Extent Of Vegetation Research Articles

Quantifying and interpreting the hysteresis patterns of monthly sediment concentration and water discharge in karst watersheds

Hysteresis loop models are one of the most common and effective tools for quantifying time-scale dynamics of sediment-discharge relationships. These models can successfully characterize sediment dynamics in watersheds and facilitate developing effective measures to manage sediment-discharge resources. Considering the characteristics of a proportional hysteresis index, an improved differential hysteresis index was developed. The improved model was used to quantify typical patterns of monthly sediment-discharge relationships in six karst watersheds in southwest China during 2003–2019. Partial least squares structural equation modeling was conducted to decouple the effects of climatic factors and vegetation extent on the hysteresis index. The results indicate that clockwise hysteresis accounted for 74 % of the total hysteresis occurring in the watersheds, whereas counterclockwise and 8-shaped hysteresis accounted for only 22 % and 3.9 %, respectively. The improved hysteresis index varied from −10 to 10, effectively reflecting the degree of hysteresis occurring in the watersheds. Partial least squares structural equation modeling shows that climatic factors (e.g., temperature and precipitation) and vegetation extent in the Hongshui, Yujiang, Liujiang and Wujiang watersheds explained 50 %∼75 % of the hysteresis between sediment concentration and water discharge. The combined effect of temperature and precipitation on the hysteresis index was larger than that of vegetation extent. The improved differential hysteresis index proposed in this study effectively extended the applicability of differential hysteresis indices and facilitated comparing the degree of hysteresis among watersheds with different sediment concentrations. This study can improve the understanding of sediment sources and transport pathways and provide valuable information for decision making on soil erosion control in karst watersheds.

Coexistence of savanna and rainforest on the ice-age Sunda Shelf revealed by pollen records from southern South China Sea

Exposure of the presently submerged continental shelf of Southeast Asia during low sea-level stands of the Quaternary is thought to be deeply involved in the biogeographic evolution of this biodiversity hotspot. Inland proxy records are mounting to argue grassland expansions over Southeast Asia during glacial periods, lending supports to the existence of a transequatorial “savanna corridor” as hypothesized. However, pollen records retrieved from marine sediments have indicated widespread rainforests on the exposed northern Sunda Shelf. To reconcile these seemingly conflicting observations, here we present new, multisite marine pollen records from the southern South China Sea focusing on the Last Glacial Maximum (LGM) time interval. It is found that the sites in front of the Sunda Shelf palaeo-rivers contain substantially more Poaceae pollen, in particular a smaller size fraction, than the site offshore North Borneo. Among the sites, abundant lowland tree pollen with similar major taxa is also observed. The co-occurrence of grass and rainforest pollen suggests a longitudinal climate gradient with increasing aridity toward the interior of glacial Sundaland. Combining our results with various palynological evidence from marine sediments seems to indicate that the vegetation on the exposed Sunda Shelf might not be fully recognized by previous studies. This is likely due to an admixture of pollen from other source regions, particularly Borneo where the rainforest was retained during glacial periods. Therefore, the extant vegetation records, from both terrestrial and marine archives, support the hypothesis of a “savanna corridor” over the LGM sundaland.

Dynamic disequilibrium: Recent widespread increases in vegetation cover on subarctic floodplains of Interior Alaska

