The control of the Australian tree Pittosporum undulatum in the Blue Mountains of Jamaica April 1997 T. Goodland and J.R. Healey, School of Agricultural and Forest Sciences, University of Wales, Bangor, LL57 2UW, U.K.  Contact email j.healey@bangor.ac.uk

 

Figure 2. The relationship between the DBH of P. undulatum trees and their fecundity (number of seeds, on the y-axis) for five successive years, 1992-96, and the effect of gap creation on fecundity. The data for the Gilbert and Juniper gaps have been combined.

P. undulatum seed production was high, the regression relationship between DBH and fecundity giving a mean of 37,500 seeds for a 8 cm DBH tree in 1992, though there was very large variability in fecundity amongst trees of a similar size. It varied substantially through the five year period, so that in 1993 only one tree produced more than 7,000 seeds, there being no discernible relationship between DBH and fecundity. After five years the pattern of fecundity can be described thus: very high in 1992, only about half that in 1993, the seed production building up gradually between 1994-1996 to near 1992 levels. Whether this pattern is governed by extrinsic factors (such as weather) or intrinsic factors (for example within-plant food reserves) is not known. The seed production of trees in the generally more open Gilbert gaps was slightly but not significantly greater than in the Juniper gaps, likewise in the understorey of both areas. For the Gilbert sites, understorey trees were more likely to bear few or no cymes, compared with gap individuals. Individuals at the Juniper site started producing cymes at a larger size than those at the Gilbert sites. This may be because before August 1992 the forest was relatively tall and undisturbed, and therefore the smaller P. undulatum trees would have been growing in a relatively low light environment. Additional data collected in 1995 showed that the fecundity often falls to very low levels on larger P. undulatum trees. Flower and fruit development To assess the number of flowers that survive to produce capsules, in February 1993 we counted the number of flowers on six flower bearing cymes on 39 P. undulatum trees <25 cm GBH (20 in a gap and 19 in the understorey). The trees were revisited in early December 1993 and the number of capsules in each marked cyme was recorded. In summary, overall 17.0% of the flowers produced capsules, with the mean number of flowers surviving slightly higher in gaps than the understorey. Twenty one of the trees produced no capsules at all. Observations made of two branches on separate trees during January 1994 showed that P. undulatum flowers took between 2 and 3 weeks between flower opening and "withering" after fertilisation. Some of the flowers had already been eaten, probably by birds; the Greater Antillean Bullfinch, Loxigilla violacea, has been seen eating P. undulatum flowers (T. Goodland, pers. obs.). 3.3 Effectiveness of biological control Type of biological control Because of the widely scattered nature of P. undulatum in lightly invaded forest classical biological control is most likely to be effective. "Augmentation" - involving direct manipulation of established populations of natural enemies through mass production or colonisation, or "Conservation" - involving habitat manipulation to encourage populations of natural enemies which kill the invader or seriously reduce its competitive ability, are not feasible in this instance. As for the use of anti-reproductive or anti-vegetative control, the former has three advantages over anti-vegetative control. Firstly, it would lead to a much more gradual opening up of heavily invaded forest, thereby avoiding the risks associated with the sudden death of most trees in large areas; secondly, it would not affect the potential for the use of P. undulatum as a woodlot / fuelwood species by local people, provided that an effective method for vegetative propagation was developed; thirdly, anti-vegetative control may be effective at reducing the vigour of P. undulatum, but is less likely to reduce population levels. However an anti-vegetative biological control agent would have advantages: seedlings are already widespread and locally common in primary forest so the reliance on an anti-reproductive biological control agent would allow many P. undulatum plants to grow and have a significant effect on parts of the forest for many decades; secondly, in lightly invaded forest rapid control is desirable, and is more likely with an agent that kills trees quickly; lastly it could be simpler and more predictable - assessing the effect a reduction in seed production would have on the population dynamics of the species is very difficult. A critical issue would be the reaction of the bird populations to such a change - if the fecundity of P. undulatum were reduced it does not necessarily follow that bird dispersal would decline proportionately, if at all (J. Wunderlie, pers. comm., 1993). Bird behaviour is of course a very complex issue which we have not had time to investigate.    Cost effectiveness There are several reasons (given below) for thinking that biological control agents would be less than wholly effective. On the other hand, P. undulatum is likely to have a narrow genetic range in Jamaica, and this might mean that it is poor at adapting to new predators or environmental fluctuations greater than that in the Blue Mountains over the last 100 or so years.  Although pests of forest trees can search for their host trees in a forest, where the target species is widely scattered, as P. undulatum is in the Blue Mountains, there may be an appreciable lag before the plant is found, by which time seed production could have already started.  As the number of P. undulatum individuals (or seeds) is reduced, it becomes harder for the agent(s) to find its target and for its population to be supported in a fluctuating environment (S. Neser, pers. comm., 1993).  The large annual variation in P. undulatum seed production may make it more difficult for a seed-attacking agent to establish and maintain a population and would very probably mean that in years of high seed production a large proportion of the seeds would survive.  