The distribution and diversity of Leptocybe invasa (Hymenoptera: Eulophidae) and its gall associates in South Africa

Leptocybe invasa is an invasive gall wasp and pest of Eucalyptus trees, which has become widely distributed in Africa, Asia, Europe and the Americas. Several other wasp species have been found to co-occur in L. invasa-induced galls. In South Africa, this includes an introduced biological control agent, Selitrichodes neseri; two known, accidentally introduced parasitoids, Megastigmus zebrinus and Quadrastichus mendeli; and M. pretorianensis, whose role in the gall is uncertain. In addition to the gall associates, a second lineage of L. invasa or cryptic species was discovered in South Africa in 2015. To determine the distribution and prevalence of these species across South Africa, a national monitoring scheme was initiated. Galled Eucalyptus material was collected at infested sites and emerging adults were collected and identified. Morphology, DNA barcoding and polymerase chain reaction (PCR) Restriction Fragment Length Polymorphism analyses were used to differentiate between the species and lineages. Results from the first two sampling periods indicated that L. invasa lineage A has spread throughout South Africa while lineage B had a more limited distribution in the country. Subsequent samples recorded the further spread of L. invasa Lineage B, which now occurs in all provinces sampled. The Leptocybe lineages were found to co-occur on individual trees, increasing the potential for admixture. From the Eucalyptus genotypes sampled, there was no indication of differences in host association between the Leptocybe lineages. Selitrichodes neseri, M. zebrinus and M. pretorianensis were present throughout South Africa and emerged from trees that contained both Leptocybe lineages, but their frequency varied with site. This study will inform future distribution of parasitoids as well as monitoring of potential changes in plant host resistance, admixture and parasitoid resistance in future.The Department of Science and Innovation–National Research Foundation, Centre of Excellence in Plant Health Biotechnology and Forestry South Africa (FSA).http://www.tandfonline.com/loi/tsfs20hj2023BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant PathologyZoology and Entomolog

Water use and potential hydrological implications of fast-growing Eucalyptus grandis x Eucalyptus urophylla hybrid in northern Zululand, South Africa

We measured the tree transpiration of 9-year-old, Eucalyptus grandis x Eucalyptus urophylla clonal hybrid (GU) trees in the commercial forestry area of northern KwaZulu-Natal, South Africa. Transpiration was measured using the heat ratio method over two consecutive hydrological years (2019/20 and 2020/21) and up-scaled to a stand level. Leaf area index (LAI), quadratic mean diameter, and soil water content (SWC) were measured over the same period using an LAI 2200 plant canopy analyser, manual dendrometers and CS616 sensors, respectively. The depth to groundwater was estimated to be approx. 28 m, using a borehole next to our study site. Results showed that transpiration followed a seasonal pattern, with daily mean of 2.3 mm‧tree−1‧day−1 (range: 0.18 to 4.55 mm‧tree−1‧day−1) and 3.3 mm‧tree−1‧day−1 (range: 0.06 to 6.6 mm‧tree−1‧day−1) for 2019/20 and 2020/21, respectively. Annual GU transpiration was higher than that found by international studies under similar conditions, but was within the same transpiration range as Eucalyptus genotypes in the KwaMbonambi area. Plantation water productivity, calculated as a ratio of stand volume to transpiration, was higher than for other published studies, which was attributed to a very high productive potential of the study site. Multiple regression using the random forests predictive model indicated that solar radiation, SWC and air temperature highly influence transpiration. There is a high possibility that our GU tree rooting system extracted water in the unsaturated zone during the dry season. Due to the use of short-term results in this study, the impact of GU on water resources could not be quantified; however, previous long-term paired catchment studies in South Africa concluded that Eucalyptus has a negative impact on water resources. Further research is suggested with long-term measurements of transpiration and total evaporation and an isotope study to confirm the use of water by GU trees in the unsaturated zone.The Department of Water and Sanitation through Water Research Commission.https://www.watersa.nethj2024Plant Production and Soil ScienceSDG-12:Responsible consumption and productionSDG-15:Life on lan

Transpiration rates from mature Eucalyptus grandis × E. nitens clonal hybrid and Pinus elliottii plantations near the Two Streams Research Catchment, South Africa

