Riparian Light Riparian Light EnvironmentsEnvironments

of Luquillo Streamsof Luquillo Streams

Joanne Fernández LópezJoanne Fernández López

Dr. Frederick N. Scatena (Mentor)Dr. Frederick N. Scatena (Mentor)

El Verde REUEl Verde REU

August 2, 2006August 2, 2006

Light is main source of energy for Light is main source of energy for life on earthlife on earth

IntroductionIntroduction

Light in streamsLight in streams--Affects primary productionAffects primary production

Light in forest edgesLight in forest edges--Differences in light transitionsDifferences in light transitions

Light and vegetation Light and vegetation structure/heightstructure/height

--Direct effects of canopy trees on Direct effects of canopy trees on

understorey light environmentsunderstorey light environments

IntroductionIntroduction

Light in Riparian zonesLight in Riparian zones

Sun

IntroductionIntroduction

Light in Riparian zonesLight in Riparian zones– E.g. streams, rivers and vegetation along the shoreline E.g. streams, rivers and vegetation along the shoreline

Light environment influenced byLight environment influenced by– Stream width and morphologyStream width and morphology– Riparian vegetationRiparian vegetation

ObjectivesObjectives

Quantify light environments in Quantify light environments in Luquillo streams and riparian Luquillo streams and riparian vegetationvegetation

Within streams of different sizeWithin streams of different size

Study SitesStudy Sites

INCLUDED:

• Headwater streams (La Prieta)• Medium-sized streams (Sonadora)• Coastal Plain streams (Espiritu Santo)

•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

Site Stream Width

DA (ha)

Length of transect (m)

Orientation of Stream

Sonadora (3) 14 265 46 SE-NW

Prieta (3) 6 17 25 E-W

Toronja (2) 1 6 14 E-W

Espiritu Santo 11.8 2243 24 SE-NW

Quebrada Grande 13 - 30 SE-NW

ES-Jimenes 22 2243 36 S-N

Bisley 6 35 29 S-N

Fajardo-Paraiso 26 3845 34 W-E

Icacos 10.5 259 20 N-S

Guaba 7 <1 10 N-S

Rio Grande 16.6 1912 26 S-N

Mameyes-Rt 3 21 3093 30 S-N

Mameyes 16 1752 30 S-N

Sabana 10.7 1001 22 N-S

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

Study Site

Figure done by Andrew Pike

MethodsMethodsLight Environment SamplingLight Environment Sampling

Transects in 14 study streams of different sizeTransects in 14 study streams of different size– Every 2 metersEvery 2 meters

Repeated sampling of randomly located vegetation zones Repeated sampling of randomly located vegetation zones along Sonadora, La Prieta, and Toronja.along Sonadora, La Prieta, and Toronja.

The vegetation zones wereThe vegetation zones were– Herb zone (<30cm)Herb zone (<30cm)– Shrub zone (30<200 cm)Shrub zone (30<200 cm)– Tree zone (>200 cm)Tree zone (>200 cm)– Moss zoneMoss zone

MethodsMethods Measure and compare % of incident light in Measure and compare % of incident light in

different habitatsdifferent habitats Equipment: AccuPAR LP-80 ceptometerEquipment: AccuPAR LP-80 ceptometer

– PAR (Photosynthetically Active Radiation)PAR (Photosynthetically Active Radiation)

– Units: µmols/m²sUnits: µmols/m²s

MethodsMethods Measure and compare % of incident light in Measure and compare % of incident light in

different habitatsdifferent habitats Light MeasurementsLight Measurements

– Above Canopy:Above Canopy: El Verde Tower,El Verde Tower, El Verde Parking,El Verde Parking, Center ChannelCenter Channel

– Below Canopy at siteBelow Canopy at site

Comparison of Comparison of Above and below Above and below canopy lightcanopy light – (Below Canopy/Above (Below Canopy/Above

Canopy) X 100= %of Canopy) X 100= %of incident lightincident light

Data Analysis Data Analysis Linear regression Linear regression

to compare stream morphology characteristicsto compare stream morphology characteristics

– Stream width vs. incident lightStream width vs. incident light– Drainage area vs. incident lightDrainage area vs. incident light

One-way ANOVA (Analysis of Variance) One-way ANOVA (Analysis of Variance)

-Comparing incident light among riparian vegetation zones and -Comparing incident light among riparian vegetation zones and center channel center channel

-Comparing incident light among vegetation zones and center -Comparing incident light among vegetation zones and center channel by streams channel by streams

Results: Results: Channel Width VS. Incident LightChannel Width VS. Incident Light

As channel width increases more incident light enter the streams.

ResultsResults:: Drainage Area vs. Incident LightDrainage Area vs. Incident Light

Increases in catchment area are directlyproportional to increases in percentages in incident light.

Results: Results: Channel Width VS. Incident LightChannel 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 LightDrainage Area vs. Incident Light

•Streams with low catchment area (e.g. Guaba) have lower % of incident light than coastal plain streams (e.g. Fajardo).

