<em><b>Josie writes:</b> I have been studying the new-growth habits of Chinese pistache trees for several years and each spring I have observed that some trees are much slower to leaf out.
My first thought was the trees that didn't exhibit the vigorous new leaf growth were troubled and would soon die. Now that it is mid-May, all the Chinese pistache trees are fully leafed-out and are obviously healthy. Can you explain why this happens each year?
By the way, all the trees are in a large parking area in a shopping center, so it is easy to make comparisons due to their proximity to each other. And, only some of trees are loaded with berries in late fall. </em>
Chinese pistache trees are diocious, meaning there are male and female trees. Both male and female growth rate is based on the species, soil and climate conditions.
However, female trees tend to be somewhat smaller and they will form and drop colorful fruits in the fall. Obviously there must be both male and female trees in the vicinity since you have observed the female trees with colorful berries in the fall.
For female trees to form fruit, they require a male tree for pollination.
A Chinese study published in 2013 found that male trees had small main branch angles and an upright tree crown with vigorous growth. Female trees had large main branch angles and an open, loose canopy.
Perhaps you are observing the early differences in leafing-out between male and female trees. It will be fun to keep a seasonal journal of their growth patterns and note their limb/canopy structure. The question is: Do male or female Chinese pistache leaf-out first?
For those readers who are interested in buying a Chinese pistache, botanically known as Pistacia chinensis, look for the fruitless male clone, "Keith Davey." It is a recommended choice for selecting a Chinese pistache tree that is to be planted by sidewalks, overhanging parking areas or in garden areas where fruit litter can be a nuisance.
Also, if there are small children in the home, take note that the female trees' berries are edible only for birds, not humans. Again, choose the male clone, "Keith Davey," a perfect specimen.