Human-induced Vegetation Changes Research Articles

Prehistoric human impact in the mountains of Bohemia. Do pollen and archaeological data support the traditional scenario of a prehistoric “wilderness”?

In the Czech Republic at least five landscape zones, differing by settlement history, can be distinguished. The main focus of this study are marginal mountainous zones: foothills, where the cultural landscape fully developed during high medieval colonization in the 13th century, and the central mountains were colonized mostly in the 16th century and later. Before colonization, these areas are thought to have been essentially wild; however, they are much less archaeologically known than the lowlands. The study focuses on the tracing of a fine-scale prehistoric human impact in two pollen diagrams from the Lusatian Mountains (foothills) and the Bohemian Forest (central mountains). The pollen records are compared with available archaeological data. A case study comparing the off-site and on-site pollen records from the Vladař hillfort (Hallstatt) is presented to demonstrate the local signal of the pollen profiles of small mires. In both studied mountainous regions, the strongest prehistoric human impact was detected during the Hallstatt/La Tène period, that is characterized by a rapid expansion of a single tree taxon (Pinus and Abies respectively) together with the consistent occurrence of Plantago lanceolata and other indicators for anthropogenic influence. The human impact was less distinct in the pollen profile from the central part of the Bohemian Forest. In both studied regions, the presumed prehistoric human-induced vegetation changes influenced the species composition of the forest for hundreds of years and were therefore not minor. The pollen sites are small mires or larger forested peat bogs and thus mostly reflect local conditions. It is also assumed that the pre-medieval human impact on vegetation must have been limited in space. Despite the limits of recent data, we present evidence for prehistoric human influence on the vegetation. Future research should be either more extensive (thorough archaeological prospection, more well-dated pollen profiles) or focused on special cases when both archaeological and pollen sites are next to each other.

Inaccessible Andean sites reveal human-induced weathering in grazed soils

Human activity affects properties and development of ecosystems across the globe, to such a degree that it is now challenging to get baseline values for undisturbed ecosystems. This is especially true for soil development, which is potentially affected by land-use history and holds a legacy of past human interventions. Therefore, it is still largely unknown for most ecozones how soil would have developed ‘naturally’. Here, we show undisturbed soil development, i.e. the processes of weathering and accumulation of soil organic matter (SOM), by comparing pristine with grazed sites in the high Andes (4500 m) of southern Peru. We located study plots on a large ledge (0.2 km2) that is only accessible with mountaineering equipment. Plots with pristine vegetation were compared to rangeland plots that were presumably under relatively constant grazing management for at least four millennia. Vegetation change, induced by grazing management, led to lower vegetation cover of the soil, thereby increasing soil surface temperatures and soil acidification. Both factors increased weathering in rangeland soils. Formation of pedogenic oxides with high surface area explained preservation of SOM, with positive feedback to acidification. Higher contents of pyrophosphate extractable Fe and Al oxides indicated the importance of organo-mineral associations for SOM stabilization on rangeland sites, which are likely responsible for a higher degree of humification. This higher degree of humification induced melanization (darker colour) of the rangeland soils which, together with sparse vegetation cover, also feeds back to soil temperature. With this work, we present a conceptual framework of positive feedback links between human-induced vegetation change, soil development and accumulation of SOM, which is only possible due to the unique baseline values of a pristine ecosystem. Using ‘inaccessibility’ as a tool to quantify human impact in future interdisciplinary studies may push research forward on evaluating anthropogenic impact on Earth’s ecosystems.

