Increase In Vegetation Height Research Articles

The International Tundra Experiment (ITEX): 30 years of research on tundra ecosystems

The International Tundra Experiment (ITEX) was founded in 1990 as a network of scientists studying responses of tundra ecosystems to ambient and experimental climate change at Arctic and alpine sites across the globe. Common measurement and experimental design protocols have facilitated synthesis of results across sites to gain biome-wide insights of climate change impacts on tundra. This special issue presents results from more than 30 years of ITEX research. The importance of snow regimes, bryophytes, and herbivory are highlighted, with new protocols and studies proposed. The increasing frequency and magnitude of extreme climate events is shown to have strong effects on plant reproduction. The most consistent plant trait response across sites is an increase in vegetation height, especially for shrubs. This will affect surface energy balance, carbon and nutrient dynamics and trophic level interactions. Common garden studies show adaptation responses in tundra species to climate change but they are species and regionally specific. Recommendations are made including establishing sites near northern communities to increase reciprocal engagement with local knowledge holders and establishing multi-factor experiments. The success of ITEX is based on collegial cooperation among researchers and the network remains focused on documenting and understanding impacts of environmental change on tundra ecosystems.

The response of the invasive princess tree (Paulownia tomentosa) to wildland fire and other disturbances in an Appalachian hardwood forest

This study examined the response of princess tree (Paulownia tomentosa) to different disturbances and its potential to spread throughout its current range in the U.S. The study was established in Shawnee State Forest in southern Ohio, USA, which has historically experienced disturbances from mining, logging, ice storms and wildfire. Plots were established for vegetation sampling where fire had occurred with and without princess tree present, and where no fire had occurred with and without princess tree present. To determine the influence of disturbance types on the density of princess tree, redundancy analysis (RDA) was used. High stem density of princess tree seedlings occurred in areas that experienced high fire intensities and herbicide treatment. Seedlings on southwest slopes increased in abundance as the time from the last logging activity increases. Princess tree saplings were present in greater densities in areas that experienced medium fire intensities and the highest ice storm damage. Sapling density is greatest as ground cover and vegetation height increases and slope decreases. Princess trees reach maximum stem density on northeast slopes in areas not impacted by the 2009 fire. All disturbances considered, including wildfire, have created conditions conducive to princess tree growth and expansion into forest areas.

Ecogeomorphology of coastal deltaic floodplains and estuaries in an active delta: Insights from the Atchafalaya Coastal Basin

We present here an integrated analysis of coastal deltaic floodplains in the active Atchafalaya Coastal Basin coupled to downstream deltaic estuaries to review how ecosystem properties self-organize around fluvial processes during river re-occupation as part of the delta cycle. The flood pulse of the river is critical to providing autogenic feedbacks between flow patterns, sediment delivery, vegetation productivity, and organic/inorganic accretion that produce spatial patterns of land elevation, habitat diversity, and estuary dynamics. Coastal deltaic floodplains form in the proximal region of an active delta as bar-shaped islands with interdistributary bays shape hydrogeomorphic zones influenced by both geophysical and ecological processes. Hydrogeomorphic zones in coastal deltaic floodplains of the proximal sedimentation zone can also be defined by time since subaerial emergence accounts for variability in vegetation community composition and soil successional development. The reduction in sedimentation and increase in both above- and belowground biomass associated with formation of hydrogeomorphic zones results in significant increase in organic matter density in soils, with higher N:P ratios reflecting the biotic feedback of ecological succession on delta floodplain development. In both the proximal and distal sedimentation regions, episodic events, such as river floods and cold fronts, control seasonal water levels, marsh platform inundation, and increase in elevation capital. In coastal deltaic floodplains, an increase in vegetation height and density has a twofold effect: it favors trapping of sediment on the islands; whereas an increase in roughness deflects water flow and sediment into the channels thus bypassing the marsh surface. There is evidence that this is in contrast to more constant positive feedback of vegetation on sedimentation in distal estuarine marsh platforms. Delta estuaries go through a transformation from a near-riverine estuary in the winter-spring season to a near-marine lagoon in the summer-fall season. Geomorphological displacement of vegetation types occurs as platform elevation increases in the proximal sedimentation zone as delta landform emerges, with specific vegetation dominating the respective subtidal, intertidal and supratidal hydrogeomorphic zones. This does not occur in the distal sedimentation zone that lack sediment input as marsh platform elevation decreases. This is due to presence of salinity and H2S that limit the capacity of biotic feedbacks to contribute to marsh stability. The growth of a coastal deltaic floodplain in the proximal sedimentation region of Atchafalaya Coastal Basin along with stable estuarine marshes in distal sedimentation region demonstrate the value of long-term riverine influence by preventing loss of wetland platform elevation.

