Open Interspaces Research Articles

Quantifying soil moisture and evapotranspiration heterogeneity within a solar farm: Implications for stormwater management

As solar energy becomes a cheap source of renewable energy, the number of major utility-scale ground solar panel installations, often called ‘solar farms,’ are growing. With these solar farms often covering hundreds of acres, there is potential for impacts on natural hydrologic processes, including runoff generation and erosion. There is still limited research in this area, and best management practices to address these impacts are variable and not well understood. To fill this gap, we conducted a field investigation of soil moisture patterns, solar radiation, and vegetation at two solar farms in central Pennsylvania, USA that are representative of the complex terrain in the region (e.g., high or variable slopes). Both solar farms also included engineered infiltration basins or trenches that were investigated. Analysis of soil moisture patterns reveals redistribution of water relative to panels, with dripline soil moisture 19 % higher than the reference, and underpanel moisture 25 % lower than the reference, on average at both solar farms over a year. There are also the greatest periods of saturation and runoff generation at the panel driplines. However, an open interspace between panel rows and existing infiltration basins and trenches are playing a critical role in managing runoff. Micrometeorological monitoring indicates reduced evapotranspiration (ET) under panels, with potential underpanel ET 37–67 % lower in summer, and minimal difference in winter. However, a survey of vegetation revealed almost complete ground coverage under panels, which is critical for supporting infiltration and reducing erosion. As solar farms expand to meet important renewable energy goals, it is essential that care be taken to design the landscape to minimize runoff generation and erosion. This work demonstrates that healthy vegetation and well-draining soils can help manage runoff on solar farms; where necessary on more challenging landscapes, engineered stormwater controls can manage any unmitigated runoff.

On the relative importance of resource availability and habitat connectivity as drivers of soil biodiversity in Mediterranean ecosystems

Abstract Soil biota influences nutrient cycling and climate regulation and represents an important fraction of global biodiversity, yet we know very little about how this soil biota responds to habitat fragmentation and degradation of habitat quality. We studied the response of different soil trophic groups (microbes and soil fauna), and their trophic structure, to changes in their habitat derived from forest long‐term management and extensive tree die‐off in a Mediterranean ecosystem. Specifically, we evaluated changes in (i) habitat size, (ii) habitat resource availability and heterogeneity and (iii) habitat connectivity. To do this, we sampled the soil biota of 43 holm oak trees (and five open interspaces) differing in size, quality, heterogeneity, connectivity and the effect of die‐off (healthy or affected). We sorted soil biota by trophic group and related their richness to habitat characteristics. Seven of the 12 trophic groups evaluated increased their species richness with soil organic carbon content, which was the most frequently selected driver of soil biota (both microbial and faunal richness). Habitat connectivity positively affected the richness of larger organisms (fauna) and plant attributes (richness, productivity and specific leaf area) also showed significant but contrasting effects depending on the group evaluated. Due to the idiosyncratic responses of different groups, the entire trophic structure (microbes and fauna) was affected by a more complex set of factors than most trophic groups in isolation, including interactions between habitat size and resource availability or connectivity. A major factor influencing habitat resource availability was the die‐off of the dominant tree species (drastically altering tree productivity). We found weaker and more negative relationships between trophic groups under trees suffering from die‐off than beneath healthy trees, particularly between microbial rather than faunal groups. Synthesis. We provide a comprehensive assessment of the response of key members of the soil food web to habitat fragmentation and tree die‐off (landscape‐level plant–soil interactions), illustrating the major role of soil carbon, habitat connectivity and tree die‐off in driving soil biodiversity and trophic structure.

Climate and plants regulate the spatial variation in soil multifunctionality across a climatic gradient

