Rehabilitation of mine sites in semi-arid landscapes is hindered by poor quality mine waste substrates, a byproduct of mining used as alternative growth media. Inorganic soil amendments, such as gypsum and urea, are sometimes used to improve the chemical and physical quality of mine waste substrates and increase native plant establishment. However, limited research is available regarding the medium and long-term effectiveness of these amendments in semi-arid post-mining landscapes. In this study, inorganic amendments were incorporated into two alternative mine substrates (mine waste and a topsoil:waste blend) in large 0.8 m(3) above-ground mesocosms in the semi-arid Pilbara region of Western Australia. These mesocosms were bare soil or seeded with one of two different mixes of plant species to determine how amendments and species diversity altered plant growth and survival, and substrate quality compared to stockpiled topsoil over a 21-month period. The unamended waste had a lower electrical conductivity (EC), soil carbon (C), soil nitrogen (N) and C/N ratio compared to the topsoil. The amendments had a strong initial effect on soil quality, increasing N, soil EC and N-mineralisation in the amended waste compared to all other soil treatments. However, N levels returned to non-amended levels after the first year and the amendments had limited influence on plant growth. Plant survival was higher in the amended substrates with the more diverse plant community, which increased substrate microbial activity to levels significantly greater than the unamended waste. The use of inorganic amendments may be ineffective at increasing long-term substrate quality and growth of native plants but may support seedling survival that in turn will improve soil chemical and biological properties of waste substrates.

AbstractRecruitment for many arid‐zone plant species is expected to be impacted by the projected increase in soil temperature and prolonged droughts associated with global climate change. As seed dormancy is considered a strategy to avoid unfavorable conditions, understanding the mechanisms underpinning vulnerability to these factors is critical for plant recruitment in intact communities, as well as for restoration efforts in arid ecosystems. This study determined the effects of temperature and water stress on recruitment processes in six grass species in the genus Triodia R.Br. from the Australian arid zone. Experiments in controlled environments were conducted on dormant and less‐dormant seeds at constant temperatures of 25°C, 30°C, 35°C, and 40°C, under well‐watered (Ψsoil = −0.15 MPa) and water‐limited (Ψsoil = −0.35 MPa) conditions. Success at three key recruitment stages—seed germination, emergence, and survival—and final seed viability of ungerminated seeds was assessed. For all species, less‐dormant seeds germinated to higher proportions under all conditions; however, subsequent seedling emergence and survival were higher in the more dormant seed treatment. An increase in temperature (35–40°C) under water‐limited conditions caused 95%–100% recruitment failure, regardless of the dormancy state. Ungerminated seeds maintained viability in dry soil; however, when exposed to warm (30–40°C) and well‐watered conditions, loss of viability was greater from the less‐dormant seeds across all species. This work demonstrates that the transition from seed to established seedling is highly vulnerable to microclimatic constraints and represents a critical filter for plant recruitment in the arid zone. As we demonstrate temperature and water stress‐driven mortality between seeds and established seedlings, understanding how these factors influence recruitment in other arid‐zone species should be a high priority consideration for management actions to mitigate the impacts of global change on ecosystem resilience. The knowledge gained from these outcomes must be actively incorporated into restoration initiatives.

Global environmental changes and other anthropogenic impacts are rapidly transforming the structure and functioning of ecosystems worldwide. These changes are leading to soil degradation with an estimated 25 % of the global land surface being affected. The need to develop cost-effective large-scale solutions to restore disturbed landscapes becomes imperative to preserve biodiversity and achieve ecosystem functionality and sustainability. As part of a large-scale industry-academia partnership, we have developed a soil research program that aims to build knowledge and design strategies to restore degraded landscapes in Western Australia and other dryland regions worldwide. Within this program, a series of laboratory experiments, glasshouse studies, and field trials, have been conducted over the past six years to advance our knowledge on soil limitations and to provide solutions to enhance soil carbon levels and restore above and belowground biodiversity in restoration programs. These studies include (i) the analysis of the influence of multi-species planting on soil organic carbon and microbial activity and diversity (ii) the evaluation of soil physicochemical and microbiological indicators to assess functionality of restored soils in degraded semiarid ecosystems and (ii) the development of nature-based strategies based on bio-tools (e.g. inoculation of soil biocrust cyanobacteria) to increase soil carbon and enhance overall soil function. In this presentation we will highlight some key findings of these studies that include the benefits of combining diverse plant species and using native microbes and organic amendments for increasing soil carbon and promote soil function in reconstructed soil substrates. We will also discuss the potential applicability of these bio-technological approaches in landscape-scale restoration programs.

