Canopy Forest Floor Roots

What is forest hydrology? Forest hydrology is the study of the interactions between the hydrological cycle and forest ecosystems. Hydrology is the study of the movement, distribution, and quality of water throughout Earth, and thus addresses both the hydrologic cycle and water resources. ( Forestry is the science that seeks to understand the nature of forests and the interactions among the parts comprising the forest. Combines aspects of two separate disciplines:

The Hydrological Cycle Interactive system: A set of reservoirs (water storage in oceans, lakes, soil, atmosphere, ice caps) & fluxes (precipitation, evaporation, river flow) with Water changing among three different states: gaseous, liquid, solid Dynamic system: Driven by solar energy and gravity Closed system/cycle: water quantities constant Recycling system: Global- scale circulation of water through atmosphere, land, oceans

Fluxes of Water Atmosphere  Oceans/Continents Over land Earth surface  Ground Within the Ground Ground  Vegetation Vegetation  Atmosphere Soils, rivers, lakes  Atmosphere How does water move in the hydrological cycle? Precipitation Sheet flow/Stream Flow Infiltration Groundwater Flow Root Uptake Transpiration Evaporation

Stocks of Water: where does water reside on earth? Oceans: 97% Earth: 3% Atmosphere: 0.001% Ice Caps: 69 % Groundwater: 30% Surface Water and Vegetation: 1% Natural water reservoirs or storage areas

Photograph by Medford Taylor Shenandoah Valley Forest

dreamstime.com Clean water

Deforestation: Impacts on watersheds

Chesapeake Bay after a heavy rainstorm

Parts of a Tree Canopy/Crown Leaves Branch Trunk Roots Vascular tissue Diagram Source:

Source: Forest Canopy Intercepts precipitation Favors condensation  Canopy Condensation Changes drop size & reduces velocity

Leaf Litter Depth & surface roughness increases infiltration of precipitation In riparian zones, slows overland flow, traps sediments, & sequesters nutrients

Rainsplash Effect of the impact of water drop on the soil surface: detachment of soil particles After deforestation we lose the sheltering effect of canopy and forest floor. The soil surface is more exposed to rainsplash. Source:

Rainwash/Sheet Erosion The soil particles detached by rain splashing are washed away & transported downhill by overland flow. These soil particles eventually reach the streams  increase in turbidity, sediment loads in streams and rivers Deterioration of water quality, loss of stream habitat for fish and other organisms Silting of lakes and reservoirs: the sediment is deposited in lakes & reservoirs  loss in water storage capacity of reservoirs, which are filled with sediments Source:

Tree Roots Stabilize soil aggregates & stream banks Increase macropore space & preferential flow/infiltration Take up water & nutrients from deep in the soil profile

Forest Canopy, Root & Litter Impacts Water flow intensity & quantity Soil erosion Sedimentation

Summary: Forests Contribution to the Water Cycle Effect amount of water reaching the ground (throughfall) Forests favor infiltration & reduce runoff & stream flow Effect evapotranspiration Effect precipitation More rainfall, more evapotranspiration  more intense regional water cycle Less soil erosion & suspended sediments  better water quality

Vascular tissue in trees Phloem & xylem

A Green versus a Desert Planet If we compare these two endpoints: Green planet: all non-glaciated land covered by trees Desert Planet: all of the planet with no vegetation Forest vegetation causes intensification of the water cycle over land: more evapotranspiration  more atmospheric moisture  more precipitation Runoff decreases in the presence of forest vegetation because of the higher soil water holding capacity and higher evapotranspiration Studies on Amazonian deforestation: The replacement of the forest with pasture results in a warmer and drier climate

Other effects of forests on the water cycle: Canopy condensation Plant canopies provide surfaces suitable for condensation In regions where humid air (low clouds/fog) move through relatively cold canopies, vegetation may “strip” atmospheric moisture off of the clouds/fog. The condensed water drips down to the ground providing a potentially important input of water in these ecosystems Regions affected by canopy condensation: Frequent presence of fog/low clouds, Close to the ocean, with forest vegetation (M. Scholl, U.S. Geological Survey)

Canopy condensation: fog forest or cloud forest

Kaho`olawe: dust storms in Hawai`i Forest canopy removed

Can we make an artificial canopy to trap water? Chungungo: small village in the Atacama desert (Chile). Experiment using polypropylene nets as “fog trappers” A view of Chunchungo (BBC)

Image: Percy Jimnez First collectors erected in 1987 Fog collectors provide more than 40 liters of water per person per day (only 14 liters/person/day were available before the project) Project is run by the community Similar projects in Peru, South Africa, the Dominican Republic, Israel, Cape Verde, the Canary Islands and Nepal The Chungungo project Yield: 10,000 liters a day of water

(after Chow et al., Applied Hydrology, 1988) 100 units =119,000 km 3 /yr