Southern Forests: a Journal of Forest Science

A tree-level analysis of baboon damage in commercial forest stands using deep learning techniques

Wed, 01 Nov 2023 00:00:00 +0000

Commercial forest plantations in South Africa are homogeneous monocultures of highly bred exotic species grown to deliver timber products of the best potential quality. As such, these stands are susceptible to adverse effects of biotic and abiotic factors, and therefore require intense management to mitigate these risks. A sustainable forest monitoring system that can detect real-time changes in the physiological state of these plantations is needed for timeous management intervention to reduce losses. The use of machine learning algorithms has recently become popular, with acceptable levels of success. This study explores the application of deep learning neural networks for early detection of damage caused by baboons in evergreen plantations of Pinus species. Using PlanetScope imagery (spectral band 590–860 nm), which is captured by a constellation of Dove nanosatellites, with a high temporal resolution available daily at 3 m spatial resolution, the study achieved an overall accuracy of 81.54%, with a kappa value of 0.69, using a deep neural network. In comparison, using a random-forest classifier produced 74.04% accuracy and a kappa value of 0.62. The study successfully mapped different levels of baboon damage within commercial pine forests. We provide a repeatable method for daily monitoring initiatives, and attest to the utility of higher-resolution imagery such as PlanetScope for mapping health and damage severity at the tree level.

Effects of Acacia melanoxylon, an alien tree species to South Africa, on Afrotemperate forest tree sapling composition

Tineke Kraaij, Johan A. Baard, B. Adriaan Grobler, Bayleigh Miles — Wed, 01 Nov 2023 00:00:00 +0000

The alien tree Acacia melanoxylon (R.Br.) occurs extensively in the Southern Cape Afrotemperate Forest (South Africa). Concerns exist about its potential negative effects on indigenous tree sapling communities, ultimately with implications for forest composition and structure. We investigated whether Acacia melanoxylon affects Afrotemperate forest tree sapling composition in the Garden Route National Park. Using a paired plot design, we compared sapling species richness, diversity and density underneath 30 overstorey Acacia melanoxylon trees and 30 indigenous counterparts of the species Podocarpus latifolius (Thunb.) R.Br. ex Mirb, Afrocarpus falcatus (Thunb.) C.N.Page, or Olea capensis macrocarpa (C.H.Wright) I.Verd. We recorded 2 503 tree saplings from 27 indigenous species and only three Acacia melanoxylon saplings in the 60 plots. There were no significant differences in the richness, diversity or density of saplings underneath Acacia melanoxylon trees versus their indigenous counterparts. Non-metric multidimensional scaling and cluster analysis accordingly showed only minor differences in sapling species composition and abundance between Acacia melanoxylon and indigenous overstorey trees. We concluded that indigenous tree sapling composition is not significantly altered by the presence of Acacia melanoxylon trees at the densities (< 3 trees ha⁻¹) at which this species commonly occurs in Afrotemperate forest in the Garden Route National Park. However, populations of Acacia melanoxylon in the forest interior act as a source of propagules for invasion in forest margins, riparian areas and neighbouring fynbos shrubland, while at high density the species may alter forest gap-forming dynamics. These invasive attributes need to be considered in the management of the species in the region.

Fine-scale variation reveals high structure and floristic heterogeneity in dry forests of the Cerrado

Wed, 01 Nov 2023 00:00:00 +0000

This study aimed to compare the floristic and tree structure of two dry forests patches located in a forest remnant encompassed in Cerrado biome, south Goiás state, Brazil. In semideciduous (SF) and deciduous (DF) dry forests, we allocated 25 permanent plots (20 × 20 m), including trees and palms individuals with diameter at breast height (DBH1.3m) ≥ 5.0 cm. The whole survey showed 2 614 individuals, 146 species and 46 families. SF showed higher basal area and average height, but DF had higher density. Due to the low equitability and smaller species richness found in DF (87 species) than in SF (113), the Shannon diversity in SF was significantly higher. Both vegetation types showed low qualitative (Jaccard, 36%) and quantitative (Morisita, 19%) similarity, as only three of the 25 species regarded as having the highest importance/value were common in both dry forests. Fabaceae predominated in the number of species and density, especially in DF. Zoochory was more abundant, although it was not different between vegetation types, whereas both anemochory and autochory dispersion mechanisms were higher in DF. Although the surveys are geographically close, differences in the vegetation structure between dry forests showed strong heterogeneity and environmental complexity, reflecting an increase in local diversity, and reinforcing the need for conservation of these forest remnants in Cerrado.

