Shrubland Biomes Research Articles

Temperature, not net primary productivity, drives continental-scale variation in insect flight activity.

The amount of energy available in a system constrains large-scale patterns of abundance. Here, we test the role of temperature and net primary productivity as drivers of flying insect abundance using a novel continental-scale data source: weather surveillance radar. We use the United States NEXRAD weather radar network to generate a near-daily dataset of insect flight activity across a gradient of temperature and productivity. Insect flight activity was positively correlated with mean annual temperature, explaining 38% of variation across sites. By contrast, net primary productivity did not explain additional variation. Grassland, forest and arid-xeric shrubland biomes differed in their insect flight activity, with the greatest abundance in subtropical and temperate grasslands. The relationship between insect flight abundance and temperature varied across biome types. In arid-xeric shrublands and in forest biomes the temperature-abundance relationship was indirectly (through net primary productivity) or directly (in the form of precipitation) mediated by water availability. These results suggest that temperature constraints on metabolism, development, or flight activity shape macroecological patterns in ectotherm abundance. Assessing the drivers of continental-scale patterns in insect abundance and their variation across biomes is particularly important to predict insect community response to warming conditions. This article is part of the theme issue 'Towards a toolkit for global insect biodiversity monitoring'.

First report of a ‘Candidatus Phytoplasma aurantifolia’ related strain (16SrII‐C) associated with Convolvulus virgatus witches'‐broom disease in Iran

Convolvulus virgatus (Convolvulaceae) is a perennial shrub which grows mainly in desert and shrubland biomes in Iran, the Arabian Peninsula and Pakistan (Wood et al., 2015). In a 2020 survey for phytoplasma diseases, witches'-broom disease of C. virgatus (WBDCV) was observed in the Roodan area (Hormozgan province, Iran). The main symptoms of WBDCV were flower and stem proliferation, shortened internodes, little leaf, severe witches'-broom, yellowing, reddening, plant sterility and decline (Figs. 1, 2). Total DNA was extracted from leaves and leaf petioles of five symptom-bearing and five symptomless C. virgatus plants using a CTAB-based method. DNA samples were tested for the presence of phytoplasmas by direct-PCR using primer pair P1/P7 (Lee et al., 1998) and nested PCR using primer pairs P1/P7 and R16F2n/R16R2 (Gundersen & Lee, 1996). The expected amplicons of c. 1,800 bp and 1,250 bp were obtained in direct and nested-PCR respectively, from all diseased plants but not symptomless ones. Two R16F2n/R16R2 amplicons were randomly selected and cloned into Escherichia coli DH5α cells using the PCR TA Cloning Kit (SinaClon, Cat. No.:CL5841, Iran) and three plasmid DNAs from recombinant colonies were sequenced. The obtained sequences were identical, and a consensus sequence was deposited in GenBank (Accession No. ON361565). BLASTn analysis of the obtained sequence showed the highest sequence identity (98.7-99.9 %) with phytoplasmas related to ‘Ca. P. aurantifolia’ (16SrII group). Phylogenetic analysis with MEGA11 software using the neighbour-joining method Fig. 3 revealed that the WBDCV phytoplasma clustered within the ‘Ca. P. aurantifolia’ (16SrII) group clade, closest to the strains of subgroup 16SrII-C. In Iran, phytoplasma strains belonging to 16SrII-C subgroup have been reported previously in Bushehr, Fars (adjacent to Hormozgan province) and Yazd provinces in several plant species including Daucus carota, Medicago sativa, Prunus dulcis, Vicia faba (Siampour et al., 2019), Alhagi maurorum and Artemisia sieberi (Esmaeilzadeh-Hosseini & Salehi, 2021); however, this is the first report of a ‘Ca. P. aurantifolia’-related strain in C. virgatus associated with WBDCV in Iran and most probably, in the world. The authors would like to thank the head of the Fars Agricultural and Natural Resources Research and Education Centre, Shiraz, Iran, for support and encouragement.

