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Understanding life history of natural forest and woodland is important as we need to prepare for, to cope with and to tackle problems associated with the ongoing global environmental changes. The present paper focuses on one of the world's terrestrial biomes, the arctic tundra, which is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. A severe threat to tundra is global warming, which causes permafrost to melt affecting species survival, and which releases soil-bound carbon in the form of greenhouse gases. Tundra vegetation is composed of dwarf shrubs, sedges and grasses, mosses and lichens - a woodland type of vegetation dominated primarily by birch shrubs. The aim of this paper is to summarize and highlight my thirty three years of genetic studies of birch woodlands in Iceland, from the discovery of introgressive hybridization in birch and estimating the extent of introgression, to uncovering past hybridization events since the end of the last glaciation about 9000 years ago. The studies use different approaches, from cytogenetic and botanical, to molecular and palynological. The overall results show clearly that hybridization between B. nana and B. pubescens is widespread in Iceland; the resulting gene flow via introgressive hybridization is bi-directional; and that the process is continuous through time and space. Iceland could be considered a birch hybrid zone, harbouring genetic variation which may be advantageous in subarctic regions. However, waves of hybridization associated with climate warming could drive one of the species into extinction. [ABSTRACT FROM AUTHOR]

This paper contributes to recent studies exploring the longue durée of human impacts on island landscapes, the impacts of climate and other environmental changes on human communities, and the interaction of human societies and their environments at different spatial and temporal scales. In particular, the paper addresses Iceland during the medieval period (with a secondary, comparative focus on Norse Greenland) and discusses episodes where environmental and climatic changes have appeared to cross key thresholds for agricultural productivity. The paper draws upon international, interdisciplinary research in the North Atlantic region led by the North Atlantic Biocultural Organization (NABO) and the Nordic Network for Interdisciplinary Environmental Studies (NIES) in the Circumpolar Networks program of the Integrated History and Future of People on Earth (IHOPE). By interlinking analyses of historically grounded literature with archaeological studies and environmental science, valuable new perspectives can emerge on how these past societies may have understood and coped with such impacts. As climate and other environmental changes do not operate in isolation, vulnerabilities created by socioeconomic factors also beg consideration. The paper illustrates the benefits of an integrated environmental-studies approach that draws on data, methodologies and analytical tools of environmental humanities, social sciences, and geosciences to better understand long-term human ecodynamics and changing human-landscape-environment interactions through time. One key goal is to apply previously unused data and concerted expertise to illuminate human responses to past changes; a secondary aim is to consider how lessons derived from these cases may be applicable to environmental threats and socioecological risks in the future, especially as understood in light of the New Human Condition, the concept transposed from Hannah Arendt's influential framing of the human condition that is foregrounded in the present special issue. This conception admits human agency's role in altering the conditions for life on earth, in large measure negatively, while acknowledging the potential of this self-same agency, if effectively harnessed and properly directed, to sustain essential planetary conditions through a salutary transformation of human perception, understanding and remedial action. The paper concludes that more long-term historical analyses of cultures and environments need to be undertaken at various scales. Past cases do not offer perfect analogues for the future, but they can contribute to a better understanding of how resilience and vulnerability occur, as well as how they may be compromised or mitigated. [ABSTRACT FROM AUTHOR]

ABSTRACT Vestra Gíslholtsvatn, a non-glacial lake in southern Iceland, provides a continuous high-resolution multi-proxy paleoenvironmental record spanning more than 10 ka. It is characterized by an interplay between volcanic and climatic controls on the lake sediment environmental proxies. Initial lake ontogeny was disrupted by deposition of the Saksunarvatn tephra (∼10.3 ka) followed by unusually slow ontogeny for 2 ka. Principal component analysis defines three climate zones between 8 and 1 ka. Quasi-stabilization and warm summer proxies between ∼8 and 5.7 ka define Holocene Thermal Maximum conditions. A subtle shift to cooler summers between ∼5.7 and ∼4.2 ka is interpreted as early Neoglaciation, intensifying after 4.2 ka. Following settlement of Iceland (∼1.1 ka) anthropogenic signals overprint the climate record. Throughout the record short-term variability is attributed to tephra fall events in the catchment from nearby explosive volcanism, whereas centennial- and millennial-scale changes are attributed to climate. When compared with other Icelandic lakes, environmental proxies from Vestra Gíslholtsvatn indicate less variability albeit similar timing of environmental change, suggesting a relatively stable flow of the Irminger Current along the south coast of Iceland compared with a more variable flow of warm Atlantic surface water along the western and northern coasts of Iceland after 8 ka. [ABSTRACT FROM AUTHOR]