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Native Plant Synoptic Garden
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Temperature and precipitation affect vegetation types and performance; the overall
patterns of temperature and precipitation can directly influence the predominant vegetation within
a given region (Harker et la., 1999; Harris et la., 2004). Local influences, however, can also
affect the climate or create microclimates; buildings, hardscapes, and large bodies of water can
alter temperatures. Buildings can raise temperatures by absorbing the heat from the sun and
radiating it; buildings can also lower temperatures by shading the sun and/or blocking the wind
(Harris et la., 2004; Reichard, 2003). Wind passing over any type of body of water can directly
alter air temperatures and humidity levels adjacent to it ( Harker et la., 1999). Data relating to the
local climate should be compared to the large-scale regional data to establish if there are any local
factors influencing vegetation patterns and temperatures (Harker et la., 1999). Many plants have
different optimal temperature requirements at different stages of growth (Harris et la., 2004).
Having a good idea of average temperatures at night, during daytime hours, seasonally,
and how the temperatures fluctuate between these times will aide in plant selection and landscape
design. Light direction and intensity will also affect the plant selection for a site; some plants
need high amounts of sunlight to grow properly and photosynthesize at optimal levels, and some
do perfectly fine in shade. “A south facing slope will always be warmer in Western Washington
than any other aspect” (Harker et la., 1999), this is because the sun moves from east to west along
a southern axis, therefore the sun spends the majority of is time on the south side of all lands in
this geographic area (Craul, 1999). Temperature and light can both be affected by hardscape,
concrete and steel can absorb or reflect light which can raise temperatures making light levels
become more intense during daytime hours; knowing this is very important when composing a
landscape plan.
A few other climatic issues and factors that require observation are precipitation/moisture
and factors relating to wind. Amounts of rainfall for a given area and the distribution of rain
throughout the seasons are very useful in a site analysis (Harris et la., 2004). In a climate such as
Western Washington, heavy rain amounts are usually limited to late fall through early spring
(Harris et la., 2004). Having an idea of average monthly precipitation is also a necessity to
landscape planning because it can help predict how much water is going into the soil and the
likelihood of events such as droughts or flooding. Flooding or heavy surface runoff is a major
concern because it causes erosion of the topsoil, organic matter, and can create anoxic conditions
in the soil which is intolerable by most plant species. For a landscape that will incorporate mostly
smaller shrubs and trees, wind direction and levels may be less important; but it is particularly
important to forecast potential hazards to these plants and other potential targets if they are larger
growing trees and susceptible to wind-throw. Wind speed affects wind throw potential, but it can
also lower plant temperatures; this is called wind-chill factor. Plants needing to be at a higher