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Mycorrhizae impacts on trees in urban landscapes

There are numerous studies showing that inoculation of pine and some other seedlings with mycorrhizae-forming fungi at planting improved tree survival and growth on many cut-over forested sites and strip mines (Marx and Cordell, 1989). There are few published studies on inoculating landscape-sized trees at planting.

One showed that shoot growth of 27-liter (7 gal) container-grown Mesquite (Prosopis alba) was inhibited, and trunk diameter and root growth not affected by inoculating with mycorrhizal-forming fungi at planting (Martin and Stutz, 1994). A second study showed that inoculating the backfill soil for field-grown Tilia tomentosa trees with an 8 cm (3 in) trunk diameter at planting had no effect on shoot growth the first two years, increased shoot growth the third year by 28 cm (11 in), and had little effect the fourth year after planting (Garbaye and Churin, 1996).

Trunk diameter increased by 3 mm (0.1 in) over a four year period when mycorrhizae-forming fungi were added to the backfill soil. There was little or no consistent impact on foliage mineral content. Gilman (2001) found no impact on tree survival or growth from adding spores of mycorrhizae-forming fungi to the backfill soil around recently transplanted trees.