Actinorhizal Trees Useful in Cool to Cold Regions

Tom Miles

Actinorhizal Trees Useful in Cool to Cold Regions
NFT Highlights,NFTA 86-03, May 1986, FACTNEt, Winrick International

A class of plants that helped develop soil on glaciated sites in the past has a future in agroforestry and land reclamation projects of today and tomorrow. These plants are known as actinorhizae, as they are nodulated by the nitrogen-fixing actinomycete, Frankia These predominately temperate trees are especially useful in areas where the mostly tropical woody legumes can not live or thrive.

Actinorhizal plants have been used historically to increase fertility in agricultural systems. Lack of knowledge about the group's ecology prevents more widespread user but the trees are currently used in the following four ways:

1. As a primary crop for timber and pulpwood (Alnus, Casuarina spp.)
2. As an interplanted "nurse" plant for other, more valuable species (Elaeagnus spp.)
3. As a component of a multipurpose agroforestry plantation (Casuarina spp.)
4 As a plantation for soil reclamation (Elaeagnus, Shepherdia, Purshia spp.)

Actinorhizal plants can contribute as much nitrogen per hectare as the most productive legumes (Torrey, 1978). A Senegal study estimated that casuarina fixed 288 kg/N/ha/yr (Gauthier et al., 1984). Alders accumulate between 40 to 200 kg/N/ha/yr, with maximum accumulations of up to 320 kg/ha/yr (Silvester, 1977).

Frankia is present in adequate amounts in most ecosystems for natural nodulation to occur. Inoculation might be necessary in disturbed soil, arid environments or sites where actinorhizal plants are not native. Pure cultures for many of the most important actinorhizal species are now available.