Akiko Ogawa’s

EFB516 Ecosystems Notes

March 20, 2001

Disclaimer:

These notes are my personal notes. The course instructor or TAs have no responsibility for the contents or any discrepancies between the materials presented in the classroom and these notes. You cannot use or refer to these notes to support or defend your answers on your exams. I suggest you use these notes to complement your own notes, and not to solely rely on.

I would appreciate your feedback on any part of these notes that I may be misunderstanding.

Lecturer: Hongqing Wang (hqwang@syr.edu)

Lecture Title: Case Study of Tropical Rainforest – LTER@LEF

Lecture Outline:

 

  1. Background of LTER-LEF*
  2. Modeling PET & GPP/NPP
  3. Disturbance
  4. Modeling SOC
  5. Conclusion
  6. *LTER =  Long Term Ecological Research. LEF =       Luquillo Experimental Forest.

 

1. Background of LTER-LEF

Location: Luquillo Experimental Forest (LEF) in Puerto Rico

Some characteristics:

 

Ø      Lat 18, Lon 45

Ø      2000/yr rain

Ø      Soil thin, reddish, yellowish. Poor in nutrients –> adaptation to reduce leaching. Most of nutrients are stored in biomass.

Ø      Higher productivity and diversity.

Ø      Has different features from mainland tropical rain forests.

 

Brief History of  LEF

Luquillo Experimental Forest (LEF) = Caribbean National Forest (CNF)

1898 PR became part of USA territory from Spanish

1917 USDA started managing this CNF

1956 LEF established

1957 Dr. H.T. Odum’s radioactive ecological research

1976 LEF joined one site of LTER of National Science Foundation (NSF). The only site representative for tropical rain forests.

 

LEF fact sheet:

Ø      Area: 11,000ha.

Ø      Elev: 100 – 1075m asl.

Ø      Mean ann. Temp: 23 – 19 deg. C

Ø      Mean ann. Rain: 2450 – 4000mm – ‘orographic effect on rainfall’

Ø      Four major vegetation types:

o       Tabonuco (150-700m)

o       Sierra Palm (steep slopes & stream beds, >500m)

o       Palo Colorado (700-900m)

o       Cloud (900m+)

forests – ‘Massenerhebung Effect’ (Flenley, 1995)*

 

*Massenerhebung Effect: the small mountains near the sea have cloud forest at lower altitudes than the large mountains inland.

2. Modeling Potential Evapotranspiration (PET) and Primary Productivity

2.1 PET (Penman – Monteith equation)

 

PET = {[slope*RAD+CP*PA*VPD/ra) / (slope+gamma(1+rs/ra))]/LE}*DAYL

 

Where,

Slope - slope of the saturation vapor pressure curve at air temp

RAD – avg. canopy NET radiation.

CP - specific hear of air.

PA – density of air.

rs – canopy aerodynamic resistance, determines the transfer of heat and water vapor from the evaporating surface into the air above the canopy.

ra – canopy surface resistance, describes the resistance of vapor flow through stomata openings, total leaf area and soil surface.

Gamma – psychrometric constant

LE – latent heat of vaporization

 

The model results indicated that low elevation has high PET and high elevation has low PET.

 

2.2 Primary Productivity (TOPOPROD model, Marley, 1998)

 

GPP = SPSN

PSN={0.27*DCO2*CC*CM)/(CC+CM)}*LAI*DAYL

 

Where,

PSN - daily canopy photosynthesis.

DCO2 – CO2 diffusion gradient from leaf to air.

CC – Canopy stomatal conductance to CO2.

CM – mesophyll conductance to CO2.

LAI – leaf area index.

DAYL – day length.

 

NPP= GPP – Rgrowth - Rmaintenance

 

2.3 Simulated results:

Ø      Monthly solar insolation (42 – 554 watts/m2): low land – high, high land – low.

Ø      Monthly rainfall: lowland – low rain, high land – high rain.

Ø      Monthly temperature: low to high elev. – temp. cools down.

Ø      GPP:  annual/January/July GPPs are similar. Decreases with south facing slope->north, and with low elev.-> high.

Ø      NPP: January is slightly less than July. Decreases as elevation goes up.

 

 2.4 Model validation <-Field data

Ø      GPP: the model overestimated <10%.

Ø      NPP (estimated from above-ground NPP from root/shoot ratio): the model underestimated.

 

Ø      GPP of LEF is generally greater than that of tropical rain forests (TRF) in general.

Ø      NPP is generally less than general TRF, indicating C mostly being used for respiration.

Ø      Respiration is generally greater than general TRF.

Ø      Meaning P/R->1, LEF as a whole is less possible as a C sink when warming although a small portion of the forest might be a sink.

 

2.5 Factors affecting spatial model accuracy:

Ø      DEM quality and resolution

Ø      Limited field climatic data

Ø      LAI image quality

Ø      No varying climate

Ø      Few observations

 

3. Disturbance

Hurricane – an important disturbance.

Summary of impacts:

  1. Sudden and massive tree mortality - normal tree mortality: avg. 1.6%/yr.
  2. Delayed pattern of tree mortality – the effects last long, over months, years.
  3. High species turnover and opportunities for species change in forests.
  4. Faster biomass and nutrient turnover – necromass decomposition.
  5. Lower above ground biomass in mature vegetation – harder to accumulate growth.
  6. A carbon sink, by:

burying woody debris under landslides;

transporting wood to less-decomposed streams, estuaries and oceans.

 

Example – hurricane Hugo.

 

Notes on some of the slides presented:

Ø      Dense forest – dark near-infrared color.

Ø      Before and After hurricane Hugo – Before: dark around LEF. After: much less dark.

Ø      Huge amount of rain is associated with hurricanes.

Ø      Biomass increases as the elevation goes from ridge, slope, valley, and down to riparian.

Ø      Ca leaching increases with the same elevational gradient.

Ø      Total N decreases with the same gradient.

Ø      SOM decreases with the same gradient.

Ø      Ca increases with the same gradient.

Ø      Vegetation type distribution is somewhat distinctive along the gradient of relative humidity and avg. solar radiation.

4. Modeling Soil Organic Carbon (SOC)

 

LEF is undergoing regrowth.

SOC simulated using CENTURAY and TOPOCLIM (from temp, rain, PET data).

SOC simulation result map shows:

Ø      High elev. in mountains has high SOC.

Ø      SOC storage is related to elevation and slope.

Ø      High elevation = cooler temp & higher rain  -> slow decomposition = low respiration rate -> high SOC.

 

5. Conclusion

Take-home message:

Think about the differences between island tropical rain forests and mainland tropical rain forests.

 

For more information about LER, refer to the following web sites.

 

Ø      University of Puerto Rico: Luquillo Experimental Forest LTER

http://www.ites.upr.edu/sunceer/

Ø      Institute for Tropical Ecosystems Studies (ITES):

http://sunites.upr.clu.edu/

 

Last modified: March 22, 2001

Any comments? E-mail to akogwa@syr.edu