Variation In Vegetation Composition Research Articles

Variation in Vegetation Composition and Structure across Mudflat Areas in the Yellow River Delta, China

Variations in vegetation composition and structure are significant signals of the succession of mudflat ecosystems and have important indicative roles in mudflat ecosystem degradation. Due to poor accessibility of vast even mudflat areas, variation in vegetation composition and structure across mudflat areas remains unclear in the Yellow River Delta (YRD), China. We provided an UAV multispectral orthomosaic with 10 cm ground sample distance to classify and compare the vegetation composition and structure across mudflat areas in the YRD. The vegetation classification overall accuracy achieved 95.0%. We found that although a significant difference (p < 0.05) was checked out in terms of the Shannon–Wiener diversity index (from 1.33 to 0.92) and evenness index (from 0.96 to 0.66) among the eight subareas from land to sea, all four dominant vegetation communities (S. salsa, L. bicolor, T. chinensis, and P. australis) were discovered at all eight subareas. Our findings support the idea that the regional environment and local microtopography are the predominant forces for variation in vegetation composition and structure across mudflat areas. From the perspective of vegetation restoration and conservation, changing the local microtopography will be an interesting way to enhance the vegetation diversity of the mudflat ecosystems in the YRD.

Plant species richness in intensively managed temperate wet grasslands: current state and the importance of edge habitats

This study investigates within-site variation in the diversity and composition of aboveground vegetation and seed bank in intensively managed wet grasslands of north-western Germany, comparing field edges, field margins and field interiors. We tested the hypothesis that unfertilized buffer strips at field edges function as refugia of characteristic species even in grasslands that are managed intensively for silage production. In 55 grassland sites on each marsh and moor soils, respectively, we conducted vegetation surveys, seed bank analyses and soil chemical measurements in field edge, margin and interior plots, and searched for the factors causing within-site variation in vegetation composition. The total species pool was small at the 110 sites, i.e. 148 species in the aboveground vegetation and 107 species in the seed bank, demonstrating severe impoverishment. The α-diversity decreased from 23 species (median) per 200 m2 at the edge to 15 species in the interior, with 38 species occurring only at field edges. The number of species with conservation value was very low in aboveground vegetation and seed bank and was only slightly higher at the edge than in the interior. Soil P availability was ca. 30% lower at the unfertilized edges than in the interior. We conclude that unfertilized buffer strips at grassland edges may help reducing nutrient leaching from high-input grassland systems, but they have mostly lost their refugial function for phytodiversity after decades of intensive management. Restoration efforts with seed or green hay transfer from richer source habitats are needed to promote biodiversity in field-edge buffer strips.

Bird-Ecosystem Relationship in an Urbanizing Habitat: Implications for Conservation and Ecosystem Stability

This study explores the association between birds and their urbanizing ecosystems. The study area was divided into 4 quadrats of area 2700 m2 each. Bird species as well as number of individuals of each species were counted using the Line Transect Method. Statistical analysis of the data was performed using Windows Microsoft Excel and SPSS v.28. The investigation revealed a significant correlation (P < 0.05) between bird species and the four distinct sites within the study area. These sites exhibit variations in vegetation composition and include notable features like water bodies. The findings underscore the heavy reliance of certain bird species in this region on specific types of vegetation for their survival and well-being. Removing even a single plant species could potentially disrupt the entire ecosystem. The study documented the presence of 42 bird species across 30 families, including one vulnerable species. Both local and seasonal migratory birds were observed during the research. Although the study identified a decline in bird diversity within the study area, it remains species-rich, displaying moderate to high diversity (Simpson’s Dominance Index: 0.0319; Margalef’s Richness Index: 4.0754). This research emphasizes the critical importance of conserving bird species and their associated vegetation to maintain ecosystem integrity. Strategic sustainable development practices along with habitat enrichment for birds is recommended to maintain the valuable avifaunal diversity of the study area. By highlighting the intricate relationship between birds and their habitat, the study highlights the significance of conservation efforts in safeguarding the overall health of the ecosystem.

