Why does the Austin area lose sycamore trees almost every summer?
Sycamores, Platanus occidentalis, are on the list of local Austin trees that are much less drought tolerant. They enjoy cooler, wetter weather, lower temperatures and more water during the summer months. Most healthy sycamores in the Austin area enjoy shaded, mulched root zones, as opposed to exposed roots in the full sun. They also thrive where extra water is applied during the hotter, dryer summer months.
Because their leaves are very large, wide, and thin, they require more water through the leaves as a cooling effect to prevent drying out and sun scald. Sycamores are typically found in riparian zones (areas along rivers and streams), along lakes and water bodies, and generally areas with poorer drainage and more long standing water.
When sycamores in the Austin area are found along right of ways where water is a limiting factor during summer months, or where the radiant heat from the street exacerbates water loss, stresses typically occur. Heat stress here is exacerbated by lack of mulch to the root zone, and direct summer sun shining on the root zone.
Heat stress problems show up as upper defoliation, as the leaves at the top of the tree burn off due to excessive heat at the top of the tree, and then cause the upper limbs to die off as they then dry. This is usually associated with an inability to get enough water to the top of the tree. Then, with no leaves to pull water through the wood and up into the upper sections, the wood simply dries out up there and dies.
In extreme cases, the stems can experience cracking and death, and the cambium dies and turns black, which is exposed as the bark breaks off. In these cases, the tree either dies or becomes hazardous and needs to be removed. This is especially true of larger trees.
The best thing to do is to plant the trees in areas where they are either on shady streets or back from the street altogether in the center of a shady front yard, preferably not North facing, and preferably in a mulched bed. Extra summer water is also a good idea during the extensive dry summer heat.
If sycamores are already in decline due to drought conditions, we recommend watering them and adding a thick 2-3 inch thick mulch layer to the root zone. Monitoring them and maintaining a frequent watering schedule (in keeping with Austin watering laws) is also recommended.
Sometimes, simply planting a different species altogether is recommended due to the overall harshness of the planting area. Other factors are can also be a play with declining trees. If you are unsure what is happening to our trees, it is always best to call me out and get a proper diagnosis.
