Brian J. Myers

Dynamics of Pinus radiata foliage in relation to water and nitrogen stress: I. Needle production and properties

Abstract Measurements of the following parameters were made over a 4 year period in 10- to 14-year-old stands of Pinus radiata subjected to markedly different degrees of water and nitrogen (N) stress: needle length, weight and specific leaf area (every 2 weeks), foliage biomass production (annually), pre-dawn needle water potential (every 2 weeks) and needle litter N concentration (monthly). Increments in needle length were a useful estimate of increments in needle weight for any given forest treatment and year because there was no consistent variation in weight per unit length of needles as they developed during the growing season. However, for well-illuminated needles, the ratio of weight per unit of needle length showed a large (approximately two-fold) variation attributable to treatment and year of foliage elongation. The ratio was loosely positively correlated with needle length (or the favourability of growing conditions) on non-irrigated plots, and appeared to result largely from increases in needle thickness rather than density. Final needle length, ranging between 40 and 160 mm, depended mainly on the amount of water and N stress experienced by trees during the growing season. The majority (greater than 90%) of needle extension occurred during a 4 month period (October–January) in spring and summer and the pattern of needle growth was affected only by water availability. Needle extension rates were negatively linearly correlated with the water stress integral (Sψ, a temporal integration of the effects of both water and N availability on needle water potentials) for monthly periods during the growing season. Needle extension, was most sensitive to the Sψ in mid-spring (October/November) when needles were elongating rapidly and still less than one-half grown. About 80% of the variation in annual foliage production (3.2–8.5 t ha−1) could be explained in terms of both (a) Sψ during the previous summer (when primordia were initiated), and (b) the water and N status of trees concurrent with needle extension. Final needle length and total foliage biomass production in the same year were poorly correlated. The specific leaf area (SLA, all sides) ranged from 10 to 17 m2 kg−1 and was greater for needles formed under low light. Irrigation or fertilisation had only an indirect effect on SLA by hastening canopy closure.

Site water balance and tree water status in irrigated and fertilised stands of Pinus radiata

Abstract Soil water content and pre-dawn needle water potential were measured at 2-week intervals for 4 years in a field study of the interaction of water and nutrients in controlling growth of 10- to 14-year-old Pinus radiata near Canberra, Australia. Growth on the shallow low-fertility duplex soil was limited by both nutrient and water deficiencies. The 40 cm deep A horizon, which contained about 85% of the fine root system, had a plant-available water (PAW) holding capacity of about 60–70 mm or about 8 days supply at peak summer transpiration rates. About 33% of total annual precipitation was unavailable to the trees because of canopy and litter interception losses (28%) and run-off (5%) resulting from dissimilarity in seasonal distribution of precipitation and potential water use. Net canopy interception was 20% of annual rainfall and litter/ understorey interception was 8%. Net interception was strongly affected by size of rainfall event during individual storms, ranging from more than 55% of a 5 mm event to less than 10% of a 40 mm event. However, stand basal area (as it reflects mass of foliage) was the main source of variation in annual net canopy interception, varying from 15% of total precipitation at a basal area of 20 m2 ha−1 to 25% at 34 m2 ha−1. Trees appeared to extract soil water below the conventionally accepted wilting point (−1.5 MPa) and progressively dried out the profile to at least 2 m depth, resulting in growth being restricted by water deficiency. Water availability was a more important determinant of water use than was canopy size, but in non-water-limited stands annual transpiration varied directly with foliage mass and ranged from 0.88 to 1.19 times pan evaporation. Seventy percent of annual water use occurred in the 6 months from October to March inclusive. Differences in water use between stands were largest in summer because of maximum differences in water availability and maximum foliage mass at that time. At soil water contents above 40% PAW, pre-dawn needle water potential was independent of soil water content, but it increased with increasing soil temperature and foliar nitrogen concentration. Below 40% PAW, pre-dawn potential decreased linearly with declining soil water content.

The Biology of Forest Growth experiment: linking water and nitrogen availability to the growth of Pinus radiata