COMPARATIVE ANALYSES OF SECONDARY ECOLOGICAL SUCCESSION FOLLOWING WILDFIRES IN THREE DISTINCT FOREST TYPES. A STUDY CASE FROM MOGUER, SPAIN

Wildfires have become increasingly prevalent and destructive in forest ecosystems worldwide, necessitating a comprehensive understanding of post-fire recovery dynamics for effective conservation and management. Remote sensing technology, coupled with vegetation indices such as Normalized Burn Ratio (NBR), Normalized Difference Vegetation Index (NDVI), Green Red Vegetation Index (GRVI), and Red Vegetation Index (RVI), offers a powerful means to investigate these processes. In this study, we utilize remote sensing techniques to conduct a comparative analysis of secondary ecological succession following wildfires in three distinct forest types (Coniferous, Sclerophyll and Mixed) of a forest affected by fire near Moguer, Spain. Through the acquisition and analysis of multispectral satellite imagery, we monitored changes in vegetation health and recovery across the region of interest. The NBR index allowed us to assess the severity and extent of wildfire damage, while NDVI quantified vegetation greenness and regrowth. GRVI and RVI provided insights into subtle variations in vegetation composition and health. We identified distinct temporal and spatial patterns in post-fire recovery among the different forest types by applying these indices for the period between 2017 and 2021. Our findings underscore the significance of understanding the diverse responses of these ecosystems to wildfires. While common recovery patterns emerged, such as an initial decrease in NDVI followed by regeneration, variations were observed in the timing and magnitude of recovery. These distinctions are attributed to differences in species composition, fire adaptations, and ecological processes specific to each forest type. In conclusion, the utilization of NBR, NDVI, GRVI, and RVI indices allows for a more nuanced evaluation of post-fire recovery dynamics.

Using the Alternative Stable States Framework to understand the persistence of secondary shrubland within a Mexican oak forest with livestock and agricultural legacies

Many forests exist in human-modified mosaic landscapes subject to logging, agriculture, and livestock grazing. These disturbances can reduce ecosystem resilience and ultimately result in crossing thresholds, leading to the transition of the ecosystem into new stable states with different plant communities. The interaction between these disturbances and forest succession is still poorly understood, despite the growing need to manage these human-modified landscapes for biodiversity and productivity. We studied abrupt changes in vegetation composition in a Central Mexican oak forest and explored how these changes could indicate the coexistence of various alternative stable states caused by agricultural and livestock legacies. We established 36 strip transects covering 9000 m2 in patches with various land use legacies where we sampled vegetation, soil characteristics, and human disturbance. We assessed future and past tendencies in vegetation spatial patterns by evaluating seedling composition and analyzed time series of NDVI signals recorded by LANDSAT images (1972–2019). We utilized NMDS, PERMANOVA, and ANOVA analyses to assess if stable states can be distinguished based on historical and current variations in vegetation composition and structure in patches with different management legacies. We then assess potential factors that may contribute to differences in plant community composition by fitting edaphic, topographic, and anthropogenic disturbance variables to the ordination analyses.We identified three distinct plant communities: oak forest (dominated by late-successional Oak species), secondary shrubland (dominated by Vachellia-Dodonaea association), and a transitional forest-shrub community (a mixture of the first two communities). Time-series analyses and seedling composition provide evidence of long-term community segregation. Variation partition analysis demonstrated that anthropogenic disturbance (particularly livestock browsing), had a greater impact on species composition differentiation than environmental variables.A state-and-transition model is proposed, where cattle browsing and agricultural legacies trigger the transition from oak forests to a stable secondary shrubland community. Three potential self-reinforcing and interacting feedbacks are suggested: (i) micro-environmental filtering, (ii) plant-trait mediated assembly process, and (iii) cascading effects on tree recruitment caused by cattle browsing. The proposed state-and-transition model explains forest successional dynamics in systems with multiple anthropogenic disturbances and provides a conceptual framework for understanding and guiding successional trajectories.

Variation in sediment characteristics between canopy gap and surrounding forest in Can Gio Mangrove Biosphere Reserve, Vietnam

This study presented the difference in the sediments under a large gap formed by the Durian typhoon in 2006 and its surrounding intact forest in Can Gio Mangrove Biosphere Reserve, Vietnam. Twelve plots previously settled in the original gap and its surrounding forest were used to collect sediments in the dry and wet season in 2019 to assess the difference in sediment properties and nutritional state caused by the self-recovery of the vegetation. Sediment temperature and pH were measured in field, while the contents of total organic carbon (Corg) and total nitrogen (Ntot) were subsequently quantified in the chemical laboratory. Sediment temperature, salinity, and pH between the gap and the surrounding forest were not statistically different. The variation of Corg concentration in the gap sediments seemingly increased with depth from 1–15 cm in the dry season. The Ntot in the gap sediments showed that it was continuously consumed in the underlying sediments during both seasons. In conclusion, the variation in vegetation composition between the gap and its surrounding forest was responsible for the differences in sediment C and N concentrations.

