History Of Vegetation Changes Research Articles

Tracing the dynamics of Late Holocene Tropical Peatland: A case study from the Bram Itam Peatland Protection Area, Coastal Sumatra, Indonesia

Tropical peatland ecosystems in Southeast Asia offer essential ecological services but face various threats such as sea level alterations, climate change and human activities. However, our understanding of the origins of peatlands and their dynamics is still limited. Reconstruction of historical vegetation and environmental changes is imperative to comprehend tropical peatlands' origins, evolution and responses to natural factors (e.g., precipitation, sea level) and to human influences (e.g., agriculture). This study employed a multi-proxy palaeoecological analysis, encompassing pollen and spore analysis, macro-charcoal examination, and radiocarbon dating, using a sediment core extracted from the Bram Itam Peatland protection area in Tanjung Jabung Barat, Jambi province. The investigation highlights four distinct palynological periods: from ca. 4750 to 1250 cal yr BP, a dominant mangrove forest thrived in the study area during high sea levels; from 1250 to 450 cal yr BP, as sea levels receded, the mangrove forest was replaced by swampy vegetation, and peatland forests developed under the influence of high precipitation, while agricultural activities with possible rice cultivation were conducted remote from the study area; from 450 cal yr BP to 1950 CE, a mature peatland forest developed. There was no evidence of agricultural practice during this period. After 1950, intensive human activities, including logging, oil palm plantation, and rice cultivation, profoundly impacted the peatland vegetation. The presence of cereal pollen dates back to around 1250 cal yr BP and the introduction of oil palm (Elaeis guineensis) since roughly 1950 CE may indicate potentially enduring changes in agricultural practices of local people in the study area. This study of peatland vegetation dynamics and environmental changes in the Bram Itam peatlands highlights its change from mangrove forest to a matured peatland forest influenced by climate, sea level and human activities.

Low sensitivity of net primary productivity to climatic factors in three karst provinces in southwest China from 1981 to 2019

Karst areas are sensitive to environmental changes due to their fragile ecological environments. It is imperative to explore the temporal and spatial variations in the characteristics of vegetation net primary productivity (NPP) and evaluate the influence of different driving factors on NPP. Taking three karst provinces in southwest China as the study area, where the historical vegetation changes and the mechanisms influencing these changes remain unclear; therefore, the present study used vegetation NPP data from 1981 to 2019 to analyze the temporal and spatial variations in the characteristics of vegetation NPP using slope trend analyses and the sequential Mann-Kendall test. The influence of each driving factor on vegetation NPP and the interaction between each driving factor were investigated using the optimal parameters-based geographic detector (OPGD) model. The results were as follows: (1) The annual variation of the total NPP in the study area from 1981 to 2019 showed a fluctuating growth trend, with a slow growth rate before 2005 followed by a rapid increase. (2) The annual fluctuations in the seasonal NPP in the study area were generally upward, and the total NPP of vegetation in summer was the highest, but the growth rate of NPP in autumn was the fastest, and the area with the largest increase in NPP in autumn was the largest. (3) NPP was related to natural factors, with slope being the primary influencing factor at the annual scale. However, at the seasonal scale, there were differences in the explanatory power of the influencing factors on vegetation NPP. The highest explanatory power was observed for surface soil moisture in spring, air temperature in summer, and precipitation in autumn and winter. (4) The spatiotemporal evolution of NPP characteristics was affected by the interaction among various natural factors. At the annual and seasonal scales, the interaction between each climatic factor and slope greatly enhanced the explanatory power of individual climatic factors. Taken together, the interaction between slope and precipitation contributes the most to NPP.

