Slash Pine Research Articles

Response strategies of slash pine (Pinus elliottii) to cadmium stress and the gain effects of inoculation with Herbaspirillum sp. YTG72 in alleviating phytotoxicity and enhancing accumulation of cadmium.

Phytoremediation using fast-growing woody plants assisted by plant growth-promoting bacteria (PGPB) on cadmium (Cd)-contaminated sites is considered a promising technique; however, its remediation efficiency is still affected by multiple factors. In this study, the mining areas' soil conditions were simulated with different Cd addition levels (0, 3, 6, 9mgkg-1) in order to investigate the response strategy to Cd stress of fast-growing economic tree species, slash pine (Pinus elliottii), and the effects of inoculation with the PGPB strain Herbaspirillum sp. YTG72 on the physiological activity and Cd accumulation of plants. The main results showed that there were significant (p < 0.05) increases in contents of chlorophyll and nutrient elements (P, K, Ca, and Mg) at low Cd addition level (3mgkg-1) compared to non-Cd addition treatment. When the additive amount of Cd increased, the growth of plants was severely inhibited and the content of proline was increased, as well as Cd in plants. Besides, the ratios of K:P, Ca:P, and Mg:P in plants were negatively correlated with the contents of Cd in plants and soils. Inoculation of P. elliottii with the PGPB strain Herbaspirillum sp. YTG72 improved the physiological functions of the plants under Cd stress and activated the antioxidant system, reduced the accumulation of proline, and decreased the ratios of K:P, Ca:P, and Mg:P in plant. More importantly, planting P. elliottii in Cd-contaminated soil could significantly (p < 0.05) reduce the Cd content in the rhizosphere soil, and furthermore, inoculation treatment could promote the reduction of soil Cd content and increased the accumulation of Cd by root. The results of the present study emphasized the Cd response mechanism of P. elliottii based on multifaceted regulation, as well as the feasibility of strain Herbaspirillum sp. YTG72 assisted P. elliottii for the remediation on Cd-contaminated sites.

Effect of the Hole Diameter in Mechanical Properties of Wood: Experimental and Numerical Approaches

Introducing openings or holes into wooden structures is a common practice for providing utility services. However, this practice leads to stress concentration, resulting in a reduction in stiffness and load-carrying capacity. Therefore, understanding the effects of holes on beam properties is important for design considerations. This study investigates the mechanical behavior of a wooden beam made from juvenile Pinus elliottii containing open cylindrical holes with three different diameters: 4, 8, and 12 mm. The mechanical properties were evaluated for compression parallel to the fibers, quasi-static bending, and tension perpendicular to the fibers. Numerical simulations were conducted using a finite element (FE) model, considering the orthotropic elastic properties determined from experimental tests and elastic ratios reported in the literature. The experimental results indicated that the influence of hole diameter was not significant on the compressive properties; however, longitudinal crack failures began to form for holes with diameters of 8–12 mm. Regardless of hole size, the compressive and bending characteristics revealed that hole location did not affect the stiffness, strength, or damage mechanisms.

Predicting Wood Density Using Resistance Drilling: The Effect of Varying Feed Speed and RPM

The IML PD series Resi is a device used to assess the drilling resistance of wood. The IML PD series Resi instrument is being widely adopted for commercial wood quality assessment due to its speed, cost-effectiveness, and precision when combined with web-based trace processing. Collecting Resi data with fixed feed speed and RPM settings is challenging due to inherent basic density variations within and between tree species. Altering these settings affects the drilling resistance amplitude of the Resi data, impacting basic density predictions. This study introduces the concept of chip thickness to combine feed speed and RPM into a single parameter to minimise the effects of different sampling conditions on the basic density predictions. Regression models, with chip thickness as the regressor variable, account for 97% to 99% of variance in mean Resi outerwood amplitude across six species. The demonstrated adaptability of chip thickness for adjusting feed speed and RPM settings, along with species-specific functions correlating it with Resi amplitude, holds promise for standardizing amplitude values across diverse feed speeds and RPM settings. Optimal sampling conditions needed to predict basic density lie within the 30%–40% amplitude range. To drill a ~30 cm diameter tree, the recommended fastest settings were 200 cm/min and 3500 RPM for Southern Pine (Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Sénéclauze)) and Radiata Pine (Pinus radiata (D. Don.)), 200 cm/min and 2500 RPM for Hoop Pine (Araucaria cunninghamii (Mudie)), 50 cm/min and 5000 RPM for Spotted Gum (Corymbia citriodora subsp. variegata (F. Muell.)), 200 cm/min and 4500 RPM for White Cypress (Callitris glaucophylla (Thompson &amp; Johnson)), and 150 cm/min and 3500 RPM for Shining Gum (Eucalyptus nitens (H. Deane &amp; Maiden) Maiden) based on the billets sampled.

