LUQ Newsletter
March 2002

From Xiaoming Zou: 

A new publication (in press) from X. Zou.

Liu, Z. G., and X. M. Zou.  In press.  EXOTIC EARTHWORMS ACCELERATE PLANT LITTER DECOMPOSITION IN PUERTO RICAN PASTURE AND WET FOREST.  Ecological Applications.

Abstract

Tropical land-use changes can have profound influence on earthworms that play important roles in regulating soil processes. Converting tropical forests to pastures often drastically increases the abundance of exotic earthworm populations such as Pontoscolex corethrurus. We initiated this study to examine the influence of exotic earthworms on the decomposition of plant leaves and roots in a tropical pasture and a wet forest of Puerto Rico. We employed two treatments: control with natural earthworm population and earthworm reduction using an electroshocking technique. Decomposition rates of plant leaves on the ground surface and root materials within the surface mineral soil were estimated using a litterbag technique. To understand the role that exotic earthworms play in altering plant litter decomposition, we also compared soil CO₂ evolution rates, soil microbial biomass, and soil physical and chemical properties between the controls and earthworm-reduced plots during an one-year period. Earthworm populations in the electroshocked enclosures were reduced by 85% and 87% as compared with pasture and forest controls by the end of the experiment. Earthworm reduction significantly decreased the annual decay rates of plant leaves, but had no effects on those of plant roots in both pasture and forest sites. Although the control had less mass remaining on every litterbag collecting date, significant treatment effects on leaf decomposition occurred only after 240 days in both sites. The decay rates were greater when organic materials had low ratios of carbon to nitrogen or phosphorus. Soil respiration was also decreased in the earthworm-reduced plots. In contrast, soil microbial biomass C was not affected by earthworm reduction. Furthermore, there were no significant differences between the two treatments in soil bulk density, moisture content, pH, and temperature at either site. Our results suggest that exotic earthworms may accelerate leaf litter decomposition through consumption/digestion or microbial activity rather than through improving soil physical-chemical conditions or altering microbial biomass.

From Matthew Larsen:

The USGS has released a new publication that is available on line at the
URL below. It is a a 4-page Fact Sheet
that summarizes a major geomorphic/hydrologic event that occurred in
northern Venezuela in 1999. See abstract and title below.

M.C. Larsen, G.F. Wieczorek, L.S. Eaton, B.A. Morgan, and H. Torres-Sierra
U.S. Geological Survey. Natural hazards on alluvial fans: the Venezuela debris flow and flash flood disaster.

Abstract
On December 1999, rainstorms induced thousands of landslides along the
Cordillera de la Costa, Vargas, Venezuela. Rainfall on December 2-3 totaled
200 mm (8 in.) and was followed by a major storm (911 mm, or 36 in.) on
December 14 through 16. Debris flows and flash floods on alluvial fans
inundated coastal communities, caused severe property destruction, and
resulted in a catastrophic death toll of as many as 30,000 people. Because
most of the coastal zone in Vargas consists of steep mountain fronts that
rise abruptly from the Caribbean Sea, the alluvial fans provide practically
the only flat areas upon which to build. Rebuilding and reoccupation of
these areas requires careful determination of hazard zones to avoid future
loss of life and property.