Wildlife-friendly farming recouples grazing regimes to stimulate recovery in semi-arid rangelands

While rangeland ecosystems are globally important for livestock production, they also support diverse wildlife assemblages and are crucial for biodiversity conservation. As rangelands around the world have become increasingly degraded and fragmented, rethinking farming practice in these landscapes is vital for achieving conservation goals, rangeland recovery, and food security. An example is reinstating livestock shepherding, which aims to recouple grazing regimes to vegetation conditioned to semi-arid climates and improve productivity by reducing overgrazing and rewiring past ecological functions. Tracking the large-scale ecosystem responses to shifts in land management in such sparsely vegetated environments have so far proven elusive. Therefore, our goal was to develop a remote tracking method capable of detecting vegetation changes and environmental responses on rangeland farms engaging in contrasting farming practices in South Africa: wildlife friendly farming (WFF) implementing livestock shepherding with wildlife protection, or rotational grazing livestock farming with wildlife removal. To do so, we ground-truthed Sentinel-2 satellite imagery using drone imagery and machine learning methods to trace historical vegetation change on four farms over a four-year period. First, we successfully classified land cover maps cover using drone footage and modelled vegetation cover using satellite vegetation indices, achieving 93.4% accuracy (к = 0.901) and an r-squared of 0.862 (RMSE = 0.058) respectively. We then used this model to compare the WFF farm to three neighbouring rotational grazing farms, finding that satellite-derived vegetation productivity was greater and responded more strongly to rainfall events on the WFF farm. Furthermore, vegetation cover and grass cover, patch size, and aggregation were greater on the WFF farm when classified using drone data. Overall, we found that remotely assessing regional environmental benefits from contrasting farming practices in rangeland ecosystems could aid further adoption of wildlife-friendly practices and help to assess the generality of this case study.

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

Abstract Examining vegetation change over decadal to centennial timescales by comparing paired sets of historic and contemporary field photographs is a tried and tested approach, used recently in many ecological studies in southern Africa. This approach, however, fails to consider the different forcing factors contributing to vegetation and landscape change over historical time periods. This Viewpoint article outlines some limitations of the analytical approaches used in such studies, and problems of reconciling different datasets related to climate, ecosystems and land management in rapidly changing landscapes. We propose an alternative and integrated methodology for analysing spatial and temporal patterns of historical vegetation change using such datasets, based on a systematic checklist of key criteria related to the landscape under examination, and the mode of photography used. The proposed methodology provides a standardized and reproducible approach that can overcome the limitations of historical photographic analysis of vegetation changes.

Reconstructing Long Term High Andean Forest Dynamics Using Historical Aerial Imagery: A Case Study in Colombia

High Andean forests are biodiversity hotspots that also play key roles in the provisioning of vital ecosystem services for neighboring cities. In past centuries, the hinterland of Andean fast-growing cities often experienced a dramatic decline in forested areas, but there are reports that forest cover has been recovering recently. We analyzed aerial imagery spanning the years 1940 to 2007 from nine administrative localities in the Eastern Andean Cordillera of Colombia in order to elucidate precise patterns of forest vegetation change. To this aim, we performed image object-based classification by means of texture analysis and image segmentation. We then derived connectivity metrics to investigate whether forest cover trajectories showed an increase or decrease in fragmentation and landscape degradation. We observed a forest cover recovery in all the examined localities, except one. In general, forest recovery was accompanied by an increase in core habitat areas. The time scale of the positive trends identified partially coincides with the creation of protected areas in the region, which very likely furthered the recovery of forest patches. This study unveils the long-term dynamics of peri-urban high Andean forest cover, providing valuable information on historical vegetation changes in a highly dynamic landscape.

Vegetation evolution-based hydrological climate history since LGM in southern South China Sea