BIO-BASED CELLULOSE-BIOCHAR-PEG CRYOGELS FOR THERMAL INSULATION

Unbleached cellulose from Pinus elliotti and polyethylene glycol (PEG) were used for the manufacturing of bio-based cellulose-biochar-PEG cryogels. The cryogels were prepared by the sol-gel method, where biochar was added to a cellulose/PEG suspension, and subsequently freeze-dried. Also, biochar from poultry little waste was employed as reinforcement, aiming to increase mechanical and thermal properties. The main resuls showed that, for cryogels with biochar (5.0 wt% in relation to cellulose) and PEG (5.0 wt% in relation to the cryogels mass), an increase of the compressive strength by about 30% was achieved. The thermal conductivity of the same samples with biochar reached similar results (0.041 W m-1.K-1). Therefore, the produced material has potential to be applied as thermal insulator as an environmentally friendly alternative, with the properties that meet the requirements for traditional thermal insulators.

UAV-driven GWAS analysis of canopy temperature and new shoots genetics in slash pine

Canopy temperature and new shoot counts are pivotal traits for evaluating the adaptability and productivity of slash pine (Pinus elliottii Engelm.). Traditional methods for assessing these traits are labor-intensive and lack the required accuracy. Despite their ecological and economic importance, the genetic and molecular underpinnings of these traits remain largely unexplored. In this study, we utilized UAV remote sensing technology for conducting high-throughput phenotyping of canopy temperature and new shoot counts and performed a Genome-Wide Association Study (GWAS) to identify key candidate genes associated with these traits. Our Manhattan plot analysis revealed intriguing patterns. The GWAS analysis of both July and August identified the same four key candidate genes for new shoot counts including scaffold119881_56626, scaffold119881_56642, scaffold96999_96025, and scaffold7133_48553 respectively. However, for canopy temperature, no key candidate genes were identified in the overall monthly analysis. Interestingly, diurnal variations in canopy temperature influenced the identification of key genes. While no key genes were identified during the afternoon and evening, two were found in the morning: scaffold33143_278946 and super3157_662643. Our UAV-based approach proved to be highly accurate and portable, with significant heritability estimates for both traits. This study represents the first GWAS analysis on these traits and underscores the importance of integrating high-throughput phenotyping and genotyping technologies for advancing forest genetic improvement programs, particularly in the selection of key candidate genes influenced by diurnal and monthly variations.

Differentiating Historical Open Forests and Current Closed Forests of the Coastal Plain, Southeastern USA

The southeastern United States was historically characterized by open forests featuring fire-adapted species before land-use change. We compared tree composition and densities of historical tree surveys (1802 to 1841) to contemporary tree surveys, with the application of a similarity metric, in the Coastal Plain ecological province of Mississippi, southeastern USA. We detected the boundary between historical pine and oak-pine open forests and differentiated historical and current forests. In the Coastal Plain, historical open forests converted from fire-tolerant longleaf pine (Pinus palustris) dominance, with pines comprising 88% of all trees, to loblolly (Pinus taeda) and slash (P. elliottii) pines within monocultures (45% of all trees). Wetland and successional tree species increased to 33% of all trees. Contemporary forests have greater tree densities, transitioning from closed woodlands (range of 168 to 268 trees ha−1) to closed forests (336 trees ha−1). In the ecotonal boundary of the northern Coastal Plain between historical pine and pine-oak woodlands, the pine component shifted over space from 88% to 34% of all trees due to a greater oak component. Fire-tolerant shortleaf pine and oak dominance converted to planted loblolly pine (52% of all trees), while successional tree species increased (20% of all trees). Historical tree densities represented woodlands (range of 144 to 204 trees ha−1) but developed into closed forests (400 trees ha−1). Historical Coastal Plain longleaf pine woodlands differed more from historical ecotonal oak-pine woodlands than contemporary forests differed from each other, demonstrating unique historical ecosystems and landscape-scale homogenization of ecosystems through forestation.

Pest categorisation of Dendrolimus punctatus.

