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The conceptual models were compiled by researchers in collaboration with a wide range of stakeholders from Natural Resource Management groups, universities and government agencies and based on available scientific information[1].

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Mount Alexandra Lookout Photo by Queensland Government
Gheerulla Valley Photo by TEQ
Semi evergreen vine thicket and rainforest Photo by Queensland Government

Rainforests

Note: While included within these models, rainforests are not wetlands.

Rainforests contain dense, moisture-dependent vegetation where a variety of shade-tolerant understory plants grow beneath an almost closed canopy. Rainforests grow where rainfall is usually higher than 2,000 mm per year[10]. They are some of the most productive and biodiverse ecosystems on the planet. In Queensland, rainforests range from evergreen to semi-deciduous, where trees lose their leaves during the dry season[11].

Key Messages for Rainforests and Nitrogen processing

  • Nitrogen (N) is required by plants and animals for their growth, and rainforests need large amounts of this nutrient to sustain their high productivity[7].
  • Tropical rainforests can accumulate and recycle large quantities of N in their trees and soils[7][12]. The N content within the trees and soils of rainforests increases with forest age. Deforestation and land degradation can cause the loss of the accumulated N[9].
  • To supply the forest with nutrients, N fixation can occur within the roots of some plants, on shallow soils, and on litterfall[7][5].
  • Denitrification occurs in wet soils of the rainforests[8].
  • Rainforests have a tightly coupled nitrogen cycle, meaning that most of the nitrogen is reused within the forest, and little is leached[14]. Small amounts of dissolved organic nitrogen (DON) or litter can be exported from rainforests (< 1 g/ha/day)[9]. Rainforests do not typically generate significant amounts of inorganic N[6][2].
  • Rainforest can receive N inputs from groundwater or runoff, especially rainforests that are lower in the floodplain and close to agricultural or urban areas[13][3].
  • Excess N leached into rainforests from agricultural or urban activities can cause an imbalance in the nutrient ratios and may favour the proliferation of weeds[15].
  • Invasive animals, such as pigs, can cause localised imbalances in the N cycle by increasing mineralisation from the soil through digging and from their faeces. Pigs concentrate N in rainforests, rather than generate it. They will also consume N from plants and animals, therefore recycling it within the forest[4].
  • Rainforests in the Great Barrier Reef catchments are mostly found in mountain ranges, but some small patches of rainforest are found in lower areas, however much of this low elevation rainforest has been cleared.
  • Rainforests in the Great Barrier Reef are generally inundated only by rainwater, with creeks running through them and feeding larger rivers downstream. Although, some forests in wetter areas next to floodplain wetlands can receive local inundation from adjacent waterways during periods of flood. During this time some exchange of N with the adjacent ecosystems can occur.
  • Rainforests in catchments where agricultural activities are dominant may receive N from leached fertilisers. This N could be rapidly taken up by the trees.

References

  1. ^ Adame, MF, Vilas, MP, Franklin, H, Garzon-Garcia, A, Hamilton, D, Ronan, M & Griffiths, M (2021), 'A conceptual model of nitrogen dynamics for the Great Barrier Reef catchments', Marine Pollution Bulletin. [online], vol. 173PA. Available at: https://www.sciencedirect.com/science/article/pii/S0025326X21009437.
  2. ^ Brodie, JE & Mitchell, AW (2005), 'Nutrients in Australian tropical rivers : changes with agricultural development and implications for receiving environments', Marine and Freshwater Research, vol. 56, pp. 279-302.
  3. ^ Connolly, NM, Pearson, RG, Loong, D, Maughan, M & Brodie, J (2015), 'Water quality variation along streams with similar agricultural development but contrasting riparian vegetation', Agriculture, Ecosystems and Environment. [online], vol. 213, no. x, pp. 11-20. Available at: http://dx.doi.org/10.1016/j.agee.2015.07.007.
  4. ^ Doupe, RG, Mitchell, J, Knott, MJ, Davis, AM & Lymbery, AJ (2010), 'Efficacy of exclusion fencing to protect ephemeral floodplain lagoon habitats from feral pigs (Sus scrofa).', Wetlands Ecology and Management, vol. 18, pp. 69-78.
  5. ^ Farnkranz, M, Wanek, W, Richter, A, Abell, G, Rasche, F & Sessitsch, A (2008), 'Nitrogen fixation by phyllosphere bacteria associated with higher plants and their colonizing epiphytes of a tropical lowland rainforest of Costa Rica', ISME Journal, vol. 2, no. 5, pp. 561-570.
  6. ^ Harris, GP (2001), 'Biogeochemistry of nitrogen and phosphorus in Australian catchments, rivers and estuaries: effects of land use and flow regulation and comparisons with global patterns', Marine and Freshwater Research. [online], vol. 52, no. 1, p. 139. Available at: http://www.publish.csiro.au/?paper=MF00031 [Accessed 4 November 2020].
  7. ^ a b c Hedin, LO, Brookshire, ENJ, Menge, DNL & Barron, AR (2009), 'The nitrogen paradox in tropical forest ecosystems', Annual Review of Ecology, Evolution, and Systematics. [online], vol. 40, no. 1, pp. 613-635. Available at: http://www.annualreviews.org/doi/10.1146/annurev.ecolsys.37.091305.110246.
  8. ^ Houlton, BZ, Sigman, DM & Hedin, LO (2006), 'Isotopic evidence for large gaseous nitrogen losses from tropical rainforests', PNAS, vol. 103, no. 23, pp. 8745-8750.
  9. ^ a b Markewitz, D, Davidson, E, Mutinho, P & Nepstad, D (2004), 'Nutrient loss and redistribution after forest clearing on a highly weathered soil in Amazonia', Ecological Applications, vol. 14, pp. 177-199.
  10. ^ NASA (1 August 2021), Rainforest: Mission: Biomes. [online] Available at: https://earthobservatory.nasa.gov/biome/biorainforest.php [Accessed 2 August 2021].
  11. ^ Queensland Government, Rainforests | Wildlife habitats. [online] Available at: https://www.qld.gov.au/environment/plants-animals/habitats/rainforests [Accessed 4 November 2020].
  12. ^ Rasiah, V & Armour, JD (2001), 'Nitrate accumulation under cropping in the Ferrosols of Far North Queensland wet tropics', Australian Journal of Soil Research. [online], vol. 39, no. 2, pp. 329-341. Available at: Scopus.
  13. ^ Rasiah, V, Armour, JD, Cogle, AL & Florentine, SK (2010), 'Nitrate import – export dynamics in groundwater interacting with surface-water in a wet-tropical environment', Australian Journal of Soil Research, pp. 361-370.
  14. ^ Vitousek, PM (1984), 'Litterfall, nutrient cycling, and nutrient limitation in tropical forests', Ecology, vol. 65, no. 1, pp. 285-298.
  15. ^ Weeds of rainforests and associated ecosystems: workshop proceedings (2003), p. 106, Rainforest CRC : CRC Weed Management, Cairns, Qld, eds. A C Grice & M J Setter.

Last updated: 3 August 2021

This page should be cited as:

Department of Environment and Science, Queensland (2021) , WetlandInfo website, accessed 29 September 2021. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/processes-systems/nitrogen-concept-model/rainforest/

Queensland Government
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