A Century of Vegetation Change on an Offshore Islet1

Relative importance of climate change and human activities for vegetation changes on China's silk road economic belt over multiple timescales

Vegetation and climate change during Marine Isotope Stage 3 in China

Coverage-dependent amplifiers of vegetation change on global water cycle dynamics

Changes in bottom-land vegetation between December 1965 and October 1972 apparently caused significant differences in stage, mean cross-sectional velocity, mean cross-sectional depth, and boundary roughness at peak discharges of three major floods in an 11.5-mile (18.5 km) study reach of the Gila River. The first flood, which had a peak flow of 39,000 ft3/s (1,100 m3/s), occurred in December 1965 when the dense bottom-land vegetation was dormant. The second flood, which had a peak discharge of 40,000 ft3/s (1,130 m3s), occurred in August 1967 when the vegetation had large amounts of foliage; however, the vegetation had been eradicated in the upstream half of the study reach prior to this flood. The third flood, which had a peak discharge of 80,000 ft 3/s (2,270 m3/s), occurred in October 1972; the vegetation had been eradicated in the whole study reach prior to this flood. Compared to the 1965 flood, the large amounts of foliage in the uncleared half of the reach during the 1967 flood apparently caused a 7 percent decrease in mean velocity, a 6 percent increase in mean depth, and an 11 percent increase in the Manning roughness coefficient at peak stage. Compared to the 1965 flood the clearing of the study reach apparently caused a 25 percent increase in mean velocity, a 15 percent decrease in mean depth, and a 30 percent decrease in the Manning roughness coefficient at peak stage in the 1967 and 1972 floods. The mean velocities of the three peak flows were relatively low where large parts of the flows moved across the meandering stream channel; the Manning coefficients and the mean depths were relatively large in these segments. After the first flood, scour was noted at seven of the nine cross sections in the study reach. After the second flood, fill was observed at all the cross sections, and, after the third flood, scour was observed at six sections. From 1964 to 1972, there was a net scour at .only one section, section 7, where the mean crosssectional velocity was relatively large for the three floods. Effects of changes of bottom-land vegetation on scour and (or) fill could not be determined. INTRODUCTION Saltcedar (Tamarix chinensis Lour1) has created problems along many streams in the arid and semiarid regions of the United States. Since about 1930 the plant has spread rapidly, consumed large amounts of water, and, in many streams, created potential flood hazards (Robinson, 1965, p. 1). The problems intensify as the demand for water mounts, the need for reducing flood 1Also referred to as Tamarix pentandra and Tamarix gallica. hazards grows, and at the same time the areal extent and density of the plant increases. Management of the saltcedar is necessary to lessen the magnitudes of the problems. As a remedial measure saltcedar has been eradicated along several streams in the western United States. The effectiveness and the side effects of this measure are not well documented. The flood plain of the Gila River in southeastern Arizona is an area where the vegetation has been managed. The low-benefit, deep-rooted vegetation, mostly saltcedar (Tamarix chinensis Lour) and mesquite (Prosopis juliflora var. velutine (Woot.) Sarg.), was replaced with a beneficial short-rooted grass (Culler, 1965, p.33-38). The saltcedar and mesquite trees are known to increase both the resistance to flow and the stability of the flood-plain boundary. Therefore, replacement of these trees with grass is likely to cause changes in rates of erosion and deposition, and to cause changes in channel width, depth, sinuosity, gradient, roughness, and even channel location. The main purpose of this report is to describe the apparent differences in hydraulic characteristics of the Gila River during three major floods owing to changes in bottom-land vegetation. The types of change in vegetation relevant to this study are seasonal increase in foliage and plant eradication. The hydraulic parameters studied are stage, mean cross-sectional velocity, mean cross-sectional depth, and the Manning roughness coefficient at peak discharge. Changes in the mean altitude of the bottom land as a result of the floods also are described. The floods occurred in December 1965, August 1967, and October 1972, with peak discharges of 39,000, 40,000, and 80,000 ft3/s (1,100,1,130, and 2,270 m3/s). These floods have a return interval of about 17 and 50 years, and they were the largest in the study reach since 1917 (Burkham, 1970, figs. 16 and 23). Discussions, descriptions, methods, and analyses presented in this report deal with averages, lumped