The EFSA Panel on Plant Health performed a pest categorisation of Dendrolimus punctatus (Lepidoptera: Lasiocampidae), following a commodity risk assessment of bonsai Pinus parviflora grafted onto P. thunbergii from China, in which D. punctatus was identified as a pest of possible concern to the European Union (EU). D. punctatus, also known as the Masson pine caterpillar, is present in China, Taiwan, Vietnam, India and has recently spread to Japanese islands close to Taiwan. Larval feeding on the needles of Pinus elliottii, P. luchuensis, P. massoniana, P. merkusii and P. tabulaeformis causes important damage. D. punctatus larvae can also feed on P. armandii, P. echinata, P. latteri, P. parviflora, P. sylvestris var. mongolica, P. taeda, P. taiwanensis and P. thunbergii, but full development on these hosts is uncertain. The pest has three to five generations per year; winter is spent as larvae on branch tips, on tree trunks and in the soil. The females lay egg clusters on pine needles. Pupation occurs in cocoons attached to branches or needles. D. punctatus could enter the EU either as eggs, larvae or pupae in the foliage of plants for planting or cut branches, as larvae on wood with bark or as overwintering larvae in branches, crevices in the bark or in the litter of potted plants. However, Annex VI of 2019/2072 prohibits the introduction of D. punctatus hosts (Pinus spp.) from countries and areas where the pest occurs. There are climate zones where the pest occurs in Asia that also occur in the EU, though they are limited, which constitutes an uncertainty regarding establishment. The pest's main hosts are not grown in the EU. However, the fact that it attacks the North American Pinus echinata, P. elliottii and P. taeda in its Asian native area suggests a potential capacity to shift to pine species occurring in the EU territory. D. punctatus satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. Whether the Pinus commonly found in Europe could act as hosts is unknown but is fundamental, affecting the criteria of establishment and magnitude of impact.

Impact of Aspergillus fumigatus inoculation on the composting of wood shaving bedding for horses.

Equine farming generates a significant amount of waste, prompting the need for effective management. Composting enhanced by filamentous fungi holds promise for this purpose. This study focused on inoculating Aspergillus fumigatus isolates in composting horse bedding made with wood shavings (Pinus elliottii). The experiment lasted 90 days, with two treatment groups, control and inoculated, analyzing temperature, pH, electrical conductivity, total organic carbon and nitrogen content, and cellulose, hemicellulose, and lignin contents. Both treatments entered the thermophilic phase by the fourth day, reaching temperatures above 55°C and mesophilic maturation at 35 days (41±0.2°C). The inoculated treatment exhibited higher electrical conductivity after 30 days and a more pronounced reduction in the total carbon content (42.85%vs. 38.29%) compared to the control. While there was no significant nitrogen difference, the inoculated treatment had a sharper reduction in carbon/nitrogen ratio, and cellulose and hemicellulose contents. Both treatments showed low coliform counts, no Salmonella sp., and reduced Strongyloides sp. larvae. Inoculating A. fumigatus in saturated horse bedding made from wood shavings improved compost quality, providing a possibility for sustainable equine farming waste treatment.

Polyethylene terephthalate (PET) as a recycled raw material for particleboards produced from pinus wood and biopolymer resin

Considering the significant demands for construction products and the increasing disposals of plastic and agroforestry residues, this research evaluated the influence of recycled particles of polyethylene terephthalate (PET) inserted in the manufacture of five particleboard prototypes based on Pinus elliottii wood and castor-oil-based polyurethane resin (CPUR). The following panel traits were obtained: 100% pine wood, 0% PET and 10% CPUR (M100P-0PET-10C); 70% pine, 30% PET, and 10% CPUR (M70P-30PET-10C); 50% pine, 50% PET, and 10% CPUR (M50P-50PET-10C); 70% pine, 30% PET, and 5% CPUR (M70P-30PET-5C); and, 50% pine, 50% PET, and 5% CPUR (M50P-50PET-5C). Panels were evaluated according to physical (density, moisture content, thickness swelling, and water absorption), mechanical (modulus of rupture, modulus of elasticity, perpendicular tensile), and morphological tests (scanning electron microscope). M50P-50PET-10C particleboards revealed the best performance in the physical and mechanical tests, as well as M70P-30PET-10C and M50P-50PET-5C panels showed equivalent results. The findings suggested a notable environmental contribution and a great economic feasibility. Thus, it is possible to obtain wood-based particleboards manufactured from recycled PET, reusing this highly discarded non-biodegradable plastic and using a smaller volume of adhesive, with physical-mechanical properties that meet the expected performance for this bioresource-based product.

