Presence Of Shrubs Research Articles

Drought resistance and resilience: The role of soil moisture–plant interactions and legacies in a dryland ecosystem

Abstract In many regions of the world, climate change is projected to reduce water availability through changes in the hydrological cycle, including more frequent and intense droughts, as well as seasonal shifts in precipitation. In water‐limited ecosystems, such as drylands, lower soil water availability may exceed the adaptive capacity of many organisms, leading to cascading ecological effects during (concurrent effects) and after drought (legacy effects). The magnitude and duration of concurrent and legacy effects depends on drought intensity, duration and timing as well as the resistance and resilience of the ecosystem. Here, we investigated the effects of drought seasonality and plant community composition on two dominant perennial grasses, Achnatherum hymenoides (C3 photosynthesis) and Pleuraphis jamesii (C4 photosynthesis), in a dryland ecosystem. The experiment consisted of three precipitation treatments: control (ambient precipitation), cool‐season drought (−66% ambient precipitation November–April) and warm‐season drought (−66% ambient precipitation May–October), applied in two plant communities (perennial grasses with or without a large shrub, Ephedra viridis) over a 3‐year period. We examined the concurrent and legacy effects of seasonal drought on soil moisture, phenology and biomass. Drought treatments had strong concurrent and legacy effects on soil moisture, which impacted the phenology and biomass of the two grasses. Drought reduced growing season length by delaying green‐up (cool‐season drought) or advancing senescence (warm‐season drought) and reduced biomass for both species. Biomass and phenology legacy effects from drought emerged in the second and third years of the experiment. While we observed differential sensitivity to drought legacies between the two grasses, we found limited evidence that shrub presence had interactive effects with the drought treatment. Synthesis. The results from this study highlight how abiotic and biotic legacies can develop and influence a community's resistance and resilience to subsequent droughts. When the frequency of repeated extreme events, such as recurring seasonal droughts, exceeds the capacity of organisms or ecosystems to recover (i.e. resilience), persistent drought legacies can reduce the resistance to subsequent drought events. Overall, these results highlight how drought legacies are a product of ecological resistance and resilience to past drought and can influence ecosystem vulnerability to future droughts.

Diversity and density of the desert seed bank: Interplays between cacti and nurse shrub species

Woody plants can modify microclimate, nutrients, and seed availability in the soil. We studied the influence of two shrub species on species diversity, and seed density in the northern Monte desert soils. We hypothesized that the presence of shrubs affects species richness and seed density. We predicted a higher richness and seed density under shrubs than open spaces between shrubs, and differences between shrubs species (Bulnesia retama and Zuccagnia punctata) influenced by variations in their attributes (crown and nutrients supply to the soil). We obtained seeds and seedlings from 20 soil samples from shrub species and open spaces. The seed bank was composed of 21 species and was dominated by perennial species (62%), mainly Cactaceae. The species richness and density were significantly higher under shrubs than open spaces, without significant differences between shrub species. The variations found among sites, samples, and years is consistent with the spatial heterogeneity of seed banks in deserts. Our study suggests a combination of the spatial heterogeneity hypothesis and the life-form hypothesis would explain the plant diversity dynamics in deserts because, for the maintenance of soil seed bank diversity, shrubs function as nurse islands among open spaces, and perennial cacti dominate the soil seed bank.

Land-use history and abiotic gradients drive abundance of non-native shrubs in Appalachian second-growth forests with histories of mining, agriculture, and logging

