Growing concern over encroaching tree line in Krkonoše Mountains
The Krkonoše Mountains are a beloved spot in Czechia, but recently, they have become the focal point of growing concern amongst environmental scientists. Movement in the tree line boundary of the mountains is threatening the existence of other important ecosystems, as environmental scientist at Charles University, Dr. Jan Tumajer, explained to us.
Can you explain what is being observed on the tree line of the Krkonoše Mountains?
“The tree line is a very important ecological boundary that separates the forest ecosystems from non-forest ecosystems like herbs-and-shrubs-dominated ecosystems. This line is determined by low temperatures. Above the tree lines trees lose their dominance, they cannot survive and they cannot compete with the simple forms of plants like herbs or shrubs. And because the temperature is increasing, the tree line tends to respond to this situation. In the Krkonoše Mountains, because the trees were stressed by low temperatures for a long time – it is a cause limit of their distribution – the trees respond positively in their growth dynamics to the current increasing temperature trends. So the tree ring width that we are currently observing in the Krkonoše Mountains is unprecedented in the last few decades or even centuries. Basically the tree ring width really went up in the last twenty years and compared to the previous period the tree rings are very wide. This means that the rising temperatures are stimulating the growth of trees there – they grow better.
“At the same time when we combine this analysis – of tree ring width – with some kind of intra-annual monitoring of growth when we are interested in the growth dynamics on the scale of individual days to weeks, we can see there is some kind of indication of drought stress, although the environment is very cold, we would expect with increasing temperatures it would be better for trees, but there is also some indication that during specific short term periods without rain during summer, the trees are stressed because they don’t have enough water to sustain their growth. This also means that there is also another process acting against the positive effect of increasing temperature, and it seems that it’s important that it increases over time. So it begs the question, whether this positive response of the tree line trees to increasing temperatures will be sustained over the next few decades.”
Why is this something we should be paying attention to in Czech society? Is this the most visible impact of climate change in Czechia?
“In general, tree line ecosystems are not very important in terms of spatial expanse in the Czech Republic. The majority of Czech forests are far from tree lines, and they have their own growth dynamics and problems. You would not imagine Czechia as a typical environment for tree lines. But the tree line impacts very important ecosystems. Basically ecosystems above the tree line like alpine grasslands and shrubs are very unique for the country because they hold some kind of plants that have been there since the glacial period. So if the tree line for instance tends to move upwards due to increasing temperatures, those alpine grasslands above the tree line will be significantly threatened because there is not much space for the alpine grasslands to exist.”
Why should we be concerned about the reduction of these alpine grasslands?
“There are many threatened fronts, and these environments host very specific biodiversity, they host plants and animals that can survive only in this environment, and they cannot adapt very quickly to increasing temperatures. So if there are habitat changes due to the tree line moving upward, the ecosystems can easily disappear from the Czech Republic. This is in contrast to the Alps, because we also have tree lines in the Alps and other high mountain ranges in Europe, but there the ecosystems above the tree line are quite large. If the tree line moved upward, there would still be lots of space for these ecosystems to survive. This is not the case in Czechia, because we have very small patches of these areas above tree line alpine ecosystems.”
