Question
ive a well established 20 year willow tree which this year has decided not to bloom or show any signs of life!! all tree in the road are now in leaf and other willows too but mine looks dead. ive had over six months much building work near tree (not digging around or near roots) but builders have been mixing sand cement lots of mud etc etc, could this have killed it?

Answer
Trees can be damaged or killed by a wide variety of construction activities. Some practices lead to obvious injuries such as broken branches or torn bark. Open wounds of this type deplete a plant's energy resources and provide entry points for insects, or for diseases such as oak wilt.

The worst damage, however, often remains hidden underground. Roots are one of the most vital parts of a tree. They are responsible for nutrient and water uptake, store energy, and anchor the plant. Because they are so important, it is critical that you protect roots that lie in the path of construction.

Tree root systems contain large, woody roots, and small, short-lived absorbing roots. Large, woody roots are perennial and grow horizontally and are mostly in the top 6 to 24 inches of the soil. Their main functions include anchorage, water and mineral transport, and nutrient and water storage.

Smaller absorbing roots, averaging 1/16 inch in diameter, constitute the majority of the root system抯 surface area. These roots grow outward and upward from the large roots, near the soil surface where minerals, water and oxygen are abundant. Their major function is to absorb water and minerals.

After a tree is established, any activity that changes the soil condition is extremely detrimental to its health. Construction traffic compacts soil most severely near the surface, the area where the majority of tree roots lie . Soil compaction decreases soil permeability and interferes with essential gas exchange processes as well as surface and subsurface drainage. When root growth is restricted by compacted soils, less nutrients and water are available for plant growth. These factors limit root growth, reduce tree vigor and can cause tree death. Decline and dieback may gradually appear over a period of years.

Check to see if the tree is dead--start near the end of an upper branch and scrape a small bit of bark off the branch and if the color under the bark is green the branch is still alive at this point on the branch, If the color is brown the branch is dead at this point on the branch. If brown continue down the branch scraping at intervals until you find green or reach the trunk. If green is not found try other branches. If no green is found the tree is dead. If green is found I would wait about a month and see if the tree will leaf out and then you can prune off the dead branches. Willows will sprout from the roots so give it time and see what happens.