Nick Ledgard Scientist Forest Research P.O. Box Fendalton CHRISTCHURCH

Transcription

1 Wilding conifers New Zealand history and research background (Presentation to workshop Managing wilding conifers in New Zealand present and future, Chateau on the Park, Christchurch, August 11, 2003) Nick Ledgard Scientist Forest Research P.O. Box Fendalton CHRISTCHURCH 1. Introduction. New Zealand is a natural environment for woody species. A combination of a temperate climate, relatively fertile soils and even rainfall distribution, means that many woody plants grow and reproduce well. Forests once covered 85-90% of the country (McGlone, 1990). However, since European colonisation around 200 years ago, and the subsequent loss of woody vegetation for pastoral farm development, the success of woody species has been partially kept in check by frequent fires (Hunter and Douglas, 1984), grazing pressure from both wild and introduced animals (Benecke, 1966; Ledgard, 1988), and as a result of these two, a lack of seed sources (Ledgard and Langer, 1999). However, over recent decades, territorial authorities have regulated to reduce the use of burning as a pasture management tool, resulting in fewer fires, and there has been less grazing pressure, due to a decline in pastoral stock numbers and better control of introduced animal pests. Of particular note, is the arrival of the rabbit calicidisease virus (RCD) in the late 1990s, a disease which has reduced the rabbit population to a fraction of their former numbers. As a result of these factors, there is a significant increase in the area of woody species reversion (native and introduced), particularly in unimproved pasture land (S. Thompson, Ministry of Agriculture and Forestry, Christchurch). In some areas, an obvious component of this reversion are wilding trees. Wildings are the natural regeneration of introduced trees. The term is usually applied to conifers, which represent most of the major forestry species of concern. Most wildings grow close to the parent seed source and are termed fringe spread. Wildings further afield are termed distant spread. They grow from seed often sourced from exposed take-off sites (ridgetops and slopes exposed to strong prevailing winds), and usually occur as scattered outlier trees. Concern about wilding spread is due to their perceived threat to: Landscape values particularly disruption of existing open and often treeless landscapes Conservation values spread can dominate or degrade the habitats of indigenous flora and fauna Existing pastoral uses grazing species can be shaded out by taller-growing trees Future land use options wilding dominated land is more expensive than open grassland to convert to other uses such as improved pasture or managed forest Existing hydrology dense wilding stands covering a significant percentage of a catchment will reduce water yields. 2. History of conifer spread The natural regeneration of introduced conifers was first noted in the late 1800s (Smith, 1903; Guthrie-Smith, 1953). Cheeseman (1925) noted that seven introduced conifers were all Forest Research/26-Oct-07 Aug11papc903.doc/Page 1

2 reproducing themselves very freely in most parts of the Dominion. From the late 1940s on there appeared to be a substantial increase in the area affected (Hunter and Douglas, 1984), probably influenced by reduced burning and grazing by farmed and wild animals (Benecke, 1967; Gibson, 1988). The issue of wilding spread first came to the attention of the public in the 1960s, as a result of contorta pine (Pinus contorta) invading large areas of the North Island s Central Plateau, including parts of Tongariro National Park (Wardrop, 1964; Cooper and Mazey, 1984). As a result, in 1983 the NZ Government declared contorta pine a Class B noxious weed in the region. A Central North Island Pinus contorta Control Group was set up, and still meets regularly today to discuss wilding spread and issues. During the 1980s, concern about wilding spread became more common (Ledgard, 1988), and Forest Research initiated a number of research trials exploring wilding life histories and control strategies. In the early 1990s the Canterbury Regional Council formed a Wilding Discussion Group to quantify the extent of the problem in that region (Belton and Ledgard, 1991), and to formulate strategies for its control and management. One outcome from this Group was a 1-page wilding spread risk assessment sheet (Ledgard, 1994), a modifed version of which is commonly used by prospective tree planters today (Ledgard and Langer, 1999). At the present point in time, 2003, there are few Regional and District plans in the more spread-susceptible areas of the country (mainly the drier eastern areas), which do not mention wildings and the need to avoid, remedy or mitigate the risk of unwanted spread. In 2001, the Department of Conservation (DOC) produced a South Island Wilding Strategy (DOC, 2001) in which it is stated that wilding conifers are the most significant weed threat in many areas, and the Canterbury (Environment Canterbury), Otago and Southland (Environment Southland) Regional Councils have all featured wildings in their Regional Pest Management Strategies (eg., Environment Canterbury, 2002). 3. Species, and areas affected In New Zealand, ten introduced coniferous species are encountered most often as wildings. These are: Bishops or muricata pine (Pinus muricata) Corsican pine (P. nigra) Dwarf mountain pine (P. mugo) Lodgepole or contorta pine (P. contorta) Maritime pine (P. pinaster) Ponderosa pine (P. ponderosa) Radiata pine (P. radiata) Scots pine (P. sylvestris) Douglas-fir (Pseudotsuga menziesii) European larch (Larix decidua) The main locations where wilding spread affects significant areas at densities >100 trees/hectare, along with the dominant species involved, are shown in Figure 1 (adapted from Ledgard, 2001). The exact area affected by wildings is difficult to estimate, due to different interpretations of the word affected. In the North Island, an area of 150,000 ha has been used (Ledgard, 2001), the main component being that affected by contorta pine in the Central Plateau area. In the South Island, Ledgard (2001) writes of 40-50,000 ha being affected, whereas DOC (2001) in the their South Island Wilding Strategy state that the uncontrolled spread of introduced conifers presently threatens over 210,000 ha of land administered by DOC in the South Island. In DOC s strategy document the Area under threat is defined as the area that is likely to be threatened by wilding conifers in years if no control is undertaken. If this definition is extended to land Forest Research/26-Oct-07 Aug11papc903.doc/Page 2

