RESULTS

The average woody debris volume for all five regions was 67 m³/ha. Differences in total woody debris volume (i.e., coarse + fine debris) by sample region were significant (F_4,18 = 13.74; P 0.001), with large mean volumes (98-132 m³/ha) associated with eyewall and immediate right-side impact zones of Hurricane Andrew (ENP-Eye and ENP-Right; Table 2). Total woody debris volume for these regions, however, differed statistically only from TAY-Left. Eastern Everglades sites (TAY-Left) around Joe Bay and the Taylor River Slough contained the smallest woody debris volume of 16 m³/ha but were also characterized by very small trees (1.6-1.9 m) and an open canopy (0.2% canopy coverage; Table 1).

Table 2. Mean volume of woody debris (±1 SE) in South Florida mangrove forests. For volume sub-totals or overall totals, values followed by the same letter in the same row are not significantly different at = 0.05. Diameter/ decay class Mean volume (m3/ha) RB-Right ENP-Right ENP-Eye ENP-Left TAY-Left Mean Coarse (>7.5 cm) Sound 0.00 0.26 0.00 0.15 0.00 0.09 (–) (0.26) (–) (0.15) (–)   Intermediate 9.47 11.22 11.54 11.29 1.36 9.28 (3.00) (3.50) (2.76) (2.02) (0.68)   Rotten 14.12 56.12 85.34 16.83 2.74 34.00 (5.15) (10.60) (14.77) (4.35) (0.93)   Subtotal 23.6 [a] 67.6 [a] 96.9 [a] 28.3 [a] 4.1 [b]   Fine (7.5 cm) 0.0–1.0 cm 1.41 2.53 1.16 1.03 0.19 1.20 (0.16) (0.54) (0.12) (0.09) (0.04)   1.0–2.5 cm 3.78 5.15 4.49 4.31 3.95 4.35 (0.45) (0.92) (0.46) (0.42) (0.97)   2.5–7.5 cm 12.53 22.36 29.88 17.79 8.06 18.48 (1.98) (3.62) (3.54) (2.44) (1.72)   Subtotal 17.7 [ab] 30.0 [a] 35.5 [a] 23.1 [ab] 12.2 [b]   Total 41.3 b 97.6 ab 132.4 a 51.4 ab 16.3 c 67.4

Differences were less pronounced when coarse and fine woody debris were analyzed separately. Although both coarse woody debris (F_4,18 = 9.10; P 0.001) and fine woody debris (F_4,18 = 7.09; P = 0.001) estimates differed significantly for sample regions, comparative groupings among components varied slightly. In particular, coarse woody debris volume from only one region, TAY-Left, differed from all other regions. The same general trend was true for fine woody debris volume, with the exception that TAY-Left did not differ from fine woody debris estimates in either RB-Right or ENP-Left. There was greater consistency for fine woody debris estimates among sites than for coarse woody debris (Fig. 2).

Figure 2. Distribution of fine and coarse woody debris by site and region (±1 SE) from South Florida mangrove wetlands. [larger image]

Variation in total woody debris volume by region suggested a fairly strong damage signature from Hurricane Andrew even 9-10 yr following impact. Sites located in the storm's eyewall (ENP-Eye) and immediately to the right of the eyewall (ENP-Right) had from 32 to 181 m³/ha (mean = 117 m³/ha) of total woody debris, while all other sites contained a range for woody debris estimates of 13-78 m³/ha (mean = 38 m³/ha; Table 1). The relative proportion of fine woody debris versus coarse woody debris also shifted near the storm's eyewall, with larger pieces occurring in the region associated with tall trees and maximum sustained Hurricane Andrew windspeeds exceeding 220 km/h (ENP-Eye and ENP-Right; Fig. 2).

Figure 3. Relationship between woody debris volume (m3/ha) and forest height for two ranges of HURASIM model-projected Hurricane Andrew windspeeds (a: >220 km/h; b: 200–205 km/h) from South Florida mangrove wetlands. [larger image]

With the exception of the TAY-Left region, JMC, and SRU, surveyed stands had a canopy height of approximately 8-15 m (Table 1). No relationship existed between tree height and combined woody debris volume for plots experiencing maximum sustained windspeeds of 200-205 km/h, while a slightly positive relationship resulted from identical comparisons at higher windspeeds (Fig. 3). All forest understories of RB-Right, ENP-Right, ENP-Eye, and ENP-Left were nearly completely shaded by undamaged vegetation or by vegetative regrowth by the time woody debris surveys were conducted (85-97%; Table 1), indicating a high level of storm resiliency among South Florida mangroves. The scrub stature of TAY-Left vegetation did not provide shading at any of the sites.