Vegetation Ecology Research Articles

Improvement of land surface vegetation ecology inhibited precipitation-triggered soil erosion in the alpine-cold river source area – A case study in Southern Gansu, China

Study regionSouthern Gansu Plateau (SGP), located in the northeastern region of the Qinghai-Tibet Plateau, is a representative alpine-cold water source area for China’s large rivers, such as the Yellow River and Yangtze River. Study focusIdentifying the contributions of dominant factors to the regional soil erosion rate (A) is important for understanding the environmental processes and benefits of water and soil conservation, although related studies have seldom been conducted in alpine-cold regions such as the SGP. Accordingly, the main objectives of this study are (1) to determine the spatiotemporal dynamics of soil erosion and its driving factors in the SGP area; (2) to quantify the relationship between the main influential factors and soil erosion; and (3) to separate the contributions of the above factors to variations in regional soil erosion on the SGP. New hydrological insights for the regionThe multiyear average regional A for the SGP region was calculated as 24.18 t·hm−2·a−1, corresponding to an overall low intensity of regional soil erosion. The contributions of various time-varying factors, such as rainfall, vegetation cover, and conservation practices, to the reduction in A were −20.01%, 81.07%, and 21.95%, respectively, indicating that the improvement in land surface vegetation ecology dominated the decrease in A under the background of climate warming. The findings are expected to contribute to soil and water conservation in alpine-cold river source regions.

Modelling of drifting object dispersion in linear wave-induced flow

The dispersal of drifting objects like plant propagule under wave action can provide important information for the restoration of the plant community in coastal areas. An improved motion equation of the drift under wave action is established by coordinate transformation under the premise that the buoyancy is always perpendicular to the free surface, considering the variation of submerged height and the pressure gradient. Its numerical solution obtained by the fourth order Runge-Kutta method was compared with the experimental results in the literature, and the rationality of the improved motion equation is then verified. Then the perturbation method and Lagrange tracking principle were used to obtain the average longitudinal drift velocity expressed by Stokes drift velocity. The effect of different forces in the motion equations to the longitudinal diffusive motion was analyzed. Finally, the hydrodynamic coefficients affecting the prediction were analyzed, and the results show that the effects of the added mass coefficient and the drag coefficient are mainly reflected in the region with higher wave heights. The findings may provide certain scientific guidance for the restoration of coastal vegetation ecology through natural colonization.

Global Mapping of Potential and Climatic Plant‐Available Soil Water

AbstractThe estimation of plant‐available soil water (PASW) is essential to quantify transpiration fluxes, the onset of heatwaves, irrigation water management, land‐use decisions, vegetation ecology, and land surface memory in climate models. PASW is the amount of stored water available for plant use. It is broadly defined as the difference between soil water content at field capacity (FC) and wilting point (WP) in the root zone. The limiting states of FC and WP are linked to gravitational drainage and plant physiology and are often deduced from soil water characteristics at prescribed matric potentials (−3.3 and −150 m for FC and WP, respectively). Evidence suggests that static definition of FC at a constant matric potential ignores dynamic effects on FC attainment affected by soil and climate. Here, we revise the definition of PASW by considering (a) soil‐specific dynamic effects and (b) local climate effects of evaporation and rainfall frequency on PASW. The new global PASW maps benefit from state‐of‐the‐art soil maps, water characteristic parameterization, and incorporation of dynamic definition of FC. For completeness we provide static and dynamic PASW estimates. Globally, ice‐free soils store up to 19,941 km3 of water in the top 1 m (representing 18% of annual terrestrial precipitation). Adjusted for local climatic conditions, global PASW storage rarely exceeds 14,853 km3 per year highlighting the need for multiple refilling of soil profiles. Differences between potential and climatic PASW are manifested primarily in arid regions (where soil profiles are rarely filled to capacity) whereas in humid regions differences in PASW storage are minor.

