Howick, South Africa
Howick, South Africa

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Crous J.W.,Sappi Forests | Burger L.,Stellenbosch University
Southern Forests | Year: 2015

Results from two coppice compared to replant trials are presented that originated from clone by site interaction (CSI) trials established on high‑ and low‑productivity sites in subtropical coastal KwaZulu‑Natal, South Africa. After the 84‑month CSI trial measurements were completed the trees were harvested. Selected plots were allowed to coppice with the remainder replanted to the same four Eucalyptus grandis×Eucalyptus urophylla hybrid clones. Growth was higher at Kwambo Timbers (average mean annual increment [MAI] 34 wet white tonnes [wwt] ha−1 y−1), characterised by a higher mean annual precipitation, than at Palm Ridge (average MAI 11 wwt ha−1 y−1). In these trials coppicing of sufficient stumps per hectare (>1 000 stumps ha−1) resulted in similar volume production on the higher‑productivity site and slightly improved (additional 3.4 wwt ha−1 y−1) yield on the lower‑productivity site compared with the planted crop. The benefit of coppicing was mainly related to a reduction in the temporary unplanted period and reduced establishment cost. This study showed that coppicing can be a viable, cost‑effective alternative to planting in commercial forestry if a number of criteria are met. However, it is recommended that the decision to coppice or to replant should be evaluated on a case‑by‑case basis. © 2015 NISC (Pty) Ltd.

Crous J.,Sappi Forests | Burger L.,Stellenbosch University | Sale G.,Sappi Forests
Southern Forests | Year: 2013

South Africa's climate is characterised by the occurrence of regular droughts. An assessment of drought mortality in KwaZulu-Natal during 1999 could not provide accurate information regarding the effect of species or planting density on mortality because of confounding species-site allocations. Thus, following the 1999 drought event a trial was established in a drought-prone area, planted to a number of genotypes that were deemed to be more tolerant to water stress than Eucalyptus grandis. Each species was planted at stand densities of 816, 1 600 and 2 066 stems ha-1, where 1 600 stems ha-1 represented the current operational prescription. The aim of the trial was, firstly, to find a genotype that would yield more utilisable timber and, secondly, to determine the effect of planting density on tree mortality and growth. It was hypothesised that planting at a lower density will reduce stand-level growth slightly, but that it will reduce tree mortality under drought conditions. Serious drought symptoms were observed in this trial during October 2010. After the drought event that occurred towards the end of the rotation, the survival of the E. grandis × E. camaldulensis hybrid clone (98.7%) and E. dunnii (72%) was superior to that of E. grandis (52%). Across all genotypes the survival percentage on the densely planted plots (2 066 stems ha-1) was significantly lower than on the other two planting densities (1 600 stems ha-1 and 816 stems ha-1). Both E. dunnii and the E. grandis × E. camaldulensis hybrid clone had better or similar growth, and showed fewer symptoms of water stress than E. grandis. This clearly illustrated the importance of selecting genotypes that can tolerate water stress for establishment on drought-prone sites. The risk of drought mortality can be further reduced by planting trees at a lower density. © 2013 Copyright © NISC (Pty) Ltd.

Poona N.K.,Stellenbosch University | Ismail R.,Sappi Forests
Southern Forests | Year: 2013

Pathogenic fungi, such as Fusarium circinatum, present a serious threat to Pinus radiata plantations. The effective management of infected trees is thus paramount. Coupled with advanced techniques, high spatial resolution remote sensing data provides the necessary tools to effectively identify and map infected trees. This paper explores the utility of transformed high spatial resolution QuickBird imagery and artificial neural networks for the detection and mapping of pitch canker disease. Individual tree crowns were delineated using an automated segmentation and classification approach within an object-based image analysis environment. Subsequently, several vegetation indices including the tasseled cap transformation were calculated and incorporated into a neural network model. The feed-forward neural network showed high discriminatory power with an overall accuracy of 82.15% and KHAT of 0.65. The results of this study show great potential for the future application of crown-level mapping of the pitch canker disease at a landscape scale. © 2013 Copyright NISC (Pty) Ltd.

du Toit B.,Stellenbosch University | Smith C.W.,Institute for Commercial Forestry Research | Little K.M.,Institute for Commercial Forestry Research | Boreham G.,Sappi Forests | Pallett R.N.,Sappi Forests
Forest Ecology and Management | Year: 2010

An important window of opportunity to increase and sustain productivity in short-rotation plantations is the period from felling through re-establishment to canopy closure. This paper explores the effects, interactions and response mechanisms of intensive silvicultural practices on plantation productivity and sustainability, using five South African case studies (a-e). (a) Land preparation trials showed that complete surface cultivation by ploughing had a significant beneficial effect when afforestation is done for the first time in grasslands, improving basal area growth by 11-52% over pitting only. However, similar treatments have not resulted in significant growth responses under re-establishment conditions. (b) Stand growth suppression resulting chiefly from soil compaction during mechanised harvesting operations is strongly related to soil type, soil textural class and residue management options. Volume growth reduction in short-rotation eucalypt crops ranged from 25% on compaction sensitive loamy soils to less than 2% in resistant sandy soils. (c) The response mechanism whereby vegetation management improves stand productivity is a reduction in both inter-specific and intra-genotypic competition for resources, as well as a decrease in stand variability. Operationally, the most important criteria in a vegetation management programme relate to the timing of control operations across diverse site conditions. In local trials, the primary factors controlling the time taken for competition-induced tree growth suppression to occur were related to altitude, slash burning and the interaction between these factors, which facilitated the development of regional vegetation management strategies. (d) Empirical fertilizer trials in short-rotation hardwood stands have shown significant improvements in final productivity (commonly 20-90 m3 ha-1 in eucalypts and 30-50 m3 ha-1 in Acacia), as well as wood density (15-30 kg m-3 for eucalypts) following improvements in early nutrition. Improved nutrition was achieved through fertilization at planting or indirectly through residue management. The response mechanism is primarily due to early canopy development and associated increases in light capture, coupled with a more modest increase in canopy quantum efficiency and above-ground carbon allocation on a dry site. On sites with abundant water supply, increased quantum efficiency is likely to be the dominant response mechanism. (e) A series of operational gains trials tested the interactive effect of genetic tree improvement, site-genotype interaction, stand density and vegetation management + fertilization on eucalypt stand growth across five sites. There were no significant interactions between factors, but importantly, the results were additive, emphasizing the need to optimise each practice in the value chain to achieve maximum productivity. © 2009.

