Litter Mat Abundance Along An Elevation Gradient

Percent of ground covered by basidiomycete litter mats, and extent of individual mats, was assessed along an elevation gradient in the Luquillo Experimental Forest (from 8 June to 4 July 1994; rainy season), by examining leaves along transects to determine if they were attached to surrounding litter by hyphal strands, cords, rhizomorphs or holdfasts (D.J. Lodge et al., unpublished). The percentage of ground covered by litter mats generally increased with slope and decreased with elevation (Figure 2).

The decrease in mat cover with elevation was not constant, however, and there was a strong dip associated with the cloud condensation level at ca. 600 m above sea level (asl) in the Palo Colorado forest type, independent of slope (Figure 2).

Inputs from leaf litter fall decreased sharply in elfin forest at high elevation in the Luquillo Mountains (Weaver et al., 1986; Lodge et al., 1991). The litter layer in high-elevation forests is discontinuous and thin (Weaver et al., 1986) — a condition unfavorable to basidiomycetes that require a nearly continuous layer of litter on the forest floor to maintain their mycelia and incorporate new resources rapidly. Most of the basidiomycetes that formed litter mats in Palo Colorado and elfin forest bound litter that was in direct contact, and lacked rhizomorphs and cords. Adding litter to the forest floor significantly increased the number of rhizomorphs and cords in a forest at lower elevation in the Luquillo Mountains (D.J. Lodge, unpublished data), indicating that litter depth and supply rate influence mat-forming basidiomycetes. It is not known why a dip in litter mat cover occurred ~600masl, but there are corresponding boundaries in plant

% Mat Cover

Slope class

H 30-40

Figure 2 Percent of land area covered by decomposer basidiomycete litter mats as a function of slope (percent) and elevation along three 5-30 m transects, in the Luquillo Mountains of Puerto Rico, laid from ridge crest to stream bank at 50 m intervals along an elevation gradient from 150 to 1,000 masl. Samples were divided into the following classes, with sample sizes (n) in parentheses. Elevation classes were: (1) 150-300 m (n = 5); (2) 301-450 m (n = 8); (3) 451-600 (n = 3); (4) 601-750 m (n = 8); (5) 751-1,000 m (n = 10). Slope classes were: (1) 0-10%; (2) 11-20%; (3) 21-30%; (4) 31-40%; (5) 41-50%.

Slope class

H 30-40

0-10

Figure 2 Percent of land area covered by decomposer basidiomycete litter mats as a function of slope (percent) and elevation along three 5-30 m transects, in the Luquillo Mountains of Puerto Rico, laid from ridge crest to stream bank at 50 m intervals along an elevation gradient from 150 to 1,000 masl. Samples were divided into the following classes, with sample sizes (n) in parentheses. Elevation classes were: (1) 150-300 m (n = 5); (2) 301-450 m (n = 8); (3) 451-600 (n = 3); (4) 601-750 m (n = 8); (5) 751-1,000 m (n = 10). Slope classes were: (1) 0-10%; (2) 11-20%; (3) 21-30%; (4) 31-40%; (5) 41-50%.

species ranges at this elevation (J. Barone, J.K. Zimmermann, J. Thomlinson, N.L. Brokaw and P. Anglada, unpublished data).

The increase in litter mat cover with increasing slope (Figure 2) was probably influenced by two factors. First, many of the shallower slopes were near stream channels that overflowed during storms, disrupting the mats. Second, litter accumulated on the upslope sides of mats located on steep slopes, providing a concentration of new resources (see below).

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