Tree Grass Research Articles

Factors affecting microhabitat use in two agamid species from south‐eastern Australia

AbstractDespite being a central aspect of a species' ecology and having important conservation implications, the use of fine‐scale habitat features (microhabitats), and how they vary over time, are poorly known for most species. In this study, we leveraged 522 relocations of radio‐tracked mallee tree dragons (Amphibolurus norrisi) and painted dragons (Ctenophorus pictus) to investigate the effect of environmental and individual variables on microhabitat use. Mallee tree dragons were more likely to use trees on hot days and in the middle of the day (the hottest time of day), whereas shrub use was more likely on cool days and in the mornings. Painted dragons were more likely to use shrubs and grass trees on warmer days and during the middle of the day, whereas burrows were used during cooler days and in the mornings and afternoons. We expect these patterns represent animals moving from refuge resources, occupied during unsuitable thermal conditions, to microhabitats offering basking, foraging and social opportunities during periods of thermal optimum. Additionally, we found evidence of an ontogenetic shift, with larger mallee tree dragons favouring tree use and higher perches, suggesting a transition from shrub to tree use with age. Our findings underscore the need for diverse microhabitats to accommodate the thermoregulatory and ontogenetic requirements of lizards. These insights can inform conservation and habitat restoration efforts, ensuring the provision of essential microhabitats to support species persistence.

Effect of cropping systems, top feeds and planting geometry on growth, yield and economics of top feeds

The present study was conducted to find out the effect of cropping systems, top feeds and planting geometry on the growth, yield and economics of different top feeds. The experiment was laid out in a split-split plot design with 18 treatment combinations and three replications. The treatments consisted of two cropping systems (C1-sole crop of top feeds, C2-intercrop of bajra napier hybrid), three top feeds [(F1-agathi (Sesbania grandiflora), F2-erythrina (Erythrina indica), F3-drumstick (Moringa oleifera)] and three planting geometry (G1-2 m x 1 m, G2- 2 m x 0.5 m, G3-paired system). The data over three years revealed that intercropping top feeds with bajra napier hybrid at a paired system (C2F1G3) recorded the highest mean number of branches in all three years. However, intercropping agathi at 2 x 0.5 m (C2F1G2) recorded the highest mean leaf stem ratio (0.82). Pooled data over three years also revealed that intercropping agathi at 2 x 0.5 m geometry recorded the highest total green fodder yield (30.16 t ha-1), total dry fodder yield (7.55 t ha-1), gross return (Rs 201200 ha-1), net returns (Rs 139000 ha-1) and B:C ratio (3.25). Hence, among different tree grass combinations, growing agathi with bajra napier hybrid at 2 x 0.5 m geometry was found as most promising system for meeting the fodder requirements of Kerala.

Study on the Microclimatic Effects of Plant-Enclosure Conditions and Water–Green Space Ratio on Urban Waterfront Spaces in Summer

In the context of waterfront-space design, this study examines the impact of plant enclosures and the ratio of water bodies to green spaces on the microclimate, aiming to enhance the climate environment and mitigate urban heat. Utilizing Fujian Agriculture and Forestry University as a case study, the research selects the summer solstice as a representative weather condition, conducts field measurements and model validation for four types of waterfront vegetation, and creates 80 scenarios with varying plant enclosures and water to green space ratios using ENVI-met 5.0.2software. This comprehensive analysis seeks to identify the optimal water–green space ratio for waterfront areas. Key findings include: (1) The efficacy and applicability of ENVI-met software for microclimate studies are confirmed. (2) Waterfront plants have cooling and humidifying effects on the microclimate environment. The order of cooling and humidifying effects of different plant community structures was as follows: tree–shrub–grass > tree–grass > shrub–grass > grass. (3) The cooling, humidification, ventilation, and human comfort levels are influenced by the specific enclosure conditions and water to green space ratios; a ratio of 1.8:1 is the most effective for cooling and improving human comfort, while ratios of 4:1 and 1:4 are better for humidification and ventilation. These results offer valuable insights for designing waterfront spaces in hot and humid climates.