A patchy distribution of soil resources is a characteristic of most natural terrestrial biomes, potentially resulting in spatial variation in multiple soil functions (soil multifunctionality). However, less is known about how soil multifunctionality and its spatial variability respond to increasing dryness across extensive climatic gradients, making it difficult to predict changes in ecosystem functions under climate change scenarios. We surveyed 150 sites along a 1500 km climatic gradient in eastern Australia, from humid forests to arid shrublands, to explore the spatial variation in soil multifunctionality with increasing aridity. We assessed four functional groups (carbon stocks, organic matter decomposition, plant structure, soil stability) of multifunctionality and average (net) multifunctionality across four vegetation patch types (tree, shrub, grass and unvegetated open interspaces). We then used average dissimilarity across these four patches as our measure of spatial variability. Our results showed that 1) net soil multifunctionality remained unchanged as aridity increased, because increases in soil stability and plant structure compensated for reductions in carbon stocks and organic matter decomposition; 2) the response of soil multifunctionality to increasing aridity differed among vegetation patch types, with the greatest increases in plant structure and reductions in carbon stocks in the open, but with marginal changes beneath trees; 3) variation in soil multifunctionality increased with increasing aridity and was driven by changes in climate (aridity, rainfall seasonality), soil (pH, sand) and to a lesser extent, variation in plant size, with impacts varying with the target functional group. Our study provides empirical evidence that soils can sustain an average level of multifunctionality across the climatic gradient by regulating the trade-offs between nutrient cycling and soil stability. Furthermore, our results demonstrate that forecasted increases in aridity will increase the spatial variation in soil multifunctionality and enhance the dominance of biocrusts, which would be critical for stabilizing soils under drier global climates.

Plant functional traits involved in the assembly of canopy–recruit interactions

AbstractQuestionsThe assembly of plant communities depends strongly on mechanisms that determine the recruitment of different plant species. Studying recruitment using a trait‐based approach may help in the search for general or dominant mechanisms involved in this process. Here, we try to disentangle what traits of saplings and established (canopy) plants can be considered as functional for recruitment, and whether the complementarity of these functional traits may be a driver of the plant community assembly.LocationRegional. Two pine–oak forest communities in Sierra Sur de Jaén and one in Sierra de Segura, southeast of the Iberian peninsula.MethodsIn each forest community, we established three 50 m × 50 m plots, where we identified the saplings of each species recruiting under the canopy of each species or in open interspaces. The study focuses on 37 woody species. Measures of 18 traits were conducted for 30 saplings and 10 adults of each species.ResultsSeed mass and the ratio height:basal diameter of saplings were positively associated with species abundance in the sapling bank under vegetation, while abundance in the sapling bank in open interspaces was only related to the type of mycorrhizal association. On the other hand, some traits of adult plants (leaf mass per unit area [LMA], seed dispersal mechanism, leaf habit and branch density) favour the recruitment of other species in their close proximity. However, we found only circumstantial evidence of canopy/recruit trait complementarity affecting recruitment.ConclusionsOur results suggest that the assembly of canopy–recruit interactions is primarily driven by the filtering effect of canopy species on recruitment, through traits that affect both seed arrival and soil properties. Species abundance in the sapling bank was related to resource acquisition traits. We did not find any clear evidence supporting that trait complementarity is involved in the interaction between canopy and recruit species.

Nanorods-assembled ZnO microflower as a powerful channel for n-butanol sensing

Assembly of one-dimensional (1D) nanorods into organized three-dimensional (3D) architectures, coupled with open interspaces, is favorable for gas-interface interaction and diffusion. In this paper, a single-crystalline nanorods-built ZnO microflower has been successfully prepared through a facile hydrothermal route. The surface morphology, crystal structure, element composition and pore characteristic of this ZnO product were also conducted using diverse technical methods. In addition, the morphology evolution process was further clarified through a time-dependent reaction. The ZnO microflower-based gas sensor declared a remarkable response towards n-butanol in terms of outstanding selectivity, low detection limit (~ 0.1 ppm), and rapid response rate (≤ 12 s for 1–100 ppm n-butanol). Moreover, this ZnO sensor still maintained a powerful response (Ra/Rg = 46.53) towards 100 ppm n-butanol when exposed to high-level relative humidity (RH = 80%). The improvement of gas-sensing response was discussed in detail. This work demonstrates that integration of 1D nanorods into rational 3D structure is an efficient strategy for fabricating high-performance gas sensor.

Assembly of stacked In2O3 nanosheets for detecting trace NO2 with ultrahigh selectivity and promoted recovery