Abstract The Biology of Forest Growth (BFG) study in a 10- to 14-year-old Pinus radiata stand comprised detailed investigations of stand growth, water balance, soil and tree N cycling, canopy dynamics and stand growth modelling The BFG study: (a) developed a method for measuring soil mineral N dynamics in situ: (b) developed the water stress integral, an index of temporally integrated water stress: (c) identified annual average needle litter N concentration as a useful measure of N uptake by and N status of P. radiata stands; (d) demonstrated a marked positive interactive effect of water and N availability on the rate of canopy development, stand foliage carrying capacity, light-use efficiency and above-ground net primary productivity; (e) identified a water stress threshold at a soil water content of 40% of ‘plant-available water’ below which the level of tree water stress is controlled by oil water content and above which the degree of water stress is determined by N status and soil temperature; (f) demonstrated that the leaf area index (LAI) of P. radiata stands varies markedly both within and between years, and that variations in LAI can be monitored indirectly using light transmision techniques provided that account is taken of the surface area of other stand components (dead foliage, branches, boles); (g) quantified the water use of irrigated plantations and its dependence on LAI; (h) quantified the effects of water and N availability on N retranslocation in foliage, and demonstrated the importance of retained foliage for the provision of N for new growth; (i) elucidated mechanisms resulting in prolonged (greater than 8 year) growth responses to N fertilisation, including long-term increases in soil N mineralisation rates; (j) constructed and evaluated a biological model (BIOMASS) of forest stand growth. The BIOMASS model estimates total CO2 uptake by a forest stand from intercepted radiation and photosynthetic properties of the foliage. Net Primary Production is obtained by subtracting respiration rates of the component parts of trees. BIOMASS simulated well the observed growth patterns of trees, especially stem and foliage components. Close similarities between the processes involved in transpiration and CO2 uptake, and good correspondence between calculated and measured soil water balances over a 4 year period, increased confidence in the total CO2 uptake predictions of the model. Research needed to improve tree growth models is briefly discussed. It is argued that long-term multidisciplinary research, such as the BFG study is necessary for advancing understanding of the links between site conditions and forest productivity.

Dynamics of Pinus radiata foliage in relation to water and nitrogen stress: II. Needle loss and temporal changes in total foliage mass

Abstract The pattern of production and fall of needles was measured over a 4 year (1983–1987) period in 10- to 14-year-old stands of Pinus radiata near Canberra. Australia which were subjected to markedly varying degrees of water and N stress. Annual needle loss (death of green needles) was estimated as annual needle fall plus the increment (or minus the decrement) in the mass of dead needles held in the crown between successive winter measurements. Monthly estimates of needle production and loss were used to calculate seasonal (3-month) changes in total live foliage mass between annual winter measurements of foliage biomass. Annual needle fall ranged from about 1.5 to 5.0 t ha−1, and although well correlated with needle loss, the two parameters differed by up to 2 t ha−1 as stands approached canopy closure. In stands closing canopy. 2–3 t ha−1 of dead needles were retained in the crown. Loss in mass of needles due to leaching and decomposition during the period between senescence and fall results in needle fall being an underestimate of the mass of needles senescing in any year. Annual needle loss was positively linearly correlated with total foliage biomass (r2 = 0.70) or stand basal area (r2=0.75) measured in the previous winter. The average life of needles declined from about 4 years in open stands not suffering severe water stress, to about 2 years after canopy closure or where water stress induced significant loss of foliage. Monthly needle fall varied from less than 100 to greater than 500 kg ha−1 and was positively linearly correlated with a measure of cumulative tree water stress (the water stress integral, Sψ) during the same month. The correlation was highest (r2=0.68) for fertilised stands which were most water stressed, and declined with declining water stress, Sψ useful as a guide to the timing of needle fall, but not as a predictor of total annual needle fall which was mainly determined by foliage biomass of the stand. Older (mostly more than 2 years old) needles were shed largely in response to water stress, and in most years needle fall peaked in the summer-autumn period. In wet years and in irrigated stands the peak in needle fall was delayed by 3–6 months.

Dynamics of stem growth of Pinus radiata as affected by water and nitrogen supply

Changes in tree stem diameter were measured every 2 weeks on sample trees, and at intervals of 3 months on all trees, as part of a major field study investigating the impact of irrigation and fertilisation on growth of 10- to 14-year-old Pinus radiata stands near Canberra, in the Australian Capital Territory. Annual basal area growth rates varied from 2.3 m2 ha−1 (untreated stands in dry years) to 7.2 m2 ha−1 (irrigated and fertilised stands). The effect on patterns of growth and total increment of a range of environmental and stand parameters, including water and nutrient availability, temperature and canopy characteristics, were examined. Water and N availability interacted positively to increase growth. In the absence of fertilisation, irrigation increased growth by about 60%. The response to N fertilisation varied from zero during drough years to 200–300% when water was plentiful. Indices of either water or N availability, when used alone, were not well correlated with growth increments. However, the water stress integral (Sψ a temporal integration of the effects of both water and N availability on pre-dawn needle water potentials), as well correlated (r2=0.91, P>0.001) with annual basal area increments, as were combinations of indices of water and N availability. Growth in winter was low but stands with adequate water and nutrients were able to maintain slow growth through most winters. On the other hand, stands sufferring either water or nutrients stress failed to grow at all in winter. Available water extended the period during which growth was possible whereas improved N availability effected by magnitude of growth but only when water was available.