Grazers affect selection on inflorescence height both directly and indirectly and effects change over time.

Selection mediated by one biotic agent will often be modified by the presence of other biotic interactions, and the importance of such indirect effects might change over time. We conducted an 11-yr field experiment to test the prediction that large grazers affect selection on floral display of the dimorphic herb Primula farinosa not only directly through differential grazing damage, but also indirectly by affecting vegetation height and thereby selection mediated by pollinators and seed predators. Exclusion of large grazers increased vegetation height and the strength of pollinator-mediated selection for tall inflorescences and seed-predator-mediated selection for short inflorescences. The direct effect of grazers on selection resulting from differential grazing damage to the two scape morphs showed no temporal trend. By contrast, the increase in vegetation height in exclosures over time was associated with an increase in selection mediated by pollinators and seed predators. In the early years of the experiment, the indirect effects of grazers on selection mediated by pollinators and seed predators were weak, whereas at the end of the experiment, the indirect effects were of similar magnitude as the direct effect due to differential grazing damage. The results demonstrate that the indirect effects of a selective agent can be as strong as its direct effects, and that the relative importance of direct vs. indirect effects on selection can change over time. A full understanding of the ecological processes governing variation in selection thus requires that both direct and indirect effects of biotic interactions are assessed.

Use of reflected GNSS SNR data to retrieve either soil moisture or vegetation height from a wheat crop

Abstract. This work aims to estimate soil moisture and vegetation height from Global Navigation Satellite System (GNSS) Signal to Noise Ratio (SNR) data using direct and reflected signals by the land surface surrounding a ground-based antenna. Observations are collected from a rainfed wheat field in southwestern France. Surface soil moisture is retrieved based on SNR phases estimated by the Least Square Estimation method, assuming the relative antenna height is constant. It is found that vegetation growth breaks up the constant relative antenna height assumption. A vegetation-height retrieval algorithm is proposed using the SNR-dominant period (the peak period in the average power spectrum derived from a wavelet analysis of SNR). Soil moisture and vegetation height are retrieved at different time periods (before and after vegetation's significant growth in March). The retrievals are compared with two independent reference data sets: in situ observations of soil moisture and vegetation height, and numerical simulations of soil moisture, vegetation height and above-ground dry biomass from the ISBA (interactions between soil, biosphere and atmosphere) land surface model. Results show that changes in soil moisture mainly affect the multipath phase of the SNR data (assuming the relative antenna height is constant) with little change in the dominant period of the SNR data, whereas changes in vegetation height are more likely to modulate the SNR-dominant period. Surface volumetric soil moisture can be estimated (R2 = 0.74, RMSE = 0.009 m3 m−3) when the wheat is smaller than one wavelength (∼ 19 cm). The quality of the estimates markedly decreases when the vegetation height increases. This is because the reflected GNSS signal is less affected by the soil. When vegetation replaces soil as the dominant reflecting surface, a wavelet analysis provides an accurate estimation of the wheat crop height (R2 = 0.98, RMSE = 6.2 cm). The latter correlates with modeled above-ground dry biomass of the wheat from stem elongation to ripening. It is found that the vegetation height retrievals are sensitive to changes in plant height of at least one wavelength. A simple smoothing of the retrieved plant height allows an excellent matching to in situ observations, and to modeled above-ground dry biomass.

Vegetation Recovery in Karst Areas in Central Guizhou, China

Due to the unique environment of karst landscapes, there are many uncertainties regarding the recovery of vegetation following human disturbance. Through standard wood parsing and growth ring investigation in Puding county in Guizhou province, China, we studied the process of vegetation restoration in karst areas. According to our results, during the recovery of karst vegetation height increases and ground diameter enlargement of tree layers occurred. Increases in the height and ground diameter followed logarithmic and growth curves, respectively. The development time of trees showed continuity, and growth points were randomly distributed. However, with large propagule quantities, vegetation can be directly restored and developed into a secondary high forest without a grass filling stage, and the recovery time is shortened.

