A mainland–maritime monsoon relay: Divergent ENSO and hydroclimatic growth signals in Tectona grandis from Thailand and Indonesia

Information from the abstract

The spatial coherence of the Asian monsoon system is a key assumption in regional dendroclimatology, however its validity across the equator remains largely untested. We investigate the potential for Mainland–Maritime hydroclimatic decoupling by comparing tree-ring growth of Tectona grandis from Umphang, Thailand (1843–2022), and Wanagama, Indonesia (1956–2023). Using standard dendrochronological techniques and bootstrapped Pearson correlations in R, we developed robust chronologies of total ring width, earlywood, and latewood (EPS > 0.96). Despite shared monsoonal climates, the overlapping period (1956–2022) shows a clear functional disconnect across the equator, with no significant correlation between the chronologies (r = 0.02). Spatial teleconnection analyses reveal two contrasting climatic regimes. The maritime Indonesian signal is strongly linked to ENSO (r = −0.410, p < 0.001) and the Indian Ocean Dipole (r = 0.310), reflecting a demand-driven system controlled by atmospheric circulation and dry-season moisture deficits. Conversely, the mainland Thailand signal exhibits less ENSO influence, relating instead to pre-monsoon moisture availability and Pacific Decadal Oscillation variability (r = −0.204, p < 0.10), indicating a supply-driven growth regime. The Monsoon Relay test (r = 0.04) confirms that the biological response to seasonal monsoon progression operates independently across the mainland and maritime sectors. Overall, these results challenge a spatially unified Monsoon Asia system. Instead, they reveal an equatorial hydroclimatic boundary where mainland and maritime forests respond to different ocean–atmosphere forcing mechanisms. This finding underscores the importance of site-specific, multi-network dendroclimatic frameworks for accurately reconstructing regional hydroclimate across the Southeast Asian corridor.

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Related topics: Plant Water Relations and Carbon Dynamics · Soil Moisture and Remote Sensing · Tree-ring climate responses