and non‐fireprone habitats. Anthropogenic influences are now modifying dormancy‐release mechanisms, usually decreasing the role of fire as exaptive effects. We conclude that contrasting fire regimes are a key driver of the evolution and maintenance of diverse seed dormancy types in many of the world's natural ecosystems.

Survival and growth of a high-mountain daisy transplanted outside its local range, and implications for climate-induced distribution shifts.

Field transplant experiments can improve our understanding of the effects of climate on distributions of plants versus a milieu of biotic factors which may be mediated by climate. We use a transplant experiment to test how survival and growth of a mountain-top daisy (Podolepis robusta), when planted within and outside its current local range, varies as a function of individual plant size, elevation, aspect and the presence of other vegetation. We expected a home-site advantage for the species, with highest survival and growth within the species’ current elevational limits, and a decline in vital rates above (due to physiological limitations) and below (due to competition with near-neighbours) these limits. Transplant survival during the beginning of the census was high (89 %), though by the third growing season, 36 % of initial transplants were remaining. Elevation had a significant negative effect on individual mortality rates; plants growing at higher elevations had a lower estimated hazard rate and thus, higher survival relative to those planted at elevations below the current lower limit of the distribution. By contrast, we detected no significant effect of elevation on growth rates. Small vegetation gaps had no effect on growth rates, though we found a negative, but non-significant, effect on mortality rates. Aspect had a very strong impact on growth. Plants transplanted to cool aspects had a significantly lower growth rate relative to transplants growing on a warm aspect. Conversely, aspect was not a significant predictor of individual mortality rates. Restrictions on the local distribution of P. robusta appear to be governed by mortality drivers at lower elevation and by growth drivers associated with aspect. We highlight that our ability to understand the drivers of distributions in current and future climates will be limited if contextual- and individual-level plant responses remain understudied.

High-resolution images and drone-based LiDAR reveal striking patterns of vegetation gaps in a wooded spinifex grassland of Western Australia

ContextVegetation patterns in hummock grasslands of Australia’s arid interior can be very complex. Additionally, the grasslands are interspersed with variable amounts of trees and shrubs.ObjectivesTo better understand the spatial arrangement of this vegetation structure, and in particular the unvegetated bare-soil gaps, we analyzed the scale-dependent patterns of gaps, trees, and shrubs.MethodsWe focused on two size categories of grassland gaps, large gaps ≥ 4 m2 known as fairy circles (FCs) and small gaps 1 to < 4 m2, and on trees and shrubs. We mapped four 200 m × 200 m study plots located east of the town of Newman in Western Australia, using drone-based aerial images and LiDAR. The RGB images were converted into binary images and the gaps and woody plants were automatically segmented. The spatial patterns of the four vegetation components were analyzed, as well as the shape properties of the vegetation gaps.ResultsThe most striking result was that small gaps appeared consistently at about 5 m distance away from the FCs, which are known as the most water-depleted locations in the grassland. The FCs were also rounder than the small gaps and this symmetry underlines their function as an extra source of water for the surrounding matrix vegetation. Trees and shrubs had spatial patterns that were unrelated to FCs, which likely results from their water uptake in deeper sub-soil layers.ConclusionsThe consistent distance of small gaps to FCs is further support that the Australian fairy circles are a self-organized vegetation pattern that results from ecohydrological feedbacks.

Definition of “fairy circles” and how they differ from other common vegetation gaps and plant rings

AbstractAimsThe fairy circles along the Namib Desert in southern Africa are round grassland gaps that have puzzled scientists for about 50 years. With the discovery of fairy circles in Australia in 2016, the debate on the origin of the circles has been extended to a new continent. Research interest on the topic has since then risen strongly but so has the use of the term “fairy circle”. This term has become more imprecise and, by analogy, has been applied to circular vegetation gaps or plant rings that are largely unrelated to fairy circles. For this reason, we define the concept of fairy circles by identifying their three main characteristics based on in situ field observations and soil excavations to larger‐scale spatial patterns, and regional‐scale distribution.ResultsFollowing this approach, fairy circles are defined by: (a) being “empty gaps” in grassland without a central insect‐nest structure; (b) their ability to form spatially periodic patterns, which are regular hexagonal patterns with an extraordinary degree of spatial ordering; and (c) their strongly regional distribution confined within a narrow arid climatic envelope. In these combined traits, fairy circles differ from other common vegetation gaps which, for example, always have a central insect‐nest structure and may occur across broad climatic gradients on continents. Also plant rings have their own specific characteristics that largely differ from the combined attributes of genuine fairy circles.ConclusionsThere are many other vegetation‐gap patterns in arid lands but if such gaps cannot jointly show the three characteristics defining the fairy circles, they should be carefully discussed on their own, rather than mixing them up with fairy circles. Our synthesis provides a new etymology for the different types of vegetation gaps and rings, aiming to guide the reader through various classes of circular plant patterns.