The morphophysiological mechanisms of light-induced net primary production of Amazonian tree species

Wed, 01 Nov 2023 00:00:00 +0000

We investigated the morphophysiological mechanisms indicative of resource uses behind net primary production in seedlings of three valuable forest species of socio-economic value in the Amazon: mahogany (Swietenia macrophylla), Brazil nut (Bertholletia excelsa) and Laurel (Cordia alliodora). The hypotheses tested were: (i) the three species will grow better under mild to high light but with different magnitudes of response; and (ii) the three species will show different mechanisms to reach a better growth under mild to high light. We measured biomass production and a set of morphophysiological leaf traits and calculated the relative growth rates (diameter and height) of seedlings subjected to low (0.9), moderate (11.3) and high (45.0 mol m−2 day−1) irradiance for 80 days. For all species, biomass and growth increase with irradiance and the magnitude of the effect were species-dependent. The changes in total biomass by
irradiance varied 1.5-fold (B. excelsa) and twofold (S. macrophylla). Light-induced changes in biomass partitioning and morphophysiological traits varied among species. S. macrophylla and C. alliodora significantly increased root/ aboveground mass ratio (R/A) under high irradiance. Gas exchange increased with irradiance for C. alliodora and B. excelsa. The non-structural carbohydrates of C. alliodora and S. macrophylla were greater in high (total soluble sugars) and moderate (starch) light environments. The traits associated with total biomass were starch, stomatal conductance and transpiration for B. excelsa; leaf area ratio, leaf area root mass ratio, total soluble sugars and starch for C. alliodora; and R/A, leaf area ratio, and leaf area root mass ratio for S. macrophylla. The species obtained a high total biomass under mild to high irradiance but following different morphophysiological mechanisms. We discussed the potential to use these mechanisms in silvicultural systems designed to supply the plants with intermediate to high levels of light, for example enrichment planting in secondary forests or reforestation on degraded areas.

Estimation of genetic parameters for growth in a population of Eucalyptus grandis × Eucalyptus nitens hybrids in KwaZulu-Natal and Mpumalanga

W. Brink, G. van den Berg, A . Nel, B. du Toit — Wed, 01 Nov 2023 00:00:00 +0000

Hybridising Eucalyptus grandis with Eucalyptus nitens produces progeny intended to combine the favourable traits of both parents. E. grandis exhibits good growth, stem form, wood properties and rooting ability for vegetative propagation. E. nitens displays superior cold tolerance, including superior frost and snow tolerance, and high wood density. Eucalypt hybrids developed specifically for improved cold tolerance tend to produce fewer viable hybrid progeny and are more recalcitrant rooters than their sub-tropical counterparts. To overcome these challenges, a novel testing strategy was developed and used to identify promising varieties for commercial deployment. As a result, a large population of E. grandis × E. nitens hybrids was developed through controlled pollinations, propagated via mini- cuttings and established in a total of 21 field trials, across the KwaZulu-Natal and Mpumalanga provinces of South Africa, to investigate growth and adaptability. Data of three growth traits, namely diameter at breast height (DBH), total tree height and volume were analysed to determine the genetic parameters of these traits. Combined-site broad sense heritability for DBH, height and volume were 0.39, 0.46 and 0.35 respectively, indicating a moderate level of genetic control. This, in conjunction with large genetic coefficients of variation (CVg = 20%, 16% and 41% for DBH, height and volume respectively) shows that substantial gains can be made through selection. Combined-site Type B genetic correlations for DBH, height and volume were 0.71, 0.68 and 0.65 respectively, indicating that there was notable genotype by environment interaction. Pairwise comparisons of rBg for volume showed large variation in the correlations of clonal rankings between trials, with rBg ranging from 0.0 to 0.90.

Predictive modelling to determine the attainable moisture content of Alstonia boonei wood using a solar kiln dryer

Joy Aduralere Ogunsuy, Jacob Mayowa Owoyemi, Olusola Samuel Makinde — Wed, 01 Nov 2023 00:00:00 +0000

Modelling of wood drying is important for predicting the performance and efficiency of solar dryers and to optimise the drying process during each season of the year. The attainable moisture content (MC) of Alstonia boonei wood was studied when dried in a laboratory- scale solar kiln. Meteorological data (temperature, relative humidity, wind speed/direction and solar radiation) were observed over a period of 31 days. For the purpose of this study, three of the variables: temperature, relative humidity and solar radiation—were used for mathematical modelling of the drying process. The average attainable MC observed over a 31-day drying period was divided into a 70:30 dataset, representing calibrating and validating sets. Several regression models were formulated using the calibrating set. The optimal model was selected based on higher values of R² and R, and lower standard error, after which validation was done using the remaining dataset (validating set) by performing tests of bias and percentage bias and a student’s t-test. To meet the required criteria for a suitable model, values of the validating parameters must be low and have p-values that denote significance. The log polynomial model MC = −16 + 3.99 ln(SR2) + 1.49 ln(T2) + 5.80 ln(H2) was judged best for computing the attainable MC of A. boonei wood using a solar dryer across the whole year in the study area (Ondo State, Nigeria). The computational results showed fair agreement between the predicted and measured MC, which established the validity of the model and its suitability for application when drying low-density wood in the range of 340–370 kg/m³.