We assessed the degree to which fencing, livestock exclusion, and replanting of riparian zones affected avian assemblages in massively cleared landscapes. Measurements were made at three creeks in the southern Murray–Darling Basin in southeastern Australia, each of which had circa 1‐km long treated sections and paired “untreated” circa 1‐km sections, where no fencing, planting, or stock exclusion was done. We measured the change in vegetation characteristics and abundances of native birds for up to 8 years after works were completed. Prior to data collection, we developed expected responses of bird species based on the anticipated time‐courses of change in vegetation structure. We used hierarchical Bayesian models to explore the effects of the management actions, and to account for within‐site variation in vegetation characteristics. There were major changes in vegetation structure (reductions in bare ground and increases in shrubs and tree recruitment) but avian responses generally were small and not as expected. There are at least four possible reasons for the limited avian responses: (1) there has been a long‐term decline in woodland birds across the region; (2) the study was conducted during the longest drought in the instrumental record in the study region; (3) the total amount of replanted vegetation was small in a massively denuded region; and (4) monitoring may have been over too short a term to detect responses to longer‐term changes in structural vegetation.

Rapid climate warming has contributed to significant changes in Arctic and boreal vegetation over the past half century. Changes in vegetation can impact wildlife by altering habitat and forage availability, which can affect behavior and range use. However, animals can also influence vegetation through foraging and trampling and therefore play an important role in determining ecosystem responses to climate change. As wildlife populations grow, density‐dependent processes can prompt range expansion or shifts. One mechanism for this is density‐dependent forage reduction, which can contribute to nutritional stress and population declines, and can also alter vegetation change trajectories. We assessed the range characteristics of a migratory caribou (Rangifer tarandus) herd in east‐central Alaska and west‐central Yukon Territory as it grew (1992–2017) then declined (2017–2020). Furthermore, we analyzed the correlation between caribou relative spatial density and vegetation change over this period using remotely sensed models of plant functional type cover. Over this period, caribou population density increased in all seasonal ranges. This was most acute in the calving range where density increased 8‐fold, from 1.5 to 12.0 animals km−2. Concurrent with increasing density, we documented range shifts and expansion across summer, post‐calving and winter ranges. In particular, summer range size doubled (12,000 km2 increase) and overlap with core range (areas with repeated year‐round use) was halved. Meanwhile, lichen cover, a key forage item, declined more in areas with high caribou density (2.4% absolute, 22% relative decline in cover) compared to areas where caribou were mostly absent (0.3% absolute, 1.9% relative decline). Conversely, deciduous shrub cover increased more in high caribou density areas. However, increases were dominated by less palatable shrubs whereas more palatable shrubs (i.e., willow [Salix spp.]) were stable or declined slightly. These changes in vegetation cover were small relative to uncertainty in the map products used to calculate change. Nonetheless, correlations between vegetation change and caribou range characteristics, along with concerning demographic trends reported over this same period, suggest changing forage conditions may have played a role in the herd's subsequent population decline. Our research highlights the potential of remotely sensed metrics of vegetation change for assessing the impacts of herbivory and trampling and stresses the importance of in situ data such as exclosures for validating such findings.

