Regional and Extra-local Pollen Evidence for Long-term Vegetation Change and Human Impact from the Hinterland of Hadrian’s Wall at Alston Moor, North Pennines, UK

Long-term directional vegetation changes in the wild landscape of southeastern Arizona since the advent of major Anglo-American settlement in the 1870s are identified and their relation to climate variations is examined. Particular emphasis is placed on verifying the purported changes in the distribution of major vegetation types and the link between velvet mesquite (Prosopis velutina Woot.) increases and precipitation trends since the turn of the century. While there is little doubt that climatic oscillations have resulted in short-term fluctuations in vegetation, precipitation variations do not appear to be connected to any major direc- tional vegetation change since 1870 in southeastern Arizona. In fact, no single trend is evident in regional precipitation during this period. Furthermore, there is no clear evidence for the upward displacement along a xeric-to-mesic gradient of any major vegetation type, and, except possibly for increases in woody xerophytes such as mesquite, all of the identified long-term vegetation changes appear to be of anthropogenic origin. Mesquite increases, however, are irregular, show no clear relation to precipitation variations, and are most likely the result of livestock grazing and/or fire exclusion.

ABSTRACTWetland vegetation assessment is a critical component of evaluating wetland protective policies and providing useful information for global climate change research. In this study, four types of wetland are chosen to evaluate their long-term changes and potential linkage to anthropogenic (e. g., agricultural activities) and natural influences (e. g., hydrometeorological effects). These wetland types include the Yancheng wetland (coastal wetland), the Chongming wetland (river wetland), the Hongze Lake wetland (lake wetland) and the Everglades wetland (marsh wetland) in the contrasting environments of China and USA. The vegetation coverages of these wetlands were evaluated from 2000 to 2011 by using over 2,200 Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m resolution images. Four vegetation indices (VIs) were compared to evaluate their effectiveness in assessing relative changes: the Normalized Difference Vegetation Index (NDVI), the Floating Algae Index (FAI), the Enhanced Vegetation Index (EVI), and the Visible Atmospherically Resistance Index (VARI). FAI performance was relatively insensitive in terms of both the statistical error and the aerosol effects compared with other VIs and was thus chosen to study the long-term vegetation changes. The results showed that 1) agricultural influence appeared to be relatively minimal compared with hydrometeorological effects in the Everglades wetland and in the core partitions of the Yancheng, Chongming, and Hongze Lake wetlands over the 12-year period, and 2) the entire partitions of the Yancheng, Chongming and Hongze Lake wetlands showed noticeable influences from agricultural activities in addition to natural variability. The cost-effective method that we demonstrate in this study may be extended to other wetlands near the same geographical location and to other satellite platforms.

Quantitative information about historical changes in natural ecosystems is important for guiding management interventions. However, few accurate data sources are available for documenting long-term vegetation changes. In this paper, we describe a neglected source of quantitative information on historical forest structure: forest inventory strip surveys, which were widely used in eastern Australia from 1915 to the 1940s. Strip surveys provide quantitative information on the species composition, stem density, basal area, stem form and size class distributions of dominant tree species. Such information is not available from other widespread data sources. Strip surveys usually surveyed 10% of the total forest area. In this paper, we describe the original survey methods, demonstrate how to decode data-book entries, and analyse a sample dataset from the Pilliga State Forests in northern New South Wales to illustrate the information that can be obtained from this material. Strip survey data-books are poorly archived. Many books exist for Eucalyptus–Callitris forests in northern and central NSW, and additional books may exist for many other forest types in eastern Australia. Strip surveys provide a valuable data source for studying long-term vegetation changes in forest ecosystems. We urge forest managers to search for and preserve this precious archival material.

A palaeoecological study was performed in the northern Scandinavian mountain range in Sweden. The aim was to study vegetation changes and shifts in forest limit altitudes during the last 5000 years in a tree-less archaeological site (Adamvalta) situated below the regional forest limit, and in a forested reference area with similar geological features but without archaeological evidence of human presence (Ajdevaratj). The suitability of uncritically using forest limit changes as indicators of climate change is also discussed. The study included analyses of pollen, pollen accumulation rates (PAR), macrofossils and loss-on-ignition. The results indicate vegetation changes in both areas plausibly caused by climate c. 3800 BP and c. 500 400 BP. However, at Adamvalta, settlements were established c. 1300 750 BP, close to the mountain birch ( Betula pubescens ssp. czerepanovi) forest limit. About 800 BP, the birch forest cover at Adamvalta decreased and the vegetation developed into an alpine heath, as a result of human-induced deforestation. The following ‘Little Ice Age’, in combination with human impact from the sixteenth century onwards, prevented forest recovery, and the site remains treeless. Such vegetation changes were not recorded at Adjevaratj. It is deduced that the present position of the forest limit at Adamvalta is governed by a combination of factors where previous human impact and climate have been the major driving forces determining the long-term vegetation development. Hence, a thorough knowledge of the site history is important when forest limits are used as a proxy for climate change.