Changes of ecological vegetation in major coal bases in North China

Changes of ecological vegetation in major coal bases in North China

Forests over limestone in Guiuan, Eastern Samar, the Philippines: Species composition and influencing environmental factors

Abstract. Buot Jr IE, Villanueva ELC, Origenes MG, Obeña RDR. 2023. Forests over limestone in Guiuan, Eastern Samar, the Philippines: Species composition and influencing environmental factors. Biodiversitas 24: 5123-5136. Forests over limestone are critical ecosystems providing numerous ecosystem services. However, the ecology of these ecosystems is less studied like the Guiuan Marine Resource Protected Landscape and Seascape (GMRPLS) in Eastern Samar, Philippines which incidentally is affected by strong typhoons. Studies on forests over limestone are even more essential to understand the vegetation ecology providing insights in crafting appropriate management strategy to sustain ecosystem services. Hence, the study aims to identify the woody vegetation diversity and composition of forests over limestone in GMRPLS, and to analyze the environmental factors influencing the physiognomy and ecology of the forests. Standard vegetation techniques were used and a total of nine plots with size of 20 × 20m each were established to assess the tree species (?1m height). Plant abundance data were recorded and computed. Soil samples were collected while climate data were obtained from the Guiuan, Eastern Samar Weather Station. Cluster analysis using relative density of trees per plot was done in order to identify major plant communities. Subsequently, a canonical correspondence analysis was carried out to pinpoint which environmental variables influenced the plant data set. Results show a total of 37 species belonging to 17 families, with 18 species are listed under by IUCN and seven species are listed by DAO 2017-11. Cluster analysis indicated 3 vegetation groupings or clusters named after the dominant species per plot, namely Cluster I (Hancea-Calophyllum-Macaranga-Ficus-Gnetum), Cluster II (Monoon-Wallaceodendron-Artocarpus-Hancea-Bago-eho), and Cluster III (Bridelia-Monoon-Neonauclea-Gnetum-Artocarpus-Sterculia-Hancea). GUI 02 plot (Cluster 1) was observed as the most diverse with the highest Simpson’s index and Fisher’s alpha, as well as the highest in total number of tree species. Canonical correspondence analysis indicated elevation, temperature and anthropogenic disturbances as the major factors influencing the vegetation diversity and composition. This can be used to formulate forest management strategies for the sustainable conservation of forests over limestone in GMRPLS.

Evaluation of the Groundwater Ecological Water Requirement in the Southeast Margin of Otindag Sandy Land Based on Allowable Groundwater Depth Drawdown

Water resources in arid and semi-arid areas are limiting factors for ecosystem health and economic development. Therefore, an accurate and reasonable assessment of ecological water demand is crucial for efficient water resource utilization. In this study, we used vegetation coverage and groundwater depth to assess the state of vegetation growth in the Zhenglanqi, located at the southeastern edge of Otindag Sandy Land. Our results indicate the existence of a statistical power index function between vegetation coverage and groundwater depth scatter plots, where even minor changes in groundwater depth can have a significant impact on vegetation growth. In order to quantitatively assess the impact of subsidence on vegetation ecology, we propose a maximum allowable subsidence level under conditions that maintain normal ecological conditions, based on the initial subsidence depth and ecological guarantee rate. Our findings suggest that regions with shallower initial groundwater depths are more sensitive to changes in their environment than regions with deeper groundwater depths. The total groundwater consumption in the study area was 83 million cubic meters while maintaining an ecological guarantee rate of 80%; thus, while ensuring normal environmental conditions, human exploitation of shallow groundwater accounts for only 16 percent.

Effect of different water and organic matter content on the resistivity of loess

The pore structure and strength of loess itself will change significantly in the process of mixing organic matter, which, as the main component of solid waste at present, is of great significance for ecological vegetation restoration in loess areas. At present, the research on the internal structure and strength performance of loess through the content of organic matter is still less, this paper takes the loess mixed with different content of organic matter (0 %–6 %) and distilled water (12 %–24 %) as the object of research, and tests the electrical resistivity and pore structure of the doped organic matter loess through the LCR digital bridge test equipment and liquid nitrogen adsorption experiments. The results show that the organic matter content and water content are important factors affecting the change of resistivity of organic soil. The electrical resistivity of organic soil is correlated with its own water content and organic matter content, which is closely related to the pore type and specific surface area within the organic soil. The results of the study provide valuable references for vegetation restoration and land use and conservation strategies in ecosystems.

