Tips for planting trees in pig paddocks

Video about the effects of trees in pig paddocks and important aspects to take into consideration prior to planting trees (in Danish).

Animal welfare is improved among other reasons because trees and bushes provide shade for the pigs in summer as well as shelter from wind and rain in colder periods of the year. Furthermore, trees pro ide the animals a mean to perform skin care. Pigs like to rub themselves against trees and bushes, especially after wallowing. The rubbing behaviour serves several purposes: excess mud from wallowing is removed and so are hair, skin flakes and ectoparasites. It has also been suggested that pigs, by rubbing themselves against specific tree species, utilize the tree's resin to repel lice and ticks.

Photo: It is recommended to combine shade and wallows and to keep approximately one-meter distance between trees and wallows to prevent soil erosion and exposure of tree roots. 

By planting trees and shrubs, the complexity of pig paddocks is increased. Experiences from designing animal enclosures in zoos suggest that complexity can be used to enrich the housing conditions thereby improving animal welfare.

Flowering native species of trees and shrubs are particularly helpful with regards to enhancing biodiversity. Furthermore, trees and shrubs effectively take up nutrients from the soil thereby reducing the environmental impact of pigs.

Not all tree species are equally suitable

Willow and poplar are the most frequently planted trees in fields for Danish organic pigs. However, it is uncertain whether these species are best suited with respect to improving animal welfare and reducing nutrient leeching from the paddocks. Therefore, the Innovation Centre for Organic Farming initiated collaboration with forest and landscape engineer Peter N. Jensen and Rasmus H. Jørgensen, University of Copenhagen, to investigate the suitability of alternative tree species for pig paddocks.

The exploratory behaviour of pigs is one of the major challenges with regards to planting trees in paddocks for pig as the trees may be severely damaged by the animals. Incidences of damage to eight selected tree species (maple, oak, elm, hazel, cherry, field maple, lilac and hawthorn) in hedgerows which gestating sows have had access to for about ten years as well as in hedgerows without sows have been investigated.

Bark damage and regrowth reveal when it is necessary to protect a tree

Pig producers can protect the trees from pigs by fencing off trees if the damage becomes too severe or if a tree attempts regrowth.

Video (in Danish): There are several good reasons for planting trees in paddocks with pigs, but the pigs may be rough on trees and bushes. It is a good idea to be aware of what is needed to take good care of the plants. 

Bark damage may be used as an indicator of how pigs interact with trees. The tree’s ability to regrow (tree suckers and watersprouts) demonstrates the tree's ability to survive/reestablish itself. Pig producers may take note of these attempts to assess whether it is time to move pigs away from an area with trees to ensure tree survival, or whether it is time to fence off individual trees to allow regrowth.

Trees with bark damages are able to survive as long as the tree is not debarked all around the trunk. If major bark damages occur, it is advisable to move the pigs out of the paddock to allow trees to heal. 

Certain tree species attempt regrowth by producing tree suckers and watersprouts. This applies, for example, to for maple, elm and lilac. If attempts at regrowth are protected (e.g. by fencing off trees or removing the pigs and allowing the trees to rest) then the suckers and watersprouts can become new trees trunks and branches. 

Pigs like to rub themselves against the trees, which can leave marks on the bark but this behaviour does not cause damage to the tree.

Trees with peeling bark generally tend to be exposed to more extensive bark damages as the pigs may tear off a big piece of bark by ripping a small strip.