Tiiu Koff

Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling

We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1° × 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.

Impact of forest disturbance on the pollen influx in lake sediments during the last century.

The pollen accumulation rates of four lakes in different regions of Estonia were estimated in order to study the relationship between pollen influx and the character and intensity of disturbances in the pollen catchment area. The pollen influx data obtained are in accordance with model calculations on the size of the pollen source areas. The influx of arboreal pollen and that of the dominant taxa (mainly Pinus) in the lakes investigated shows that, in the case of small lakes (area 3-6ha) in a forested landscapes, the bulk of the pollen originates from an area within 100-200m around the lake. The distribution patterns of influx from two lakes situated close to each other but at different distances from forest fires show that past disturbances can be reliably detected when the disturbance occurred in the immediate vicinity of the lake and at least 25% of the local pollen source area was involved. In the case of a large lake (137ha) only fires embracing thousands of hectares can be detected in the pollen diagrams.

Pollen influx into Tauber traps in Estonia in 1997–1998

Modern pollen trapping data, obtained in the years 1997 and 1998 from 32 modified Tauber traps in different landscape regions of Estonia, are discussed. Preliminary analyses have revealed great variability of pollen influx values. The influx of arboreal pollen (AP) in 1998 was in general three to four times higher than in 1997. In both years, Betula and Alnus pollen dominated, accounting for up to 70% of total AP. The share of non-arboreal pollen (NAP) was much higher in pollen traps than in samples from lake and bog sediments and this reflects the influence of very local vegetation. Cerealia-type pollen influx values are closely correlated with the distance of the study site from the nearest field and also show the existence of some background values in the atmosphere.

Pollen analysis of honey from the Baltic region, Estonia

Abstract The present study reports the results of pollen analyses of Estonian honey collected from 2000 to 2011. Altogether, the pollen content of 325 honey samples was analysed with an average of 400 pollen grains counted in a sample. The main focus was on the floristic spectrum of plants and on the identification of the most common and important plant sources for honey. More than 120 pollen types were identified in the examined honey samples. The results showed that the pollen types of Rosaceae, Brassicaceae, Salix and Trifolium were the most abundant among the samples. The pollen of Apiaceae, Fabaceae, Asteraceae, Poaceae, Fagopyrum esculentum, Frangula alnus and Calluna were present in more than 25% of samples. Typical Estonian honey is polyfloral, the average number of species is 13 taxa per sample. During the study period, changes observed were that the percentage of the Rosaceae and Calluna pollen types had decreased, while the proportions of the Brassicaceae and Salix pollen grains showed an increase. The concentration of pollen grains per gram of honey varies from 100 to 700 000. The current information provides new insights into the pollen composition of Estonian honey and could be used to develop analytical standards for the pollen content of Estonian honey.

Possibilities for detailed dating of peat bog deposits.

Geochemical and palynological data as well as radiocarbon dating were used to study the peat bog deposits in Niinsarre bog, northeast Estonia. The aim of this study was to establish criteria for determining a detailed chronology, which is important, for example, in studying paleoevents and historical monitoring. In some cases, they can use cumulative pollen data, as well as cumulative chemical and peat bulk density data. Material was gathered for [sup 14]C dating from three parallel samples taken from cores ca. 10--20 cm apart using a Russian peat sampler. Samples for peat bulk density, palynological and chemical measurements were taken from the same cores. To measure peat bulk density, the authors used a continuous sampling method. Sampling frequency was calculated to cover layers formed over 50 yr.

Climate Change During the Holocene (Past 12,000 Years)

This chapter summarises the climatic and environmental information that can be inferred from proxy archives over the past 12,000 years. The proxy archives from continental and lake sediments include pollen, insect remnants and isotopic data. Over the Holocene, the Baltic Sea area underwent major changes due to two interrelated factors—melting of the Fennoscandian ice sheet (causing interplay between global sea-level rise due to the meltwater and regional isostatic rebound of the earth’s crust causing a drop in relative sea level ) and changes in the orbital configuration of the Earth (triggering the glacial to interglacial transition and affecting incoming solar radiation and so controlling the regional energy balance). The Holocene climate history showed three stages of natural climate oscillations in the Baltic Sea region: short-term cold episodes related to deglaciation during a stable positive temperature trend (11,000–8000 cal year BP); a warm and stable climate with air temperature 1.0–3.5 °C above modern levels (8000–4500 cal year BP), a decreasing temperature trend; and increased climatic instability (last 5000–4500 years). The climatic variation during the Lateglacial and Holocene is reflected in the changing lake levels and vegetation , and in the formation of a complex hydrographical network that set the stage for the Medieval Warm Period and the Little Ice Age of the past millennium.

Application of 14C data for the estimation of sphagnum peat increment in Estonian ombrotrophic mires

We calculated apparent increment values based on the radiocarbon dates of 21 Estonian ombrotrophic mires (raised bogs). For short periods, the values vary significantly, but the integrated increment for the total complex of ombrotrophic peat shows a strong increasing tendency with decreasing peat age. This is probably due to the decay of accumulated organic matter. Our hypotheses concern the mechanisms of decay and methods for increasing the reliability of the interpolation and extrapolation of (super 14) C data.

Vulnerability and Adaptation Assessments for Estonia

Because of its geography, wide coastal areas, water resources, forests, and wetlands, the environment of Estonia is sensitive to climate change and sea level rise. Therefore, the vulnerability and adaptation assessments focused on these sectors. This chapter gives preliminary results of our study. The CERES-Barley and SPUR2 models were used to assess crop productivity. A sea level rise of 1.0 m was used to evaluate the responses of the physical and natural systems in the low-lying coastal territories in the West Estonian Plain and the West Estonian Archipelago. To estimate the responses of forests to proposed climate change scenarios, two case study areas with different types of climate (continental and maritime) were selected and a modified forest gap model was used. In addition, an analysis was conducted using paleogeographical data from Estonia and neighboring areas. These data indicate that between 7,000 and 5,000 years ago (Holocene “climatic optimum’) the temperatures in Estonia were similar to predicted future temperatures. Thus we can compare the state of ecosystems in the past with those predicted for future global climate change.

Development of vegetation and human activities on the new emergent coastal areas of northwestern Estonia

The development of vegetation and agriculture on the uplifting coastal areas of northwestern Estonia was studied with palaeobotanical methods. On the basis of the land-uplift curves the dynamics of new land appearance was reconstructed. From these reconstructions, we could better understand the pollen and macrofossil records, though some taxa often interpreted as anthropogenic indicators (Ranunculus, Rumex, Chenopodiaceae) are in this case the indicators of pioneer vegetation. The comparison of historical, archaeological and palaeogeographical data from coastal northwestern Estonia demonstrate that the first strong signals about agricultural activity appear in different sections at different time: about AD 292 ± 55 in the northern area and about AD 1080 in the vicinity of Paslepa village.