Vegetation and soil ecology of threatened Himalayan Trillium habitats in Kashmir Himalaya

Understanding the vegetation and soil ecology of natural habitats harbouring threatened species is critical in conservation planning and restoration. The present study investigated the vegetation composition and soil physico‐chemical properties of natural habitats of Trillium govanianum – a threatened Himalayan endemic species. We laid 120 quadrats across eight randomly selected sites where the species was growing in the Kashmir Himalaya. We collected the soil samples from these sites and determined soil physico‐chemical properties using standard methods. Across all the sites, we found a total of 57 plant species with dominance of Rosaceae and Ranunculaceae. The importance value index (IVI) results revealed that Fragaria nubicola, Corydalis diphylla, Galium aparine, and Leucanthemum vulgare, were the dominant species in T. govanianum habitats. The density, abundance and IVI of three‐leaf vegetative plants was higher than one‐leaf vegetative and three‐leaf reproductive plants across all the study sites. We found that T. govanianum alone forms 23.5% positive, 0 negative, 76.4% random co‐occurrences with other associated species in its habitats. Our results reveal that the variations in vegetation composition among the sites was influenced by differences in soil properties. Principal component analysis (PCA) revealed that several soil properties such as organic carbon (OC), nitrogen, potassium, and sulphur were concentrated in five sites, namely Dara, Drung, Bangus, Gulmarg and Doodhpathri, which also showed the highest density, frequency, and abundance of T. govanianum. Overall, our study contributes quantitative information on the vegetation and soil ecology of T. govanianum‐habitats, which in turn can help in developing conservation strategies for this threatened species, and its sustainable management and habitat restoration.

Exploring the power of moth samples to reveal community patterns along shallow ecological gradients

Abstract Analysing the effects of environmental variation on species assemblages is a key topic in community ecology. However, the outcome may strongly depend on the focal species group. Moths have often been used as the target in ecological studies due to their fast response to environmental change. Yet, some moth subgroups might be more sensitive than others to reflect environmental differences, depending on their functional and physiological characteristics. We investigated which moth subsets are especially suitable to mirror responses to subtle variation in vegetation. We analysed the susceptibility of different subsets to local weather conditions and inter‐annual fluctuations. Finally, we checked for the importance of including abundance information. We analysed moth communities (392 species, 23.870 individuals) at 60 sites within two Mediterranean forest reserves and investigated relationships between community composition and environment of (1) all moths (with and without taking abundances into account), and of subsets comprising only (2) small‐sized species, (3) host‐plant specialists, (4) moss, lichen and detritus feeding species, (5) ‘microlepidoptera’, (6) ‘macro‐moths’ and (7) random subsets of 50, 100 and 200 species. Incidence data performed similarly to abundance data in matrix regression models. Host plant specialists responded especially sensitive to small‐scaled variation in vegetation composition. Macro‐moth samples in contrast were highly prone to local weather conditions and to inter‐annual abundance fluctuations. Accordingly, a focus on host‐specialists and micro‐moths is the best way to analyse relationships between shallow environmental gradients and insect communities.

Charcoal morphotypes and potential fuel types from a Mexican lake during MIS 5a and MIS 3

Charcoal particles vary in size and form, but they can preserve morphological characteristics used to infer the type of vegetation being burnt. To deduce potential fuel and fire type, we reconstructed local fire activity analyzing macrocharcoal morphologies and pollen data of the sediment core CHA08-V from Lake Chalco from the sub-stage MIS 5a to MIS 3, with CHAR data and Z-Score analysis. We identified the following fuel types: i) wood, characterized by blocky and quadrilateral morphologies with solid, foliated or striated surface textures; ii) grass, represented by rectangular-porous and rectangular-latticed morphologies; and iii) herbs, characterized by long-thin filaments and polygonal porous particles. Arboreal pollen components were associated to wood morphotypes whereas non-arboreal pollen related to herbs and grass morphotypes, indicating that variation in vegetation composition was important regulating factor determining fire types in the Basin of Mexico. This study provides the first long-term record of charcoal morphotypes for Mexico region to emphasize the importance of charcoal morphotypes analyses to complement paleoenvironmental interpretation of past fire regimes.