Effects of Water Control and Nitrogen Addition on Functional Traits and Rhizosphere Microbial Community Diversity of Haloxylon ammodendron Seedlings

Water and nitrogen sources have always been the primary limiting factors for vegetation growth in arid and semi-arid regions and play an important role in the physiological ecology of vegetation. In this work, we studied the effects of water deficit and nitrogen addition on the physiological traits and rhizosphere bacterial microbial community of Haloxylon ammodendron seedlings in sterilized and non-sterilized soil habitats. A pot experiment was conducted to control the water and nitrogen sources of H. ammodendron seedlings. The water deficit treatment was divided into two groups based on gradient: a normal water group (CK, 70% field water holding capacity) and water deficit group (D, 30% field water holding capacity). The nitrogen addition treatment was divided into a no addition group (CK, 2.8 mg·kg−1) and addition group (N, 22.4 mg·kg−1). At the end of the growing season, the biochemical indexes of H. ammodendron seedlings were measured, and the rhizosphere soil was subjected to 16S rDNA-high-throughput sequencing to determine the rhizosphere bacterial community composition of H. ammodendron seedlings under different treatments. The results showed that the root-to-crown ratio of H. ammodendron seedlings increased significantly (p < 0.05) under the water deficit treatment compared to the control and nitrogen addition treatments, indicating that H. ammodendron seedlings preferred to allocate biological carbon to the lower part of the ground. In contrast, plant height and root length were significantly lower (p < 0.05) under water deficit treatment compared to the control, and no significant change was observed under water deficit and nitrogen addition compared to the control, indicating that water deficit inhibited the growth of H. ammodendron seedlings and nitrogen addition mitigated the effect of water deficit on the growth of H. ammodendron seedlings. Under sterilized soil conditions, both water deficit and nitrogen addition significantly increased the abundance and diversity of bacterial communities in H. ammodendron seedlings (p < 0.05). Conversely, under non-sterilized conditions, both inhibited the diversity of microbial bacterial communities, and the microbial characteristic species under different controls were different. Therefore, in the short-term experiment, H. ammodendron seedlings were affected by water deficit and allocated greater quantities of biomass to the underground part, especially in the non-sterile microbial environment; different initial soil conditions resulted in divergent responses of rhizosphere bacterial communities to water deficit and nitrogen addition. Under different initial soil conditions, the same water deficit and nitrogen addition treatment will lead to the development of distinct differences in rhizosphere bacterial community composition.

What Drives the Morphological Traits of Stress-Tolerant Plant Cynodon dactylon in a Riparian Zone of the Three Gorges Reservoir, China

The cyclical process of water storage and recession in the regular operation of the Three Gorges Reservoir creates a unique habitat stress that alters the structural and functional attributes of vegetation ecology within the riparian zone. The stress-tolerant plant Cynodon dactylon (L.) Pers is the dominant plant species in the riparian zone of the Three Gorges Reservoir. In this study, the riparian zone of the Daning River, a tributary located in the center of the Three Gorges Reservoir, was selected as our study area. To identify the drivers of the morphological traits of C. dactylon in the riparian zone of Daning River, we examined plant biomass and plant characteristics across different elevation gradients, with reference to abiotic factors to determine the distribution patterns of plant morphological traits. Results indicated that in the two main soil types of the riparian zone, plant biomass showed a consistent trend along the elevation gradient, with a “middle-height expansion” pattern; biomass increased and then decreased with rising water levels. Plant biomass positively correlated with soil total nitrogen and negatively correlated with soil pH, electrical conductivity, and total phosphorus. C. dactylon adapted to prolonged flooding in the riparian zone by having a significant negative correlation between plant height and erect stem length with soil moisture content to facilitate root respiration.