EFFECT OF RESIDENTIAL STOVE TECHNOLOGY ON GASEOUS EMISSIONS FROM BIOMASS COMBUSTION

The growing use of biomass for cooking and heating raises environmental concerns about atmospheric air pollution from flue gases emitting during its combustion. In this work, the gaseous emissions from two residential wood stoves were examined. Emissions from conventional single-stage and triple-stage combustion logwood stoves were compared using Eucalyptus grandis (EUG) and Pinus elliottii (PIE) woods as fuels. Carbon monoxide emissions were reduced in 102% and 240%, when PIE and EUG wood logs were burned in triple-stage combustion stove. The triple combustion system showed total volatile organic compounds and formaldehyde emissions higher than obtained in conventional system possibly due to the mixture of both gaseous emissions with water vapor releasing during combustion. The results indicated that the utilization of triple combustion stove with some adjustments would be beneficial to local air quality, individual health and reduced global climate change.

Assessing the potential impact of retaining native off‐site tree species in woodland restoration

Reestablishing appropriate tree species is an important step in converting off‐site monocultures into woodlands. Species conversion is often necessary, as off‐site exotic species rarely function like woodland species. However, when off‐site tree species are native, and functionally redundant to woodland species, conversion may be unnecessary. To explore this possibility in the southeastern United States, we reviewed the literature on trait differences among the primary southern pines and qualitatively assessed the effect of their identity at the species and stand‐levels. In this region, woodland restoration focuses on removing loblolly (Pinus taeda) and slash pine (P. elliottii) to reestablish longleaf (P. palustris) or shortleaf pine (P. echinata). Our review found minimal variation among species in understory flammability, fire resistance at maturity, and Red‐cockaded Woodpecker (Leuconotopicus borealis) habitat at the stand‐level. Longleaf and shortleaf pine were generally more resistant to abiotic and pest disturbance at the tree‐level; however, stand‐level differences in wind, drought, and boring insect resistance among southern pines growing in open forests were considered minimal. Retaining loblolly and slash pine will improve stand‐level productivity in the short term, but creates regeneration problems due to low juvenile fire resistance and resilience. Ice resistance and long‐term carbon sequestration will also likely be reduced by retaining loblolly and slash pine. Collectively, these results suggest that southern pine species are generally interchangeable at the stand‐level in woodlands; although woodlands featuring loblolly and slash pine may be less stable in the face of disturbance than those dominated by shortleaf and longleaf pine.

The Carbon Storage of Reforestation Plantings on Degraded Lands of the Red Soil Region, Jiangxi Province, China

To assess the effects of reforestation on ecosystem carbon storage, a long-term Forest Restoration Experimental Project (FREP) was established in 1991 on southern degraded red soil in Taihe County, Jiangxi Province, China. In this study, we selected five types of plantations: Schima superba plantation (SS), Liquidambar formosana plantation (LF), Pinus massoniana plantation (PM), Pinus elliottii plantation (PE), and P. elliottii and broadleaf mixed plantation (MEB). The unforested land was used as an experimental control check (CK). We aimed to assess the changes in carbon storage in plantations and the factors affecting them. Thirty years after reforestation, the ecosystem carbon storage of the five types of plantations was significantly higher than that of the control site, and there were also significant differences in the ecosystem carbon storage between the different plantation types (p &lt; 0.05). The ecosystem carbon storage of SS, MEB, LF, PM, and PE were 211.71 Mg ha−1, 199.02 Mg ha−1, 160.96 Mg ha−1, 155.01 Mg ha−1, and 142.88 Mg ha−1, respectively. Compared to the CK, these values were increased by 436.8%, 404.6%, 308.1%, 293.1%, and 262.3%, respectively. The ecosystem carbon storage was significantly positively correlated with soil porosity, total nitrogen (TN), and stand density, and was significantly negatively correlated with pH, Pielou’s evenness index (PEI), and the Shannon–Weiner diversity index (SWDI). The soil water content (SWC), bulk density (BD), SWDI, and stand density can be used as indicators of the impact of reforestation plantings on ecosystem carbon storage. The research results has shown that reforestation plantings significantly increase ecosystem carbon storage, and that afforestation should be encouraged on degraded land.