Abstract The reconstruction of vegetation evolution and climate changes at low latitudes since the Last Glacial Maximum (LGM) remains incomplete. In this study, we reconstructed the palynological history of vegetation changes since the LGM using a sediment core collected from the slope in the southern South China Sea (SCS). The chronology of the core was based on eight AMS14C dates, and 85 stratigraphic samples were palynologically analyzed. Our results denote that the vegetation reconstructed during the LGM in the southern SCS was characterized by a relatively high percentage of herb pollen and a modest decrease in the number of fern spores, suggesting a temperature decline and humidity change in this region. Further, the preservation of a rich diversity of pollen from the tropical lowland rainforest indicated that the rainforests might have covered large areas of the exposed Sunda Shelf during the LGM. The dynamic concentration of the Pinus pollen in the core, which is a proxy for the East Asian winter monsoon (EAWM), satisfactorily matched the changes in the Atlantic meridional overturning circulation and Australian-Indonesian summer monsoon, especially during the Heinrich Stadial 1. This suggests that the climate at the high latitudes of the Northern Hemisphere can drive the Intertropical Convergence Zone (ITCZ) southwards based on the enhanced EAWM. The southward-shifting ITCZ may change the hydrological climate of the equator and the Southern Hemisphere. The pteridophyte spores, which are good regional precipitation indicators, were positively correlated with the warm pool convection and inversely related with the EAWM, possibly indicating the considerable impact of the high-latitude climate in the Northern Hemisphere on precipitation in the tropical regions. Our results indicate that during the last deglaciation, the tropical hydrological changes were relatively moderate when compared with the drastic change observed at high latitudes and were attributed to the regulation of the El Nino-Southern Oscillation-like state. Our sequence of pollen and spores from the southern SCS can be used to observe the detailed dynamics of climatic evolution in tropical regions. The results of this study are essential to understand the complicated climate processes and the relation between high and low latitudes.

Temperature, Wind, Cloud, and the Postglacial Tree Line History of Sub-Antarctic Campbell Island

Campbell Island, which is 600 km south of New Zealand, has the southernmost tree line in this ocean sector. Directly under the maximum of the westerlies, the island is sensitive to changes in wind strength and direction. Pollen records from three peat cores spanning the tree line ecotone provide a 17,000-year history of vegetation change, temperature, and site moisture. With postglacial warming, tundra was replaced by tussock grassland 12,500 years ago. A subsequent increase of shrubland was reversed at 10,500 years ago and wetland-grassland communities became dominant. Around 9000 years ago, trees spread, with maximum tree line elevation reached around 6500 to 3000 years ago. This sequence is out of step with Southern Ocean sea surface temperatures, which were warmer than 12,500 to 9000 years ago, and, subsequently, cooled. Campbell Island tree lines were decoupled from temperature trends in the adjacent ocean by weaker westerlies from 12,500 to 9000 years ago, which leads to the intrusion of warmer, cloudier northern airmasses. This reduced solar radiation and evapotranspiration while increasing atmospheric humidity and substrate wetness, which suppressed tree growth. Cooler, stronger westerlies in the Holocene brought clearer skies, drier air, increased evapotranspiration, and rising tree lines. Future global warming will not necessarily lead to rising tree lines in oceanic regions.

Stable isotope analysis of vegetation history and land use change at Laguna Santa Elena in southern Pacific Costa Rica

Laguna Santa Elena (8.9290° N, 82.9257° W, 1055 m a.s.l.) is a small lake in the Diquis archaeological sub-region of southern Pacific Costa Rica. Previous analyses of pollen and charcoal in a sediment core from Santa Elena revealed a nearly 2,000 year history of vegetation change, maize cultivation and site occupation that is consistent with the archaeological record from the lake basin and surrounding area. Here we present the results of new loss-on-ignition, geochemical and bulk stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of the Santa Elena sediments that supplement and refine the previous reconstruction. Like many lakes in Central America and the Caribbean, Laguna Santa Elena was a magnet for humans throughout its history. As a result, the lake experienced vegetation modification by humans and maize cultivation at varying intensities over a long duration. The Santa Elena sediments provide a record of palaeoenvironmental change during times of major culture change and increasing cultural complexity in the Diquis region, which occurred during intervals of broader changes driven by external forcing mechanisms, including the Terminal Classic Drought (TCD), the Little Ice Age (LIA) and the Spanish Conquest. Our high resolution lake sediment study from Santa Elena reveals details of these events at the local scale that are unobtainable by other means, including the timing of the initial intensification of maize cultivation at ca. 1,570 cal bp (ad 380) and two intervals of population decline coinciding with the TCD at ca. 1,085 cal bp (ad 865) and near the start of the LIA at ca. 683 cal bp (ad 1267).

