Boreal (age) - Flora

Flora

During the Pre-Boreal pollen zone IV, large quantities of tree pollen began to replace the pollen of open-land species, as the most mobile and flexible arboreal species colonized their way northward, replacing the ice-age tundra plants. Foremost among them were the birches, Betula pubescens and Betula pendula, accompanied by Sorbus aucuparia and Quaking Aspen, Populus tremula. Especially sensitive to temperature changes and moving northward almost immediately were Juniperus nana and J. communis, the dwarf and shrub Juniper respectively, which reached a maximum density in the Pre-Boreal, before their niches were shaded out. Pine soon followed, for which reason the resulting open woodland is often called a birch or a pine-birch forest.

In the yet warmer early Boreal pollen zone V, Corylus avellana (hazel) and pine expanded into the birch woodlands to such a degree that palynologists refer to the resulting ecology as the hazel-pine forest. In the late Boreal it was supplanted by the spread of a deciduous forest called the mixed-oak forest. Pine, birch and hazel were reduced in favor of Quercus, Ulmus, Tilia and Alnus. The former tundra was now closed by a canopy of dense forest. In the marshland Typha latifolia prevailed. Less cold-tolerant species such as ivy and mistletoe were to be found in Denmark.

• Corylus coppice

• Typha latifolia

• Oak forest

• An alder forest at Strömsinlahti, Roihuvuori, Helsinki