Invasion by non-native species is a consequence of previous anthropogenic disturbance that can be expected to differ between land-use histories with contrasting impacts on the physical and biotic environment. Mining, agriculture, and logging all alter environmental character in different ways through their different effects on soils and surrounding vegetation. We used second-growth forests with histories of mining, agriculture, logging, and older forest (>120 years) with no recent disturbance history to test the hypotheses that invasion is driven by 1) lasting environmental impacts of land use or 2) colonization following niche opening due to disturbance. We sampled shrub cover, environmental variables, and soils in forests with histories of mining, agriculture, logging, and older second-growth with no recent history of land use in four 10-meter2 plots per site. Our analysis focused on the two most common non-native shrubs, Berberis thunbergii and Rosa multiflora. Cover of B. thunbergii was marginally significantly higher in post-agricultural and mined forests than logged sites or older second growth, whereas R. multiflora was most frequent in mined sites. Both species showed a significant relationship with environmental variables such as soil pH, water-holding capacity, and elevation. Soil texture differed with land-use history: post-agricultural sites were significantly higher in silt and clay, and lower in sand, than the mined, logged, or old forest sites, reflecting the interaction of land-use history with landform. Most environmental variables did not differ between land-use histories. Non-native shrubs were associated with land-use histories involving soil disturbance despite the lack of lasting contrasts in most soil variables, indicating that invasion primarily reflects past opportunities for colonization and environmental gradients that are not impacted by land use. We conclude that the presence of non-native shrubs is a biotic legacy of past disturbance that outlasts altered environmental conditions that may be present at the time of abandonment.

Woody species have stronger facilitative effects on soil biota than on plants along an aridity gradient

AbstractQuestionsWoody‐shrub encroachment affects community structure and composition. However, most studies focus on their effects on understorey plant communities, and the relative importance of shrubs in affecting plants vs soil biota communities is poorly known.LocationInner Mongolian Steppe, China.MethodsWe examined the effect of shrubs on multiple community attributes, including plants, soil biota (bacteria, fungi and nematodes), and soil fertility, and quantified how these effects changed from semi‐arid to hyperarid conditions (from 281 mm to 110 mm of mean annual precipitation). In addition, we assessed whether the effects of shrubs on plant communities were directly mediated by biotic filtering in seed germination and establishment, or indirectly mediated by plant biomass or soil fertility in the case of soil organisms.ResultsThe effect of shrubs on soil biota was generally more positive than on plants, and it increased with aridity. We found that a larger proportion of below‐ground taxa depended on shrub presence (36%) than plants (20%). Soil nematodes and soil bacteria were directly influenced by shrub presence whereas soil fungi were indirectly influenced by enhanced soil fertility. Shrubs also increased plant biomass under all conditions but only increased plant species richness in the most arid conditions. Despite the generally positive effect of shrubs, and the fact that they weakened the filtering effects of aridity on seed germination, aridity was a stronger predictor of changes in species composition than shrub presence was, particularly for plants.ConclusionsOur results illustrate the variety of positive effects of shrubs and show that they are particularly important in supporting biodiversity in the most arid conditions. These strong and positive effects could partially buffer the impacts of increasing aridity on dryland soil biodiversity, but our study suggests that facilitative interactions may not be able to completely mitigate the impacts of increasing aridity on drylands.

New northern snowpack classification linked to vegetation cover on a latitudinal mega-transect across northeastern Canada

ABSTRACT Changes in mass, extent, duration, and physical properties of snow are key elements for studying associated climate change feedbacks in northern regions. In this study, we analyzed snowpack physical properties along a ‘mega’ transect from 47°N to 83°N (4,000 km) in northeastern Canada, which includes marked transitions between ecozones from boreal forest to subarctic and arctic ecosystems. Our unique dataset of 391 detailed snowpits acquired over the last 20 years, complemented with snow data from weather stations, shows that snowpack properties such as snow water equivalent, snow depth, density, grain size and basal depth hoar fraction (DHF) are strongly linked to vegetation type. Based on these results, we propose an updated classification of snow types in three classes: boreal forest snow (47–58°N), tundra snow (58–74°N) and polar desert snow (74–83°N), which is more appropriate to the study area than the general north hemisphere classification commonly used. We also show that shrub presence along the transect contributes to a significant increase in DHF development which contributes most strongly to the thermal insulation properties of the snowpack. Overall, our analysis suggests that snow–vegetation interactions have a positive feedback effect on warming at northern latitudes.