Vegetation and climate change in the Pro-Namib and Namib Desert based on repeat photography: Insights into climate trends

This paper presents empirical evidence of historical vegetation and climate change in the arid Pro-Namib and hyper-arid Namib Desert spanning the late 19th century to the present based on one hundred archival landscape photographs that have been re-photographed or ‘matched’. Each photo site was evaluated for changes in woody cover and taken together serve as a proxy for how climate has changed in the region. Vegetation change was related to values for precipitation and temperature derived from the Global Land Data Assimilation System for the period 1948–2017 as well as the number of fog days expected at a site. The resulting analysis reveals a trend of increased vegetation cover associated with increased precipitation (fog and rain) in the coastal Fogbelt and the inland Savanna transition with a shrinking of the hyper-arid Minimum zone between the two. These findings accord with projected effects of global warming on the Benguela upwelling system but are at variance with regional climate model forecasts that project widespread aridification. In the absence of long-term climate data, the results of this research are an important contribution of evidence-based knowledge of past climate trends and their relationship to future climate change scenarios for the region.

An assessment of the impacts of climate extremes on the vegetation in Mongolian Plateau: Using a scenarios-based analysis to support regional adaptation and mitigation options

Climate change is known to have an impact on the vegetation and on the well-being of ecosystems. Whereas there is a limited number of studies which have assessed historical vegetation changes in the Mongolian Plateau (MP), there are even fewer considering future changes. This paper therefore fills a gap in the literature, by investigating such changes in temporal and spatial scales, and by assessing their effects (1982–2100). The methods used in the study mainly included Pearson correlation and Mann-Kendall test. Results showed that climate extremes in MP, significantly influence vegetation growth. In addition, vegetation trends in MP, vary according to different scenarios. Potentially vulnerable areas of grassland and forest in the future are pointed out. Among the adaptation options available, better management of farmland and water resources should be pursued, and planting of vegetation types should be considered separately. Improvement of the barren area in MP requires international cooperation between Mongolia and China and it is necessary to integrate adaptation options into relevant policies. For mitigation, the projection indicates the emission under Scenario A1B is better for grass growth in MP and great attention should be paid to the greenhouse gas (GHG) emissions from grassland systems in detail, apart from the high quality and low GHG emission animal species, the types of intake grass also need to be seriously considered. In addition, management of sheepfolds in MP is also an important way to reduce GHG emissions. The results from this study will provide useful information about appropriate adaptation and mitigation strategies which may influence vegetation growth in MP.

Hydrologic responses to restored wildfire regimes revealed by soil moisture-vegetation relationships

Abstract Many forested mountain watersheds worldwide evolved with frequent fire, which Twentieth Century fire suppression activities eliminated, resulting in unnaturally dense forests with high water demand. Restoration of pre-suppression forest composition and structure through a variety of management activities could improve forest resilience and water yields. This study explores the potential for “managed wildfire”, whereby naturally ignited fires are allowed to burn, to alter the water balance. Interest in this type of managed wildfire is increasing, yet its long-term effects on water balance are uncertain. We use soil moisture as a spatially-distributed hydrologic indicator to assess the influence of vegetation, fire history and landscape position on water availability in the Illilouette Creek Basin in Yosemite National Park. Over 6000 manual surface soil moisture measurements were made over a period of three years, and supplemented with continuous soil moisture measurements over the top 1m of soil in three sites. Random forest and linear mixed effects models showed a dominant effect of vegetation type and history of vegetation change on measured soil moisture. Contemporary and historical vegetation maps were used to upscale the soil moisture observations to the basin and infer soil moisture under fire-suppressed conditions. Little change in basin-averaged soil moisture was inferred due to managed wildfire, but the results indicated that large localized increases in soil moisture had occurred, which could have important impacts on local ecology or downstream flows.

Spatial variability and long-term change in pollen diversity in Nam Co catchment (central Tibetan Plateau): Implications for alpine vegetation restoration from a paleoecological perspective

