Dynamics of a savanna-forest mosaic in the Australian monsoon tropics inferred from stand structures and historical aerial photography
Daniel S. Banfai A B and David M. J. S. Bowman AA ARC Key Centre for Tropical Wildlife Management, Charles Darwin University, Darwin, NT 0909, Australia.
B Corresponding author. Email: daniel.banfai@cdu.edu.au
Australian Journal of Botany 53(3) 185-194 https://doi.org/10.1071/BT04141
Submitted: 8 September 2004 Accepted: 24 February 2005 Published: 26 May 2005
Abstract
Stratified ground-truthing was undertaken within an area of approximately 30 km2 of tropical savanna across an abrupt sandstone escarpment in the monsoon tropics of Australia. Comparison of aerial photographs from 1941 and 1994 had previously revealed a landscape-wide expansion of closed forest and contraction of grassland patches. Good congruence between field measurements and the vegetation classifications from the 1994 aerial photography supported the authenticity of the vegetation changes. The relative abundance of rainforest and non-rainforest tree species also concurred with mapped vegetation transitions. Changes in individual size classes of rainforest species, which are relatively fire sensitive, were consistent with the primacy of fire in controlling the distribution of the closed-forest formation. Fire scars previously mapped from satellite imagery were used to derive a fire activity index for contrasting vegetation transitions. Savannas that had converted to closed forest had lower fire activity than did stable savannas. Conversely, closed forests that converted to savanna had the highest fire activity index. The landscape-wide expansion of rainforest is associated with the cessation of Aboriginal fire management, possibly in conjunction with elevated CO2 and increasing annual rainfall.
Acknowledgments
We thank David Fuller for his hospitality during the fieldwork, Ray Petherick for permission to work on his property and his contribution of historical information and Andrew Edwards for providing access to the fire mapping data. The Australian Research Council supported this project through the Key Centre for Tropical Wildlife Management.
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Appendix 1. Tree species recorded but not included in Table 2
Rainforest: Acacia pellita O.Schwarz, Breynia cernua (Poir.) Mull.Arg., Buchanania arborescens (Blume) Blume, Corymbia polycarpa (F.Muell.) K.D.Hill & L.A.S.Johnson, Cyclophyllum schultzii (O.Schwarz) S.T.Reynolds, Diospyros calycantha O.Schwarz, Diospyros cordifolia Roxb., Drypetes deplanchei (Brongn. & Griseb.) Merr., Elaeocarpus arnhemicus F.Muell., Ficus congesta Roxb., Gmelina arborea Roxb., Gmelina schlechteri H.J.Lam, Ilex arnhemensis (F.Muell.) Loes., Leptospermum maddidum A.R.Bean, Litsea glutinosa (Lour.) C.B.Rob., Maranthes corymbosa Blume, Memecylon pauciflorum Blume, Neolitsea brassii Allen, Pouteria richardii (F.Muell.) Baehni, Pouteria sericea (Aiton) Baehni, Premna acuminata R.Br., Rapanea benthamiana Mez., Schefflera actinophylla (Endl.) Harms, Syzygium forte (F.Muell.) B.Hyland, Wrightia pubescens R.Br., Xanthostemon paradoxus F.Muell.
Non-rainforest: Acacia difficilis Maiden, Acacia dimidiata Benth., Acacia holosericea A.Cunn. ex G.Don, Acacia lamprocarpa O.Schwarz, Acacia oncinocarpa Benth., Acacia plectocarpa A.Cunn. ex Benth., Acacia tolmerensis G.J.Leach, Alstonia actinophylla (A.Cunn.) K.Schum., Antidesma ghesaembilla Gaertn., Brachychiton diversifolius R.Br., Brachychiton megaphyllus Guymer, Brachychiton paradoxus Schott & Endl., Bridelia tomentosa Blume, Callitris intratropica R.T.Baker & H.G.Sm., Calytrix exstipulata DC., Choriceras tricorne (Benth.) Airy Shaw, Clerodendrum floribundum R.Br., Corymbia bella K.D.Hill & L.A.S.Johnson, Corymbia dichromophloia (F.Muell.) K.D.Hill & L.A.S.Johnson, Corymbia grandifolia (R.Br. ex Benth.) K.D.Hill & L.A.S.Johnson, Corymbia kombolgiensis (Brooker & Dunlop) K.D.Hill & L.A.S.Johnson, Corymbia latifolia (F.Muell.) K.D.Hill & L.A.S.Johnson, Croton arnhemicus Mull.Arg., Cycas armstrongii Miq., Denhamia obscura (A.Rich.) Meisn. ex Walp., Dolichandrone filiformis (Fenzl) F.Muell., Eucalyptus phoenicea F.Muell., Eucalyptus tectifica F.Muell., Exocarpos latifolius R.Br., Ficus brachypoda (Miq.) Miq., Ficus opposita Miq., Flemingia lineata (L.) Roxb. ex W.T.Aiton, Grevillea heliosperma R.Br., Jacksonia dilatata Benth., Margaritaria dubium-traceyi Airy Shaw & B.Hyland, Melaleuca leucadendra (L.) L., Owenia vernicosa F.Muell., Planchonia careya (F.Muell.) Kunth, Pouteria arnhemica (F.Muell. ex Benth.) Baehni, Timonius timon (Spreng.) Merr., Syzygium eucalyptoides ssp. bleeseri (O.Schwarz) B.Hyland, Terminalia grandiflora F.Muell., Terminalia pterocarya F.Muell., Verticordia cunninghamii Schauer, Wrightia saligna (R.Br.) F.Muell. ex Benth.
