The surprising role of northern trees
25 – 50% of a living tree is water, depending on the species and the season. Until recentlythe water in the trees was seen as insignificant but resent work of thje university of Fairbanks (Alaska, USA) has shown that this water is very important, anyway in the northern forests The absorption of meltwater by the deciduous trees plays a big role in the water cycle of the boreal forests
the findings are very important for our understanding of the hydrology and ecology of the boreal forests ans give us insight in factors like
the water content of the soils, the availability of fresh water, the health of the trees and especially on the way trees influence the local weather, and especially the occurrance of thunderstorms. All of these are important for understanding the occurrance and frequency of forestfires.
rees absorb water from the soil and eventually give it to the atmosphere through theis leaves or needles. The scientists measured the water content of the conifers and the deciduous trees in different areas and different seasons
They discovered that deciduous trees take up enormaous amounts of water in the period between the melting of the snow and the sprouting of the leaves. They absorbed 21 – 15%of the available melting water – untill they are completely saturated. In the boreal forests of Alaska, and western Canada this means 17 – 20 billion cubic meter or about 8 million Olympic swimming pools.
They also measured the transpiration of the trees. The deciduous trees transpired 2 – 12% of the water immediately after the sprouting of the leaves. This short period if strong traqnspiration causes stronger convection in the air and thus thunderstorms – often the start of forest fires in these thinly populated regions
It is important to calculate how much water the trees can absorb. The number of deciduous trees will probably grow 1 – 15% in the next century – and thus the absorption of meltwater.
This is the first showing that the absorption of meltwater plays a big – as yet unseen – rolein the northjern water cycle Insight in the dynamics of absorbed water is needed to understand the reactions of trees on drought and factors like hunidity of soils and climate. The boreal forests are important, they cover 11% of the landsurvice of the planet and 25% of the closed foliage on earth
Northern forests give rain – and forest fires
The aspen is one of these northern deciduous trees, growing around the north Pole in both eurasia and northern america (the american type is Populus tremuloides, the Eurasian for is Populus tremulus). The aspen is – after the pine tree – (Pinus sylvestris) the most widely distributed tree in the world: from Iceland and Ireland to Kamtsjatka and Japan, but also more south in the Pyrenese mountains and the Atlas mountains in northewest Africa. This is thanks to its great tolerance for different hardships like frost, shadow, water, wind and competition.
The aspen can grow in cold climates because it has some special tricks. One of them is the rattling leaves (it is also called quaking aspen or trembling aspen): its thin flexible flattened petioles make the leaves move easily with the wind, This makes the tree unsensible for hard winds and storms. But the most important trick is its ability to recover quickly after a forest fire. It can take over whole areas where pine and spruce don not manage to survive. They can do this because they have long horizontal roots that can grow new sprouts. Other northern trees like the paper birch can do the same, but aspen can grow roots 80 meter long. If the forest burns in spring or summer the organic topsoil also burns and everything dies, but when the fire is in winter or early spring, the soil is frozen and/or saturated with water. In thet case the aspen roots can survive and quikcly give new sprouts