Fig 1.
Geographic setting of the study area.
A: Map showing the altitudinal zoning of vegetation that characterizes the El Yunque National Forest, over a shaded relief of the Luquillo Mountains. Black outline: border of El Yunque National Forest. Inset: Location of the forest on Puerto Rico island. Vegetation data from (Gould et al., 2008) [14]. Tabonuco Forest: tall lower montane rainforest, Sierra Palm Forest and Palo Colorado Forest: monocot and dicot-dominated montane rainforests, Elfin: dwarfed forest on mountain tops. B: topographic map showing the limits (red line) of the studied area (1). The extent of the study area was determined by exclusion of areas lacking either LiDAR coverage (2) or the quartz necessary for 10Be-based quantification of erosion rates (3), and by exclusion of areas affected by accelerated erosion (4).
Fig 2.
Sampling locations chosen for 10Be measurements in soils and river sediments.
The map shows the extent of the watershed feeding river borne quartz used for 10Be detrital rates measurements, in this study and earlier studies [9, 12]. Grey lines: contour lines with 25 m elevation spacing (10 m-resolution DEM). Large catchment names: CUY: Cubuy, ES: Espiritú Santo, IC: Icacos, PRI: Prieto, SAB: Sabana.
Fig 3.
Maps of the mesoscale topography.
A: Map of slopes steeper than the landslide threshold (30°), used to delineate cove walls. HF: hornfels (silicified volcanoclastics). B: Depth of incision of the coves below the shallower landscape represented by broad low-curvature hilltops (yellow). Black solid contour lines (spacing 25m): elevation of the surface enveloping the broad hilltops.
Fig 4.
Correlation between topography and forest composition.
A: composite classified satellite image of vegetation. Variations of Palm forest, as a function of elevation (B), aspect (C), slope steepness (D), and entrenchment, i.e., sheltering behind hilltops (E) (S2 Table 1 in S2 File). Circle areas are proportional to the areas of forest contributing to each bin of elevation (10m), aspect (1°), slope (1°), and depth (1 m). Dashed lines: linear regressions. Dotted lines bracketing shaded areas: 2σ envelopes. Dashed blue line: second order polynomial regression on elevation (B), and linear regression including floodplains and volcanoclastic aprons (blue circles, D).
Fig 5.
10Be-derived denudation rates as function of soil and catchment slope.
Tmin, Tmax: arrows linking average values of erosion rates in the soils to the average values of erosion rates in streams, for the coarse and fine river sediment fractions. These two end-member fractions are used in the calculation of the time required to produce the observed landforms (see discussion).
Fig 6.
Conceptual model of relief development due to faster erosion in the coves.
E: denudation rate from terrestrial 10Be analysis. Ao: soil litter, Bt: clay accumulation horizon (see S2 Fig 2 in S2 File for corresponding field photographs).