AbstractBoreal forest and tundra ecosystems are undergoing rapid climatic and environmental changes with consequences for ecosystem structure, function, and services. Although riparian zones occupy a small footprint within subarctic landscapes, they have disproportionately high value as foci of hydrological processes, biogeochemical cycling, ecological disturbance, biodiversity, and wildlife activity. Recent observations of increased winter discharge, reduced peak flows, and increased connectivity between catchments, streams, and groundwater in subarctic riparian zones have prompted predictions of altered riverine disturbance regimes, increased channelization, and a decline in the extent of active floodplains. However, few observational data exist concerning the spatiotemporal dynamics of subarctic floodplain vegetation, which can serve as a bioindicator to corroborate such predictions. We analyzed the distribution and extent of riparian ecotypes across a network of streams in 12 Interior Alaska watersheds using high‐resolution image pairs from circa 1981–2010. All stream reaches encompassed pronounced elevational gradients and included elevational forest–tundra ecotones. We classified riparian ecotypes using an image‐based point‐intercept sampling approach, calculated the probability of ecotype transitions, and evaluated relationships between ecotype transitions and environmental covariates. Our results reveal widespread increases in the stature, density, and extent of riparian vegetation spanning gradients of elevation, floodplain morphology, and climate. Ecotype transitions occurred at >20% of sample points, and there was a strong imbalance toward forward successional transitions (16.5%) versus backward transitions (4.0%). That is, we observed a strong tendency toward increasing cover, stature, and density of vegetation communities across our extensive sampling domain across our approximately 30‐year sample period. This relatively rapid riparian “greening” signal tended to be most pronounced in our glaciated watersheds. Although the streams we studied displayed high local variability in ecotype transitions, our results support hypotheses of increasing channelization and reduced extent of unvegetated surfaces on subarctic floodplains. They also likely reflect a trend toward more rapid and extensive plant recruitment and growth due to processes associated with conspicuous warming in northern ecosystems, consistent with greening documented in other subarctic landscape segments along gradients of elevation and latitude.

Fire Dynamics in an Emerging Deforestation Frontier in Southwestern Amazonia, Brazil

Land management and deforestation in tropical regions cause wildfires and forest degradation, leading to a loss of ecosystem services and global climate regulation. The objective of the study was to provide a comprehensive assessment of the spatial extent and patterns of burned areas in a new deforestation frontier in the Amazonas state. The methodology applied cross-referenced burned area data from 2003 to 2019 with climate, land cover, private properties and Protected Areas information and performed a series of statistical tests. The influence of the Multivariate ENSO Index (MEI) contributed to a decreasing rainfall anomalies trend and increasing temperature anomalies trend. This process intensified the dry season and increased the extent of annual natural vegetation affected by fires, reaching a peak of 681 km2 in 2019. The results showed that the increased deforestation trend occurred mostly in public lands, mainly after the new forest code, leading to an increase in fires from 66 to 84% in 2019. The methods developed here could identify fire extent, trends, and relationship with land cover change and climate, thus pointing to priority areas for preservation. The conclusion presented that policy decisions affecting the Amazon Forest must include estimates of fire risk and impact under current and projected future climates.

Perspectiva paleobotánica y geológica de la biodiversidad en México

El origen de la vegetación actual de México y su diversidad tiene larga historia. Posiblemente es la extensión de esta historia el punto en que discrepan las propuestas, una planteando que inicia en el Cretácico (ca. 132 ma) y otras haciendo énfasis en procesos restringidos al Plio-Pleistoceno (5.3 ma), sobre todo si se refieren al origen de la vegetación actual. El aumento del conocimiento sobre la evolución geológica de México, y del constante cambio en su fisiografía, así como del estudio de las angiospermas fósiles de la región, genera un concepto más claro de cómo y cuándo las formas de vida fueron llegando y asociándose. Se presenta una hipótesis en la que se combinan procesos geológicos y cambios fisiográficos, con la presencia de plantas y vegetación en las partes emergidas que se van desarrollando. Se propone que la biodiversidad actual efectivamente inicia hace ca. 132 millones de años, aunque linajes que hoy viven en México se pueden reconocer desde este tiempo, es complicado ubicarlos en familias, pues posiblemente representen miembros del grupo troncal. En el Paleógeno (65-32 ma) las familias, y aun géneros, que continúan viviendo en el país son más fácilmente reconocidos, pero grupos extintos o que hoy crecen en otras regiones siguen siendo comunes. Es en el Neógeno (32-1.8 ma) que desde un punto de vista de la morfológico/anatómico las plantas fósiles se parecen más a las que viven de forma natural actualmente en el país, pero muestran diferencias que en general permiten proponer nuevas especies. Si las plantas fósiles y actuales de México se relacionan morfo/anatómicamente más solo en tiempos relativamente recientes, es de esperar que con los tipos de vegetación suceda algo similar. El registro fósil sugiere que a partir de comunidades que se desarrollaron bajo condiciones cálido-húmedas en el Cretácico, divergieron tipos de vegetación con capacidades diferentes ante el estrés hídrico, y comunidades que se favorecieron de condiciones templadas a frías. Esto sucede aparentemente en dos momentos distintos en dos regiones diferentes; durante el Paleógeno se afecta al norte y en al Neógeno al centro y sur del país. Trabajo geológico y paleobotánico conjunto y comparativo permitirá refinar esta propuesta que sugiere que los cambios que activan o restringen respuestas biológicas forman parte de otros componentes del Sistema Tierra.