Ismail R.,Sappi Forests | Ismail R.,University of KwaZulu - Natal | Kassier H.,Sappi Forests | Chauke M.,Sappi Forests | And 2 more authors.
Southern Forests | Year: 2015

In commercial forestry, regular terrestrial enumerations of the growing stock are required for the valuation, sustain-able management and planning of current and future timber supplies. In this study we examined whether the combination of synthetic aperture radar (ALOS PALSAR) and optical satellite (SPOT 4) image data can accurately predict the timber volume of even-aged Eucalyptus plantations located in South Africa. Results from this study show that the combination of ALOS PALSAR and SPOT 4 produces a R 2 value of 0.68 for the planted model, whereas the coppiced model produced a R 2 value of 0.55. However, by including stand age as an independent variable in the stepwise model, there was a 15% improvement for the planted model, whereas the coppiced model produced a 27% improvement. The final model developed in this study produced a R 2 value of 0.83 and a RMSE of 31.71 m3 ha−1 for planted stands, whereas the model for coppiced stands produced a R 2 value of 0.82 and a RMSE of 27.70 m3 ha−1. As it is not practical or financially feasible for commercial forestry companies to carry out terrestrial enumerations for all plantations on an annual basis, the model developed in this study presents an alternative and accurate method to calculate timber volume for even-aged Eucalyptus plantations. © 2015 NISC (Pty) Ltd.

Crous J.W.,Sappi Forests | Morris A.R.,Sappi Forests | Scholes M.C.,University of Witwatersrand
Forest Science | Year: 2011

Previous research indicated that the application of phosphorus (P) and potassium (K) fertilizer to Mexican weeping pine (Pinus patula Schiede ex Schltdl. & Cham.) on gabbro-derived soils was necessary to correct a second rotation yield decline. To plan efficient fertilization of subsequent rotations, the fate and utilization of the applied K fertilizer was investigated using the rubidium (Rb)/K reverse tracer technique whereby the naturally occurring Rb in the soil was used as an indicator of native soil K. At the age of 15 years, samples from the soil, forest floor, bark, wood and live foliage were collected from a trial in which various amounts of P and K fertilizer were applied at different stages of stand development. No significant quantity of the applied K remained in the soil at the end of the 15-year rotation, but sufficient plant-available P remained on plots where 80 kg ha-1 P and K was applied. Significantly greater quantities of P per ha were found in the forest floor, wood, and foliage on the plots that received 40 or 80 kg ha-1 P and K compared with the control. The application of 80 kg ha-1 P and K increased the P content of the wood and foliage over that recorded in the 40 kg ha-1 P and K treatment. The application of 80 kg ha-1 P and K increased the K content of the forest floor and foliage compared with that of the control. Across all PK quantities, fertilizer K contributed 28, 17, and 8% to the quantity of K in the wood, bark, and foliage, respectively. The export of up to 52 kg K ha-1 from the site in wood and bark will necessitate the reapplication of at least 104 kg K ha-1 to the subsequent rotation to produce timber sustainably on the gabbro-derived soils at Usutu. © 2011 by the Society of American Foresters.

Crous J.W.,Sappi Forests
Southern Forests | Year: 2016

The quantity of available water in soil is crucial for plant growth, especially after transplanting as this water will enable the growth of new roots to facilitate nutrient and water uptake. Water absorbed by a hydrogel (superabsorbent polymer) has the potential to reduce drought stress after planting and to improve seedling survival. This article provides an overview of the concepts of post-plant water stress, a review of trials that tested application of hydrogels to forest tree species, and discussion on probable reasons for failure or success in the use of hydrogels. Hydrogels applied in pot trials, under controlled conditions, tended to have a higher frequency of positive survival responses compared with field trials (14 studies of the 17 (82%) in pot trials vs 15 of the 25 (60%) in field trials). In field trials, the application of hydrogels at planting had no effect on survival in seven of the 25 (28%) trials and had a negative effect in three of the 25 (12%) field trials included in this review. In the trials showing a positive response a hydrogel and water application improved survival by 18% and across all trials by 8%. The efficiency of hydrogels was probably influenced by the (1) chemicals present in the soil, (2) hydrogel quantity applied, (3) type of polymer, (4) hydrogel particle size distribution, (5) soil texture, (6) physical restrictions to hydrogel expansion, (7) hydrophilic nature of hydrogels, (8) unsaturated hydraulic conductivity between the substrate and the hydrogel particles, (9) application method and (10) planting conditions and rewatering. Due to this complexity and interactions between these factors it is difficult to provide site-specific recommendations for successful application of hydrogels in a forestry field setting. In general, application of hydrogels has been found to be more beneficial in sand or clay soils and to be of limited benefit in loam soils. Use of a hydrogel is not a replacement for good silviculture and has limited use as insurance against short periods of low rainfall. All efforts should be made to plant when environmental conditions are favourable for tree growth (i.e. wet soil and high probability of rainfall). © 2016 NISC (Pty) Ltd

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