3 outside the DOC estate, then the area potentially affected in the South Island is unlikely to be under 300,000 ha. 4. Wilding research In this article, wilding research is divided into two categories: Descriptive case studies of specific field sites Formal trials investigating: ~ Aspects of operational control (such as the use of chemicals and fire) ~ Stages in the life history of wilding conifers. 4.1 Case studies It could be argued that the current knowledge and awareness of wilding spread has arisen as much from case study reports on specific field sites as it has from formal trials. Virtually all the sites shown in Figure 1 have been the subject at some time to reports addressing wilding management issues. Although the first area to attract wide attention was the Central Plateau of the North Island (Wardrop, 1964; Cooper and Mazey, 1984; Burns et al, 2001), most attention since the 1980s has been focused on spread in the dry, eastern hill and high country of the South Island. The majority of case study writing has not been formally published, occurring as public presentations (eg., Queenstown area - Allen, 1984), or in the form of local officer reports (eg., Leatham State Forest Hayward and Wishart, 1975). Table 1 lists other case study reports written under contract by the author. Student dissertations have also contributed for example at Rainbow Mountain, just south of Rotorua (Watt, 1987), Central Plateau area (Cooper and Mazey, 1984; Zoete, 1988), Abel Tasman National Park (Sanson, 1978), Mt Barker, near Lake Coleridge (Langford, 1984), Flagstone Scenic Reserve, just outside Dunedin (Calder, 1988), and on the slopes behind Queenstown (Cleary, 1982). By far the most detailed case study is DOC s South Island Wilding Conifer Strategy (DOC, 2001). This document quantifies the wilding problem in the South Island, identifies the conservation values at risk, outlines DOC s obligations, and identifies actions for effective control. 4.2 Formal trials - operational Formal research on wilding conifers in New Zealand has not had a long history. Contorta pine was the first species to attract major attention, and it featured in the earliest research trials. In 1964, Udo Benecke of the NZ Forest Research Institute (FRI), conducted the first formal trial at the Broken River Field station of the Department of Agriculture, close by the Craigieburn Range Control by grazing Benecke s trial looked at the use of sheep at five grazing levels for controlling contorta pine wildings established as seedlings and from seed in improved (fertilised) pasture plots, and on unimproved grassland (Benecke, 1967). Results showed that contorta pine is unlikely to establish naturally from seed on improved pasture or fertilised and oversown tussock grassland (whether it is grazed or not), but that there is a strong possibility of establishment in unimproved grassland where carrying capacity is less than 0.5 stock units / hectare. (A single stock unit is the equivalent of one 2-year-old female sheep). After the Benecke trial, apart from some evaluations of chemicals for the control of contorta pine on the North Island s Central Plateau (Davenhill and Preest, 1974), it was almost 20 years before the next formal research trials were initiated. Following on from Benecke s finding of the importance of sheep browsing for wilding control, a study by Gibson (1988) on the Hossack station alongside the Amuri Range, showed that cattle were not nearly as effective as sheep in controlling wilding, and a trial by Crozier and Ledgard (1990) ranked the relative palatability of seven conifers to browse by sheep(see 4.3.5). Forest Research/26-Oct-07 Aug11papc903.doc/Page 3

4 4.2.2 Chemical control During the 1980s, chemical control investigations were undertaken in both the North and South Island. Preest (1985) used mixtures incorporating 2,4-D / glyphosate/paraquat and diesel, and bromacil granules to successfully kill scattered lodgepole pine seedlings up to 3 m tall in the Central Plateau area. In a test of five herbicides on seven conifer species (mean height of 0.5m) at FRI s Rangiora nursery in Canterbury, Crozier (1990) had mixed results, with higher mortalities occurring from summer than winter application. Glyphosate, metsulfuron,and picloram killed Corsican, contorta, ponderosa, radiata and Scots pine, Douglas-fir and European larch seedlings when applied in the summer. Triclopyr applied in the summer killed only European larch seedlings, and 2,4-D was ineffective at the concentration tested. Winter spraying of glyphosate killed all conifer species except larch, but metsulfuron was ineffective against all species except Douglas-fir. Triclopyr and 2,4-D were ineffective on all species when applied in winter. When considering these results, it must be remembered that it was only possible to test all chemicals at one application rate. In recent years, metsulphuron (at g/ha) in mixture with a surfactant and either glyphosate (5 kg/ha), or paraquat (5.6 litres/ha) has been used by contractors to broadcast spray and kill wildings under 3 m tall usually along roadsides. More recently still, a new range of chemicals and surfactants have been used experimentally from the air on dense areas of wilding contorta, Scots and Corsican pine. Results to date have been variable, and operational trials are continuing. Most wilding removal is undertaken by felling as close to ground level as possible, making absolutely sure that all green foliage is removed. If all live foliage cannot be removed readily due to stones or thick vegetation around the stump, it is often more efficient to cut the trees higher up the stem and then kill the stump with chemicals. Four chemicals have been tested on freshly cut stumps of contorta, Scots and dwarf mountain pine (Crozier et al, 1988). Sodium chlorate (applied as a powder), ammonium sulphamate, 2,4-D and glyphosate (applied in liquid form) were effective in killing all three species. 2,4-D was effective on contorta pine, but not so effective on the other two species. Sodium chlorate was the fastest and most easily handled in the field, but it is a powerful oxidising agent and is classified as a hazardous substance Burning Burning is a very important element of wilding tree control in South Africa (Richardson and Higgins, 1998). However, there is no history of frequent fire use in New Zealand, apart from in the Central Plateau area, where it has been used successfully on contorta pine both on its own and in conjunction with crushing and spraying prior to burning (Ledgard, 2001). Very recently, there has been renewed interest in the use of fire to remove larger areas of spreading conifers in the South Island (Molesworth, Amuri Range, Mackenzie Basin and Mid Dome), and experimental burn plans are being formulated, with and without pre-burn chemical desiccation, and with a range of post-burn revegetation options. To date, there is no evidence that fires will trigger a new generation of seedling regeneration the author considers this to be due to little seed surviving the fire, and to the rapid post-fire invasion of vigorous exotic grasses Physical removal Physical removal either by hand or using motorised tools such as scrub cutters and chainsaws, remains the most common means of control. Little formal research has been carried out in this area. The most cost-effective means for employing such methods is generally determined by work studies and field evaluations carried out by land management agencies or the operators themselves. 4.3 Formal trials life history The majority of life cycle research was initiated in the 1980s by FRI - after a survey of exotic trees in the Canterbury high country (Ledgard and Belton, 1985) revealed the frequency that wilding spread was associated with planted trees (Table 2). Wildings were observed at 39% of the 249 sites inspected. Forest Research/26-Oct-07 Aug11papc903.doc/Page 4