Satellite and sUAS Multispectral Remote Sensing Analysis of Vegetation Response to Beaver Mimicry Restoration on Blacktail Creek, Southwest Montana

Beaver dam analogs (BDAs) are being installed on streams where restoration goals include reconnecting the stream to its floodplain, increasing water storage in the stream corridor, and improving the extent and vigor of riparian vegetation. This study evaluated the effects on vegetation vigor of a BDA treatment on Blacktail Creek in southwest Montana, USA, using data from Sentinel-2 satellites and a small unmanned aerial system (sUAS; a.k.a. drone). The goal of this research was to determine if BDA installation increased the health of riparian vegetation. Sentinel-2 remote sensing data from 2016 to 2021 were used to compare the pre- and post-treatment periods, and to evaluate effects in the treated area relative to control areas. Enhanced Vegetation Index (EVI) values were calculated to quantify vegetation response from the addition of BDAs. These data suggest that installing BDAs at this site has not led to an apparent increase in late-summer vegetation vigor relative to the controls. One potential explanation for these results is that the vegetation was not water limited prior to treatment in this study reach. This is an important consideration for water resource managers prior to installation of BDAs if the main restoration goal is the improvement of riparian vegetation health. Two high spatial resolution sUAS multispectral datasets were collected to evaluate the bias introduced by using the relatively course resolution (10 m) satellite imagery to assess these changes. High-resolution sUAS data allow fine-scale differences in vegetation and inundated area to be distinguished; however, historical sUAS datasets are rarely available. Satellite-based remote sensing has much lower resolution; however, Sentinel-2 satellite data have been available for the entire earth since 2016. This study demonstrates that the combination of sUAS and satellite based remote sensing data provides a method to compare high-resolution datasets for spatial analysis while gaining insight into relatively low-resolution historical data for temporal analysis.

Comparison between Sentinel-2 and WorldView-3 sensors in mapping wetland vegetation communities of the Grassland Biome of South Africa, for monitoring under climate change

Monitoring changes in the areal extent and geographic distribution of wetland vegetation has become more critical considering the impact of anthropogenic and climate changes. We compared the capabilities of the optical space-borne sensors Sentinel-2 and WorldView-3 (WV3) to distinguish between wetland and terrestrial vegetation for improved reporting to the Sustainable Development Goal (SDG) sub-indicator 6.6.1a, and also map different wetland vegetation communities for two catchments in the Grassland Biome of South Africa. Ground truthing of vegetation communities was conducted between 2016 and 2018. A Random Forest classification algorithm was used with a 100-fold cross-validation to assess mean accuracies using all combinations of bands, a digital elevation model generated from fine-scale contours, spectral vegetation indices (VIs) and above-ground biomass (AGB). Five and eight wetland vegetation classes were mapped for Hogsback and Tevredenpan, respectively, of a total of 13 classes for each of the sites. Wetland and terrestrial vegetation were found to be highly separable, with overall accuracies (OAs) attaining 91–99% and individual user's accuracies 88–99% for both sensors and study areas. Even though the wetland vegetation communities consisted of a mosaic of smaller communities, monodominant species and plant functional type classes, they were found to be highly separable across sensors and study areas. The highest average OA of 83% for Hogsback's wetland vegetation communities was achieved using WV3 bands with elevation, AGB and the VIs, while the Sentinel-2 bands, elevation, AGB and VIs attained an average OA of 78%. For Tevredenpan, the use of the Sentinel-2 bands and elevation achieved the highest mean OA of 79% for the classification of wetland vegetation communities, while the WV3 (in this case the short-wave infrared bands were not available owing to shortage of funding) maximized at 74%. The inclusion of elevation data and spectral indices in the classification scenarios of wetland vegetation communities increased the OA by 4–17%. Omitting the red-edge and shortwave infrared bands for classification of vegetation classes resulted in a varied response across sensors and study areas, but decreased the OA by 4.8–7.3% when using the Sentinel-2 sensors. These results show promise for improved reporting and monitoring of the extent and types of palustrine wetlands in the Grassland Biome of South Africa using freely-available Sentinel-2 data.

