Tree plantations can enhance Rainforest regeneration February 2001

Tropical deforestation and Such extensive deforestation has In her PhD studies, Rainforest CRC reforestation caused disruptions to major ecosys- student Martina Langi investigated Natural rainforests in the tropics are tem functions such as biodiversity, the differences between these two being degraded or fragmented at an nutrient cycles, and water balances, systems of forest restoration by alarming rate. Over the past decade, with the degree of disruption dictated comparing production and nutrient more than 90% of the total global by the severity of the disturbance. In turnover in plantations of different deforestation has taken place in moist reversing this destructive process, native species and in previously tropical forests. This rate continues to various forms of reforestation are logged natural rainforests. increase, placing remaining natural being undertaken in different parts of rainforests under significant threat. the world to restore some of the The reduction of original forest cover functions of degraded ecosystems. In The nature of the study due to logging or forest conversion tropical north Queensland, reforesta- The study area in tropical north to other simplified land uses has been tion initiatives include the establish- Queensland includes several forest at least 42% in tropical America, 21% ment of native timber plantations and plantations and secondary natural throughout Asia and Australia, and the protection of previously logged, rainforests within close geographical 52% in Africa. or secondary rainforests. proximity and between the ages of fifty-five and sixty-four years.

Above: Flindersia plantation with rich understorey and other tree species comparable to its adjacent rainforest Left: Auracaria plantation invaded by other species from adjacent rainforest Sites were selected in the Wongabel, Thus a 0.25 ha quadrat in the or stem growth, tended to follow a Gadgarra, and Danbulla State Forests Flindersia plantations at Gadgarra similar pattern. Litter decomposition where three adjacent but distinct contained 94 species of trees and was generally similar among the for- forest types were investigated: understorey species while the est types but the rate of fine root • Hoop pine (Araucaria Araucaria plantation contained 73 turnover was higher in the rainforest cunninghamii) plantation species. The rainforest plot at the and Flindersia plantations in compari- • Queensland Maple (Flindersia same site had 100 species. Similar son with the Araucaria plantations. brayleyana) plantation, and patterns were found at the other sites. • Secondary natural rainforest The three forest types differed in that had been logged several Forest production and nutrient terms of the nutrient capital they decades earlier. turnover contained although the greatest A number of significant results The highest basal area was invariably nutrient store tended to be present in emerged. measured in Araucaria plantations the Flindersia plantations and natural with lowest values usually measured rainforest stands while smaller Plant density and species richness in Flindersia plantations and interme- nutrient stores were present in the The two plantation species were diate values in the secondary forest. Araucaria plantations at each site. established as monocultures but the Among sites, basal area was found to Turnover, measured as nutrient close proximity of the plantations and be highest on basaltic soils at return via litterfall and litter decom- rainforest at each site facilitated the Gadgarra and lowest at Danbulla position, was invariably greater in recruitment of native rainforest where soils are derived from meta- rainforest stands than in either species into the plantation stands. morphic parent material. Gadgarra plantation type. Many of these trees subsequently also experiences the highest rainfall grew up to join the upper canopy of all three sites. Conclusions and Further Research layers. The three forest types differ in terms Large differences occurred in the of biomass and productivity. They The highest density of colonizing standing biomass of the three forest also differ in nutrient content and rainforest tree species was found in types. The Araucaria plantations nutrient turnover. Current work is the Flindersia plantations at each site. tended to have the highest biomass examining the relationship between Similarly, the highest overall species while the Flindersia plantations the biomass, productivity, nutrient richness was also found in the tended to have the least. Productiv- turnover and tree species richness in Flindersia plantations at each site. ity, which was measured by litterfall the various stands. Future studies will explore the efficiency of nutrient use in plantations and natural forest and the influence of differing levels of tree species richness on these attributes.

For Further Information Martina Langi or Dr David Lamb, Botany Department University of Queensland Phone: (07)3365 2045 Typical north Queensland rainforest opening showing patches of remaining rainforest Fax: (07)3365 1699 with plantation plantings on the left - both systems benefit from their close proximity Email: [email protected]