Landscape and environmental conditions for the late Holocene in the eastern Pampa-Patagonia transition (Argentina): a phytolith analysis of the El Tigre archaeological site

The El Tigre archaeological site (39°46′49″ S; 62°22′32″ W) is located in the south of Provincia de Buenos Aires, Argentina, on an ancient delta of the Rio Colorado. Its sedimentary sequence shows periods of landscape stability and soil formation processes during the period ca. 1,000–400 years bp. The aim of this paper is to investigate the evolutionary history of the vegetation in order to understand palaeoenvironmental changes during the late Holocene. The study of microremains, mainly phytoliths, from the sedimentary sequence indicates that cold and dry conditions predominated at 2,700–2,200 cal bp, from deposition of non-pedogenetic, aggradational sediments in arid or semi-arid environments and/or sparse vegetation cover. Then the climate became much warmer at ca. 2,200–1,200 cal bp, with greater availability of moisture and the presence of xerophytic shrubs and halophytic grasslands, and also extra-regional trees and shrubs. The records indicate that for ca. 1,500–300 cal bp the climate conditions changed to temperate with periods of greater water availability and the presence of a saline steppe and a greater abundance of Monte-Caldenal scrub vegetation elements. This climatic trend is also in agreement with the soil formation processes defined in the archaeological site sequence. The upper layers of the El Tigre site show lower temperatures in the last 300 years, accompanied by variations in the availability of moisture, with alluvial processes characterized by the presence of saline grasslands with xerophytic shrubs and an increase in Asteraceae and Poaceae, continued by the recent top samples with ruderal communities and sandy grasslands.

Faktor yang Berhubungan dengan Kejadian Filariasis di Desa Denduka Kecamatan Wewewa Selatan Kabupaten Sumba Barat Daya

Filariasis is a chronic infectious disease caused by filarial worms and transmitted by mosquitoes. In 2017, a total of 113 filariasis cases were reported in Southwest Sumba Regency of which 35 cases were found in Puskesmas Tena Teke. Denduka village recorded 18 cases. This study aims to analyze factors related to the incidence of filariasis in Denduka Village. This research was analytical observational with cross-sectional design. The sample consisted of 100 people. The data were analyzed using chi square (α=0.05). The results showed that the presence of mosquito breeding places (p-value= 0.020) and shrubs (p-value= 0.020) related to the incidence of filariasis while age (p=0.799), gender (p-value=1,000), occupation (p-value=0.554), income (p-value=1,000), net use (p-value=0.065) and duration of work (p-value=0.055) were unrelated to the incidence. The community needs to reduce contact with vectors by frequently cleaning houses and surrounding environment, and using mosquito nets while sleeping.

Not herbs and forbs alone: pollen‐based evidence for the presence of boreal trees and shrubs in Cis‐Baikal (Eastern Siberia) derived from the Last Glacial Maximum sediment of Lake Ochaul

ABSTRACTA new accerator mass spectrometry (AMS)‐dated sedimentary record from Lake Ochaul (54°14′N, 106°28′E; 641 m a.s.l.) in Eastern Siberia covers the interval from ca. 27 850 to 20 400 cal a bp at ca. 180‐year resolution and contributes to a better understanding of the complex spatial vegetation pattern during the Last Glacial Maximum (LGM). Non‐arboreal pollen taxa are abundant in the pollen assemblages (mean value ca. 92.6%), but boreal trees are represented by all major taxa that grow in the lake catchment today, including Betula sect. Albae (0.6–4.8%), Picea (0.6–2.8%), Pinus sibirica (Haploxylon type) (up to 1.5%), Pinus sylvestris (Diploxylon type) (up to 2%), Larix (up to 0.6%) and Abies (up to 0.6%). Betula sect. Nanae/Fruticosae (2–5.2%) and Salix (up to 3.2%) are the most representative boreal shrub taxa. Together with existing modern and fossil pollen data from the wider study region, the current record provides further evidence for the long‐debated presence of boreal trees and shrubs in Eastern Siberia throughout the LGM. Our results show that the Upper Lena was a region in which refugia for arboreal taxa existed and that far‐distant pollen transport can be ruled out as the source of the detected arboreal pollen.

