Centre for Environmental Management

Major government funds have been allocated to revegetation of degraded catchments in Australia in order to enhance biodiversity, protect stock and improve water quality. However, the success or otherwise of the different restoration practices used has not been assessed. To redress this deficiency we audited these practices by measuring biotic and abiotic variables in two field surveys, one at a landscape scale and the second at a local scale. The landscape survey comprised 21 sites in western Victoria, a third of the sites were revegetated and were between 8 and 12 years old, a third carried remnant native vegetation and a third were degraded and not revegetated. In the local survey the results of the landscape survey were tested by sampling sites within a small area using the same methods but including pine plantations as an untreated site. Here we report on density and species composition of soil and surface active fauna, native and exotic Collembola and decomposition rates as measured with bait laminae. Fifty seven species of Collembola were found on the landscape survey and 47 on the local survey. Densities ranged from 17,000 to 45,000 m -2 in soil. In both the surveys we found decomposition was directly related to soil moisture and in the landscape survey exotic Collembola (Hypogastrura and Ceratophysella spp) to abundance of exotic grass species. MDS analysis of soil Collembola in the landscape survey placed remnant sites separate from the revegetated sites and untreated sites, which tended to cluster together. A suite of nine native Collembola species were found exclusively on remnant sites in the landscape survey. In the local survey, the revegetated sites, here with a ground cover of native not exotic grasses, were found to have nine characterising species, four of which were the same indicators as in the landscape survey. The pine plantations were dominated by acidophil exotic Collembola species. MDS analysis of pitfall data in local survey placed all sites in the same space, except for one remnant because of domination by the same exotic species as in the landscape survey. In contrast, MDS of the soil-core data separated all three treatments with the revegetated sites occupying the space between the remnants and the pines as in the landscape survey. When exotic species were removed, there was spatial separation of each treatment. We conclude that, in some circumstances, soil fauna of revegetated sites can develop characteristics of remnant sites in terms of native Collembola even after only 8 to 12 years. The bait lamina method must be used with caution as it is strongly influenced by soil moisture.

Gall induction by arthropods results in a range of morphological and physiological changes in their host plants. We examined changes in gas exchange, nutrients, and energetics related to the presence of stem galls on Parthenium hysterophorus L. (Asteraceae) induced by the moth, Epiblema strenuana Walker (Lepidoptera: Tortricidae). We compared the effects of galls on P. hysterophorus in the rosette (young), pre-flowering (mature), and flowering (old) stages. Gall induction reduced the leaf-water potential, especially in flowering stage plants. In young and mature stage plants, galling reduced photosynthetic rates considerably. Gall induction reduced the transpiration rate mostly in mature plants, and this also diminished stomatal conductance. Energy levels in most galls and in shoot tissue immediately below the galls were significantly higher than the energy levels in stem tissue immediately above the galls, indicating that the gall acts as a mobilizing sink for the moth. Galling had significant effects on concentrations of minerals such as boron, chloride, magnesium, and zinc. In galled plants, reduced leaf-water potential and reduced rates of photosynthesis, transpiration, and stomatal conductance may have altered mineral element levels. These observed effects demonstrate that E. strenuana has the potential to regulate P. hysterophorus.

Competition in a natural system may be interspecific or intraspecific. In semiarid ecosystems, competition for resources between established neighboring grass species and newly recruited seedlings is very high. To examine the effects of grass species density, growing space and time of establishment on Eucalyptus victrix seedlings (interspecific competition), and the effect of density and growing space within E. victrix (intraspecific competition) we conducted an experiment under controlled conditions. We tested four hypotheses (i) E. victrix seedling growth is not affected by grass density; (ii) there is no difference in E. victrix survival and growth between early and later grass establishment; (iii) interspecific competition is not more intense than intraspecific competition in E. victrix ; and (iv) growth of E. victrix seedlings is not dependent on available growing space. In a monoculture of E. victrix , seedling mortality was higher (10%) in large pots. In mixed culture pots, where E. victrix seedlings and grass seedlings were planted on the same day, E. victrix seedlings survived for up to 4 weeks, but started to die after week five in the smallest pots. However, mortalities occurred in pots of all sizes when grass was established before E. victrix seedlings. Results also indicated that the resources necessary for the growth of individual E. victrix seedlings were more limiting under conditions of increased density of neighboring grass species rather than intraspecific competition. In particular, photosynthetic area of E. victrix seedlings was drastically reduced in mixed cultures. Although density, pot size and time of planting had impacts on E. victrix seedlings, the patterns of these impacts were variable.