Effects of stochastic perturbations on the tree–grass coexistence in savannas

Effects of stochastic perturbations on the tree–grass coexistence in savannas

Spatial heterogeneity of nitrification contributes to tree–grass coexistence in West African savannas

Abstract In savannas, the coexistence between trees and grasses is determined by complex mechanisms based on water partitioning and disturbances. But little is known about the contribution of other resources, such as soil nitrogen (N). In West African savannas, nitrification inhibition by grasses and nitrification stimulation by trees create spatial heterogeneity in nitrification fluxes and N stocks. Savanna trees can also extend part of their roots in the surrounding open area to absorb N. To investigate the role of the spatial heterogeneity of nitrification in tree–grass coexistence, we used a two‐patch model that simulates N dynamics between an open patch (without trees) and a tree clump patch (trees with grasses under their canopy). The open patch was characterized by a low nitrification rate, while the tree clump patch was characterized by a high nitrification rate. Both patches were connected through horizontal fluxes due to soil horizontal exploration by tree roots. We tested coexistence for different spatial tree distributions, as they are known to strongly influence savanna dynamics. Our results show that the spatial heterogeneity of nitrification induces spatial partitioning between ammonium (NH4+) and nitrate (NO3−) promoting tree–grass coexistence. As nitrification inhibition by grasses leads to high NH4+ availability in the open, the possibilities of coexistence are optimized when trees have different preferences in the open versus under their canopy. Thus, tree–grass coexistence is observed when grasses prefer NH4+, while trees prefer NH4+ in the open and NO3− under their canopy. Contrary to random tree distribution, tree clumping enhances tree–grass coexistence. Intraspecific aggregation strengthens the effect of spatial heterogeneity, which decreases interspecific competition and favours tree–grass coexistence. On the contrary, increasing the surface explored by tree roots in the open tends to increase tree–grass competition. This enhances the competitive ability of trees for N acquisition and consequently favours tree invasion. Synthesis. This study shows that this new coexistence mechanism based on mineral N partitioning into NH4+ and NO3− can be determinant in the functioning of West African humid savannas. This mechanism likely interacts with mechanisms based on disturbances, but such interactions should be studied using new models.

Understorey vegetation moderates climate in open forests: The role of the skirt‐forming grass tree Xanthorrhoea semiplana F.Muell

AbstractMicrosites are created by abiotic and biotic features of the landscape and may provide essential habitats for the persistence of biota. Forest canopies and understorey plants may moderate wind and solar radiation to create microclimatic conditions that differ considerably from regional climates. Skirt‐forming plants, where senescent leaves create hut‐like cavities around the stem, create microsites that are sheltered from ambient conditions and extreme weather events, constituting potential refuges for wildlife. We investigate day and night temperatures and humidity for four locations (grass tree cavities, soil, 20 cm above‐ground, 1 m above‐ground) in a South Australian forest with relatively open canopy of stringybark eucalypts (Eucalyptus baxteri, E. obliqua) and an understorey of skirt‐forming grass trees (Xanthorrhoea semiplana) at 5, 10, 20, and 40 m from the forest edge. We also measured the percentage of canopy and understorey covers. Generally, temperature and humidity differed significantly between more sheltered (grass tree cavities, soil) and open‐air microsites, with the former being cooler during the day and warmer and more humid during the night. Furthermore, our results suggest that canopy cover tends to decrease, and understorey cover tends to increase, the temperature of microsites. Distance to the edge was not significantly related to temperature for any microsite, suggesting that the edge effect did not extend beyond 10 m from the edge. Overall, grass trees influenced microclimatic conditions by forming a dense understorey and providing cavities that are relatively insulated. The capacity of grass tree cavities to buffer external conditions increased linearly with ambient temperatures, by 0.46°C per degree increase in maximum and 0.25°C per degree decrease in minimum temperatures, potentially offsetting climate warming and enabling persistence of fauna within their thermal limits. These climate moderation properties will make grass trees increasingly important refuges as extreme weather events become more common under anthropogenic climate change.

