John C. Grant

Silvicultural implications arising from a simple simulation model for Endospermum medullosum in Vanuatu

SUMMARY Whitewood (Endospermum medullosum) is a tree species that shows promise for plantation timber production in Vanuatu, but few growth data are available to inform yield forecasts. Three simple relationships summarizing stand dynamics, namely height-age, diameter-height-stocking, and mortality-basal area relationships, were calibrated with data from 15 plots to form the basis of a model for silvicultural and management decisions. Despite the simplicity of the model, it offers predictions consistent with independent data. The model suggests that the optimal silviculture involves planting 635 stems/ha, thinning at 20 and 26 years, and clearfelling at age 36 when trees have a diameter of 55 cm dbh. However, many options offer a net present value within 5% of this nominal optimum. The flexibility to vary the timing and intensity of harvests over a wide range while maintaining good financial returns, coupled with good growth and timber properties, suggests that whitewood warrants further domestication and promotion in Vanuatu.

Spacing Affects Stem form, early Growth and Branching in Young Whitewood (Endospermum medullosum) Plantations in Vanuatu

SUMMARY This paper investigates the early growth response, branching and stem quality of Endospermum medullosum (whitewood) at different spacings. Whitewood plantings were established at stockings of 400–833 trees per hectare and early growth, tree stem quality and branching were quantified up to age 3 years. Growth, number of live branches and branch size were negatively correlated with stocking. The stocking of trees of acceptable quality had high spatial variation. Initial spacing in whitewood plantations can be used to manipulate branch size, crown rise and stem size; all of which are important for development of pruning and thinning regimes to produce high quality logs. If unimproved whitewood stock is used, to ensure that there are 300 stems per hectare of acceptable quality to produce sawlogs, more than 600 trees per hectare should be established at planting.

A review of site-preparation, fertilizer and weeding practices for tropical plantation species with recommendations for whitewood (Endospermum medullosum) in Vanuatu

SUMMARY The development of plantations with a new species, such as is occurring with the endemic tree Endospermum medullosum (whitewood) in Vanuatu, requires the resolution of appropriate establishment techniques. Site preparation, fertilisation and weed control have a very large impact on plantation productivity and represent major risks to plantation success. Establishment techniques for tropical species are reviewed and preliminary site preparation and fertilisation trials for whitewood reported. Trials were established at a site on Espiritu Santo island using available general purpose fertiliser with and without micronutrients at two rates. There was no effect of fertiliser over various rates of complete fertiliser with and without micronutrients, designed to provide adequate phosphorus in volcanic ash soils. Ripping had no significant effect on growth, however insufficient hand clearing of vegetation resulted in lower growth due to competition and complete machine clearing of vines results in high temperatures and decreased survival. A serious issue for whitewood establishment in single species plantations is weed management, especially vine control (Merremia spp). The time needed for weed control is influenced by initial planting density and spacing. When inter-planted with mixed gardens of food crops, weed control is not an issue due to more regular tending.

Constraints to whitewood (Endospermum medullosum) plantation development on Santo Island, Vanuatu

SUMMARY Valuable timber trees in accessible sites in Vanuatu have been mostly removed by logging. There are large areas where plantations would likely be successful. Yet plantation establishment among landholders in Vanuatu has been limited to date, even with considerable extension support. There has been little systematic investigation of why this has occurred. The purpose of this research was to identify constraints to whitewood (Endospermum medullosum) plantation development. A participatory social research approach was used on Espiritu Santo Island to look for trends in attitudes toward plantations. This was achieved through the use of mixed methods social research to survey 139 local landholders from 42 villages. Most landholders on Santo Island were not convinced that there are good reasons to plant whitewood, at least not in large extensions. Future efforts should be focused on the development of local capacity for plantation establishment, maintenance, processing and export marketing, at a variety of scales.

Site Index Prediction of 'Eucalyptus dunnii' Maiden Plantations with Soil and Site Parameters in Sub-tropical Eastern Australia

Summary The Eucalyptus dunnii Maiden plantation estate in north-eastern NSW and south-eastern Queensland is significantly expanding on ex-grazing land. Thirty-one growth plots (average age 5.2 y) covering a latitudinal range of about 3.2° (370 km) and at altitudes from 8 m to 740 m asi in NSW were used to evaluate the correlation of site, soil and climatic variables with growth of E. dunnii. Using height at an age of 10 y as a standard, site indices for E. dunnii across the 31 sites averaged about 16 m, ranging from around 5 m to 26 m. The factors available-water storage capacity of the soil, rainfall and altitude accounted for 62% of the variation in site index. Inclusion of measures of fertility did not improve the predictive capacity of the model, possibly because of the limited size of the data set with soil chemical analyses. The predictive model, based on simple, easily assessable site factors, has the capacity to improve the quantitative evaluation of the productivity of sites for E. dunnii plantations. The need for a simple field assessment procedure for selection of suitable sites was highlighted by the wide range of productivity exhibited across the plots.

Bell miner associated dieback: nutrient cycling and herbivore crown damage in Eucalyptus propinqua

ABSTRACT Various interactions appear to be involved in bell miner associated dieback (BMAD) of eucalypts. Native bell miner birds (Manorina melanophrys) defend the psyllids from predation by other birds while a dense understorey (notably Lantana camara) appears to favour the bell miners. The understory is likely to influence soil nutrient availability to the trees by changing the carbon to nitrogen ratio. We investigated the link between soil and leaf nutrient status and crown health as measured by crown index (CI) for Eucalyptus propinqua. Study sites included Bald Knob State Forest (SF), Donaldson SF, Mt Lindesay SF around Woodenbong and two locations on a Toonumbar private property in north-eastern New South Wales. Comparison of E. propinqua leaf macro- and micronutrient status using the ‘paired data sign test’ detected leaf nutrient differences between lightly and severely BMAD-affected tree crowns. Single and multivariate analysis investigated nutrient association with CI. Sign test results across all sites indicated that leaf iron content in trees with low CI (less healthy trees) was significantly higher (P = 0.01) than in healthy trees. In the three SFs the affected crowns also had significantly higher nitrogen to potassium ratios (P = 0.02). Other elements correlated with low CI were low boron (P = 0.06) across all sites and high zinc (P = 0.09) and low sodium values (P = 0.09) for Toonumbar sites. The correlation between soil and leaf nutrients was not significant and we found no significant correlations between soil nutrients and CIs. We did not detect any clear association between understorey (L. camara) and soil nutrients. During leaf sampling we found few psyllids but many concealer moth caterpillars. The scarcity of psyllids during sampling, inconclusive nutrient cycling results and nutrient correlations with CI were likely to be due to drought. Resampling under normal weather conditions with more typical organic matter decomposition rates is recommended.