Anthony Jan Mills

• PhD Soil Science
• C4 EcoSolutions

Scatterplots of biological datasets often have no‐data zones, which suggest constraint or promotion of dependent variables. Although methods exist to estimate boundary lines—that is, to fit lines to the edges of scatters of data points—there are, to our knowledge, none available to assess the significance of the areal extents of no‐data zones. Acco...

Macrotermes termite mounds in the Kruger National Park occupy a significant part of the savanna landscapes, occurring at densities of up to 70 km⁻² and often exceeding 10 m in width and 4 m in height. The mounds are usually devoid of trees, but have dense grass cover in wet years. As a result, these mounds form large patches of grassland amongst th...

Restoring the hundreds of millions of hectares of degraded ecosystems worldwide will require new approaches to raise the required funds and new systems to implement at the required scales. Two decades of large-scale restoration in the subtropical thicket biome in the Eastern Cape, South Africa, have generated valuable information for developing suc...

Restoration of degraded subtropical succulent thicket, via the planting of Portulacaria afra (spekboom) truncheons, is the focus of a public works programme funded by the South African government. The goals of the programme, which started in 2004, are to create jobs, sequester carbon, restore biodiversity, reduce erosion, improve soil water holding...

Treeless grasslands occur within landscapes that are predominantly wooded savannas in the central Kruger National Park, South Africa. As a first step in identifying soil properties potentially underpinning differences in vegetation structure in these landscapes, we analysed the soil chemistry of the pedoderm (0–2 cm) in a grassland and two adjacent...

The small tree, Dichrostachys cinerea, occurs in dense patches within grasslands on gabbro-derived soils in the southern Kruger National Park. It is not known whether soil properties in the grasslands affect tree establishment. As a first step in identifying soil properties potentially underpinning differences in vegetation structure, we analysed t...

The woody plant, Colophospermum mopane, occurs as either a shrub or tree in shrublands and woodlands, respectively, in the central Kruger National Park, South Africa. As a first step in identifying which soil properties potentially influence the structure of C. mopane in these landscapes, we investigated the soil chemistry of the pedoderm in shrubl...

Treed savannas and treeless grasslands occur across Mokala National Park, South Africa. To identify soil properties potentially underpinning these marked differences in vegetation structure, we analysed the soil chemistry of 27 composite pedoderm samples in both savannas and grasslands. Savannas had a greater pH and greater mean concentrations of P...

Insights from biome-wide experiments can improve efficacy of landscape-scale ecological restoration projects. Such insights enable implementers to set temporal and geographical benchmarks and to identify key drivers of success during the often decades-long restoration trajectory. Here we report on a biome-wide experiment aimed at informing the ecol...

Estimation and monitoring of soil organic carbon (SOC) stocks is important for maintaining soil productivity and meeting climate change mitigation targets. Current global SOC maps do not provide enough detail for landscape-scale decision making, and do not allow for tracking carbon sequestration or loss over time. Using an optical satellite-driven...

Invasion by invasive alien trees is a major threat to the biodiversity of the fynbos biome in South Africa. The environmental factors influencing the intensity of invasion are, however, largely unknown. In particular, the effects of soil nutrients on the invasion of alien trees in the fynbos biome have not been investigated. The Catabolic Theory pr...

Societal Impact Statement Ecosystem‐based adaptation (EbA) is increasingly being used to reduce the impacts of climate change on vulnerable people and landscapes. The international EbA South project implemented EbA interventions across three countries (Mauritania, Nepal, the Seychelles), piloting the restoration of mountain, desert and coastal ecos...

South Africa is a megadiverse country in terms of biodiversity, with continental South Africa composed of nine terrestrial biomes. This diversity is in part due to the wide range of climatic and topographic conditions that exist in the country. This chapter explores how these environmental features influence biological invasions (focusing on terres...

Fungus-growing termites ( Macrotermitinae ) collect water to air-condition their fungi and have been recorded tunnelling deeper than 80 m for groundwater. This collection of water ultimately results in solute accumulation and nutrient enrichment of their termitaria. We consequently hypothesized that nutrient enrichment of termitaria constructed by...

Improvements in land use and management are needed at a global scale to tackle inter‐connected global challenges of population growth, poverty, migration, climate change, biodiversity loss, and degrading land and water resources. There are hundreds of technical options for improving the sustainability of land management and preventing or reversing...

