Action: Improve soil quality after tree planting (excluding applying fertilizer)
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- One of two randomized, replicated, controlled studies in Australia found that different soil enhancers had mixed effects on tree seedling survival and height, but no effect on tree seedling health. The other found that combinations of soil enhancers did not increase seedling survival, height, diameter or health.
Using soil enhancers (excluding fertilizers) can improve soil properties and may therefore enhance tree growth and biodiversity in degraded forest areas. However, it may also enhance growth of other undesired plants.
Supporting evidence from individual studies
A randomized, replicated, controlled study in 1995–2007 in a limestone quarry in Western Australia (Ruthrof, Bell & Calver 2009) found that adding a variety of soil enhancers together to the soil did not increase the survival, height, diameter or health of tree seedlings. Experiment one found that three soil enhancers did not affect survival (no data), height (soil enhancers: 0.06–7m; untreated: 4.4–5.2 m), diameter (soil enhancers: 0.3–12.9 cm; untreated: 4.6–7.8 cm) or health class (soil enhancers: 2–5; untreated: 3–4.4) of tuart Eucalyptus gomphocephala and Limestone Marlock E. decipiens seedlings. Experiment two found that adding three soil enhancers with fertiliser tablets did not affect survival (no data), height (soil enhancers: 1.6–6 m; untreated: 1.6–6.8 m), diameter (soil enhancers: 1.5–6.5 cm; untreated: 2–7.9 cm) or health (soil enhancers: 2.3–5; untreated: 3.5–4.5) of tuart, Limestone Marlock and coojong Acacia saligna seedlings. Experiment one consisted of four blocks each containing six plots (6 × 10 m). Experiment two consisted of four blocks each with four plots (5 × 6 m). In experiment one, treated plots received all but one of the following treatments: fertiliser tablets, added topsoil, sewage sludge and micronutrients (details see paper). In experiment two, treated plots received all four treatments. Half the plots in each experiment received one application of broadcast fertilizer (superphosphate: 400 kg/ha and potassium chloride: 100 kg/ha). Five seedlings of each species were planted/plot. After 12 years, the survival, height, diameter and health class (index based on stress, herbivory and nutrient deficiencies, 1: dead; 5: healthy) of all seedlings was assessed.
A randomized, replicated, controlled study in 2008–2009 in two sites in degraded tuart Eucalyptus gomphocephala woodlands in Western Australia (Ruthrof et al. 2012) found that adding soil enhancers (other than fertilizers) had mixed effects on tuart seedling survival and height but no effect on seedling health. At one site, seedlings were taller in plots treated with a biological stimulant for soil microbes (approx. 106 cm) than in untreated plots (approx. 82), but smaller where a clay-based amendment was added (approx. 63 cm; data taken from a graph). No other treatments had an effect on height (see paper for additional data). None of the treatments increased survival rate. At a second site, seedlings height and survival were higher in plots with fertilizer + moisture retaining chemicals (survival: 80%; height 39 cm) or fertilizer + moisture retaining chemicals + metal ion retaining agent (survival: 82%; height 37 cm) than in untreated plots (survival: 54%; height 28 cm). However, they did not differ from plots treated with fertilizer tablets (survival: 96%; height 50 cm). None of the other treatments had an effect on survival or height. None of the treatments had an effect on plant health class at either site. Each site had three blocks each with six plots (6 × 10 m) containing 20 tuart seedlings. Each plot received one of the following treatments: fertilizer tablets, a clay-based amendment, a biological stimulant for soil microbes, fertilizer + moisture retaining chemicals, fertilizer + moisture retaining chemicals + metal ion retaining agent, or was left untreated (for details see study, fertilizer treatments differed). After one year the survival, growth and health of all seedlings was assessed. Seedling health class was based on general vigour, crown density, colour and amount eaten by herbivores.
- Ruthrof K., Bell R. & Calver M. (2009) Establishment of Eucalyptus gomphocephala (Tuart) woodland species in an abandoned limestone quarry: effects after 12 years. Pacific Conservation Biology, 15, 278-286
- Ruthrof K., Douglas T., Calver M., Craig M., Dell B. & Hardy G. E. St J. (2012) The efficacy of soil ameliorants to improve early establishment in trees and shrubs in degraded Eucalyptus gomphocephala woodlands. Pacific Conservation Biology, 18, 310-318