Assembly of two-dimensional (2D) nanosheets into organized three-dimensional (3D) architectures, coupled with open interspaces and surface-rich nanopores, is favorable for gas-interface diffusion and reaction. In this case, this kind of In2O3 morphology consisted of stacked nanosheets is successfully prepared through a facile hydrothermal and subsequent annealing route. And its morphology evolution route is also investigated using a time-dependent reaction. The gas sensor fabricated using this In2O3 product shows a remarkable response (Rgas/Rair = 5208.57) towards 20 ppm NO2, and an obvious response to 0.1 ppm NO2 at 100 °C. Moreover, the sensor signal can achieve a fast recovery after NO2-sensing event using a pulse-heating strategy. A negligible interference is also observed when exposed to other interfering vapors (including ethanol, acetone, toluene, NH3, and H2S), even though the concentrations of these gases are 100-folds than that of NO2. This ultrahigh selectivity towards NO2 is further confirmed by the first-principles theoretical results. The apparent NO2-sensing of this stacked In2O3 nanosheet could be tracked from following aspects: well-defined 3D architectures (ultrathin 2D nanosheets with abundant active sites, interspaces and nanopores for fast gas-transfer), strong adsorption energy of NO2 molecules on the exposed In2O3{111} facet, and favorable desorption kinetics at suitable temperature.

High fire frequency reduces soil fertility underneath woody plant canopies of Mediterranean ecosystems

Spatial heterogeneity of soil properties plays a major role in regulating ecosystem structure and functioning. In general, soil resources accumulate beneath woody plant-covered patches more than in the open interspace, making them function as fertility islands. Whilst wildfire is a common disturbance, little information is available on the role of particular plant species in maintaining soil fertility underneath in areas that are subjected to recurrent fires. This is an important issue given that land abandonment, together with a warmer and drier climate, is increasing fire danger in regions such as the Mediterranean. We determined whether increasing fire frequency, producing changes from a Quercus ilex L., woodland to a shrubland, modifies the effect of woody plant canopy on soil fertility. Additionally, the effect of fire history on species-specific leaf and litter nutrient concentration was assessed. Areas affected by none, one, two or three fires were selected. Within each area, soil fertility was measured underneath Cistus ladanifer L., Retama sphaerocarpa L., Phillyrea angustifolia L. and Quercus ilex canopies and in open interspace. Unburned soils located underneath P. angustifolia and Q. ilex canopies were significantly more fertile than in open interspaces. The microsite effect on soil fertility was fire frequency dependent. As fire frequency increased, the plant canopy microsite effect decreased for soil organic matter (SOM), cation exchange capacity (CEC), total C, P, Ca, K and Mg, labile phosphate, arylsulfatase and acid phosphatase activities. Total N, ammonium, nitrate and β-glucosidase activity decreased with increasing fire frequency, but their spatial variability was maintained along all fire frequency scenarios. Fire frequency decreased foliar N concentration but increased P concentration in some species, leading to a decrease in their N:P ratio. Our findings suggest that soil fertility heterogeneity will be reduced with increasing fire frequency. This could compromise the recovery of soil and ecosystem functioning.

Do pioneer species enhance early performance of native species in subtropical shrublands? An examination involving six native species in South China

This paper examines the following questions: (1) Do early pioneer species have a greater impact on the survival and growth of different successional native trees compared to the shrub Rhodomyrtus tomentosa? (2) Do canopy treatments affect soil nutrients and light availability? (3) What is the mechanism underlying the interaction between nurse species and target species? Degraded shrubland sites (Heshan, Guangdong, China), under moist subtropical conditions were studied. About 1-year-old seedlings of Pinus massoniana, Schima wallichii, Schefflera heptaphylla, Castanopsis hystrix, Cryptocarya chinensis and Castanea chinensis were transplanted under the canopy of R. tomentosa, Dicranopteris dichotoma and in open interspaces without vegetation. Survival and growth were recorded from the first growing season after planting. Leaf gas exchange, water potential, soil physicochemical characters and irradiation were then measured. Canonical redundancy analyses (RDA) were used to evaluate the relationships between environmental factors and seedling survival and growth conditions. Both R. tomentosa and D. dichotoma canopy treatment facilitated seedling survival and growth either directly or indirectly. Irradiance/radiation was considered the most important resource (factor) for seedling growth in subtropical regions, however, soil nutrients and species are yet to be examined simultaneously with irradiance/radiation under field conditions. We conclude that early successional species facilitates the survival and growth of late successional species in subtropical shrublands. However, further predictions of successional trajectories remain elusive and are influenced by stochastic processes, including arrival order, shade tolerance, physiological character of the colonizing species and their competitive interactions.

