Changes in the understory plant community and ecosystem properties along a shrub density gradient

Understanding habitat affinities of wintering grassland birds is pertinent to their conservation. The objectives of this study were to evaluate the 1) effect burn history has on vegetation structure in coastal prairie; 2) habitat associations of the most common avian species; and, 3) home range size and site fidelity of Le Conte's Sparrow (LCSP). Data were collected on sites with 1-, 2- and 3-year burn histories during the winter of 2002 at Brazoria National Wildlife Refuge, Texas. Line transects were conducted to estimate bird abundance and vegetation measurements were recorded for herbaceous density, shrub density, and community type. Twenty-six Le Conte's Sparrows (Ammodramus lecontii) (LCSP) were radio-marked, in 1- and 2-year burn units, and located for approximately 10 days. One hectare plots on each burn unit were flush-netted once each month. Burn history was highly correlated with herbaceous vegetation and shrub density. LCSP were most common in areas of medium herbaceous density, low to medium litter densities, and areas with tall vegetation. LCSP also occurred in areas with low shrub densities, but abundance was significantly higher in areas with dwarf wax myrtle (Morella cerifera). Savannah Sparrows (Passerculus sandwichensis) were most often found in areas with low herbaceous and shrub densities. Sedge Wrens (Cistothorus platensis) (SEWR) were most common in areas with dense herbaceous vegetation, but showed no relationship to shrub density. SEWR were associated with areas where saltbush and tallow were present. Swamp Sparrows (Melospiza georgiana) were most common in areas of high shrub densities, but demonstrated no relationship to herbaceous vegetation densities. LCSP were sedentary during winter with a mean home range of 2.41 ha (72% < 1 ha) with a 50% probability, and 10.31 ha (44% < 1 ha and 55% < 1.5 ha) with a 95% probability. Home range size did not significantly differ between burn year (p = 0.227). LCSP appeared to exhibit a behavioral response to capture (p < 0.001) with estimated capture probability of 0.462 and recapture probability of 0.056. Maintaining a mosaic of prairie, in three year burn rotations, and controlling woody invasives will provide sufficient overwintering habitat for SAVS, LCSP and SEWR.

A reciprocal transplant experiment was conducted to uncouple genetic and environmental effects on plant fitness of a range‐expanding indigenous shrub, Leptospermum scoparium . Patterns of encroachment differed significantly between three regions of Eucalyptus camaldulensis woodland in the Grampians National Park, south‐eastern Australia, with greater shrub densities found in the Victoria Valley region. Higher shrub densities in this region are likely due to greater fruit production/shrub, increased field germination and increased early seedling survival. The results of the reciprocal transplant experiment showed increased fitness appears to be due to phenotypic plasticity in response to favourable environmental conditions rather than genotypic variation. Field germination and seedling survival were influenced by region of planting and not seed origin. However, differences in shoot length and biomass of seedlings between the regions were detected after five months of growth in uniform conditions which may indicate genetic differentiation. The results, however, suggest range expansion is partly due to increased plant fitness which is likely a plastic response to favourable environmental conditions, especially soil moisture.

Diversity patterns of the rhizosphere and bulk soil microbial communities along an altitudinal gradient in an alpine ecosystem of the eastern Tibetan Plateau

Studies on plant-pollinator interactions have largely neglected the potential negative effects of the predators of pollinators on seed output, even though anti-predatory behaviour of pollinators may affect visitation patterns, pollen transfer, and therefore potentially, plant reproductive output. We tested the hypothesis that the presence of lizards and insectivorous birds, by reducing pollinator visitation, can have significant negative effects on seed output in the insect-pollinated, genetically self-incompatible lower alpine Andean shrub, Chuquiraga oppositifolia (Asteraceae). The lower alpine belt supports a high density of territorial Liolaemus (Tropiduridae) lizards and low shrubs interspersed among rocks of varying sizes, the latter inhabited by lizards and commonly used by flycatchers Muscisaxicola (Tyrannidae) as perching sites. In a 2x2 factorial predator-exclusion experiment, visitation rates of the most frequent pollinators of C. oppositifolia (the satyrid butterfly Cosmosatyrus chilensis and the syrphid fly Scaeva melanostoma), the duration of pollinator visits, and seed output, were 2-4 times greater when lizards were excluded, while birds had no effect. In a natural experiment, visits by S. melanostoma were 9 times shorter, and pollinator visitation rates of C. chilensis and S. melanostoma, and C. oppositifolia seed output were 2-3 times lower on shrubs growing adjacent to lizard-occupied rocks compared to those growing distant from rocks. Our results, verified for additional Andean sites, suggest that lizard predators can alter the behaviour of pollinators and elicit strong top-down indirect negative effects on seed output. Such effects may be especially important in high alpine plant communities, where pollinator activity can be low and erratic, and pollen limitation has been reported.