Cloud detection algorithm using SVM with SWIR2 and tasseled cap applied to Landsat 8

Landsat satellite images are subject to cloud cover effects resulting in erroneous analysis and observations of ground features. In this work, we present a novel algorithm (STmask) combining tasseled cap band 4 (TC4) with short wave infrared spectral band 2, SWIR2 (2.107–2.294 μm) for generating cloud, water, shadow, snow and vegetation masks. A support vector machine (SVM) with a non-linear kernel is trained on a feature space of TC4 versus SWIR2 for generating feature masks. To develop a generic and unbiased algorithm, the SVM is trained using reference data comprised of 12891 pixels from Landsat 8 scenes from ten spatially and temporally diverse biomes including deciduous forest, rainforest, great plain, savanna, desert, ocean, freshwater, taiga, tundra, and icesheet. 960000 text pixels spanning 96 scenes across 8 biomes from the USGS Landsat cloud cover assessment data set are used for accuracy assessment of STmask as well as to compare its performance with the operational Landsat algorithm, C function of mask (CFmask). Using McNemar's statistic, STmask is shown to maximize both the precision and sensitivity of the classification of all features compared to CFmask. It addresses the challenges of CFmask through statistically significant improvement in the precision of cloud detection over snow/ice, barren, water, urban, and shrubland biomes. Aggregated over all biomes, the average improvement in cloud detection over CFmask is observed to be ∼3.8% using the F-measure. The classification of non-cloud features exhibits promising improvements and mostly comparable performance to CFmask. Overall classification performance is promising, and thus STmask is a novel, biome-independent, parsimonious, and computationally efficient alternative (and/or a cloud screening addition) to the operational CFmask algorithm. The work is timely and is targeted as an innovative processing solution for the land surface remote sensing research community.

Global terrestrial biomes at risk of cacti invasion identified for four species using consensual modelling

Cacti invasion of natural ecosystems and grazing lands threaten native biodiversity and reduces economic output from infested grazing lands. Yet, few studies exist about potential hotspots of cacti invasion on a global scale. We used maximum entropy, boosted regression model and generalised additive models, calibrated using geo-referenced data from both the native and introduced ranges to construct ecological niche models for four invasive alien cacti species: Opuntia ficus-indica (the sweet prickly pear), Opuntia stricta (the sour prickly pear), Cylindropuntia imbricata (the tree cholla) and Cylindropuntia fulgida (the jumping cholla). The models were combined, using the average weighted method approach and projected onto the geographic space to predict terrestrial biomes, as well as areas of special conservation concern at risk of cacti invasion. The results indicate that the Mediterranean, tropical savanna and desert and xeric shrubland biomes are the most susceptible to cacti invasion. Eleven global biodiversity hotspots including the Mediterranean basin, Cape floristic region and Southwest Australia were associated with high risk of cacti invasion. The global maps of potential cacti distribution presented in this work have the potential to serve as an important contribution towards the implementation of a global policy to avoid the negative consequences of cacti invasion.

Electric crows: powerlines, climate change and the emergence of a native invader

AbstractAimClimate change and other anthropogenic global change drivers act in complex, mutually exacerbating ways to alter the abundance and distribution of species. In South Africa, pied crows Corvus albus have increased in numbers and range in recent decades. Popular opinion links these changes to urbanisation and infrastructure development, but there has been no empirical test of this idea. We aimed to clarify the drivers of pied crow population changes in South Africa.LocationSouth Africa.MethodsWe used publicly available long‐term datasets, the Southern African Bird Atlas Project and University of Delaware Gridded Climate Database, and spatial data from government bodies, to assess relationships between pied crow population and range changes, land use, infrastructure, urbanisation and climate change.ResultsPied crow numbers have increased significantly in the past three decades, but rate of increase varied geographically, with crows declining in the northeast and increasing in the south‐west of South Africa. Pied crow population changes were strongly correlated with climate change. Crows have benefited most from climate warming in the shrubland biomes of south‐western South Africa. Pied crows are tree nesters, and within these shrublands, there is a strong positive relationship between the rate of population increase and the density of powerline infrastructure, which may facilitate pied crows’ increase by providing nesting sites.Main conclusionsPied crow numbers have increased in response to climate warming, with their spread facilitated by electrical infrastructure in south‐western South Africa, providing a clear example of compound influence of multiple global change drivers promoting a significant change in species range and reporting rate. Pied crows are generalist predators and there is popular concern about their ecological impact in areas where increases have occurred. We highlight the importance of understanding the ecosystem‐level implications of increased numbers of pied crows in South Africa's shrubland biomes.

A 50 year study shows grass cover has increased in shrublands of semi-arid South Africa

In many parts of the world the boundaries between grassland and shrubland biomes have changed substantially over the course of the last century. Many are projected to shift further from being grass-dominated to shrub-dominated by 2050 under global climate change and land use change projections. This paper used long-term surveys and repeat photography to assess vegetation change at the shrubland-grassland ecotone in semi-arid, South Africa. Changes in several climate variables as well as in the cover of grasses and dwarf shrubs over three time periods (1962, 1989 and 2009) were investigated at eight localities within a broad 500 km ecotone between the Grassland and Nama-karoo biomes. Results showed that for most sites grass cover has increased and that dwarf shrub cover has decreased over time. This contradicts earlier views which warned against the expansion of dwarf shrublands in response to over-grazing as well as more recent views which suggest that more mesic biomes in the Karoo Midlands will contract in response to climate-induced aridification. The decline in stocking densities and more conservation-friendly land management practices together with an increase in large wet events in the Nama-karoo biome may have contributed to the increase in grass cover.