Vegetation Response to Juniper Reduction and Grazing Exclusion in Sagebrush-Steppe Habitat in Eastern Oregon

Western juniper expansion is one of the largest threats to conserving sagebrush steppe ecosystems in the northwestern United States. Juniper expansion has degraded the sagebrush steppe by altering fire regimes and outcompeting shrubs and herbaceous vegetation for limited resources. We characterized the effect of juniper removal in a severely degraded sagebrush steppe habitat for 3 yr following juniper cutting. In addition, we measured the effect of low-intensity seasonal grazing on plant community recovery through cattle exclusion treatments. We monitored plant community composition (exotic annual grasses, preferred grasses, preferred forbs, and shrubs); fuel loads; and juniper recruitment in a factorial design of juniper removal and grazing exclusion. We found that although there were significant differences between cut and uncut juniper treatments, there were no consistent trends across all 3 yr. Our results suggest that other factors, such as timing of precipitation, may also have strong short-term effects on plant community composition. We detected no significant grazing effects during the study period, suggesting the current grazing regime is appropriate for the area. The cutting of juniper increased total fuel loads and herbaceous fuel loads. Compared with open interspace, a twofold increase in juniper seedlings and saplings was detected beneath juniper piles, which will act as sources for future juniper encroachment.

Conspecific plants are better 'nurses' than rocks: consistent results revealing intraspecific facilitation as a process that promotes establishment in a hyper-arid environment.

Harsh environmental conditions in arid ecosystems limit seedling recruitment to microhabitats under nurse structures, such as shrubs or rocks. These structures, however, do not necessarily afford the same benefits to plants because nurse rocks provide only physical nurse effects, whereas nurse plants can provide both physical and biological nurse effects. Nevertheless, if the nurse plant is a conspecific, the benefits it provides may be outweighed by higher mortality due to negative density-dependent processes; consequently, negative density-dependence is expected to limit plants from acting as nurses to their own seedlings. The degree to which an abiotic nurse may be more beneficial than a conspecific one remains largely unexplored. Here, we examine the role and elucidate the mechanisms by which conspecific plants and rocks promote plant establishment in a hyper-arid desert. For 4 years, we examined establishment patterns of Myrcianthes coquimbensis (Myrtaceae), a threatened desert shrub that recruits solely in rock cavities and under conspecific shrubs. Specifically, we characterized these microhabitats, as well as open interspaces for comparison, and conducted germination, seed removal and seedling survival experiments. Our results revealed that conspecific shrubs and nurse rocks modified environmental conditions in similar ways; soil and air temperatures were lower, and water availability was higher than in open interspaces. We found no evidence on negative density-dependent recruitment: seed removal was lowest and seedling emergence highest under conspecific plants, moreover seedling survival probabilities were similar in rock cavities and under conspecific plants. We conclude that the probability of establishment was highest under conspecific plants than in other microhabitats, contrasting what is expected under the Janzen-Connell recruitment model. We suggest that for species living in stressful environments, population regulation may be a function of positive density-dependence and intraspecific facilitation may be a process that promotes the persistence of some plant species within a community.

Effects of sampling effort on estimates of the structure of replacement networks

AbstractAimsImportant aspects of plant community dynamics depend on interactions between plant species that affect the processes of recruitment and the replacement of dead individuals by new ones. These interactions blend in the replacement network of the community. The qualitative and functional structure of replacement networks can provide insights on community stability properties. The goal of this study was to analyse how sampling effort affects estimates of different descriptors of replacement networks.LocationMixed pine‐oak forests in southern Spain.MethodsWe sampled the replacement networks of nine forest patches. In each forest we surveyed 16 plots of 25 m × 25 m, locating all the saplings of woody species and noting whether they were recruiting under the canopy of some plant species or in open interspaces. Using the replacement networks from the plots of each forest we constructed curves relating network descriptor estimates to sampling effort. Additionally we calculated the completeness of basic network elements (number of species and interactions) using rarefaction and extrapolation techniques.ResultsNumber of species (S) and connectance (C) stabilized within our range of sampling effort. The estimates of S reached completeness values above 97%. However, the number of interactions in the network (L) and the mean number or interactions per species (k) did not stabilize, although the estimates of L reached completeness values above 86%. With few exceptions, the parameters describing the functional structure of the network and those related to community stability stabilized within our range of sampling effort.ConclusionsOur results suggest that most replacement networks descriptors in the studied forests can be reliably estimated from samples of around 1 ha. Since plots used in forest ecology are commonly around that size, replacement network monitoring can be easily incorporated in forest ecology studies as a highly cost‐effective tool to explore community dynamics. The reliability of replacement network estimates will provide both a solid foundation for further developments and also a straightforward comparison of results obtained from multiple communities.

