# Assessment of the Mass and Surface Area of the Scots Pine (_Pinus sylvestris_ L.) Needles
## 2 Materials and Methods
### Field and Laboratory Measurements  
The sample trees were chosen in such a way as to represent trees with different DBH (and thus with different crowns, heights, etc.). The DBH measurement of all trees on the plot was used to determine the number of sample trees. The 18 sample trees were selected based on the DBH distribution. The selection was made using the English method developed by [PERSON], based on the formula [53]:  
\[k=\frac{N}{n} \tag{1}\]  
wherein:  
\(N\)--total number of trees in a research area,  
\(n\)--assumed number of sample trees.  
Equation (1) yielded a number of 35 that indicated which tree should be filled. We began from one of the corners of the plot, and filled every \(k\)-th tree, so that the sample trees from which the needles were collected were evenly distributed over the entire plot [53]. The selected sample trees were filled in March before the start of the growing season. Each sample tree was measured to find its DBH, tree height (H), and length of the live crown (H\({}^{*}\)). All the branches with needles were taken from the crowns of the felled trees. They were separately labeled, weighed, and transported to the laboratory in big plastic bags. In the laboratory, the needles were removed manually from all the branches (without taking into account the needle age). The branches and needles were then weighed separately. The needles lose water rapidly, and their weight changes dynamically, while the weight of the branches is more stable. The weight of the needles for a sample tree was determined from the difference in the weight of the branches with and without the needles. The conversion factor of fresh pine needles weight to their dry weight was also figured out, and the number of needle pairs in the sample trees was established. To this end, random samples of the needles were taken from the upper, middle, and lower parts of the canopy immediately after felling the trees. The samples were placed into small airtight plastic bags and transported to the laboratory, where 1000 pairs of needles were counted and weighed for each sample tree. The dry matter of needles for each sample tree was calculated by subtracting from their fresh matter the weight lost measured after drying the needles at 105 \({}^{\circ}\)C in a forced-air circulation oven (Digitheat-TFT, [PERSON]; Barcelona, Spain). Both in the laboratory and field conditions, the branches and needles were weighed using a mobile electronic scale, max. capacity 60 kg and accuracy 0.01 kg (WPT 60C4 Radway, Radom, Poland). The 1000 needle pairs were weighed using an analytical balance, capable of weighing a maximum of 200 g with an accuracy of 0.001 g (WPT 2C Radway, Radom, Poland).  
The length of the needles (LN) was measured after collecting random samples for tests. Next, 200 needle pairs were taken from each test sample consisting of needles from individual crowns, and the longer fresh needle in each pair was measured with a ruler with an accuracy of 1 mm. The length measurement was completed before the lapse of two days from the time of the sample collection. The needles were kept at \(\sim\)16 \({}^{\circ}\)C until the measurements were performed.  
The surface area of needles (SN) for each tree was calculated using the procedure described below. Knowing the surface area of individual needles with different lengths [54], the total surface area of needles was calculated for each sample tree, taking into account the variation of needle mass, length, and number. For the 200 measured lengths of needle pairs from each sample tree, 11 length classes (\(number\)\(of\)\(classes=3/4\sqrt{n_{n}}\); \(n_{n}=200\) needle pairs) [55] were established, determining the middle of the class interval, the number of needles for each class, and percentage share. Next, the number of needles in each length class was calculated and their surface area was computed. Details on the calculation of SN can be found in our earlier work [3].