Road impacts to sheetflow-dependent ecosystems in the Sonoran Desert

Roads affect ecological functioning at local to landscape scales, but little is known about the indirect effects on hydrology and vegetation outside road corridors. These impacts are of particular concern in arid landscapes such as the southwestern US, where road networks have rapidly expanded in recent decades. This study quantified impacts to vegetation where roads eliminated downslope sheetflow runon and identified how road and landscape characteristics affect the probability of sheetflow disruptions at Organ Pipe Cactus National Monument, in the Sonoran Desert of southern Arizona, USA.The abundance of perennial grasses, drought-deciduous subshrubs, and trees were significantly reduced in downslope plant communities where entrenched graded roads and above-grade paved roads diverted or impounded sheetflow. The remaining vegetation was dominated by annual herbaceous plants and the drought-resistant evergreen shrub creosotebush (Larrea tridentata [de Candolle] Coville), resulting in lower species and functional group richness. Sheetflow runon reductions also significantly decreased the growth, vigor, and survival of woody plants, particularly for the winter-deciduous tree velvet mesquite (Prosopis velutina Wooten).Hydrologic alterations affected the density and extent of nearby vegetation at 25% of 484 locations where roadways intersected sheetflow paths. Primitive roads such as off-highway vehicle routes produced the smallest topographic changes and were the least likely to disrupt runon, while graded roads had a 48% cumulative probability of ecohydrological impacts due to their tendency to become entrenched below ground. Paved roads were most likely to alter hydrologic connectivity due to embankments and roadside ditches and berms. Geologic substrate and soil type affected the probability of sheetflow impacts, which were most frequent on Quaternary alluvium and young soils lacking restrictive horizons. These results were used to map landscape sensitivity to sheetflow path disruption by roadways throughout Organ Pipe Cactus National Monument and to provide recommendations for sustainable management of existing and future roads.

Effects of orbital forcing, greenhouse gases and ice sheets on Saharan greening in past and future multi-millennia

Abstract. Climate archives reveal alternating arid and humid conditions in North Africa during the last several million years. Most likely the dry phases resembled current hyper-arid landscapes, whereas the wet phases known as African humid periods (AHPs) sustained much more surface water and greater vegetated areas that “greened” large parts of the Sahara region. Previous analyses of sediment cores from the Mediterranean Sea showed the last five AHPs differed in strength, duration and rate of change. To understand the causes of such differences we perform transient simulations of the past 190 000 years with the Earth system model of intermediate complexity CLIMBER-2. We analyse the amplitude and rate of change of the modelled AHP responses to changes in orbital parameters, greenhouse gases (GHGs) and ice sheets. In agreement with estimates from Mediterranean Sea sapropels, we find the model predicts a threshold in orbital forcing for Sahara greening and occurrence of AHPs. Maximum rates of change in simulated vegetation extent at AHP onset and termination correlate strongly with the rate of change of the orbital forcing. As suggested by available data for the Holocene AHP, the onset of modelled AHPs usually happens faster than termination. A factor separation analysis confirms the dominant role of the orbital forcing in driving the amplitude of precipitation and vegetation extent for past AHPs. Forcing due to changes in GHGs and ice sheets is only of secondary importance, with a small contribution from synergies with the orbital forcing. Via the factor separation we detect that the threshold in orbital forcing for AHP onset varies with GHG levels. To explore the implication of our finding from the palaeoclimate simulations for the AHPs that might occur in a greenhouse-gas-induced warmer climate, we extend the palaeoclimate simulations into the future. For the next 100 000 years the variations in orbital forcing will be smaller than during the last 100 millennia, and the insolation threshold for the onset of late Quaternary AHPs will not be crossed. However, with higher GHG concentrations the predicted threshold drops considerably. Thereby, the occurrence of AHPs in upcoming millennia appears to crucially depend on future concentrations of GHGs.