Grass(mannian) trees and forests: Variations of the exponential formula, with applications to the momentum amplituhedron

The Exponential Formula allows one to enumerate any class of combinatorial objects built by choosing a set of connected components and placing a structure on each connected component which depends only on its size. There are multiple variants of this result, including Speicher's result for noncrossing partitions, as well as analogues of the Exponential Formula for series-reduced planar trees and forests. In this paper we use these formulae to give generating functions for contracted Grassmannian trees and forests, certain graphs whose vertices are decorated with a helicity. Along the way we enumerate bipartite planar trees and forests, and we apply our results to enumerate various families of permutations: for example, bipartite planar trees are in bijection with separable permutations. It is postulated by Livia Ferro, Tomasz Łukowski and Robert Moerman (2020) that contracted Grassmannian forests are in bijection with boundary strata of the momentum amplituhedron, an object encoding the tree-level S-matrix of maximally supersymmetric Yang-Mills theory. With this assumption, our results give a rank generating function for the boundary strata of the momentum amplituhedron, and imply that the Euler characteristic of the momentum amplituhedron is \(1\).Mathematics Subject Classifications: 05A05, 05A15, 05C10Keywords: Generating functions, permutations, planar forests

Linking resource- and disturbance-based models to explain tree-grass coexistence in savannas.

Savannas cover a significant fraction of the Earth's land surface. In these ecosystems, C3 trees and C4 grasses coexist persistently, but the mechanisms explaining coexistence remain subject to debate. Different quantitative models have been proposed to explain coexistence, but these models make widely contrasting assumptions about which mechanisms are responsible for savanna persistence. Here, we show that no single existing model fully captures all key elements required to explain tree-grass coexistence across savanna rainfall gradients, but many models make important contributions. We show that recent empirical work allows us to combine many existing elements with new ideas to arrive at a synthesis that combines elements of two dominant frameworks: Walter's two-layer model and demographic bottlenecks. We propose that functional rooting separation is necessary for coexistence and is the crux of the coexistence problem. It is both well-supported empirically and necessary for tree persistence, given the comprehensive grass superiority for soil moisture acquisition. We argue that eventual tree dominance through shading is precluded by ecohydrological constraints in dry savannas and by fire and herbivores in wet savannas. Strong asymmetric grass-tree competition for soil moisture limits tree growth, exposing trees to persistent demographic bottlenecks.

Flowering grass tree usage

Flowering grass tree usage

Elevated Wildfire and Ecosystem Carbon Loss Risks Due to Plant Hydraulic Stress Functions: A Global Modeling Perspective

Wildfire risks are increasing due to the atmospheric and vegetation aridity under global warming. Plant hydraulic stress (PHS) functions regulate water transport along the soil–plant–atmosphere continuum under water stress conditions, which probably results in shifts in ecosystem wildfire regimes. Currently, how the PHS functions affect wildfire occurrence and subsequently the ecosystem carbon cycle via carbon loss at a global scale remains unclear. Here, we conducted global simulations during 1850–2010 using Community Land Model version 5 with and without the PHS configuration and quantified the PHS-induced changes. From the global perspective, the PHS functions increased plant transpiration, induced hydraulic redistribution (HR) of soil water by root, and decreased soil moisture; then, the functions increased fire occurrence (count), fire induced carbon loss, and ecosystem net primary productivity by 72%, 49%, and 15%, respectively. Spatially, the PHS functions greatly promoted fire occurrence and the consequent carbon loss in circumboreal forests and tropical savannas; whereas, the fire occurrence was limitedly affected or even decreased in equatorial rainforests. The strong downward HR process in the humid rainforests transported rainwater into deep soil layers, and strict stomatal regulation of the tropical trees restricted transpiration increment under atmospheric aridity, both of which helped to buffer the rainforests against drought and thus decreased fire risk. In contrast, dry savannas showed substantial upward HR, which increased water loss via soil evaporation and transpiration of the grasses with shallow roots. The tree–grass competition for limited soil moisture in the savannas benefited soil evaporation, which could aggravate plant hydraulic failure and increase wildfire risk.