Pollen diversity offers abundant clues into the floristic diversity and history of vegetation change. Few palynological studies investigated modern pollen diversity or the past floristic diversity on the Tibetan Plateau (TP). Based on modern pollen assemblages from 37 topsoils and 63 surface lake sediments in the Nam Co catchment on the central TP, this study quantitatively explored spatial distribution of modern pollen diversity using Shannon-Wiener index (H) and palynological richness (E(T n ), n =600). Pollen diversity indices showed spatial variability among vegetation types, reflecting the differences in terrestrial floristic diversity in the lake catchment. Their values were high in the southeastern region of the lake catchment which is covered by alpine steppe, while values were low for alpine meadow and marsh meadow. The pollen diversity in lacustrine pollen assemblage could be an effective proxy to document past floristic diversity. The past floristic diversity in the lake catchment, recovered from a fossil pollen record of NMLC-1, showed a long-term change of ascending overlaid by several rapid diversity changes during the last 8400 years due to the downward shift of altitudinal vegetation belt driven by a general climatic cooling. The results imply that under the environmental challenge of climate warming and vegetation degradation, alpine vegetation restoration in the Nam Co catchment and the central TP should pay attention to altitudinal vegetation belt and zonal vegetation of alpine steppe, and use the long-term change of floristic diversity as a historical analogue.

Remote Sensing for Wetland Mapping and Historical Change Detection at the Nisqually River Delta

Coastal wetlands are important ecosystems for carbon storage and coastal resilience to climate change and sea-level rise. As such, changes in wetland habitat types can also impact ecosystem functions. Our goal was to quantify historical vegetation change within the Nisqually River watershed relevant to carbon storage, wildlife habitat, and wetland sustainability, and identify watershed-scale anthropogenic and hydrodynamic drivers of these changes. To achieve this, we produced time-series classifications of habitat, photosynthetic pathway functional types and species in the Nisqually River Delta for the years 1957, 1980, and 2015. Using an object-oriented approach, we performed a hierarchical classification on historical and current imagery to identify change within the watershed and wetland ecosystems. We found a 188.4 ha (79%) increase in emergent marsh wetland within the Nisqually River Delta between 1957 and 2015 as a result of restoration efforts that occurred in several phases through 2009. Despite these wetland gains, a total of 83.1 ha (35%) of marsh was lost between 1957 and 2015, particularly in areas near the Nisqually River mouth due to erosion and shifting river channels, resulting in a net wetland gain of 105.4 ha (44%). We found the trajectory of wetland recovery coincided with previous studies, demonstrating the role of remote sensing for historical wetland change detection as well as future coastal wetland monitoring.

A 4000-yr multi-proxy record of Holocene hydrology and vegetation from a peatland in the Sanjiang Plain, Northeast China

Reconstructing historical hydrologic and vegetation conditions can provide useful insights into the mechanisms underlying peatland development and can be used to construct baselines for peatland restoration. In this study, we present numerous physical and biological indices for a 4000-year core from the Honghe National Natural Reserve (HE), a dish-like depression peatland in the Sanjiang Plain of Northeast China. The history of vegetation change was reconstructed by combining plant macrofossils and pollen data from the core, and the water level changes were reconstructed through a multi-proxy study of plant macrofossils, charcoal, stable carbon isotopes, testate amoebae, sediment grain size, loss on ignition, humification degree and magnetic susceptibility. We found that the HE peatland featured wet condition from 4000 to 3600 cal yr BP, which was in accordance with the extreme flooding event at 4.0 ka in northern China. Significant drier shifts were recorded at 3600 and 1200 cal yr BP, while significant wetter shifts were recorded at 2600 and 500 cal yr BP. Factor analysis were applied to all of the proxies to reduce the seven variables to two factors, and the biological indicators, such as plant macrofossils, charcoal and stable carbon isotopes, were found to be more sensitive than the other parameters to water level changes over the last 4000 years. Furthermore, the multi-proxy reconstruction of the wetness of the HE peatland resembles the pattern observed at other sites in Northeast China.

Historic vegetation and environmental changes since the 15th century in the Korean Peninsula

