African mahogany in northern Australia: some observations (with particular emphasis on small-scale forestry)

Transcription

1 African mahogany in northern Australia: some observations (with particular emphasis on small-scale forestry)

2 Acknowledgements Qld & NT Government forestry researchers, especially Geoff Dickinson, David Lee, Garth Nikles, Beau Robertson and Don Reilly Small-scale growers of African mahogany, particularly from AFG North & West Qld Northern Tropical Timbers All opinions expressed are my own

3 Khaya senegalensis in Northern Australia Kununurra, WA Weipa, Qld Darwin, NT Douglas-Daly, NT Katherine, NT Cooktown, Qld Townsville, Qld Bowen, Qld Climate map sourced from: Sunshine Coast, Qld

4 Brief overview of African mahogany in Australia 1970s CSIRO Trials (NT) and Weipa mine rehabilitation (150 ha) Small-scale tree growers and research trials (NE Qld 250 ha, WA 100 ha) Major research by Qld & NT governments Gunn Point CSIRO trials sampled and germplasm conserved 2004 Mareeba Prospects for high value timbers 2006 Townsville Where to from here with R&D 2011 Darwin African mahogany plantation industry forum (abstracts available online) Nikles et al (2014) Domesticating African mahogany in northern Australia AFG conference proceedings Legacy assets (trials, seed production areas) Since 2005 commercial monoculture plantings, mainly in the NT; more than 10, 000 hectares Oldest small plantations approaching harvest

5 Growth rates north east Queensland DAF Expt 867ATH 52 growth plots Since 2004, some measured three times Variation due to stocking, management, site, genetics, seasons Basal area more useful for comparisons between sites than volume 7, 8 4, 5, 6 9, 10 43, 44, 45 1, 2, 3 46, 47 48, 49 21, 22, 23, 41 30, 31, 42 39, 40 36, 37, 38 19, 20, 24 14, 15, 29, 35 52, 50, , 33 25, 26 11, 12, , 34, 17

6 Growth rates north east Queensland (2) Basal area (m2) Basal area Townsville region (multiple measures) Age (years)

7 Growth rates single plot (760, 450, 310 sph)

8 Thinning trials DAF Expt 788HWD 2 sites, thinned 2011 Bowen site planted 1998 at 666 sph Cooktown site planted 2006 at 408 sph Replicated trial with three rates of thinning and one with fertiliser

9 Response to thinning per tree Bowen (666, 400, 250 sph) Cooktown (408, 320, 240 sph) No thin 40% thin 60% thin No stems removed 20 % stems removed BASAL AREA (m2) BASAL AREA (m2) AGE (Years) AGE (Years)

10 Response to thinning per hectare Bowen (666, 400, 250 sph) Cooktown (400, 320, 240 sph) No stems removed 40 % stems removed No stems removed 20 % stems removed 60% stems removed 40% stems removed BASAL AREA (m2 per Ha) BASAL AREA (m2 per Ha) AGE (Years) AGE (Years)

11 Response to thinning key points Khaya senegalensis is highly responsive to thinning Thinning provides an opportunity to remove small and poorly formed trees, accentuating the volume growth There is a lag time between thinning and dbh response In non-thinned stands, small trees maintain slow growth rates, while large trees decelerate Growth is strongly related to soil moisture availability, which varies throughout the year, between years and across the site Reference: Arndt, S.K., Sanders, G.J., Bristow, M., Hutley, L.B., Beringer, J., Livesley, S.J. (2015) Vulnerability of native savanna trees and exotic Khaya senegalensis to seasonal drought. Tree Physiology

12 Fertiliser and Nutrition No growth response to fertiliser at Elderslie Early fertiliser trials at Weipa (Nicholson) indicated a response in young trees, 12 years later. Perhaps an interactive effect (establishment and weed control) Reference values for foliar samples of young trees from 1970s (Rance, Cameron, Bevege) N Threshold values may be different for mature trees (at least for N & Zn) Seasonal fluctuations Zn Critical Sep Feb Sep

13 Climatic tolerance: dry, wet, cool, fire, cyclones Severe Tropical Cyclone Ita, Estimated wind speed >200 km/hr Teak was severely damaged Native forest was severely damaged Mahogany had minimal damage Recently thinned area was damaged

14 Pests and diseases few of concern Termites Hypsipyla Pink disease Others Off-site issues Airflow

15 Weed risk African mahogany has a reputation for being a potential weed, maybe due to perceived similarity with African tulip tree, but there is little evidence, except where there has been site disturbance Growers are more concerned with managing the post-thinning weed growth, and coppice African TULIP tree (Spathodea campanulata) IS a weed

16 Genetic variation Enormous variation in relation to form, especially straightness, apical persistence and % stem Most older plantations are from land race seed Since 2000, most seed from wild sources in Africa Qld & NT governments established clone trials and seed orchards as the basis for a local breeding program

17 Wood Poor form limits length & harvest economics Wood properties of young logs uncertain Genetic variation in heartwood Zbonak, A., Brown, T., Harding, K., Innes, T. and Davies, M. (2010) Wood properties and processing outcomes for plantation grown African mahogany (Khaya senegalensis) trees from Clare, Queensland (18 and 20 year-old trees) and Katherine, Northern Territory (14 year-old trees).

18 Attributes for agricultural landscapes POSITIVES Growth rate best, improved form through breeding Drought tolerant, responds to conditions, high Leaf Area Index High value timber, potential for income diversification Minimal pest & disease (to date) Fire tolerant (once mature) Cyclone resilient (on this occasion at least) NEGATIVES Not a legume or fodder tree; wood not for farm use Not a native, limited habitat value??? Weed risk

19 Integrating trees into grazing systems

20 Thank you