Fertile soils contain organic matter and minerals suitable for plant growth. Some forests have nutrient rich soils which are well drained and contain a diversity of organisms. These fertile forests often lie on soils such as alluvial, alfisol, andosol, and riparian.
Rainforest
Temperate forests go through cold and warm seasons and have soil rich in weatherable minerals. In North America's Pacific coastal rainforests, a greater organic carbon content and cation exchange capacity allows the soil to retain more nutrients (Carpenter et al., 2014). Therefore, the soil under temperate rainforests tends to be of higher fertility compared to tropical rainforests.
In the UK, these temperate rainforest biomes are found along the western coast. The Ausewell Wood in Devon is home to dense woodland and a variety of tree species, such as oak, alder and birch. This humid environment is situated on loamy soil along the river Dart, a suitable habitat for the royal fern and ash-black slug (Woodland Trust).
Dark earthy Terra preta soils are anthropogenic and contain weathered charcoal. It is thought that indigenous populations added to ferralsol soil to improve land fertility for food production, in a manner to what modern agronomists are doing with biochar. Doughty et al., (2014) studied the carbon cycling of the Amazonia soil. It was found that trees grown from the fertile terra preta soils had a greater carbon fixation, therefore had a greater total net primary production which they allocated mostly to root growth.
Forest fungi
In a temperate forest made up of European Beech, a fungal group known as saprotrophic ascomycetes seem to thrive when soil fertility is high. However, fungal success correlated with increased respiration rates (Mayer et al., 2021). In boreal forests, basidiomycetes also thrive in fertile forest soil. Sterkenburg et al., (2015) showed fungi abundance is determined more so from soil pH and nitrogen, compared to soil carbon content.
Forests near waterbodies
Riparian forests grow alongside waterbodies; these fertile soils are thriving in species abundance and richness (Khan et al., 2022). Trees benefit rivers by reducing soil erosion, along with providing shelter and food for fish. Fallen branches shape the riverbed, in turn, creating habitat and reducing flooding. One type of nitrogen fixing tree, known as Alder, thrives on riparian soils, sequentially, increasing soil fertility.
Alluvial soils (soils deposited by slow-moving water) are nutrient-rich, they are formed from fine particle river deposits (Figure 1). A study in southern New Zealand found that riparian species grew at a variety of rates when soil fertility was high and where less light could reach the undergrowth (Coomes et al., 2009).
Figure 1: Riparian and alluvial soil
Alfisol soils (slightly acidic to basic soils with a clay subsoil) can be found in the Midwestern regions of south America, such as the Ohio river valley. These soils are rich in potassium, calcium, and magnesium, as they are not weathered away by extreme leaching (Kumar et al., 2016). These minerals are ideal for plant species to thrive, leading to the natural succession of a forest (primary colonisers through to mature trees).
Volcanic Forests Forests soils which surround volcanoes (e.g., Mt. Fuji) are high in minerals from lava and ash deposits, these soils are known as andosol soils (Figure 1). Two tree species which thrive in these fertile environments are the Southern Japanese Hemlock (Tsuga sieboldii) and the Hinoki Cypress (Chamaecyparis obtuse).
Figure 2: Andosol soils beneath a volcanic forest
Summary
Forests can grow on a variety of soils. The fertility of soil under temperate rainforests is normally higher than tropical climates. The addition of carbon rich soil to forests could increase carbon fixation. Though fungi abundance is more greatly influenced by pH and nitrogen. Volcanic and river deposits provide an abundance of minerals to soil. Plant species thrive from nutrient-rich fertile soil.
Reference
Carpenter, D.N., Bockheim, J.G., and Reich, P.F., 2014. Soils of temperate rainforests of the North American Pacific Coast. USDA-ARS / UNL Faculty, 1413.
Coomes, D.A., Kunstler, G., Canham, C.D. and Wright, E., 2009. A greater range of shade‐tolerance niches in nutrient‐rich forests: an explanation for positive richness–productivity relationships? Journal of Ecology, 97(4), 705-717.7-790.
Doughty, C.E., Metcalfe, D.B., da Costa, M.C., de Oliveira, A.A., Neto, G.F., Silva, J.A., Aragão, L.E., Almeida, S.S., Quesada, C.A., Girardin, C.A. and Halladay, K., 2014. The production, allocation and cycling of carbon in a forest on fertile terra preta soil in eastern Amazonia compared with a forest on adjacent infertile soil. Plant Ecology & Diversity, 7(1-2), 41-53.
Khan, N., Jhariya, M.K., Banerjee, A., Meena, R.S., Raj, A. and Yadav, S.K., 2022. Riparian conservation and restoration for ecological sustainability. Natural Resources Conservation and Advances for Sustainability, 195-216.
Kumar, V., Kant, S., Shikha, and Kumar, A., 2016. Morphological and pedological features of Alfisols. Agriways, 4(2), pp.159-167.
Mayer, M., Rewald, B., Matthews, B., Sanden, H., Rosinger, C., Katzensteiner, K., Gorfer, M., Berger, H., Tallian, C., Berger, T.W. and Godbold, D.L., 2021. Soil fertility relates to fungal‐mediated decomposition and organic matter turnover in a temperate mountain forest. New Phytologist, 231(2), 77
Sterkenburg, E., Bahr, A., Brandström Durling, M., Clemmensen, K.E. and Lindahl, B.D., 2015. Changes in fungal communities along a boreal forest soil fertility gradient. New Phytologist, 207(4), 1145-1158.
Woodland trust, N/A. Ausewell Wood. Available at: https://www.woodlandtrust.org.uk/visiting-woods/woods/ausewell-wood/ (accessed 16.06.2022)