Summary
Nelson et al. (1994) report a non-uniform distribution of large (0.33 to 33 km2) blowdowns in the rainforests of Amazonia. Occurrence of such large disturbances in the wet, low wind speed regime of the Amazon Basin cannot be explained by conventional mechanisms such as fire or hurricanes. While downdrafts from deep convective clouds are likely candidates, this paper draws upon meteorological observations from the central Amazon Basin to show that the requisite magnitudes of wind speed can be reached but only under conditions which would explain the observed horizontal distributions of the large blowdowns. Outflow velocities due to density driven downdrafts in the convective clouds are shown from observations to reach 15 m/s and correspond to the propagation velocities of longlived Amazon squall lines. Maintenance over 48 h of these squall lines depends upon the correspondence between the outflow velocity and the propagation velocity. The storms propagate within a basic current moving at 5 m/s, increasing the outflow velocities to 21 m/s. The development of a storm-generated pressure field must be called upon to increase the magnitude of the density and basic currents to more than 30 m/s. Such conditions occur only when the convection is embedded in squall lines which reach their diurnal maximum at locations nearly coincident with the observed locations of the maxima in large blowdowns. The characteristics of the observed blowdowns in terms of orientation, size and shape are consistent with winds derived from the postulated downward moving density currents being deflected and accelerated orthogonally at canopy top and forest floor.
The causes and distribution of large blowdowns in the wet, low wind regime of the Amazon rainforest are shown to be important in explaining the disturbance regime of that system. Such disturbances are necessary in maintaining diversity of the system by locally disrupting the canopy, altering levels of incident radiation received at the surface and changing patterns of nutrient cycling, carbon uptake and storage.
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References
Aubréville, A., 1933: La forêt de la Côte d'Ivoire.Bull. Com. Afr. Occid. France.,15, 205–261.
Aubréville, A., 1938: La forêt colonaile: les foréts de l' Afrique occidentale francaise. Annales Academic Sciences Colonaile, 9, 1–245. Translated byEyre, S. R. 1991. Regeneration patterns in the closed forest of Ivory Coast, pp. 41–55. In: Eyre, S. R. (ed.)World Vegetation Types. London: MacMillan.
Augstein, E., Garstang, M., Emmitt, G. D., 1980: Vertical mass and energy transports by cumulus clouds in the tropics.Deep Sea Res., Spec. Vol., 9–21.
Bonan, G. B., Shugart, H. H., 1989: Environmental factors and ecological processes in boreal forests.Ann. Rev. Ecol. Syst.,20, 1–28.
Bormann, F. H., Likens, G. E., 1979a:Pattern and Process in a Forested Ecosystem. New York: Springer.
Bormann, F. H., Likens, G. E., 1979b: Catastrophic disturbance and the steady state in northern hardwood forests.Amer. Scient.,67, 660–669.
Brokaw, N. V. L., 1985a: Gap-phase regeneration in a tropical forest.Ecol.,66, 682–687.
Brokaw, N. V. L., 1985b: Treefalls, regrowth, and community structure in tropical forests. In: Pickett, S. T. A., White, P. S. (eds.)The Ecology of Natural Disturbance and Patch Dynamics, pp. 101–108. New York: Academic Press.
Brokaw, N. V. L., Grear, J. S., 1991: Forest structure before and after Hurricane Hugo at three elevations in the Luquillo Mountains, Puerto Rico.Biotropica,23, 386–392.
Brokaw, N. V. L., Walker, L. R., 1991: Summary of the effects of Caribbean hurricanes on vegetation.Biotropica,23, 442–447.
Browning, K. A., 1986: Morphology and classification of middle-latitude thunderstorms. In: Kessler, E. (ed.)Thunderstorm Morphology and Dynamics, 2nd edn. Norman, OK: University of Oklahoma Press, pp. 133–142.
Cohen, J. C. P., Nobre, C. A., Silva Dias, M. A. F., 1989. Mean distribution and characteristics of the squall lines observed over the Amazon basin.Proc. AMS Third Internat. Conf. on Southern Hemisphere Meteorology and Oceanography, Buenos Aires, Argentina, 13–17 November, 205–207.
Denslow, J. S., 1980: Gap partitioning among tropical rainforest trees.Biotropica,12, 47–55 [Suppl.].
Denslow, J. S., 1985: Disturbance-mediated coexistence of species. In: Pickett, S. T. A., White, P. S. (eds.)The Ecology of Natural Disturbance and Patch Dynamics. Orlando, FL: Academic Press, pp. 307–323.
