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Group 3 All-Group Field Exercises

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Tropical watershed integrity in human-dominated landscape: the Rio Jaba (Las Cruces)

Costa Ricans depend on streams for drinking water, agriculture, hydroelectric power generation and many other goods and services. Forest cover is important for maintaining the integrity of streams by reducing the variation in discharge, by preventing erosion that can change the conformation of a watershed, and by increasing water clarity & purity through biotic processes. For this reason, Costa Rica and many other countries have made it a priority to preserve forests at the headwaters of watersheds, and preserve riparian forest cover along the length of the water course. Our travels will show how this goal has not been met with total success in Costa Rica.

We will ask whether small forest patches serve to maintain or even improve stream integrity. We will identify and measure abiotic & biotic indicators of stream integrity, and then compare the status of the Rio Jaba or other streams while they flow through the Las Cruces forest, flow through pasture, and flow through the town of San Vito de Rio Jaba.

References

We will have various reports of biotic & abiotic measurements of water quality in the Rio Jaba watershed performed by various parties, and collected by Rodolfo Quiros Bode RW (1989) Biological stream testing: Methods for use in schools. New York State Dept. of Environmental Conservation Cummins KW, Wilzbach MA (1985) Field procedures for analysis of functional feeding groups of stream macroinvertebrates. Pymatuning Laboratory of Ecology Jones JC, Reynolds JD (1996) Environmental variables. In Ecological Census Techniques: A Handbook (Sutherland WJ ed) Sanford RL, Paaby P, Luvall JC, Phillips E (1994) Climate, geomorphology, and aquatic systems. In La Selva (McDade LA, Bawa KS, Hespenheide HA, Hartshorn GS eds) Schelhaus J (1996) Land-use choice and forest patches in Costa Rica. In Forest Patches in Tropical Landscapes (Schelhaus J, Greenberg R eds.)

Abiotic and biotic edge effects and a tropical forest-pasture boundary (La Selva)

'No park is an island' - DH Janzen

Forest reserves are impacted at their edges by influences from the surrounding, human-dominated matrix within which they lie. Such 'edge effects' can include abiotic factors that differ between forest edges and deeper in the interior (e.g. light, wind, relative humidity, frequency of fire) and biotic factors (e.g. prevalence of invasive or weedy species of plants & animals). Since a feature of tropical landscapes is the fragmentation and insularization of forest remnants, edge effects are likely to become a dominate component or remaining forest reserves.

We will ask whether there is evidence of significant 'edge effects' impacting the La Selva forest reserve. We will investigate it from both the standpoint of abiotic & biotic indicators of edge effects. We will then calculate what proportion of the reserve is likely to be altered from the past, when it was nestled deep within a landscape of continuous forest cover.

References

Chen J et al. (1999) Microclimate in forest ecosystem and landscape ecology. Bioscience 49:288-297

Murcia C (1995) Edge effects in fragmented forests: implications for conservation. Trends in Ecology & Systematics 10:58-62

Redford KH (1992) The empty forest. Bioscience 42:412-422 Sutherland WJ (1996) Ecological Census Techniques: A Handbook Turner IM, Corlett RT (1996) The conservation value of small, isolated fragments of lowland tropical rainforest. Trends in Ecology & Systematics 11:330-333