Effects of Miconia on HydrologyEffects of Miconia on Hydrology

(A version of this was presented by Thomas W. (A version of this was presented by Thomas W. Giambelluca at the 2009 International Miconia Giambelluca at the 2009 International Miconia

Conference May 4-7 2009 Keanae, Maui, Hawai‘i) Conference May 4-7 2009 Keanae, Maui, Hawai‘i)

Hydrology:Hydrology:

The branch of science concerned with the properties of the earth's water, especially its movement in relation to land.

But until recently, no one had demonstrated exactly how alien trees affect the water cycle.

Scientists from the University of Hawai‘i at Mānoa, University of South Carolina, and National University of Singapore sought to measure the hydrological effects of miconia.

Alien Trees in Hawaiian Forests

Miconia Calvescens: a slender, fast-growing tree from South America

Biologists observed that alien trees damage rather than support hydrological functions, especially ground-water recharge.

How might invasive trees affect the water cycle? How might invasive trees affect the water cycle?

What are their possible hydrological impacts?What are their possible hydrological impacts?

• large leaves shade out understory plants large leaves shade out understory plants that act as a natural spongethat act as a natural sponge

• large leaves cycle high percentage of large leaves cycle high percentage of rainfall out of system through rainfall out of system through transpirationtranspiration

• shallow roots create conditions for hard, shallow roots create conditions for hard, packed soil packed soil

• all of the above increases likelihood of all of the above increases likelihood of soil erosionsoil erosion

•MiconiaMiconia Pilot Study in Hawai‘iPilot Study in Hawai‘i

• Abundance of light under canopyAbundance of light under canopy• Ground coverGround cover• Throughfall drop size and velocityThroughfall drop size and velocity• Root exposure as a measure of soil lossRoot exposure as a measure of soil loss

Light abundanceLight abundance

Thurston: Native Forest Onomea: Miconia Stand

Ground CoverGround Cover

RRainwater that hits trees or other obstructions on its way to the earth

Throughfall:

Results of Drop Size

Survey

Natural Rain

Artificial Spray

Miconia median drop size = 3.8 mm

Very high compared with previous observations

Median drop size Miconia: 5.5 mm ‘ohia: 3.7 mm

Miconia Covered Area vs. an Open Area:

• Decreased number of raindrops impacting the soil surface

• Significant increases in drop size (mass), and therefore significant increases in kinetic energy (KE) and momentum

Result: more erosive rainfall that has a greater effective KE to erode and transport sediment, organics and nutrients

Root exposure: an obvious sign of soil erosion.