Table 1.

Seasonal variation of forest structural variables at four different climate zones in Amazon

Climate zones†	Dry season duration	Forest structure layers‡	Annual mean LAI, m2/m2	LAI change§, m2/m2
				Mar to Jun	Jun to Oct	Oct to Mar
Southern Amazon	May to Oct	Canopy	4.52	0.38*	-0.27*	−0.11*
		Understory	0.61	−0.03*	0.03*	0.00
Central Amazon	Jul to Dec	Canopy	4.57	0.03	0.22*	−0.24*
		Understory	0.56	−0.02	-0.02	0.03*
Northern Amazon	Nov to Apr	Canopy	3.76	−0.13	−0.05	0.19*
		Understory	0.82	0.07*	−0.08*	0.00
Western Amazon	No dry season	Canopy	4.67	−0.01	0.07	−0.06
		Understory	0.48	0.00	−0.03*	0.03*

^†Climate zones were created based on dry and wet season timing using monthly aggregated precipitation data from the TRMM (Materials and Methods and Fig. S2). The wet-to-dry season transition progresses seasonally from south to north (with the approximate seasonal start set in italics in Table 1), except for the western Amazon, which has no pronounced dry season compared with the other regions (17).

^‡A height threshold of 10 m was used to separate understory from the canopy layer, and the understory defined here does not distinguish among young regenerating trees and lower canopy (Fig. S7).

^§Canopy and understory LAI changes in individual climate zones were estimated from aggregations of corresponding 1° cells (*P < 0.05; the change observed is different from 0 in bold). The LAI change is expressed as the later period minus the earlier one (e.g., June − March).