5 Trials explored the ecology and demography of wilding spread, to gain a better understanding of the wilding life cycle and the stages of that cycle where control strategies could most cost-effectively be implemented. Life history research has focused on seed production and dissemination, seed bank longevity in the soil, seedling microsite preferences, factors influencing seedling emergence and early survival (plant competition, animal browse, mycorrhizal presence), and the incorporation of this information into predictive models. The major life history stages are illustrated in Figure Seed production The seed and cone production of the major spreading conifers has been quantified on a limited range of eastern South Island sites (Ledgard, unpublished data). Large quantities of seed can be produced from relatively young trees (Table 3) one 21-year-old Corsican pine in the Mackenzie Basin producing almost 45,000 full seed in a single year (Ledgard, 2001). But seed production varies significantly between years (Table 4), and between location. Production appears to drop off with increasing altitude, with some species such as Corsican pine and Douglas-fir ceasing cone production around 1000 m and 1200 m respectively (Ledgard, unpublished data), whilst others such as contorta pine (Ledgard and Davis, 1988) and dwarf mountain pine (Ledgard, unpublished data) will happily produce seed and parent wildings well above native tree line (approximately 1400 m in the central South Island). Cone production per unit area of ground may vary according to tree density. It seems logical that the cone and seed production of open-grown or marginal trees (with green crowns virtually to ground level) should be greater than that from internal trees at denser stockings. In the Mackenzie Basin, trees in a 40-year old Corsican pine shelterbelt produced considerably more cones on the exterior of the belt compared to interior trees. Edge trees produced a mean number of 652 cones/tree, whereas the internal trees produced only 266 cones/tree (Buckley and Ledgard, unpublished data). This knowledge is important, as it indicates that by planting a margin of less spread-prone species around a stand of a spread-prone species (for example, a margin of ponderosa pine around a stand of Douglas-fir), the risk of unwanted wilding spread could be reduced significantly Seed dissemination Seed is released from cones in the autumn / winter period, and the time of release varies with species. A monthly study of seed content within cones of five conifer species over a single 9 month period in the Craigieburn Range, revealed that Douglas-fir was the first to open and release most of its seed (in February/March), followed by contorta and dwarf mountain pine (March/April). Scots pine was the last to release most of its seed (August/September), whilst the release of European larch seed was low but consistent from March to September (Ledgard, unpublished data). The major dissemination agent for conifer seed in New Zealand is wind. Field evidence indicates that there are considerable differences between species as far as the distances seed can be carried. A pilot trial involving eight conifer species, in which the dispersal distance of winged seed was compared after dropping through a fixed-speed airflow, indicated that seed wing loading, or mass unit per wing area, was more closely related to distance of dispersal than seed weight alone (Ledgard, unpublished data). Table 5 shows that contorta pine had the lightest seed and seed wing loading, and was dispersed furthest, followed (in descending order) by Douglas-fir, Corsican, Scots and dwarf mountain pine, European larch, and radiata and ponderosa pine. Data on the exact distances and directions of seed dispersal can be obtained by GIS mapping of fringe and distant wildings occuring downwind from known seed sources. This information is currently being gathered for inclusion into a wilding spread model (see below) Seed bank longevity in the soil The period that seed can remain viable after dissemination is an important aspect in the control of any weed species (Richardson and Higgins, 1998). Consequently, the question as to Forest Research/26-Oct-07 Aug11papc903.doc/Page 5