Interrelationships between fire, habitat, and mammals in a fragmented heathy woodland

Altered fire regimes threaten biodiversity, but there is limited understanding of the mechanisms driving population declines. Relationships between mammal occurrence and time since fire can be unclear because mammals respond directly to changes in habitat structure rather than time since fire per se, and patterns of regeneration can be highly variable. Previous studies have examined how mammals respond to time since fire and habitat structure separately, but rarely considered the three factors together. Furthermore, fires may interact with other threats such as habitat loss and fragmentation, also rarely incorporated into fire studies but known to influence mammal communities. Understanding each of these mechanisms and how they interact is critical for using fire effectively in conservation.We simultaneously related ground-dwelling mammal species activity to habitat structure, habitat structure to post-fire vegetation growth stage, and species activity to growth stage and landscape structure (extent of heathy woodland vegetation) using structural equation models (SEMs). This allowed us to find direct effects of growth stage on mammals, indirect effects mediated by habitat structure, and additional effects of landscape structure.Understorey cover, litter depth, and coarse woody debris responded to growth stage and were important contributors in all SEMs. Four of seven mammal species responded to at least one habitat structure variable. None of the mammal species were related directly to growth stage, but mammals were indirectly related to growth stage through the mediating influence of habitat structure. For example, western grey kangaroos were linked to recently burnt sites, but only through their negative association with litter depth. Extent of heathy woodland vegetation was also an important driver of mammal activity and was related to all but one species; two species showed a positive relationship, and four negative.Important relationships between fire and ground-dwelling mammals may be overlooked unless changes in important habitat resources are also considered. Fire management planning for fauna conservation should incorporate habitat responses as mammal responses to the fire regime may be mediated by fire-driven changes in resources. Knowing how time since fire affects important habitat structures can improve the effectiveness of using fire to manipulate these to support mammal species. Our results will help land managers understand direct and indirect effects of fire in a landscape where multiple drivers threaten biodiversity, and guide the use of prescribed fire to promote aspects of habitat structure that benefit mammals.

Revegetation of an area impacted by iron ore tailings: evaluating fertilization alternatives in native pioneer and secondary trees.

The iron ore tailings released into theRio Docebasin after the Fundão dam collapse (Brazil), suppressed a large extent of local vegetation. The use of native species and appropriate fertilization techniques, with less economic and environmental impact, must be considered in the process for the restoration of affected areas by the tailings. For this purpose, six native tree species, pioneer (Anadenanthera colubrina,Bixa orellana,andPeltophorum dubium) and secondary (Cedrela fissilis,Handroanthus impetiginosus,andHandroanthus serratifolius), were selected. We used different conditions of fertilization: (1) inorganic fertilization, (2) inoculation with arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria, (3) combined treatment (fertilizer + inoculum), to evaluate leaf nutrient concentrations, photosynthetic capacity [chlorophyll index, maximum quantum efficiency of photosystem II (Fv/Fm) and gas exchange variables], and oxidative metabolism (H2O2, MDA, and antioxidant enzymes). Inoculation resulted in higher concentrations of foliar nitrogen, especially in pioneer species. In all treatments, the secondary species exhibited iron values considered phytotoxic, but showed reduced photosynthetic capacity only when inoculated. The highest concentrations of MDA were observed in inoculated plants of both successional groups. The antioxidant system proved to be effective in preventing oxidative damage for most of the species. These results showed that the use of inoculum can be considered an ecological alternative to inorganic additives in the area affected by iron ore tailings. Despite presenting different photosynthetic and antioxidant strategies, the evaluated species demonstrated potential for use in tailings revegetation projects.

Using Ocean Accounting towards an integrated assessment of ecosystem services and benefits within a coastal lake

Coasts lie at the interface between terrestrial and marine environments, where complex interrelationships and feedbacks between environmental, social and economic factors provide a challenge for decision-making. The knowledge and data needed to link and measure these multiple domains are often highly fragmented and incoherent. Ocean Accounting provides a means to organise relevant ocean data into a common framework, grounded in existing international statistical standards for national and environmental-economic accounting. Here, we test Ocean Accounting within Lake Illawarra, New South Wales (Australia), compiling accounts for the years between 2010 and 2020, inclusive, to measure the extent of coastal vegetation (mangrove, tidal marsh and seagrass) and associated ecosystem services flows (climate change mitigation, eutrophication mitigation) in physical and monetary terms and associated production and employment within sectors of the ocean economy. The accounts show an increase in mangroves by 2 ha and a decrease in seagrass of 80 ha. A net increase was observed in the amount of carbon, nitrogen and phosphorus sequestered across coastal vegetation, due to the expansion of mangroves. Alongside changes in ecosystem extent, a 2-fold increase in full-time ocean-related employment was observed. Fisheries catch also showed significant variation over the 10-year period, where dependencies were observed between commercial species with seagrass and tidal marsh. The relationships and measures derived from accounts provide a cohesive and integrated understanding to provide information for the management and standardised ecosystem service assessments.

