Dead leaf turnover in monodominant forest of the marcescent palm Lodoicea maldivica.

Abstract

The palm Lodoicea maldivica is marcescent, with dead leaves remaining attached to the trunk for an extended period. To investigate how this trait affects the distribution and turnover of dead leaf material in Lodoicea forest, we measured dead leaf production and standing crops of dead leaves attached to palms (D_M) and in the litter layer (D_L); for comparison, we measured D_L in stands of the non-marcescent species Martellidendron hornei and Deckenia nobilis. In a litterbag experiment, we investigated the decomposition of four types of leaf material: newly dead marcescent Lodoicea, old marcescent Lodoicea, and newly dead Deckenia and Martellidendron. Rates of decomposition were very slow and varied significantly amongst types (P < 0.001), with mean annual decomposition constants (k values) of 0.41, 0.37, 0.25 and 0.47 y^-1 for new and old Lodoicea, Deckenia and Martellidendron, respectively. Decomposition rates also varied significantly with location in the forest (P < 0.001), apparently due to variable moisture conditions resulting from the funneling of water by Lodoicea leaves. Compared to other tropical forests, N and P concentrations in dead leaves of all species were very low, while total quantities of dead leaf material were extremely high (24.0, 22.3 and 16.7 t dry weight ha^-1 for Lodoicea, Deckenia and Martellidendron, respectively). In the Lodoicea plot, marcescent leaves accounted for 46% (11.2 t dry weight ha^-1) of all dead leaf material. We discuss the ecological significance of marcescence and its implications for management, especially in making Lodoicea forest vulnerable to fire.