A slight increase in soil pH benefits soil organic carbon and nitrogen storage in a semi-arid grassland

Grassland soil organic carbon and nitrogen storage (SOC storage and SNC storage) have been regarded as indicators to evaluate impacts of global climate change on ecosystem functions due to their significant impact on atmospheric carbon (C) concentration. The variations in vegetation and soil properties in diverse vegetation patch types may change soil C and nitrogen (N) sequestration capacity. However, the quantities of SOC and SNC stored and the mechanisms behind the variation in this storage under diverse vegetation patches in grassland ecosystems are still unclear. Here we conducted a field experiment to measure the variations in vegetation composition, soil properties and SOC storage and SNC storage among five common vegetation patch types in the Eastern Eurasian steppe. Then we investigated the link between vegetation variation and the SOC and SNC storage. The results showed that (1) the combined effects of competitive ability and physiological stress drove the unimodal relationship between species diversity and soil pH. (2) Biomass production did not reach its maximum in patch types with the greatest plant diversity due to saline-alkaline stress, but the live vegetation N storage reached its maximum in these highly diverse patches due to complementary resource utilization effects. (3) Although biomass production of patches with the greatest biodiversity did not reach a maximum due to a slight increase in soil pH, the largest SOC and SNC storage values were found in the highly diverse patches. Our study implies that in natural grassland, high levels of species diversity may accelerate the decomposition rate, resulting in more recalcitrant organic C and N are released into the soil. At the same time, our observation that reductions in the area of the originally dominant patch type due to the expansion of other species during grassland degradation suggests that comprehensive measurements of SOC and SNC storage in different vegetation patches should be undertaken for accurate evaluation of the C and N sequestering capacity of grasslands. Our results can also help policy makers determine how to achieve sustainable development of grasslands based on C and N sequestration.

Environmental changes during MIS6-3 in the Basin of Mexico: A record of fire, lake productivity history and vegetation

The responses of lake productivity, vegetation, and fire events in the Basin of Mexico to orbital changes from late MIS 6 to MIS 3 (146–35 ka) have been studied based on geochemical (Ti, TIC, TOC, C/N), charcoal (CHAR) and pollen data of the sediment core CHA08 from Lake Chalco. The paleoenvironmental reconstruction identifies the MIS 6 as a wetter period with episodes of dry conditions, low forest cover and low fire activity. A sudden change from wetter to dry environments with low to high forest cover and fire activity episodes characterized the end of the MIS 6 (132–130 ka) coincident with high spring insolation. Variations in vegetation composition, with a tendency towards higher forest cover, fire-activity, runoff, and organic matter availability, are recorded during the MIS 5, MIS 4, and MIS 3. However, a reduction in the fire-activity was recorded for the cold and dry MIS 4. Spectral analysis based on the titanium concentration record of Lake Chalco suggests a precessional forcing on runoff variations. We explored the impact of the Intertropical Convergence Zone latitudinal migrations which have been related to the summer insolation at 65° N by comparing runoff data with other sedimentary records from North and Central America. Our results highlight the sensitivity of the high altitude tropical basin to climate variations.

Holocene vegetation changes according to sea-level and climate dynamics on tidal flats of the Formoso River estuary, northeastern Brazil

The aim of this work was to carry out a paleoenvironmental study of Holocene sedimentary deposits in the southern sector of Pernambuco's coast (northeastern Brazil). This work addresses an important aspect of Quaternary research that has implications for current climate debates, for instance, how does vegetation react to changing climate and rising sea levels. Thus, we provide a combined approach using sedimentological, palynological, geochemical analyses (stable isotopes i.e., δ13C, δ15N and C:N), in addition to AMS 14C dating from two surficial sediment cores i.e. T4 (up to 150 cm depth) and T5 (up to 136 cm depth) collected from the Formoso River estuarine system. Climatic oscillations show variation in precipitation and atmosphere humidity, marked by areas of expansion and/or retraction of herbaceous plain and forest vegetation. Variations in vegetation composition over the last 7168–7260 cal yr BP in the Formoso River estuary reflects the strong influence of sea-level variations, which were responsible for changes in coastal paleogeography and paleogeomorphology. Changes in vegetation composition indicate its close relationship with transgressive and regressive marine events and corresponding variation of the depositional environment like lakes to coastal lagoons, tidal channels, sandy strand-plain, and the modern estuary of the Formoso River.