Reconstruction of past vegetation is an important process in understanding vegetation history and global climate change. This research reconstructed the past vegetation range based upon historical records in the Korean Peninsula, especially for conifers and bamboos, and determined the factors responsible for historic change. Time-spatial changes in distribution of three conifer trees, two by-products of red pine and two bamboos from 1454 to 1931 were reconstructed with information about the local produce and tribute descriptions on seven historical documents. Plant distribution data were collated over time and space and plotted on county maps using a GIS software package.Cold tolerant Korean pines were grown on the northern Democratic People's Republic of Korea (DPRK) and eastern parts of Republic of Korea (ROK) with high mountains and hostile climate but absent from the western and southern lowlands of ROK showing low elevation and mild climate. Warmth tolerant red pines were present nation-wide, apart from the northern high mountains. Reconstructed ranges of red pines based on two by-products, e.g., pine mushroom and tuckahoe, matched well with the distribution of red pines. Warmth loving torreya tree were confined in their distribution to the southwestern tips of ROK with gentle terrains and mild and wet climate, especially in the winter. Giant timber bamboo mainly occurred on the southern parts of ROK, but some in the eastern ROK. Arrow bamboo showed a broader distribution, along the coast of ROK as well as the eastern coast of DPRK.Historical records can be used as good sources for reconstructing past vegetation change and climate change. Spatiotemporal distributional change of conifers and bamboos in the Korean Peninsula seems to be the result of both climatic change and anthropogenic cultivation, but no clear indication for the little ice age can be found from the historical vegetation.

Evidence of a tipping point in a southern African savanna?

Many ecosystems exhibit threshold behaviour, where periods of relative stability are punctuated by rapid transitions between alternate stable states when an ecological threshold, or tipping point, is reached. This is of concern in grass-dominated habitats, many of which appear to be on the point of conversion to more wooded vegetation assemblages. However, changes in grass-dominated ecosystems are often difficult to interpret, because it is not always clear whether grasslands are ancient or are anthropogenically derived from past deforestation. As a result, the conservation, maintenance and restoration of ancient grasslands are sometimes neglected.In this study, the history of vegetation change in the savannas of the Hluhluwe-iMfolozi Park, KwaZulu-Natal, South Africa, are investigated by analysing stable carbon isotopes (δ13C) from soil profiles. Without exception, the data show that C3 dominated thicket, forest, and densely wooded savanna now occur on sites that were previously C4 grassland or open savanna. Although the drivers of this change are not clear, there is potential for management intervention because tree density can be manipulated through fire, a natural part of this dynamic landscape. The study identified two sites which are at a threshold between C4 and C3 dominance, and highlighted them as priorities for conservation management intervention.

Congruent phylogeographical patterns of eight tree species in Atlantic Central Africa provide insights into the past dynamics of forest cover

Cycles of Quaternary climatic change are assumed to be major drivers of African rainforest dynamics and evolution. However, most hypotheses on past vegetation dynamics relied on palaeobotanical records, an approach lacking spatial resolution, and on current patterns of species diversity and endemism, an approach confounding history and environmental determinism. In this context, a comparative phylogeographical study of rainforest species represents a complementary approach because Pleistocene climatic fluctuations may have left interpretable signatures in the patterns of genetic diversity within species. Using 1274 plastid DNA sequences from eight tree species (Afrostyrax kamerunensis, A.lepidophyllus, Erythrophleum suaveolens, Greenwayodendron suaveolens, Milicia excelsa, Santiria trimera, Scorodophloeus zenkeri and Symphonia globulifera) sampled in 50 populations of Atlantic Central Africa (ACA), we averaged divergence across species to produce the first map of the region synthesizing genetic distinctiveness and standardized divergence within and among localities. Significant congruence in divergence was detected mostly among five of the eight species and was stronger in the northern ACA. This pattern is compatible with a scenario of past forest fragmentation and recolonization whereby forests from eastern Cameroon and northeastern Gabon would have been more affected by past climatic change than those of western Cameroon (where one or more refugia would have occurred). By contrast, southern ACA (Gabon) displayed low congruence among species that may reflect less drastic past forest fragmentation or a more complex history of vegetation changes. Finally, we also highlight the potential impact of current environmental barriers on spatial genetic structures.

