Post-Pasture Regeneration in Northern Australia’s Moist Tropics
By Cove Desormeax
Keywords: Australia, Moist Tropics, Forest Regeneration, Non-Native Species
Summary
This case study looks at the use of non-native species in rain forest restoration efforts in abandoned pasture lands in the Atherton Tablelands region, in northeastern Australia. Since the highly fertile soils of this region made it an attractive area for settlers to establish farmlands, the area saw massive deforestation and habitat fragmentation in the nineteenth and early twentieth century. Now, efforts are being made by local land managers and researchers to recover some of the region’s lost biodiversity by aiding in rain forest regeneration. Faced with the establishment of many non-native species, decision makers have created restoration plans that allow introduced species, namely Solanum mauritianum (wild tobacco), to play the role of a facilitator in forest regeneration, while still working towards the goal of increasing native biodiversity and historical ecological function. This approach to restoration is new, there is a significant amount of uncertainty in terms of the long-term outcome. By exploring this approach to human intervention in forest regeneration, this case study aims to showcase the creativity going into the efforts to achieve widespread regeneration of moist tropical forests in the Atherton Tablelands.
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Ecological Genealogy
The Atherton Tablelands are in Queensland, Australia, in the island continent’s northeast portion. This region is part of the Australian upland tropics that once supported large areas of indigenous closed-canopy rainforest, around thirty meters tall, containing diverse tree species of many families (Catterall, 2016). Fire-prone eucalypt dominated forests occupied the drier adjacent areas, and sometimes made their way into the rain forest. The traditional owners and stewards of the lands known today as the Atherton Tablelands are the communities in the Djirrbalngan language group. The rainforests of the Tablelands were home to the Djirrbal and Ngadjonji tribes, while the dry and more open forested areas, further west, were home to the Jibadal and Barbarum peoples. Archaeological evidence of the region’s oldest human occupation site, the Walkunder Arch Cave, estimates it to be 18,000 years old (Birkett, 1985). Pollen analyses indicate an even longer history of human occupation, with frequent fires beginning approximately 45,000 years ago. The traditional way of life for these peoples included camps that can be described as semi-permanent. They were not completely nomadic, and their use of the land included both clear base-camp areas and frequently used walking paths.
The Atherton Tablelands are named after the first European settler in the region, John Atherton, who settled near what is now known as the town of Mareeba in 1877. This region’s period of rich native biodiversity was threatened by the agriculture and other land use changes post-European contact in the late eighteenth and early nineteenth centuries (Bradshaw, 2012). The Atherton Tablelands are an extremely fertile plateau, making it a highly favourable location for agricultural development. This region saw mostly dairy farming and sugarcane growing – both practices that resulted in mass deforestation and landscape changes (Huxley, 2002). In addition to European settlement, the region also saw a large population of Chinese people who, like European settlers, were drawn to the region by the prospect of gold mining. Many of those who did not return to China following the goldrush ended up contributing significantly to the region’s farming activity through partnerships with European settlers (The North Queensland Register, 1905). Use of the land for agriculture, especially cattle farming and other practices involving animal grazing, slowed over the course of the twentieth century, allowing for patches of rainforest regrowth (Figure 1). When large areas of forest vegetation are cut down, burnt, or otherwise disturbed, changes in physical conditions, such as increased sunlight availability, allow for the formation of dense, ground-covering mats of various grass, herb, fern, and vine species (Catterall, 2016). More recently, moist tropical forests have been highly valued for their indigenous diversity, which will remain threatened and continue to decline without the rapid restoration of vast areas of moist tropical forest habitat capable of supporting their native biota (Catterall, 2016). The areas previously used for pasture in the twentieth century, mostly for cattle grazing, became dominated by non-native grasses and other planted or invasive species (Elgar et al., 2014). The tropical grass species found on these sites include Urochloa decumbens (signal grass) and Megathyrsus maximus (guinea grass) (Elgar et al., 2014). For the abandoned pastureland of the Atherton Tablelands, human activities have made novel changes to the region’s abiotic conditions. For instance, the soil has undergone increased compaction, changes in chemistry, and changes in moisture levels (Catterall, 2016; Elgar et al., 2014). Because this shift in growing conditions has allowed for a plethora of non-native species to thrive, researchers and ecological decision makers in the area have been searching for ways forward for the restoration of stands of lost moist tropical forests in hopes of supporting the return of native flora and fauna. |
Present Tense
A recent study analyzing the functional traits of native and non-native species in Australia’s wet tropics has identified a number of non-native species that have the potential to aid in restoration by facilitating forest succession. The criteria for useful non-native facilitator tree species include: short lifespan; high fecundity; seeds that are both capable of wide dispersal on clear landscapes and predated by forest fauna; seedlings that are shade intolerant, grow quickly in sunlight, and are capable of outcompeting pasture plants; adult trees that are not competitive with seedlings of desired, late-successional native species (Catterall, 2016). Solanum mauritianum and Lantana camara possess most of these attributes for Australian moist tropics. In this case, another term that can be used to describe facilitator species is ‘pioneer species,’ which refers to species that are first to move into previously cleared sites, setting them up for further regeneration.