Checklist and Comparison of Butterfly Species found in Zoological and Botanical Gardens, University of Nigeria, Nsukka, Enugu State, Nigeria

Butterflies are creatures of nature with great economic importance as pollinators and bio-indicators. This study provides checklist of butterfly species present in Zoological and Botanical gardens of University of Nigeria, Nsukka and was conducted for three Months. Butterflies were sampled twice a week between 7.00 -10.00am from May to July 2019; using sweep net along existing transects within the gardens. Non-invasive method was adopted, butterflies were captured, photographed and released. Photographed samples were identified to species level by cross matching with relevant keys. A total of 91 butterflies belonging to 16 species, 10 genera and 3 families were sampled. Alpha diversity test showed a significant difference (p<0.05) in terms of Relative Abundance, Diversity and Dominance of butterfly species between the two gardens. The Botanical garden had Relative Abundance of 63.73%, Dominance of 0.23 which was higher compared to Zoological garden which had 36.16% and 0.10; but these was contrary to species diversity where Zoological garden was more diverse (H1=2.48) than botanical garden (H1=1.82). The differences observed could be attributed to variations in vegetation composition.

Barred Owl Effects on Spotted Owl Resource Selection: A Meta‐Analysis

ABSTRACTWe quantified the effects of barred owls (Strix varia) on fine‐scale (~2 ha), spatially explicit selection of putative foraging habitat by 175 radio‐tagged northern spotted owls (Strix occidentalis caurina) from 1998 to 2012 in western Oregon and northern California, USA. We constructed annual nighttime discrete‐choice resource selection functions (RSFs) for northern spotted owls in 8 study areas. We compared RSFs from pooled data from 4 study areas where barred owls were absent or rare (≤14% of spotted owl territories potentially influenced by barred owls) with RSFs from 4 study areas where barred owls were abundant (≥89% of spotted owl territories potentially influenced by barred owls), and we conducted a meta‐analysis of all 8 study areas. Top‐ranked RSFs for individual study areas indicated that the relative probability a forest patch was selected by northern spotted owls for foraging was most strongly associated with basal area of large coniferous trees (≥66 cm diameter at breast height [dbh]) or quadratic mean diameter (QMD, the diameter of trees of average basal area) of all coniferous trees. The influence of such trees was non‐linear, usually quadratic, in 7 study areas, suggesting that an optimal basal area of large‐diameter trees or QMD may be associated with selection of foraging patches. The relative probability of selection of such trees decreased nonlinearly with increasing distance from nest sites in ≥4 study areas. Basal area of all or specific hardwood tree species was linearly associated with increases in the relative probability of a patch being used for foraging in 7 of 8 study areas. The relative probability of selection was also positively associated with densities of large snags (>50 cm dbh), coarse woody debris, and undergrowth shrubs in most study areas where we estimated those covariates. The relative probability that a patch was selected decreased nonlinearly with increasing distance from streams (7 study areas), increasing elevation (5 study areas), and decreasing slope (5 study areas). Barred owls exerted strong effects on habitat selection by spotted owls, which may have attempted to minimize interference competition via spatial segregation. Spotted owls occupying study areas where barred owls were abundant used foraging patches at greater distances from streams, at greater distances from nest sites, and on steeper and warmer slopes than those occupying areas with few or no barred owls. In addition, northern spotted owls in areas where barred owls were abundant exhibited reduced selection for large‐diameter trees close to nest sites but may have compensated by increasing use of large trees in home‐range locations distant from nest sites. Programs that seek to improve the link between spotted owl demographic performance or occupancy rate and habitat conditions should account for the influences of fine‐scale variation in vegetation composition and structure and physiographic conditions. Forest managers may contribute to spotted owl conservation via silvicultural prescriptions that retain coarse woody debris and large snags, promote undergrowth shrubs, and retain intermediate to high densities of large, old shade‐intolerant early‐seral trees and riparian hardwoods within and beyond core areas surrounding nest sites. © 2019 The Wildlife Society.