6 the longevity of conifer seed banks in the soil is frequently asked. In 1986, a well replicated, delayed germination trial was established with seven conifer species at four sites - FRI s Rangiora nursery near Christchurch (70 m altitude, annual rainfall 680 mm), Melrose Station, upper North branch of the Waipara River ( 800 m, 1000 mm), Craigieburn Forest Park (850 m, 1350 mm), and Ribbonwood Station, near L. Ohau (700 m, 800 mm). Seed was sown at the rate of 3000 viable seeds/m 2 onto mineral soil at Rangiora, and natural tussock grasslands at the other three sites. Protection was given from mice and birds for the duration of the trial. Live and dead seedlings were counted and removed every autumn for 6 years. Results are given in Table 6 (Langer, 1993). On mineral soil (Rangiora), no seedling germination occurred after the end of the second growing season. On the three high country grassland sites, the vast majority of seedlings were found in the first 3 years, with no seedlings counted after the fifth growing season. Despite these results, the author is often told of situations where seedlings have allegedly appeared more than 5 years after the seed source was removed. In all but one situation where these sites have been inspected, the seedlings have been incorrectly aged as being younger than they actually were. Small seedlings are not necessarily young seedlings browsing and lack of mycorrhizae (see 4.3.5) can result in seedlings still only being a few centimeters tall after a number of years. In the case of the exception (involving contorta pine), the seedlings may have germinated from seed which had remained viable in cones left on trees after they had been felled Seedling microsite preferences The successful spread of wilding conifers depends strongly on the presence of safe sites for seed germination, seedling survival and growth. Contrary to what many might believe, bare soil does not always offer the safest sites, due to rapidly changing extremes of surface temperature and moisture, and winter frost heave, which can often prevent any vegetation growth surviving more than 1 year (Ledgard, 1976 and 1979). In a recent trial looking at the establishment from sown seed of nine conifer species in natural grassland and on mineral soil, the number of seedlings emerging in the grassland after 2 years has exceeded emergence in the mineral soil treatment (Ledgard, unpublished data). The best sites are often those with a light vegetation or stone cover. Where vegetation is present, the safeness of a site is influenced by the vegetation structure and composition of the invaded community. Mariana Cattaneo (2002) studied differences in the microsite preferences of Douglas-fir and contorta pine in open shrublands. She found that litter had a significant negative effect on contorta pine, but favoured Douglas-fir establishment. Douglas-fir was rarely found amongst lichens and bryophytes, but favoured a cover of mat-like woody plants, whereas contorta was found more frequently amongst herbs. Although vascular cover > 5 cm tall reduced the establishment of both species, she found that Douglas-fir s establishment in open shrublands can be facilitated by the light shade and shelter (from desiccation and frosts) offered by widespaced shrubs. Some seedlings were actually able to establish within shrubs. Contorta pine, on the other hand, favoured the open intershrub areas, and although no seedlings were found actually growing through shrubs, it too probably benefited slightly from the shelter offered by adjacent tall vegetation. This is supported by Allen and Lee (1990), who observed contorta pine to grow in the proximity (30 cm) of tall tussocks. Langer (unpublished data) also found that the best establishment of six conifer species was in open shrubland (Figure 3), followed by grassland, and a mountain beech (Nothofagus solandri var. cliffortioides) canopy gap, with zero survival under closed-canopy mountain beech. Research indicates that none of the common introduced conifers can readily establish under closed-canopy forest or shrubland (Chavasse, 1979; Ledgard, 1988). Major disturbance is a prerequisite to open up the canopy before seedlings are likely to establish successfully. All the same, as the most shade-tolerant of the common introduced conifer species, young Douglas-fir seedlings can be found under beech forest canopies (Klijzing, 2002), where the understory vegetation is scarce. However, unless situated under a light-well or canopy gap, most of these Forest Research/26-Oct-07 Aug11papc903.doc/Page 6

7 seedlings do not last more than a few years and the few that might survive grow exceedingly slowly (Ledgard, 2002, Dickson, 2001). Where introduced conifers can be seen growing within an intact shrub cover (such as in many parts of the Marlborough Sounds), they have usually established before the shrubs have become dominant, after a disturbance (such as fire) or immediately after the removal of grazing animals (such as after farm abandonment). Once the shrub cover forms a closed canopy, opportunities for further wilding invasion are only likely to occur if disturbance creates openings in the vegetation Factors influencing seedling survival Research on the factors affecting seedling survival have concentrated on browsing, competition from other plants (notably introduced grasses), and the role of mycorrhizal fungi. Browsing. Browsing by introduced and wild animals is probably the major influence on the survival of young seedlings in New Zealand. Benecke (1967) demonstrated the effect of different levels of browsing pressure by sheep, showing that a sheep stocking level as low as 0.5 stock units / hectare was enough to significantly depress contorta pine seedling survival. Gibson (1988) found that sheep were far more effective in controlling wildings than cattle. Crozier and Ledgard (1990) tested the palatability of seven conifers to sheep browsing in the field. Two-year old seedlings were planted and fenced from stock for 10 months. They were then exposed to sheep browsing for a year, before assessment of browse damage. Corsican pine was the least preferred species followed by Douglas-fir, Scots pine, European larch, contorta and ponderosa pine, with radiata pine the most browsed species. In a simulated browsing trial, the same authors (Crozier and Ledgard, 1990) found that seedlings could be readily killed by removal of all green foliage before age 2 - after that time shoots had become sufficiently woody and robust to make it much harder for browsing animals to remove all needles, and hence ensure mortality. In parts of New Zealand, rabbits have had a major effect on vegetation cover (McCaskill, 1973), and have had a significant impact on the establishment of young wildings. Davis (1996) looked at the effect of excluding rabbits, birds and insects from young radiata pine seedlings during their first year of growth from seed. Rabbits were clearly the major cause of seedling failure (Figure 4). Where rabbit numbers have been significantly reduced, such as after the arrival of RCD in the late 1990s, all woody seedlings, including wildings, have had a much greater chance of survival. Competition. Although seedling establishment can be aided by the shade and shelter provided by some types of vegetation cover (see above), the establishment success of wildings generally declines with increasing vegetation competition. Benecke (1967) showed how, in ungrazed circumstances, no contorta pine seedlings survived more than 18 months in improved pasture, whereas survival after 2 years in unimproved grasslands was 94%. Davis (1989) direct drilled contorta pine seed into improved (sown and fertilised) and unimproved grassland. Forty-seven percent of the viable seed germinated to young seedling stage. In improved grassland no seedlings survived to the end of the first season except where a herbicide treatment was added (75% survival). Seedling survival in the unimproved grassland was 100%. Cattaneo (2002) in a glasshouse pot trial involving contorta pine and Douglas-fir, showed that grass competition significantly reduced the seed germination and early growth of both species. Her results indicated that Douglas-fir performed better than contorta pine in the presence of grass. All the Douglas-fir was inoculated with mycorrhizae. The above results indicate that, in spread-susceptible areas surrounding plantations, there may be a role for the use of fertilisers to increase the competitive effect of grasses (and probably other plants as well), and in so doing, to lower the risk of unwanted wilding spread. Mycorrhizae. Symbiotic mycorrhizal fungi are increasingly suspected of having one of the most important roles in the successful early establishment of wilding seedlings. Davis (1996) found that the survival after 3 years, of radiata and Corsican pine seedlings inoculated with the mycorrhizal fungus, Rhizopogon rubescens, was significantly higher than seedlings growing from seed which had not been inoculated (Figure 5). The influence of mycorrhizae can be dramatic in one seeding trial, a mycorrhizal seedling was over 1 m tall after 4 years, while less Forest Research/26-Oct-07 Aug11papc903.doc/Page 7