The difference in the climate between the Blue Mountains and P. undulatum's native range is appreciable (Healey et al. 1992b) and so may present an added difficulty in establishing a classical biological control agent.  P. undulatum's spread in Australia, often in areas close to or contiguous with its "natural" 19th century limits, suggests that its population level was held in check by factors other than native predators, factors such as lack of native dispersers and fire.  The likely cost of a biological control programme against P. undulatum could be US$1,000,000, and take about 7-10 years. Because of the fixed costs of building and equipping facilities in Jamaica the costs of attempting biological control against P. chinense or H. gardneranum could be considerably less than that against P. undulatum alone. Environmental aspects Introducing an exotic agent to Jamaica inevitably involves some risk to native species, though release of biological control agents is nowadays undertaken only after a rigorous screening programme. There are no native members of the Pittosporaceae in Jamaica which may mean that the risks of any introduced agent attacking native plants is reduced (S. Neser, pers. comm., 1993). However, if introduced agents did kill all P. undulatum it is possible that the agent(s) would attack native species, especially as the population of P. undulatum declined. Evidence from South Africa indicates that the disease which is attacking P. undulatum there does not affect other species, however this would clearly need to be fully tested in Jamaica before any introduction of it to Jamaica. A major problem with the intentional or accidental release of an effective lethal agent in Jamaica is that the sudden death of all P. undulatum in heavily invaded forest could have serious ecological consequences. The light levels on the forest floor would be increased substantially, almost certainly enhancing the growth of Hedychium gardneranum and probably facilitating the germination and growth of Polygonum chinense. The large quantity of dead wood could, during an exceptionally dry period, leave these areas vulnerable to fire, either accidentally started, or by people deliberately taking advantage of the opportunity to clear forest for farming with the minimum of effort. The consequences would be very serious, with fire resistant weeds, such as Melinis minutiflora, benefitting. Perhaps a lethal, vegetative blight could be introduced eventually, once the dominance (and fuel load) of P. undulatum in heavily invaded forest had been reduced through management. In summary, it may be able to reduce the rate of P. undulatum spread, and its final density, but would be very unlikely to eliminate P. undulatum from the Blue Mountains altogether. In addition, it may well be politically unacceptable to introduce a disease that kills P. undulatum, as any proposal that may lead to the loss of forest cover would be hard to justify in a country that has lost so much. The use of biological rather than manual control favours scientists and technicians, many from richer countries, instead of local people who would be employed to carry out manual eradication. Therefore, careful political and socio-economic analysis of this option is required and it is crucial that the decision is taken at an appropriate local level. Contact should be maintained with researchers in South Africa, because of the potential of the unidentified agent currently killing P. undulatum in the Cape Province to be used as a biological control agent in Jamaica. However, should further research into the potential for biological control become necessary full attention should be given to an assessment of its risks and the costs of a proper screening programme before any decisions are taken. 3.4 The use of fire as a way of controlling P. undulatum in the Blue Mountains Controlled burning is being tried at present as a potentially cost effective way of controlling invading P. undulatum in Australia (Narayan 1993; R. Gleadow, pers. comm., 1993). For example, in New South Wales, a combination of fire and insect attack is used, where intense and moderate fire (100% leaf scorch) kills P. undulatum. If the fire is less intense, damage to the trunk is still severe and then borers (presumably longicorn) attack, killing the plant within a few months (R. Buchanan, pers. comm, 1994). Following a controlled fire in Victoria, Australia at a temperature of about 200-2500C 20% of monitored P. undulatum individuals resprouted from basal buds, but all P. undulatum in areas suffering from higher temperatures were killed (Narayan 1993). A low temperature fire of 1200C led to a net recruitment of P. undulatum seedlings (Narayan 1993). Twenty percent of two and a half year old P. undulatum seedlings exposed to 2000C in laboratory conditions resprouted (Narayan 1993). The bark of P. undulatum trees is thin and resinous, reaching 6.5 mm thick on a trunk 30 cm DBH in its native range (Gleadow & Ashton 1981). It is more resistant to fire than many marginal rainforest tree species, but is still susceptible compared with fire resistant species such as Eucalyptus (R. Gleadow, pers. comm., 1993). Fire is frequent in the Blue Mountains, especially on hillsides covered by the African grass Melinis minutiflora (Aldrich 1993). It is unlikely that heavily P. undulatum dominated forest would burn without disturbance even during an exceptionally dry period, partly because of the thin litter layer and small quantities of woody debris characteristic of these secondary forests. However, a scrubby area (which probably had more fuel due to a dense layer of shrubs and ferns as well as abundant P. undulatum) did burn in the dry dry season of 1989 and P. undulatum trees had been killed by a fire about 5-10 years ago in another area. This evidence, and what is known about P. undulatum in Australia, does suggest that P. undulatum would be partially or totally eliminated from an area suffering an intense fire. However, although there are some native species that can readily colonise burnt areas (such as a shrub Dodonaea viscosa and bracken Pteridium aquilinum) the main beneficiaries would probably be introduced weeds, particularly M. minutiflora. In addition, fires result in soil erosion and loss of soil fertility through oxidation and volatilisation, hence the use of fire as a cheap method of controlling P. undulatum in the Blue Mountains would be highly undesirable. 