Jacobs Ragwort will grow on pastures that are overgrazed, or been trampled by other means.
The source of this answer is a Dutch paper from the Louis Bolk Institute: 'Biology & Control of Jacobs Ragwort' by Merijn Bos.
At number 5.4, we find the note:
"In case of good composting (at least 4 days 60-70° C), any seeds lose their ability to germinate, so the material is no more toxic in a few weeks time."
And from the Dutch website 'Jacobs Ragwort, facts and fables', some facts here:
"All ragwort herbs and species like Jacobs Ragwort, including Butterbur and Senecio congestus contain pyrrolizidine alkaloids. These toxins can also be found in Comfrey. All over the world, there are about 6,000 plants that produce PA's, which is 3% of all flowering plants."
"Jacobs Ragwort is a biennial herb. In its first year rosettes are growing. These can be found throughout the year. Jacobs Ragwort flowers are usually formed in the second year (June to October). After the plant formed seeds in the second year, it dies."
Wich tells us, that the plant can be mowed best before it bears flowers, so that it can not spread.
"Live ragwort plants are eaten in exceptional cases only, or during food shortages. However in dried form animals do not recognize Jacobs Ragwort as a toxic plant. Ragwort poisoning may thus occur when it gets into hay, intended for consumption."
"After you mowed the field with Jacobs Ragwort, it is worth trying to sow Lucerne (Honey Clover), which also grows on bare and dry land. It makes the land to much fruitful for Jacobs Ragwort to grow. The competitiveness of ragwort is low. Ragwort is a pioneer and is followed within 2-5 years by numerous other plants, as long as the property is not mowed or grazed excessively."
So Jacobs Ragwort is not a real strong loan shark... It only grows where it can: on bare spots.