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