Spatial and Temporal Distribution of Soil Microbial Properties in Two Shrub Intercrop Systems of the Sahel

The Sahel is an ecologically vulnerable region where increasing populations with a concurrent increase in agricultural intensity has degraded soils. Agroforestry offers an approach to remediate these landscapes. A largely unrecognized agroforestry resource in the Sahel are the native shrubs, Piliostigma reticulatum, and Guiera senegalensis that to varying degrees already coexist with row crops. These shrubs improve soil quality, redistribute water from the deep soil to the surface (hydraulic lift), and can improve crop growth. However, little information is available on whether these shrubs affect spatial and temporal dynamics of microbial communities. Therefore, the objective of this study was to determine microbial composition and activity in the wet and dry seasons of soil in the: shrub rhizosphere (RhizS), inter-root zone (IntrS), and outside the influence of shrub soil (OutS) for both G. senegalensis and P. reticulatum in Senegal. A 3 × 2 factorial field experiment was imposed at two locations (490 and 700 mm annual rainfall with G. senegalensis and P. reticulatum, respectively), that had the soil sampling treatments of three locations (RhizS, IntrS, and OutS) and two seasons (wet and dry). Soils were analyzed for: microbial diversity (DGGE with bacterial 16S or fungal 28S rRNA gene sequences phospholipids fatty acid, PLFA); enzyme activities; microbial biomass carbon (MBC); and nitrogen (N) mineralization potential. For the DGGE profiling, the bacterial community responded more to the rhizosphere effect, whereas, the fungal community was more sensitive to season. PLFA, MBC, enzyme activities and inorganic N were significantly higher in both seasons for the RhizS. The presence of shrubs maintained rhizosphere microbial communities and activity during the dry season. This represents a paradigm shift for semi-arid environments where logically it would be expected to have no microbial activity in the extended dry season. In contrast this study has shown this is not the case that rather the presence of shrub roots maintained the microbial community in the dry season most likely due to hydraulic lift and root exudates. This has implications when these shrubs are in cropped fields in that decomposition and mineralization of nutrients can proceed in the dry season. Thus, enabling accumulation of plant available nutrients during the dry season for uptake by crops in the rainy season.

The Effects of Native Shrub, Fencing, and Acorn Size on the Emergence of Contrasting Co-Occurring Oak in Mediterranean Grazed Areas

Research Highlights: The regeneration of Quercus species is usually very difficult in many oak woodlands transformed by livestock farming. Some studies have reported that shrubs can facilitate regeneration. However, the strength of interaction may vary depending on, among other factors, the shrub species and the stress tolerance of the oak species. Moreover, further studies are necessary to clarify the relative importance of the two facilitation mechanisms in the same community. Background and Objectives: Cytisus multiflorus (L’Her.) Sweet is a predominant shrub species in the Mediterranean grazed open-oak-woodlands found in the central west of the Iberian Peninsula (bioclimatic limit) and is present with Quercus pyrenaica Willd and Quercus ilex subsp. ballota Samp trees. Thus, we assessed the effect of these native shrubs and acorn size, and the effect of excluding large herbivores, on the seedling emergence of two contrasting co-occurring Quercus species under a bioclimatic limit. Materials and Methods: A manipulative field experiment was carried out considering four treatments as a combination of shrubs (shrub/no-shrub) and fence (fenced/open) factors. A total of twenty plots, five replicates for each treatment were available. In each plot, 20 acorns were sown: 10 acorns (5 small and 5 large) for each Quercus species. Acorn emergence was recorded during the first four years following the sowing. Results: Seedling emergence took place mostly in the spring of the first year after sowing. The presence of shrub was the main significant factor and incremented the emergence of both Q. ilex and Q. pyrenaica. The effect of the fence depended on the Quercus species considered, improving only the emergence of Q. pyrenaica. A negative effect with the small acorns was detected but only for Q. pyrenaica. In all treatments, Q. ilex emerged more than Q. pyrenaica. Conclusions: C. multiflorus had a clear facilitative effect on the seedling emergence of Q. ilex and Q. pyrenaica, which was much greater than the physical effect that acorn size and excluding large herbivores had. As such, this native shrub may have a key role in oak regeneration in Mediterranean grazed areas. Furthermore, in these areas of contact between marcescent and sclerophyllous Quercus species, Q. ilex currently emerges more than Q. pyrenaica. This could be indicative of a shift towards more xeric climatic conditions, which could lead to a change in the dominant tree species in the future. However, this change could be modulated by the effects of native shrub and large herbivores.