Predicting Wood Density Using Resistance Drilling: The Effect of Instrument and Operator

The IML PD series Resi is an instrument designed to measure the drilling resistance of wood. Use of the IML PD series Resi instrument is rapidly becoming a routine method among Australian forest plantation growers for wood quality assessments. The major driver in the commercial uptake of the IML Resi is that it is fast, cheap, and sufficiently precise for commercial use, particularly when the data are processed through a user-friendly, web-based processor. This study examined whether the accuracy of wood density predictions was impacted by the use of different Resi tools and different operators, which has never been examined before. Seven Resi instruments were evaluated across six sites with two operators on plantation-grown Southern Pine (Pinus caribaea var. hondurensis (Sénéclauze) or hybrids between Pinus elliottii var. elliottii (Engelm) × P. caribaea var. hondurensis) trees. Two types of Resi instruments were used (IML Resi PD-400 and IML Resi PD-500), and all had been recently serviced or were new. The instruments were operated by experienced operators. Constant sampling conditions of feed speed 200 cm/min and 3500 RPM were used. The order of instrument use, and hence the order of operator assessment at each site, was randomized. The variance between Resi instruments was small. The measured mean basic density of 50 mm outerwood cores across all plots was 542 kg/m3, while Resi-predicted basic density varied among instruments between 535 and 547 kg/m3. One Resi instrument underpredicted basic density by 9 kg/m3 and another overpredicted by 5 kg/m3. The operator had no effect on the basic density prediction. Resi PD400 or PD500 instruments gave similar basic density predictions.

Estimating canopy chlorophyll in slash pine using multitemporal vegetation indices from uncrewed aerial vehicles (UAVs)

Estimating canopy chlorophyll in slash pine using multitemporal vegetation indices from uncrewed aerial vehicles (UAVs)

Enhancing genomic association studies in slash pine through close-range UAV-based morphological phenotyping.

In forestry genetics and industry, tree morphological traits such as height, crown size, and shape are critical for understanding growth dynamics and productivity. Traditional methods for measuring these traits are limited in efficiency, scalability, and accuracy, posing challenges for large-scale forest assessments. This study focuses on integrating unmanned aerial vehicle (UAV) technology with GWAS to improve genomic association studies in slash pine (Pinus elliottii). Seven key morphological traits have been identified (canopy area (CA), crown base height (CBH), crown length (CL), canopy volume (CV), crown width (CW), crown width height (CWH), and tree height (H)) through advanced UAV-based phenotyping. These associations account for a remarkable range of heritability in slash pine, with traits such as CBH, CL, CV, and H showing relatively high heritability across both Single nucleotide polymorphisms (SNP) and pedigree methods, indicating strong genetic influence, while traits such as CWH show lower heritability, suggesting greater environmental influence or non-additive genetic variance. The GWAS identified 28 associations, including 22 different SNPs localized to 16 candidate genes, that were significantly associated with the morphological traits of Slash Pine. Notably, two of these candidate genes, annotated as putative DEAD-like helicase and ethylene-responsive element binding factor (ERF), were present at different mutation sites and were significantly associated with CW and CA traits, respectively. These results demonstrate that the UAV imaging enables a comprehensive analysis of the Morphological growth response of slash pine and can facilitate the discovery of informative alleles to elucidate the genetic structure underlying complex phenotypic variation in conifers.

Genetic selection for growth, wood quality and resin traits of potential Slash pine for multiple industrial uses.

This study aims to understand the genetic basis of key industrial traits in Slash pine (Pinus elliottii Engelm. var. elliottii) to enhance improvement efficiency. Detailed analyses were conducted on inter-family differences, genetic parameters, correlations, and breeding values (BVs) for growth, wood properties, and resin traits of Slash pine planted in Changle Forest Farm of Hangzhou, leading to the identification of elite families. It indicates that growth traits are primarily influenced by environmental effects, while wood properties exhibit a significant impact of genetic effects. The variation in resin traits arises from both genetic and environmental effects. Notably, Beta-pinene exhibits the highest variability and genetic gains among the traits analyzed. The family heritability ranges for growth, wood properties, and resin traits are 0.543-0.794, 0.870-0.885, and 0.285-0.695, respectively. Significant positive correlations are evident between growth and resin traits, while a negative correlation is observed between growth and wood properties. Elite families identified through single-trait and multi-trait combined selection are 8-126 for growth traits, 2-325 and 0-373 for wood properties, and 8-131 for resin traits. The average genetic gains for these elite families are 7.44%, 7.17%, and 8.84%, respectively. These findings provide valuable insights for high-generation breeding of Slash pine and lay a genetic foundation for formulating effective breeding strategies for conifers.