Results: Results: Road vs. Stream TransectRoad vs. Stream Transect

CC:12m-18m

Results: Results: Vegetation TypesVegetation Types

When including all streams, the When including all streams, the vegetation zones in the riparian vegetation zones in the riparian areas were different.areas were different.

A B DCC C

N=95 N=275 N=275 N=98 N=275 N=275

F= 206.93, DF=5, P<0.0001

Median

25%

75%

90%

10%

All streams combined

A B BC B C

N=20 N=90 N=90 N=90 N=90

F= 15.17, DF=4, P<0.0001

Toronja

A B BC B C

N=34 N=85 N=85 N=85 N=85

F= 131.11, df=4 , P<0.0001

La Prieta

N=41 N=100 N=100 N=98 N=100 N=100

A C C B D D

F=114.54, DF=5, P<0.0001

Sonadora

DiscussionDiscussion

Percent of incident light of all transects with two different stream size Percent of incident light of all transects with two different stream size indexes (catchment area and channel width), described the increase indexes (catchment area and channel width), described the increase in light entrance.in light entrance.

– However, in coastal plain streams there was more light variation because of However, in coastal plain streams there was more light variation because of differences in vegetationdifferences in vegetation

There was a relationship between channel width and the size of There was a relationship between channel width and the size of canopy gap above channel as other studies have found (Davies-canopy gap above channel as other studies have found (Davies-Colley & Quinn 1998).Colley & Quinn 1998).

DiscussionDiscussion

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

DiscussionDiscussion Vegetation Zones:Vegetation Zones:

– There were significant differences in % incident light There were significant differences in % incident light among vegetation zone groups per stream.among vegetation zone groups per stream.

Even in Toronja stream we observed these differences.Even in Toronja stream we observed these differences.

– When all vegetation types of the three streams were When all vegetation types of the three streams were combined in One-way ANOVA test, it tells us: combined in One-way ANOVA test, it tells us:

Center Channel (Most Light)Center Channel (Most Light)

Herbs Zone Herbs Zone Moss Zone Moss Zone Shrub Zone Shrub Zone

Tree Zone (Least Light) Tree Zone (Least Light)

same range of incident light

ConclusionConclusion• Channel width and canopy trees in riparian zones have

direct effects on streams and understorey light environments.

1. Channel width controls size of canopy gap above channel. • Toronja (Least Incident Light)

• Sonadora (High Incident Light)

2. 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.

ReferencesReferences

Canham, C. D.; 1988. An index for understory light levels in and around Canham, C. D.; 1988. An index for understory light levels in and around canopy gaps. canopy gaps. EcologyEcology. 69(5): 1634-1638. 69(5): 1634-1638

Davies-Colley, R. J. and Quinn, J. M. 1998. Stream lighting in five regions of 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. North Island, New Zealand: control by channel size and riparian vegetation. New Zealand Journal of Marine and Freshwater Research.New Zealand Journal of Marine and Freshwater Research. 32: 591-605. 32: 591-605.

Fernandez, D. S. and Fetcher, N. 1991. Changes in Light Availability Following Fernandez, D. S. and Fetcher, N. 1991. Changes in Light Availability Following Hurricane Hugo in a Subtropical Montane Forest in Puerto Rico. Hurricane Hugo in a Subtropical Montane Forest in Puerto Rico. BIOTROPICA. BIOTROPICA. 23(4a): 393-399.23(4a): 393-399.

  Harper, K. A. and Macdonald, S. E. 2001. Structure and composition of riparian Harper, K. A. and Macdonald, S. E. 2001. Structure and composition of riparian boreal forest: new methods for analyzing edge influence. boreal forest: new methods for analyzing edge influence. EcologyEcology. 82(3): . 82(3): 649-659.649-659.

Scatena, F. N. 1993. Luquillo Experimental Forest. In Scatena, F. N. 1993. Luquillo Experimental Forest. In Stream Research in the Stream Research in the LTER Network, LTER Network, ed. LTER Network, 73-79.ed. LTER Network, 73-79.

Smith, R. L. and Smith, T. M.; 2001. Smith, R. L. and Smith, T. M.; 2001. Ecology&BiologyEcology&Biology. Sixth Edition. . Sixth Edition. N.Y.C.:Benjamin CummingsN.Y.C.:Benjamin Cummings

AcknowledgementsAcknowledgements

Mentor: Dr. Fred Scatena, Dr. Tamara Heartsill, Mentor: Dr. Fred Scatena, Dr. Tamara Heartsill, Andrew Pike, Sharon Machín, Pablo Peña, Andrew Pike, Sharon Machín, Pablo Peña, Rebecca Clasen, Jose Fumero, Staff of the Rebecca Clasen, Jose Fumero, Staff of the

El Verde Field Station, National Science Foundation, El Verde Field Station, National Science Foundation, my grandfather Dr. Francisco “Pepito” Fernández, my grandfather Dr. Francisco “Pepito” Fernández, and my father, Dr. Juan C. Fernández for laptop and my father, Dr. Juan C. Fernández for laptop facility and my mom Marisol López Machín for facility and my mom Marisol López Machín for

moral support and God.moral support and God.