Intensive goat farming has transformed more than a million hectares of subtropical thicket in South Africa from a dense closed-canopy shrubland into an open savanna-like system. Restoration of the degraded thicket landscapes can be achieved by planting truncheons of spekboom (Portulacaria afra). The sale of carbon sequestered by spekboom can potent...

The causes of the worldwide problem of encroachment of woody plants into grassy vegetation are elusive. The effects of soil nutrients on competition between herbaceous and woody plants in various landscapes are particularly poorly understood. A long-term experiment of 60 plots in a South African savanna, comprising annual applications of ammonium s...

Tree abundance, cumulative height of trees, and soil properties in relation to experimental treatments at Towoomba. Means and standard errors are presented. All soil properties are reported in mg kg-1 except where indicated. SP = superphosphate. [See file number 6; “S6 Table.doc”.] (DOCX)

Correlation coefficient matrix for data on woody plants and soil properties. [See file number 7; “S7 Table.doc”.] (DOCX)

Test statistics (Q value) and p values for non-parametric Friedman tests for one-way repeated measures analysis of variance by ranks across the Towoomba experiment. [See file number 8; “S8 Table.doc”.] (DOCX)

Tree abundance, cumulative height of trees, and soil properties in relation to all experimental treatments at Towoomba. Means and standard errors are presented. All soil properties are reported in mg kg-1 except where indicated. AS = ammonium sulphate; SP = superphosphate. [See file number 9; “S9 Table.doc”.] (DOCX)

Tree abundance relative to pH (H2O), acidity, electrical conductivity (EC), water-dispersible clay (WDC) and nutrient concentrations. In the top row, four categories of tree abundance (i.e. 0–1, 2–4, 5–8 or >8 individual trees per plot) are shown, with data points depicted as grey circles, and means ± standard errors depicted with black circles and...

Raw data from which reported results were generated. [See file number 15; “S1 Raw Data.xlsx”.] (XLSX)

Layout of the Towoomba experiment showing the 5 x 3 factorial design with four replications for each treatment. [See file number 1; “S1 Table.doc”.] (DOCX)

Mean yields of hay (tonnes ha-1) and standard error (SE) in different experimental treatments at Towoomba over the period 1949 to 1981. AS = ammonium sulphate; SP = superphosphate. [See file number 3; “S3 Table.doc”.] (DOCX)

Tree abundance, cumulative height of trees, and soil properties in relation to experimental treatments at Towoomba. Means and standard errors are presented. All soil properties are reported in mg kg-1 except where indicated. AS = ammonium sulphate. [See file number 5; “S5 Table.doc”.] (DOCX)

Tree species and their maximum height in 2011/12, according to experimental treatment. Values are numbers of individual trees. Abbreviations in parentheses indicate the species with the maximum height for each plot (V. k. = Vachellia karroo; V. ger. = Vachellia gerrardii; V. r. = Vachellia robusta). AS = ammonium sulphate; SP = superphosphate. [See...

Additional information on the vegetation in the Towoomba experiment. [See file number 10; “S1 Text.doc”.] (DOCX)

Boundary line analyses. [See file number 11; “S2 Text.doc”.] (DOCX)

Results of boundary line analyses on soil properties and nutrient ratios. Inter-quartile factors (IQFs) are presented for data-negative zones. All 91 nutrient ratios were analysed, but only those nutrient ratios with IQFs >1 are presented. NA values indicate instances where zones of no-data were not identified (i.e. fewer than four points delineati...

Theoretical relationship between biotic response and any given soil property. A boundary line separates a data-negative zone from a data-positive zone in a scatter plot [i, ii], which enables delineation of bands of constraint as well as potential for the y variable. [See file number 12; “S1 Fig.tif”.] (TIF)

Relationship between inter-quartile factor (IQF) and the quartiles of a distribution of random permutations of x and y values. For -1<IQF<0, the observed data (OD) falls between the median and the 1st quartile (Q1) for values smaller than the median, or the 3rd quartile (Q3) for values larger than the median. For 0<IQF<1, OD falls between Q1 and Q1...

A shortage of water currently threatens the development of the South African economy and the well-being of its people. Climate change, land degradation and an inherently semi-arid, variable climate are making it increasingly difficult for water service providers to deliver sufficient quantity and quality of water to meet escalating demand. Investme...