Modelling the water balance of effluent-irrigated trees

Irrigation of effluent is an increasingly popular treatment option due to concern about nutrient additions to rivers and coastal waters. Since some studies have shown that irrigation with waste water can lead to contamination of groundwater resources, there is need for a model to predict the fate of irrigated water, salt, and nitrogen that can be applied to a variety of different soils, climates, and crops. We present the development of the water balance part of such a model, APSIM for Effluent, and carry out a comparison against data obtained from an effluent-irrigated plantation of Eucalyptus grandis. Over 10 months, modelled tree water use was within 1.5% of that obtained by sap-flux measurements. When compared over 5 years of the experiment, modelled drainage lay above that estimated by a water balance technique, which was known a priori to underestimate drainage, and was close to that estimated by the chloride mass balance technique. Simulated chloride accumulated in the soil was within the scatter of the observations, although it was consistently at the lower end of the range of the data. There was good agreement between the model predictions and measured chloride concentration distribution with depth in the soil. A considerable amount of water was lost as deep drainage, even for the treatment that aimed to add only enough effluent to replace that lost by evaporation. During 5 years, of the 3370 mm rainfall and 4480 mm effluent received by that treatment, 6710 mm was lost by the various evaporative routes, and 1080 mm was lost by deep drainage.

Guide to the identification of some tropical rainforest species from large-scale colour aerial photographs

Abstract The key characteristics for identification of 35 species of the Queensland tropical rainforests from large-scale colour aerial photographs are described.

Effluent loading rates for irrigated plantations—a water balance model

Summary Disposal of municipal and industrial effluents to rivers is a major source of river pollution in Australia. Since an increasingly popular alternative for reducing discharge of nutrients to rivers and promoting wood production, is to use effluents to irrigate tree plantations, there is a strong demand for accurate information on the water and nutrient consumption of effluent-irrigated plantations. Research on growth and water-use of Pinus radiada (D. Don) plantations treated with a wide range of water and nutrient supplements over 4 years has resulted in the development of WATLOAD, an empirical water-balance model of irrigated plantations. The central biological parameter is the amount of foliage carried by the trees, which affects throughfall and stemflow, the transpiration rate of the trees and the evapotranspiration rate of the pasture grass or understorey. The model calculates the monthly amount of effluent that can be applied to a plantation in a given climate from planting to canopy closure w...

Hail damage in Australian pine plantations II. Aerial photographic techniques for mapping the damage

Summary A brief discussion is presented of five aspects which must be considered when planning an aerial photographic mission to map mechanical hail damage of pine plantations per se or the subsequent dieback due to infection by Diplodea pinea. These are the timing of photography, the film, scale and format to be used and the likely costs. A number of recommendations are made which will enable forest managers to prescribe a suitable aerial survey of any particular damage event.

Eucalypt Taxa for Low- to Medium-rainfall Farm Forestry in South-Eastern Australia

Summary Enhanced knowledge of on-farm forestry opportunities in the low to medium (500–750 mm) mean annual rainfall zone of south-eastern Australia is needed to maximise commercial and environmental benefits. Key research issues include species and provenance selection, site preparation and silviculture. As part of the ‘Heartlands Initiative’, CSIRO established several taxa evaluation trials in southern NSW and northern Victoria (within the Murray Darling Basin) in 2002. Results from four of these trials, comprising 16 taxa, are presented. Large differences in survival were evident amongst sites and species. Mean survival after 5 y was highest (89%) at Coomalong (near Violet Town, north-eastern Victoria), followed by Brooklyn West (near Wagga Wagga, NSW; 85%), Byawatha Hills (near Springhurst, north-eastern Victoria; 76%) and Koora (near Holbrook, NSW; 54%). Mean stem diameter and calculated stem volume at 5 y were greatest at Coomalong, but mean height was similar at the three sites. Survival of the commercial Eucalyptus camaldulensis × E. globulus hybrid clone, E. cladocalyx, E. argophloia and E. camaldulensis was consistently high. Eucalyptus camaldulensis × E. globulus hybrid clone had the best growth across all sites, followed by E. benthamii, E. botryoides and Corymbia maculata. Best tree form was achieved by E. camaldulensis × E. grandis, E. camaldulensis × E. globulus, E. benthamii, C. maculata and C. variegata. Growth of E. crebra was consistently poorest, with E. occidentalis also having slow growth and poor form. Selection of suitable taxa and best-practice establishment and silviculture are critical to establishing good plantations on these sites.