ISSUE 4 SEPTEMBER 2005 AA NewNew RoleRole forfor WeedsWeeds inin RainforestRainforest Restoration?Restoration? Issues in Tropical Forest Landscapes

Rainforest cover has been removed from many landscapes with adverse consequences for biodiversity, climate, land condition and water quality. Rapid, large-scale reforestation is required to restore biodiversity and ecosystem health in extensively and heavily cleared areas. While tree planting can re-establish a diverse rainforest on cleared land, the practice is expensive and only small areas of land have been reforested to date. Sometimes, forest cover can return to cleared land through natural processes. Most rainforest plants have fleshy fruits that are attractive to fruit- eating birds. As the birds move between remnant rainforest and regrowth patches they disperse the seeds of rainforest plants. These processes have the potential to cost- effectively restore forest cover to large areas of cleared land. In areas that have been cleared for long periods of time, regrowth may be dominated by introduced weedy plants. For example, regrowth dominated by camphor laurel trees covers extensive areas of cleared rainforest land in Australia. However, camphor laurel patches attract fruit- eating birds that disperse the seeds of rainforest plants. Many seedlings of rainforest plants have recruited to camphor laurel patches and, in the long-term, may come to dominate the regrowth. This process could be hastened by careful and strategic management interventions, but this requires a change in current attitudes towards the role of weeds in ecosystem restoration. An example of regenerating rainforest beneath camphor laurel regrowth. Succession is a process of progressive change in tree species composition following disturbance to a forested area.

Later- Camphor laurel dominated regrowth adjacent to extensive forests of the Nightcap Range in north eastern New South Wales. successional Forest Clearing and rainforest is one possible way of achieving reforestation, but is very rainforest species Restoration expensive ($20,000 - $30,000 per The clearing of rainforests over the hectare). Over large areas, past century has resulted in a strategies that make use of natural are characteristic substantial loss of habitat for species regenerative processes may be of native animals and plants. Forest considerably more cost-effective. of undisturbed areas that remain are often The establishment of any form of reduced to fragments surrounded woody vegetation cover can help by agriculture or urban initiate the process of rainforest forests. development. By revegetating regeneration by shading out heavily cleared areas we can aggressive grasses and herbaceous improve ecosystem health and vegetation and improving The process of reduce the threat of extinction to microclimatic conditions. native species. Frugivorous (fruit-eating) animals can then greatly assist rainforest rainforest Changing patterns of land use such regeneration by dispersing the as the abandonment of marginal seeds of rainforest plants to areas restoration seeks agricultural lands present an of regenerating forest. Most opportunity for the restoration of rainforest plants bear fleshy fruits forest cover to degraded that are eaten by frugivorous birds to speed up landscapes. In some cases, or mammals. Birds in particular are rainforest will naturally recolonise important seed dispersers in abandoned agricultural land but Australian rainforests. succession the potential for this to occur will be limited by the intensity of farming activities that have taken place towards a self- Exotic Species in and the length of time farming was Degraded Landscapes conducted. Soil seed banks quickly become depleted following Landscape modification by sustaining, rainforest clearing. In most cases, humans has been accompanied reforestation will depend on the by the introduction of an increasing rainforest-like deliberate or natural dispersal of number of plant species, often plants from remnant forests to originating from other continents cleared land. (exotic species). In fact, the presence of exotic species is often ecosystem. Replanting an area to emulate the used as an indicator of land density and diversity typical of degradation. In some areas, weedy canopies merge. Due to concern over its spread, camphor laurel has been declared a ‘Class 3 pest plant’ in Queensland and a noxious weed by a number of local governments in New South Wales. Some people have campaigned strongly for government-assisted removal of camphor laurel as a matter of urgency, arguing that its aromatic compounds, such as cineole and camphor, may be poisonous to other plants and animals. It is known that camphor laurel can suppress pasture growth and it was feared that native plants may be unable to establish beneath these long lived trees, effectively ‘locking up’ the land, Camphor laurel grows in pasture when grazing pressure is reduced. When the trees form reducing productivity and a closed canopy, rainforest seedlings may recruit to a patch. biodiversity. exotic plants may come to Camphor laurel is a native of Asia dominate a site and prevent and was first introduced as an establishment of native species. On ornamental and shade tree in the the other hand, exotic species 1800s. Camphor laurel trees bear might be useful in restoring function abundant crops of round, bluish- to highly degraded areas where black fruits approximately ten native species have become millimetres in diameter. Each fruit extinct or where current contains a single seed. In Australia, environmental conditions prevent a mature camphor laurel tree can their growth. produce one hundred thousand fruits in a year. These fruits are eaten These new, emerging issues in and the seeds dispersed by many environmental management birds and bats, helping to spread remain poorly understood. the species into new areas. However recent research into the Camphor laurel seedlings on farmland. role of the exotic tree species, camphor laurel (Cinnamomum camphora: Lauraceae), is helping to fill this knowledge gap.

