Water as an Ecological Factor
1. Influences on the water status of a site
a. Macro- and microclimatic conditions
i. Sources of water, e.g., rain, snow, fog, dew
ii. Effects of temperature, humidity, and wind on evapotranspiration
b. Topography, e.g., effects on drainage, mountain barriers creating rain shadows, higher elevation areas,
which serve as watersheds for lower elevation sites
c. Soil conditions related to infiltration, hydraulic conductivity, water retention capacity
d. Water use by plants
Precipitation = Evaporation + Transpiration + Runoff + Infiltration
f. Anthropogenic influences, e.g., drainage, irrigation, impoundment
2. Significance of water for plants
a. Large amount needed per unit dry matter production
b. Necessary high water content of turgid herbaceous tissue
c. Solvent for material transport within the plant
d. Coolant with evapotranspiration; thermal buffer because of high specific heat
e. Raw material for photosynthesis:
electrons, hydrogen ions, and oxygen as a byproduct
3. Significance to humans working with plant materials
a. Water is one of the key factors affecting primary production and soil development.
b. To some degree, humans have to live within the constraints of natural water conditions and select
appropriate plant materials or use native plants already present.
c. Although augmentation of water supplies is sometimes possible, that can be expensive and politically
difficult to accomplish among competing interest groups.
4. Water uptake and use
a. Water movement is related to water potential gradients which are determined by osmotic (solute), matric
(adsorptive materials), pressure (hydrostatic pressure on liquid; vapor pressure), and gravitational factors.
b. In terrestrial environments, water follows a pathway from the soil solution to the root, through the plant to