Silvopasture, the intentional combination of trees, forage plants, and livestock together as an integrated, intensively-managed system, is an agroforestry practice improving landscapes throughout the world. There is a form of silvopasture, called intensive silvopasture, which has been experiencing rapid growth in tropical climates since its Australian beginnings in the 1970s (Cardona et al. 2014). Intensive silvopasture is the combination of healthy pastures with as many as 4000 nitrogen-fixing trees planted per acre. The trees are grazed along with the pasture, and livestock are rotated out of the paddock to let the trees and pasture recover. Although this system is proving itself a catalyst for significantly increasing food yields, and biological diversity in the tropics (Cardona et al. 2014), there are few temperate climate examples.
What would establishing a new cold-climate-intensive silvopasture system look like? To answer this question, we would need to consider many criteria, including cost to adopt the practice or species selection. Because of its many uses, including timber, honey-bee forage, shade for improved summer pasture, carbon sequestration, improving degraded soils, and even livestock fodder, the Princess tree (Paulownia tomentosa), may be an appropriate candidate. Princess tree is a deciduous tree native to China that has been planted all over the world including the northeast United States. Typically, it is known as an ornamental tree, or escaped exotic in the US, planted for its fast growth and lovely purplish spring flowers.
In most warm temperate zones, princess tree will grow into a tree, flower, and set seed. In colder climates like Vermont, New Hampshire, and Upstate New York, princess tree is a “die back perennial”. That is, the tree can grow as tall as 15 feet in the first year, yet be tender enough that the trunk gets frosted back to the roots. In succeeding years, the root will resprout shrubby, tender leaves, and be too young to flower and spread seed, overall acting like a natural coppice (Figure 1).
Let us consider some livestock, tree, and forage characteristics this intensive silvopasture might include:
- Long lived perennial tree or shrub adapted to cold temperate climates
- High nutrition and palatability value for ruminants
- Easy to propagate for low-cost installation
- Quick to establish and maintain grazable end of first year
Remember one of the key aspects to the intensiveness of this system is that the livestock are rotated through a paddock eating the pasture and the densely planted tree layer. Could princess tree replace the nitrogen fixing trees found in tropical systems? Princess tree is not a legume, but its leaves are very high in crude protein (25 percent) (Luske 2017). Being a 'C4' tree, princess tree is one of the fastest growing trees in the world. In terms of installation cost, princess tree is extremely simple to propagate by root cuttings, sprouted from seed, or active leaf-node cuttings.
Through farm observation and personal communications, I have learned that princess trees’ feed value would not be through direct browsing, although that has yet to fully tested, but by livestock eating the leaves once they fall off the tree in autumn. Thus, princess tree could be a summer rotation shade tree, reducing heat stress on the livestock and pasture, rotating the livestock back through in late fall or early winter to eat the high-protein leaves that drop to the ground (Figure 2).
Some readers might be wondering why not Black Locust, a livestock favorite, for intensive silvopasture? Black locust has some challenges, such as spreading by root suckers, having thorns, and eventually growing into a timber tree. Princess tree is an easier to manage, faster growing, and perennially available high-nutrient forage. Could there be other nitrogen-fixing shrubs or trees to use for cold-climate-intensive silvopasture? I encourage readers of this article to go out there and try experimenting with intensive silvopasture on a small scale, using Princess tree or not. I am excited to learn your results!
Cardona C et al (2014) Contribution of intensive silvopastoral systems to animal performance and to adaptation and mitigation of climate change. Revista Colombiana de Ciencias Pecuarias 27:76-94. http://www.scielo.org.co/scielo.php?script=sci_arttext&pid=S0120-06902014000200003 Accessed 11 February 2019
Luske B et al (2017) Online fodder tree database for Europe. Louis Bolk Institute. http://www.voederbomen.nl/nutritionalvalues/. Accessed 15 January 2019