During the Dark Ages, which include the Late Roman period (ad 270–450) and the Early Middle Ages (ad 450–1050), large-scale vegetation development in northwest Europe was characterised by widespread regeneration of woodlands. This regeneration phase represents a break from the extensive reduction in woodland from human activities in late Holocene vegetation history. In the Netherlands, possible causes for this reversal can be found in a decreased human impact on the landscape, a colder and possibly wetter climate, and geomorphological changes. This paper presents a synthesis from 38 pollen records from a range of sites across the Netherlands, from which regional differences in the degree of woodland regeneration and vegetation composition before and during the Dark Ages have been identified. Both original data as well as vegetation abundance modelled by REVEALS were used to assess the regrowth of the woodland cover. The observed trends were considered in terms of the landscape setting and population estimates in order to disentangle the relative importance of these forcing factors. The results indicate that landscape and human impact were the most important factors determining the vegetation structure and changes to it. The pollen data show that in the Netherlands, the clearance of woodland in the Roman period followed by its regrowth afterwards were greatest in the river area. This can be linked to a high population density there during the Roman period followed by a strong decrease of population in the Dark Ages and to increased flooding.

This study concerns the stand-scale palaeoecological reconstruction of the subsequent stages of late Holocene vegetation development on habitats recently covered by beech-dominated woodland in the southern Baltic region. The data, based on pollen, non-pollen palynomorphs, macrofossil and charcoal analyses from two close-lying sites, demonstrated that each of the subsequent late Holocene shifts in dominating forest communities took place because of human impact coupled with climatic events or episodic human-made disturbances. Shifts from the Tilia dominated forest to the Quercus-Corylus plant community at around 3300 bc was most probably driven by the coupled effect of climate change and human activity. Human impact was the primary driver of the final Corylus decline and concurrent major Carpinus expansion at c. 460 bc, and the Carpinus decline followed by Fagus expansion at c. ad 900. Carpinus had been lingering on the edge of a major expansion in the local forest for at least 2,500 years while Fagus had persisted in a small admixture for no fewer than 1,500 years before becoming important forest constituents. Our data illustrate the role of episodic disturbances as turning points that initiate long-term vegetation changes.

The aim of this paper is to improve trend analysis for non-stationary Normalized Difference Vegetation Index (NDVI) time series (TS) over different areas in Tunisia based on the wavelet transform (WT) multi-resolution analysis (MRA-WT), statistical test, and meteorological data. The MRA-WT was applied in order to decompose the TS into different components. However, the most challenge for TS analysis using MRA-WT laid in the selection of two optimum parameters: the level of decomposition and mother wavelet (MW). In this work, both factors were investigated. Firstly, the level of decomposition was calculated for 18 different MWs, and secondly the energy to Shannon entropy ratio criterion was investigated to choose the most suitable MW. The Mann-Kendall test (MK) and Sen's slope were applied to the last approximation component in order to analyze long-term vegetation changes. Finally, the influence of meteorological data for trend was analyzed. The results were first computed for different sites in Tunisia using MODIS NDVI TS from 2001 to 2017. The obtained results proved the importance of MW selection. Level 5 was considered for the TS as the best level of decomposition for long-term vegetation changes. The Daubechies and Symlets MWs (db9 and sym4) showed the highest energy to entropy ratio for three selected vegetation canopies. A combination of the two MW was proposed to derive a trend vegetation analysis at image level. A degradation in the forest area and a few increases in cropland and vegetation area were presented.

Long-term vegetation changes in permanent plots along two transects from the low to the high salt marsh at the Boschplaat on Terschelling between 1953 and 1990, were analysed in relation to sedimentation and flooding. In both transects, the number of plant species decreased between 1953 and 1990. In lower parts of the two transects the dominant plant species of the vegetation changed from Puccinellia maritima in 1953/54 to Limonium vulgare in 1980 to Atriplex portulacoides in 1990. The increase in A. portulacoides between 1980 and 1990 coincided with an increase in the thickness of the silt layer, caused by a sedimentation rate of about 5 mm per year. This sedimentation led to an increase in elevation but not to large changes in flooding frequency between 1953 and 1990, probably due to a sea level rise during the same period. In the higher parts of the salt-marsh transects Elymus athericus strongly increased and this species became dominant in 1980 and 1990. In these parts of the salt marsh, a small increase in elevation, in thickness of the silt layer, and in flooding frequency occurred between 1953 and 1990. The described changes in vegetation are discussed in terms of general succession of salt-marsh vegetation in relation to flooding and sedimentation.

