Introduction 4 ha plot spanning forest-savanna boundary • This study examined the spatial patterns of tree diversity in a fire- influenced mosaic of deciduous forest and savanna (780 m elev), in Thung Yai Naresuan Wildlife Sanctuary, western Thailand.

• The study provides a baseline for interpreting the ecological dynamics between forest and savanna, which are little known in Southeast and likely to be influenced by climate change.

Tree composition and structure

• Number of trees (>5 cm dbh): 2277 • Tree density: 569 /ha • Basal area: 22 m2 /ha • 86 tree species: 79 in forest, 44 in savanna • 12 grass species • Ground cover: grass in savanna; shrubs + seedlings in forest Savanna in late-dry season Savanna in mid-dry season, after fire, grass low grass high Most abundant trees:

1. Shorea siamensis, (315 trees) 2. Cycas pectinata, Cycadaceae (177) 3. villosa, Euphorbiaceae (163) 4. Ziziphus rugosa, Rhamnaceae (138) 5. Quercus kerrii, Fagaceae (118) Bent tree stems in 6. retusa, Euphorbiaceae (111) Deciduous forest savanna, from gaur browsing 7. Stereospermum neuranthum, Bignoniaceae (109)

Tree community responses to habitat type 10 of 19 species tested for association with forest vs. savanna Small trees (5-10 cm) were 2 times denser in savanna, showed significant responses. The most common response (7 sp.) whereas large trees (>10 cm) had the opposite pattern—1.5 was higher sapling abundance in savanna (P < 0.01). times denser in forest (P < 0.002). Sample units were 400 m2 subplots. Examples of species with significantly higher Mean stem density densities of small trees (5-10 cm) in savanna 12 Large trees Shorea siamensis Quercus kerrii 10 Forest Small trees Savanna 8 Forest 6

Density Edge 4 2 Savanna 0 Large trees Small trees Stereospermum neuranthum Hiptage benghalensis parviflora Conclusions

• Population recruitment of many dominant species (i.e. Shorea) was occurring mainly in savanna, not forest (despite many adults in forest). • Tree density was 13-15% higher in edge plots than forest or grassland, and we observed no ‘dying edge’. • Thus, forest appears to be encroaching into savanna, perhaps due to reduced fire frequency in the savanna which permits increased tree recruitment.

This research was funded by WWF Thailand and the National Geographic Society Authors: E.L. Webb, R. Steinmetz, M. van de Bult, W. Chutipong, N. Seuaturien Thank you: Department of National Parks, Wildlife, and Conservation; Thung Yai Naresuan Wildlife Sanctuary; National Research Council of Thailand; Sarayudh Bunyavejchewin; J.F. Maxwell