modeling the impact of invasive vegetation on stream flow in the hamakua coast

Modeling the impact of invasive vegetation on stream flow in the Hamakua Coast

Ayron M. Strauch, Univ. of Hawai’i at ManoaRich MacKenzie, Greg Bruland, Christian Giardina,

Chris Heider, Ed Salminen, Tara Holitzki

Using a precipitation gradient to understand climate change

Plant invasions can also impact hydrology and aquatic ecosystems

Establishing long-term study sites

Long-term monitoring

•Establishes a baseline dataset•Examine inter-annual variations in stream flow•Helps to validate our model

Remote Sensing and Model Development: DHSVM

• Data driven- recreate “reality”– Climate, Hydrology, Soils, Vegetation, other data

• Compare “reality” with actuality at specific points and actual events on the landscape (gages)

• Run Scenarios and Compare Effects

• 157 Watersheds• Climate• Stream flow• Soil• Vegetation

DHSVM: using station data to model hydrology

*Current model uses parameters developed for global applications...not very specific to Hawai’ian conditions

Reality Check: Validation

• Modeled Flow vs Gauge Observation • 97% Agreement in Total Water Balance

Site 90: N. Laupāhoehoe

YELLOW: Existing invasive species types

RED: 300 m expansion areas

Scenario I: Invasive Species – Laupāhoehoe River

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec-30%

-25%

-20%

-15%

-10%

-5%

0%

5%

Average 5-10% less water

Certain years >20% reduction in flows

% c

han

ge in m

onth

ly fl

ow

Moving forward, developing partnerships

•integrate research across forest and aquatic ecosystems to examine how climate change and invasive species impact watersheds at the landscape scale

•coordinate research amongst various state, federal and NGO’s

•provide knowledge and tools to address impacts from climate change and invasive strawberry guava

Future work• continue to improve the DHSVM as well as run the model under different climate scenarios

• initiate stream sampling/monitoring over the next four years

• set up field experiments to determine how invasive species are impacting sediment loads and hydrology of streams

• establish downstream study sites that will include ecological parameters of native gobies (o`opu) and shrimp (opae)

Greg Bruland, Rich MacKenzie, Christian Giardina, Topaz Collins, Ka`eo Duarte, Tom Giamballuca,, Chris Heider, Tara Holitzki, Caitlin Kryss, Imiola Lindsey, Jamie Wong, Tom Schmidt, Keali’i Sagum

Research was/is funded by NSF REAP, PRISM, and the USDA FS

Feral pigs may also be influencing hydrology

Pig erosion Pig exclusion