Through the Subtropical Thicket Restoration Programme (STRP), about 21.5 million cuttings of spekboom (Portulacaria afra) were planted over the period 2004–2016 in the Addo Elephant National Park, Great Fish River Nature Reserve and the Baviaanskloof Nature Reserve. This planting includes a large experiment of 330 quarterhectare plots in which 14 d...

The puzzling exclusion of native trees from grassland under mesic climates can hypothetically be explained by nutritional regimes that make grasses competitively superior to trees. One hypothesis holds that where nutrient concentrations in soils allow catabolism to be as rapid as anabolism at the scale of the whole plant, photosynthates are respire...

Commonly cited requirements for bridging the "science-practice divide" between practitioners and scientists include: political support, communication and experimentation. The Subtropical Thicket Restoration Programme was established in 2004 to catalyse investment in large-scale restoration of degraded subtropical thicket in the Eastern Cape, South...

The ultimate reasons for treelessness in the natural grassland of the Highveld of southern Africa have long eluded biologists. This is partly because of the ambivalence of adaptive determinism versus biogeographical/phylogenetic accidents, and partly because of entanglement between cause and effect. For example, waterlogging and grass fires, arguab...

Is the maximum rate of carbon sequestration reported for the CAM-C3 plant Portulacaria afra (spekboom), viz. 15.4 t CO2 ha−1 yr−1, unusual in comparison with other plants with similar physioliogies, or could such rates be expected routinely in restoration with P. afra? Private sector investors in thicket restoration need an answer to this question...

The influence of soil organisms on the availability of nutrients to other biota within ecosystems can be context-dependent. Fungus-culturing termites, for example, are known to concentrate nutrients by building large mounds in nutrient-poor savannas, but several factors determine the nutritional value of the mounds – whether by geophagy or consumpt...

An accepted criterion for measuring the success of ecosystem restoration is the return of biodiversity relative to intact reference ecosystems. The emerging global carbon economy has made landscape-scale restoration of severely degraded Portulacaria afra (spekboom)-dominated subtropical thicket, by planting multiple rows of spekboom truncheons, a v...

Carbon credits are a potential source of funding for restoration initiatives that contribute to achieving conservation targets in important biodiversity areas. Here we investigated whether fallowing sequesters carbon; a first step in as-sessing the viability of using carbon financing to promote restoration of threat-ened vegetation in agricultural...

The scarcity of indigenous trees on the Highveld of eastern South Africa is usually attributed to frost, fire and drainage, regardless of whether the soils are nutrient-poor (sourveld grasslands) or nutrient-rich (sweetveld grasslands). However, soil physicochemical properties—such as nutrient availability—are likely to affect vegetation structure...

Large tracts of fynbos on the Agulhas Plain are being converted to agriculture. Carbon (C) stocks in fynbos, pastures and vineyards were measured in this preliminary study to determine whether conservation of fynbos results in greater C storage relative to agricultural land uses. Fynbos had greater aboveground C than pastures (12.7 ± 1.7 vs 0.8 ± 0...

Climate change adaptation is widely acknowledged as an urgent need for African countries. However, African governments face considerable challenges in prioritising adaptation interventions and, in particular, aligning these adaptation interventions with existing national development priorities. This article focuses on the Africa Adaptation Programm...

Aerosols play important roles in soil genesis and plant nutrition, at both local and intercontinental scales, by redistributing nutrients through the atmosphere. Aerosol capture by tree crowns is a possible mechanism by which trees significantly augment their nutrition, particularly in trace elements. Forests capture considerable amounts of aerosol...

The influence of soil nutrients on woody plants is poorly understood. Are trees - fire and other disturbance factors being equal - generally promoted by nutrient-rich or by nutrient-poor soils? To determine the edaphic parameters controlling woody cover, we sampled soils and summed the extent of the crowns of trees and tall shrubs on 364 plots at 2...

Summary of Key Points: - Ecosystem-based Adaptation (EbA) provides numerous opportunities for natural solutions to manage the impacts of climate change. - EbA interventions generate a range of significant social, economic, and environmental co-benefits by reducing society’s vulnerability to natural hazards, improving the availability of ecosyst...

“Non rainfall” atmospheric water (dew, fog, vapour adsorption) supplies a small amount of water to the soil surface that may be important for arid soil micro-hydrology and ecology. Research into the direct effects of this water on soil is, however, lacking due to instrument and technical constraints. We report on the design, development, constructi...