Holocene climate–fire–vegetation feedbacks in tropical savannas: Insights from the Marura sinkhole, East Arnhem Land, northern Australia

AbstractAimsInformed management of savanna systems depends on understanding determinates of composition, structure and function, particularly in relation to woody‐plant components. This understanding needs to be regionally based, both past and present. In this study, Holocene plant patterns are explored at a site within the eucalypt savannas of northern Australia. Australian savannas are the least developed globally and uniquely placed to track ecological change.LocationNorthern Territory, Australia.MethodsPalynological analyses were undertaken on a 5‐m sediment core, spanning the last 10,700 calendar years. Pollen was categorised to capture vegetation type, classified further according to plant function and/or environmental response. Detrended Correspondence Analysis was used to quantify ecological dissimilarities through time.ResultsAt the Pleistocene transition, grasses were abundant then declined and remained low relative to increased woody cover from the mid‐late Holocene. Savanna composition gradually transitioned from Corymbia to Eucalyptus dominance until significantly disturbed by a phase of repeated, extreme climate events. Highest non‐savanna variability in terrestrial and wetland plant types formed mixed vegetation communities through the mid‐Holocene.ConclusionsSavannas are not homogeneous but the product of plant changes in multiple dimensions. In the Northern Territory, dynamic though restricted non‐eucalypt shifts are embedded within larger, slower eucalypt change processes. Primary climate–vegetation relationships determine the long‐term fire regime. The role of large but infrequent disturbance events in maintaining savanna diversity are significant, in degrees of impact on tree–grass turnover, its form and the extent of vegetation recovery. People's landscape interactions were found to be interwoven within this feedback hierarchy.

Effects of Sewage Sludge Application on Plant Growth and Soil Characteristics at a Pinus sylvestris var. mongolica Plantation in Horqin Sandy Land

The application of domestic sewage sludge (SS) may affect plant growth and soil quality through altering nutrient availability. However, the effect of SS application on the plant–soil system in sandy soils is poorly understood. In this study, we established SS application treatment plots (SL, 25 t ha−1) and control treatment plots without sewage sludge application (CK, 0 t ha−1). SS was applied to the soil surface of a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Horqin Sandy Land, Inner Mongolia, China, to assess its potential effects on plants and soil. We analyzed tree growth performances (tree height, basal diameter, and diameter at breast height), understory traits (species diversity, coverage, and aboveground biomass), soil physical and chemical parameters (nutrient content, dissolved organic carbon, soil water content, bulk density, pH), and proxies of ecosystem services (soil organic carbon and total nitrogen stocks). The results showed that SS addition not only significantly increased soil nutrient contents, but also markedly enhanced aboveground productivity and plant coverage. Specifically, SS addition decreased soil bulk density and increased concentrations of soil organic carbon, total nitrogen, and total phosphorus and mineral nitrogen, and it also increased soil carbon and nitrogen stocks. Furthermore, the addition of SS significantly increased soil dissolved organic carbon contents and enhanced the fluorescence intensities of dissolved organic carbon components (humic acid-like and UV fulvic acid-like) in the topsoil (0–5 cm). This study provides evidence that SS is an acceptable, and possibly preferred organic fertilizer for improving the soil quality and tree–grass growth of Mongolian pine plantations.

