Jing Hu University of Queensland Dynamics of a Logged Tropical Forest-Following Different intensity Silvicultural Treatments over 48 years (Mt Baldy, Atherton) Jing Hu University of Queensland
Why set up this long-term experiment in 1960s? North Queensland rainforests managed for timber production prior to 1988 No logging, no silvicultural treatment (removing non-commercial species) Set up in 1967 to look at effects of different intensity silvicultural treatments on commercial timber volume.
Today’s situation: balance between timber provision and maintaining ecosystem services Did silvicultural treatments promote commercial timber volume, and which intensity perform best? How would above-ground tree biomass, species diversity and composition recover following different intensity treatments over 48 years?
Study site Mount Baldy, Atherton, north Queensland
Inventory years 1967 Mar,1969 Aug, 1969 1973 1981 1989 1997 2015 1968 (logging) Treatment
≥ 10cm DBH; DBH, mortality and recruitment; Species ID
Did silvicultural treatments promote commercial timber volume, and which intensity perform best?
Medium intensity treatment performed best in increasing commercial timber volume. Indication: treatment effects may still work for the next several decades. Low intensity Logging only High intensity Fig. 1 Harvestable timber volume of top 5 commercial species >40 cm in DBH
The number of trees ≥40 cm DBH in MT increased most. The number of trees <40 cm DBH in HT increased most. High intensity Medium intensity Logging only Low intensity Prediction: For the next several decades, the timber volume in HT may increase most with L least.
Will the increase of the abundance of commercial species alter the community functional composition? Canopy opening regeneration of early successional species with rapid growth rates and low wood density lower community weighted wood density
How about a polycyclic silvicultural system were applied? Trade-off between the number of commercial species and early- successional species
Did above-ground tree biomass, species diversity and composition recover to their pre-logging levels following different intensity treatments over 48 years?
Effects on biomass and species composition-- Immediate effects: Reduced basal area and species density through silvicultural treatments Treatments L LT MT HT Basal area (m2 ha−1) Initial basal area pre-logging (1967) 61.7 53.2 48.1 58.0 Basal area reduction through treatment c 0 (0%) 12.4(40.8%) 17.2 (55.6%) 19.3 (65.4%) Basal area post-treatment (1969) 35.6 17.8 13.7 10.2 The total number of species in each treatment (0.4 ha) Initial number of species pre-logging (1967) 70 74 75 The number of species reduction through treatment 0(0%) 11 (20.0%) 24 (32.3%) 49 (70.5%) The number of species post-treatment (1969) 55 48 42 18
Similar biomass increasing rates between treatments Medium-term effects: Similar biomass increasing rates between treatments Only L and HT did not recover to their pre-logging levels. How about long-term effects? Logging only Low-intensity Medium-intensity High-intensity
Things behind the biomass trajectories: High intensity treatments resulted in less competition, pushed forests back to earlier successional states, with less remnants and more recruits, higher growth rates. Fig.5 Ratio of the number of remnants post-treatment to the number of recruits over 46 years.
Species richness recovered to their pre-logging levels in L, LT and MT. Reason: probably disperse from adjacent natural forests or from local seed and seedling bank.
Species composition in HT was altered by silvicultural treatment, and partially recovered over 46 years. Takes longer for species composition to recover
Compositional similarity between treatments recovered. Implication on large scales: Lacking dispersion and local seed pools low resilience can not recover to original state divergence
Next step research Is silviculture worthwhile in natural forests?- Financial analysis Tree growth rates- Competition between individuals
Thanks very much for your listening! jing.hu1@uq.net.au