Structure, Ecology and Phythogeographical Characteristics of Riparian Vegetation Along the Bârzava and Caraş Rivers (Banat, Romania)

Abstract The riparian vegetation in the studied area have its particularties, due to the geographic position in the South-Western part of Romania with mountains and plains. These come together to give a most interesting and unique mosaic of habitats of riparian vegetation with a remarkable biodiversity. The climatic conditions and the relief with plains and mountains elements give the specific character to the studied riparian vegetation.

Bird communities and effects of management in Heathy Woodlands in the Grampians/Gariwerd National Park

ABSTRACT Measuring biodiversity across time and space is fundamental in assessing effects of ecological management actions. Monitoring bird species richness and abundance within the Victorian Grampians/Gariwerd National Park (GGNP) Heathy Woodland Ecological Vegetation Class (EVC) is used to assess seasonal changes in bird community and foraging guild composition. Two 2-ha/20-min bird surveys were undertaken at 36 sites in each of six seasonal surveillance periods over 2 years (total 432 surveys), detecting 90 species. Mean site diversity was 8.40 species (se = 1.91, n = 36 sites) and mean abundance was 19.52 birds (se = 6.91, n = 36 sites). Spatial and temporal shifts in abundance and species richness are compared with data collected using the same method by Possingham et al. in SA’s Mt Lofty Ranges (MLR) stringybark habitat and with data from the same GGNP sites in 2008 after widescale 2006 wildfires. Neither mean diversity nor abundance at each site changed significantly in the same season between years, but mean diversity in spring was higher than in both autumn and winter. Within Heathy Woodland habitat, the foliage searcher guild was the most diverse and abundant foraging guild across sites. With potential for ecosystem collapse in the MLR stringybark community and threats to the GGNP community, ongoing study of avian communities has potential to guide effective management both in the MLR and the GGNP. We assessed outcomes of GGNP fire history on avian diversity and abundance. A more diverse bird community may result where a mosaic burn of stringybark woodlands is achieved and in longer unburnt sites.

Changing characteristics of ecosystem and water storage under the background of warming and humidification in the Qilian Mountains, China

The Qilian Mountains provide an ecological security barrier, and the region is an important river runoff area in China. Water resources play an essential role in the natural environment of Northwest China. This study used daily temperature and precipitation data from meteorological stations in the Qilian Mountains from 2003 to 2019, Gravity Recovery and Climate Experiment, and Moderate Resolution Imaging Spectroradiometer satellite data. Additionally, we used the Gravity Recovery and Climate Experiment satellite's monthly gravity field model data. Furthermore, we analyzed the characteristics of climate warming and humidification in the eastern, central, and western sections of the Qilian Mountains based on spatial precipitation interpolation and linear trend analysis. Finally, we examined the relationship between water storage changes and precipitation and its impact on vegetation ecology. The results revealed a significant warming and humidification trend in the western Qilian Mountains. The temperature increased significantly, and the increased precipitation rate in summer reached 1.5–3.1 mm/10a. Water storage in the Qilian Mountains displayed an increasing trend, with an increase of approximately 14.3 × 108 m3 over the 17 years study period, averaging an increase of 8.4 mm/year. The spatial distribution of water storage in the Qilian Mountains increased from north to south and east to west. There were noticeable seasonal differences, with the largest surplus occurring in the western Qilian Mountains (71.2 mm in summer). The fractional vegetation coverage in 95.2 % of the western Qilian Mountains and net primary productivity in 90.4 % of the area displayed an increasing trend, and vegetation ecology improved significantly. This study aims to investigate the characteristics of ecosystem and water storage changes in the Qilian Mountain area under the background of climate warming and humidification. The results obtained from this study provided an assessment of the vulnerability of alpine ecosystems and helped in making spatially explicit decisions for the rational utilization of water resources.