Shifts in Salt Marsh Vegetation Landcover after Debris Flow Deposition

On 9 January 2018, Carpinteria Salt Marsh Reserve received a large quantity of sediment following debris flows in Montecito, California. Because disturbances potentially impact the ecosystem services and functions that wetlands provide, an understanding of how the ecosystem responded to the debris flows is important for the management of salt marsh systems. However, a lack of field data before and after this disturbance makes this task impossible to complete by field methods alone. To address this gap, we used Sentinel-2 satellite imagery to calculate landcover fractions and spectral indices to produce maps of landcover before, during, and after the debris flow using a random forest classifier. Change detection showed that vegetation extent in November 2020 approached pre-debris flow conditions. While total vegetated area experienced little net change (0.15% decrease), there was a measurable change in the areal extent of vegetation type, with high marsh vegetation transitioning to mid marsh vegetation in regions that initially showed an increase in bare soil cover. These results are uniquely quantifiable using remote sensing techniques and show that disturbance due to debris flows may affect ecosystem function via plant community change. These impacts will need to be taken into consideration when managing wetlands prone to depositional events.

Modern pollen–vegetation relationships along an altitudinal transect in the Western Higher Himalaya, India: Palaeoclimatic and anthropogenic implications

Palynology is one of the most reliable tools for the reconstruction of past vegetation and climate and modern pollen analogues are important for the calibration of fossil pollen assemblages. The present study analyses the pollen–vegetation relationships along a steep altitudinal gradient (2700–3680 m), in the western Higher Himalayan region. On the basis of altitude, three vegetation zones were demarcated: Zone I (2700–3100 m) is composed of mixed-temperate forest vegetation, dominated by Quercus semecarpifolia and Rhododendron arboreum; Zone II (3100–3250 m) is marked by sub-alpine forest vegetation, characterised by R. campanulatum and R. barbatum, along with Abies spectabilis and Q. semecarpifolia; Zone III (3250–3680 m) is above the tree-line (3250 m) and represented by alpine-scrub and meadows. Thirty-five surface soil samples (twenty, seven and eight from each zone, respectively) were analysed along the altitudinal transect to decode the representation of the extant vegetation in the pollen-rain. The pollen–vegetation relationship is non-linear due to the over-representation of extra-local Pinus pollen in each zone. Nonetheless, the modern pollen assemblages show a general correlation with the local broad-leaved taxa and the herbaceous elements; with the exception of Rhododendron pollen, which is under-represented. Among the non-pollen palynomorphs (NPPs), the presence of coprophilous fungal spores is compatible with the grazing activities in the area. Multivariate statistical analyses performed on the surface pollen data indicate that the dataset can efficiently distinguish the different vegetation zones across the altitudinal gradient. This work provides the modern analogues for pollen-based palaeoclimatic reconstructions for the Western-Higher Himalayan region, and would also help to decipher the inception and intensification of anthropogenic activities in the region.

Concurrent assessment of functional types in extant vegetation and soil seed banks informs environmental constraints and mechanisms of plant community turnover in temperate forests of south-eastern Australia