Summary Shrub encroachment has been widely observed in savanna regions. This study analysed the causes of shrub encroachment in the lowveld savanna of north‐eastern Swaziland, southern Africa, and highlighted management regimes that can be used to reduce or prevent it. The rates and dynamics of shrub encroachment were quantified for the period 1947–90 using aerial photographs, and for 1997 using a ground survey. Five similar areas with different land‐use histories were compared to investigate the relative importance of fire, herbivory, rainfall, soil type and shrub density in driving shrub dynamics. In the study area as a whole, shrub cover increased from a mean of 2% in 1947 to 31% in 1990. Dichrostachys cinerea accounted for most of the increase in cover, contributing 81% to total shrub cover during 1997. Shrub cover was strongly correlated with shrub density and weakly negatively correlated with tree cover. Shrub encroachment varied across land‐use fence lines. The key determinants of shrub dynamics were grazing, through its negative effect on fire frequency and an interaction between drought frequency and high shrub cover. Browsing pressure had a significant but minor impact on dynamics, while soil type had no significant effect. High grazing pressures through their effect on fire frequency were critical throughout the study period in promoting shrub encroachment, while the interaction between drought and high shrub cover produced declines in the later stages. Browsing had an impact on encroachment only in the early stages. Frequent fires, facilitated by low grazing pressures, were capable of preventing shrub encroachment. When coupled with drought, frequent fires could reduce high shrub densities. As cover and density were strongly correlated, it can be inferred from the negative correlation between change in cover (density) and initial cover (density) that the rate of shrub encroachment was cover (density)‐dependent and that there was a shrub equilibrium of 40% cover, approximating to 2400 plants ha−1. Shrub population growth was driven by events (fire, drought) as well as continuous agents (density dependence, mean browsing and grazing pressure). Bush encroachment can be reversed by a combination of management (frequent fires) and climatic events (drought). The implications for savanna management are discussed.

Summary 1. Ecosystem properties may be determined by the number of different species or groups of species in a community, the identity of those groups, and their relative abundance. The mass ratio theory predicts that the effect of species or groups of species on ecosystem properties will be dependent on their proportional abundance in a community. 2. Single plant functional groups (graminoids, legumes, non‐leguminous forbs) were removed from a natural grassland in northern Canada to examine the role of group identity in determining both ecosystem properties and biomass compensation by remaining species. Removals were conducted across two different environmental treatments (fertilization and fungicide) to examine the context dependency of functional group identity effects. 3. The degree of biomass compensation in the first 4 years after removal was influenced by the identity of the functional group removed and also of those remaining. When graminoids were removed, none of the remaining functional groups compensated for the loss of biomass. Graminoids partially compensated for the removal of forbs or legumes, with the degree of compensation depending on environmental treatments. 4. Light interception, soil moisture and soil nutrients were all influenced by functional group identity, with graminoids having a greater impact than expected based on their biomass contribution to the community. Legumes, in contrast, had very little effect on any of the ecosystem properties measured. 5. For most ecosystem properties measured, the role of plant functional groups was not context dependent; functional groups had the same effect on ecosystem properties regardless of fertilization or fungicide treatments. 6. Synthesis. We have shown that the effects of losing a functional group do not solely depend on the group’s dominance. In this northern grassland, there are greater effects of losing graminoids than one would predict based on their biomass contributions to the community, and functional group identity plays a critical role in determining the effects of diversity loss.