4. Strategy for Pittosporum undulatum control If the primary objective is to slow or stop an invasion, modelling highlights the importance of eradicating small outlying populations before starting to eradicate the main original population, even if it is expanding slightly faster than the satellite populations (Moody & Mack 1988). Although it is less urgent to remove P. undulatum from heavily invaded forest than from lightly invaded forest, it should still be a long term objective, not least because of the value of P. undulatum wood. However, it is very important to discover ways of removing the species without leading to the forest becoming even more heavily invaded by alien weeds. The very high recruitment of P. undulatum and the generally low recruitment of other species following the removal of P. undulatum trees has been examined in the accompanying report. As long distance dispersal of P. undulatum by birds is so prevalent it is essential that an integrated approach to its management in the Blue Mountains be adopted. This means that the management options for lightly invaded and heavily invaded forest and land outside the forest has to co-ordinated. For example, looked at on its own, it would seem to make little sense to try to eliminate P. undulatum outside the forest (where it probably does little harm and may even be beneficial), but if the ultimate objective were to remove all risk of the species re-invading the forest, its removal outside the forest may be essential. The various options as to which areas could be cleared of invasive plants are discussed below, in order of increasing ambitiousness. They are not strict alternatives, as easier options could be steps towards a more complete control of the species in Jamaica.  4.1 Restricted areas of forest Areas to be kept weed free could include: Trails. The invasion of all three main weeds may be hastened by the more open environment along trails. As it would be relatively easy to clear P. undulatum from them, this would be a cost effective way of reducing the invasion rate where they pass through little invaded forest. It would be essential if this were done to control P. chinense and H. gardneranum as well, otherwise they could be the main beneficiaries. Their rampant growth that can quickly make trails impassable.  Areas near or highly visible from trails, especially the Blue Mountain trail. To do this would decrease the rate of trail re-invasion and save remnants of natural uninvaded forest for visitors.  Sites (small areas of less than a hectare) of particular scientific/archeological interest or those with research uses. The act of removal itself is a disturbance, so for some of these areas it may be better to leave the invasion to proceed undisturbed.  Representative areas of natural habitat. These could be modelled on "Special Ecological Areas", a concept originating from the Hawaii Volcanoes National Park in Hawaii (Tunison & Stone 1992). These are areas of a hundred to a few thousand hectares that make the removal and exclusion of alien plants particularly worthwhile. Areas are delimited because of such attributes as high conservation value, a low degree of invasion and easy accessibility. Such areas could either be incorporated into one of the existing Blue and John Crow Mountains National Park management zones, such as the Special Conservation Zones or could be established separately. Two obvious areas are the forest in the vicinity of Portland Gap and the Blue Mountain Peak trail (a more extensive area than in 2. above), and the forest along and close to the Grand Ridge of the Blue Mountains between Morces Gap and John Crow Peak, because of its great diversity of forest types, research interest and accessibility.  4.2 All primary forest The removal of P. undulatum from lightly invaded forest should receive top priority. Almost all primary forest is much less invaded than secondary forest and generally has a higher conservation value. But there is about three times as great an area of it than heavily invaded forest, and it is mostly remote and inaccessible. A major problem with trying to remove weeds from all primary forest is that some of the slopes in the Blue Mountains are so steep and craggy - places in which P. undulatum thrives - that they are only accessible with rope, dramatically increasing the risk and cost of control. We have had to make a number of simplifying assumptions in order to calculate the cost of doing this: age/size at which P. undulatum starts to produce seed (a typical height of 3 to 5 m, age 5-10 years). Given the inaccessibility of much of the forest there is a clear case for removing P. undulatum plants significantly shorter than this. In follow-up clearance operations the target should be to ensure that all P. undulatum individuals are removed before they get to 3 m.  persistence of the P. undulatum seedling bank.  time period over which P. undulatum seedlings are recruited from any seedbank.  maximum growth rate of P. undulatum seedlings.  time needed to find and then kill different sized plants. As P. undulatum grows more rapidly in gaps, greater control effort will inevitably be needed there. These disturbed areas are localised, often small, and workers should be alerted to the importance of checking for P. undulatum in any gaps they encounter.  