Late Holocene climate change and human impact inferred from the pollen record, Haman area, southern Korea

A pollen record (ca. 200 cal. BC–1210 cal. AD) from swamp deposits exhibits climate change and human-induced vegetation change in the Haman area, southern Korea. The predominance of deciduous Quercus, Alnus and Pinus from ca. 200 cal. BC to 80 cal. AD indicates a cool temperate mixed coniferous and deciduous broadleaved forest, cooler than today. The rise of warm temperate evergreen broadleaved trees in combination with the retreat of boreal taxa (Picea, Abies and Betula) from ca. 80 to 360 cal. AD indicates climatic amelioration similar to the modern temperate condition of the study area. The increase of Pinus and cultivated Gramineae pollen (>40 μm) during this period also suggests human impact. The high representation of Pinus and cultivated Gramineae pollen, and regular occurrence of farmland weed from ca. 360 to 1010 cal. AD indicate intensive cultivation, related to the growth of an ancient small kingdom (Aragaya). A climatic cooling from ca. 1010 to 1210 cal. AD is indicated by the retreat of warm temperate evergreen broadleaved trees and the rise of boreal coniferous and deciduous broadleaved trees, while intensive cultivation was persistent.

Evapotranspiration and water yield over China's landmass from 2000 to 2010

Abstract. Terrestrial carbon and water cycles are interactively linked at various spatial and temporal scales. Evapotranspiration (ET) plays a key role in the terrestrial water cycle, altering carbon sequestration of terrestrial ecosystems. The study of ET and its response to climate and vegetation changes is critical in China because water availability is a limiting factor for the functioning of terrestrial ecosystems in vast arid and semiarid regions. To constrain uncertainties in ET estimation, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model was employed in conjunction with a newly developed leaf area index (LAI) data set, MODIS land cover, meteorological, and soil data to simulate daily ET and water yield at a spatial resolution of 500 m over China for the period from 2000 to 2010. The spatial and temporal variations of ET and water yield were analyzed. The influences of climatic factors (temperature and precipitation) and vegetation (land cover types and LAI) on these variations were assessed. Validations against ET measured at five ChinaFLUX sites showed that the BEPS model was able to simulate daily and annual ET well at site scales. Simulated annual ET exhibited a distinguishable southeast to northwest decreasing gradient, corresponding to climate conditions and vegetation types. It increased with the increase of LAI in 74% of China's landmass and was positively correlated with temperature in most areas of southwest, south, east, and central China. The correlation between annual ET and precipitation was positive in the arid and semiarid areas of northwest and north China, but negative in the Tibetan Plateau and humid southeast China. The national annual ET varied from 345.5 mm in 2001 to 387.8 mm in 2005, with an average of 369.8 mm during the study period. The overall rate of increase, 1.7 mm yr−1 (R2 = 0.18, p = 0.19), was mainly driven by the increase of total ET in forests. During 2006–2009, precipitation and LAI decreased widely and consequently caused a detectable decrease in national total ET. Annual ET increased over 62.2% of China's landmass, especially in the cropland areas of the southern Haihe River basin, most of the Huaihe River basin, and the southeastern Yangtze River basin. It decreased in parts of northeast, north, northwest, south China, especially in eastern Qinghai-Tibetan Plateau, the south of Yunnan Province, and Hainan Province. Reduction in precipitation and increase in ET caused vast regions in China, especially the regions south of Yangtze River, to experience significant decreases in water yield, while some sporadically distributed areas experienced increases in water yield. This study shows that the terrestrial water cycles in China's terrestrial ecosystems appear to have been intensified by recent climatic variability and human induced vegetation changes.

