Читать книгу North American Agroforestry - Группа авторов - Страница 88

Damage to trees from associated animal species in certain agroforestry practices such as silvopasture can be substantial. Browsing animals such as goats, sheep, or deer are more likely to eat foliage, while large ruminants such as cattle are more likely to trample young trees. Generally, younger animals are more likely to damage trees than older, more experienced ones (Nowak, Blount, & Workman, 2002). Any browsing of the terminal shoot may result in deformity and loss of growth. Similarly, physical damage to bark or stem can result in loss of vigor and eventual death of saplings and young trees (Jose & Dollinger, 2019).

In a young silvopastoral system in Missouri, Lehmkuhler et al. (2003) reported significant damage to tree seedlings during the second year after planting when cattle were introduced. Seedlings that received protection using electric fencing were mostly undamaged (Figure 4–4). In a study in the Swiss Alps, Mayer, Stockli, Konold, and Kreuzer (2006) assessed cattle damage on naturally regenerated young Norway spruce [Picea abies (L.) Karst] following a summer grazing period. They observed that 4% of the young trees were browsed on the apical shoot, 10% were browsed on lateral shoots, and 13% of the trees showed other damage. The percentage of browsed or damaged (physical damage such as breaking seedlings or trampling) trees was positively correlated with the cattle stocking rate (livestock units per hectare) (Figure 4–5). This suggests that higher cattle stocking rates not only increase browsing pressure but also the risk of unintentional trampling of trees.

Damage or injury to animals as a result of trees can also occur in silvopastoral systems. In a recent survey of silvopastoral farmers in the northeastern United States, Orefice, Caroll, Conroy, & Ketner (2017) reported that farmers were concerned about falling tree branches as health risks for the animals. They also reported at least two forms of livestock injuries, one resulting from cows’ tails being caught and torn off by woody vegetation and the other relating to hoof injury to pigs.

Fig. 4–4. Extent of damage to trees by cattle during second year after planting with and without electric fence protection in a silvopastoral system in Missouri

(based on data from Lehmkuhler et al., 2003).

Fig. 4–5. Relationships between cattle stocking rate (livestock units, LU) and percentage of browsed trees, otherwise damaged trees, and the sum of browsed and otherwise damaged trees

(modified from Mayer et al., 2006).