Our assessment of the cost of clearing P. undulatum from the 1020 ha with an estimated density of <100 trees per hectare, is in the range of US$110,000 and US$145,000. It would be highly desirable to remove the other two serious alien weeds in primary forest, Hedychium gardneranum and Polygonum chinense, at the same time, but we can estimate the cost of doing this with much less confidence. It could easily cost as much again in labour and material costs, but with little increase in fixed costs. Therefore the total costs of removing the three main weeds from lightly invaded forest would likely be in the range of US$220,000 to US$290,000. We must stress that these costs are not based on actual data on controlling weeds in lightly invaded forest, so may be very inaccurate, more likely to be underestimates than overestimates. The Blue Mountains are different from almost all other areas where much effort has been expended on the control of alien plants in that there are many people who live locally who would be willing and able to work on a manual control programme. Elsewhere labour has either been expensive (such as Hawaii or New Zealand) or scarce (such as the Galapagos Islands or Mauritius, where labour is only available when the sugar cane is not being harvested (W. Strahm, pers. comm., 1993)). A manual control programme would be labour intensive and therefore clearly beneficial in an area with high unemployment and under-employment (R. Kerr, pers. comm., 1993). Rather than hiring local people on a casual basis as labourers, it would be preferable to build up a committed team of people and train them rather like forest rangers, so that they will be able to take a wide responsibility for protecting the forest and promoting it amongst local people. 4.3 Heavily invaded forest As the harvesting of P. undulatum from heavily invaded forest has the potential to be self-financing it could be a policy that could be self-justifying and could be pursued independently of action in lightly invaded forest. The key issue in heavily P. undulatum invaded forest is the effect of P. undulatum management on the degree of invasion of alien weeds. The proximity of these areas to very heavily invaded land on the forest fringes could mean that the areas become heavily invaded within a few decades, mostly by H. gardneranum and P. chinense as well as P. undulatum. This could lead to a permanent loss of tree cover within a few decades. (Both H. gardneranum and P. chinense have already spread into non-P. undulatum invaded primary forest, (though the latter only in a few places), so management in heavily P. undulatum invaded forest would make little difference to their rate of invasion throughout the Blue Mountains). We have found H. gardneranum surviving, if not growing, beneath the densest canopy of P. undulatum, an environment where very little else can grow. The species also benefits from canopy opening, by increasing its rate of vegetative spread, as displayed in natural gaps and man-created clearings in the upper Clyde valley. It would unwise to remove P. undulatum without removing H. gardneranum if the latter were beneath it. The potential effect of P. undulatum on Polygonum chinense is greater than that on H. gardneranum. P. chinense does not occur beneath dense tree canopies, as some disturbance is necessary for its establishment. A significant finding of the Heavily Invaded Forest Experiment in July 1995 was the presence of at least twelve healthy newly-established P. chinense plants, up to four metres long, in the Remove all P. undulatum treatment in a heavily invaded block. In that plot, P. undulatum had comprised only 9.5% of the total basal area (of stems over 3 m tall) so it appears that P. chinense is able to colonise sites after the removal of relatively minor amounts of P. undulatum. P. chinense can also get established in gaps created by the fall of large P. undulatum trees. The understorey of heavily invaded forest is sparser than lightly invaded forest, benefitting species that are recruited as a result of gap creation. On the other hand P. undulatum is a more aggressive coloniser of gaps than most native tree species, (not just in terms of height but also crown growth), so there is probably a greater chance that the P. chinense would be suppressed in gaps where P. undulatum regeneration is dominant. It is important to find out whether P. chinense will invade forest that is presently heavily invaded (by P. undulatum) faster if large P. undulatum trees are left to grow and eventually fall, creating gaps, or if they are killed standing and allowed to disintegrate without such pronounced gap formation. It might be possible to eliminate P. undulatum from heavily invaded forest by the gradual removal of trees taking care not to cause so much disturbance that P. chinense or P. undulatum are recruited (H. gardneranum can grow without such disturbance). As data from HIFE indicates the paucity of native seedling recruitment following P. undulatum removal, these areas could be replanted or resown with native species. There are likely to be major problems with the raising of large numbers of tree seedlings of some species in nursery conditions, and probably with the survival of planted seedlings. Lack of resources may mean that the re-planting of such areas would have to be an alternative to the planting of (mostly different) species outside the forest as part of efforts to restore tree cover to the denuded slopes. As some forest is so heavily invaded it could even be sensible to convert the less steep and most accessible land to non-forest tree cover, such as agroforestry or forest plantations. After the cutting and uprooting of all P. undulatum, the timber could be extracted, the abundant foliage left on the soil surface to provide some protection and help to suppress weed regeneration, care taken to prevent fire, then plant either native species or exotic N-fixing species.   