Holocene land-cover change in Eastern Asia for climate modeling

This workshop was held at Hebei Normal University in China, and contributed to the PAGES Focus 4 theme Land Use and Cover (LUC). A major goal of LUC is to achieve Holocene land-cover reconstructions that can be used for climate modeling and testing hypotheses on past and future effects of anthropogenic land cover on climate. Collaborations initiated between Linnaeus University (Sweden; M.-J Gaillard), University of Hull (Britain, Jane Bunting), Hebei Normal University (China; Q. Xu and Y. Li), the French Institute (Pondicherry, India; A Krishnamurthy) and Lucknow University (India; P. Singh Ranhotra) are in line with the goals of Focus 4-LUC and follow the strategy of the European LUC-relevant LANDCLIM project (Gaillard et al. 2010). The aim of these collaborations is to develop quantitative reconstructions of past vegetation cover in India and China using pollen-vegetation modeling and archaeological/historical data together with other land-cover modelling approaches. The objective of this workshop in China was to initiate the necessary collaborations and activities to make past land-cover reconstructions possible in Eastern Asia. The three major outcomes of the workshop are (i) the building of a large network of experts from Eastern Asia, Europe and USA now working together to understand past changes in land use and land cover in Eastern Asia, (ii) that all existing East Asian pollen databases will be integrated into the NEOTOMA Paleoecology Database by 2014 (coordinated by Eric Grimm, Illinois State University, USA), and (iii) that a review paper will be prepared with the working title “Past land-use and anthropogenic land-cover change in Eastern Asia evaluation of current achievements, potentials and limitations, and future avenues”. It is planned to submit this article this fall. It will include 1) a review of Holocene human-induced vegetation and land-use changes in Eastern Asia based on results presented at the workshop; 2) a discussion of the existing anthropogenic land-cover change scenarios (HYDE, Klein Goldewijk et al. 2010; KK 10, Kaplan et al. 2009) in the light of the reviewed proxy-based knowledge; and 3) a discussion on the implications of these results for future climate modeling and the study of past land cover-climate interactions. These significant outcomes are the result of three intense days of presentations and discussion sessions. During the lectures, results were presented for historical, paleoecological and pollenbased reconstructions; pollen-vegetation relationships; past human-impact studies; and model scenarios of anthropogenic land-cover changes in the past. Some of the conference was also dedicated to reviewing the state of existing pollen databases and more generally, database building. Plenary and group break-out discussions focused on more technical aspects such as improving pollen databases, especially for the East Asian region; planning the review paper; and scientific topics such as the use of pollen-based and historical land-cover reconstructions for the evaluation of model scenarios of past anthropogenic land-cover change (Fig. 1), and the integration of model scenarios with paleoecological or historical reconstructions.

Distinguishing between human-induced and climate-driven vegetation changes: a critical application of RESTREND in inner Mongolia

Changes in the spatiotemporal pattern of vegetation alter the structure and function of landscapes, consequently affecting biodiversity and ecological processes. Distinguishing human-induced vegetation changes from those driven by environmental variations is critically important for ecological understanding and management of landscapes. The main objectives of this study were to detect human-induced vegetation changes and evaluate the impacts of land use policies in the Xilingol grassland region of Inner Mongolia, using the NDVI-based residual trend (RESTREND) method. Our results show that human activity (livestock grazing) was the primary driver for the observed vegetation changes during the period of 1981–2006. Specifically, vegetation became increasingly degraded from the early 1980s when the land use policy—the Household Production Responsibility System—led to soaring stocking rates for about two decades. Since 2000, new institutional arrangements for grassland restoration and conservation helped curb and even reverse the increasing trend in stocking rates, resulting in large-scale vegetation improvements in the region. These results suggest that most of the degraded grasslands in the Xilingol region can recover through ecologically sound land use policies or institutional arrangements that keep stocking rates under control. Our study has also demonstrated that the RESTREND method is a useful tool to help identify human-induced vegetation changes in arid and semiarid landscapes where plant cover and production are highly coupled with precipitation. To effectively use the method, however, one needs to carefully deal with the problems of heterogeneity and scale in space and time, both of which may lead to erroneous results and misleading interpretations.

