Physical Properties of Strand.

1. Daily and annual solar radiation of the unobstructed beach environment can be relatively high, especially in the tropical, subtropical, and warm temperate zones. Full sun on a cloudless day can yield very high instantaneous values of intercepted light, because white sand has high albedo and, therefore, a substantial amount of solar radiation that strikes the white sand is reflected from the surface. On the other hand, coastal fog and overcast skies may also occur daily or seasonally, so that during much of the daytime leaves may be exposed to lower solar radiation than they would intercept in a cloudless, inland habitat at the same latitude.
2. Mean annual air temperature (also annual range) varies greatly along a gradient of tropical to arctic sites, but typically each is less extreme than for comparable inland sites from the same latitudes, because coastal temperature highs and lows (most sites have little or no freezing) are moderated by maritime conditions. Temperature at the surface of reflective, dry sand greatly exceeds air temperature during full-sun conditions, being significantly higher for leaves resting on the sand surface than several inches above the sand.
3. Daily land and sea breezes are typical for many beaches. Some strand sites receive calm to mild winds year-round, some regularly receive strong to moderate winds, and many are strongly affected by winds of violent, catastrophic storms. Wind reduces boundary layer thickness (i.e., unstirred air) next to leaf and sand, thereby increasing evapotranspiration while also decreasing leaf and sand temperature, if winds are strong enough. Strand may have markedly different wind microhabitats on windward and leeward sides of dunes and established plants.
4. In addition to the influence of high tides, strand plants obtain moisture (freshwater) from precipitation and fog drip (intercepted by shoots) and may as well benefit from moisture condensation (dew) on the shoot and sand surface. To be physiologically significant, the sand must be sufficiently wetted in the region used by roots.
5. Salt spray is a minute aerosol formed above heavy surf, generated when bubbles of saltwater break. Salt spray is therefore highest at water's edge and decreases dramatically inland. The vegetation on the ocean-facing edge consequently receives the highest concentrations of salts, but these levels are very weak. Vertical surfaces have much higher interception rates of salt spray than horizontal ones; linear surfaces higher than broad ones; structures high above the sand intercept substantially more than structures close to the sand.
6. The outer edge of vegetation will experience the greatest effects of physical buffeting and salinity from soaking high tides and swells during storm surges.
7. Dry surface sand is mobile. Plants can be damaged by sand blast, roots are sometimes exposed, and shoots frequently are buried by shifting sand, pushed by strong winds. To move sand grains, wind speed must be at least four meters per second.
8. Beach sand has a low capacitance to retain water and is nutrient-poor, with < AHREF="d0428tx.html">little organic matter. Surface sand, which experiences rapid wet-dry episodes, is a stressful environment for plant roots. Deep sands may remain moist, receiving and storing water while the surface sand stays dry much of the time. Roots and rhizomes can penetrate sand rapidly, in comparison with growth within heavy soils having clay.

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