Geomorphology

LANDSCAPE AND REGIONAL IMPACTS OF HURRICANES IN PUERTO RICO

Boose, E.R., Serrano, M.I. & Foster, D.R. (2004) Landscape
and regional impacts of hurricanes in Puerto Rico. Ecological
Monographs, 74, 335–352.

Abstract: 
Puerto Rico is subject to frequent and severe impacts from hurricanes, whose long-term ecological role must be assessed on a scale of centuries. In this study we applied a method for reconstructing hurricane disturbance regimes developed in an earlier study of hurricanes in New England. Patterns of actual wind damage from historical records were analyzed for 85 hurricanes since European settlement in 1508. A simple meteorological model (HURRECON) was used to reconstruct the impacts of 43 hurricanes since 1851. Long-term effects of topography on a landscape scale in the Luquillo Experimental Forest (LEF) were simulated with a simple topographic exposure model (EXPOS). Average return intervals across Puerto Rico for F0 damage (loss of leaves and branches) and F1 damage (scattered blowdowns, small gaps) on the Fujita scale were 4 and 6 years, respectively. At higher damage levels, a gradient was created by the direction of the storm tracks and the weakening of hurricanes over the interior mountains. Average return intervals for F2 damage (extensive blowdowns) and F3 damage (forests leveled) ranged from 15 to 33 years and 50 to 150 years, respectively, from east to west. In the LEF, the combination of steep topography and constrained peak wind directions created a complex mosaic of topographic exposure and protection, with average return intervals for F3 damage ranging from 50 years to .150 years. Actual forest damage was strongly dependent on land-use history and the effects of recent hurricanes. Annual and decadal timing of hurricanes varied widely. There was no clear centennial-scale trend in the number of major hurricanes over the historical period.

Mudslide-caused ecosystem degradation following Wenchuan earthquake 2008

Ren, D., et al., 2009. Mudslide-caused ecosystem degradation following Wenchuan earthquake 2008. Geophysical Research Letters 36, L05401.

Abstract: 
We have applied a scalable and extensible geo-fluid model that considers soil mechanics, vegetation transpiration and root mechanical reinforcement, and hydrological processes to simulate two dimensional maps of the landslides occurrence following the 2008 Wenchuan earthquake. Modeled locations and areas generally agree with observations. The model suggests that the potential energy of earth was lowered by 1.52×1015 J by these landslides. With this, the vegetation destroyed transfer ~235 Tg C to the dead respiring pool and transforms 5.54×10-2 Tg N into unavailable sediments pools and the atmosphere. The cumulative CO2 release to the atmosphere over the coming decades is comparable to that caused by hurricane Katrina 2005 (~105 Tg) and equivalent to ~2% of current annual carbon emissions from global fossil fuel combustion. The nitrogen loss is twice as much as that released by the 2007 California Fire (~2.5×10-2 Tg). A significant proportion of the nitrogen loss (14%) is in the form of nitrous oxide, which can affect the atmospheric ozone layer.

The Role of Disturbance, Topography, and Forest Structure in the Development of a Montane Forest Landscape

The Role of Disturbance, Topography, and Forest Structure in the Development of a Montane Forest Landscape
Keith S. Hadley
Bulletin of the Torrey Botanical Club
Vol. 121, No. 1 (Jan. - Mar., 1994), pp. 47-61

Abstract: 
Human set fires beginning in the mid 1800s and repeated insect outbreaks of western spruce budworm (Choristoneura occidentalis Free.) and Douglas-fir bark beetle (Dendroctonus pseudotsugae Hopk.) during the past 50 years have resulted in a dramatic change in the montane (<ca. 2900 m) forest landscape of the Colorado Front Range. Here, I examine the historical and spatial relationship between these disturbance agents and topography using stand structure and dendroecological data from 38 contiguous stands. These data suggest that aspect and relief are important factors determining the spatial and temporal patterns of disturbance, succession, and rates of stand development. The rate of postfire stand development and hence, subsequent stand susceptibility to insect outbreaks appears to be related to aspect. North-facing stands experience rapid postfire development and greater susceptibility to insect attack due to higher host tree densities, larger mean tree size, and a more uniform distribution of host trees over larger contiguous areas. Postfire stand recovery on south facing slopes appears to be slower and stand susceptibility to insect attack is less due to lower host densities, smaller mean tree size, and a less uniform distribution of host trees over smaller areas. Relief, independent of aspect, enhances the structural diversity of the forest landscape by promoting irregular burn patterns and intensities, thus creating a fire-induced mosaic of different aged stands. As these different aged stands continue to grow older, they reach a stage of development susceptible to insect outbreaks at different times. As a result, insect-induced changes in the structural characteristics of the current landscape emulate fire-induced landscape patterns that developed largely due to human activities beginning in the 1860s.