DATA AVAILABILITY : Due to the high frequency of the data used in this paper, all data with linked figures and tables have been uploaded to the central database at the Centre for Water Resources Research (CWRR) at the University of KwaZulu-Natal in Pietermaritzburg. The author, Nkosinathi David Kaptein, can be contacted for these data at [email protected] plantations are the dominant species currently planted within the South African commercial forestry industry. Improvements in bio-economy markets for dissolving wood pulp products have seen an expansion in fast-growing Eucalyptus plantations due to their higher productivity rates and better pulping properties than pine. This has raised concerns regarding the expansion of Eucalyptus plantations and how they will affect water resources as they have been reported to have higher water use (quantified using transpiration rates) than pine. We measured transpiration rates (mm yr−1), diameter at breast height (quantified as quadratic mean diameter, Dq, m) and leaf area index of an 8-year-old Eucalyptus grandis × Eucalyptus nitens clonal hybrid (GN) and a 20-year-old Pinus elliottii. Transpiration rates were measured for two consecutive hydrological years (2019/20 and 2020/21) using a heat ratio sap-flow method, calibrated against a lysimeter. In the 2019/20 year, annual transpiration for P. elliottii exceeded GN by 28 %, while for the 2020/21 hydrological year, there was no significant difference between the transpiration of the two species, despite a 17 % and 21 % greater leaf area index for P. elliottii than GN in 2019/20 and 2020/21 measurement years respectively. Quadratic mean diameter increments were statistically similar (p > 0.05) in 2019/20, whereas the 2020/21 year produced significant differences (p<0.05). Tree transpiration is known to be influenced by climatic variables; therefore, a random forest regression model was used to test the level of influence between tree transpiration and climatic parameters. The soil water content, solar radiation and vapour pressure deficit were found to highly influence transpiration, suggesting these variables can be used in future water-use modelling studies. The profile water content recharge was influenced by rainfall events. After rainfall and soil profile water recharge, there was a rapid depletion of soil water by the GN trees, while the soil profile was depleted more gradually at the P. elliottii site. As a result, trees at the GN site appeared to be water stressed (reduced stem diameters and transpiration), suggesting that there was limited access to alternative water source (such as groundwater). The study concluded that previous long-term paired catchment studies indicate that eucalypts use more water than pine; however, periods of soil water stress and reduced transpiration observed in this study must be accommodated in hydrological models. Long-term total soil water balance studies are recommended in the same region to understand the long-term impact of commercial plantations on water resources.The South African Department of Water and Sanitation through a Water Research Commission project.https://www.hydrology-and-earth-system-sciences.nethj2024Plant Production and Soil ScienceSDG-15:Life on lan

First report of the wattle rust pathogen, Uromycladium acaciae (Raveneliaceae, Pucciniales) in Ethiopia

DATA AVAILABILITY STATEMENT : The data underlying this article are available in the GenBank Nucleotide Database at https://www.ncbi.nlm.nih.gov/ and can be accessed with accession number listed in Table 2.Australian Acacia species are among the most important trees planted for wood and pulp production in several African countries, including Ethiopia. In 2020, symptoms of a serious shoot and leaf rust disease were observed on black wattle (Acacia mearnsii De Wild.) trees across the three main wattle growing regions of Ethiopia. The aim of this study was to describe the disease and identify its causal agent based on morphological characteristics as well as DNA sequence data for the ITS and LSU regions of ribosomal DNA. Here we report for the first time, the presence of the wattle rust pathogen, Uromycladium acaciae, in Ethiopia.The Australian Government and the ACIAR.https://academic.oup.com/forestry2024-08-09hj2023BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant PathologyPlant Production and Soil ScienceSDG-15:Life on lan

A spatio-temporal analysis of baboon damage using Sentinel-2 imagery and Extreme Gradient Boosting

The use of remote sensing for forest health monitoring has increased in popularity over the years, improving quality, spatial and spectral resolutions. However, revisit times of satellites is too slow for real-time detection. The need exists for high resolution monitoring, to quantify biotic damage, which is more difficult to detect due to the diversity of severity. Sentinel-2 MSI data, with 10 - 60 m spatial resolution and 443 - 2190 nm spectral range was used. Through strategical bands and derived vegetation indices, an accuracy of 89,34% with a Kappa of 0.85 using XGboost, was achieved. The study found: (1) Sentinel-2 identified baboon damage with high accuracy, with field measured data (2) different damage severities could be distinguished. SAVI and SIPI were most influential variables, due to good discrimination of structural variations in the canopy. The method provides an accurate and repeatable framework for rapid damage mapping at a sub-compartment scale

Water use and potential hydrological implications of fast-growing Eucalyptus grandis x Eucalyptus urophylla hybrid in northern Zululand, South Africa

We measured the tree transpiration of 9-year-old, Eucalyptus grandis x Eucalyptus urophylla clonal hybrid (GU) trees in the commercial forestry area of northern KwaZulu-Natal, South Africa. Transpiration was measured using the heat ratio method over two consecutive hydrological years (2019/20 and 2020/21) and up-scaled to a stand level. Leaf area index (LAI), quadratic mean diameter, and soil water content (SWC) were measured over the same period using an LAI 2200 plant canopy analyser, manual dendrometers and CS616 sensors, respectively. The depth to groundwater was estimated to be approx. 28 m, using a borehole next to our study site. Results showed that transpiration followed a seasonal pattern, with daily mean of 2.3 mm‧tree−1‧day−1 (range: 0.18 to 4.55 mm‧tree−1‧day−1) and 3.3 mm‧tree−1‧day−1 (range: 0.06 to 6.6 mm‧tree−1‧day−1) for 2019/20 and 2020/21, respectively. Annual GU transpiration was higher than that found by international studies under similar conditions, but was within the same transpiration range as Eucalyptus genotypes in the KwaMbonambi area. Plantation water productivity, calculated as a ratio of stand volume to transpiration, was higher than for other published studies, which was attributed to a very high productive potential of the study site. Multiple regression using the random forests predictive model indicated that solar radiation, SWC and air temperature highly influence transpiration. There is a high possibility that our GU tree rooting system extracted water in the unsaturated zone during the dry season. Due to the use of short-term results in this study, the impact of GU on water resources could not be quantified; however, previous long-term paired catchment studies in South Africa concluded that Eucalyptus has a negative impact on water resources. Further research is suggested with long-term measurements of transpiration and total evaporation and an isotope study to confirm the use of water by GU trees in the unsaturated zone