The impact of deforestation and pasture abandonment on soil properties in the wet tropics of Australia

Abstract

Limited information exists on the changes in soil properties, particularly from the wet tropics of Australia, under long-term abandoned pasture, which was previously grazed and was established on deforested tropical rainforest. This information may be help in successful forest reestablishment. The objectives of this study were to assess the cumulative impact deforestation, grazed and abandoned pasture on selected soil physico-chemical properties from (i) an abandoned pastureland and (ii) a recently planted rainforest (PRF), planted in the abandoned pastureland. The experimental site is a field in the Northeast Queensland (NEQ) wet tropical region of Australia. This site was deforested approximately 70 years ago and brought under unfertilized grazed pasture for 30 years. Subsequently the grazed pastureland was abandoned and remains un-grazed for 40 years. A section of the abandoned pastureland was planted, 10 years ago, with native forest species, involving different combinations in five treatments in a completely randomised block design. A nearby undisturbed rainforest is used as the background against which assessment was carried out. Soil samples from 0-to 15-cm depth were collected in July 2000 and analyzed for nitrate-N, ammonium-N, total N, total soil organic C (SOC) and labile-C, pH (in water and CaCl 2 ), electrical conductivity (EC), exchangeable Ca, Mg, Na, K, and Al, and bulk density. Compared to the rainforest, the N and C concentrations of different forms under abandoned pasture and PRF were significantly less, exclusive of the total N under abandoned pasture. More specifically, the SOC under the abandoned pasture was 37,600 mg/kg compared with 74,800 mg/kg under rainforest and 27,000 mg/kg in the PRF. The exchangeable Al under rainforest was 8.5 c mol c /kg compared with 42.4 to 80.2 c mol c /kg under abandoned pasture and PRF. In general exchangeable cations (sum of Ca, Mg, K, and Na) under the rainforest were higher than the abandoned pasture. Soil under the abandoned pasture and PRF are more acidic by 0.5 to 1 units than the rainforest. Higher bulk densities under abandoned pasture and PRF led to 0.03% to 0.07% reductions in total porosities. Though we did not anticipate the soil under the abandoned pasture to recover 100% in 30 -40 years, the results indicate that 40 years under abandoned pasture or 30 years of abandoned pasture plus 10 years under PRF was not sufficient to bring about substantial improvement in soil properties comparable to the rainforest. This implies the resiliency of tropical soils, in general, to recover from deforestation and cultivation induced degradation is poor. D

Can Soil Organic Carbon Pools Indicate the Degradation Levels of Pastures in the Atlantic Forest Biome?

“…The results in Tables 3 and 4 show that the conversion of the forest sites for the establishment of pastures or agriculture can result in decreasing levels of SOC, as already reported in literature (Rasiah et al, 2004;Marchão et al, 2009;Benites et al, 2010). By contrast, some authors found that soils under pasture can show higher contents of SOC when compared to forest sites, which can be due to the management of pastures Oliveira et al, 2004;Martins et al, 2009).…”

Environmental benefits inferred from impact of reforestation of deforested creek bank on soil conditioning: a case study in Victoria, Australia

“…In this regard, the results from our study is unique in that they support the claim that creek bank reforestation led to the improvement in soil attributes. Interestingly, in the wet tropics of north Queensland, Australia, such improving trends were not explicit even 10 years after reforestation (Rasiah et al 2004). The discrepancy is attributed to the differences in soil and climate factors between the Victorian temperate and Queensland tropical environment.…”

“…Deforestation of native forest and grasslands for other uses, particularly for crop production and animal husbandry, has generally led to adverse effects on soil condition, transport of agricultural pollutants to streams, increases in salinity, losses in biodiversity, degradation of aesthetic values, and reduction in C-stocks (Lal 1981;Misra 1993;Islam and Well 2000;Liu et al 2002;McNeely 2004;Rasiah et al 2004;Schroth et al 2004;Millennium Ecosystem Assessment 2005;Montagnini 2006;Nair et al 2009;Mendez et al 2009;Kauffman et al 2009;Jose 2009;Zaman et al 2010). However, the recent trends regarding the inclusion of agroforestry in cropping systems, and reforestation of less productive marginal lands, bare stream banks, other bare strips and fence lines, together with the establishment of windbreaks using native species, are considered to be important in addressing landscape deterioration (Garrett and McGraw 2000;Brandle et al 2004;Garrity 2004;Jose 2009;Nair et al 2009).…”

A study of the effects of land use changes on soil physical properties and organic matter

“…In the first site, TP was lower in dry farming areas by 11.7 and 11.1% at 0-15 and 15-30 cm, respectively. A decrease of 3.88% was observed at a depth of 15-30 cm at the second site (Table II), which may be caused by tillage (Rasiah et al, 2004). Li et al (2007) showed that the BD and TP were significantly affected by land use.…”