Riparian vegetation

A riparian vegetation association is found along a drainage channel,
stream, or river. 
 
	The waterway may be permanent, with surface water available at all times

	It may be intermittant, with surface water present only during and just after
	the rainy season, but there usually is subsurface water available all year

These are quite unstable environments, with water levels fluctuating with
storms and flood events and the change in seasons, so, for plants, there's
a bit of a mixed blessing!

The more water there is and the more persistent it is over the year, the
greater the structural diversity of the associated vegetation:  trees 
constitute vertically diverse structures and they create diverse microclimates
in, under, and around them (shading, cooler temperatures, less evaporation)

The more water there is and the larger the watershed a channel drains, the
more biodiverse the vegetation and its associated animal life is:  These are
generally the most biodiverse habitats in California

Riparian corridors are spatially zoned:

	Vegetation that grows right on the banks:  trees, including some quite tall 
	species  (e.g., sycamores (Platanus racemosa), bigleaf maples (Acer macrophylla), 
	box elder (Acer negundo), cottonwoods (Populus fremontii)

	vegetation that either can't take being soaked that persistently or that
	are displaced by other species that are better at exploiting that amount of 
	water is found just beyond the banks, on the floodplains, or on shady
	canyon slopes nearby: trees (e.g., valley oaks (Quercus lobata), coastal live 
	oaks (Q. agrifolia), white alders (Alnus rhombifolia), willows (Salix spp.), 
	California bay (Umbellularia californica), walnuts (Juglans californica) and 
	shrubs (e.g., willows, such as S. lasiolepis)

	Lower vegetation that does well in persistently damp soil:  shrubs (willows,
	mulefat (Baccharis salicifolia, roses (Rosa californica), blackberries (Rubus
	ursinus), California currants (Ribes aureum), subshrubs (mugwort (Artemisia
	douglasiana), vines (wild grapes (Vitis californica), ferns, and lilies.

Interestingly, this is the vegetation association that has the most true deciduous,
(winter deciduous) species in California.
  
	Winter deciduousness is the original deciduousness that evolved in tropical 
	wet-dry climates to cope with their winter drought.  

	This adaptation proved 	effective when the descendants of these species 
	migrated into cold winter climates.  

	It is not helpful in California because of our dry summer Mediterranean 
	climate by shutting down photosynthesis when water is available in winter.  

	In riparian situations, however, and near springs, it becomes possible to 
	dump your leaves in winter and photosynthesize in summer because of the 
	year round availability of water in streams or just underground in ephemeral
	streams.  

	So, we have winter deciduous sycamores, alders, maples, and deciduous oaks 
	in and around our streams.