Emmitt, G. D., 1978: Tropical cumulus interaction with and modification of the subcloud layer.J. Atmos. Sci.,35, 1485–1502.
Fujita, T. T., 1976: Spearhead echo and downburst near the approach end of a John F. Kennedy Airport runway, New York City. SMRP Res. Paper 137, University of Chicago, 55 pp.
Fujita, T. T., 1981: Tornadoes and downbursts in the context of generalized planetary scales.J. Atmos. Sci.,38, 1511–1534.
Fujita, T. T., 1983: Andrews AFB microburst. SMRP Res. Paper No. 205, Department of Geophys. Sci., University of Chicago, Chicago, IL, 38 pp.
Fujita, T. T., Wakimoto, R.M., 1983: JAWS microbursts revealed by triple-Doppler radar, aircraft and PAM data.Preprints AMS 13th Conf. Severe Local Storms, Tulsa, OK, 97–100.
Garstang, M., Scala, J., Greco, S., Harriss, R., Beck, S., Browell, E., Sachse, G., Gregory, G., Hill, G., Simpson, J., Tao, W.-K., Torres, A., 1988: Trace gas exchanges and convective transports over the Amazonian rain forest.J. Geophys. Res.,93, 1528–1550.
Garstang, M., Ulanski, S., Greco, S., Scala, J., Swap, R., Fitzjarrald, D., Martin, D., Browell, E., Shipham, M., Connors, V., Harriss, R., Talbot, R. 1990: The Amazon Boundary Layer Experiment (ABLE-2B): A meteorological perspective.Bull. Amer. Meteor. Soc.,71, 19–32.
Garstang, M., Massie, H. L., Halverson, Jr. J., Greco, S., Scala, J., 1994: Amazon coastal squall lines. Part I: Structure and kinematics.Mon. Wea. Rev.,122, 608–622.
Greco, S., Swap, R., Garstang, M., Ulanski, S., Shipham, M., Harriss, R. C., Talbot, R., Andreae, M. O., Artaxo, P., 1990: Rainfall and surface kinematic conditions over central Amazonia during ABLE-2B.J. Geophys. Res.,95, 17,001–17,014.
Greco, S., Ulanski, S., Garstang, M., Houston, S., 1992: Low-level nocturnal wind accelerations over the central Amazon Basin.Bound.-Layer Meteor.,58, 91–115.
Grubb, P. J., 1977: The maintenance of species-richness in plant communities: The importance of the regeneration niche.Biol. Rev.,52, 107–145.
Hall, J. B., Swaine, M. D., 1981:Distribution and Ecology of Vascular Plants in a Tropical Rain Forest: Forest Vegetation in Ghana. Boston, MA: Junk, The Hauge, Kluwer, 383 pp.
Henderson-Sellers, A., 1987: Effects of change in land use on climate in the humid tropics. In: Dickinson, R. E. (ed.)The Geophysiology of Amazonia, New York: Wiley-Interscience, pp. 463–493.
Huston, M., 1979: A general hypothesis of species diversity.Am. Nat.,113, 81–101.
Moncrieff, M. W., Miller, M. J., 1976: The dynamics and simulation of tropical cumulonimbus and squall lines.Quart. J. Roy. Meteor. Soc.,104, 413–427.
Moncrieff, M. W., So, D. W. K., 1989: A hydrodynamical theory of conservative bounded density currents.J. Fluid Mech.,198, 177–197.
Nelson, B. W., Kapos, V., Adams, J. B., Oliveira, W. J., Braun, O. P. G., do Amaral, I. L., 1994: Forest disturbance by large blowdowns in the Brazilian Amazon.Ecol.,75, 853–858.
Oldeman, R. A. A., 1978: Architecture and energy exchange of dicotyledonous trees in the forest. In: Tomlinson, P. B., Zimmerman, M. H. (eds.)Tropical Trees as Living Systems. Cambridge: Cambridge University Press, pp. 525–560.
Oldeman, R. A. A., 1991:Forests: Elements of Silvology. Berlin: Springer.
Oldeman, R. A. A., van Dijk, J., 1991: Diagnosis of the temperament of tropical rainforest trees. In: Gómez-Pompa, A., Whitmore, T. C., Hadley, M. (eds.)Rain Forest Regeneration and Management. Man and the Biosphere Series, 6 Paris: UNESCO, pp. 21–66.