Archaeobotanical Evidence for Indigenous Burning Practices and Foodways at CA-SMA-113

On the central California coast, the low incidence of lightning fires, coupled with a relatively predictable regional vegetation succession pattern, leads to the expectation that in the absence of regular anthropogenic burning, the landscape would have been dominated by dense woody shrubland and forest cover with few plant food resources. Assessment of historical vegetation change in the Quiroste Valley research area supports this hypothesis. Archaeobotanical research at site CA-SMA-113 indicates that during the late Holocene (ca. cal AD 1000–1300), site inhabitants relied heavily on grassland seed foods, producing archaeobotanical assemblages much like those in contemporaneous interior central California sites. The CA-SMA-113 assemblage also contains several culturally or ecologically fire-associated plants in proportions higher than would be expected in the absence of anthropogenic burning. The CA-SMA-113 wood charcoal assemblage is composed mostly of taxa that are compatible with low intensity fire, in sharp contrast to the fire-susceptible trees and shrubs that dominate the landscape today. A synthetic interpretation of the CA-SMA-113 botanical data supports the hypothesis of frequent anthropogenic landscape burning around Quiroste Valley during the late Holocene.

Holocene and historical vegetation change and fire history on the north-central coast of California, USA

Pollen, non-pollen palynomorphs (NPPs), and charcoal particle stratigraphies are used to determine environmental change at Glenmire, Point Reyes Peninsula, northcentral coastal California, over the last c. 6200 years. Pollen was not preserved in early Holocene sediments when climate was drier than present. However, groundwater tables rose after c. 6200 cal. BP, allowing for greater subsequent preservation of organic matter. Middle and late Holocene environments were a mosaic of vegetation types, including mixed conifer forest with coastal scrub grassland prior to c. 4000 cal. BP. Subsequently, hardwoods such as alder (Alnus) and coastal scrub (e.g. Artemisia, Baccharis) expanded until c. 2200 cal. BP, followed by tanoak (Lithocarpus densiflorus), Douglas fir (Pseudotsuga menziesii), and coast redwood (Sequoia sempervirens). With increasing amounts of oak (Quercus), this mosaic of vegetation types continued to dominate until the arrival of Euro-Americans in the early to mid-1800s. The fire history is probably tied closely to human settlement, since natural ignitions are rare. Elevated charcoal amounts coincide with increased sedentism of the native populations by about 3500 cal. BP. Increased sedentism may have caused a more intense and constant use of the coastal environment around Glenmire. For the most recent centuries, we compared historical records of explorations, Spanish Mission establishment, consolidation of the native Coast Miwok population, ranching by Mexican nationals, and dairying by Americans at the height of California’s gold rush with the paleoecological record. The Glenmire record thus documents changing fire use following the ad 1793 fire suppression proclamation; declines in native forest species; introductions of non-native species, including those associated with livestock grazing and land disturbance; and an increase in coprophilous fungi (NPPs) associated with the presence of large numbers of sheep and cattle, among other changes. During the historical period, the sedimentary record of historical fires closely matches the nearby fire-scar tree-ring record.

Searching for ancient forests: A 2000 year history of land use in northeastern French forests deduced from the pollen compositions of closed depressions

Evidence of the agricultural use, during Roman or Medieval times, of forested areas formerly considered to be ancient, as well as legacies of this former land use on plant biodiversity and soil properties, have encouraged the search for archives of former land use in forests. In central Lorraine (northeastern France), thousands of small closed depressions (CD) on marlstone have been inventoried in forests over the past 150 years, and we hypothesised that these CDs could be used to reconstruct patterns of land use. Closed depressions near the Seille and Sarre valleys were selected and cored for pollen and sediment analyses. Principal Components Analysis (PCA) was used to analyse variations of pollen assemblages during the last two millennia. The history of vegetation changes depicts five main phases. During the Roman period, the region appears to have been primarily covered by grasslands, with some croplands but few forests. All areas were reforested by the end of the Roman period. During the early Medieval period, croplands with grasslands developed in the region, while the late Medieval was characterised by cereal cropping, with especially intense use at sites near the Seille valley, and a lesser extension of grasslands. The present forest cover developed over the past 500 years because of the development of the salt industry in the Seille valley, which required firewood, and the general decrease of agricultural pressure over the past 150 years. Previous investigations had provided evidence of large-scale Roman field systems in the forests covering the limestone plateau and the Vosges foothills on sandstone, areas west and east of the research focus, respectively. These convergent findings suggest that that forests considered to be ‘ancient’ on the basis of historical documents may have been used for pasture or agriculture over extensive periods during the last 2000 years.