Changes of soil organic matter (SOM) stability in alpine ecosystems can alter carbon release from the soil and consequently feed back to climate change. We sought to explore the altitudinal patterns of SOM stability and their relationships with climatic, vegetational and edaphic factors. We combined a number of biological, thermal, chemical, molecular and isotopic indices to characterize SOM stability in two soil layers (0–10 and 10–30 cm) of alpine grassland along two altitudinal gradients of 3200–4200 m (Haibei) and 4400–5200 m (Damxung) on the Tibetan Plateau, respectively. There were significant altitudinal variations in SOM stability between the two transects. Greater biological, chemical and isotopic indices of SOM stability were observed in the middle altitude in Haibei, while opposite results were observed in Damxung. Except for a decreasing trend of SOM stability along altitudinal gradient in subsurface soils (10–30 cm) in Damxung, there was no significant altitudinal trend of thermal and molecular indices of SOM stability. The multiple indices of SOM stability were mutually associated and all showed greater SOM stability in subsurface soils than in surface soils across regions and altitudes. Along the altitudinal gradient, SOM stability showed opposite unimodal patterns in Haibei and Damxung, and had higher values in subsurface soils than in surface soils of the alpine grassland. Climatic, vegetational and edaphic factors collectively control SOM stability rather than just temperature or precipitation.

The Eastern Arc Mountains are part of the Eastern Afromontane global biodiversity hotspot with a remarkable concentration of endemic species. Wildfire is among the major threats to biodiversity of forested mountains. This study assessed the effect of forest fire on the vegetation and understory birds in the Magamba montane forest, 5 years post a major fire outbreak. Mist‐net transects were used to sample understory birds. During the breeding season, active bird nests were searched using the time‐constrained method in both burnt and unburnt forests. Vegetation plots were sampled along the mist‐net transects, and shrubs and trees were identified and counted. The diversity of trees and shrubs, tree density per plot and canopy cover were significantly higher at unburnt than burnt sites with no difference in shrub density per plot. Bird species composition and number of nests between burnt and unburnt forests differed significantly with a considerable decline of forest interior bird specialists in burnt areas. An invasive plant species, Acacia melanoxylon, was found in dense groves within burnt sites and if not controlled, would escalate the fire regimes to further affecting plants and avian communities. Fire management, restoration and rehabilitation of burnt areas are among the immediate recommended actions.

Shifts in soil microbial communities over altitudinal gradients and the driving factors are poorly studied. Their elucidation is indispensable to gain a comprehensive understanding of the response of ecosystems to global climate change. Here, we investigated soil archaeal, bacterial, and fungal communities at four Alpine forest sites representing a climosequence, over an altitudinal gradient from 545 to 2000 m above sea level (asl), regarding abundance and diversity by using qPCR and Illumina sequencing, respectively. Archaeal community was dominated by Thaumarchaeota, and no significant shifts were detected in abundance or community composition with altitude. The relative bacterial abundance increased at higher altitudes, which was related to increasing levels of soil organic matter and nutrients with altitude. Shifts in bacterial richness and diversity as well as community structure (comprised basically of Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes) significantly correlated with several environmental and soil chemical factors, especially soil pH. The site at the lowest altitude harbored the highest bacterial richness and diversity, although richness/diversity community properties did not show a monotonic decrease along the gradient. The relative size of fungal community also increased with altitude and its composition comprised Ascomycota, Basidiomycota, and Zygomycota. Changes in fungal richness/diversity and community structure were mainly governed by pH and C/N, respectively. The variation of the predominant bacterial and fungal classes over the altitudinal gradient was the result of the environmental and soil chemical factors prevailing at each site.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-016-0748-2) contains supplementary material, which is available to authorized users.

