What Trees and Humans Have in Common

Brazilian pepper tree (Schinus terebinthifolius)

A notable Biblical passage asks: “Is man a tree of the field?” (Deuteronomy 20:19).

Analogies comparing roots to deep, sustaining faith are frequently made and we all know about “the fruit of our labor,” but parallels are also anatomically applied.
When biologists speak of both humans and trees, they describe the circulation of vital fluid, whether blood or sap, through a “vascular system.”  In people, the vascular system consists of arteries, through which blood is pumped out of the heart and into all parts of the body, and veins, through which blood turns around and flows back towards and into the heart.  In trees, the vascular system consists of xylem vessels, through which sap containing water and minerals is drawn up from the roots into all parts of the tree and phloem vessels, through which carbohydrate manufactured in the leaves is distributed downward to all parts of the tree as well.
There is a difference, though, when it comes to outer coverings.  Human skin is a flexible organ that expands with growth of the tissues below and then stops expanding when full human size is reached at the age of 21 or so.  Trees, however, have a hard, inflexible covering known as bark which, although it does expand with the growth of underlying tissues, cannot always keep up with what is growing below and sometimes cracks, causing sap to leak out.  Still, bark never stops expanding, and will continue to do so throughout the life of the tree.
“The Brazilian pepper tree in my yard has trunks that are profusely oozing sap. Is this something to be concerned with or just typical of this tree type?  A neighbor had mentioned that this was an indication of some sort of stress.  The tree is about 10 years old and grew from a seed apparently.”
Lawrence Voelker, Torrance
Your neighbor is correct.  Sap exuding from a tree is usually a result of stress.  The stress may lead to the presence of fungi or bacteria as immediate agents of the oozing sap or the sap could just be a sign of stress brought on by excessive lateral growth of cells beneath the bark.  Generally speaking, insects are not responsible for oozing sap, except in the case of aging cherry,plum, or peach trees, where boring beetle larvae may be involved.
The picture you sent shows a young tree of incredible vigor so I would not be too concerned about its overall health..  It may well be that the heavy rainfall we experienced after years of drought could be responsible for a sudden growth spurt and the consequent oozing of sap.
Keep in mind that sap oozing from branches or trunks is not necessarily a sign of declining health.  It points to the fact that the tree’s life blood is flowing, even if it  is doing so excessively.  Consider the possibility that your tree is growing so well that cracks in the bark, even if microscopic and invisible to the naked eye, have developed from where the sap is leaking out.
A tree does not grow only vertically but laterally or radially, through thickening of branches and trunk, as well.  There is a cambium layer of actively growing tissue just below the bark, differentiating into phloem cells on the outside towards the bark and xylem cells towards the inside.  Growth of xylem and phloem together can be so rapid that the bark, unable to contain this expansion, cracks and sap leaks out.
If I were you, I would just wait and I would not be surprised if your tree stops oozing sap.  Besides, it is unlikely that you can do anything therapeutic at this point except, perhaps, to thin out the branches to improve air circulation through the tree.  If you decide to prune, make sure this work is done by a professional arborist who knows how to prune both minimally and artistically.
The fact that the tree apparently originated as a volunteer seedling also speaks to its resiliency.  It would not have grown so well if it were not suited to that spot.
In the case of trees, if not plants in general, stress is almost always the result of too much or too little water.  Too much water, however, does not necessarily mean over irrigation or too much rain but rather inadequate soil drainage or leaf or stem surfaces that do not dry out because of excess shade, poor air circulation, mechanical injury, or pruning cuts done from spring to early summer, when growth is most active and sap flow is most intense.
It is never advisable to block air circulation around a tree, or any plant for that matter.  When a tree is planted close to a wall, for instance, moisture on leaf or stem surfaces may not dry out due to lack of air circulation and excess moisture is always an invitation to pathogenic fungi.
Alternatively, build up of pressure in the phloem can cause a condition known as bacterial slime flux, often seen in magnolia trees, where sap exudes from the tree, causing a large wet spot on the bark.  This condition is caused by inadequate soil drainage or excessive shade and the best course of action is to reduce watering to a minimum and make sure the tree is regularly pruned so that branches and trunk get some sun exposure.
The idea of bringing trees close to buildings or homes is a relatively recent phenomenon which, from the stand point of tree health, makes no sense, even though many of our trees (including my own!) overhang the roofs of our homes.  There was a time when not only trees but gardens, too, were completely separate from the house.  If you visit colonial gardens in Virginia, for example, you will appreciate this separation.
Both Brazilian pepper tree (Schinus terebinthifolius) and California pepper tree (Schinus molle) are members of Anacardiaceae, the cashew or sumac family of plants.  The sap of these trees has a dermatitic, if not caustic, quality, and protecting  your skin is essential when pruning them.  Poison ivy and poison oak are also family members.
Anacardiaceae comes from the Greek for “without (ana) heart (cardia).”  It has been suggested that the highly toxic sap from plants in this family suggests heartless species.  However, there is another explanation for the family name, derived from the phenomenon of cashew nuts growing, most curiously, outside the so-called cashew apple when, if they behaved like true nuts, they would grow in the “heart” of the fruit.  Actually, technically speaking, the cashew is a seed that grows inside a fruit of its own consisting of nothing more than a hard shell.  Although cashew trees are too tropical to grow outdoors in California, you can grow them as indoor plants.  Seeds may be procured through online vendors for about a dollar each.  Cashews you find in the market, even if raw, will not germinate.  They only germinate when still encased in their shells.
Tip of the Week:  Pistachio and mango are noteworthy members of the cashew family.  Pistachios cannot grow in Southern California because of our mild winters but mangoes do quite well here.  Mangoes are distinguished by having seeds which grow into trees with sweet fruit, a characteristic not shared by most fruit trees whose seeds, when germinated, grow into trees with bland fruit.  However, seed germinated from a supermarket mango will be quite tasty — even if you have to wait seven or eight years until you get a crop — and the tree it grows on will be more robust than a clonally propagated nursery tree.   To germinate a mango seed, remove its hard outer shell.  You probably want to wear gloves during this process to avoid the possibility of an allergic reaction to mango sap.  Place the seed on its side in some potting soil, cover it up, and you should see it sprout within two weeks.

Leave a Reply

Your email address will not be published. Required fields are marked *