Heavy ionic pollution disrupts assemblages of algae, macroinvertebrates and riparian vegetation

Urban streams display consistent ecological symptoms that commonly express degraded biological, physical, and chemical conditions: the urban stream syndrome (USS). Changes linked to the USS result in consistent declines in the abundance and richness of algae, invertebrates, and riparian vegetation. In this paper, we assessed the impacts of extreme ionic pollution from an industrial effluent in an urban stream. We studied the community composition of benthic algae and benthic invertebrates and the indicator traits of riparian vegetation. The dominant pool of benthic algae, benthic invertebrates and riparian species were considered as euryece. However, ionic pollution impacted these three biotic compartments' communities, disrupting these tolerant species assemblages. Indeed, after the effluent, we observed the higher occurrence of conductivity-tolerant benthic taxa, like Nitzschia palea or Potamopyrgus antipodarum and plant species reflecting nitrogen and salt contents in soils. Providing insights into organisms’ responses and resistance to heavy ionic pollution, this study sheds light on how industrial environmental perturbations could alter the ecology of freshwater aquatic biodiversity and riparian vegetation.

Evaluating Impacts of Opencast Stone Mining on Vegetation Primary Production and Transpiration over Rajmahal Hills

Opencast mining has significantly triggered vegetation degradation in many ecologically sensitive regions across the globe. The detailed spatio-temporal information on mining-induced vegetation degradation and associated primary production loss are crucial inputs to authorities and policymakers to frame and implement sustainable development programs in the mining regions to conserve vegetation ecology. Thus, the present study aimed to decipher the mining-induced vegetation cover and subsequent productivity losses over the Rajmahal Hills in Jharkhand (India). The Gross Primary Productivity (GPP), Net Primary Productivity (NPP), and Vegetation Transpiration (VT) datasets were used for analyzing the mines-induced losses in vegetation cover and associated productivity. The key findings indicated a loss of vegetation cover by ~340 km2 and an expansion of the mining area by ~54 km2 over the Rajmahal Hills during 1990–2020. The change detection analysis at the decadal period revealed that ~3.06 km2, 8.10 km2, and 22.29 km2 of vegetation cover were lost only due to the mining activity during 2000–2010, 2010–2020, and 2000–2020, respectively. The replacement of vegetation cover by mining area has caused GPP loss of 0.01 tonnes carbon (tC) per day, 0.04 tC/day, and 0.09 tC/day; NPP loss of ~1.25 tC, 2.77 tC, and 7.27 tC; VT loss of 5200 mm/day, 13,630 mm/day, and 30,190 mm/day during 2000–2010, 2010–2020, and 2000–2020, respectively. Hence, the present study revealed that the mining-induced vegetation losses have caused an alteration of carbon sequestration, carbon stock, and VT over the Rajmahal Hills.

The Geographical Analysis of Environmental Threats to Natural Plants in the Sharbazher District

The Sharbazher district is rich in natural vegetation with (49%) of the area consisting of forest and other natural vegetation belts. Protecting this vegetation belt is an environmental necessity, as it has faced several environmental threats in the last two decades. The study identified environmental threats and evaluated the measures and efforts taken to protect this vegetation belt. The research used a (reading) method, followed by analytical and comparative methods. Field surveys of the study area were conducted on several different dates, data were collected and scenes were observed. The study found that along with natural threats, manmade threats are more significantly affecting the vegetation ecology of the region. Rainfall fluctuations have had a more notable impact on short vegetation and pastures. From summer to early winter, an environmental instability occurred that resulted in damaging riverside vegetation and streams, many of which during the years (20172022-) about (2310) trees were cut down, most of which were (Oak) trees, but according to the study’s estimation, more than (16000) trees were cut down during the same period. Until now, charcoal is made in coal furnaces from natural forest trees and this is carried out without official permission, during the years (20172022-) more than (20,000 acres) of weed and natural forests in the region have been burned. Also during the years (20012020-), there have been changes in the vegetation belts and land cover of the region, the area of dense and medium forest belts has increased, but the area of open forest belts has decreased, and there have been major changes in the land area of human settlements. The study outlines ways to protect the vegetation belt and emphasises the enforcement of Implemented laws on the protection of plants and forests. Keywords: Natural plants, Environmental threats, Forest law, Sharbazher district.