Soil degradation and conservation is an environmental, social, economical and cultural issue concerning the wellbeing of all humankind. With one-fifth of the world's soils currently degraded, and continuing to degrade at a rate of 5-10 billion hectares annually, the burden and responsibility of addressing soil conservation and managment falls on every individual; farmer, land owner, indigenous community, politician, scientist, worldleader and the general public. The causes of soil degradation are multifaceted with natural and anthropogenic drivers of global change creating a reduction in soil function, ecosystem services and land productivity, resulting in the deterioration of the social and economic framework of society. To combat land degradation among other issues, the United Nations General Assembly created 17 Sustainable Development Goals (SDGs) as part of the "2030 Agenda for Sustainable Development". These goals highlight the importance of soil conservation by uniting landholders globally to achieve Zero Net Land Degradation. However, these SDGs are only the first step in identifying the issues associated with land degradation and future targets. Further consideration of soil indicators along with landholder engagement is required to evaluate the progress of sustainable land. Governments and scientists need to nurture collaboration with farmers, create policy that supports and strengthens sustainable land management and increase knowledge sharing at all levels of governance and in the education system. Through coordinated, collaborated and sustainable management of our soils we can create resilient and productive landscapes capable of supporting a growing human population in the context of global change.

In a time when global climate variability threatens the sustainability and productivity of arid ecosystems, the development of effective strategies to recover and protect soil resources and biota is crucial for the survival of these landscapes. With 20% of arid systems degraded and estimates of up to 10 Mha of land degrading each year, this issue is of global importance. In the semi-arid Pilbara region of north-west Western Australia, climatic projections suggest reductions in annual rainfall and high unpredictability of rain events. However, as these ancient landscapes are already degraded due to meteorological processes and anthropogenic activities, such as mining, the rehabilitation of this land is severely challenging. Here, we present a case study that examines, under different rainfall scenarios, the effect of two inorganic amendments (gypsum and urea) on substrate quality and growth of two plant species (Acacia inaequilatera and Triodia wiseana) native to the Pilbara region. Through an extensive glasshouse experiment, two doses of inorganic amendments were tested and compared to unamended mining waste (overburden) substrates extracted from an iron-ore mine of moderately alkaline pH and low nitrogen status. Our results showed that the addition of urea (nitrogen-based fertiliser) produced a three-fold increase of plant growth in A. inaequilatera and up to a 25-fold increase in T. wiseana compared to unamended substrates when grown under the higher watering regime but this effect was not evident in the lower water regimes. The inorganic amendments decreased pH and increased EC, total nitrogen and N-mineralisation but did not have a significant effect on soil microbial activity. Overall, water was the dominant driver for determining the effectiveness of the substrate amendments to improve the quality of mine waste substrates and increase plant growth. This study contributes to unravelling the role of inorganic amendments in post-mining rehabilitation in arid regions faced with climate change.

Rehabilitation of degraded drylands is challenged by environmental and anthropogenic constraints, such as limited availability of locally-sourced topsoil and poor quality alternative soil substrates. Current rehabilitation practices, at times, utilise inorganic soil amendments to improve the physicochemical and biological characteristics of reconstructed soil profiles. These approaches may be appropriate for dryland rehabilitation, but there is limited research available regarding the benefits of using these amendments. Here, we present a study in the Pilbara region of Western Australia, an arid landscape subject to intensive mining that currently uses inorganic soil amendments (gypsum and urea) in post-mining rehabilitation. The aim of this study was to assess the effectiveness of these amendments to (1) promote seed germination, seedling emergence and seedling growth across five plant species and, (2) re-instate soil quality in mine waste substrates. A series of glasshouse experiments assessed eight application combinations of these amendments in two alternative substrates and compared these to unamended substrates and topsoil. Soil amendments had a limited influence on seed germination, were detrimental to seedling emergence and resulted in increased seedling mortality. Mortality in the waste ranged from 2 to 61% but increased to 7-92% in amended waste. Seedling growth improved with high doses of amendments in waste, with a 1.3-5.6-fold increase across all plant species. Soil quality was relatively unaffected by amendments with soil nitrogen ranging from 0.01 to 0.08%, organic carbon from 0.01 to 0.12% and soil microbial activity from 2.3 to 2.4 ppm-CO2 in the amended and unamended waste. The use of soil amendments in mine rehabilitation requires consideration of the trade-off between initial reductions in seedling recruitment and enhanced seedling development at later stages. Future rehabilitation should consider the timing of amendment application to avoid detrimental impacts on seedling recruitment and maximise the benefits to seedling growth.