Many vegetation restoration works have been undertaken in Australia but only a few of those projects have been assessed for effectiveness. Revisiting earlier restoration attempts and analysing data from them is fundamental to the development of evidence-based prescriptions for future restoration work. Therefore, this study's objectives were to (I) compare plant species composition of different age direct-seeded revegetated sites and (II) determine the effect, if any, of different ages of revegetated sites on the natural recruitment of native plants. The study investigated four fenced restoration sites, dating from 2000, 2001, 2004 and 2005. Results showed that the density of plants surviving varied widely between plots of different ages. The highest density was found in the 2001 plot (2195Á.7 stems ha À1 ), followed by 2000 (1877Á8 stems ha À1 ), 2004 (197Á6 stems ha À1 ) and 2005 (195Á4 stems ha À1 ). An ANOVA showed that the overall amount of seed broadcast does not play a significant ( p ¼ 0Á437) role in the establishment rate. Overall, Eucalyptus ovata was found to be dominant in the 2000 (794Á4 ha À1 ) and 2001 (971 ha À1 ) sites. In contrast, Eucalyptus camaldulensis and Eucalyptus viminalis densities were highest in the 2004 (41 ha À1 ) and 2005 (60Á4 ha À1 ) sites, respectively. PERMANOVA showed highly significant differences in the present plant composition between plots ( p < 0Á0001), despite similar species mixes used in sowing. Recruitment was not found in any of the sites. The least weed cover and the highest litter cover were found in the 2001 plot. A similar trend was found in the 2000 plot. In contrast, high weed cover and low litter cover were found in the 2004 and 2005 plots. Since one of the major impediments to developing better restoration strategies is the inadequate documentation of past practices, studies such as these may shed some light on how the direct-seeded technique operates in a farm situation.

Deterioration in soil physical quality under intensive tillage practices is a norm rather than an exception. The objectives of this study were to (i) evaluate total porosity (TP) as an indicator parameter to assess the impact of banana cropping on compaction and infiltration in soils, and (ii) assess the effectiveness of different interrow grass-covers in minimising the deteriorating trends. Depth-incremented TP under banana rows and interrows from 4 sites, corresponding forest sites, and from 3 interrow grass-cover treatments were computed from bulk density measurements. The TP results show the compacted depth ranged from 0.35 to 0.45 m in banana rows and from 0.35 to 1.0 m in the interrows. The TP in 0.10 m depth increments decreased in the order: forest > rows > interrows, and was positively correlated with soil organic C (OC) and negatively with wheel traffic stress (WTS). The multiple regression analysis showed that 77% of the variability in TP was accounted for by clay + silt, OC, and WTS. We show that a threshold compaction index (DI t ) of 0.81-0.83 can be estimated from TP regardless of the soil type. Depending on the soil type and the cultural practices followed, infiltration decreased from 0.75 mm/s in rainforest to 0.23 mm/s under banana in 1 soil type compared with 2.55 mm/s in forest and 0.85 mm/s under banana in another. After 18 months of interrow grass-covers we found the deterioration in TP was minimum under the indigenous grass-cover but not under the 2 improved species. We conclude the interrow grass-covers were effective in minimising WTS associated compaction and reduction in infiltration.

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

Information regarding changes in soil condition after reforestation may help in inferring environmental and ecosystem benefits. A case study was undertaken in Victoria State, Australia, to investigate the changes in soil condition after reforestation of a deforested creek bank to infer environmental benefits. The study was conducted at four sites in a large farm. At each site a *150 m strip of land that ran perpendicular to a creek from the bank to cropping area was selected. The results show that total organic carbon (TOC) and total mineral nitrogen (TN) in the cropped segment (CS) of a strip at a given site were significantly higher than in the corresponding reforested segment (RS) which in turn was higher than in the bare segment (BS) whilst the electrical conductivity (EC) and bulk density (BD) were in the order BS [ RS [ CS. Six years after reforestation, TOC and TN in the RS increased by 30 and 24 %, respectively, compared with 9 and 8 % for 3 years. The EC, BD, and pH decreased by 26, 14, 14 %, respectively, 6 years after reforestation. Creek bank reforestation associated improvements in TOC, TN, BD, EC, and pH may have positive impact on pollutant and salinity abatement.