MTSC-Net: A Semi-Supervised Counting Network for Estimating the Number of Slash pine New Shoots.

The new shoot density of slash pine serves as a vital indicator for assessing its growth and photosynthetic capacity, while the number of new shoots offers an intuitive reflection of this density. With deep learning methods becoming increasingly popular, automated counting of new shoots has greatly improved in recent years but is still limited by tedious and expensive data collection and labeling. To resolve these issues, this paper proposes a semi-supervised counting network (MTSC-Net) for estimating the number of slash pine new shoots. First, based on the mean-teacher framework, we introduce the improved VGG19 to extract multiscale new shoot features. Second, to connect local new shoot feature information with global channel features, attention feature fusion module is introduced to achieve effective feature fusion. Finally, the new shoot density map and density probability distribution are processed in a fine-grained manner through multiscale dilated convolution of the regression head and classification head. In addition, a masked image modeling strategy is introduced to encourage the contextual understanding of global new shoot features and improve the counting performance. The experimental results show that MTSC-Net outperforms other semi-supervised counting models with labeled percentages ranging from 5% to 50%. When the labeled percentage is 5%, the mean absolute error and root mean square error are 17.71 and 25.49, respectively. These findings demonstrate that our work can be used as an efficient semi-supervised counting method to provide automated support for tree breeding and genetic utilization.

Ultrasound-assisted extraction of polyphenols from pine needles (Pinus elliottii): Comprehensive insights from RSM optimization, antioxidant activity, UHPLC-Q-Exactive Orbitrap MS/MS analysis and kinetic model

Extracting polyphenolic bioactive compounds from Pinus elliottii needles, a forestry residue, promises economic and environmental benefits, however, relevant experimental data are lacking. Herein, a comprehensive investigation of the polyphenolic composition of pine needles (PNs) was carried out. Ultrasound-Assisted Extraction (UAE) was applied to extract the polyphenolic compounds of pine needles. The optimal conditions of extracts were determined by Response Surface Methodology (RSM). The maximum total phenolic content (TPC) of 40.37 mg GAE/g PNs was achieved with solid–liquid ratio of 1:20, 60 % ethanol, and 350 W for 25 min at 45 °C. Polyphenolic extracts showed antioxidant activity in scavenging free radicals and reducing power (DPPH, IC50 41.05 μg/mL; FRAP 1.09 mM Fe2+/g PNs; ABTS, IC50 214.07 μg/mL). Furthermore, the second-order kinetic model was also constructed to describe the mechanism of the UAE process, with the extraction activation energy estimated at 12.26 kJ/mol. In addition, 37 compounds in PNs were first identified by UHPLC-Q-Exactive Orbitrap MS/MS, including flavonoids and phenolic acids. The results suggest that Ultrasound-Assisted is an effective method for the extraction of natural polyphenolic compounds from pine needles and this study could serve as a foundation for utilizing phenolics derived from PNs in the food and pharmaceutical industries.

Understory vegetation diversity patterns of Platycladus orientalis and Pinus elliottii communities in Central and Southern China.

As a vital component of arbor forests, understory vegetation serves as an essential buffer zone for storing carbon due to its strong capacity for community regeneration. This study aimed to identify the diversity pattern and construction mechanism of Platycladus orientalis and Pinus elliottii understory vegetation based on large-scale sample surveys. The Bayesian Information Criterion value of species abundance distribution (SAD) indicated that the Zipf and Zipf-Mandelbrot models were the best-fitting models. The SAD and gambin fitting results suggested that the Pi. elliottii community had a more balanced structure, with most species being relatively abundant. The multiple regression tree model detected four and six indicator species in P. orientalis and Pi. elliottii communities, respectively. The α-diversity index increased with a rise in altitude and showed a wavy curve with latitude. Linear regression between the β diversity and environmental and geographic distance indicated that the P. orientalis and Pi. elliottii understory communities tended to be dominated by different ecological processes. The partition of β diversity indicated that both communities were dominated by turnover processes, which were caused by environmental classification or spatial constraints. This study helped to understand the diversity maintenance in the P. orientalis and Pi. elliottii understory vegetation communities, and will benefit for diversity restoration and conservation of pure conifer forests.

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

Abstract. Pine 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 &gt; 0.05) in 2019/20, whereas the 2020/21 year produced significant differences (p&lt;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.