Palynological evidence for agriculture and environmental change from the late Holocene deposits, Hampyeong area, southwestern Korea

A pollen record (ca. 1090–1380 cal. AD) from swamp deposits exhibits human-induced vegetation change and subsequent environment change in the Hampyeong area, southwestern Korea. The predominance of Pinus and Gramineae from ca. 1090 to 1340 cal. AD indicates human-induced cropland and Pinus-dominated forest. The high representation of cultivated Gramineae, regular occurrence of farmland weeds, and low representation of deciduous broadleaved taxa imply intensive rice cultivation. The expansion of warm temperate evergreen broadleaved forest and the retreat of Pinus dominated forest from ca. 1340 to 1360 cal. AD represent a climate-induced vegetation shift, while intensive cultivation was persistent. The conspicuous reduction of cultivated Gramineae and farmland weed, and the abrupt rise of riparian Cyperaceae and fern spores from ca. 1360 to 1380 cal. AD indicate devastation of the cropland. Along with palynological evidence, sedimentological and historiographical data suggest that this decline of agricultural activities was caused by inundation coupled with social insecurity during the period of regime change from the Goryeo Dynasty to the Joseon Dynasty.

Describing and Mapping Human-Induced Vegetation Change in the Australian Landscape

Australian reporting requirements for native vegetation require improved spatial and temporal information on the anthropogenic effects on vegetation. This includes better linkage of information on vegetation type (e.g., native vegetation association), extent and change, vegetation condition, or modification. The Vegetation Assets, States and Transitions (VAST) framework is presented as a means for ordering vegetation by degree of anthropogenic modification as a series of condition states, from a residual or base-line condition through to total removal. The VAST framework facilitates mapping and accounting for change and trends in the status and condition of vegetation. The framework makes clear the links between land management and vegetation condition states, provides a mechanism for describing the consequences of land management practices on vegetation condition, and contributes to an understanding of resilience. VAST is a simple communication and reporting tool designed to assist in describing and accounting for anthropogenic modification of vegetation. A benchmark is identified for each vegetation association. Benchmarks are based on structure, composition, and current regenerative capacity. This article describes the application of the VAST framework as a consistent national framework to translate and compile existing mapped information on the modification of native vegetation. We discuss the correspondence between these compiled VAST datasets at national and regional scales and describe their relevance for natural resource policy and planning.

Late Holocene Pollen Sequence of the Ilan Plain Northeastern Taiwan, and its Environmental and Climatic Implications

Pollen analysis of a 15.0 m core covering the past 3500 years from the Ilan Plain, northeastern Taiwan, displays a record of environmental changes and climate trends for the late Holocene. At about 3500 yr B.P., brackish water-tolerant elements, such as Bruguiera and Acrostichum, dominated the vegetation, reflecting that the environment was influenced by marine excursions. Following this period, wetland elements Poaceae and Cyperaceae were abundant between ca. 3350 and ca. 3100 yr B.P. Then pioneer taxon Alnus increased at the expense of those herbs in the later part of the interval ca. 3100 and ca. 2000 yr B.P. This suggests a shift from a primarily coastal (ca. 3500 yr B.P.) to wetland (ca. 3350 yr B.P.) and then finally terrestrial (ca. 2000 yr B.P.) environment at the coring site. Since then, the present fluvial plain has existed. Humidity conditions which were interpreted from the amount and variations of fern spore probably indicate a strengthening of the monsoon at ca. 3200, ca. 2000, and ca. 900 yr B.P., respectively. The Medieval Warm Period is also apparent indicated by the amount of arboreal elements based on pollen concentrations ca. 1300 to ca. 900 yr B.P. Significant human-induced vegetation changes occurred between ca. 1300 and ca. 900 yr B.P. and over the last 400 years.