Restoration of degraded arid and semi-arid land faces the challenge of reinstating vegetation communities exposed to limited and variable rainfall events that in combination with a deficit of original topsoil may exceed thresholds for seedling development. In a series of glasshouse experiments, we evaluated variation in drought responses of (i) 21 arid zone plant species from the mining intensive Pilbara region of Western Australia in an original topsoil substrate and (ii) four selected species (Acacia inaequilatera, Acacia spondylophylla, Eucalyptus leucophloia and Triodia epactia) in three different soil substrates (topsoil, overburden material and a blend of both soil materials) that may be considered as an alternative substrate for restoration. Seedling drought responses were tested using ecophysiological indicators (e.g. stomatal conductance and leaf water potential ((leaf)) at the time of stomatal closure, among others) during soil drying. Our results showed that plant life form and morphological traits interact with ecophysiological indicators to show that trees are significantly less tolerant to drought-related stress than shrubs and herbs (p005). When grown in overburden material seedlings experienced a decline in overall plant growth (87% in T.epactia and 62% in E.leucophloia) and ecophysiological drought tolerance. These responses are evidence of the low quality of the overburden substrate, which has a depleted nutrient content and low water retention capacity. Overall, this study highlights the sensitivity of early seedling development and the importance of facilitating seedling recruitment and survival to secure successful arid zone restoration. Copyright (c) 2016 John Wiley & Sons, Ltd.

One of the most critical challenges faced in restoration of disturbed arid lands is the limited availability of topsoil. In post-mining restoration, alternative soil substrates such as mine waste could be an adequate growth media to alleviate the topsoil deficit, but these materials often lack appropriate soil characteristics to support the development and survival of seedlings. Thus, addition of exogenous organic matter may be essential to enhance plant survival and soil function. Here, we present a case study in the arid Pilbara region (north-west Western Australia), a resource-rich area subject to intensive mining activities. The main objective of our study was to assess the effects of different restoration techniques such as soil reconstruction by blending available soil materials, sowing different compositions of plant species, and addition of a locally abundant native soil organic amendment (Triodia pungens biomass) on: (i) seedling recruitment and growth of Triodia wiseana, a dominant grass in Australian arid ecosystems, and (ii) soil chemical, physical, and biological characteristics of reconstructed soils, including microbial activity, total organic C, total N, and C and N mineralisation. The study was conducted in a 12-month multifactorial microcosms setting in a controlled environment. Our results showed that the amendment increased C and N contents of re-made soils, but these values were still lower than those obtained in the topsoil. High microbial activity and C mineralisation rates were found in the amended waste that contrasted the low N mineralisation but this did not translate into improved emergence or survival of T. wiseana. These results suggest a short- or medium-term soil N immobilisation caused by negative priming effect of fresh un-composted amendment on microbial communities. We found similar growth and survival rates of T. wiseana in topsoil and a blend of topsoil and waste (50:50) which highlights the importance of topsoil, even in a reduced amount, for plant establishment in arid land restoration.

Global environmental changes and other anthropogenic impacts are rapidly transforming the structure and functioning of ecosystems worldwide. These changes are leading to land degradation with an estimated 25 % of the global land surface being affected. Landscape-scale restoration of these degraded ecosystems has therefore been recognised globally as an international priority. In the resource-rich biodiverse semi-arid Pilbara region of north-west Western Australia hundreds of thousands of hectares are disturbed due to established and emerging iron-ore mine operations. At this scale, the need to develop cost-effective large-scale solutions to restore these landscapes becomes imperative to preserve biodiversity and achieve functionality and sustainability of these ecosystems.