Variation in vegetation cover between shrubland, woodland and forest biomes invaded by Phytophthora cinnamomi

Pathogen mediated changes in vegetation cover were determined from variation of ground cover and canopy closure between diseased and adjoining healthy areas of Banksia shrubland, Banksia woodland and Eucalyptus marginata forest biomes invaded by Phytophthora cinnamomi. For healthy areas, ground cover tended to be greatest in the relatively low rainfall areas where canopy closure was the least. Ground cover significantly decreased, but canopy closure significantly increased with plant height in healthy areas. Disease caused by P. cinnamomi resulted in a mean decrease in ground cover of ~28% for infested woodland and forest biomes. This decrease was significantly greater than the mean decrease in ground cover of 14% for shrubland biomes. In contrast disease decreased mean canopy closure in shrubland biomes by 32% which was significantly greater than the decrease of ~22% for diseased woodland and forest biomes. Re-establishment of vegetation cover using resistant selections of local dominant plant species may substantially return to infested areas the functionality of healthy areas.

Grassland Management and Conversion into Grassland: Effects on Soil Carbon

Grasslands are heavily relied upon for food and forage production. A key component for sustaining production in grassland ecosystems is the maintenance of soil organic matter (SOM), which can be strongly influenced by management. Many management techniques intended to increase forage production may potentially increase SOM, thus sequestering atmospheric carbon (C). Further, conversion from either cultivation or native vegetation into grassland could also sequester atmospheric carbon. We reviewed studies examining the influence of improved grassland management practices and conversion into grasslands on soil C worldwide to assess the potential for C sequestration. Results from 115 studies containing over 300 data points were analyzed. Management improvements included fertilization (39%), improved grazing management (24%), conversion from cultivation (15%) and native vegetation (15%), sowing of legumes (4%) and grasses (2%), earthworm introduction (1%), and irrigation (1%). Soil C content and concentration increased with improved management in 74% of the studies, and mean soil C increased with all types of improvement. Carbon sequestration rates were highest during the first 40 yr after treatments began and tended to be greatest in the top 10 cm of soil. Impacts were greater in woodland and grassland biomes than in forest, desert, rain forest, or shrubland biomes. Conversion from cultivation, the introduction of earthworms, and irrigation resulted in the largest increases. Rates of C sequestration by type of improvement ranged from 0.11 3.04 Mg C.ha(-1) yr(-1), with a mean of 0.54 Mg C.ha(-1).yr(-1) and were highly influenced by biome type and climate. We conclude that grasslands can act as a significant carbon sink with the implementation of improved management.

GRASSLAND MANAGEMENT AND CONVERSION INTO GRASSLAND: EFFECTS ON SOIL CARBON

Grasslands are heavily relied upon for food and forage production. A key component for sustaining production in grassland ecosystems is the maintenance of soil organic matter (SOM), which can be strongly influenced by management. Many management techniques intended to increase forage production may potentially increase SOM, thus sequestering atmospheric carbon (C). Further, conversion from either cultivation or native vegetation into grassland could also sequester atmospheric carbon. We reviewed studies examining the influence of improved grassland management practices and conversion into grasslands on soil C worldwide to assess the potential for C sequestration. Results from 115 studies containing over 300 data points were analyzed. Management improvements included fertilization (39%), improved grazing management (24%), conversion from cultivation (15%) and native vegetation (15%), sowing of legumes (4%) and grasses (2%), earthworm introduction (1%), and irrigation (1%). Soil C content and concentration increased with improved management in 74% of the studies, and mean soil C increased with all types of improvement. Carbon sequestration rates were highest during the first 40 yr after treatments began and tended to be greatest in the top 10 cm of soil. Impacts were greater in woodland and grassland biomes than in forest, desert, rain forest, or shrubland biomes. Conversion from cultivation, the introduction of earthworms, and irrigation resulted in the largest increases. Rates of C sequestration by type of improvement ranged from 0.11 to 3.04 Mg C·ha−1 yr−1, with a mean of 0.54 Mg C·ha−1·yr−1, and were highly influenced by biome type and climate. We conclude that grasslands can act as a significant carbon sink with the implementation of improved management.