4.4 Eradicate entirely from the Blue Mountains area This would involve not only removing P. undulatum (and other weeds) from the heavily invaded forest around the less invaded core but also control of them outside the forest. Additionally, there are good reasons for control of the Hardwar Gap invasion as the area is much visited by tourists, with the main visitor centre for the park nearby, and it does contain a forest type not described from the Blue Mountains (the Very Wet Ridge forest of Grubb & Tanner (1976)) - the extent of P. undulatum there is apparently quite limited so the costs of its elimination would be low. If eradication of the three main weeds were achieved there would be little chance of any of them ever reaching the area again, as we have no evidence that any of them occur in Jamaica outside the western Blue Mountains area. However, we have not attempted to cost this policy as it would be very expensive, unlikely to succeed, and of questionable merit, though it may be feasible in the long term. 4.5 Biocontrol Recent correspondence with two leading experts on the control of invasive alien plants has lead us to consider that the potential of biological control (as much a method as a strategy) may be much higher than we had originally thought. On the Atlantic island of St Helena both Pittosporum undulatum and P. viridiflorum are exotic and invasive (as well as many other alien weeds). A joint South African/Australian project will be proposing biological control of these two species, as apparently there are already agents known to attack the species. Further details are lacking at the moment. The fact that there are no native members of the Pittosporaceae should make the process relatively straightforward and will thus require minimal work on specificity of natural enemies (S. Neser, pers. comm., 1996). Ian Macdonald, an authority on invasive plants, thought that the potential for biological control is greater than indicated in Goodland & Healey 1996. In particular, he thought biological control would be much less expensive than suggested in the report, and also that it would be safer (with little chance of an introduced agent attacking native plants, as long as the screening had been rigorous enough). 5. Recommendations Clearance of P. undulatum from lightly invaded forest Eradication of P. undulatum from lightly invaded forest is highly desirable and seems to be feasible, so trial control should start as soon as possible. Two topographically well-defined areas of 2-5 ha typical of those invaded should be cleared of all P. undulatum. There are good reasons for removing the other two serious weeds, Hedychium gardneranum and Polygonum chinense, as well, at least until we have a better idea as to the feasibility of their eradication. For convenience these areas should be in the forest north of Cinchona; two possible areas are the north facing hillside below Morces Gap and the northern slopes of Sir Johns Peak (areas highlighted on map).  The density of P. undulatum and % cover (to the nearest 10%) of the ginger and redbush should be estimated in these areas before treatment and, initially, one year afterwards to judge its effectiveness. The terrain will be too dificult to set up square plots, so a number (ideally 10) of circular plots (5.64 m in radius, giving 100 m-2 each) should be set up in representative areas. The centre should be marked with bright flagging.  All the P. undulatum trees in the lightly invaded forest in these two areas should be small enough to cut down with machete (or axe). Immediately apply sufficient undiluted glyphosate to thoroughly wet the cut surface without letting (much) glyphosate flow off the stump.  Killing ginger will be more difficult. The best type of herbicide is Escort together with Pulse. Assuming these are not presently available in Jamaica (and they are expensive) physical methods seem to be the best option: Slash stems and dig out all rhizomes, and pull out young seedlings. (N.B. old shade-suppressed plants may appear small but have a string of rhizomes attached to them). Stems and leaves may be left to mulch. Do not mulch or compost rhizomes because they always resprout. Keep out of ground contact or pile and later burn them. (NB Chemical: spray foliage or slash stems and spray cut stumps. Use Escort + Pulse and apply from spring to late autumn. Rates: handgun 25g Escort + 100 ml Pulse/100 litres water. Knapsack 5g Escort + 10 ml Pulse/10 litres water). Killing redbush will also be difficult, but there may not be any in these areas (though it is present on the north slopes). A combination of cutting and glyphosate should work, but more trials are needed.  A record of the number of people employed on how many days plus how herbicide used will need to be kept.  The work would be suitable for a team of a park ranger, a knowledeable local man, and other local manual workers. If results from the trials are encouraging, larger scale clearance of P. undulatum should proceed. The highest priority is control of the small "nucleus" population in the Whitfield Hall/Blue Mountain Peak area. A high priority should also be attached to the killing of the isolated P. undulatum trees in the north slope forests north of Cinchona and this could be commenced before the Whitfield Hall population is completely eliminated.   Assessing distribution The commisioning of a set of aerial photographs will not be necessary until a widespread control programme is initiated. P. undulatum trees would be readily seen on aerial photographs at the scale of 1:5,000, so given the complex topography of the Blue Mountains, such a set of photographs would offer the best chance of mapping its distribution. Aerial photography should use normal colour photography, but, if possible, some colour infra-red photographs should also be taken for comparative purposes. Methods of killing P. undulatum As uprooting is effective and because of the lack of need of herbicide, this method should be used whenever individuals need to be killed. The high density of P. undulatum seedlings in some areas will preclude the eradication of the species at this size. Small trees. Plants too large to be uprooted can be cut. There are then two ways of killing the stumps. Immediately apply herbicide. All stumps treated (in 1995) with sufficient undiluted glyphosate to thoroughly cover the cut surface had died by 1996. It would be sensible to find out if a less concentrated solution worked as well.  Strip the bark off the stump. Our trial attempts at this seem to be completely effective as long as all the bark down to soil level or lower is removed. If any is left, the stump will resprout (but perhaps die if weak and in a heavily shaded location). It becomes very difficult and time consuming to successfully do this with larger trees, as the roots are often large and convoluted. It would be well worthwhile exploring this technique further.  