Elsevier

Forest Ecology and Management

Volume 255, Issue 7, 20 April 2008, Pages 2118-2128
Forest Ecology and Management

Growth and nutrition of Pinus radiata in response to fertilizer applied after thinning and interaction with defoliation associated with Essigella californica

https://doi.org/10.1016/j.foreco.2007.12.020Get rights and content

Abstract

Infestations of Essigella californica following the installation of post-thinning fertilizer trials in Pinus radiata plantations provided an opportunity to examine the impact of repeated defoliation over a period of 8 years (1997–2005). Replicated treatments (n = 4) of nil fertilizer (control), N (300 kg ha−1) as urea, P (80 kg ha−1) and S (45 kg ha−1) as superphosphates were applied immediately after thinning at three sites and this was followed by a second application of NPS fertilizers 6 years later with N applied at 300 kg ha−1 as urea and ammonium sulphate and P at 80 or 120 kg ha−1. Defoliation of untreated P. radiata gradually increased to 50% over a period of 8 years. Basal area growth was negatively correlated with average defoliation for two consecutive post-fertilizer periods of 6 and 2 years. Growth responses to fertilizer varied considerably between sites but the largest improvement in growth was due to NPS fertilizer, this increased basal area by 30–80%. Application of N fertilizer raised total N levels in foliage and increased defoliation with a commensurate loss in growth under conditions of deficiencies of S or P. Repeated infestations gradually increased the percentage of trees with severe defoliation (>80% loss of foliage) indicating that nutrient-deficient trees have a reduced capacity for foliage recovery between episodes of peak infestation. In contrast, treatment with N fertilizer in combination with S- and P-corrected deficiencies of these nutrients, raised levels of total N in foliage and reduced defoliation to approximately 20%. Basal area growth responses to NPS fertilizers reflected improved nutrition as well as reduced insect damage. The reduction in defoliation under conditions of balanced tree nutrition was most likely due to enhanced needle retention following correction of P deficiency as well as greater availability of nutrients enabling a more vigorous recovery of P. radiata after an episode of E. californica activity. Treatment with fertilizer therefore reduced the long-term impact of aphid damage and improved growth of P. radiata.

Introduction

The superfamily Aphidoidea (aphids) consists of approximately 4400 species worldwide, placed in almost 500 genera. These include about 170 species of pine-feeding aphids (Blackman and Eastop, 1994, Wylie, 2000). In their native range, pine-feeding aphids are not considered major forest pests, but in some countries where they have been introduced they have had considerable economic impact. Aphids are predominantly a northern temperate group with few species endemic in the tropics and southern hemisphere. However, several northern hemisphere species which have been introduced into the tropics and southern regions have flourished. These include the Cypress aphid, Cinara cupressi (Buckton) that infest twigs and branches of many conifers in the northern hemisphere and Africa (Ciesla, 1991a, Ciesla, 1991b, Wylie, 2000) and the woolly pine aphid, Pineus pini (Macquart), which has been introduced into several countries in Africa and Australia during afforestation programs using Pinus spp. (Mailu et al., 1980). Eulachnus thunbergii (Wilson), a species which is widespread in Asia, also occurs in Australia, mainly in New South Wales and Queensland, where it causes low levels of damage.

Prior to 1998, the impact of pine aphids in Australia was generally low. P. pini had been responsible for infrequent damage, such as the reported 20% loss in basal area in the Australian Capital Territory where 30% of a mature stand of Pinus radiata (D. Don) was badly infested (Tanton and Alder, 1977, Wylie, 2000). Branch deformity in stands of P. pinaster and P. radiata has also been attributed to P. pini, and it was also considered responsible for some deaths of P. patula in Queensland in the 1970s (Elliott et al., 1998).

In March 1998, Essigella californica (Essig.), more commonly known as the Monterey pine aphid, was first detected in Australia in P. radiata plantations near Canberra, with subsequent surveys showing it had spread throughout New South Wales and northern Victoria (Carver and Kent, 2000, Kent and Carver, 2000, May and Carlyle, 2003, Wharton et al., 2004). By 2000 it had spread throughout all pine growing regions of Australia and New Zealand. E. californica is native to the west coast of North America where it has a wide pine species host range, although it is most commonly found on P. radiata (Sorensen, 1994, King, 2002, May, 2004). It is not of economic importance in its native range, and is seldom found in large populations apart from infrequent occurrences where it is associated with the production of honeydew and sooty mould. However, in Australia it has become a major pest species of the softwood plantation industry, especially in south-eastern Australia. Here loss of productivity caused by defoliation associated with E. californica has been estimated to be worth $21 million per year (May, 2004).

Symptoms of damage include mottled chlorosis of the older needles followed by premature needle shed, with defoliation most predominant in the upper crown between early autumn and late winter. This period of high-aphid activity during autumn coincides with average temperatures of 22–25 °C which are optimal for aphid breeding (May, 2004). Defoliation is observed most frequently in P. radiata stands older than 15 years, although it has been observed occurring in stands of all age classes (Collett, 2000). E. californica is most active in P. radiata plantations in the upland areas of south-eastern Australia where significant levels of defoliation occur on a yearly basis. E. californica is also present in plantations located in coastal regions, but here levels of defoliation have generally been light or moderate.