THE EFFECTS OF BIOTURBATION ON SOIL PROCESSES AND SEDIMENT TRANSPORT

Emmanual J Gabet, O J Reichman, and Eric W Seabloom (2003)
The Effects of Bioturbation on Soil Processes and Sediment Transport
Annual Review Earth Planet Science:249-73.

Abstract: 
Plants and animals exploit the soil for food and shelter and, in the process, affect it in many different ways. For example, uprooted trees may break up bedrock, transport soil downslope, increase the heterogeneity of soil respiration rates, and inhibit soil horizonation. In this contribution, we review previously published papers that provide insights into the process of bioturbation. We focus particularly on studies that allowus to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production. Using geometrical relationships and data from others’ work, we derive simple sediment flux equations for tree throw and root growth and decay.

Exploring Potential Spatial-Temporal Links Between Fluvial Geomorphology and Nutrient-Periphyton Dynamics in Streams Using Simulation Models

Doyle, MW, Stanley EH. 2006. Exploring potential spatial-temporal links between fluvial geomorphology and nutrient-periphyton dynamics in streams using simulation models. Annals of the Association of American Geographers. 96:687-698.

Abstract: 
Understanding stream ecosystem processes necessitates an awareness of not only the physical, chemical, and biological systems, but also how these separate systems interact with each other. Using a nutrient retention and periphyton growth model coupled to a dynamic geomorphic template, we explore the potential role of channel shape, slope, and sediment texture on downstream nutrient retention, and attempt to determine if physical changes alone can drive or influence changes in nutrient-periphyton dynamics. The overall model results suggest there is a strong potential control of both nutrient retention and periphyton biomass by channel morphology. For example, with constant biochemical process rates, geomorphic variations alone could alter spatial distribution of nutrient retention over a 4-km study reach by between 11 percent and 52 percent. These results suggest channel geomorphology has a potentially strong influence on both nutrient retention and basal food sources in streams. Key Words: biogeochemistry, ecohydrology, ecosystem ecology, river restoration.

REDUCTION OF BEDROCK BLOCKS AS CORESTONES IN THE WEATHERING PROFILE: OBSERVATIONS AND MODEL

Fletcher RC, Brantley SL. 2010. Reduction of bedrock blocks as corestones in the weathering profile: observations
and model. Am. J. Sci. 310:131–64

Abstract: 
the Espiritu Santo and Mameyes rivers within the Luquillo Experimental Forest (Puerto Rico) are interpreted as corestones, reduced from initial joint-bounded bedrock blocks by subsurface weathering. Maximum corestone size, expressed as the geometric mean of the three dimensions, S 3 abc, shows a smooth envelope when plotted against elevation. We postulate that, for each catchment, they represent in situ corestones within a stratified weathering profile, many tens of meters in thickness, that has been subsequently exhumed by younger erosion. We formulate a simplified one-dimensional model for reduction in corestone size within a steady-state weathering profile that incorporates: (i) vertical fluid transport of the reactant and the soluble products of chemical weathering; (ii) linear kinetics of corestone reduction; and, subsequently, (iii) erosion. The rate of advance of a steady-state weathering profile is a statement of the mass balance between entering reactants and weathering components, here idealized as H and albite. The mathematical relations, tie the laboratory-determined rate constant for dissolution of albite (k) to a generalized kinetic constant for the rate of decrease (K) in corestone diameter to the advance rate of the weathering profile (V ). The last parentheses contain an effective roughness at the scale of the weathering profile, where S0 is the maximum size of initial bedrock blocks, inferred to be set by initial bedrock fracture spacing, and 3L* is the profile thickness. The laboratory scale roughness value, , is the ratio of the surface area accessed by BET analysis to that of the corestone grain scale. In the model, erosion is not coupled with weathering, although the presence of corestones of finite size, SE>0, exiting at the erosional surface may be postulated to affect the erosional flux. The thickness of the corestone weathering profile derived for the model for the distance between bedrock and a corestone-free saprolite cap is approximately This expression is the product of the effective pH buffering-adjusted input reactant flux per unit area times a stoichiometeric factor linking this to net albite dissolution, divided by the rate of corestone size reduction at the input concentration of protons. Further, the profile thickness scales with the input “particle” size, S0. The model fit, which yields the ratio is consistent with a rate constant for albite dissolution that lies between laboratorymeasured and field-estimated values. Sensitivity to the reaction order of albite dissolution with respect to H, N, is small, except near the base of the profile. This model yields insights into the relationship between fracture spacing and the evolution of particle size and chemistry in weathering profiles.