Purple Martin Nest House Selection in Central Alberta, Canada

ABSTRACTPurple martins (Progne subis) are declining in North America and the eastern subspecies is almost fully dependent on human‐provided nesting houses. We assessed nest house selection by purple martins located at the northern edge of their range. Guidebooks anecdotally describe the importance of house color, building material, hole shape, height, presence of shrubs, vertical accessibility, and distances to trees, water bodies, human houses, and neighboring nest houses; however, these recommendations have little supporting research. Based on data from 2006 to 2018 in Camrose, Alberta, Canada, occupancy was predicted by vertical accessibility, the absence of shrubs at the base of a nest house, location on city‐owned land, and closer proximity to water. Purple martin landlords can build and manage nest houses with certain characteristics to promote greater nesting occupancy by purple martins, thus contributing to more effective purple martin conservation efforts. © 2021 The Wildlife Society.

Differential responses of litter decomposition in the air and on the soil surface to shrub encroachment in a graminoid-dominated temperate wetland

Graminoid-dominated wetlands have been subjected to widespread shrub encroachment, yet the effect of this shift in species composition on litter decomposition remains unclear, especially in the standing-dead stage. We collected labile (Deyeuxia angustifolia) and recalcitrant (Carex schmidtii) graminoid leaf litter from a freshwater wetland in northeast China, and used the litterbag method to characterize litter ash-free dry mass (AFDM) loss and nitrogen (N) release in the air and on the soil surface in open wetlands and two shrub islands (Salix floderusii producing phenol-poor litter and Betula fruticosa producing phenol-rich litter) over 360 days of decomposition. Litter decomposition in the air and on the soil surface responded differentially to shrub expansion. In the air, AFDM loss and N release for both labile and recalcitrant litter were often lower in shrub islands than in open wetlands. On the soil surface, labile litter decomposition was decelerated in the presence of shrubs with phenol-rich litter, but accelerated in the presence of shrubs with phenol-poor litter. Despite the absence of significant differences in N release, recalcitrant litter AFDM loss was lower in shrub islands than in open wetlands after 360 days of decomposition on the soil surface. Shrub encroachment retards litter decomposition in the air, but the effects on litter decomposition on the soil surface vary with shrub type and litter degradability in graminoid-dominated wetlands. Moreover, these findings emphasize that standing litter decomposition should be considered to enhance our understanding of shrub encroachment effects on litter decomposition in these wetlands.

Facilitation and biodiversity jointly drive mutualistic networks

AbstractFacilitation by nurse plants increases understorey diversity and supports ecological communities. In turn, biodiversity shapes ecological networks and enhances ecosystem functioning. However, whether and how facilitation and increased biodiversity jointly influence community structure and ecosystem functioning remains unclear.We performed a field experiment disentangling the relative contribution of nurse plants and increasing understorey plant diversity in driving pollination interactions. Both the presence of nurse shrubs and increased understorey plant diversity increased pollinator diversity and visitation rates. While nurse and understorey diversity effects on pollinator visitation rates did not interact, the effects of increasing understorey plant diversity on pollinator diversity were stronger in the absence than in the presence of shrubs, meaning that nurse shrubs attenuated the effects of high understorey diversity and buffered the effects of low understorey diversity.We also found positive complementarity effects among understorey species as well as complementarity between nurse plants and understorey species at high diversity. Results also indicate negative selection effects, suggesting that species with generally few pollinators benefit the most in the polyculture while a species (possibly the nurse plant) with generally lots of pollinators does not. The corresponding changes in pollination networks with the experimental treatments were due to both changes in the frequency of visits and turnover in pollinator community composition.Synthesis. Plant–plant facilitative systems, where a nurse plant increases understorey plant diversity, are common in stressful environments. Here, we show that these facilitative systems positively influence mutualistic interactions with pollinators via both direct nurse effects and indirect positive effects of increasing plant diversity. Conserving and supporting nurse plant systems is crucial not only for maintaining plant diversity but also for supporting ecosystem functions and services.