Our understanding of how environmental heterogeneity shapes plant community dynamics is largely based on above-ground diversity despite the importance of seed banks as reservoirs of genetic and taxonomic diversity that buffer plant populations and influence vegetation following disturbance. Using a plant functional trait approach, this study examined the importance of fire-related germination cues and environmental determinants of plant community turnover in wet forests of south-eastern Australia – forests of both high conservation value and the focus of current timber harvesting. We surveyed extant vegetation, soil seed banks, forest structure and edaphic properties across 62 sites burnt in 1939 and not subsequently affected by wildfire or logging. A total of 46 families, and 99 species were identified in extant vegetation with 43 and 126 respectively in the soil seed bank, with only 32% of species co-occurring in both species’ pools. Despite historically long fire return intervals, the soil seed bank demonstrated a clear positive response to fire-related germination cues (heat in combination with smoke) that were concentrated in hard-seeded species dispersed by ants. Seeds from early successional species showed no response to fire cues, while species typical of the wetter margins of these forests were killed by high heat. The soil seed bank was dominated by species associated with early successional stages, consistent with the initial floristics model of succession. Woody species were largely restricted to extant vegetation and replacement is most likely to occur from future seed rain. Spatially structured environmental heterogeneity shaped plant turnover with the relative strength of environmental controls differing among functional types and pools of diversity. Differential response of the combined species pool relative to extant vegetation demonstrates that the soil seed bank provides a storage effect. Forest management practices that generate patchy and heterogenous environments, including the intensity of regeneration burns and density of overstorey species, will benefit biodiversity conservation through overstorey structural controls on resource availability and diversity of understorey vegetation, that is transferred to soil seed banks via tight abiotic controls and seed inputs.

Extent, accuracy and repeatability of bare sand and vegetation cover in dunes mapped from aerial imagery is highly variable

Vegetation cover on coastal sand dunes has been increasing worldwide since at least the 1940s. Analysis of aerial and satellite imagery has been the principal source used to measure this change, however no studies have systematically evaluated the accuracy of remotely sensed estimates. Using established land cover classification methods and in-situ field measurements, we show that both the extent and accuracy of remotely sensed areas of bare sand and vegetation in dunes varies with image resolution and classification method. We found that supervised methods of classification (semi-automatic), whilst mapping a greater extent of bare sand and being more accurate than manual digitisation, had poor repeatability, exhibiting a relatively large range of bare sand and vegetation extent between classifications replicated under the same conditions. In contrast, areas of bare sand and vegetation classified by manual digitisation had high repeatability but a relatively low percentage of observed agreement with data collected in the field. For all classification methods, observed agreement with field data generally increased with image resolution. Our results demonstrate that users of land classification data in dunes should be cautious when interpreting trends of bare sand and vegetation cover due to substantial repeatability error in supervised classification methods, and relatively poor observed agreement with field data of manual classification. We recommend that analysis of bare sand and vegetation cover in dunes should be based on multiple replicates using supervised classification, employing the highest resolution imagery available and that all results presented should also include the range measured by multiple replicates.

Large contribution of woody plant expansion to recent vegetative greening of the Northern Great Plains

AbstractAimExtensive portions of high‐latitude grasslands worldwide have recently experienced increased vegetative productivity (i.e., greening) and have undergone a rapid transition towards woody plant dominance via the process of woody plant expansion (WPE). This raises the underlying question: To what degree are WPE and greening spatiotemporally linked? Given that these vegetative changes are predicted to continue, we seek to understand how recent changes in vegetation extent and productivity have interacted under recent climate change and anthropogenic disturbance to provide insights surrounding the future trajectory of temperate grasslands broadly.LocationNorthern Great Plains (NGP), North America.TaxonWoody plants.MethodsGreening was measured as the significant increase in three metrics between 2000 and 2019: leaf area index (LAI), annual maximum normalized difference vegetative index (NDVI) and annual mean NDVI. WPE was measured as the significant proportional increase in percent tree cover change between 2000 and 2019 in grasslands. We then examined these variables across a host of 26 potential driving variables.ResultsWe show that average proportional greening increased by 0.2–1.3% year−1 (depending on metric), and proportional WPE increased by 6.9% year−1 since 2000 across the NGP. Both changes are largely driven by the absence of wildfire and changing climate. Furthermore, WPE was spatially coherent and positively associated with a large component of recent greening, as revealed by their coupling across 34.1%–40.6% of grassland area and as evidenced by the 9.7%–19.7% of the variability in greening explained by WPE.Main conclusionsWPE and greening are spatiotemporally coupled across large portions of the NGP. Under continued climate change and wildfire suppression, WPE and greening are likely to continue across large swathes of grasslands globally. Furthermore, our results show that using a single greening metric may be insufficient to capture the large‐scale vegetative changes such as the expansion of woody vegetation.