The Importance of Soil Elevation and Hydroperiods in Salt Marsh Vegetation Zonation: A Case Study of Ria de Aveiro

Salt marshes are among the most valuable ecosystems on earth; however, previous research has reported global losses in their extent accompanied by an impairment of their ecological processes. Nonetheless, investigations on salt marsh vegetation ecology are still lacking in many sites, including in Ria de Aveiro. As such, this study aimed to (1) monitor, characterize, and understand the evolution of salt marsh vegetation communities at three different study sites with different environmental conditions and stages of degradation, where we also sought to (2) identify the main delimiting abiotic factors associated with the distribution of the main species. To do so, a multidisciplinary approach that involved the survey of vegetation from permanent transects and the collection of ecological, physicochemical, and hydrodynamic data at sampling points within the monospecific stands of the main species was reported. The results showed that, of the abiotic factors deemed as the main delimiting forces of salt marsh vegetation, the soil elevation and hydroperiod were the most restrictive factors, as they ultimately influenced species composition at the different study sites and explained most of the variation observed between the studied monospecific stands.

Photosynthetic Physiological Basis of Forage Mass Stability in a Progeny of Rhizome-Rooted ‘Qingshui’ Medicago sativa L.

Rhizome-rooted alfalfa (Medicago sativa L.) is an excellent forage for establishing grazing and ecological grasslands, requiring a high and stable yield. Studying the genetic and physiological basis of stable expression of biomass traits is essential for improving production performance in rhizome-rooted alfalfa. We analyzed forage mass and photosynthetic physiological indices of the improved progenies (RSA−01, RSA−02, and RSA−03), parental “Qingshui” (CK1), and “WL168” (CK2) at ages one and five years and their relationships, then revealed heterotic stability. Moreover, we explored the effects of interannual dynamics and genetic differences on tested indices. The results revealed compared with the forage mass of CK1, RSA−03 at ages one and five years increased by 22.17% and 19.72%, respectively, while RSA−01 and RSA−02 varied from 1.40% to 8.65%, indicating obvious heterosis in forage mass of RSA−03. At one year of age, Gs value, Car content and SS content of RSA−03 were higher than those of CK1; SS content of RSA−03 were higher than those of CK2 and RSA−02; Ci, Gs and Tr values of RSA−03 were higher than those of RSA−01. At five years of age, Pn, Gs, and WUE values, and Sta content of RSA−03 were higher than those of CK1; Ci value and Suc content of RSA−03 were higher than those of CK2; Car content and Gs value of RSA−03 were higher than those of other progenies. The forage mass; Chl(a/b) ratio; Pn, Gs, and WUE values; Suc content of RSA−03 at age five years were higher than those at age one year by 9.99%–44.24%. Through path analysis, Gs and NSC were direct factors affecting forage mass at age one year, and both Pn and SP affected forage mass indirectly through Gs; Gs and Chl(a+b) were direct factors affecting forage mass at age five years, and SS affected forage mass indirectly through Gs. Interestingly, Chlb, Chl(a/b), Pn, Tr, Gs, Ci, Suc, SP, and SS were more influenced by age than genetics, while the opposite was true for Car and Sta. Accordingly, RSA−03 showed obvious and stable heterosis in forage mass and photosynthetic physiology, recommending the establishment of grazing pastures and ecological vegetation.

Ecosystem Services and Disservices of Bay-Delta Primary Producers: How Plants and Algae Affect Ecosystems and Respond to Management of the Estuary and Its Watershed

The Sacramento–San Joaquin Delta (Delta) is a case-study of the Anthropocene “great accelerations,” with exponentially increasing temperatures and sea level over time, leading to rapid change in other ecosystem components. In nearly all these interconnected changes and across scales, primary producers play a major role, with diverse effects that mitigate or exacerbate rapid change induced by climate or other human-driven perturbations. Through this anthropocentric lens, primary producers can be viewed as performing numerous ecosystem services—which ultimately benefit humans—as well as ecosystem disservices, which have negative effects on human communities. For example, through carbon sequestration, wetlands can perform ecosystem services of mitigating warming at a global scale and combating relative sea-level rise at a local scale, while generating food that supports regional food webs and fisheries. On the other hand, invasive aquatic vegetation (IAV) can trap sediment before it reaches wetlands, exacerbating local subsidence and relative sea-level rise while incurring great costs to recreation, fishing, and agencies tasked with its control. Effectively managing these ecosystem services and disservices requires understanding of how they are connected. For example, wetland restoration often creates opportunities for IAV, which may inhibit sediment deposition on the wetland and outcompete native species. As the Delta science community works toward a more integrative understanding of how different components of the Delta interact as a whole and across scales, the pervasive effects of the ecosystem services and disservices of primary producers serve as foundational knowledge. In this topically themed edition of State of Bay-Delta Science, we review these effects. Individual chapters focus on the historical ecology of the primary productivity of aquatic vegetation, the ecology and control of invasive aquatic vegetation, harmful algal blooms, carbon sequestration and subsidence reversal by wetlands, and remote sensing methods for quantifying the ecosystem services and disservices of Delta primary producers.