There has been a significant interest in S. mauritianum as a potential pioneer tree species, as it possesses ecological properties that facilitate forest succession. Solanum mauritianum, commonly known as wild tobacco, is a woody shrub species native to South America (Figure 2). It is a seed-propagated, opportunistic plant often found in large quantities in pastures in coastal Queensland and New South Wales, but it is not a restricted or prohibited introduced species under Queensland’s 2014 Biosecurity Act (State of Queensland Department of Agriculture and Fisheries, 2020). The controlled use of Solanum mauritianum for assisting the regeneration of cleared areas of rain forest is a significant component of an experimental restoration project that is thoroughly discussed and analyzed by Elgar et al. (2014). At the time of the article, the project consisted of three pasture conversion sites that border large areas of conserved rainforest. The native vegetation of this area is complex notophyll to mesophyll vine forest, but the landscape vegetation at the time of the study was a mixture of remnant rain forest, cleared areas that were formerly livestock pasture, and patches of forest regrowth that vary in age. The study sites are retired pasture with red basaltic soil, mostly dominated by non-native tropical grasses (e.g., Urochloa decumbens), pasture legumes, and other planted and invasive species. In this case, S.mauritianum is the most promising non-native pioneer species because of its capacity to colonize pasture, forming a shady canopy and quickly producing fruits attractive to seed-dispersing frugivores. These traits make this species more effective than native rainforest species when it comes to reducing the ecological barriers of ground competition and propagule supply – something that is key in facilitating subsequent forest regeneration (Elgar et al., 2014). Because it is a lower strata species that is very light-demanding, it can serve as the means by which native species of taller canopy trees can enter these abandoned pasture sites, then decline over time as successful forest succession closes the canopy gaps. Considering this species’ potential as a non-native pioneer species, experimental plots were created wherein herbicides were applied to pasture grasses, allowing for the establishment of stands of S. mauritianum (Figure 3). While approaches may vary, this study contains valuable insights into the possibility of using non-native species in efforts to assist the regeneration of native rain forests in this region. |
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Future Trajectory
References
"Agricultural Conference at Atherton", The North Queensland Register (Townsville, Qld.: 1892 - 1905), http://nla.gov.au/nla.news-article85123749]
Bradshaw, C. J. A. (2012). Little left to lose: deforestation and forest degradation in Australia since European colonization. Journal of Plant Ecology, 5(1), 109–120. https://doi.org/10.1093/jpe/rtr038
Catterall, C. P. (2016). Roles of non-native species in large-scale regeneration of moist tropical forests on anthropogenic grassland. Biotropica, 48(6), 809–824. https://doi.org/10.1111/btp.12384
D’Antonio, C., & Meyerson, L. A. (2002). Exotic Plant Species as Problems and Solutions in Ecological Restoration: A Synthesis. Restoration Ecology, 10(4), 703–713. https://doi.org/10.1046/j.1526-100X.2002.01051.x
Elgar, A. T., Freebody, K., Pohlman, C. L., Shoo, L. P., & Catterall, C. P. (2014). Overcoming barriers to seedling regeneration during forest restoration on tropical pasture land and the potential value of Woody Weeds. Frontiers in Plant Science, 5. https://doi.org/10.3389/fpls.2014.00200
Goosem, M. (2007). Fragmentation impacts caused by roads through rainforests. Current Science (00113891), 93(11), 1587–1595.