Urban agriculture as a component of the concept of energy efficient community

Issues of quality and diversity of available food, environmental safety and guarantees of sustainable energy supply are becoming critical for the population of urban areas. Part of the urbanized areas cannot be used directly for food production for environmental reasons, but it is quite suitable for the production of energy from biomass. In order to create strategies for processing organic biomass from urban plantations of parks and squares, it is necessary to determine the tools for obtaining and interpreting data on the available and prospective amount of biomass in cities, which was the purpose of our work. Unmanned aerial vehicle studies were conducted at the Botanical Garden of the National University of Life and Environmental Sciences of Ukraine using the Slantrange 3P multispectral sensor system from an industrialtype UAV platform. The study of squares and lawns of the city was conducted using an archive of satellite images in the visible range of high resolution — 0.5 m/pixel and a specialized agricultural service EO Browser with a resolution of images of 10 m/pixel. Monitoring of the park using the Slantrange 3P complex, with specialized SlantView software, allowed to identify tree crowns and grass cover, while it was not possible to distinguish vines. The best identification results for the Slantrange complex were obtained for the red and infrared measurement channels. Using satellite monitoring data, the possibility of identifying the biomass of trees and shrubs occurs in drought conditions, when the grass on the lawns suffers more than trees and shrubs, apparently due to the developed root system. It is noted that satellite imagery is usually carried out at different angles and, accordingly, fixed both roofs and partially walls of buildings, and accordingly, such imagery is more suitable for assessing the biomass of promising vertical landscaping with vines.

Burn hot or tolerate trees: flammability decreases with shade tolerance in grasses

In ecosystems where trees and grasses coexist, some grass species are found only in open habitats and others persist under trees. The persistence of shade intolerant grasses in ecosystems such as open woodlands and savannas depends on recurrent fires to open the tree canopy. Therefore, grasses that depend on open sites might benefit from high flammability. We tested if shade intolerant grasses are more flammable than shade tolerant grasses and if flammability differences affected post‐fire grass growth. We examined the relationship between shade tolerance and flammability by determining individual‐level flammability and species shade tolerance of 17 grass species. We also measured grass traits to determine trait effects on flammability and the post‐fire response. Grass species varied in flammability, mainly in the amount of heat produced during burning. Shade tolerant species produced less heat at 50 cm above the ground. Biomass and live fuel moisture had the greatest effects on heat release. However, the negative effect of live fuel moisture on heat release at the soil surface was weakened in plants with high specific leaf area. In addition, grass bulk density negatively influenced heat release at 50 cm height. Heat release at the soil surface negatively influenced post‐fire growth. However, the influences of soil heating and species‐specific traits on individual survival were more complex with 2‐ and 3‐way interactions. Shade tolerance was negatively correlated with a major axis of flammability variation: shade tolerant grasses produced less heat where that heat could damage tree boles. Such heterogeneity in grass flammability may help maintain the tree–grass mixture in natural plant communities. If shade tolerant grasses near trees cause less fire damage to woody plants, especially tree saplings, this may weaken positive grass‐fire feedbacks and thus aid the long‐term coexistence of trees and grasses.

Fire‐ and herbivory‐driven consumer control in a savanna‐like temperate wood‐pasture: An experimental approach

Abstract Fire and herbivory are fundamental top‐down processes, structuring grass–tree ratios in ecosystems across a diversity of climates. Both are plant consumers that can strongly control the recruitment of woody seedlings and saplings to taller height classes. Without consumer control, many grass‐dominated ecosystems would convert into woodlands or forests. While extensively studied in savannas, few have explored the effects of these disturbance regimes on woody recruitment under temperate conditions. We exposed saplings of five common European tree species to fire and herbivory in a full factorial experiment in a savanna‐like wood‐pasture. After 3 years, we evaluated the effects of fire and herbivory on tree sapling survival and height increment. The tree species used, varying in traits and in expected response to fire and herbivory, were Scots pine Pinus sylvestris, Norway spruce Picea abies, European oak Quercus robur, Silver birch Betula pendula and Small‐leaved lime Tilia cordata. Fire and herbivory had a negative effect on sapling survival for all species except for Q. robur, which was not affected by fire. Both processes reduced height increment of B. pendula, while only herbivory reduced the height increment of P. sylvestris and Q. robur. At the same time, B. pendula and P. sylvestris had some of the highest increments, together with P. abies, which had unaffected height increment in all treatments. T. cordata, on the other hand, had a negative height increment across all treatments. Overall, the combined effect of fire and herbivory was similar to the effect of herbivory alone on both survival and height increment, indicating no additional effect of fire when herbivores were present. Synthesis. Our experiment showed how fire and herbivory can strongly affect the recruitment of European temperate tree saplings on a wood‐pasture, potentially leading to comparable consumer control described for ecosystems elsewhere (e.g. savannas). Two strategies to deal with fire and herbivory were identified: tolerance (Q. robur) and avoidance (P. sylvestris and B. pendula). We conclude that both fire and herbivory may have been important drivers of structure and species composition in open ecosystems in temperate Europe in the past.