Large trees. Large trees in remote areas (where harvesting is unlikely to be feasible) should be killed standing with the use of herbicide. Those trees that can be harvested should have their stump treated with glyphosate as with smaller trees. There are three methods of applying herbicide to standing trees that we think are potentially useful.  Frill girdling. Further tests are needed to see if all the bark should be removed, as well as making the frills and applying the herbicide. The application of glyphosate to frills is certainly a method that we recommend.  Drilling holes and pouring in herbicide. This is very effective, if at least one hole is drilled for every 10 cm of stem girth, but is slower than frilling. Its effectiveness as a way of applying herbicide cannot at present be compared with that of frill girdling, as we used glyphosate with the drilled holes and Tordon with the frill girdling. It should be possible to plug the holes after the herbicide has been poured (or syringed) in, allowing work to continue during the wettest periods.  The third way is to use hypohatchets. We recommend that these be tried as they offer a way of quickly delivering a known dose of herbicide safely. They cost about £200, and should be tough and reliable as they are used in commercial forestry in the USA. Spare parts would be unavailable in Jamaica. If management has difficulty in locating suppliers we will be able to help.  Harvesting of P. undulatum from heavily invaded forest Removal of P. undulatum from heavily invaded forest is less urgent, but harvesting could start also on a limited scale. Because of the very high recruitment of P. undulatum following canopy disturbance and the commoness of other serious weeds in more accessible forest, great care needs to be taken in any control or harvesting. It would be very difficult to manage forest for timber production which is threatened by three alien weeds with such different characteristics. If the overriding objective is to leave the slopes of the Blue Mountains forested there is the real possibility that not clearing P. undulatum from heavily invaded forest would be the best policy. A moderately high priority is an investigation into ways to deal with large P. undulatum trees in heavily invaded forest. They are vulnerable to windthrow and when the next hurricane strikes this could provide many nuclei for the further spread of Polygonum chinense and Hedychium gardneranum. Harvesting the P. undulatum trees for timber may have a similar effect. Thus, if P. undulatum is to be controlled or harvested in heavily invaded forest, every effort must be taken to maximise the regeneration success of native species in the disturbed areas, rather than creating the conditions that favour exotic species. Therefore, the effect on the regeneration of exotic and native species of killing large P. undulatum trees by felling versus killing them while still standing should be experimentally tested. If the timber is harvested the effect on the regeneration of the resulting soil disturbance should also be investigated. We suggest an experiment with three control treatments: · cut and treat stump with glyphosate · girdle and treat girdle with glyphosate · undisturbed control and two levels of soil disturbance. At least six large (>25 cm DBH) P. undulatum trees should be included in each treatment. The most suitable area would probably be upper Clydesdale but other areas should be considered. The seedling bank around each tree should be recorded before and after treatment (but this need not be taken to the level of labelling of individuals). This would be suitable for an MSc project or similar. Kill all P. undulatum (cut, harvest and apply herbicide) (or for larger badly formed trees girdle and apply herbicide); also remove larger seedlings (>2m tall) at same time. Go back in about 5-10 years, just before those P. undulatum seedlings left have started to produce seeds. Planting trees should be a policy of last resort for the restoration of natural forest cover following control of P. undulatum because of the likely cost. However, should it be necessary, species suitable for planting in areas cleared of P. undulatum should preferably be native, fast growing and with a dense crown enabling the suppression of exotic invasive species. They would probably be a subset of the species that are successful in gaps in the natural forest. A wide range should be tested initially, the actual species selected for a particular area should be largely determined by the degree of canopy opening caused by the removal of P. undulatum. We have made an initial list, ordered in approximate order of decreasing requirement for gaps for establishment: Brunellia comocladiifolia, Alchornea latifolia, Turpinia occidentalis, Clethra occidentalis, Symplocos octapetala, Juniperus lucayana, Podocarpus urbanii, Guarea glabra. The ease of propagation of bare root cuttings, survival after transplanting and subsequent growth of a number of these species is currently being tested at Cinchona Botanic Garden by M.A. McDonald in ODA FRP project R6290 and the results of this trial will provide further criteria for species selection. In order to determine whether commercial use of harvested P. undulatum timber could make a contribution towards the costs of control in heavily invaded forest, more information is needed on the working properties, acceptability and market value of P. undulatum wood. Logs of P. undulatum should be distributed to a cross section of Kingston wood processors to obtain this information. It would also be valuable to obtain a better idea of the economic viability and environmental impact of making charcoal from P. undulatum than has been obtained so far; this could readily be carried out in the Cinchona area.  