Hur kopplad är asp till tidigare jordbruksmark?
en studie av aspförekomst och tidigare markanvändning i fem län i Mellansverige
Aspen (Populus tremula) is a tree that is important for biodiversity. It is a pioneer tree that is favored by much light. It is possible that aspens that regenerated on agricultural land have a different importance for biodiversity than aspens that regenerated in forests, since their conditions have been different. By studying how the land use have changed you can see how many of today?s aspens regeneretad on agricultural land. This paper studies three questions and includes five regions (Stockholm, Uppsala, Västmanland, Örebro and Värmland):
* How has the land use changed from the time the historical map was made (1860-1911) until now?
* Is aspen more frequent in today?s forests on land that used to be agricultural land than coniferous trees are?
* How many percent of today?s aspens have grown up on land that used to be agricultural land?
A historical map was used to analyse the land use, separated into forest, agricultural land and the border between agricultural land and forest. Data from the Swedish National Forest Inventory were used, including plots with an age of the forest of 70 years or more, and more than 10 % aspen or with 0 % aspen and more than 90 % spruce and/or pine.
The percentage of agricultural land and forest were compared on the historical map and on the modern map to analyse how the land use had changed. The agricultural land had decreased in all the regions while the forest had increased.
The results show that aspen is more frequent on land that historically was agricultural land compared to spruce and/or pine. The percentage of aspen that regenerated on agricultural land is higher in the forest regions Värm-land (30,8 %) and Örebro (23,5 %) than in the agricultural regions Stockholm and Uppsala, while the agricultural land has decreased equally in all the regions. A possible reason is that small meadows and fields have been abandoned in Värmland and Örebro, but farms have merged and become bigger implying a small change in the total area of agricultural land. Aspen can establish quickly on abandoned agricultural land, which leads to a high percentage on old fields and meadows.