8 than 2 m away a non-mycorrhizal seedling of the same age had yet to exceed 5 cm in height. The importance of mycorrhizae for the good establishment and early growth of plantation-grown Douglas-fir is now well recognised (Chu-Chou and Grace, 1983). Similarly, mycorrhizae appear to play a major part in the early survival of Douglas-fir wildings. At Burnt Face on the slopes of the Craigieburn Range, the number of Douglas-fir seedlings counted under a light mountain beech cover has increased ten fold since counts first began in 1989 (Ledgard, 1989; Dickson, 2001). In 1989, the vast majority of young seedlings appeared unhealthy and chlorotic they were persisting (at <50 mm height) with little growth for some years, before either dying, or becoming green and starting good growth. This greening up is very likely associated with the roots becoming mycorrhizal. Since the trial began, the number of mycorrhizal seedlings has increased markedly - from virtually none in 1989, to 6% in 1996, to 60% in 2001 (Dickson, 2001). The incidence of Douglas-fir wilding spread appears to have been on the increase over the past decade (Ledgard, 2002). This could well be due to a greater presence of mycorrhizal fungi generally, resulting in higher ambient levels of mycorrhizal spores, and consequently an increased likelihood of young wildings becoming mycorrhizal in their early years Modelling of wilding spread. Most of the research outlined above has been undertaken over the past two decades. The ultimate aim has always been to utilise the results in the construction of a wilding population dynamic model. It is envisaged that this model will enable land managers to predict spread and growth of populations of wildings from plantation sources. Major progress in this direction was made in the first half of 2002, during the visit to New Zealand of Dr Yvonne Buckley, from the Centre for Population Biology, Imperial College, London. A life history diagram and transition parameters for Corsican pine are presented in Figure 6, and at the time of writing, the first draft of a working matrix model for this species has been completed. During its construction, data gaps have been identified, particularly in the area of seed dissemination this data is now being gathered with the aim of having a spatial model working sometime in Wilding models will not only assist in determining the life history stages most susceptible to interception, but they can also be used to assess the efficacy of other control strategies, such as the introduction of biocontrol agents, or removal of trees of different ages. The model could also be linked to a GIS framework to enable simple visualisation of changes at a landscape scale. This would be most useful for educational and awareness purposes. 5. Outreach efforts to improve land manager education and awareness, operational efficiency, and to promote wilding prevention strategies. There is common agreement that more education and awareness about wilding conifer spread is urgently needed. If the facts were better known, land owners and managers would be able to envisage future problems, and hence plan for prevention or control, so that the risks of unwanted conifer spread are avoided or minimised. Although it has taken some time for land owners and managers to become aware of the problems associated with wilding spread, considerable progress has been made in dealing with the problem. Most Regional and District councils in the more spread-susceptible areas are including wilding regulations in their Regional Pest Management Strategies and District Plans. Staff in the largest single land administrating agegncy, DOC, are well aware of the problem, and have produced a Wilding Conifer Strategy for the South Island. In some regions they are spending more of their weed control funding on wilding conifers than on any other plant. Most of this money is being spent on controlling spread from historical plantings, often carried out in mountainlands for erosion control reasons (McKelvey, 1995). The majority involve species such as contorta, Corsican, Scots and dwarf mountain pine and it is important to note that none of these species are planted at all widely today. However, the areas affected by wilding spread can be extensive - to the level that physical removal is often beyond the means of limited resources available. In such circumstances, the use of cheaper control agents such as Forest Research/26-Oct-07 Aug11papc903.doc/Page 8