Management of other invasive species Tests should be made of the effect of physical and chemical treatments on the control of Polygonum chinense and Hedychium gardneranum. These two invasive species should be eradicated from the Vinegar Hill Trail (and any other trails opened up). Existing contacts should be maintained, and new ones developed, with other organisations concerned with the control of H. gardneranum (e.g. in New Zealand, South Africa, Azores, Madeira and Réunion) and P. chinense and any other invasive species found to be problematic in the Blue Mountains. The two known Syzygium jambos populations should be eradicated because of the extent to which this species has become invasive in other countries.   Biological control We do not recommend any action to investigate the potential of biological control at present. Steps towards it only need to be taken if the trial weed clearance shows that the feasibility of manual control is low. The next steps should be an exploratory visit to the native range of P. undulatum (New South Wales) and further consultations with biological control experts.   Use of Pittosporum undulatum outside the forest Despite the local popularity of P. undulatum as a source of fuel-wood, charcoal and for other uses, the environmental damage being caused to the natural forests by harvesting of native species for these uses and the potential of community woodlots to alleviate this pressure, we cannot recommend the planting of P. undulatum outside the forest because of the risk that these trees will act as a source of seeds for the invasion of nearby forest. Park management favour the use of native species for planting in the park or the buffer zone (Kerr et al 1993). The ability of the great majority of native trees to establish outside the forest is likely to be poor (E.V.J. Tanner, pers. comm., 1991). However, this is currently the subject of trials by Dr Morag McDonald in ODA FRP project R6290. The one location where trial planting of Pittosporum species (P. undulatum and P. viridiflorum) currently entails little risk to the forest is in the Cinchona area, because the species are already so well established there. However, even in this case uncontrolled planting by farmers should be discouraged; it is only in a smaller number of woodlots that management could ensure that trees are cut before they start to bear seed. In order to investigate the potential for a female sterile line to enable planting to be carried out without risking an increase in the invasion, it would be necessary to determine whether any of the standard, low-technology, vegetative propagation techniques (that can be used by farmers) will work for Pittosporum. Although sterile lines may have great potential to allow safer use of potentially invasive species in environments which might be vulnerable to invasion (C. Hughes, 1993), great care should be taken to consider all of the potential draw-backs of this approach so as to caution against such a high technology fix being seen, naively, as a fail-safe solution to a fundamental ecological problem.  In any case, given the local value of Pittosporum as well as its potential threat to the natural forests, local participation in decisions over its management and control is vital for their success.   Further research The forest permanent sample plots established and recorded during this project represent one of the best networks in any area of tropical montane forest in the world. They must be maintained and re-enumerated at regular intervals (e.g. for the plots of E.V.J. Tanner and co-workers every five years, next due in 1999) in order to monitor the rate of invasion of exotic species, their impact on native species, the interaction of different disturbance events (e.g. hurricane impact), and the dynamics of the native forest community that control its vulnerability to invasion.   So far, our research on the impact of P. undulatum has concentrated on its effects on terrestrial plant biodiversity. New research is needed on the interaction of the invasion and animal biodiversity, especially birds. The attractiveness of P. undulatum fruit to native bird species has played an important role in the spread of the invasion. On the other hand, forest heavily invaded by P. undulatum has a greatly reduced diversity of types of fruit and a reduced structural complexity (which may greatly reduce the diversity of epiphytes and of invertebrates) with potentially serious negative effects for bird biodiversity. In the wake of the pioneering research work of Dr Andrew Lack, the Jamaican bird fauna (including many endemic species) has received international conservation interest. Dr Nigel Varty of Birdlife International carried out detailed studies of the impact of Hurricane Gilbert on the bird fauna of the Blue Mountains. These contacts should be developed to enable the necessary research to be carried out on the interaction of P. undulatum and animal biodiversity.  New research is needed on the impact of the other invasive exotic plant species (H. gardneranum and P. chinense) on biodiversity; the effects are likely to be severe.  Given the catchment protection importance of these forests new research on the impact of all three invasive exotic plant species on hydrological and soil parameters is justified. The high leaf area index and dense shade of P. undulatum may have a significant negative impact on water yield and slope stability. Nonetheless, such research would be costly to undertake properly (L.A. Bruijnzeel, pers. comm.). Acknowledgements This publication is an output from a research project partly funded by the United Kingdom Department for International Development (DFID) for the benefit of developing countries.  The views expressed are not necessarily those of DFID.  R4742 Forestry Research Programme.  The work was co-funded by the Darwin Initiative of the United Kingdom Department of Environment, Transport and the Regions. Funding No substantial progress will be possible with any of the main recommendations without external funding. The outputs of this project and the resulting trial clearance should be used to make a case to donor agencies/international conservation organisations for such funding. The case should be based on our assessment of the extent and severity of the threat posed by the invasion, information that will improve in quality with further analysis and monitoring of permanent sample plots, and a more accurate costing of control measures.