Ditches are widespread and common elements of the agricultural landscape. Although they can provide habitats for aquatic biodiversity, their ecosystem integrity and processes are generally limited or even unknown due to anthropogenic pressures and the paucity of studies on this type of aquatic ecosystem. This study aimed to enhance the knowledge on the biodiversity, ecosystem attributes and ecological status of agricultural ditches by analyzing the macroinvertebrate communities of six different ditches and those of the main river in the same area. While negligible differences in taxonomic richness were observed, macroinvertebrate community composition significantly varied among sites as a function of the heterogeneous habitat conditions. These compositional differences strongly affected the relative abundance of functional feeding groups among sites and their derived ecosystem attributes. Moreover, the ecological status assessment depicted different scenarios depending on the biomonitoring indices applied. By means of a multifaceted, but still poorly adopted, analysis of the macroinvertebrate community, ranging from the taxonomic and functional diversity to ecosystem attributes and biomonitoring indices, the results obtained in this study offer useful information on the ecology of agricultural ditches with potential insights to improving their management.

To investigate the characteristics of rhizosphere soil microbial communities associated with Schisandra sphenanthera across different altitudinal gradients and to reveal the driving factors of microbial community dynamics, this study collected rhizosphere soil samples at four elevations: 900 m (HB1), 1100 m (HB2), 1300 m (HB3), and 1500 m (HB4). High-throughput sequencing and molecular ecological network analysis were employed to analyze the microbial community composition and species interactions. A null model was applied to elucidate community assembly mechanisms. The results demonstrated that bacterial communities were dominated by Proteobacteria, Acidobacteriota, Actinobacteriota, and Chloroflexi. The relative abundance of Proteobacteria increased with elevation, while that of Acidobacteriota and Actinobacteriota declined. Fungal communities were primarily composed of Ascomycota and Basidiomycota, with both showing elevated relative abundances at higher altitudes. Diversity indices revealed that HB2 exhibited the highest bacterial Chao, Ace, and Shannon indices but the lowest Simpson index. For fungi, HB3 displayed the highest Chao and Ace indices, whereas HB4 showed the highest Shannon index and the lowest Simpson index. Ecological network analysis indicated stronger bacterial competition at lower elevations and enhanced cooperation at higher elevations, contrasting with fungal communities that exhibited increased competition at higher altitudes. Altitude and soil nutrients were negatively correlated with soil carbon content, while plant nutrients and fungal diversity positively correlated with soil carbon. Null model analysis suggested that deterministic processes dominated bacterial community assembly, whereas stochastic processes governed fungal assembly. These findings highlight significant altitudinal shifts in the microbial community structure and assembly mechanisms in S. sphenanthera rhizosphere soils, driven by the synergistic effects of soil nutrients, plant growth, and fungal diversity. This study provides critical insights into microbial ecology and carbon cycling in alpine ecosystems, offering a scientific basis for ecosystem management and conservation.

Shrublands serve as an important component of terrestrial ecosystems, and play an important role in structure and functions of alpine ecosystem. Accurate estimation of biomass is critical to examination of the productivity of alpine ecosystems, due to shrubificationunder climate change in past decades. In this study, 14 experimental plots and 42 quadrates of the shrubs Potentilla fruticosaand Caragana jubatawere selected along altitudes gradients from 3220 to 3650 m a.s.l. (above sea level) on semi-sunny and semi-shady slopein Hulu watershed of Qilian Mountains, China. The foliage, woody componentand total abovegroundbiomassper quadratewere examined using a selective destructivemethod, then the biomass were estimated via allometric equations based on measured parameters for two shrub species. The results showed that C. jubataaccounted for1–3 times more biomass (480.98g/m2) than P. fruticosa (191.21 g/m2). The aboveground biomass of both the shrubs varied significantly with altitudinal gradient (P<0.05). Woody component accounted for the larger proportion than foliage component in the total aboveground biomass.The biomass on semi-sunny slopes (200.27 g/m2and 509.07 g/m2) was greater than on semi-shady slopes (182.14 g/m2and 452. 89 g/m2) at the same altitude band for P. fruticosa and C. jubata. In contrast, the foliage biomass on semi-shady slopes (30.50g/m2) was greater than on semi-sunny slopes (27.51 g/m2)for two shrubs. Biomass deceased with increasing altitude for P. fruticosa,whereas C. jubata showed a hump-shaped pattern with altitude. Allometric equations were obtained from the easily descriptive parameters of height (H), basal diameter (D) and crown area (C) for biomass of C. jubataand P. fruticosa. Although the equations type and variables comprising of the best model varied among the species, all equations related to biomass were significant (P < 0.005), with determination coefficients (R2) ranging from 0.81 to 0.96. The allometric equations satisfied the requirements of the model, and can be used to estimate the regional scale biomass of P. fruticosaand C. jubata in alpine ecosystems of the Qilian Mountains.