Forest and woodland expansion into forestry plantations informs screening for native agroforestry species, Maputaland South Africa

ABSTRACTExpansion of natural forest or woodland in forestry plantations can potentially provide insight about the behaviour of plant communities in human-modified ecosystems. Here, we investigate the expansion of native woody vegetation into abandoned areas within timber plantations, whereby management decisions (and consequently different conditions of land abandonment) had led to variation in vegetation composition and structure. These differences were assessed to identify native species suitable for agroforestry systems within forestry plantations. Elements of sub-tropical dry forest (the reference forest) had expanded into (i) clear-felled and then abandoned plantations, and (ii) unharvested abandoned plantations. Two-way indicator species analysis, Non-metric multidimensional scaling, and Indicator species analysis were used to describe compositional intergradation between natural forest and secondary vegetation, and to assess correlation with environmental variables of fire and stand structure. Areas of vegetation expansion contained 53 native woody species from 26 families, about half the number sampled in the reference forest. The understory composition of unharvested plantation sites closely resembled regrowth forest, whereas clear-felled plantations had developed a species composition resembling woodland, comprising savanna species. Substantial intergradation among compositions of woodland, plantations and regrowth forest implied that regrowth forest was a likely propagule source for native species, but that past plantation management practices acted as an environmental filter resulting in slightly different vegetation types. Useful woody species Sclerocarya birrea, Vangueria infausta, Trichilia emetica, Strychnos spinosa, Annona senegalensis, and Hyphaene coriaceae were considered ecologically suitable for testing in silvo-pasture agroforestry systems owing to their occurrence in disturbed, open-canopy, fire-exposed environments (see also the graphical abstract in the supplemental files).

Rodent community responses to vegetation and landscape changes in early successional stages of tropical dry forest

The extent to which the array of land covers dominating anthropogenic landscapes impacts on biodiversity remains today an open question of great relevance. The characteristics of the animal communities inhabiting tropical forest early successional stages can determine, to a large extent, the course of secondary succession and natural regeneration. In this study, we evaluated the response of terrestrial rodents to variations in vegetation and landscape attributes, in early stages of tropical dry forest succession, at three integration levels: (1) communities, (2) populations, and (3) individuals. Our results reveal a rodent response to the variation in vegetation and landscape attributes, which indeed was largely modulated by seasonality, and determined by the focal spatial scale considered. In general, most of the species were favored by vegetation structure simplification and increase in understory density, probably due to the increase in refuge and trophic resources. Nevertheless, one species, Lyomis pictus, was sensitive to variation in vegetation composition and negatively affected by a reduction in vegetation structural complexity, which could be explained by the high number of tree seeds included in their diet. We found a higher diversity of rodents in sites surrounded by a high coverage and connectivity of dry and riparian forest, probably because large forest patches act as sources of species and the forest connectivity favors the colonization process toward sites under regeneration. Our results showed that preserving remnants of the original vegetation and implementing management actions at different spatial scales in anthropogenic landscapes is critical for preventing: (1) an increase in generalist populations, (2) rapid faunal homogenization, (3) defaunation, and (4) the loss of specialist species; with profound implications for the ecology of forest, ecosystem services and human health.

The linkages with fires, vegetation composition and human activity in response to climate changes in the Chinese Loess Plateau during the Holocene

Holocene paleo-records of the Chinese Loess Plateau loess–soil profiles were used to reconstruct wildfire patterns and landscape evolution. We examine black carbon and charcoal influx, combined with the Magnetic susceptibility, δ13C values of soil organic matter, pollen counts and other paleo-environmental proxies to discuss interactions with biomass–climate during the Holocene. The history of fires from the charcoal and black carbon (BC, char and soot) influx at the two sites demonstrates a transition from climate-controlled low amplitude variations with peaks during the Early and Middle Holocene (11-3.1kyearsB.P.) to higher amplitude variability in fire occurrence decoupled from climate and tied to human activities during the Late Holocene (3.1-0kyearsB.P.). The difference in fire patterns was attributed to regional effective moisture and human land use over the entre Loess Plateau; meanwhile, fire activities observed during the Holocene are consistent with variations in vegetation composition inferred from δ13C values in soil organic matter, pollen counts, and paleoclimate proxies. Regional wildfires rarely occurred on the desert steppe dominated by a weedy C3 taxon (Artemisia, Compositae, and Chenopodiaceae dominated)during the late glacial period. A limited biomass would not meet fire propagation in the extreme colder and drier environment of the Loess Plateau during those periods, though. As the climate became ameliorated during the early Holocene, there was an increasing biomass and a sufficient contribution do to high fuel accumulation from C4 taxon (Gramineae). As the middle Holocene progressed toward warmer and wetter conditions, fire events were less frequent on the steppe and forest-steppe (e.g. expansion of trees C3,Quercus, Corylus) of the Loess Plateau. Subsequently, the number of local and regional fire events have largely increased with the colder and drier climate conditions (e.g. expansion of C3 weedy), which have been decoupling with intensive anthropogenic burning for farming since the past 3kyr.These data suggests that the regional fire patterns vary strongly along environmental gradients in the effective moisture and regional fuel availability as well as the spatial and temporal distributions of Neolithic burning practices over the Loess Plateau in response to the weakening East Asian monsoon during the Holocene.