Temporally changing drivers for late-Holocene vegetation changes on the northern Tibetan Plateau

Contradictory views are still existing on the dominating drivers and the underlying mechanisms for the overall increasing evapotranspiration (ET) in China, a region has undergone substantial vegetation and climate changes. Particularly, some studies conclude that climate change is the dominating factor, while other researchers believe that it is the vegetation change. To fill this knowledge gap, here we developed a physical‐based ET model by combining the modified Penman–Monteith model and a newly developed canopy resistance model, which effectively links ET and its potential drivers, with the mean correlation and relative RMSE between the observed and modeled canopy resistance being 0.83 ± 0.09 and 3.4 ± 1.6%, respectively. The reliability of the model was also demonstrated by comparing the derived sensitivity of canopy resistance to air CO2 concentration (mean of 0.14 ± 0.03% ppm−1) and the observations (∼0.15% ppm−1). Based on this model and a scenario analysis approach, we demonstrated that vegetation change, air temperature, air CO2 concentration and soil moisture were the dominating factors of ET variabilities during 1982–2014, which dominated ET changes at 36.0 ± 16.3%, 16.5 ± 4.5%, 20.2 ± 11.6 and 18.2 ± 10.9% of the land grids, and averagely contributed 0.72 ± 0.32, 0.28 ± 0.15, −0.51 ± 0.15 and 0.13 ± 0.78 mm yr−2, respectively. These indicated that vegetation change was the most important factor for the increasing ET over China during the past several decades. These findings and the model are helpful for assessing the ecohydrological cycles in a changing environment.

A greater negative impact of future climate change on vegetation in Central Asia: Evidence from trajectory/pattern analysis

Uncovering the impact of climate and vegetation changes on runoff in karstic regions of southwest China

Analysing trajectories of vegetation and landscape change in southern Africa from historical field photographs

The mid-Holocene (MH) was characterized by substantial vegetation changes over northern Africa, termed the Green Sahara. Concurrently, several proxy reconstructions have indicated anomalous warmth over some Arctic regions during the MH, with some records also indicating an abrupt cooling coinciding with the Saharan desertification. This has prompted studies into a potential teleconnection between the MH Green Sahara and the Arctic, leading to conflicting hypotheses regarding the dominant direction and mechanism for this teleconnection. In this study, we analysed outputs from four fully coupled global climate models to identify the impact of the Green Sahara on the Arctic region. Through the difference of two sets of mid-Holocene simulations – with and without the Green Sahara – we isolated the effect of the northern African vegetation and land cover changes on Arctic temperatures. We show that simulations incorporating the Green Sahara yield considerably higher Arctic warming relative to simulations without explicit prescriptions of vegetation changes. We also conducted atmosphere-only global climate model simulations to identify whether or not Arctic temperature changes impacted northern African precipitation. Our results suggest that while the Arctic temperature changes induced changes to the atmospheric circulation over northern Africa, they were too weak to substantially contribute to Saharan desertification.

Biomarker signature in tropical wetland: lignin phenol vegetation index (LPVI) and its implications for reconstructing the paleoenvironment

The Database of German North Sea Salt Marshes (GIVD ID EU-DE-029) comprises 423 1m²-plots from German North Sea salt marshes, tracing back to the project Thematic Mapping and Sensitivity Study of Mudflat Areas in the German Wadden Sea. In 1987-1991 and again in 2007, plots along 31 transects - covering the mainland coast of Schleswig-Holstein - were investigated for their vascular plant species composition (species' presence and cover using Londo scale) as well as structural and spatial variables like grazing management, position and elevation in relation to mean high tide. Frequent vegetation-types were Spartinetum anglicae, Puccinellietum maritimae and Festucetum rubrae. This consistent data set allowed and still aims to determine spatial and geographical differences regarding changes in species diversity, dominance structure and functional traits in relation to driving environmental variables, and, especially, to study changes in elevation (due to accretion and subsidence) and vegetation in the salt marshes with regard to future sea level rise. Further, our data provide a baseline for future studies of possible changes in biodiversity, vegetation composition and species distribution pattern caused e.g. by invasive plant species, conservation management or sea level rise, which may in turn further improve future salt marsh management.

Impacts on watershed-scale runoff and sediment yield resulting from synergetic changes in climate and vegetation