"Non-rainfall" water is important to the soil water balance and ecology of arid ecosystems. A component of this "non-rainfall" water in the Namib Desert, fog, exhibits spatial variation implying variability in composition and significance of each vector (dew, fog, vapour adsorption) to ecology at different locations. The composition of "non -rainfa...

Restoration of degraded thicket landscapes can be achieved by planting Portulacaria afra (spekboom) cuttings. The factors determining P. afra abundance in thicket types not dominated by P. afra are of interest to restoration practitioners because they could influence restoration protocols using P. afra cuttings in these landscapes. We consequently...

Mean annual soil respiration correlates with net primary productivity and therefore provides an indication of ecosystem functioning. Soil respiration, however, varies considerably in space and time owing to the influence of factors such as soil nutrient content, temperature and water content. Comparing soil respiration across a fence-line separatin...

The effect of desert pavements (gravel mulch) on near surface soil micro-hydrology has been inadequately studied. Micro-hydrology in arid ecosystems occurs due to a daily non rainfall atmospheric water cycle, consisting of an input phase (dew, fog, vapour adsorption) and an evaporation phase. A winter comparative study between a bare soil (control)...

The present study was undertaken to assess baseline distribution patterns for soil lichens occurring in the principal biomes of southern Africa, and to analyse their relationship to selected environmental parameters. Among the lichen species found across our survey sites, four distinct groups could be delineated, each as distinct consortium of lich...

Although numerous hypotheses have been proposed to explain geophagy, the primary driver of this behaviour remains elusive. Supplementation of scarce nutrients is one commonly cited explanation. We examined the element concentration of three licks relative to adjacent topsoils to infer the possible reasons for geophagy at Loskop Dam Nature Reserve....

Many of the skills and resources associated with botanic gardens and arboreta, including plant taxonomy, horticulture, and seed bank management, are fundamental to ecological restoration efforts, yet few of the world's botanic gardens are involved in the science or practice of restoration. Thus, we examined the potential role of botanic gardens in...

Subtropical thicket dominated by the leaf- and stem-succulent tree Potulacaria afra (spekboom) accumulates extraordinarily high amounts of soil organic carbon for a semi-arid ecosystem. This has been attributed to high leaf litter production of canopy trees — especially spekboom — and the relatively cool beneath-canopy temperatures, which reduces m...

Relationships between species richness per plant life form and the soil properties: infiltrability, clay plus silt content, salinity, and pH were investigated at eighteen study sites located in western South Africa and Namibia. Plant species data were categorized into five life forms: phanerophytes, chamaephytes, hemicryptophytes, therophytes, and...

We propose that a basic biological imperative of all organisms is to maximise energy (E) intensity, defined as the average rate of energy use per unit area of the Earth's surface. The dominant organism in any given environment is predicted to be that exerting the greatest E intensity regardless of evolutionary origin. Our 'theory of biological E in...

The feasibility of restoring subtropical thicket using carbon markets is largely a function of its carbon sequestration potential. We measured below-ground carbon stocks and analysed soil properties in intact, degraded and old agricultural landscapes in Baviaans Spekboom Thicket – a highly degraded thicket type earmarked for restoration. Soil and r...

Biodiversity is important for sustaining life on Earth yet it is threatened globally. The BIOTA Southern Africa project analysed the causes, trends, and processes of change in biodiversity in Namibia and western South Africa over nearly a full decade, from 2001 until 2010. This book, which is comprised of three volumes, offers a summary of the resu...

Soils of South Africa is the first book in seventy years that provides a comprehensive account of South African soils. The book arranges more than seventy soil forms into fourteen groups and then provides, for each group: • maps showing their distribution and abundance throughout South Africa • descriptions of morphological, chemical and physical p...

Fire-breaks, by legislation, are burnt annually before mid-winter in the southern Drakensberg, affecting 5–10% of the landscape, and resulting in marked selection for the early season flush by both livestock and wildlife. This study investigated whether this severe defoliation regime has had an effect on surface soil properties, botanical compositi...

Rare earth element (REE) and trace element concentrations of ten termite mounds and adjacent topsoil from central and northeastern Namibia were used to investigate the processes underlying the alteration of soil chemical and physical properties by termites (Macrotermes spp.). Accumulation of micro-nutrients in the mounds was of particular interest...

