Are Namibian "fairy circles" the consequence of self-organizing spatial vegetation patterning

Causes of over-dispersed barren "fairy circles" that are often surrounded by ca. 0.5 m tall peripheral grasses in a matrix of shorter ( ca. 0.2 m tall) grasses in Namibian grasslands remain mysterious. It was hypothesized that the fairy circles are the consequence of self-organizing spatial vegetation patterning arising from resource competition and facilitation. We examined the edaphic properties of fairy circles and variation in fairy circle size, density and landscape occupancy (% land surface) with edaphic properties and water availability at a local scale (<50 km) and with climate and vegetation characteristics at a regional scale. Soil moisture in the barren fairy circles declines from the center towards the periphery and is inversely correlated with soil organic carbon, possibly indicating that the peripheral grass roots access soil moisture that persists into the dry season within fairy circles. Fairy circle landscape occupancy is negatively correlated with precipitation and soil [N], consistent with fairy circles being the product of resource-competition. Regional fairy circle presence/absence is highly predictable using an empirical model that includes narrow ranges of vegetation biomass, precipitation and temperature seasonality as predictor variables, indicating that fairy circles are likely a climate-dependent emergent phenomenon. This dependence of fairy circle occurrence on climate explains why fairy circles in some locations may appear and disappear over time. Fairy circles are only over-dispersed at high landscape occupancies, indicating that inter-circle competition may determine their spacing. We conclude that fairy circles are likely to be an emergent arid-grassland phenomenon that forms as a consequence of peripheral grass resource-competition and that the consequent barren circle may provide a resource-reservoir essential for the survival of the larger peripheral grasses and provides a habitat for fossicking fauna

The influence of disturbance scale on the natural recovery of biological soil crusts on the Colorado Plateau

Up to 35% of global drylands have experienced degradation due to anthropogenic impacts, including physical disturbances like trampling and soil removal. These physical disturbances can result in the loss of soil communities known as biological soil crusts (biocrusts) and the important functions they provide, such as soil stability and fertility. The reestablishment of biocrust organisms after disturbance is determined by many factors, including propagule availability, climate, and vascular plant community structure. The role of these factors in natural recovery may be intensified by the extent (or size) of a disturbance. For example, large disturbances can result in reduced propagule availability or enhanced erosion, which impact both the dispersal and establishment of biocrust organisms on disturbed soils, leading to a slower natural recovery. To test how disturbance extent impacts biocrust's natural recovery, we installed four disturbance extents by completely removing biocrust from the mineral soil in plots ranging from 0.01 m2 to 1 m2 and measured productivity and erosion resistance. We found that small disturbance extents did not differ in chlorophyll a content, total exopolysaccharide content, or soil stability after 1.5 years of natural recovery. However, the concentration of glycocalyx exopolysaccharide was higher in the smallest disturbances after the recovery period. Our results indicate that disturbances &lt;1 m2 in scale recover at similar rates, with soil stability returning to high levels in just a few years after severe disturbance. Our findings align with prior work on biocrust natural recovery in drylands and highlight the opportunity for future work to address (1) cyanobacteria, moss, and lichen propagule dispersal; (2) rates and mechanisms of biocrust succession; and (3) the role of wind or water in determining biocrust colonization patterns as compared to lateral growth

Impacts of disturbance on the terrestrial carbon budget of North America

Because it is an important regulator of terrestrial carbon cycling in North America, extensive research on natural and human disturbances has been carried out as part of the North American Carbon Program and the CarboNA project. A synthesis of various components of this research was carried out, and the results are presented in the papers contained in this special section. While the synthesis primarily focused on the impacts of fire, insects/disease, and harvesting on terrestrial carbon cycling in forests, several groups focused on impacts of disturbance on woody encroachment in western U. S. dry lands and on soil carbon present in northern high-latitude regions. Here, we present a summary of the results from these papers, along with the findings and recommendations from the disturbance synthesis. Citation: Kasischke, E. S., B. D. Amiro, N. N. Barger, N. H. F. French, S. J. Goetz, G. Grosse, M. E. Harmon, J. A. Hicke, S. Liu, and J. G. Masek (2013), Impacts of disturbance on the terrestrial carbon budget of North America, J. Geophys. Res. Biogeosci., 118, 303-316, doi:10.1002/jgrg.20027.Keywords: Permafrost thaw, United States, Mountain pine beetle, Boreal forest, Canada, Climate change, Dynamics, Fire severity, Ice storm damage, Forest gap model

Author Correction: Drivers of seedling establishment success in dryland restoration efforts

1 Pág. Correción errata.In the version of this Article originally published, the surname of author Tina Parkhurst was incorrectly written as Schroeder. This has now been corrected.Peer reviewe

Data from: Declines in pinyon pine cone production associated with regional warming

Global climate change is expected to produce large shifts in vegetation distribution and has already increased tree mortality, altering forest structure. However, long-term shifts will be partly dependent on the ability of species to reproduce under a novel climate. Few studies have examined the impact of climate change on the reproductive output of long-lived ‘masting' species, or species characterized by episodic reproductive events. Here, we show that seed cone production among pinyon pine (Pinus edulis), a masting species, declined by 40% from the 1974 decade (1969–1978) to the 2008 decade (2003–2012) in revisited stands throughout New Mexico and northwestern Oklahoma. Seed cone production was highly correlated with late summer temperatures at the time of cone initiation. Further, declines in seed cone production were greatest among populations that experienced the greatest increases in growing season temperatures, which were the populations located at the cooler, upper elevations. As growing season temperatures are predicted to increase across this region over the next century, these findings suggest seed cone production may be an increasingly important bottleneck for future pinyon pine regeneration, especially in areas with greater increases in temperature. Declines in seed cone production may not only affect pinyon pine population dynamics but also the various wildlife species that rely on pinyon pine seeds. Because pinyon pine has similar reproductive strategies as other semi-arid pine species, increasing temperature may negatively influence reproductive output of other conifers. Further investigation into the full geographic and taxonomic extent of these seed declines is warranted

Variation in regional fairy circle (FC) landscape occupancy with mean annual precipitation (MAP).

<p>Landscape occupancy was based on aerial photograph analysis (black points) and ground survey (NamibRand Nature reserve site average; red point). MAP was based on Bioclim data (<a href="http://www.worldclim.org" target="_blank">www.worldclim.org</a>; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070876#pone.0070876-Hijmans1" target="_blank">[38]</a>), which is averaged over 1950–2000 and differs from the MAP collected within the reserve (2006–2011). The broken line represents the 90^th quantile piecewise non-linear regression line <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070876#pone.0070876-Koenker1" target="_blank">[45]</a> to define the upper limit of landscape occupancy.</p

The relative influences of the three predictor variables that were retained in the simplified BRT model for fairy circle (FC) presence/absence.

<p>The variables are mean annual precipitation (MAP), the 1^st principal component of the enhanced vegetation index (1^st PC of EVI) and temperature seasonality (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070876#pone.0070876.s003" target="_blank">Fig. S3</a>). The relative interaction sizes (in parentheses) for two-way interactions between these variables were calculated using BRT analyses. The ranges are between the 5 and 95 percentiles of sites sampled either with or without fairy circles (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070876#pone.0070876.s001" target="_blank">Fig. S1</a>).</p

Soil moisture and organic carbon variation across fairy circles and into matrix.

<p>Variation with distance from the fairy circle center of soil moisture (A) and organic C (B) weight-summed over sampled depths (mean ± SE; n ≤5). The co-variation of soil moisture and soil organic C (C) is shown with the coefficient of determination (r²) and probability value (P) for the subset of data from the barren fairy circle interior.</p