Riparian Light Environments of Luquillo Streams

1. Riparian Light Environmentsof Luquillo Streams Joanne Fernández López Dr. Frederick N. Scatena (Mentor) El Verde REU August 2, 2006

2. Light is main source of energy for life on earth

3. Introduction • Light in streams -Affects primary production • Light in forest edges -Differences in light transitions • Light and vegetation structure/height -Direct effects of canopy trees on understorey light environments

4. Introduction • Light in Riparian zones Sun

5. Introduction • Light in Riparian zones • E.g. streams, rivers and vegetation along the shoreline • Light environment influenced by • Stream width and morphology • Riparian vegetation

6. Objectives • Quantify light environments in Luquillo streams and riparian vegetation • Within streams of different size

7. Study Sites • Research was conducted at El Verde Field Station, located at 350 m of elevation within the LEF (congruent with the Caribbean National Forest), Puerto Rico in a Tabonuco-dominated Forest (Dacryodes excelsa) and underlined by volcanoclastic sandstones • INCLUDED: • Headwater streams (La Prieta) • Medium-sized streams (Sonadora) • Coastal Plain streams (Espiritu Santo)

8.    Study Sites with stream width, drainage area, distance of transects and orientation

9. Study Site Figure done by Andrew Pike

10. MethodsLight Environment Sampling • Transects in 14 study streams of different size • Every 2 meters • Repeated sampling of randomly located vegetation zones along Sonadora, La Prieta, and Toronja. The vegetation zones were • Herb zone (<30cm) • Shrub zone (30<200 cm) • Tree zone (>200 cm) • Moss zone

11. MethodsMeasure and compare % of incident light in different habitats • Equipment: AccuPAR LP-80 ceptometer • PAR (Photosynthetically Active Radiation) • Units: µmols/m²s

12. MethodsMeasure and compare % of incident light in different habitats • Light Measurements • Above Canopy: • El Verde Tower, • El Verde Parking, • Center Channel • Below Canopy at site • Comparison of Above and below canopy light • (Below Canopy/Above Canopy) X 100= %of incident light

13. Data Analysis • Linear regression to compare stream morphology characteristics • Stream width vs. incident light • Drainage area vs. incident light • One-way ANOVA (Analysis of Variance) -Comparing incident light among riparian vegetation zones and center channel -Comparing incident light among vegetation zones and center channel by streams

14. Results: Channel Width VS. Incident Light As channel width increases more incident light enter the streams.

15. Results:Drainage Area vs. Incident Light Increases in catchment area are directly proportional to increases in percentages in incident light.

16. Results: Channel Width VS. Incident Light • Headwater streams with small channel widths (e.g. Toronja) have lower percentages of incident light than coastal plain streams with bigger channel widths (e.g. Mameyes) Drainage Area vs. Incident Light • Streams with low catchment area (e.g. Guaba) have lower % of incident light than coastal plain streams (e.g. Fajardo).

17. Results: Road vs. Stream Transect CC:12m-18m

18. Results: Vegetation Types • When including all streams, the vegetation zones in the riparian areas were different.

19. N=95 N=275 N=275 N=98 N=275 N=275 All streams combined F= 206.93, DF=5, P<0.0001 90% 75% Median 25% 10% C C B C D A

20. N=20 N=90 N=90 N=90 N=90 Toronja F= 15.17, DF=4, P<0.0001 A B BC B C

21. N=34 N=85 N=85 N=85 N=85 La Prieta F= 131.11, df=4 , P<0.0001 A B BC B C

22. N=41 N=100 N=100 N=98 N=100 N=100 Sonadora F=114.54, DF=5, P<0.0001 A C C B D D

23. Discussion • Percent of incident light of all transects with two different stream size indexes (catchment area and channel width), described the increase in light entrance. • However, in coastal plain streams there was more light variation because of differences in vegetation • There was a relationship between channel width and the size of canopy gap above channel as other studies have found (Davies-Colley & Quinn 1998).

24. Discussion • Light at roads, with vegetation and canopy along the sides, seems to behave as light in streams.

25. Discussion • Vegetation Zones: • There were significant differences in % incident light among vegetation zone groups per stream. • Even in Toronja stream we observed these differences. • When all vegetation types of the three streams were combined in One-way ANOVA test, it tells us: • Center Channel (Most Light) • Herbs Zone • Moss Zone • Shrub Zone • Tree Zone (Least Light) same range of incident light

26. Conclusion • Channel width and canopy trees in riparian zones have direct effects on streams and understorey light environments. • Channel width controls size of canopy gap above channel. • Toronja (Least Incident Light) • Sonadora (High Incident Light) • Transects shows high % of incident light at center channel and a decrease as we move into the riparian forest. • Vegetation zones have distinct light environments.

27. References Canham, C. D.; 1988. An index for understory light levels in and around canopy gaps. Ecology. 69(5): 1634-1638 Davies-Colley, R. J. and Quinn, J. M. 1998. Stream lighting in five regions of North Island, New Zealand: control by channel size and riparian vegetation. New Zealand Journal of Marine and Freshwater Research. 32: 591-605. Fernandez, D. S. and Fetcher, N. 1991. Changes in Light Availability Following Hurricane Hugo in a Subtropical Montane Forest in Puerto Rico. BIOTROPICA. 23(4a): 393-399. Harper, K. A. and Macdonald, S. E. 2001. Structure and composition of riparian boreal forest: new methods for analyzing edge influence. Ecology. 82(3): 649-659. Scatena, F. N. 1993. Luquillo Experimental Forest. In Stream Research in the LTER Network, ed. LTER Network, 73-79. Smith, R. L. and Smith, T. M.; 2001. Ecology&Biology. Sixth Edition. N.Y.C.:Benjamin Cummings

28. Acknowledgements Mentor: Dr. Fred Scatena, Dr. Tamara Heartsill, Andrew Pike, Sharon Machín, Pablo Peña, Rebecca Clasen, Jose Fumero, Staff of the El Verde Field Station, National Science Foundation, my grandfather Dr. Francisco “Pepito” Fernández, and my father, Dr. Juan C. Fernández for laptop facility and my mom Marisol López Machín for moral support and God.