Map showing susceptibility to earthquake-induced landsliding, San Juan Metropolitan Area, Puerto Rico

Santiago Marilyn, Map showing susceptibility to earthquake-induced landsliding, San Juan Metropolitan Area, Puerto Rico, 2 plate.em>

Abstract: 
Analysis of slope angle and rock type using a geographic information system indicates that about 66 percent of the San Juan metropolitan area (SJMA) has low to no susceptibility to earthquake-induced landslides. This is at least partly due to the fact that 45 percent of the SJMA is constructed on slopes of 3 degrees or less, which are too gentle for landslides to occur. The areas with the highest susceptibility to earthquake-induced landslides account for 6 percent of the surface area. Almost one-quarter (23 percent) of the SJMA is moderately susceptible to earthquake-induced landslides. These areas are mainly in the southern portions of the SJMA where housing development pressures are currently high because of land availability and the esthetics of greenery and hillside views. The combination of new development and moderate earthquakeinduced landslide susceptibility may indicate that the southern portions of the SJMA may be at greatest risk.

predicting landslide vegetation in patches on landscape gradients in puerto rico

Myster, R.W., Thomlinson, J.R., and Larsen, M.C., 1997, Predicting landslide vegetation in patches on landscape gradients in Puerto Rico: Landscape Ecology, v. 12 p. 299-307.

Abstract: 
We explored the predictive value of common landscape characteristics for landslide vegetative stages in the LuquilloExperimental Forest of Puerto Rico using four different analyses. Maximum likelihood logistic regression showed that aspect, age, and substrate type could be used to predict vegetative structural stage. In addition it showed that the structural complexity of the vegetation was greater in landslides (1) facing the southeast (away from the dominant wind direction of recent hurricanes), (2) that were older, and (3) that had volcaniclastic rather than dioritic substrate. Multiple regression indicated that both elevation and age could be used to predict the current vegetation, and that vegetation complexity was greater both at lower elevation and in older landslides. Pearson product-moment correlation coefficients showed that (1) the presence of volcaniclastic substrate in landslides was negatively correlated with aspect, age, and elevation, (2) that road association and age were positively correlated and (3) that slope was negatively correlated with area. Finally, principal components analysis showed that landslides were differentiated on axes defined primarily by age, aspect class, and elevation in the positive direction, and by volcaniclastic substrate in the negative direction. Because several statistical techniques indicated that age, aspect, elevation, and substrate were important in determining vegetation complexity on landslides, we conclude that landslide succession is influenced by variation in these landscape traits. In particular, we would expect to find more successional development on landslides which are older, face away from hurricane winds, are at lower elevation, and are on volcaniclastic substrate. Finally, our results lead into a hierarchical conceptual model of succession on landscapes where the biota respond first to either gradients or disturbance depending on their relative severity, and then to more local biotic mechanisms such as dispersal, predation and competition.

Luquillo Mountains Puerto Rico A water energy and biogeochemical budgets program site

Larsen MC, Stallard RF. Luquillo Mountains, Puerto Rico–a water,
energy, and biogeochemical budgets program site. US geological
survey fact sheet. Washington, D.C.7 U.S. Geological
Survey; 2000. p. 163– 99.

Abstract: 
The Puerto Rico research site consists of the 113 square-kilometer Luquillo Experimental Forest (LEF), administered by the U.S. Forest Service, and the nearby Río Grande de Loíza drainage basin, an urbanized and agriculturally- developed watershed. This combined region serves as a terrestrial laboratory for the study of issues related to the global loss of tropical forest, and the associated changes in land-use practices. Findings from the WEBB research help scientists understand how vegetation, landscape, and people interact to affect the quantity and quality of water and the erosion of the landscape. The results of this work can be applied not only to Puerto Rico, but also to many other regions, where deforestation and rapid land-use change are issues.

Landslides Triggered by Hurricane Hugo in Eastern Puerto Rico, September 1989

Larsen, M. C., and Torres-Sánchez, A. J., 1992, Landslides triggered by Hurricane Hugo in eastern Puerto Rico, September 1989: Caribbean Journal of Science, vol. 28, no. 3-4, p. 113-125.

Abstract: 
On the morning of September 18, 1989, a category-four hurricane struck eastern Puerto Rico with a sustained wind speed in excess of 46 m/s. The 24-h rainfall accumulation from the hurricane ranged from 100 to 339 mm. Average rainfall intensities ranging from 34 to 39 mm/h were calculated for 4 and 6 h periods, respectively, at a rain gage equipped with satellite telemetry, and at an observer station. The hurricane rainfall triggered more than 400 landslides in the steeply sloping, highly dissected mountains of eastern Puerto Rico. Of these landslides, 285 were mapped from aerial photography which covered 6474 ha. Many of the mapped landslides were on northeast- and northwest-facing slopes at the eastern terminus of the mountains, nearest the hurricane path. The surface area of individual landslides ranged from 18 m2 to 4500 m2, with a median size of 148 m2. The 285 landslides disturbed 0.11% of the land surface in the area covered by aerial photographs. An approximate denudation rate of 164 mm/1000 y was calculated from the volume of material eroded by landsliding and the 10-y rainfall recurrence interval.
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