One of the most common challenges for trees in cities, towns and suburbs  is Urban Tree Decline.  Namely this is the constant assault on tree  roots that occur in urban environments that ultimately put the tree is Decline.    There are 3 primary reasons for Urban Decline

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1. Lack of Green Space

 Parking lots , sidewalks,  roads and driveways are root dead  zones for two reasons.  Firstly,  the impervious pavement does not allow  for any rain  water to percolate down into the soil.  and second; The areas under the pavement do not  have an "A" horizon ( basically a topsoil zone). The "A" Horizon is the business zone where  roots interact with  fungi and other microorganisms to make sure nutrients are available to the tree.  .

 so a growing tree has very limited growth under these areas and sooner or later the Canopy of the tree will get too big for the amount of root zone otherwise available, making the tree susceptible to drought  or even a moderate dry period.   

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 2. Compaction

Similar to Lack of Green Space above, areas of heavy traffic such as trails, school yards, even pet runs can result in compaction.  Compaction means the soil is beaten down and compacted so there is no pore space.  No pore space means air and water cant get into the soil. This means the "A" Horizon (topsoil) layer falls apart  and the lack of pore space  means water and air (as all parts of a tree need to breath) don't reach the roots.   The roots either die or cant keep up with the growth and demands of the canopy and decline ensues.    ​

3. Construction

 Road  work, driveways being redone, or installing municipal servicing means roots get cut.  Its not the big roots of a tree that do most of the water and nutrient uptake - its the little fine hairs similar to human capillaries that get the job done and when the big roots close to the tree get cut, so do all those fine  hairs at the end of the roots.   After construction, the tree may not have  enough of the fine roots left to provide enough water.  The problem is compounded in  mid summer because that's when there is the least amount of  water in the soil. but that's when the tree needs water the most.

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What Can be Done:

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Many trees suffering from Urban decline can be salvaged if caught early enough.    Watering the tree through dry periods and removing the sources of compaction are the most obvious courses of action.  This is one of the rare situations where fertilizing is recommended as it maximizes the opportunities  for root growth recovery.    Pruning the Canopy back on hardwoods to reduce the demands on the roots  can also give the tree a second chance.  

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Note:  Urban tree decline and decline because of vascular wilts ( verticillium, nectria, botryosphaeria, etc.) can often look very similar and the differences can be subtle.  The main differences is that vascular wilts tend to be very sudden (within one growing season) and the leaves tend to brown and stay attached while decline usually is slow over several years and results in leaf chlorosis (rather than browning) and early leaf drop.  

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