Holocene climate, fire and vegetation dynamics at the treeline in the Northwestern Swiss Alps

Treelines are expected to rise to higher elevations with climate warming; the rate and extent however are still largely unknown. Here we present the first multi-proxy palaeoecological study from the treeline in the Northwestern Swiss Alps that covers the entire Holocene. We reconstructed climate, fire and vegetation dynamics at Iffigsee, an alpine lake at 2,065 m a.s.l., by using seismic sedimentary surveys, loss on ignition, visible spectrum reflectance spectroscopy, pollen, spore, macrofossil and charcoal analyses. Afforestation with Larix decidua and tree Betula (probably B. pendula) started at ~9,800 cal. b.p., more than 1,000 years later than at similar elevations in the Central and Southern Alps, indicating cooler temperatures and/or a high seasonality. Highest biomass production and forest position of ~2,100–2,300 m a.s.l. are inferred during the Holocene Thermal Maximum from 7,000 to 5,000 cal. b.p. With the onset of pastoralism and transhumance at 6,800–6,500 cal. b.p., human impact became an important factor in the vegetation dynamics at Iffigsee. This early evidence of pastoralism is documented by the presence of grazing indicators (pollen, spores), as well as a wealth of archaeological finds at the nearby mountain pass of Schnidejoch. Human and fire impact during the Neolithic and Bronze Ages led to the establishment of pastures and facilitated the expansion of Picea abies and Alnus viridis. We expect that in mountain areas with land abandonment, the treeline will react quickly to future climate warming by shifting to higher elevations, causing drastic changes in species distribution and composition as well as severe biodiversity losses.

Vegetation responses to rapid warming and to minor climatic fluctuations during the Late-Glacial Interstadial (GI-1) at Gerzensee (Switzerland)

High-resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to NorthGRIP. (1) A primary succession: The vegetation responded to the rapid rise of temperatures around 14,685 yr BP, with a primary succession on a decadal to centennial time scale. The succession between ca 15,600 and 13,000 yr BP included: (1.1.) The replacement of shrub-tundra by woodland of Juniperus and tree birch (around 14,665 yr BP) (1.2.) The response of Juniperus pollen to the shift in oxygen isotopes in less than 20 yr, (1.3.) A sequence of population increases of Hippophaë rhamnoides (ca 14,600 yr BP), Salix spp. (ca 14,600 yr BP), Betula trees (ca.14,480 yr BP), Populus cf. tremula (ca. 14,300 yr BP), and Pinus cf. sylvestris (ca. 13,830 yr BP). (2) Biological processes: Plants responded to the rapid increase of summer temperatures on all organisational levels: (2.1) Individuals may have produced more pollen (e.g. Juniperus); (2.2) Populations increased or decreased (e.g. Juniperus, Betula, later Pinus), and (2.3) Populations changed their biogeographical range and may show migrational lags. (2.4) Plant communities changed in their composition because the species pools changed through immigration and (local) extinction. Some plant communities may have been without modern analogue.These mechanisms require increasing amounts of time. (2.5) Processes on the level of ecosystems, with species interactions, may involve various time scales. Besides competition and facilitation, nitrogen fixation is discussed. (3) The minor fluctuations of temperature during the Late-Glacial Interstadial, which are recorded in δ18O, resulted in only very minor changes in pollen during the Aegelsee Oscillation (Older Dryas biozone, GI-1d) and the Gerzensee Oscillation (GI-1b). (4) Biodiversity: The afforestation at the onset of Bølling coincided with a gradual increase of taxonomic diversity up to the time of the major Pinus expansion.

A model-data comparison of Holocene timberline changes in the Swiss Alps reveals past and future drivers of mountain forest dynamics

Mountain vegetation is strongly affected by temperature and is expected to shift upwards with climate change. Dynamic vegetation models are often used to assess the impact of climate on vegetation and model output can be compared with paleobotanical data as a reality check. Recent paleoecological studies have revealed regional variation in the upward shift of timberlines in the Northern and Central European Alps in response to rapid warming at the Younger Dryas/Preboreal transition ca. 11700years ago, probably caused by a climatic gradient across the Alps. This contrasts with previous studies that successfully simulated the early Holocene afforestation in the (warmer) Central Alps with a chironomid-inferred temperature reconstruction from the (colder) Northern Alps. We use LandClim, a dynamic landscape vegetation model to simulate mountain forests under different temperature, soil and precipitation scenarios around Iffigsee (2065m a.s.l.) a lake in the Northwestern Swiss Alps, and compare the model output with the paleobotanical records. The model clearly overestimates the upward shift of timberline in a climate scenario that applies chironomid-inferred July-temperature anomalies to all months. However, forest establishment at 9800 cal. BP at Iffigsee is successfully simulated with lower moisture availability and monthly temperatures corrected for stronger seasonality during the early Holocene. The model-data comparison reveals a contraction in the realized niche of Abies alba due to the prominent role of anthropogenic disturbance after ca. 5000 cal. BP, which has important implications for species distribution models (SDMs) that rely on equilibrium with climate and niche stability. Under future climate projections, LandClim indicates a rapid upward shift of mountain vegetation belts by ca. 500m and treeline positions of ca. 2500m a.s.l. by the end of this century. Resulting biodiversity losses in the alpine vegetation belt might be mitigated with low-impact pastoralism to preserve species-rich alpine meadows.