COMPARISON OF VEGETATION ANOMALIES TO EL NIÑO-SOUTHERN OSCILLATION IN CHINA AND AUSTRALIA

Abstract. The El Niño-Southern Oscillation (ENSO), as one of the main factors driving extreme climate events, exerts a major influence on interannual climate variability around the world. However, ENSO effects on vegetation, especially regarding the extent, intensity, direction, are not well understood. Here, we characterize and compare the variability in vegetation response to ENSO across China and Australia and explore their underlying mechanisms. Results show that the spatial extent of ENSO-sensitive vegetation differed between China and Australia and across land cover types. For both China and Australia, the intensity and direction of vegetation anomalies were closely related to the type of ENSO events. In particular, vegetation anomalies to the Central-Pacific (CP) type ENSO events were stronger than that to the Eastern-Pacific (EP) type events of the same intensity and generally responded in an opposite way, resulting from different controls of CP-type and EP-type ENSO on precipitation and temperature. Our findings highlight the diverse response of vegetation triggered by different types of ENSO in China and Australia, which can improve our understanding of ENSO impacts on ecosystems in the northern and southern hemispheres.

How long do seeds float? The potential role of hydrochory in passive revegetation management

AbstractDespite research into the dynamics of seed transport in fluvial systems, few consider how far seeds will travel, and how far from local or upstream seed sources passive regeneration can occur. We experimentally test the seed floating time of 60 plant species (50 native and 10 exotic) commonly found in riparian corridors of southeastern Australia. Around 50% of species had seeds that floated for 2 days or less, and for most species' (90%) all seeds had sunk within one week. Seeds of native species tended to sink more quickly than exotic, with 64% of native species' seeds floating for less than 2 days. In contrast, most exotic species (80%) floated for longer than 2 days, and 40% had seeds still floating after one week. This suggests that exotic species are good floaters and likely to travel long distances, making them excellent hydrochores. Finally, we applied the findings to a real case study, Wollombi Brook, NSW, Australia. We combined the findings from the seed floating experiment with low flow hydrology calculations to map the potential travel distance of seeds from known extant vegetation sources. We show that maximum seed travel distance per day could be up to 21 km. Thus, species that float for a week could potentially travel almost 150 km downstream before sinking or being deposited. We discuss how local versus upstream seed sources, and hydrochory, could be utilised in passive revegetation and weed management of riparian corridors.

Two Sides of the Same Desert: Floristic Connectivity and Isolation Along the Hyperarid Coast and Precordillera in Peru and Chile

In this study we aim at refining our understanding of the floristic connectivity of the loma- and precordillera floras of southern Peru and northern Chile and the parameters determining vegetation cover in this region. We used multivariate analyses to test for floristic- and environmental similarity across 53 precordillera and loma locations in Peru and Chile. We propose the use of predictive modeling in estimating the extent of desert vegetation as a complementary method to remote sensing. We created habitat suitability models for the vegetation on the coast and in the precordillera based on a combination of latent bioclimatic variables and additional environmental predictors using Maxent. We found Peruvian and Chilean lomas to be strongly floristically differentiated, as are the Chilean precordillera and lomas. Conversely, there is clear connectivity between both the Peruvian loma- and precordillera floras on the one hand and the Peruvian and Chilean precordillera floras on the other. Divergent environmental conditions were retrieved as separating the precordillera and lomas, while environmental conditions are not differentiated between Peruvian and Chilean lomas. Peruvian and Chilean precordilleras show a gradual change in environmental conditions. Habitat suitability models of vegetation cover retrieve a gap for the loma vegetation along the coast between Peru and Chile, while a continuous belt of suitable habitats is retrieved along the Andean precordillera. Unsuitable habitat for loma vegetation north and south of the Chilean and Peruvian border likely represents an ecogeographic barrier responsible for the floristic divergence of Chilean and Peruvian lomas. Conversely, environmental parameters change continuously along the precordilleras, explaining the moderate differentiation of the corresponding floras. Our results underscore the idea of the desert core acting as an ecogeographic barrier separating the coast from the precordillera in Chile, while it has a more limited isolating function in Peru. We also find extensive potentially suitable habitats for both loma- and precordillera vegetation so far undetected by methods of remote sensing.