Trees in big cities are adopted for the surrounded conditions more than the same species of wood put down their roots in the natural conditions. In other words, we are speaking again about influence of salt-affected soil, metal heavy, gases, etc.
Level of development for a tree was defined by the degree of its organs’ development, particularly leaves. We researched differences between the natural territory, for example, parks, green areas – the leaves were larger and contain less heavy metals there. Instead, leaves grown in the streets were not so.
We measured individual surface area. For this task we scanned leaves, put images into a PC software, it calculates shaded pixels, then these pixels were transferred to the area and this process took a lot of time.
By the way, we used unlicensed program. It seemed that it worked, brought some results but we cannot prove them and think that these results were accurate. This method was the simplest.
Other methods where scientific based, for example, “carving” method, when we were doing die-cutting of leaves but again it was not precision. Taking the leaf and die-cutting from the other leaf, the measurements are not the same.
Grid count method using millimetre graph paper bring the same results. Human error is presented: one person has seen a small square but other person has not seen. Measurements of leaf area are influenced by human factor too much.
Correlation index is also discussed in scientific literature but not works perfectly for our tasks.
In other words, individual leaf surface measurement was a very time-consuming and exhaustive work.
We had 6 variations with 3 replicates. In fact, one breed of tree gave 2400 leaves. We had 5 – 6 tree breeds. So we had to take 2400 leaves from each breed and measure leaf area of all leaves.
We spent 2 – 3 days for 1 variation. We have done only sampling and have not measured leaf area of all 2400 leaves but calculated the average measurement.
But with Petiole we measure area of 10 – 15 leaves in a minute.