Carbon storage versus albedo change: radiative forcing of forest expansion in temperate mountainous regions of Switzerland

In this study, we assess the climate mitigation potential from afforestation in a mountainous snow-rich region (Switzerland) with strongly varying environmental conditions. Using radiative forcing calculations, we quantify both the carbon sequestration potential and the effect of albedo change at high resolution. We calculate the albedo radiative forcing based on remotely sensed data sets of albedo, global radiation and snow cover. Carbon sequestration is estimated from changes in carbon stocks based on national inventories. We first estimate the spatial pattern of radiative forcing (RF) across Switzerland assuming homogeneous transitions from open land to forest. This highlights where forest expansion still exhibits climatic benefits when including the radiative forcing of albedo change. Second, given that forest expansion is currently the dominant land-use change process in the Swiss Alps, we calculate the radiative forcing that occurred between 1985 and 1997. Our results show that the net RF of forest expansion ranges from −24 W m−2 at low elevations of the northern Prealps to 2 W m−2 at high elevations of the Central Alps. The albedo RF increases with increasing altitude, which offsets the CO2 RF at high elevations with long snow-covered periods, high global radiation and low carbon sequestration. Albedo RF is particularly relevant during transitions from open land to open forest but not in later stages of forest development. Between 1985 and 1997, when overall forest expansion in Switzerland was approximately 4%, the albedo RF offset the CO2 RF by an average of 40%. We conclude that the albedo RF should be considered at an appropriately high resolution when estimating the climatic effect of forestation in temperate mountainous regions.

Middle to Late Holocene vegetation history of the Upper Engadine (Swiss Alps): the role of man and fire

o reconstruct the vegetation and fire history of the Upper Engadine, two continuous sediment cores from Lej da Champfèr and Lej da San Murezzan (Upper Engadine Valley, southeastern Switzerland) were analysed for pollen, plant macrofossils, charcoal and kerogen. The chronologies of the cores are based on 38 radiocarbon dates. Pollen and macrofossil data suggest a rapid afforestation with Betula, Pinus sylvestris, Pinus cembra, and Larix decidua after the retreat of the glaciers from the lake catchments 11,000 cal years ago. This vegetation type persisted until ca. 7300 cal b.p. (5350 b.c.) when Picea replaced Pinus cembra. Pollen indicative of human impact suggests that in this high-mountain region of the central Alps strong anthropogenic activities began during the Early Bronze Age (3900 cal b.p., 1950 b.c.). Local human settlements led to vegetational changes, promoting the expansion of Larix decidua and Alnus viridis. In the case of Larix, continuing land use and especially grazing after fire led to the formation of Larix meadows. The expansion of Alnus viridis was directly induced by fire, as evidenced by time-series analysis. Subsequently, the process of forest conversion into open landscapes continued for millennia and reached its maximum at the end of the Middle Ages at around 500 cal b.p. (a.d. 1450).

Reconstruction of Holocene vegetation dynamics at Lac de Bretaye, a high-mountain lake in the Swiss Alps

A deeper understanding of past vegetation dynamics is required to better assess future vegetation responses to global warming in the Alps. Lake sediments from Lac de Bretaye, a small subalpine lake in the Northern Swiss Alps (1780 m a.s.l.), were analysed to reconstruct past vegetation dynamics for the entire Holocene, using pollen, macrofossil and charcoal analyses as main proxies. The results show that timberline reached the lake’s catchment area at around 10,300 cal. BP, supporting the hypothesis of a delayed postglacial afforestation in the Northern Alps. At the same time, thermophilous trees such as Ulmus, Tilia and Acer established in the lowlands and expanded to the altitude of the lake, forming distinctive boreo-nemoral forests with Betula, Pinus cembra and Larix decidua. From about 5000 to 3500 cal. BP, thermophilous trees declined because of increasing human land use, mainly driven by the mass expansion of Picea abies and severe anthropogenic fire activity. From the Bronze Age onwards (c. 4200–2800 cal. BP), grazing indicators and high values for charcoal concentration and influx attest an intensifying human impact, fostering the expansion of Alnus viridis and Picea abies. Hence, biodiversity in alpine meadows increased, whereas forest diversity declined, as can be seen in other regional records. We argue that the anticipated climate change and decreasing human impact in the Alps today will not only lead to an upward movement of timberline with consequent loss of area for grasslands, but also to a disruption of Picea abies forests, which may allow the re-expansion of thermophilous tree species.