9 fire, have to be considered seriously if increasingly extensive and costly wilding control operations are to be avoided in the future. In any of these control situations, it is essential that well considered management plans are produced before any serious control operations are carried out. The basic topics they should cover are the history of spread leading to the current situation, the major factors that are influencing the spread rate, how fast this spread is occurring, the options for control (usually elimination, containment, or do nothing ), and the estimated costs and priorities for such control. Without an appreciation of these factors, it is not possible to implement the most cost-effective management. Too often, no such plan exists, and wellintentioned efforts are being wasted. This leads not only to poor use of limited resources, but also to disillusioned participants and observers, and a loss of impetus for on-going control. Maintaining impetus is more important than often realised, as a major wilding control operation cannot be completed without long-term commitment probably for more than a decade. Of equal importance to controlling existing spread problems is the importance of ensuring that new areas of unwanted wildings do not arise in the future. Without doubt, the establishment of conifer plantations will continue, sometimes in regions where there are ample opportunities for wilding spread. It is critical that the risk of unwanted spread from these new plantings is avoided, or at least kept within manageable limits. Today, that should be possible, as risk can be assessed before any planting is undertaken (Ledgard, 1994), and there are good guidelines containing strategies to minimise the risk of unwanted spread (Ledgard and Langer, 1999). 6. Conclusion Many introduced conifers grow well in New Zealand. A number regenerate naturally, some more vigorously than others. This is the price we pay for living in a country which has an environment which promotes the growth of woody plant species. Introduced trees have tremendous prospects for enhancing New Zealand s long-term environmental, social and economic well-being, but in order to realise these gains properly, we have to be well aware of the problems. The risk of unwanted wilding spread is one of these. 7. Acknowledgements This paper contains a number of references to unpublished data, most of which is the result of investigations carried out by Forest Research. This has been entered into a structured data base, as part of Landcare Research s Invasive Weeds research programme. The author is very grateful to Rowan Buxton of Landcare Research for helping to archive this material in a form which allows ready accessed by other researchers. Thanks also go to Dr Yvonne Buckley of Imperial College, London, and Lisa Langer, of Forest Research for permission to include some of their unpublished data, and to Lisa Langer for comments on the manuscript. Forest Research/26-Oct-07 Aug11papc903.doc/Page 9

10 References Allen, R.B. 1984: Naturalised conifers around Queenstown. Unpublished lectures, talks, and submissions series, No13. June issue of Otago Tree Societies Newsletter, Dunedin. Allen, R.B., Lee, W.G Seedling establishment of exotic conifers in Chionochloa rigida tussock grassland, Otago, New Zealand. N. Z. Jl. Bot., 27: Belton, M.C., Ledgard, N.J A study of the spread of exotic trees in the Canterbury high country. Review 48, Jl. N. Z. Mountain Lands Institute, Lincoln Univ., Canterbury, New Zealand: Benecke, U The weed potential of lodgepole pine. Review 13, Jl. N. Z. Mountain Lands Institute, Lincoln Univ., Canterbury, New Zealand: Burns, B.; Williams, P.; Fitzgerald, M. 2001: Review of Pinus contorta control programme, Waiouru Military Training Area. Landcare Research Contract Report prepared for Property Management Setion, Waiouru Military Camp, P Bag 1702, Waiouru: 20 pp Calder, J. 1988: Woody species invasion and burning: preservation of the snow tussock grassland of the Flagstaff Sccenic Reserve, Dunedin Cattaneo, Mariana. 2002: Effects of microsite characteristics, competition and grazing on Pinus contorta and Pseudotsuga menziesii seedling estalishment. Unpublished M.Sc. Hons thesis, School of Forestry, University of Canterbury: 154 pp Cheeseman, T.F. 1925: Manual of the New Zealand Flora. Government Printer, Wellington, New Zealand: 1163 pp Chavasse, G.C.R. 1979: Spread of exotic tree species into native forests. Forest Research Institute Report No 131, Forest Research, Private Bag, Rotorua: 49 pp Chu-Chou, M.; Grace, L.J. 1983: Characterisation and identification of mycorrhizas of Douglasfir in New Zealand. European Journal of Forest Pathology 13: Cleary, E.A. 1982: Ecological apsects of Douglas-fir invasion of mountain beech forest on Ben Lomond Reserve, Queenstown, New Zealand. M.Sc thesis, Botany Dept., Univ., of Otago. Cooper, William, Mazey, John The spread and control of Pinus contorta within and adjacent to Tongariro National Park. Diploma in Parks and Recreation Thesis, Lincoln Univ., Canterbury, New Zealand. Critchfield, W.B., Little, E.L. Jr Geographic distribution of the pines of the world. U. S. Dept. of Agric., For. Serv. Misc. Publ., 991: 97 pp Crozier, E.R Chemical control of wilding conifer seedlings. In Popay A.J. (Editor), Proc. of the 41 st N. Z. Weed and Pest Conf., P.O. Box 1654, Palmerston North, New Zealand: Crozier, E.R., Ledgard, N.J Palatability of wilding conifers and control by simulated sheep browsing. In Bassett et al (Editors), Alternatives to the chemical control of weeds. Proc. Forest Research/26-Oct-07 Aug11papc903.doc/Page 10