Pickett, S. T. A., White, P. S., (eds.) 1985:The Ecology of Natural Disturbance and Patch Dynamics. Orlando, FL: Academic Press.
Putz, F. E., 1983: Treefall pits and mounds, buried seeds, and the importance of soil disturbance to pineer trees on Barro Colorado Island, Panama.Ecol.,64, 1069–1074.
Putz, F. E., Appanah, S., 1987: Buried seeds, newly dispersed seeds and the dynamics of lowland forest in Malaysia.Biotropica,19, 326–333.
Riehl, H., 1954:Tropical Meteorology. New York: 392 pp. McGraw-Hill Publishers.
Riehl, H., Malkus, J. S., 1958: On the heat balance in the equatorial trough zone.Geophysica,6, 503–538.
Rotunno, R., Klemp, J. B., Weisman, M. L., 1988: A theory for strong, long-lived squall lines.J. Atmos. Sci.,45, 463–485.
Scala, J., Garstang, M., Tao, W.-K., Pickering, K., Thompson, A., Simpson, J., Kirchhoff, V. W. J. H., Browell, E., Sachse, G., Torres, A., Gregory, G., Rasmussen, R., Khalil, M. A. K., 1990: Cloud draft structure and trace gas transport.J. Geophys. Res.,95, 17015–17030.
Shugart, H. H., Leemans, R., Bonan, G.B., (eds.) 1992:A Systems Analysis of the Global Boreal Forest. Cambridge: Cambridge University Press, 542 pp.
Simpson, R. H., Riehl, H., 1981:The Hurricane and its Impact. New Orleans: Louisiana State University Press, 398 pp.
Sousa, W. P., 1984: The role of disturbance in natural communities.Ann. Rev. Ecol. System.,15, 353–391.
Specht, R. L. (ed.), 1979:Ecosystems of the World, Vol. 9a: Healthlands Related Shrublands of the World. Amsterdam: Elsevier.
Strong, D. R., 1977: Epiphyte loads, treefalls and perennial forest disruption: a mechanism for maintaining higher tree species richness in the tropics without animals.J. Biogeogr.,4, 215–218.
Swain, M. D., Hall, J. B., 1988: The mosaic theory of forest regeneration and the determination of forest composition in Ghana.J. Trop. Ecol.,4, 253–269.
Tanner, E. V. J., Kapos, V., Healey, J. R., 1991: Hurricane effects on forest ecosystems in the Caribbean.Biotropica,23, 513–521.
Vitousek, P. M., 1985: Community turnover and ecosytem nutrient dynamics. In: Pickett, S. T. A., White, P. S., (eds.)Ecology of Natural Disturbance and Patch Dynamics. Orlando, FL: Academic Press, pp. 325–334.
Wakimoto, R. M., 1985: Forecasting dry microburst activity over the high plains.Mon. Wea. Rev.,113, 1131–1143.
White, P. S., Pickett, S. T. A., 1985: Natural disturbance and patch dynamics: An introduction. In: Pickett, S. T. A., White, P. S., (eds.)The Ecology of Natural Disturbance and Patch Dynamics. Orlando, FL: Academic Press, pp. 3–16.
Whitmore, T. C., 1974: Change in time and role of cyclones in the tropical rainforest on Kolombangara, Solomon Islands. Commonwealth Forestry Institute Paper 46.
Whitmore, T. C., 1975:Tropical Rain Forests of the Far East. Oxford: Clarendon Press, 282 pp.
Whitmore, T. C., 1978: Gaps in the forest canopy. In: Tomlinson, P. B., Zimmerman, M. H., (eds.)Tropical Trees as Living Systems, New York, Cambridge University Press, pp. 639–655.
Whitmore, T. C., 1982: On pattern and process in forests. In: Newman, E. I., (ed.),The Plant Community as a Working Mechanism, 45–59, (Spec. Publ. No. 1) British Ecological Society, Blackwell Scientific Publ., Oxford.
Zipser, E. J., 1994: Deep cumulonimbus cloud systems in the tropics with and without lightning.Mon. Wea. Rev.,112, 1837–1851.
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Garstang, M., White, S., Shugart, H.H. et al. Convective cloud downdrafts as the cause of large blowdowns in the Amazon rainforest. Meteorl. Atmos. Phys. 67, 199–212 (1998). https://doi.org/10.1007/BF01277510
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DOI: https://doi.org/10.1007/BF01277510