Large herbivores suppress liana infestation in an African savanna

African savannas are the last stronghold of diverse large-mammal communities, and a major focus of savanna ecology is to understand how these animals affect the relative abundance of trees and grasses. However, savannas support diverse plant life-forms, and human-induced changes in large-herbivore assemblages-declining wildlife populations and their displacement by livestock-may cause unexpected shifts in plant community composition. We investigated how herbivory affects the prevalence of lianas (woody vines) and their impact on trees in an East African savanna. Although scarce (<2% of tree canopy area) and defended by toxic latex, the dominant liana, Cynanchum viminale (Apocynaceae), was eaten by 15 wild large-herbivore species and was consumed in bulk by native browsers during experimental cafeteria trials. In contrast, domesticated ungulates rarely ate lianas. When we experimentally excluded all large herbivores for periods of 8 to 17 y (simulating extirpation), liana abundance increased dramatically, with up to 75% of trees infested. Piecewise exclusion of different-sized herbivores revealed functional complementarity among size classes in suppressing lianas. Liana infestation reduced tree growth and reproduction, but herbivores quickly cleared lianas from trees after the removal of 18-y-old exclosure fences (simulating rewilding). A simple model of liana contagion showed that, without herbivores, the long-term equilibrium could be either endemic (liana-tree coexistence) or an all-liana alternative stable state. We conclude that ongoing declines of wild large-herbivore populations will disrupt the structure and functioning of many African savannas in ways that have received little attention and that may not be mitigated by replacing wildlife with livestock.

Off-Flavor Removal from Sheep Placenta via Fermentation with Novel Yeast Strain Brettanomyces deamine kh3 Isolated from Traditional Apple Vinegar.

Animal placentae can be used as health-promoting food ingredients with various therapeutic efficacies, but their use is limited by their unpleasant odor and taste. This study aimed to investigate the possibility of deodorization of sheep placenta via yeast fermentation. A yeast strain was successfully isolated and identified as a novel Brettanomyces strain (Brettanomyces deamine kh3). The deodorizing efficacy of fermentation of the sheep placenta with B. deamine kh3 was evaluated by 42 panels, based on evaluation of preference, ranking, and aroma profiles, and compared with normal placenta and placenta fermented with B. bruxellensis. The results of the sensory evaluation indicated that fermentation of the sheep placenta with B. deamine kh3 may improve its palatability by increasing flavors such as that of grass (tree), rubber, and burnt, and by decreasing the odor and soy sauce flavor. Solid-phase microextraction-gas chromatography (SPME-GC) showed that major off-flavors in sheep placenta, such as ammonia, dimethyl disulfide, and 1,3-dioxolane, were completely diminished in the sheep placenta fermented with B. deamine kh3. This study presents those major volatile compounds, including 2-isobutyl\\-4,4-dimethyl-1,3-dioxane, and 3-methyl-1-butanol, could be crucial in improving the palatability of the sheep placentae fermented with B. deamine kh3. This study provides a good starting point for the industrial application of a new deodorization method.

