Saturday, December 1, 2012

Should You Pave the World or Plant It

     I have clients and acquaintances who feel compelled to pave every possible inch of their property.  They think that any areas left to grow are going to require maintenance, and they do not want to have to provide or pay for it.  The reality is that they will have to provide maintenance - whether they choose to plant something or choose to pave an area.  There is nothing that is absolutely maintenance free.  Asphalt will last approximately 12 -15 years.  Concrete will crack and break up often in as little as 10-15 years and typically last 20 - 27 years.  Gravel has to be continuously added to areas done in gravel because it breaks up and sinks into the soil.  And yes, grass requires mowing and plant beds and ground cover areas require weeding.  Plus all planted areas require replanting at some point in time.
     What people rarely consider when choosing paving over planting are some of the other factors besides maintenance.  Paving can definitely take foot and vehicular traffic, but it also will alter the micro-climate of your site.  Typically it will make the site hotter in the summer because it absorbs more solar insolation (incoming solar radiation) than plants and because it does not transpire.  Plants take water out of the soil and lose it into the atmosphere around them through transpiration which then acts to cool the area.  Plants also shade the soil which helps to regulate heat.  In the winter, paving will typically freeze more quickly and take longer to thaw than planted areas because the soil is acting to regulate the temperature of the surface in the planted areas.
     Paving is a disaster on the storm water flow of an area.  Water is simply passed on down stream because it cannot enter the soil.  As it flows over paving, water picks up speed.  This is not the case with water that passes over planted areas because the vegetation with its many surfaces and stems coming up out of the surface act to hold it back.  Water allowed to flow faster becomes a major erosion factor.  That water flowing over paving not only hits the edge in greater quantity it hits it with greater force, often taking a good deal of material downstream with it as it flows away from the paving.
     Those planted areas also act to filter dust and pollutants from the air making the area immediately around them cleaner and healthier to be in.  One tree, for instance, can remove up to 26 pounds of carbon dioxide from the air in a year.  A grassed area of 2500 square feet produces enough oxygen to supply the needs for a family of four.  This is not the case for paving.
     Although it is hard to quantify because everyone has a different sense of aesthetic, paving is not as pleasing to look at or inhabit.  People naturally gravitate to planted areas to stay for a period of time and use paved areas for passing through.  They are not often places where people care to remain.  Studies have been done that confirm the psychological benefits of green areas.  People feel calmer and more relaxed when they are surrounded by plants than they do when surrounded by paving which acts to elevate their stress levels.
     With all of the negative aspects of paving, it becomes difficult to justify the maintenance argument.  Is that little bit of maintenance saving really worth the sacrifice?  I would suggest that it is not and that proper design of the planted areas will probably result in a site that does not require much more maintenance than paving.

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