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Most Aleppo pines are known for irregular branch structure and a leaning habit. They have light-green needles and small cones.
Photograph by Shari Kaplan
Good tree care in winter leads to a healthier spring
By Tony Tomeo
I was once told by one of my arborist colleagues that the valley oak next door to my home is the largest within an urban area of the Santa Clara Valley. It is at the northern edge of an impressive grove of very large valley oaks and coastal live oaks that dominates the neighborhood to the south. The homes and street were constructed around them so that they could be preserved.
The grove was once even more impressive, but nearly half of the trees have been removed as they have succumbed to root damage caused by development of the neighborhood and subsequent landscape irrigation. Unfortunately, not much was known about their intolerance to such damage at that time.
Ever since I watched one fall seemingly onto my neighbors' home, miraculously causing only minor damage as it really fell across the neighboring front garden, I get rather anxious during windy storms. In fact, the most recent storm broke two cables in the tree next door. As I write this, Williams Tree Service from Santa Cruz is here repairing the cables and thinning the foliar canopy. They are actually doing a great job--anyone who reads this column regularly knows how critical I am of arborists.
Winter weather is less than pleasurable for the arborists who work in it, but coincides with the dormancy of most species. Arboricultural procedures that may be performed any time may be less stressful to some sensitive trees now. They emerge from dormancy in spring with no idea of what was done to them. This somehow reminds me of waking up without my wisdom teeth.
Trees predisposed to sun scald on formerly shaded stems that become exposed by pruning are less sensitive to it during winter when the sun is lower in the sky. By the time solar intensity is sufficient to cause scald, spring growth provides sufficient protection. Silver maple and English walnut are examples of trees that can be damaged by sun scald in summer, but not during winter when they are completely defoliated anyway.
Winter pruning is also preferred by trees that bleed if pruned while active, such as the fig and fruitless mulberry, or trees that produce tender new growth prior to frost if pruned at the wrong time, such as jacaranda. It seems many trees expect to be pruned in winter, as they would in a natural ecosystem by severe weather, and become confused if their cycle is violated.
The necessity of arboriculture becomes more obvious during stormy winter weather. Most structural failure caused by wind occurs early in winter when some of the deciduous species are not yet completely defoliated. Such failure later in the season is usually limited to evergreen species that maintain their wind resistance and actually become more unstable as soil becomes saturated.
Various arboricultural procedures may be employed to minimize wind resistance, correct some structural instability and modify weight distribution. In many situations, these procedures are necessary to help trees adapt to landscape conditions (or prior abuses) that are unnatural for them. Instability is often the result of response to such stimuli. For example, Aleppo pines that are naturally sparse with deep roots are very stable, but they are more densely foliated with shallow roots in dense soil that is well irrigated.
Incidentally, not all structural failure is caused by stormy weather, but may occur when the weather is exactly the opposite of stormy. During summer, warm and humid air without breeze can damage trees in a more passive manner. Increased foliar activity stimulated by warmth accelerates translocation of moisture that cannot be evapotranspirated (evaporated) into the already saturated air. Consequently, some limbs gain more weight than can be supported, and sometimes fall. This is occasionally a problem among, but not limited to, sweetgum, coast live oak and most species of eucalyptus.
Tree of the Week: Aleppo pine
As tough as the Aleppo pine, Pinus halepensis, is, it prefers less irrigation than most gardens get, particularly in the endemic, dense soil. It is useful in unrefined areas that are not landscaped or irrigated and will eventually naturalize.
Individual trees often exhibit multiple main trunks and almost all lean in one direction or another. The delicate but rugged light-green needles are about three inches long on limber branches with small cones. Aleppo pines grow rapidly when young, slowing with maturity, but eventually reach 50 feet.
Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.
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Sunnyvale, California Since 1994