Estimating total horizontal aeolian flux within shrub‐invaded groundwater‐dependent meadows using empirical and mechanistic models

AbstractWind erosion is a significant environmental problem that removes soil resources from sensitive ecosystems and contributes to air pollution. In regions of shallow groundwater, friable (puffy) soils are maintained through capillary action, surface evaporation of solute‐rich soil moisture, and protection from mobilization by groundwater‐dependent grasses and shrubs. When a reduction in vegetation cover occurs through any disturbance process, there is potential for aeolian transport and dust emission. We find that as mean gap size between vegetation elements scaled by vegetation height increases, total horizontal aeolian sediment flux increases and explains 58% of the variation in total horizontal aeolian sediment flux. We also test a probabilistic model of wind erosion based on gap size between vegetation elements scaled by vegetation height (the Okin model), which predicts measured total horizontal aeolian sediment flux more closely than another commonly used model based on the average plant area observed in profile (Raupach model). The threshold shear velocity of bare soil appears to increase as gap size between vegetation elements scaled by vegetation height increases, reflecting either surface armoring or reduced interaction between the groundwater capillary zone and surface sediments. This work advances understanding of the importance of measuring gap size between vegetation elements scaled by vegetation height for empirically estimating Q and for structuring process‐based models of desert wind erosion in groundwater‐dependent vegetation.

Measuring the turbulent characteristics in an open channel using the PIV method

Investigation of open channel flows is very important for a wide range of applications, including restoration and enhancement of river aquatic systems. As a result, the scientific community has focused on providing further insights on the flow characteristics in vegetated channels. Vegetation may be submerged or emerged, rigid or flexible with high or low density. For rigid vegetation, the hydraulic behaviour of the channel is similar to the behaviour of a channel with macro-roughness which could be caused by the presence of geometrical elements (e.g. cylinders, cubes). For flexible vegetation, both the flexibility of the vegetation and the hydrodynamic of the flow contribute to the generation of several formations such as erect, gently swaying, and prone.
 In this study, the characteristics of turbulent flow in an open channel were studied experimentally using Particle Image Velocimetry (PIV). This method assumes that the particles of a fluid faithfully follow the flow dynamics, hence the motion of these seeding particles are used to calculate velocity information of the flow. The experiments were conducted for both impermeable and permeable beds in a channel of 6.5m length, 7.5 cm width and 25 cm height. Two grass-like vegetation types of different height (2 and 6 cm) were used to represent permeable beds. These conditions are typical of flows encountered in sediment transport problems. Hydraulic characteristics such as distributions of velocities, turbulent intensities and Reynolds stress are investigated at a fine resolution using the PIV. Velocity is measured above the vegetation at different heights. Results show that velocity over the vegetation region is a function of the vegetation height and the total flow depth; velocity decreases as the vegetation height increases. In addition, we show that velocities above the vegetation region are much lower than velocities above an impermeable bed. This is due to the turbulent shear stresses and the existence of turbulence in the vegetation region, which reduce the mean velocity above the vegetation region. In addition, results show a region of zero velocity; between 3 and 6 cm and 1 and 2 cm for a 6 cm and 2 cm vegetation. This result shows that 50% of the vegetation behaves like an impermeable bed.

Effect of land abandonment on the vegetation of upland semi-natural grasslands in the Western Balkan Mts., Bulgaria

The area of semi-natural grasslands in Bulgaria has decreased tremendously in the past century due to agricultural intensification or abandonment. As these grasslands host valuable biodiversity, conservation measures are needed for their sustainable maintenance. We studied the effect of pastureland abandonment on plant communities at the Ponor Mt., a part of the Balkan Mts., Bulgaria. Data on floristic composition, vegetation structure and several abiotic parameters were collected in 137 randomly located 16-m2 plots in 2008. Canonical correspondence analysis (CCA) was used to analyse how species composition is related to abiotic and land use factors. Analyses of covariance (ANCOVAs) were used to test for the effects of sheep grazing vs. abandonment on vegetation structure and composition. The main environmental factors explaining the compositional variation were related to the altitude, sheep grazing and soil depth. Pastureland abandonment led to an increase in vegetation height and of the richness of mesophytes and leafy plants, and red-list species. Grazed plots had higher total species richness, more xerophytes, rosette forming and spring-flowering species. To ensure the persistence of the species of both the open grasslands and mid-successional grassland communities, the management should be carried out in an extensive way and with a zonation regime.