Initial constraints in seedling dynamics of Juniperus macrocarpa Sm.

The micro-forests dominated by Juniperus macrocarpa inhabiting coastal dunes in the Mediter- ranean Basin are European priority habitats. Their conservation is hindered by both anthropic and natural causes, although the regeneration problems for J. macrocarpa are still poorly understood. In this study, several factors influencing emergence and mortality of J. macrocarpa seedlings were investigated. For this purpose, permanent plots were placed in coastal dunes of Sardinia (Italy) and periodically monitored to record seedling parameters (emergence, survival and growth), as well as several biotic and abiotic variables (solar radiation, tree cover, herbaceous plus scrub cover, number of female cones on the soil and number of herbivory traces). Linear mixed models were fitted to test the effects of several types of explanatory variables on seedling dynamics. A total of 536 seedlings were marked, most of which emerged in winter. The microhabitat was the most important factor in models explaining emergence, with the number of emerged seedlings decreasing with solar radiation. Survival was very low, reaching the highest mortality percentage in the first summer. Herbivory and location in open interspaces had significant negative effects on seedling survival. In conclusion, the recruitment of J. macrocarpa is highly limited in the initial life cycle phases, with microhabitat and herbivory constraints influencing seedling dynamics. The identification of critical stages in the recruitment process of J. macrocarpa, together with factors influencing them, suggests some implication for management as well the hypotheses for future studies about conservation and recovery of the J. macrocarpa habitat.

Soil Seed Banks of the Exotic Annual Grass Bromus rubens on a Burned Desert Landscape

Red brome (Bromus rubens), an exotic annual grass, can dominate soil seed banks and poses serious threats to mature native plant communities in the Mojave Desert by competing with native species and providing fine fuels that facilitate widespread wildfire. By exploring how seed bank density and composition in burned areas change over time since fire (TSF), we can improve our understanding of how the seed banks are affected by fire. Samples of the 5-cm-deep soil seed bank were collected from two microsites (under shrubs, in open interspaces) within paired burned and unburned areas on 12 fires ranging from 5–31yr TSF. Seed bank samples were assayed using the emergence method and seed densities were compared among TSFs, burn status (burned, unburned), and microsites for the species that emerged. Red brome soil seed bank density was spatially variable and TSF rarely predicted abundance. Overall, undershrub seed densities did not differ between burned and unburned areas. However, at some fire sites, seed densities in interspaces were greater in burned than unburned areas. Although native seed densities were low overall, they did not appear to differ according to burn status. Studies have shown that red brome plant and seed bank densities can be greatly reduced immediately after fire. Management efforts that focus on this initial colonization window may be able to take advantage of diminished red brome seed densities to limit its reestablishment while facilitating the establishment of native species. However, this window is brief, as our findings indicate that once reestablished, red brome soil seed densities in burned areas can be similar to those in unburned areas within 5yr.

Ni nanowire supported 3D flower-like Pd nanostructures as an efficient electrocatalyst for electrooxidation of ethanol in alkaline media

A Ni nanowire array (NiNWA) supported three-dimensional flower-like Pd nano-electrocatalyst with high electrocatalytic performance for the electrooxidation of ethanol in alkaline media has been fabricated by borohydride hydrothermal reduction method. This novel hybrid NiNWA/PdNF (nanoflowers) electrocatalyst exhibits large electrochemically active surface area (EASA, 45m2g−1(Pd)), excellent electrocatalytic activity (765mAmg−1(Pd)), and high level of the poisoning tolerance (If/Ib=1.2) to the carbonaceous oxidative intermediates for the electrooxidation reaction in alkaline media. In addition, the electrochemical stability of NiNWA/PdNF is significantly higher than that of NiNWA/PdNP (nanoparticles) electrocatalyst, as evidenced by chronoamperometry experiments in which the electrooxidation current of nanoflowers is controlled by the diffusion transport of ethanol species rather than the carbonaceous poisoning. This high electrocatalytic activity can be attributed to the more open structure with higher electrochemically active sites and shape of Pd nanoflowers. This is further enhanced by the core support NiNWA with a very large surface area and the open interspaces that ensure easy alcohol access even to remote active sites for fast ion adsorption/desorption.