Mid- to late-Holocene vegetation history of Greater Exmoor, UK: estimating the spatial extent of human-induced vegetation change

This paper presents the results from three pollen profiles from a group of small spring mire sites on the southern edge of Exmoor in south west England. The size and topography of these sites allow detailed local landscape histories around each site to be reconstructed which broadly cover the mid- to late-Holocene. Comparison of the individual local landscape histories demonstrates the scale of spatial variation in vegetation around the upland edge, and facilitates understanding of human-landscape interactions from the early Neolithic onward. In the early Neolithic significant short-term woodland disturbance is recorded around the upland fringe, including clearance of oak-hazel-elm woodland, suggesting that the shift from Mesolithic to Neolithic is not marked by a gradual environmental transition. Following this, there is clear evidence of Neolithic management of upland heath using fire, presumably for the management of upland grazing. Woodland clearances are recorded throughout the later Prehistoric period; however, the use of multiple profiling suggests that woodland clearance is spatially discrete, even within an area of 4 km2. Pastoral land use is dominant around the uplands until around 900–1,000 a.d., and there is no discernible Roman or post-Roman period impact in the vegetation, suggesting cultural stability from the late Iron Age to the early Medieval period. By 1,100 a.d., there is a shift to mixed arable-pastoral farming which appears to continue well into the post-Medieval period.

Environmental and sea-level changes in London from 10 500 BP to the present: a case study from Silvertown

Results of stratigraphic and palaeoecological studies carried out on deposits at Silvertown in east London are discussed in relation to current models of Late glacial and Holocene alterations to river form, relative sea-level change, vegetation development and archaeology in the lower Thames. The data indicate that the braided bedform typical of British cold stage rivers evolved into a lower energy meandering form around 10 500 BP, a process that caused channel cut-off. The fill of one of these contained organic sediments and in-washed sands dating from 10 500-9300 BP in which there was palynological evidence for the replacement of Late Devensian tundra by early Holocene pine forest. Biostratigraphic evidence for the period 9000-5500 BP was limited owing to the absence of organic sediments and, instead, deposition was of in-channel sands. Peat formation began at c. 5500 bp , and these organic sequences contain evidence of the elm decline at 5010±70 BP and the lime decline at 3070±60 BP. The latter event was accompanied by forest clearance for Bronze Age agriculture and a consequent alteration to both the marsh and dry ground flora. Around 2500 bp the peats were submerged beneath estuarine muds as a result of further sea-level rise. A series of age/altitude points relating to Holocene sea-levels were constructed from the site data and were found to fit relatively well with current ideas of sea-level change in the post-glacial period. The results from Silvertown reflect data from shorter sequences in the London area, combining evidence of the Late glacial to early Holocene transition, with information on river development, changes in sea-level tendency and human-induced vegetation change.

Reversal of human-induced vegetation changes in Sequoia National Park, California

We resampled 76 permanent plots that had been established in the woodlands and forests of Sequoia National Park in 1969. Our objectives were to describe vegetation changes in the tree and shrub layers and determine the effects of prescribed burning that began in the 1960s. We compared changes in species importance and tree size class distributions between sample dates and between burned and unburned plots. Species composition had remained similar in all nine vegetation types sampled except in the ponderosa pine forest where Pinus ponderosa Dougl. ex P. & C. Laws. decreased in importance from 28 to 15% and Abies concolor (Gord. & Glend.) Lindl. increased from 18 to 31%. Structural changes were more common, as tree density decreased in the blue oak woodland (19%), and live oak woodlands (15%), as well as in ponderosa pine forest (41%), white fir forest (5%), giant sequoia groves (39%), and red fir forest (24%). Decreases in density were greater in burned plots but occurred in unburned plots as well, indicating that prescribed fire and self-thinning contributed to decreases in density. Tree density was unchanged in the lodgepole and subalpine forests, but increased in the Jeffrey pine forest (58%). The decreases in tree density represent a reversal of earlier trends.

Reversal of human-induced vegetation changes in Sequoia National Park, California

Reversal of human-induced vegetation changes in Sequoia National Park, California

A high resolution record of storm-induced erosion from lake sediments, New Zealand

The sustainable management of erodible pastoral hill country is a major focus of land use research in New Zealand. A multi-disciplinary study, using a high resolution lake sedimentation record, is being conducted to determine the role that cyclonic storms and natural and human-induced vegetation changes play in the erosion history of a landslide-prone hill country watershed.