Data from 199 plots in the semi-arid Karoo showed that relationships between soil infiltrability and plant cover/species richness, as depicted by boundary lines, yielded ecological insights not evident if only commonly measured soil properties such as pH, electrical conductivity and the content of clay, silt, sand, nitrogen and carbon were consider...

Soils in the Knersvlakte are particularly prone to crusting and have lower inherent infiltrability than other soils across western southern Africa. Micromorphological techniques were used to examine the structure and porosity of soil crusts in the Knersvlakte to ascertain why crusting is so intense in this region. Quantile regression using boundary...

The regeneration dynamics of South African subtropical thicket are poorly understood. This lack of knowledge hampers the development of appropriate restoration protocols in degraded landscapes. To address this we compared the magnitude of seed production and the frequency seedlings of canopy species in intact and browsing-degraded forms of Portulac...

Termite mounds are commonly enriched in clay and nutrients relative to surrounding topsoils. We hypothesized that: (1) nutrient enrichment of mounds differs between fungus-culturing (FC) and non-FC termites; (2) FC termites preferentially acquire materials rich in scarce nutrients which promote growth of their fungus cultures; and (3) micro-nutrien...

The influence of particle size fractions on infiltrability was investigated in soils sampled across Namibia and western South Africa. Infiltrability was determined using a laboratory technique calibrated with rainfall simulation, which measures the passage of a suspension of soil particles through a packed soil column. Water-dis-persible soil parti...

The vegetation of the Albany Thicket Biome of South Africa 's southern coastal belt comprises a closed shrubland that exhibits rainforest-like functioning, despite the region's semi-arid climate. Most of the arid (250-350 mm yr-1) thicket, where the succulent shrub Portulacaria afra (spekboom) is dominant, have been degraded by injudicious pastoral...

The effects of particle size, electrical conductivity (EC) and exchangeable sodium percentage (ESP) on infiltra-bility were investigated in 35 soils from Namibia and western South Africa. Samples were grouped as follows: sand (5–9% clay + silt), loamy sand (16–20%) and silty loam (73–80%). Subgroups included: low EC and low ESP (LL); low EC and hig...

Semi-arid succulent thicket in South Africa has experienced extensive livestock-induced transformation, reflected in extensive structural changes and loss of biodiversity, biomass and soil carbon. The ecological mechanisms contributing to this transformation are not fully understood but are believed to include the breakdown of ecosystem processes i...

Dew, fog/mist and water vapour adsorption, the 3 vectors by which non-rainfall water can be added to soil water, may play a critical role in ecosystem function in arid zones. This paper explores a methodology for overcoming the challenges of measuring small daily inputs of non-rainfall water in the harsh environment of the Knersvlakte on the West C...

The grassland biome of the southern Drakensberg region of South Africa is characterized by a relatively rich floral biodiversity, including a high level of endemics. Land use in the area was traditionally dominated by livestock ranching based mainly on indigenous grassland that conserved biodiversity to some degree. Currently however, market demand...

The soil mantle in Namaqualand is immature in terms of weathering. Despite or even because of this, the diversity and spatial variability of soil physical and chemical properties is exceptionally high and could be fundamental in governing biodiversity and ecosystem function. In arid landscapes, the way the soil sheds, admits, stores, diverts and tr...

South Africa is in the process of setting up a national environmental observatory system (SAEON) to monitor and gain a predictive understanding of the effects of climate change and land use on biodiversity, carbon and nutrient fluxes, soils and sediments, primary and secondary productivity, hydrology and disturbance regimes. It is intended that the...

Wildlife and livestock in the Ngorongoro Conservation Area (NCA), Tanzania, commonly practise geophagy. We investigated the nutrient content of nine earth licks and adjacent topsoils in the NCA, and for comparative purposes, two salt pans in north-eastern Tanzania, licks in central Tanzania and a lick near Puerto Maldonado, Peru. The licks had no c...

A recently proposed meaning of pedoderm is more formally defined so as to contrast it with an older definition that is used infrequently in soil stratigraphy. It is defined here as the thin layer of soil at the interface with the atmosphere, a few millimetres to centimetres thick, within which certain properties may exhibit a marked vertical change...

An understanding of the factors governing grass–tree coexistence in savannas and exclusion of trees in grasslands remains elusive. We contend that progress in understanding these factors is impeded by a reliance on a falsification approach and an excessive concern over type I errors (false positives), which results in premature rejection of hypothe...