The role of climate, forest fires and human population size in Holocene vegetation dynamics in Fennoscandia

AbstractQuestionsWe investigated the changing role of climate, forest fires and human population size in the broad‐scale compositional changes in Holocene vegetation dynamics before and after the onset of farming in Sweden (at 6,000 cal yr BP) and in Finland (at 4,000 cal yr BP).LocationSouthern and central Sweden, SW and SE Finland.MethodsHolocene regional plant abundances were reconstructed using the REVEALS model on selected fossil pollen records from lakes. The relative importance of climate, fires and human population size on changes in vegetation composition was assessed using variation partitioning. Past climate variable was derived from the LOVECLIM climate model. Fire variable was reconstructed from sedimentary charcoal records. Estimated trend in human population size was based on the temporal distribution of archaeological radiocarbon dates.ResultsClimate explains the highest proportion of variation in vegetation composition during the whole study period in Sweden (10,000–4,000 cal yr BP) and in Finland (10,000–1,000 cal yr BP), and during the pre‐agricultural period. In general, fires explain a relatively low proportion of variation. Human population size has significant effect on vegetation dynamics after the onset of farming and explains the highest variation in vegetation in S Sweden and SW Finland.ConclusionsMesolithic hunter‐gatherer populations did not significantly affect vegetation composition in Fennoscandia, and climate was the main driver of changes at that time. Agricultural communities, however, had greater effect on vegetation dynamics, and the role of human population size became a more important factor during the late Holocene. Our results demonstrate that climate can be considered the main driver of long‐term vegetation dynamics in Fennoscandia. However, in some regions the influence of human population size on Holocene vegetation changes exceeded that of climate and has a longevity dating to the early Neolithic.

Continental-scale quantification of post-fire vegetation greenness recovery in temperate and boreal North America

Knowledge and information of post-fire vegetation recovery are essential for our understanding of ecosystem stability and resilience in response to present and future disturbances. Although previous studies have examined the post-fire vegetation recovery at landscape and regional levels, the lack of continent-wide analysis limits our understanding of fire effect on vegetation recovery across ecoregions and climate zones. With advanced technology in satellite observations as well as large-scale database development, it is possible for us to explore the large-scale effect of concurrent and lagged responses of terrestrial ecosystems to fire disturbances. In this study, we investigated the recovery of vegetation greenness in the early post-fire period in North America by integrating two national-level fire perimeter datasets and multiple Moderate Resolution Imaging Spectroradiometer (MODIS) products. We developed a new algorithm to estimate fire effect on the Normalized Difference Vegetation Index (NDVI) by comparing fire pixels with their surrounding unburned pixels. Our results showed the fire effect on needleleaf trees was stronger than on other vegetation types, and the high-latitude ecoregions had larger NDVI reduction and longer recovery time than the mid-latitude ecoregions. We also found the variations in vegetation composition and fire severity can explain a large fraction of post-fire vegetation greenness recovery. Our satellite-based analysis showed a longer NDVI recovery time than the existing estimates, which indicates a stronger fire effect on ecosystems than previously thought. Findings in this study indicate that more sophisticated parameterization schemes of fire severity and post-fire vegetation recovery are needed for the vegetation-fire models to better simulate the terrestrial carbon cycling and climate-ecosystem feedbacks.

Quantifying the effects of land use and climate on Holocene vegetation in Europe

Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen-based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming practices and forestry in response to population growth and industrialization. This is a unique signature of anthropogenic impact within the Holocene but European vegetation remains climatically sensitive and thus may continue to respond to ongoing climate change.