Case study of past biodiversity loss

Plant fossils (mostly pollen, leaves, fruits, and wood) demonstrate that during the Quaternary Period (the past 2.6 million years) a number of tree genera progressively disappeared from Europe, while they persisted in East Asia and/or eastern North America.

A good example is the genus Tsuga (helmlock) which includes 11 living species which are found in Eastern and Western North America, Himalaya, China, and Japan.

Modern range distribution of worldwide hemlock species.

During a large part of the Quaternary, Tsuga was widely distributed in Europe and even a dominant tree in interglacial periods between 1.5 and 1 million years ago. Thereafter, it started disappearing until it was entirely gone from Europe around 500 thousand years ago.

Various hypotheses have been advanced to explain the extinctions of tree species from Europe, including:

•  the presence of barriers to migration in the form of west-east oriented mountain ranges (e.g., Pyrenees, Alps, and Carpathians), and,
• a much smaller area of forest vegetation persisting during glacial stages in Europe compared to North America and East Asia due to a considerable extent of glaciated and periglacial surfaces at high latitudes, and to dryness in the Mediterranean regions.

Studying the relationships between climate change and ecological traits, as well as the genetic characteristics of plants that went extinct in Europe during the Quaternary is important in terms of modern biodiversity conservation. This is because a better understanding of the ability of species to survive abrupt warming tells us what to expect in terms of biodiversity loss due to anthropogenic climate change.

Linking studies of modern biodiversity and ecosystem patterns with studies of past climate and ecological change offers important scientific advances in both reconstructing the climatic conditions under which past extinction events happened and inferring how present-day biodiversity patterns may be affected by anthropogenic climate change.