Plantations of P. radiata have been established across a wide range of soils and climate zones in southern Australia with rainfall generally in excess of 600 mm (Turner et al., 2001). A large part of the pine plantation estate is on highly weathered soils dominated by secondary minerals with a low nutrient supply capacity. Therefore, productivity is often limited by nutrient availability and phosphorus deficiency is one of the most common nutrient disorders in P. radiata plantations. Consequently, fertilizers are often applied at establishment and at various stages during the rotation, especially at thinning, to correct nutrient deficiencies and to enhance tree growth and wood production.

The recent arrival of E. californica has already made a significant impact on tree growth and productivity of plantations (May and Carlyle, 2003); furthermore it has also raised the issue of the interaction between aphid-associated defoliation and changes in the nutrient status of plantations in response to fertilizer. Fertilization in general raises the nutrient content of foliage and can make it more palatable to folivorous insects, especially where nitrogen is applied (Kyto et al., 1996). Therefore, forest fertilization has the potential to exacerbate defoliation by insects and this could reduce the gains in growth and productivity expected from the treatment of plantations. While several interacting factors may be responsible for aphid outbreaks including temperature, rainfall, canopy structure and pressures of predator populations, many studies suggest that nitrogen availability in foliage is a key factor in observed increases in aphid populations and defoliation.

The effects of nitrogen and phosphorus fertilizers on aphid populations and their activity have been reported as both positive and negative for several conifer species in their natural environment (Mitchell and Paul, 1974, Parry, 1974, Thomas and Miller, 1994, Kyto et al., 1996, Chilima and Leather, 2001, Straw and Green, 2001, Day et al., 2004, Williams et al., 2005). For example, Mitchell and Paul (1974) showed a significant increase in populations of aphids (Adelges cooleyi) on 7-year-old Pseudotsuga menziesii during the 1st but not the 2nd year following treatment with N fertilizer. Chilima and Leather (2001) showed that significant seasonal variation in population density and outbreaks of pine woolly aphid Pineus boerneri on young Pinus kesiya were linked to temporal increases in total N in foliage. In contrast, defoliation of 11-year-old Picea sitchensis associated with an infestation of green spruce aphid E. abietinum showed little difference between treatments of N fertilizers applied monthly at low rates but fertilized trees recovered more rapidly (Thomas and Miller, 1994). Likewise, May and Carlyle (2003) found little difference in defoliation of P. radiata by E. californica between N and P fertilizer treatments applied 3–4 years earlier.

In the mid-1990s, field trials were established to determine growth responses of P. radiata to nitrogen and phosphorus fertilizers applied after thinning as part of a study on the nutrient management of plantations across a range of sites in Victoria. Two of these trials were located in areas infected by E. californica within 1 year of treatment and this provided the opportunity to examine the effect of aphid damage on growth and the interaction with fertilization. The variation in defoliation between individual trees and the effects on tree growth as well as the initial impact of fertilizer on defoliation were reported for one of the sites by Smith et al. (2000). Monitoring of growth, aphid-associated defoliation, and tree nutrition was continued for 6 years after treatment when the trials were given a second application of fertilizer and monitoring resumed for a further 2 years. Since the initial identification, populations of E. californica have spread to other parts of Victoria and a third experimental site was infected at the time when the second fertilizer treatment was applied in 2003. This paper reports the long-term impact of defoliation by E. californica on growth and the interaction with consecutive treatments of fertilizer in mature stands of P. radiata.

Section snippets

Site description

The experimental sites at Warrenbayne and Stanley in north-eastern Victoria were established in 1997 following completion of the second thinning at age 21 and 22 years, respectively. Infestation of E. californica was discovered in P. radiata plantations at Warrenbayne in 1997 and subsequent plantation health surveys identified E. californica at Stanley later that year. In contrast, E. californica and associated defoliation was not observed until 2002 at the third experimental site established

Tree nutrition

The initial stand conditions prior to treatment at Warrenbayne and Stanley in 1997 and prior to the second application of fertilizer at Daylesford in 2003 were similar in terms of age, stocking, height and basal area (Table 3). Foliage analysis showed low levels of N at Daylesford compared with Warrenbayne and Stanley. The latter sites were deficient in P (<1.0 g kg−1) and S as indicated by N/S ratios (>16). Ratios of N/S greater than 16 indicate an imbalance of these nutrients consistent with S

Growth and defoliation

Annual monitoring of the nutrient levels in foliage showed that P. radiata was deficient in P and S at two sites, and low in N and marginal to sub-optimal in P at the third site. Treatment with NPS fertilizer corrected these deficiencies and increased 6-year basal area increment from 10 to 15 m2 ha−1 at Warrenbayne and from 10 to 13 m2 ha−1 at Stanley during phase I (1997–2003); this represents a response of approximately 50% and 30%, respectively for this period. Likewise the second treatment with

Conclusions

Infestations of E. californica after thinning of P. radiata gradually increased average defoliation to 50% in control treatments of fertilizer trials over a period of 8 years. Basal area growth was negatively correlated with average defoliation in post-thinning fertilizer trials at three sites. Application of N fertilizer raised total N levels in foliage and increased defoliation with a commensurate loss in growth under conditions of deficiencies of S or P. It is suggested that the enhanced

Acknowledgements

This study was funded by HVP Plantations Pty Ltd. as part of an on-going research program of the health and nutrition of P. radiata plantations. The authors gratefully acknowledge the technical assistance by former and present staff of the School of Forest and Ecosystem Science of The University of Melbourne including Ross Bickford, Paul Clements, Carolien Schoenborn, David Smith and Gaby Szegedy. The authors also thank the reviewers of the manuscript for their constructive and insightful

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