11 Int. Conf., For. Res. Inst., Rotorua, New Zealand, July For. Res. Inst. Bull., No. 155: Crozier, E.R., Zych, T.R., Ledgard, N.J Control of wilding conifers by applying chemicals to cut stumps. In Popay A.J. (Editor), Proc. 41 st N. Z. Weed and Pest Conf., P.O. Box 1654, Palmerston North, New Zealand: Davenhill, N.A., Preest, D.S Interim evaluation of several soil sterilants for the control of contorta pine. Proc. 27 th N. Z. Weed and Pest Conf., N. Z. For. Serv. Reprint No 777, For. Res. Inst., P.O. Box 3020, Rotorua, New Zealand: Davis, M.R Establishment of conifer plantations in the South Island high country by direct drilling. N. Z. For. 34(3): Davis, M.R., Grace, L.J., Horrell, R.F Conifer establishment in the South Island high country: influence of mycorrhizal inoculation, competition removal, fertiliser application, and animal exclusion during seedling establishment. N. Z. Jl. For. Sci. 26(3): Dickson, A. 2001: The invasion of Douglas-fir (Pseudotsuga menziesii) into mountain beech (Nothofagus solandri var. cliffortioides) forest on Burnt Face, Craigieburn Conservation Park. Unpublished B. For Sc dissertation, School of Forestry, University of Canterbury: 56 pp Department of Conservation (DOC), 2001: South Island Wilding Conifer Strategy. Department of Conservation, Christchurch: 25 pp Environment Canterbury, 2002: Regional Pest Management Strategy Biodiversity Pests. Environment Canterbury, P.O. Box 345, Christchurch: 71 pp Gibson, R Change from sheep to cattle promotes conifer spread. Review 45, Jl. N. Z. Mountain Lands Inst., Lincoln Univ., Canterbury, New Zealand: Guthrie-Smith, H Tutira - the story of a New Zealand sheep station. William Blackwood and Sons Ltd, Edinburgh and London: 444 pp Hayward, J.D., Wishart, C.J A decade of revegetation work in Leatham State Forest - Nelson Conservancy. N. Z. For. Serv. Int. Rep., Available from - Dept. of Conservation, Nelson, New Zealand: 51 pp Hunter, G.G., Douglas, M.H Spread of exotic conifers on South Island rangelands. N. Z. Jl. For. Sci. 29(1): Klijzing, Krista. 2002: A study of Douglas-fir (Pseudotsuga menziesii) dispersal into native beech (Nothofagus spp) forest and microsite factors predisposing seedling establishment. Unpublished thesis towards Degree of Bachelor of Tropical Forestry, Larenstein College, Netherlands. Langer, E.R. 1993: Delayed germination of introduced conifers in Canterbury. Unpublished Forest Research Institute Contract Report, Christchurch: 17 pp Langford, M.D. 1984: Natural regeneration of exotic conifers at Lake Coleridge sheep-run. Unpublished B. For Sc dissertation, School of Forestry, University of Canterbury, Christchurch: 54 pp Forest Research/26-Oct-07 Aug11papc903.doc/Page 11

12 Ledgard, N.J. 1976: Research into the direct seeding of woody plants in high country vegetation. NZ Jl For 21(2): Ledgard, N.J First-year losses of Pinus mugo seed and seedlings on an exposed high country subsoil. N. Z. Jl. For. 24(1): Ledgard, N.J The spread of introduced trees in New Zealand's rangelands - South Island high country experience. Review 44, Jl. N. Z. Mountain Lands Inst., Lincoln Univ., Canterbury, New Zealand: 1-7 Ledgard, N.J. 1994: A form for assessing the risk of conifer spread in the South Island high country. NZ Forestry 39 (1): Ledgard, N.J. 2002: The spread of Douglas-fir into native forests. NZ Jl Forestry 47(2): Ledgard, N.J.; Langer E.R. 1999: Wilding prevention guidelines for minimising the risk of unwanted spread from new plantings of introduced conifers. Forest Research, Box 29237, Fendalton, Christchurch: 21 pp Ledgard, N.J. 2001: The spread of Lodgepole pine (Pinus contorta, Dougl.) in New Zealand. Jl of Forest Ecology and Management 141: Ledgard, N.J.; Baker, G.C. 1988: Mountainland forestry - 30 year's research in the Craigeiburn Range, New Zealand. New Zealand Forest Research Institute Bulletin No 146: 64 pp. Ledgard, N.J., Belton, M.C Exotic trees in the Canterbury high country. N. Z. Jl. For. Sci. 15(3): McCaskill, L.W. 1973: Hold this Land A history of soil conservation in New Zealand. A.H. and A. W Reed Ltd, 182 Wakefield Street, Wellington. McGlone M.S. 1989: The Polynesian settlement of New Zealand in relation to environmental and biotic chnages. N.Z. Jl. of Ecology 12: Preest, D.S Chemical aids for planting site preparation. N. Z. For. Res. Inst., For. Res. Inst. Bull. No 100, Private Bag, Rotorua, New Zealand: 48 pp Richardson, D.M., Higgins, S.I Pines as invaders in the southern hemisphere. In Richardson D.M. (Editor), Ecology and Biogeography of Pinus. Cambridge Univ. Press, Cambridge: Sanson, L.V. 1978: Invasion of Maritime pine in Abel Tasman National Park. Unpublished B. For. Sc. dissertation, School of Forestry, University of Canterbury. Smith, W. W. 1903: Plants naturalised in the county of Ashburton. Trans. Proc. N.Z. Inst., 36: Wardrop, T.N Reconnaissance survey of the occurrence of Pinus contorta on the Waiouru Military Reserve. For. Man. Rep. No 1, For. Res. Inst., P.O. Box 3020, Rotorua, New Zealand: 31 pp Forest Research/26-Oct-07 Aug11papc903.doc/Page 12

13 Watt, V.J Pine invasion in Maungakakaramea (Rainbow Mountain). M.Sc. Thesis, Waikato Univ., Hamilton, New Zealand: 206 pp Zoete, Toivo. 1988: Population structure of Pinus contorta and its control. Unpublished B. Sc. dissertation for Centre for Resource Management, Lincoln University. Forest Research/26-Oct-07 Aug11papc903.doc/Page 13