Soil Fertility, Salinity and Nematode Diversity Influenced by Tamarix ramosissima in Different Habitats in an Arid Desert Oasis

The aim of this paper was to assess the influence of tamarisk shrubs on soil fertility, salinity and nematode communities in various habitats located in an arid desert-oasis region in northwest China. Three habitats were studied: sand dune, riparian zone and saline meadow, where tamarisk shrubs have been established in recent decades in order to vegetation restoration used as desertification control and saline land rehabilitation projects and become the dominant plant community. The parameters measured include soil organic carbon (SOC), total nitrogen, available phosphorus (P) and potassium (K), pH, salt component, and nematode community characteristics. Enrichment ratios (a comparison of the soil measurements between soils under canopy and in the open interspaces) for soil nutrients and salinity were used to evaluate fertility and salinity islands underneath the tamarisk shrubs. The soil nematode community was used as a biological indicator of soil condition. SOC and available P and K were higher beneath the plant canopy than in the open interspaces outside that canopy. The enrichment ratios for SOC and nutrients were highest for the sand dune habitat and tamarisk shrubs clearly created islands of greater salinity under the canopies. Nematode abundance per 100 g dry soil varied considerably between the locations and habitats, with the highest abundance found in sand dune and the lowest in saline meadow. A significantly higher nematode abundance and a lower trophic diversity were found in soils under the canopy compared to the soils in the open interspaces. With the exception of saline meadow, the abundance of bacterivores increased and fungivores decreased under the canopy relative to the open interspaces, and bacterivores dominated under the canopies in the sand dune and riparian habitats. The enrichment ratios for salinity were higher than for fertility, suggesting that improved soil fertility can not limit the impact of salinization beneath tamarisk shrubs. The adverse effect of salt accumulation on the soil environment should be taken into account when using tamarisk as restoration plant species, especially in saline meadow and controlling of tamarisk density should be considered when undertaking re-vegetation projects in the arid desert oasis regions.

Positive effects of shrubs on plant species diversity do not change along a gradient in grazing pressure in an arid shrubland

Facilitative or positive interactions among species are driven mainly by the environmental amelioration or protection from grazing provided by nurse plants. Some studies have suggested that protection from grazing is inconsequential in water-limited environments because of low herbivore densities and their grazing effects. Others, however, argue that herbivores have a major effect on semi-arid plant communities, and that protection from grazing is a significant factor driving positive plant–plant interactions in such environments. We identified a gradient in grazing pressure in a semi-arid shrubland in south-eastern Australia along which we compared soil condition, incident radiation and plant composition beneath two nurse shrub species with open (shrub-free) interspaces. Our aim was to assess the degree of microclimatic amelioration provided by both shrubs, and changes in the interactions (intensity, importance and frequency) between both nurse shrubs and their understorey species, and their effects on species richness at the community level. Both the relative interaction intensity (RII) and interaction importance (Iimp) indices of plant–plant interactions were generally positive and independent of grazing pressure. Soil beneath both nurse plants had significantly greater indices of nutrient cycling and infiltration, and contained more C and N than soil in the open. Almost twice as many species occurred under the canopies of both shrubs (44 species) than in the open (23 species), and the composition of species differed significantly among microsites. Fifty-four percent of all perennial plant species occurred exclusively under shrubs. Our results suggest that environmental amelioration is a stronger driver of the facilitatory effect of shrubs on their understorey species than protection from grazing. Our conclusions are based on the fact that the substantial effect of plant–plant interactions on plant species richness was largely independent of grazing pressure. Irrespective of the underlying mechanism for this effect, our study illustrates the ecological role of shrubs as refugia for understorey plants in semi-arid environments and cautions against management practices aimed at reducing shrub populations.

Can environmental variation affect seedling survival of plants in northeastern Mexico?

The effects of global warming increase the frequency and intensity of many climate events such as rainfall. We evaluated the effects of environmental conditions on early stage seedling survival of the native thorn scrub species Caesalpinia mexicana A. Gray, Celtis pallida Torr., Cordia boissieri A. DC., and Ebenopsis ebano (Berland.) Barneby and J.W. Grimes, during the summer of 2009 and 2010. The experimental design had two factors, two levels of rainfall and three microhabitats of thorn scrub: (i) open interspace, (ii) thorn scrub edge and (iii) under the canopy of dense thorn scrub. In dense thorn scrub, seedling survival was higher for Caesalpinia mexicana and Celtis pallida, and for Cordia boissieri and Ebenopsis ebano seedling survival was higher in dense thorn scrub and thorn scrub edge. The effect of rainfall on seedling survival depended on the year. Rainfall in 2010 and dense thorn scrub increased seedling survival of native species. For survival, the limiting factors of microhabitats appear to change across the years. Besides rainfall events, biological aspects like competition and mycorrhiza effects would need to be considered in models of plant establishment.