The influence of abiotic and spatial variables on woody and herbaceous species abundances in a woodland–grassland system in the Eastern Terai of India

AbstractThe environmental factors that influence tree–grass abundances in tropical savanna and grasslands are not well understood, particularly for woodland–grassland mosaics in humid zones. We studied the effects of abiotic and spatial variables on woody and herbaceous species distributions in a Terai ecosystem of northeastern India. We evaluated the importance of climatic and non-climatic factors that maintain variable tree–grass ratios across the landscape, and also accounted for spatial connectivity and dispersal. We measured species abundances of woody and herbaceous plant species in 134 plots with each 30 m × 30 m in a 519 km2 protected Terai habitat, and derived several climatic and non-climatic environmental factors. We constructed variables based on different models of spatial connectivity among sites, to test their influence on species abundances. We then used redundancy analyses and variation partitioning to quantify the importance of environmental variables and spatial structure on variation in tree–grass abundances. We found that environmental variables including rainfall, fire, water stress, topography and soil nutrients had statistically significant effects on species abundance and tree–grass ratios. Spatial structure was significant, and the best spatial model was an inverse distance-weighted model with linkage extending to 23.5 km, indicating weak dispersal limitation. About 21% of the variation in species abundance was explained by the selected environmental and spatial factors. The results indicate that dynamic plant communities in which spatial–temporal variation in environmental factors may drive stochasticity in species distribution and abundance, thus dominantly influencing on the vegetation mosaic.

Short-term impact of fire on the total soil microbial and nitrifier communities in a wet savanna.

Savannas are characterized by the coexistence of grasses and trees. Fires are critical for their coexistence, because they decrease the survival of tree seedlings and saplings and their recruitment to the adult stage. In some humid savannas, perennial grasses inhibit nitrification and trees stimulate nitrification, which likely favors coexistence between trees and grasses. However, fires may influence plant capacity to control nitrogen cycling, which could subsequently influence tree–grass coexistence and savanna nitrogen budget. Therefore, we sampled soil in a humid savanna of Ivory Coast under the dominant nitrification‐inhibiting grass species and the dominant nitrification‐stimulating tree species and under bare soil before and after (i.e., 5 days) fire during the long dry season. We quantified the total microbial and nitrifier abundances and transcriptional activities and the nitrification enzyme activity. Fire decreased soil water content, probably by increasing evaporation and, maybe, by triggering the growth of grasses, and increased soil ammonium availability likely due to ash deposition and increased mineralization. Fire did not impact the total archaeal, bacterial, or fungal abundances, or that of the nitrifiers. Fire did not impact archaeal transcriptional activity and increased bacterial and fungal total transcriptional activities. In contrast, fire decreased the archaeal nitrifier transcriptional activities and the nitrification enzymatic activity, likely due to the often reported resumption of the growth of nitrification‐inhibiting grasses quickly after the fire (and the subsequent increase in root exudation). These results pave the way for a better understanding of the short‐term effects of fire on nitrogen cycling and tree–grass competition for nitrogen.

Evaluating the 3D cooling performances of different vegetation combinations in the urban area

ABSTRACT Vegetation has been considered as an effective strategy to combat the urban heat island effect. Most researches have focused on evaluating the cooling effect of trees in the urban thermal environment, while little attention has been paid to the cooling effect of the vegetation combinations. Moreover, most studies are focused on the horizontal cooling performance of plants, ignoring their vertical influence. Therefore, this study evaluates the 3D (horizontal and vertical) cooling performances of the three vegetation combination scenarios in the urban area using the ENVI-met model. The study indicates that the tree-grass (TG) combination has the best 3D cooling effect, followed by the tree-shrub-grass (TSG) combination, while the shrub-grass (SG) combination has the weakest 3D cooling effect. Besides, it is economical to plant TSG combinations because fewer trees are needed than planting TG combinations. Therefore, the study recommends the tree-shrub-grass combination rather than TG or SG combination in urban areas to effectively improve the thermal environment. The study also shows that the relationship between increasing tree coverage and the resulting cooling effect is not linear. The results of this study can effectively guide the design of greening strategies in urban areas to improve thermal comfort.