Laser will tell how fast trees grow
Polish scientists used forest measurements with a laser scanner attached to a plane to develop a new method for modelling tree growth. It can be used to measure tree height and growth rate in the entire Polish territory.
Until now, the estimation of tree growth in large areas of the country was imprecise and based on obsolete models, notes Prof. Jarosław Socha from the Faculty of Forestry of the University of Agriculture in Kraków. His team has developed a novel tree growth modelling method, which allows for such estimates. To develop the method , researchers used the results of aerial laser scanning.
"We are the first in the world to show that repeated aerial scanning allows to develop tree growth models" - says Prof. Jarosław Socha.
The new method was developed with funds obtained from the National Centre for Research and Development. It consists in performing laser scanning (at specified intervals), the results of which is a cloud of points containing the coordinates of the terrain surface and, among other things, the tops of trees. Then, the difference in the height of the trees and in their number is calculated. This allows to evaluate the growth of individual trees and entire stands.
"Laser scanning allows to develop local models and enables tree observations on tens of thousands of hectares, or even the entire Poland. Previously, it was impossible due to logistical reasons, it would also involve a huge amount of work" - says Socha.
Researchers now say that this process can be improved. It is enough to scan a part of the forest from the plane - and based on its analysis develop a model that will work for larger areas. Diagram of growth that emerges from the measurements of Prof. Socha`s team is universal for the entire area of Poland.
Until now, when trying to estimate the rate of tree growth, foresters primarily used tables developed for most species in the pre-war period, mainly by the German Forest Research Institutes. New research shows that those data are unreliable when it comes to the current conditions of tree growth. "The models were not consistent with reality, because due to the changing environmental conditions, the rate of tree growth has also changed" - Socha believes.
According to the model developed by Prof. Socha`s team, trees in Poland grow at a much faster rate than can be determined on the basis of tables - on average as much as 30 percent faster. Why? Prof. Socha mentions global warming as a contributing factor. As a result, the growing season is longer compared to previous decades. The second factor is the increase in the amount of nitrogen in soils.
New forest growth models can be updated based on further data from laser scanning. "This allows to more precisely determine the amount of carbon dioxide absorbed by forests. Using new models, foresters can also make better decisions about the amount of timber to be harvested. The amount of timber currently harvested in Poland is only slightly higher than half of the growth, which is why the richness of Polish forests continues to grow and is now more than twice as high as at the beginning of the 1970s" - Socha says.
The researcher adds that his team has already started to analyse factors that weaken the growth of tree stands, affecting their vitality and stability. "We conduct such research for trees such as spruces, which in some regions of Poland are weakened by droughts and woodworms, and consequently die" - he says.
Marcin Pierzchalski from the University of Agriculture in Kraków and Radomir Balazy and Mariusz Ciesielski from the Forest Research Institute also took part in the work related to the use of scanning for the tree growth measurement.
PAP - Science in Poland
author: Szymon Zdziebłowski
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