Soil seed bank characteristics in relation to different shrub species in semiarid regions

AbstractLittle information is available about the effects of different species of shrubs on the composition of the soil seed bank (SSB) in the semiarid regions. We determined the role of three dominant shrub species on SSB characteristics and evaluated their potential for their possible use in rangeland restoration projects. Fifteen sites, each containing three shrub species (Amygdalus scoparia, Daphne mezereum and Ebenus stellata) and a herbaceous patch (control) in close proximity, were sampled and their SSB density, species richness and diversity at 0–10 cm depth were determined. The results showed that the density of the SSB was highest under A. scoparia and lowest in the control. The highest SSB density of grasses was found under A. scoparia, while the highest SSB density of forbs was found under E. stellata. Species diversity of the SSB was significantly greater under E. stellata than under the other shrubs and control. This study revealed that the extent to which shrubs affected SSB characteristics did not only depend on the presence of shrubs, but also on the species of shrubs. These different roles of different species of shrubs on SSB are advised to be considered in the restoration of degraded areas through the SSB in the semiarid areas. In the case of changing management type from intensive grazing to extensive grazing or non‐grazing, the role of different shrub species in the conservation herbaceous species through their SSB can be different.

A multivariate approach to assess the structural determinants of large wildfires: evidence from a Mediterranean country

This paper analyses the factors behind wildfire propagation in a Mediterranean European country, Portugal, using a set of variables related to vegetation and climatic, topography and human aspects. Spatial cluster analysis was used to find homogeneous regions, and two-part regression models were used to model the contribution of the different elements driving extensive fire propagation. Our findings confirm the presence of spatial variability in the contribution exerted by most structural factors driving large wildfire spread. Additionally, the results of this study show that vegetation types, in particular the presence of shrubs, and a lack of human activities, such as agriculture, represent the main factors facilitating fire spread in this region, corroborating information from previous work. This research provides relevant input for implementation in different fields, from large fire awareness and prevention to the development of wildfire policies, as well as addressing methodological concerns in fire danger and fire risk analyses.

Shrub encroachment affects tundra ecosystem properties through their living canopy rather than increased litter inputs

Deciduous shrub encroachment in tundra ecosystems affects the soil microclimate and, in turn, could affect soil nutrients and microbial processes. Although numerous effects of shrubs on tundra ecosystem properties have been described, there has been little focus on the mechanisms through which they impact tundra functioning. In alpine tundra of northern Canada, we examined 1) the effects of the living shrub canopy and separated them from 2) the effects of increases in litter quantity and quality. In this 4-year study we experimentally manipulated shrub presence (shrub present or removed) and litter quantity (none, natural abundance, and 2x natural abundance) in a fully factorial design. Shrub presence affected soil temperatures by increasing winter and decreased summer soil surface temperatures by about 0.8 °C and 0.6 °C respectively, and also decreased mid-summer soil moisture. Shrub presence also affected both nutrient cycling and microbial processes including decreased summer available nitrogen (N), increased N-immobilization, increased microbial biomass as well as variable effects on potential exoenzyme activity. Increased litter inputs had few significant effects on tundra ecosystems, although additional litter increased both soil C:N ratios and microbial biomass. Our results indicate that shrub encroachment is likely to affect tundra soil properties primarily through mechanisms associated with the presence of the living shrub rather than from the accompanied changing litter quality and quantity. Because of opposing effects of shrubs between seasons and years, we encourage an increased focus on the mechanisms through which shrubs may affect tundra ecosystem functions and year round assessments of these processes.

Facilitation Effects of Haloxylon salicornicum Shrubs on Associated Understory Annuals, and a Modified "Stress-Gradient" Hypothesis for Droughty Times.