Ecology and Ecosystem Impacts of Submerged and Floating Aquatic Vegetation in the Sacramento–San Joaquin Delta

Substantial increases in non-native aquatic vegetation have occurred in the upper San Francisco Estuary over the last 2 decades, largely from the explosive growth of a few submerged and floating aquatic plant species. Some of these species act as ecosystem engineers by creating conditions that favor their further growth and expansion as well as by modifying habitat for other organisms. Over the last decade, numerous studies have investigated patterns of expansion and turn-over of aquatic vegetation species; effects of vegetation on ecosystem health, water quality, and habitat; and effects of particular species or communities on physical processes such as carbon and sediment dynamics. Taking a synthetic approach to evaluate what has been learned over the last few years has shed light on just how significant aquatic plant species and communities are to ecosystems in the Sacramento-San Joaquin Delta. Aquatic vegetation affects every aspect of the physical and biotic environment, acting as ecosystem engineers on the landscape. Furthermore, their effects are constantly changing across space and time, leaving many unanswered questions about the full effects of aquatic vegetation on Delta ecosystems and what future effects may result, as species shift in distribution and new species are introduced. Remaining knowledge gaps underlie our understanding of aquatic macrophyte effects on Delta ecosystems, including their roles and relationships with respect to nutrients and nutrient cycling, evapotranspiration and water budgets, carbon and sediment, and emerging effects on fish species and their habitats. This paper explores our current understanding of submerged and floating aquatic vegetation (SAV and FAV) ecology with respect to major aquatic plant communities, observed patterns of change, interactions between aquatic vegetation and the physical environment, and how these factors affect ecosystem services and disservices within the upper San Francisco Estuary.

Relationship of Plant Species Diversity and Sampling Area Under Different Grazing Intensities in the Steppe of Northern China

The relationship between sampling area of plant community and number of species contained in it has an importance in vegetation ecology. Using a nested quadrat survey, the relationship between plant species and sampling area was discussed under different grazing pressure in the steppe and the determination of minimum sampling area was calculated herein. Ten curve models were selected to fit the species-area relation of plant community in a typical steppe of northern China. The residual standard deviation, correlation index, average value of absolute deviation, and average value of absolute relative deviation were used as the evaluation indexes for model fitting. The results show that the curve equations S = B + CAZ and S = C(1-e−BA)Z have the best simulation effect. According to the simulation results, the minimum sampling areas are determined as 1.16 m2 (T0), 1.23 m2 (T7), 1.28 m2 (T10), and 1.10 m2 (T14), presenting the minimum sampling area is feasible when the second derivative is zero. Generally, sheep grazing reduced the species richness of steppe, though some of the plans flourished while some others disappeared or dismissed, but increased spatial heterogeneity, especially on a smaller scale. However, there are also variances in different area scales and grazing intensities. When the sampling area was small (< 2 m2), heavy grazing T14 increased the number of plant species per unit area, yet light grazing T8 reduced the number of plant species per unit area of steppe. When the sampling area was large (> 16 m2), grazing reduced the number of plant species per unit area in the natural steppe. Anyhow, the effect of grazing intensity on plant species fluctuated greatly when the sampling area was medium (2 m2 ∼ 16 m2). In general, the similarity of plant communities had an increasing trend with accumulated sampling area, though it varied at different grazing intensities.