References Adams, C.D. 1972. Flowering plants of Jamaica. University of West Indies, Mona, Jamaica.  Aldrich, M. 1993. Is there a role for agroforestry in smallholder farming systems in the Blue Mountains of Jamaica? MSc dissertation, University of Edinburgh, Edinburgh, U.K..  Dowler, C.C. & Tschirley, F.H. 1970. Effects of herbicides on a Puerto Rican rain forest. In: A tropical rainforest. Ed. H. Odum. B315-23.  Forestry Commission. 1990. Guide to the use of herbicides in the forest. Field book 8. Edinburgh, UK.  Gillespie, P. 1991. Woody weed control in the Dandedong Ranges National Park. Plant Protection Quarterly, 6(3), 130-1.  Gleadow, R.M. 1982. Invasion by Pittosporum undulatum of the forests of central Victoria. II: Dispersal, germination and establishment. Australian Journal of Botany, 30, 185-98.  Grossbard, E. & Atkinson, D. (Eds). 1984. The herbicide Glyphosate. Butterworths, London, UK.  Healey, J.R., Goodland, T.C.R. & Hall, J.B. 1992. The impact on forest biodiversity of an invasive tree species and the development of methods for its control. First annual report of ODA Forestry Research Project R4742, School of Agricultural and Forest Sciences, University of Wales, Bangor, U.K.  Hering, E.M. 1962. Galls of Agromyzidae (Dipt.) on Pittosporum undulatum Andr. Proceedings Linnaean Society N.S.W., 87(1), 84-91.  Jones, L.J. & Elliot, W.R. 1986. Pests, diseases and ailments of Australian plants. Lothian Publishing Co., Melbourne.  McMaugh, J. 1985. What garden pest or disease is that? Lansdowne Press, Sydney. Kodak. 1987. Applied infra-red photography. Kodak publication No. M28.  Markin, G.P. & Gardner, D.E. 1993. Status of biological control in vegetation management in forestry. Canadian Journal of Forest Research, 23, 2023-31.  Moody, M.E. & Mack, R.N. 1988. Controlling the spread of plant invasions: the impotrance of nascent foci. Journal of Applied Ecology, 25, 1009-21.  Narayan, I. 1993. Can invasions of Pittosporum undulatum be controlled by fire? BSc thesis, University of Melbourne, Melbourne, Australia. Office of Technology Assessment. 1993. Harmful NIS in the US. Washington DC, USA.  Richardson, D.M. & Brink, M.P. 1985. Notes on Pittosporum undulatum in the south-western cape. Veld and Flora, 71, 75-7.  Sayn-Wittgenstein, L. 1978. Recognition of tree species on aerial photographs. Forest Management Institute, Ottawa, Ontario, Canada.  Tunison, J.T. 1992. Alien plant control strategies in Hawaii Volcanoes National Park. In: Stone et al. 1992, 485-506.  Tunison, J.T. & Stone, C.P. 1992. Special ecological areas: an approach to alien plant control in Hawaii Volcanoes National Park. In: Stone et al. 1992, 781-98. Personal communications Mr Robin Buchanan, Sydney, Australia Dr Harry Evans, International Institute of Biological Control, Silwood Park, Surrey, U.K. Dr Donald Gardner, Department of Botany, Honolulu, Hawaii, USA. Mr Neville Geddes, Forest Enterprise, Thornthwaite, Cumbria, U.K. Dr Roslyn Gleadow, University of Melbourne, Australia Mr Robert Kerr, Former Manager, Blue and John Crow Mountains National Park Dr David Lee, Director, PARC project, Kingston Dr I.A.W. MacDonald, Director for Conservation, South African Nature Foundation, South Africa. Dr Mike Morris, Plant Protection Research Institute, Pretoria, South Africa. Dr Stefan Neser, Plant Protection Research Institute, Pretoria, South Africa. Dr Wendy Strahm, IUCN, Geneva, Switzerland. Dr Jeremy Williams, SAFS, University of Wales, Bangor, U.K. Dr Joe Wunderlie, Institute of Tropical Forestry, Puerto Rico, USA.