The shrubRhodomyrtus tomentosaacts as a nurse plant for seedlings differing in shade tolerance in degraded land of South China

Questions: What are the nurse effects of Rhodomyrtus tomentosa in degraded land of South China? Are canopy or soil factors responsible for the main nurse effect? Do facilitative effects increase with the shade tolerance of the target species? Location: Degraded shrubland in South China. Methods: Seedlings of three native climax woody species (Schima superba, Michelia macclurei, Castanopsis fissa) that differ in shade tolerance were subjected to four treatments by transplantation: (1) under the canopy of R. tomentosa shrubs; (2) in open interspaces without vegetation cover (control); (3) under the canopy of R. tomentosa from which canopies had been removed; and (4) in open interspaces without vegetation but covered by branches and leaves of R. tomentosa. Results: At low soil nutrient levels, increased canopy shade, soil porosity and soil moisture under the canopy of R. tomentosa increased seedling survival of the climax tree species S. superba, C. fissa and M. macclurei, and shoot height of S. superba. The nurse effect (a form of facilitation) of R. tomentosa depended more on canopy shade than on soil amelioration. The magnitude of facilitation or nurse effect was positively correlated with shade tolerance of the target species. Conclusions: Use of nurse plants in restoration differs from traditional reforestation (clearing and/or burning to reduce interspecific competition between target tree species and non-target species) because it focuses on positive interactions between nurse plants and target plants that increase establishment of target species and reduce time required for restoration. Because nurse effects of R. tomentosa shrubs tended to be larger on target species with greater shade tolerance, shade-tolerant plants are suggested as target species to accelerate restoration.

Distribution of carbon and nitrogen in sagebrush steppe after six years of nitrogen addition and shrub removal

Widespread loss of sagebrush ( Artemisia tridentata) in much of the western US represents a major shift in the dominant species type and may trigger changes in ecosystem characteristics such as the distribution of nutrients. We examined total nitrogen (N) and carbon (C) content of soils directly below and away from Wyoming big sagebrush ( A. tridentata ssp. tridentata) canopies in undisturbed areas, where shrubs had been removed for six years, and in areas that have received annual additions of nitrogen, to improve our understanding of the effects of shrub canopies and perturbations on nutrient distribution. Soils below shrub canopies had more C and N than soils in open interspaces; resource islands were still present six years after shrubs were removed. Soil carbon content in the top 10 cm was 25% greater on shrub removal plots than on control plots. There was no difference in total N or C on plots that received annual additions of N when compared to control plots.

Moms are better nurses than dads: gender biased self‐facilitation in a dioecious Juniperus tree

AbstractQuestions: Can gender of nurse plants affect regeneration patterns and spatial population structure? Is there a seed‐seedling conflict in the regeneration process? What factors are responsible for the clumped spatial population structure observed for adult trees?Location: Mediterranean cold semi‐arid high mountains in Spain.Methods: The spatial pattern of adult Juniperus thurifera trees was studied by means of Ripley's K‐analysis. χ2 analyses were used to test for natural seedling frequency in each of three main microhabitats: (1) under female and (2) male tree canopies and (3) in open interspaces. The observed pattern was explained experimentally by studying seed and seedling survival for two years. Survival probabilities were calculated across life stages for each of three main microhabitats.Results: Adult J. thurifera trees were aggregated in space. Most seedlings were found underneath female J. thurifera trees. Experimental studies demonstrated that from seed dispersal to seedling survival all life stages showed the same positive or negative trend within a given microhabitat, indicating stage coupling and no seed‐seedling conflicts. Attraction of frugivo‐rous birds by reproductive female junipers and improvement of environmental conditions beneath tree canopies were the main factors responsible for the variation in seedling density among microhabitats; highest underneath female trees and lowest in open interspaces.Conclusions: In dioecious species, the gender of nurse plants can significantly determine the spatial population structure. In J. thurifera forests, facilitation beneath female trees occurs among all life stages without any sign of seed‐seedling conflict. The most critical factors shaping the spatial population structure were directed seed dispersal and environmental amelioration beneath female conspecific trees.