Case Study: Camphor Laurel in the Big Scrub – Scourge or Saviour? From the nineteenth century, eastern Australian rainforests were targeted for clearing. Those that remain today are mostly restricted to steep slopes. The Big Scrub in The Big Scrub landscape today – macadamias in the foreground, camphor laurel dominated northern New South Wales was regrowth towards the centre, and young plantations on the hills in the background. once Australia’s largest tract of lowland subtropical rainforest but Concentrations of camphor laurel by the early 1900s it had been occur in areas where rainforests reduced to a few small, scattered have been cleared from basalt soils remnants, accounting for less than and pastures have been one percent of the original 75,000 established. When farmland is hectares. As the dairy and banana withdrawn from production or industries in this area have declined grazing reduced, camphor laurel over the last forty years, woody trees can rapidly recruit and grow. vegetation has returned to the A shrubland of abundant small landscape, mainly in the form of individuals first forms, then a regrowth dominated by camphor developing forest patch emerges laurel. as the trees grow and their The first camphor laurel trees to colonise a cleared area are often situated along fencelines. However, some observers have that once supported rainforest species were found to be common found that patches of camphor vegetation but had been used for and widespread in the regrowth, laurel regrowth can support a agriculture for many years. In each including the figbird, pied variety of native rainforest plants patch, the birds and plants were currawong, rose-crowned fruit- and animals. It has been suggested assessed within a 0.6 ha survey plot. dove and topknot pigeon. that camphor laurel patches can Most frugivorous birds used the provide important habitat for Birds in Camphor surveyed patches in winter (see species such as some types of fruit- Figure 1) when camphor laurel is in pigeon, whose populations have Many species of frugivorous birds fruit. Large flocks of topknot pigeons declined following the clearing of were recorded in camphor laurel flew across the landscape between rainforests. Camphor laurel may regrowth (see Table 1) – ten species remnant forest and regrowth also act as a catalyst for further with high potential to disperse patches throughout the winter, rainforest regeneration. rainforest seeds, six with medium potential and eighteen with low however many frugivorous birds These divergent viewpoints have potential. Birds that often eat fruit also used the patches in summer fuelled a heated public debate and also have a large gape (the when camphor laurel was not in over the value of camphor laurel width of the base of the beak) have fruit but when most native rainforest and the best strategies for the highest potential to disperse trees were fruiting. management of its spread. To seeds of a wide range of rainforest resolve such different and plant species, while birds that rarely Plant Recruitment conflicting viewpoints, independent eat fruit have the lowest. A number Plant surveys identified 181 species and factual information is needed. of the high dispersal potential of local rainforest plants in the 24 selected regrowth patches, including life forms typical of rainforest such as trees, palms, shrubs, vines, epiphytes and ferns at all stages of growth. There were also 23 species of exotic plants, mostly trees and shrubs, as well as four local non-rainforest species. The surveys clearly showed that the seedlings of native trees are able The rose-crowned fruit-dove disperses many to survive and grow in camphor rainforest plant seeds and was recorded laurel patches. Fifty species of local rainforest trees were recorded as Griffith University researchers Dr John frequently in camphor laurel regrowth. The species is listed as Vulnerable under the adults in the regrowth patches (in Kanowski (left) and Stephen McKenna a total sampled area of 6 ha), while survey plants in camphor laurel regrowth New South Wales Threatened Species Act 75 species of local rainforest trees in the Big Scrub. 1995 (Image: © Tom Tarrant).