High-mountain environments are regarded as susceptible to environmental change such as the global warming of climate (Grabherr et al. 1995; Korner 1999). It has been predicted that, in a warmer climate, lowland plants would migrate upwards and plant communities typically found in areas with late or moderate snow cover would be invaded by plant species characteristic of more favourable, lowland habitats (Holten and Carey 1992).Grabherr et al. (1994) presented evidence of upward migration of plants on mountain tops. Although migration may increase species richness in some habitats, elsewhere it may pose a threat. Some mountain plants are expected to decrease due to increased competition and changes in environmental conditions (Saetersdal and Birks 1997). Recent experiments have shown that temperature conditions strongly affect plant performance in alpine environments (Galen and Stanton 1993; Molau and Alatalo 1998; Totland and Nylehn 1998); however, short-term experiments may give insufficient information on long-term vegetation changes.

Reconstructing the environmental impact of mining on mountain lakes.

Mountain lakes are particularly fragile ecosystems undergoing important transformations associated with ongoing global change. However, the history of anthropogenic impacts on mountain lakes and their catchments is much longer, in many cases featuring millennia of summer pastoral farming. More recently, the growing demand for raw materials and energy linked to industrialization, particularly accelerated since the 19th century CE, meant a further increase in human impact on mountain areas. The Cantabrian Range (northern Spain) constitutes a paradigmatic case of southern European mountain range experiencing intense human impact during the past few millennia and particularly the past two centuries. Here, we have reconstructed the environmental dynamics of this area during the last millennium, with a particular focus on the impact of mining, based on the multidisciplinary analysis (sedimentology, biogeochemistry, magnetic susceptibility, diatoms, pollen, charcoal and dung fungal spores) of sediment cores from Lago de La Cueva (43°03′N, 6°06′W, 1550 m a.s.l.). Changing land use and climate have driven lake dynamics during the last centuries. A major fire-caused deforestation event dated to the late 15th century CE increased erosion and the frequency of intense runoff episodes, in the context of the wetter and colder Little Ice Age. The onset of iron mining activities in the catchment ca. 200 years ago had a strong impact on the lake. Sedimentation rates notably raised and mining waste containing hematite and potentially toxic elements (e.g. Fe, Co, As) was washed into the lake. Additionally, diatom assemblages showed that lake regulation since the early 20th century CE severely altered the natural hydrological regime introducing rapid seasonal lake-level oscillations and increased lakeshore erosion, water turbidity and nutrient loads. The recent environmental restoration, finished in 2006, has involved the re-deposition of large volumes of mine tailing. Although some mining wastewater still arrives into the lake because mine drainage is still active, restoration works have succeeded in reducing erosion rates and nutrient loads. Lower land-use intensity has also contributed to natural vegetation recovery, further diminishing erosion. This study illustrates the complex interactions between human activities (grazing, mining, hydropower) and climate change in defining mountain landscape shifts through time. Moreover, our results highlight the usefulness of paleolimnological research to quantitatively assess the effectiveness of lake restoration programs.

Long-term changes in vegetation and soil chemistry in a calcareous and sandy semi-natural grassland

The Mongolian Plateau, comprising the nation of Mongolia and the Inner Mongolia Autonomous Region of China, has been influenced by significant climatic changes and intensive human activities. Previous satellite-based analyses have suggested an increasing tendency in the vegetation cover over recent decades. However, several ground-based observations have indicated a decline in vegetation production. This study aimed to explore long-term changes in vegetation greenness and land surface phenology in relation to changes in temperature and precipitation on the Plateau between 1982 and 2011 using the normalized difference vegetation index (NDVI). Across the Plateau, a significantly positive trend in the growing season (May–September) NDVI was observed from 1982 to 1998, but since that time, the NDVI has not shown a persistent increase, thus causing an insignificant trend over the entire study period. For the steppe vegetation (a major vegetation type on the Plateau), the NDVI increased significantly in spring but decreased in summer. Precipitation was the dominant factor related to changes in steppe vegetation. Warming in spring contributed to earlier vegetation green-up only in meadow steppe vegetation, implying that water deficiency in typical and desert steppe vegetation may eliminate the effect of warming. Our results also suggest a combined effect of climatic and non-climatic factors and highlight the need to examine the role of regional human activities in the control of vegetation dynamics.

Long-term vegetation, climate and ocean dynamics inferred from a 73,500 years old marine sediment core (GeoB2107-3) off southern Brazil

A floristic assessment of the Turfloop Nature Reserve was undertaken, with specific reference to the vegetation structure, species of conservation importance (i.e. Red Data species, protected, endemic species, species of medicinal value and biotic and a biotic environment). Releves were compiled in 33 random sample plots placed in the study area. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed eight plant communities. A hierarchical classification, description and ecological interpretation of plant communities are presented. The general structure in terms of growth forms and dominant species of vegetation has changed, compared to a similar survey conducted 39 years ago. Three new plant communities occur and changes also occurred within existing communities. The abundance of vegetation on certain areas has decreased due to severe unsustainable exploitation of resources by surrounding villages, leading to the demise of old and the establishment of new plant communities. The study addresses the long-term changes in vegetation, including the effect of human intervention. It has implications for all involved in veld management, illustrating the effects of over-exploitation on natural resources.