Perennial shrub-annual plant interactions play key roles in desert regions influencing the structure and dynamics of plant communities there. In the present study, carried out in northwestern Saudi Arabia, we examined the effect of Haloxylon salicornicum shrubs on their associated understory annual species across four consecutive growing seasons, along with a record of the seasonal rainfall patterns. We measured density and species richness of all the annual species in permanent quadrats located beneath individual shrubs, as well as in the spaces between shrubs. During wet growing season H. salicornicum shrubs significantly enhanced the density and species richness of sub-canopy species, whereas in the relatively dry seasons they exerted negative effects on the associated species. In all growing seasons, the presence of shrubs was associated with enhanced soil properties, including increased organic carbon content, silt + clay, and levels of nutrients (N, P and K). Shrubs improved soil moisture content beneath their canopies in the wet growing season, while in the dry seasons they had negative effects on water availability. Differences in effects of H. salicornicum on understory plants between growing seasons seem due to the temporal changes in the impact of shrubs on water availability. Our results suggest the facilitative effects of shrubs on sub-canopy annuals in arid ecosystems may switch to negative effects with increasing drought stress. We discuss the study in light of recent refinements of the well-known “stress-gradient hypothesis”.

The effects of woody plant encroachment and wildfire on plant species richness and composition: Temporal changes in a forest–steppe mosaic

AbstractQuestionsWoody plant encroachment and wildfire may both have major effects on species richness and composition, yet studies that assess these two factors in combination are rare. We asked the following specific questions: (1) how did juniper cover change over a decade in the study area; what are the effects of juniper encroachment and subsequent wildfire on(2) plant species richness; and (3) vegetation composition?LocationSand forest–steppe in Kiskunság, Central Hungary.MethodsWe studied a juniper‐encroached grassland hit by a wildfire. We assessed changes in plant species richness and composition in burnt and unburnt grassland and juniper plots for 11 years following the wildfire. Yearly vegetation sampling was performed in permanent quadrats of 1 m2and 25 m2using visual cover estimation. Temporal changes in juniper cover and species richness were evaluated with generalized linear mixed‐effects models. Compositional changes were analysed by non‐metric multidimensional scaling and fidelity analysis.ResultsAt the beginning of the study, the presence of individual juniper shrubs increased species richness, and did not alter species composition. However, microsites covered by junipers were extremely species‐poor. Juniper growth during the study period caused a sharp decline in species richness at the edge of juniper shrubs and a shift in species composition compared to grassland plots. Wildfire increased species richness both in grassland and juniper plots. It caused only transient compositional responses in grasslands, but converted juniper habitats back to the grassland state.ConclusionsWe conclude that neither moderate juniper encroachment nor wildfire have negative effects on plant species richness in the studied ecosystem. However, as juniper thickening may cause species loss and devastating fires, conservation management should prevent the development of dense juniper stands.

تاثیر الگوهای فضایی ساختار سبز شهری برتغییر دمای جزایر حرارتی مورد مطالعه: شهر تهران

تاثیر الگوهای فضایی ساختار سبز شهری برتغییر دمای جزایر حرارتی مورد مطالعه: شهر تهران

Boreal tree regeneration after fire and fuelwood harvesting in coastal Nunatsiavut

Consecutive landscape-scale disturbances are known to influence boreal forest regeneration, yet few published data exist on the compounding effects of natural and anthropogenic disturbance on regeneration in subarctic forests. We conducted a dendroecological study of eastern coastal boreal forest regeneration two decades after fire at three subarctic forest stands that are important sources of fuelwood for the people of Nunatsiavut (Labrador, Canada). We quantified spruce (Picea spp.) and balsam fir (Abies balsamea (L.) Mill.) seedling regeneration, standing dead tree density, trees harvested within burned forests, and aged proximal unburned stands. Age of unburned forest varied with site; however, each exhibited continuous regeneration over several decades. Despite low seedling regeneration at each site (stems·m−2; less than 35% of pre-fire stem density), model results indicated harvesting post-fire did not impact seedling regeneration. Findings suggest a negative pressure on seedling abundance from increased presence of tall multi-stemmed shrubs, yet we argue that because stands exhibit a range in tree age, shrubs may be a set of early successional species rather than indicating a change in successional trajectory. Examination of a larger chronosequence within coastal forest stands of Nunatsiavut is warranted to further understand forest regeneration in the eastern subarctic under changing disturbance regimes.