Effects of large herbivores on murid rodents in a South African savanna

Abstract:Our study presents experimentally based results on how large herbivore species affect savanna vegetation and thus murid rodents in the Hluhluwe-iMfolozi Park in KwaZulu-Natal, South Africa. We permanently excluded groups of large herbivore guilds of various body sizes (ranging from white rhino to hares) from sixteen 40 × 40-m plots of vegetation by using different fence types. We determined grass species composition and vegetation height and collected capture–mark–recapture data on murid rodents. Nutrient concentrations of the dominant grass species and rodent diet compositions were analysed. We found that herbivore species of different body sizes had different effects on murid rodents. The exclusion of medium-sized herbivores, such as warthog, impala and nyala increased the abundance of high-quality grass species, especiallyPanicum maximum. However, the dominant rodent speciesLemniscomys rosaliapreferred the most abundant grass species, rather than high-quality grasses. The absence of large bulk feeders, such as zebra, buffalo and white rhino led to an increase in vegetation height. In response, tall vegetation promoted both rodent abundance and species diversity and altered rodent species composition. Ultimately, our results indicate that the greatest effect on murid rodents came from the reduction of vegetation cover by large bulk feeders, which likely increased rodent predation risk.

Short-Term Effect of Cattle Exclosures on Columbia Spotted Frog (Rana luteiventris) Populations and Habitat in Northeastern Oregon

Livestock grazing is a common land use across the western United States, but concerns have been raised regarding its potential to affect amphibian populations. We studied the short-term effects of full and partial livestock grazing exclosures on Rana luteiventris (Columbia Spotted Frog) populations using a controlled manipulative field experiment with pre- and posttreatment data (2002-2006). Despite a significant increase in vegetation height within grazing exclosures, we did not find treatment effects for egg mass counts, larval survival, or size at metamorphosis 1-2 years following grazing exclosure installation. Water samples taken in late summer showed concentrations of nitrite, nitrate, ammonia, and orthophosphate that were low or near detection limits across all ponds and years. The results of this experiment do not support a hypothesis that limiting cattle access to breeding ponds will help conserve R. luteiventris populations in our study area. Further research is needed to evaluate regional variation and long-term effects of grazing exclosures on R. luteiventris populations.

Vegetation structure, species diversity, and ecosystem processes as measures of restoration success

Most restoration projects have focused on recovery of vegetation to assess restoration success. Nevertheless if the goal of a restoration project is to create an ecosystem that is self-supporting and resilient to perturbation, we also need information on the recovery of other trophic levels and ecosystem processes. To provide an example on how to assess restoration success, we compared four measures of vegetation structure, four measures of species diversity, and six measures of ecosystem processes among pre-reforested, reforested, and reference sites. In addition, we described how Bray Curtis Ordination could be used to evaluate restoration success. Vegetation structure recovered rapidly due to the increase in vegetation height and the decrease in herbaceous cover. Other measures such as litter cover, number of litter layers, and DBH size class values are recovering at slower rates, but they also have increased vegetation heterogeneity in the reforested site. Species diversity recovered rapidly. The increase in vegetation structure changed the local conditions in the reforested site facilitating the colonization of woody seedlings, ants, reptiles, and amphibians. Ecosystem processes, particularly litter production and turnover, have enhanced the incorporation of nutrients and organic matter in the soil. By including vegetation structure, species diversity, and ecosystem processes measures we have better information to determine the success of a restoration project. Moreover, the Subjective Bray Curtis Ordination is a useful approach for evaluating different restoration techniques or identifying measures that are recovering slowly and would benefit from additional management.

Ecology of coastal dune fauna

The distinguishing feature of coastal dunes is their connection to the shore. This maritime influence results in most coastal dunefields exhibiting a marked shore-normal gradient of decreasing physical stress and increasing complexity and vegetation cover landwards. Physical stresses include sand movement, salt spray, temperature variability, wind and disturbances such as storms. Increasing vegetation cover, often coupled to succession, mediates physical stress, creates stable microenvironments and is responsible for a general increase in habitat complexity landwards. Fauna respond to this gradient in a number of ways. Crustaceans of marine origin decrease in abundance landwards. Many of the special adaptations, which equip fauna for psammophilic lifestyles and allow them to cope with salt spray and temperature extremes, are only encountered near the beach. Insects, vertebrates and interstitial fauna increase in abundance landwards as vegetation cover, height and diversity increase, soil develops and greater stability is attained. Biological interactions and impacts of fauna on vegetation via grazing, seed dispersal and disturbance also increase landwards. There may be a shift from primarily r-strategist species near the beach to k-strategists inland and birds may replace small mammals as vegetation height increases. Coastal dune fauna differs from that of deserts in being more diverse and having a well developed interstitial component. Furthermore, coastal dune inhabitants are less specialised to cope with physical extremes and are seldom unique or endemic to these systems. However, this fauna has received considerably less attention than that of desert dunes and much research is warranted on subjects such as adaptations to sand movement and salt spray, endemism, trophic relations and exchanges with adjacent systems. Wind is the major factor impinging on these dune ecosystems.