(1) Botanical composition, utilization of vegetation and animal biomass were compared on the 12 000 ha cattle section and 8 000 ha game section of Buffalo Range Ranch in south eastern Rhodesia. (2) Ten large herbivore species were present on the game section. The total animal biomass on the game section was approximately the same as that on the cattle section, where a few game animals were present. (3) Percentage utilization of herbaceous vegetation on the game section was 43% but only 28% on the cattle section. Twelve grass species were utilized more than 10% by cattle, as opposed to twenty species by game. (4) Up to 20% of the available browse (woody trees and shrubs) was utilized by game compared to 7-8% on the cattle section, where only a few game were present. (5) Grazing by cattle was less area-specific than that by game animals. This was due partly to controlled management of the cattle and partly to inherent behavioural patterns of the wild species. The game showed a wider choice of plant species but both game and cattle preferred the same herbaceous (grass) plants. (6) Cover abundance, litter cover and height of grass were greater on the cattle section, whilst soil capping, moribund grass and the extent of soil erosion were lower on the game section. There was also a higher density of shrubs (woody plants < 3 m) on the cattle section.

Conventional conservation policies in Europe notably rely on the passive restoration of natural forest dynamics by setting aside forest areas to preserve forest biodiversity. However, since forest reserves cover only a small proportion of the territory, conservation policies also require complementary conservation efforts in managed forests in order to achieve the biodiversity targets set up in the Convention on Biological Diversity. Conservation measures also raise the question of large herbivore management in and around set-asides, particularly regarding their impact on understory vegetation. Although many studies have separately analyzed the effects of forest management, management abandonment, and ungulate pressure on forest biodiversity, their joint effects have rarely been studied in a correlative framework. We studied 212 plots located in 15 strict forest reserves paired with adjacent managed forests in European France. We applied structural equation models to test the effects of management abandonment, stand structure, and ungulate pressure on the abundance, species richness, and diversity of herbaceous vascular plants and terricolous bryophytes. We showed that stand structure indices and plot-level browsing pressure had direct and opposite effects on herbaceous vascular plant species diversity; these effects were linked with the light tolerance of the different species groups. Increasing canopy cover had an overall negative effect on herbaceous vascular plant abundance and species diversity. The effect was two to three times greater in magnitude than the positive effects of browsing pressure on herbaceous plants diversity. On the other hand, a high stand density index had a positive effect on the species richness and diversity of bryophytes, while browsing had no effect. Forest management abandonment had few direct effects on understory plant communities, and mainly indirectly affected herbaceous vascular plant and bryophyte abundance and species richness and diversity through changes in vertical stand structure. Our results show that conservation biologists should rely on foresters and hunters to lead the preservation of understory vegetation communities in managed forests since, respectively, they manipulate stand structure and regulate ungulate pressure. Their management actions should be adapted to the taxa at stake, since bryophytes and vascular plants respond differently to stand and ungulate factors.

Research into the relationship between biodiversity and ecosystem functioning has mainly focused on the effects of species diversity on ecosystem properties in plant communities and, more recently, in food webs. Although there is growing recognition of the significance of nontrophic interactions in ecology, these interactions are still poorly studied theoretically, and their impact on biodiversity and ecosystem functioning is largely unknown. Existing models of mutualism usually consider only one type of species interaction and do not satisfy mass balance constraints. Here, we present a model of an interaction web that includes both trophic and nontrophic interactions and that respects the principle of mass conservation. Nontrophic interactions are represented in the form of interaction modifications. We use this model to study the relationship between biodiversity and ecosystem properties that emerges from the assembly of entire interaction webs. We show that ecosystem properties such as biomass and production depend not only on species diversity but also on species interactions, in particular on the connectance and magnitude of nontrophic interactions, and that the nature, prevalence, and strength of species interactions in turn depend on species diversity. Nontrophic interactions alter the shape of the relationship between biodiversity and biomass and can profoundly influence ecosystem processes.