14 Table 1. Case study reports involving wildings, written by the author Ledgard, N.J. 1988: Introduced conifer management on Acheron Bank (Reserve 1578).. Ledgard, N.J. 1989: The spread of Douglas-fir into mountain beech forest on Burnt Face, Craigieburn Forest Park. Ledgard, N.J.; Stewart, G.A. 1989: Management plan for the removal of exotic conifers from Mt Tarawera. Belton, M.C.; Ledgard, N.J. 1991: Canterbury high country exotic tree spread study. Field Sheet Books Nos 1-5. Ledgard, N.J. 1993: The spread of introduced conifers at Mt Aurum Station: background, present situation and management options. Ledgard, N.J. 1993: Conifer spread in the Amuri Range area; range, composition, likelihood of future spread and management options. Ledgard, N.J. 1994: Exotic wilding tree spread in the Kaikoura District. Ledgard, N.J. 1996: Operational plan for the control and management of introduced conifers in the Red Hills, Gordon s Range and Beebies Ridge area of Mt Richmond Forest Park. Ledgard, N.J.; Baker, G.C 1997: Management options for introduced trees on Ruataniwha Farm, around lakes Tekapo, Pukaki and Ruataniwha and within the Tekapo, Pukaki and Ohau rivers. Ledgard, N.J. 1997: Conifer wilding issues at proposed Lowmount / Gowan Lea and Flagpole forestry areas. Ledgard, N.J. 1998: The spread of introduced conifers on Molesworth Station - present situation and future control options. Ledgard, N.J. 1998: Introduced trees in Coronet Peak Recreation reserve: present situation and future management options. Ledgard, N.J. 1999: The spread of introduced conifers at Mid Dome / Cupola, Southland. Ledgard, N.J. 2001: Report on the management of introduced conifers in the Beebies Ridge area of Mt Richmond Forest Park. Ledgard, N.J. 2001: Report on the control of introduced conifers in, and adjacent to, Jollies Pass Scenic Reserve and the Hossack Conservation Area, North Canterbury. Ledgard, N.J. 2001: Report on Ernslaw One wilding conifer issues; with particular emphasis on Gowan Hills, Morven, Dunkeld, Rankleburn, Beaumont, West Tapanui and Naseby Forests. Forest Research/26-Oct-07 Aug11papc903.doc/Page 14

15 Ledgard, N.J (March): Report on wilding conifer control and management in the Wye and Waihopai catchments, inland Marlborough. Ledgard, N.J (Feb): The spread of introduced trees in the Queenstown / Wanaka area (an outline report). Ledgard, N.J (June): A strategy for control of wilding conifers in South Marlborough. Ledgard, N.J (Sept): A strategy for control of wilding conifers in North Marlborough. Plus unpublished Notes written for land managers on the wilding spread situation in: * Kaweka Range, Hawkes Bay * Karioi / Waiouru area, Central Plateau * Marlborough Sounds * Upper Maitai ultramafic area, behind Nelson. * Branch / Leatham catchments, upper Wairau catchment, Marlborough * Tarndale and upper Clarence areas, Molesworth * Craigieburn Forest Park, upper Waimakariri catchment Other reports written for private individuals are not included. Forest Research/26-Oct-07 Aug11papc903.doc/Page 15

16 Table 2. Frequency of wilding spread in the Canterbury high country. Species n Number of sites with spread European larch Corsican pine Ponderosa pine Douglas-fir Radiata pine (62%) 24 (42%) 22 (37%) 15 (36%) 13 (25%) TOTAL (39%) Abridged from Ledgard and Belton (1985) Forest Research/26-Oct-07 Aug11papc903.doc/Page 16

17 Table 3. Estimated numbers of viable (filled) seed per tree produced in 1 year for seven introduced conifer species growing in eastern South Island, New Zealand (Ledgard, 2001). Species Tree age (yrs) Mean numbers of filled seed per tree (n) Estimated Maximum number of filled seed per tree Lodgepole pine (1250 mm an. rainfall) (52) 1566 " " (700 mm an. rainfall) (17) Corsican pine (10) Scots pine (10) Radiata pine (14) 3086 Mountain pine (10) 2467 Dwarf mountain pine (10) Douglas-fir (10) 2792 Forest Research/26-Oct-07 Aug11papc903.doc/Page 17

18 Table 4. The range in cone production over 5 years of Corsican pine at Lake Ruataniwha in the Mackenzie Basin (Ledgard, unpublished data). Tree No Age (1992) Number of cones Mean no of cones Forest Research/26-Oct-07 Aug11papc903.doc/Page 18

19 Table 5. Seed dispersal of ten conifer species after releasing into a fixed speed airflow.* Mean full seed weight, seed wing loading, and the percentage of seed landing closest (0-2 m) and furthest (5-7 m) from the start point (author, unpublished data). Species Mean full seed weight (g) Seed wing loading (weight of full seed wing length x width) (mg/mm 2 ) carried Distance Closest Furthest to source, fr source, 0-2 m ** 5-7m** (% of seed) (% of seed) Contorta pine a 21 a Douglas-fir a 21 a Corsican pine ab 17 ab Scots pine abc 12 abc Dwarf mountain pine abc 7 bc European larch bcd 4 bc Radiata pine cd 8 bc Ponderosa pine d 2 c * Airflow speed: At seed drop point = 30 km/hr. At 5 m from seed drop point = 11 km/hr ** Values followed by the same letter are not significantly different at the 5% level Forest Research/26-Oct-07 Aug11papc903.doc/Page 19

20 Table 6. Mean percentage of seedlings germinated for seven conifer species at three sites over 6 years after sowing. Site Species 1986/ / / / / /92 Rangiora Contorta pine Corsican pine Ponderosa pine Radiata pine Scots pine European larch Douglas-fir Craigieburn Contorta pine Corsican pine Ponderosa pine Radiata pine Scots pine European larch Douglas-fir Melrose Contorta pine Corsican pine Ponderosa pine Radiata pine Scots pine European larch Douglas- fir Ribbonwood Contorta pine Corsican pine Ponderosa pine Radiata pine Scots pine European larch Douglas-fir Forest Research/26-Oct-07 Aug11papc903.doc/Page 20