Mapping spatially explicit vegetation gaps in Florida rosemary scrub using unmanned aerial vehicles

AbstractAdvances in remote sensing technologies offer new means to monitor habitats of importance on large scales. Florida rosemary scrub is one such threatened habitat, found in patches across the landscape in relatively elevated areas, and is often characterized by shrub‐less areas (gaps) among the dominant shrubs, which provide favorable microhabitats for many endemic and endangered plants and animals. However, gaps are difficult and time‐consuming to characterize, especially across large areas, using traditional ground‐based field methods. We developed and tested a method for rapidly classifying gaps using an unmanned aerial vehicle (UAV or drone). Aerial data were collected by a UAV‐mounted camera in April 2018, and stratified, random ground surveys to verify UAV data were conducted March through April 2018 at Archbold Biological Station in south‐central Florida, USA. We used mosaicked and georeferenced digital surface and terrain models to calculate vegetation height across 33 rosemary scrub sites (~230,000 m2 at 0.064 m2 pixel resolution). Gaps were defined as &gt;1 m2 areas where vegetation height was &lt;10 cm. We found that gap areas from UAV models and field surveys were significantly correlated across varying gap sizes, times‐since‐fire, and relative elevations. We also observed a significant decrease in mean gap area and percent gap space with increasing time‐since‐fire, a pattern consistent with smaller‐scale, ground‐based sampling, and a marginally significant increase in gap area with relative elevation. This remote sensing method lends itself to better exploration of how gap areas, their spatiotemporal patterns, and associated fire history, elevation, soil, and other geographic data affect structural vegetation dynamics across the landscape. This study illustrates the success of UAV modeling of gap space in Florida rosemary scrub, a result of regional consequence for the southeastern United States, but more broadly, it encourages the use of UAV technology as a tool to enhance traditional field‐based methods in systems globally. As habitat fragmentation and loss become increasingly problematic for the conservation of threatened habitats, understanding these complex spatial dynamics is crucial to the conservation and management of vegetation communities and their biodiversity.

Hydrogen Emanations in Intracratonic Areas: New Guide Lines for Early Exploration Basin Screening

Offshore the emissions of dihydrogen are highlighted by the smokers along the oceanic ridges. Onshore in situ measurements in ophiolitic contexts and in old cratons have also proven the existence of numerous H2 emissive areas. When H2 emanations affect the soils, small depressions and vegetation gaps are observed. These depressions, called fairy circles, have similarities with the pockmark and vent structures recognized for long time in the sea floor when natural gas escapes but also differences. In this paper we present a statistic approach of the density, size, and shape of the fairy circles in various basins. New data from Brazil and Australia are compared to the existing database already gathered in Russia, USA, and again Brazil. The comparison suggests that Australia could be one of the most promising areas for H2 exploration, de facto a couple of wells already found H2, whereas they were drilled to look for hydrocarbons. The sum of areas from where H2 is seeping overpasses 45 km2 in Kangaroo Island as in the Yorke Peninsula. The size of the emitting structures, expressed in average diameter, varies from few meters to kilometers and the footprint expressed in % of the ground within the structures varies from 1 to 17%. However, globally the sets of fairy circles in the various basins are rather similar and one may consider that their characteristics are homogeneous and may help to characterize these H2 emitting zones. Two kinds of size repartitions are observed, one with two maxima (25 m and between 220 m ± 25%) one with a simple Gaussian shape with a single maximum around 175 m ± 20%. Various geomorphological characteristics allow us to differentiate depressions of the ground due to gas emissions from karstic dolines. The more relevant ones are their slope and the ratio diameter vs. depth. At the opposite of the pockmark structures observed on the seafloor for which exclusion zones have been described, the H2 emitting structures may intersect and they often growth by coalescence. These H2 emitting structures are always observed, up to now, above Archean or Neoproterozoic cratons; it suggests that anoxia at the time the sedimentation and iron content play a key role in the H2 sourcing.