Table 1: Frugivorous birds that potentially disperse rainforest seeds to 24 Solving the Puzzle: Birds, selected camphor laurel patches in the Big Scrub region, New South Wales. Plants and Camphor Seed dispersal potential was determined from the proportion of fruit in each Laurel Regrowth individual’s diet, its gape width and whether it disperses viable seeds Rainforest CRC researchers set out Occurrence to objectively assess the potential Birds with high potential to disperse seeds % of patches for rainforest regeneration to occur in areas of camphor laurel regrowth Figbird Sphecotheres viridis 96 in the Big Scrub region. They Pied currawong Strepera graculina 96 investigated which bird species in Rose-crowned fruit-dove Ptilinopus regina 92 the region consume the fruits of Topknot pigeon Lopholaimus antarcticus 63 rainforest plants and disperse their Green catbird Ailuroedus crassirostris 42 seeds; how common these birds Olive-backed oriole Oriolus sagittatus 24 are in camphor laurel regrowth Satin bowerbird Ptilonorhynchus violaceus 17 patches; which rainforest plants are Wompoo fruit-dove Ptilinopus magnificus 13 recruiting in these patches; and Channel-billed cuckoo Scythrops novaehollandiae 4 how many recruiting plants are Paradise riflebird Ptiloris paradiseus 4 present as seedlings. Occurrence Birds with medium potential to disperse seeds % of patches Researchers measured the diversity and abundance of birds and plants Lewin's honeyeater Meliphaga lewinii 100 in 24 patches of well developed Silvereye Zosterops lateralis 100 camphor laurel regrowth using Mistletoebird Dicaeum hirundinaceum 58 repeatable and quantitative survey Varied triller Lalage leucomela 54 methods. Each of the patches Barred cuckoo-shrike Coracina lineata 4 formed an area of at least three Regent bowerbird Sericulus chrysocephalus 4 hectares and occurred on land Figure 1: Number of frugivorous birds recorded in camphor laurel regrowth patches in winter and summer at three distances from the largest areas of remnant rainforest. H = bird species which have a high seed dispersal potential; M = medium; L = low. Numbers are averaged across seven to nine sites in each distance class, with three to four repeat visits per patch (Images: Terry Reis). were found to be recruiting as especially those of later 2. A well-developed camphor young trees within a 1.2 ha subset successional stages, were laurel patch usually has a dense of this area. becoming increasingly prevalent canopy that shades out grasses among the recruits. and herbaceous plants which The individual adult trees counted are otherwise likely to inhibit were mostly mature camphor seedlings of rainforest trees; and laurels (66%), with 9% privet Can Camphor Laurel 3. The tree canopy and leaf litter (Ligustrum lucidum) and 25% native layer may further contribute to species. However, the emerging Facilitate Rainforest regrowth by creating a generation of young tree recruits Regrowth? microclimate suitable for the displayed a different population Camphor laurel is readily germination and establishment structure with only 22% of the establishing in the former Big Scrub of rainforest plants. individuals being camphor laurel, landscape. It can colonise pasture 31% privet and 47% natives. Many and rocky sites and grows rapidly This suggests that there is potential native tree species typical of to maturity, enabling it to play a to manage camphor laurel mature rainforest were appearing pioneer-like role in regrowth on regrowth to facilitate rainforest as young plants even though they pasture sites. regeneration over large areas, were uncommon as adults. Most especially where strategic of these species are dispersed by Three ecological features of reforestation will be beneficial, for birds (see Figure 2). camphor laurel patches facilitate example, increasing total forest rainforest regrowth: cover or providing linkages Statistical analyses showed that 1. Camphor laurel attracts between areas of remnant forest. bird-dispersed native tree species, frugivorous birds that disperse the seeds of rainforest plants;

