Stand thickness of dominant tree species in the State Forests divided into stand age classes over the years 2019-2023

Changes compared to version 1.0:

The data has been cleaned and organized using OpenRefine. A column with the average age of trees was added for each type of dominant tree species.The data has been cleaned and organized using OpenRefine.
A column with the average standing timber volume on afforested forest lands was added for each type of dominant tree species
The dataset contains data illustrating changes in the distribution of dominant tree species in the State Forests divided into stand age classes over the years 2019-2023. Dominant species can be defined as the species in the stand with the largest share in terms of area, thickness or number. Stand thickness means the gross thickness of the timber, i.e. the thickness of trunks and branches with a thickness of at least 7 cm at the thinner end when measured with bark.
It should be noted that this only concerns forests managed by the State Forests National Forest Holding.  the span of the age class is 20 years (e.g. age class I – tree stands up to 20 years old, class II – 21 – 40 years, class III – 41 – 60 years, etc.). The average age is determined as a weighted average, with the area in individual age classes and subclasses taken as the weight. The term forest area refers to the area of forests excluding land related to forest management. The main source of information for the study is the Forest Data Bank (www.bdl.lasy.gov.pl).
The dominant tree species included in the dataset are:

So - pine
Św - spruce
Jd - fir
Bk - beech
Db - oak
Gb - hornbeam
Brz - birch
Ol - black alder
Tp - poplar
Os - aspen

相较于1.0版本的更新内容如下：
本数据集已通过OpenRefine进行数据清洗与整理，并新增了针对每类优势树种的林木平均年龄列，同时新增了针对每类优势树种的造林地立木平均蓄积量列。
本数据集涵盖2019-2023年间，由国家森林控股公司（State Forests National Forest Holding）管理的森林中，按林分年龄组划分的优势树种分布变化相关数据。优势树种指在林分中，面积、材积或株数占比最高的树种。林分材积指林木总材积，即带皮测量时，较细端直径不小于7厘米的树干与枝条的材积总和。
需说明的是，本数据集仅涵盖由国家森林控股公司管理的森林。林分年龄组的跨度为20年，例如：年龄组I对应树龄不超过20年的林分，年龄组II对应21至40年的林分，年龄组III对应41至60年的林分，以此类推。平均年龄采用加权平均法计算，以各年龄组及子组的面积作为权重。本数据集所定义的森林面积，指森林自身的占地面积，不包含与林业管理相关的土地。本数据集的主要信息来源为森林数据库（Forest Data Bank，网址：www.bdl.lasy.gov.pl）。
本数据集涵盖的优势树种及其对应代码如下：
So - 松树
Św - 云杉
Jd - 冷杉
Bk - 山毛榉
Db - 栎树
Gb - 鹅耳枥
Brz - 桦树
Ol - 黑桤木
Tp - 杨树
Os - 山杨