Mycorrhizal associations as indicators of forest quality after land use practices

Abstract

Counting mycorrhizal infective propagules (spores, fruitbodies, colonized roots) in forest soils was used to assess impacts of shifting cultivation and selective logging on habitat partitioning and abundance of inoculum of arbuscular mycorrhizal and ectomycorrhizal fungi in south Cameroon. Intact soil cores, disturbed soil samples and fruitbodies were collected from late successional forest stands inside and outside the crown projection of ectomycorrhizal clumps, early successional forest stands, fallows of Chromolaena odorata with and without Gnetum lianas, fields of food crops, forestry practices including skid trails and bare soil landings. Fractional mycorrhizal colonisation was assessed by the gridline intersect method. Spores of arbuscular mycorrhizal fungi were extracted by the wet-sieving and decanting method followed by sugar centrifugation and counted under microscope. Fruitbodies of ectomycorrhizal fungi were collected, described in fresh state, dried before microscopic examination and identification. Due to creation of skid trails, landings and forest roads, selective logging had a very large negative impact on both ectomycorrhizae and arbuscular mycorrhizae (AM) whereas shifting cultivation had only a slight positive effect on arbuscular mycorrhizas and a negative effect on ectomycorrhizae. Both types of mycorrhizal inocula were differently partitioned: AM inoculum was continuous throughout the landscape while ectomycorrhizal inoculum was patchy, suggesting the need for different management approaches for both arbuscular mycorrhizal and ectomycorrhizal forest patches. Ectomycorrhizal forest clumps indicated least disturbed forest stands. Owing to their specific biodiversity, they should be included as indicators of sustainable forest management; Carpophores of ectomycorrhizal fungi classify as sub-indicators in the principles, criteria and indicators of African Timber Organization/International Tropical Timber Organization (ATO/IITO).