Hobbs, R. J., Higgs, E., & Harris, J. A. (2009). Novel ecosystems: implications for conservation and restoration. Trends in Ecology & Evolution (Amsterdam), 24(11), 599–605. https://doi.org/10.1016/j.tree.2009.05.012
Huxley, M. (2002). The Ngadjonji lands. In Canada and the world backgrounder (Vol. 67, Issue 6, pp. 19-). Rupert J. Taylor.
Lindenmayer, D. B., Fischer, J., Felton, A., Crane, M., Michael, D., Macgregor, C., Montague-Drake, R., Manning, A., & Hobbs, R. J. (2008). Novel ecosystems resulting from landscape transformation create dilemmas for modern conservation practice. Conservation Letters, 1(3), 129–135. https://doi.org/10.1111/j.1755-263X.2008.00021.x
Shoo, L. P., & Catterall, C. P. (2013). Stimulating Natural Regeneration of Tropical Forest on Degraded Land: Approaches, Outcomes, and Information Gaps. Restoration Ecology, 21(6), 670–677. https://doi.org/10.1111/rec.12048
Shoo, L. P., Freebody, K., Kanowski, J., & Catterall, C. P. (2016). Slow recovery of tropical old-field rainforest regrowth and the value and limitations of active restoration. Conservation Biology, 30(1), 121–132. https://doi.org/10.1111/cobi.12606
State of Queensland Department of Agriculture and Fisheries. (2020). Wild Tobacco Solanum mauritianum. https://www.daf.qld.gov.au/__data/assets/pdf_file/0007/60991/wild-tobacco.pdf
Bradshaw, C. J. A. (2012). Little left to lose: deforestation and forest degradation in Australia since European colonization. Journal of Plant Ecology, 5(1), 109–120. https://doi.org/10.1093/jpe/rtr038
Catterall, C. P. (2016). Roles of non-native species in large-scale regeneration of moist tropical forests on anthropogenic grassland. Biotropica, 48(6), 809–824. https://doi.org/10.1111/btp.12384
D’Antonio, C., & Meyerson, L. A. (2002). Exotic Plant Species as Problems and Solutions in Ecological Restoration: A Synthesis. Restoration Ecology, 10(4), 703–713. https://doi.org/10.1046/j.1526-100X.2002.01051.x
Elgar, A. T., Freebody, K., Pohlman, C. L., Shoo, L. P., & Catterall, C. P. (2014). Overcoming barriers to seedling regeneration during forest restoration on tropical pasture land and the potential value of Woody Weeds. Frontiers in Plant Science, 5. https://doi.org/10.3389/fpls.2014.00200
Goosem, M. (2007). Fragmentation impacts caused by roads through rainforests. Current Science (00113891), 93(11), 1587–1595.
Hobbs, R. J., Higgs, E., & Harris, J. A. (2009). Novel ecosystems: implications for conservation and restoration. Trends in Ecology & Evolution (Amsterdam), 24(11), 599–605. https://doi.org/10.1016/j.tree.2009.05.012
Huxley, M. (2002). The Ngadjonji lands. In Canada and the world backgrounder (Vol. 67, Issue 6, pp. 19-). Rupert J. Taylor.
Lindenmayer, D. B., Fischer, J., Felton, A., Crane, M., Michael, D., Macgregor, C., Montague-Drake, R., Manning, A., & Hobbs, R. J. (2008). Novel ecosystems resulting from landscape transformation create dilemmas for modern conservation practice. Conservation Letters, 1(3), 129–135. https://doi.org/10.1111/j.1755-263X.2008.00021.x
Shoo, L. P., & Catterall, C. P. (2013). Stimulating Natural Regeneration of Tropical Forest on Degraded Land: Approaches, Outcomes, and Information Gaps. Restoration Ecology, 21(6), 670–677. https://doi.org/10.1111/rec.12048
Shoo, L. P., Freebody, K., Kanowski, J., & Catterall, C. P. (2016). Slow recovery of tropical old-field rainforest regrowth and the value and limitations of active restoration. Conservation Biology, 30(1), 121–132. https://doi.org/10.1111/cobi.12606
State of Queensland Department of Agriculture and Fisheries. (2020). Wild Tobacco Solanum mauritianum. https://www.daf.qld.gov.au/__data/assets/pdf_file/0007/60991/wild-tobacco.pdf