Drought years in peatland rewetting: rapid vegetation succession can maintain the net CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; sink function

Abstract. The rewetting of peatlands is regarded as an important nature-based climate solution and intended to reconcile climate protection with the restoration of self-regulating ecosystems that are resistant to climate impacts. Although the severity and frequency of droughts are predicted to increase as a consequence of climate change, it is not well understood whether such extreme events can jeopardize rewetting measures. The goal of this study was to better understand drought effects on vegetation development and the exchange of the two important greenhouse gases CO2 and CH4, especially in rewetted fens. Based on long-term reference records, we investigated anomalies in vegetation dynamics, CH4 emissions, and net CO2 exchange, including the component fluxes of ecosystem respiration (Reco) and gross ecosystem productivity (GEP), in a rewetted fen during the extreme European summer drought in 2018. Drought-induced vegetation dynamics were derived from remotely sensed data. Since flooding in 2010, the fen was characterized by a patchy mosaic of open-water surfaces and vegetated areas. After years of stagnant vegetation development, drought acted as a trigger event for pioneer species such as Tephroseris palustris and Ranunculus sceleratus to rapidly close persistent vegetation gaps. The massive spread of vegetation assimilated substantial amounts of CO2. In 2018, the annual GEP budget increased by 20 % in comparison to average years (2010–2017). Reco increased even by 40 %, but enhanced photosynthetic CO2 sequestration could compensate for half of the drought-induced increase in respiratory CO2 release. Altogether, the restored fen remained a net CO2 sink in the year of drought, though net CO2 sequestration was lower than in other years. CH4 emissions were 20 % below average on an annual basis, though stronger reduction effects occurred from August onwards, when daily fluxes were 60 % lower than in reference years. Our study reveals an important regulatory mechanism of restored fens to maintain their net CO2 sink function even in extremely dry years. It appears that, in times of more frequent climate extremes, fen restoration can create ecosystems resilient to drought. However, in order to comprehensively assess the mitigation prospects of peatland rewetting as a nature-based climate solution, further research needs to focus on the long-term effects of such extreme events beyond the actual drought period.

Navigating in a challenging semiarid environment: the use of a route-based mental map by a small-bodied neotropical primate.

To increase efficiency in the search for resources, many animals rely on their spatial abilities. Specifically, primates have been reported to use mostly topological and rarely Euclidean maps when navigating in large-scale space. Here, we aimed to investigate if the navigation of wild common marmosets inhabiting a semiarid environment is consistent with a topological representation and how environmental factors affect navigation. We collected 497h of direct behavioral and GPS information on a group of marmosets using a 2-min instantaneous focal animal sampling technique.We found that our study group reused not only long-route segments (mean of 1007m) but entire daily routes, a pattern that is not commonly seen in primates. The most frequently reused route segments were the ones closer to feeding sites, distant to resting sites, and in areas sparse in tree vegetation. We also identified a total of 56 clustered direction change points indicating that the group modified their direction of travel. These changes in direction were influenced by their close proximity to resting and feeding sites. Despite our small sample size, the obtained results are important and consistent with the contention that common marmosets navigate using a topological map that seems to benefit these animals in response to the exploitation of clustered exudate trees. Based on our findings, we hypothesize that the Caatinga landscape imposes physical restrictions in our group's navigation such as gaps in vegetation, small trees and xerophytic plants. This study, based on preliminary evidence, raises the question of whether navigation patterns are an intrinsic characteristic of a species or are ecologically dependent and change according to the environment.

Effect of Habitat Structure and Crop Diversity on Common and Threatened Birds Breeding in Semi-Natural Field Margins