Figure 2: The average density of the most common native rainforest trees in camphor laurel regrowth (adults and recruits separately), shown in order of decreasing adult density. Dark bars show later- successional species, a variety of which are appearing as juveniles, even though they are uncommon as adults. Bird-dispersed species are marked with an asterisk (*). Without the forest-like structure that Exotic Plants and CONTACTS camphor laurel brings to the Rainforest Restoration landscape, regrowth may not have progressed as rapidly past a This study shows how some exotic combination of exotic pasture species may have a positive role grasses and herbaceous plants. in facilitating forest recovery in cleared landscapes, however this Camphor laurel management will need to be assessed on a case- could involve two phases: CRC Research by-case basis. Some invasive exotic 1. Tolerating the development of Telephone (07) 4042 1246 species can seriously degrade camphor laurel regrowth until Facsimile (07) 4042 1247 ecosystem function without any the canopy has closed and a Email [email protected] positive effects on biodiversity. On sufficiently large pool of native www.rainforest-crc.jcu.edu.au the other hand, in highly modified recruits has established; and landscapes, certain exotic plant 2. Progressively removing species have come to play an camphor laurel trees and important role in ecosystem seedlings to assist the rainforest function and native species now recruits to grow more rapidly to depend on them for survival. full size. Centre for Innovative Given the large changes in the These actions may need to be Conservation Strategies environment that have occurred combined with an enrichment since clearing of rainforest in most Griffith University planting program of native landscapes, it is highly unlikely that Telephone (07) 3735 5394 rainforest trees, along with regenerating forests can ever be Facsimile (07) 3735 5014 continued strategic control of identical to those that previously Email [email protected] exotic seedlings that may appear. existed. The conservation of www.griffith.edu.au/centre/cics Field trials and further research are remnants of original forest remains needed to test whether such an a priority for management, as they approach is feasible and is cost are critical reference points, effective. heritage sites and genetic resources. But in many areas, preservation of remnants alone will be insufficient to maintain even the Big Scrub Rainforest present biodiversity. Achieving long- Landcare Group term conservation and restoration www.bigscrubrainforest.org.au may require a shift in the current thinking about best management practices for reforesting landscapes Members of the community discuss the and the role of weeds in the issue of camphor laurel regrowth at a Big functioning of ecosystems. Scrub field day.

FURTHER READING Big Scrub Rainforest Landcare Group (2005) Subtropical Rainforest Restoration. Second Edition. Bangalow, NSW. Neilan, W., Catterall, C.P., Kanowski, J. and McKenna, S. Do frugivorous birds assist rainforest succession in weed-dominated oldfield regrowth of subtropical Australia? Biological Conservation (in press). Scanlon, T., and NSW North Coast Camphor Laurel Taskforce (2000) Camphor Laurel Kit. Available at: http://www.fncw.nsw.gov.au/camphor_kit.html Zavaleta, E., Hobbs, R., Mooney, H. (2001) Viewing invasive species removal in a whole- ecosystem context. Trends in Ecology and Evolution 16: 454-459. ACKNOWLEDGEMENTS This paper was prepared by Wendy Neilan, Carla Camphor laurel regrowth at the end of a rainbow (Image A Rohlfe). Catterall, John Kanowski, and Stephen McKenna, with support from the Rainforest CRC and Griffith University Community Partnerships. We acknowledge the contribution of Cath Moran and Hank Bower to field surveys, and the assistance of Scott Piper, Naima Fine, Peter Benson, Terry Reis, Shannon Hogan, Annette Bryan, Big Scrub landholders, local authorities and Landcare groups.