Mangrove cover in the Red Sea (1972-2013)

Across the Earth, mangroves play an important role in coastal protection, both as nurseries and carbon sinks. However, due to various human and environmental impacts, the coverage of mangroves is declining on a global scale. The Red Sea is in the northern-most area of the distribution range of mangroves. Little is known about the surface covered by mangroves at this northern limit or about the changes experienced by Red Sea mangroves. We sought to study changes in the coverage of Red Sea mangroves by using multi-temporal Landsat data (1972, 2000 and 2013). Interestingly, our results show that there has been no decline in mangrove stands in the Red Sea but rather a slight increase. The area covered by mangroves is about 69 km**2 along the African shore and 51 km**2 along the Arabian Peninsula shore. From 1972 to 2013, the area covered by mangroves increased by about 0.29%/y. We conclude that the trend exhibited by Red Sea mangroves departs from the general global decline of mangroves. Along the Red Sea, mangroves expanded by 12% over the 41 years from 1972 to 2013. Losses to Red Sea mangroves, mostly due to coastal development, have been compensated by afforestation projects.

Identification of Degraded Land in the Canary Islands; Tests and Reviews

Degraded Land is an area that either by natural causes (fires, floods, storms or volcanic eruptions) or more by direct or indirect causes of human action, has been altered or modified from its natural state. Restoration is an activity that initiates or accelerates the recovery of an ecosystem. It can be defined as the set of actions taken in order to reverse or reduce the damage caused in the territory. In the case of the Canary Islands there is a high possibility for the territory to suffer processes that degrade the environment, given that the islands are very fragile ecosystems. Added to this they are territories isolated from the continent, which complicates the process of restoring them. In this paper, the different types of common degraded areas in the Canary Islands are identified, as well as the proposed solutions for remediation, such as afforestation of agricultural land or landfill closure and restoration.

Vulnerabilidade à queda de árvores por meio de simulações microclimáticas

Muitos são os benefícios provenientes da arborização de vias públicas, como aumento da vida útil do asfalto por meio do sombreamento, filtragem de poluentes, absorção de CO2, interceptação da água da chuva e da radiação solar e mitigação de ilhas de calor; porém, por questões culturais, é considerada muitas vezes pela população como algo negativo, cujas folhas entopem calhas, raízes destroem calçadas, troncos e folhas atrapalham fiação elétrica e, principalmente, elas estão susceptíveis às quedas. A pesquisa teve como objetivo estudar o comportamento das quedas de árvores no município de Piracicaba/SP, Brasil, com atenção especial ao regime de ventos na cidade, baseado em dados fornecidos pelo Corpo de Bombeiros de Piracicaba, Secretaria de Defesa do Meio Ambiente de Piracicaba (SEDEMA) e Estação Meteorológica da Escola Superior de Agricultura \"Luiz de Queiroz\" (ESALQ). De caráter inédito, o principal resultado foi a relação direta entre quedas e zonas urbanizadas, que, em constantes alterações no uso do solo, acabam por danificar a sustentação das árvores (raízes), fato justificado pela alta concentração de quedas na parte central (36,7%), com destaque para as estações da primavera e do verão, ou seja, ventos e chuvas, na qual, juntas, somaram 78,0% do total. O período de retorno esperado para ventos superiores a 75 km h-1, classificados como temporais na Escala de Vento de Beaufort, foi de 2,8 eventos por ano. Enquanto verificou-se o predomínio de ventos alísios de sudeste, pertencentes ao quarto quadrante, a direção das rajadas de vento teve maior variação e, assim, com predomínio daqueles ventos, é recomendável instalações de parques industriais nas zonas norte, noroeste e oeste, haja vista a importância de evitar que os poluentes adentrem a cidade. As espécies de maior vulnerabilidade foram: Pachira aquatica Aubl. (monguba), Handroanthus sp. (ipê roxo) e Tipuana tipu (Benth.) Kuntze (tipuana). Por meio de simulação microclimática computacional, utilizando o programa ENVI-met versão 3.1, em dois estudos de caso, sendo um em bairro residencial e outro na Praça José Bonifácio, foi possível identificar locais de maior atenção quanto às quedas de árvores, em função da rugosidade do local, capaz de alterar a velocidade e a direção do vento.

Plantation timber on the island of Oahu, 1966 /

"This inventory supplements the initial Forest survey of the State completed in 1963."

A record of forest plantings in Hawaii.

"Literature cited": p.4.

Forest tree planting manual for Illinois : a manual dealing with the distribution and planting of forest tree seedlings for the production of timber crops and for the conservation of soil, water, and wildlife in Illinois.

Subtitle varies slightly.

Memoria sobre a necessidade e utilidades do plantio de novos bosques em Portugal ...

Mode of access: Internet.