Field margins are inherent elements of European agricultural landscapes, thought to be crucial for maintaining a high biodiversity level. The interactions between the structure of field margins and biota have been recognized, yet the understanding of the importance of various components of the margins and adjacent areas is still incomplete. The aim of our study was therefore to determine the relative importance of structural features of the margins and diversity of adjacent crops for birds breeding in field margins. The study was carried out in 70 field margins covered with semi-natural vegetation, situated in SW Poland. Both the number of species and bird density were most strongly positively related to the development of tree and shrub layers, while presence of ditches and percentage of reed cover (positive effects) had much less importance. Analyses conducted at the species level revealed the complexity of bird-habitat interactions resulting from various requirements of individual species. Overall, for 22 abundant species and for the threatened species, the development of the shrub layer turned out to be a particularly important feature of field margins positively associated with occurrence of e.g. Emberiza citrinella, Linaria cannabina and Streptopelia turtur. Other significant positive effects had the development of the tree layer (e.g. Turdus merula and Turdus philomelos), presence of ditch (e.g. Acrocephalus palustris, Sylvia communis), and number of gaps in woody vegetation (e.g. Lanius collurio). The diversity of adjacent crops had positive effects only to some threatened species (e.g. L. collurio and E. calandra). Abundances of common and threatened birds were not correlated, which reflects different habitat demands of these two groups. Because of diverse bird-habitat relationships, maintaining a variety of field margins (in particular the shrubby ones), should be accepted as a rule in biodiversity-oriented management of agricultural landscapes.

Gapped vegetation patterns: Crown/root allometry and snaking bifurcation

Nonuniform spatial distributions of vegetation in scarce environments consist of either gaps, bands often called tiger bush or patches that can be either self-organized or spatially localized in space. When the level of aridity is increased, the uniform vegetation cover develops localized regions of lower biomass. These spatial structures are generically called vegetation gaps. They are embedded in a uniform vegetation cover. The spatial distribution of vegetation gaps can be either periodic or randomly distributed. We investigate the combined influence of the facilitative and the competitive nonlocal interactions between plants, and the role of crow/root allometry, on the formation of gapped vegetation patterns. We characterize first the formation of the periodic distribution of gaps by drawing their bifurcation diagram. We then characterize localized and aperiodic distributions of vegetation gaps in terms of their snaking bifurcation diagram.

Dieback and expansions: species-specific responses during 20\xa0years of amplified warming in the high Alps

The largest alpine–nival vegetation permanent plot site in the Alps, the GLORIA mastersite Schrankogel (Tirol, Austria), provided evidence of warming-driven vegetation changes already 10 years after its establishment in 1994. Another decade later, in 2014, substantial compositional changes with increasing ratios of warmth-demanding to cold-adapted species have been found. The current study deals with species-specific responses involved in an ongoing vegetation transformation across the alpine–nival ecotone on Schrankogel by using presence/absence as well as cover data from permanent plots, situated between 2900 and 3400 masl. The number of occupied plots per species remained constant or even increased during the first decade, whereas disappearance events became more frequent during the second one, especially for cold-adapted specialists (subnival–nival species). Remarkably, the latter was accompanied by continued strong losses in cover of all subnival–nival species. These losses were more frequent in plots with a more thermophilous species composition, suggesting an increasing maladaptation of subnival–nival species to warmer habitat conditions and a successive trailing-edge decline. Several species with a distribution centre at lower elevations (alpine–subnival) markedly increased in cover, comparatively more so in colder plots, indicating a leading-edge expansion. Moreover, our findings show an increase in occupied plots and cover of almost all snowbed species, suggesting that areas previously with a too long snowpack period are now becoming suitable snowbed habitats. Vegetation gaps arising from population dieback of cold-adapted species, however, could only be partly filled by advancing species, indicating that species declines have occurred already before the onset of strong competition pressure.

A multi‐scale study of Australian fairy circles using soil excavations and drone‐based image analysis

AbstractFairy circles (FCs) are extremely ordered round patches of bare soil within arid grasslands of southwestern Africa and northwestern Australia. Their origin is disputed because biotic factors such as insects or abiotic factors such as edaphic and eco‐hydrological feedback mechanisms have been suggested to be causal. In this research, we used a multi‐scale approach to shed light on the origin of Australian FCs. At a local scale, we investigated the potential cause of FCs using analyses of soil compaction and texture within FCs, the surrounding matrix vegetation, and in nearby large bare‐soil areas. We found that soil hardness and clay content were similarly higher inside the FCs and in the large bare‐soil areas. When compared to the matrix soils with protective grass cover, the 2.6–2.8 times higher clay content in FCs and large bare‐soil areas is likely sourced via multiple abiotic weathering processes. Intense rainfall events, particle dispersion, surface heat, evaporation, and mechanical crust building inhibit plant growth in both areas. At the landscape scale, a systematic survey of 154 soil excavations within FCs was undertaken to evaluate the presence of pavement termitaria that could inhibit plant growth. We show that in up to 100% and most of the excavations per plot, no hard pavement termitaria were present in the FCs. This fact is substantiated by the observation that small, newly forming FCs are initiated on soft sand without evidence of termite activity. At the regional scale, we investigated the spatial properties of FCs and common termite‐created gaps in Western Australia, using spatially explicit statistics. We mapped three 25‐ha FC plots with a drone and compared them with three aerial images of typical vegetation gaps created by harvester and spinifex termites. We demonstrate that the small diameters, the lower ordering, and the heterogeneous patterns of these common termite gaps strongly differ from the unique spatial signature of FCs. Our multi‐scale approach emphasizes that FCs are not trivial termite gaps and that partial correlation with termites at some sites does not imply causation. Instead, we highlight the need to study the edaphic and eco‐hydrological drivers of vegetation‐pattern formation in water‐limited environments.

Spatial prediction of stream physicochemical parameters for the Napo River Basin, Ecuador

Major threats to freshwater ecosystems in the Andean-Amazon region include agriculture, point and nonpoint source pollution, hydroelectric dams, oil extraction, mining and road building, yet little is known about the baseline values and current state of rivers and streams, or how expanding urban, industrial and agricultural activities could affect and change these freshwater ecosystems and their diversity. Therefore, there is a need to understand physicochemical parameters at the basin scale in many large river systems in the Andean-Amazon such as the Napo River, a world biodiversity hotspot. Establishing baselines for these parameters under less developed conditions will be impossible after development in the watersheds increases and hydroelectric projects reach completion. In addition to collecting data to fill in information gaps in geology, vegetation, disturbance, and other parameters that influence water quality, it is important to use existing data in the Napo to predict chemical parameters throughout the watershed to set a baseline from which deviations from development and climate change can be assessed and to guide data collection efforts. In this study, we provide the first basin-wide estimates of physicochemical parameters (pH, conductivity, dissolved oxygen and temperature) for the entire Napo River Basin using a recently developed geostatistical technique called top kriging. Basin-wide predictions aligned well with observed values and a model validation test showed a strong goodness-of-fit for parameter estimates. Furthermore, our predictions aligned well with observed values from independent datasets from the Napo Basin. These predictions could be useful in developing water quality reference baselines for the basin and for monitoring relative changes to parameters, assist in the identification of priority areas within the basin for management and conservation efforts, direct future research, and be applied in other data-scarce basins in remote regions worldwide.

What predicts the richness of seeder and resprouter species in fire‐prone Cape fynbos: Rainfall reliability or vegetation density?

AbstractIn ecosystems subject to regular canopy fires, woody species have evolved two general strategies of post‐fire regeneration. Seeder species are killed by fire and populations regenerate solely by post‐fire recruitment from a seed bank. Resprouter species survive fire and regenerate by vegetative regrowth from protected organs. Interestingly, the abundance of these strategies varies along environmental gradients and across regions. Two main hypotheses have been proposed to explain this spatial variation: the gap dependence and the environmental‐variability hypotheses. The gap‐dependence model predicts that seeders are favoured in sparse vegetation (vegetation gaps allowing effective post‐fire recruitment of seedlings), while resprouters are favoured in densely vegetated sites (seedlings being outcompeted by the rapid crown regrowth of resprouters). The environmental‐variability model predicts that seeders would prevail in reliable rainfall areas, whereas resprouters would be favoured in areas under highly variable rainfall that are prone to severe dry events (leading to high post‐fire seedling mortality). We tested these two models using distribution data, captured at the scale of quarter‐degree cells, for seeder and resprouter species of two speciose shrub genera (Aspalathus and Erica) common in fire‐prone fynbos ecosystems of the mediterranean‐climate part of the Cape Floristic Region. Contrary to the predictions of the gap‐dependence model, species number of both resprouters and seeders increased with values of the Normalized Difference Vegetation Index (a widely used surrogate for vegetation density), with a more marked increase for seeders. The predictions of the environmental‐variability hypothesis, by contrast, were not refuted by this study. Seeder and resprouter species of both genera showed highest richness in environments with high rainfall reliability. However, with decreasing reliability, seeder numbers dropped more quickly than those of resprouters. We conclude that the environmental‐variability model is better able to explain the abundance of woody seeder and resprouter species in Southern Hemisphere fire‐prone shrublands (fynbos and kwongan) than the gap‐dependence model.