Plant trees with agronomic diligence
This past July, I made the journey to finally see the birthplace of my grandfather. He was born in Għajnsielem, and spent his youth playing soccer, diving for sponges, and fishing in the shining blue sea surrounding Gozo. As my background lies in soil science and agronomy
(plant science), I noted how the ground was alkaline and rather thin in some areas. All of this was quite a contrast from my home in the Midwestern United States. The state I reside in, Minnesota, is blessed with dark topsoil, a suitable pH, and ample—frequently too much— rainfall. Nevertheless, the Gozitan farmers knew their land well, and grew a bounty of potatoes and other vegetables. The more productive farms were concentrated in the valleys, and doubtless fertilizers and water was applied according to the region’s landscapes and the crop’s needs.
During my visit, I also saw how much everyday Maltese care about trees, seeking shade to escape the torrid heat of summer. Soon after returning home to Minnesota, I read about protests in Attard, with people voicing their concerns about the Central Link project, in which some 500 trees would be uprooted, including protected species. The widespread destruction of green spaces is unfortunately common to both Minnesota and Malta. Many hectares of pristine land was degraded by man in each country—tallgrass prairie for the Midwest, and the Mediterranean forests in Malta.
As a University of Minnesota Extension agent, I frequently consult with homeowners about choosing tree or grass species that are well adapted to the area to replace what was lost. One of the most depressing things I hear from some of my older clients is “I’m going to be dead in a decade or so, let’s just plant something that grows fast.” This short-sightedness can often cause issues for future generations, which may have to deal with a maladapted tree rife with disease or reduced lifespan. Forethought is extremely important to have successful tree establishment and to avoid costly removal due to disease or stress. Think about how farmers plan their rotations and adapt them to what land they have. Governments and people planting trees should take the same mindset.
For starters, look at the ground beneath you and the surroundings. How tall will the planted trees get if they survive? Will
some interfere with existing buildings or power lines? A residential area will likely have compacted soil and limited space for roots to move through to gather nutrients. Often, construction equipment adds to compaction and can force up deep layers of coarse material that should not be brought to the surface. For example, the holm oak/balluta (Quercus ilex), also a native tree of Malta, will likely suffer an early death if just 15% of the upper soil consists of gravel, according to a 2012 Spanish study.
The first couple of years of a tree’s life are incredibly important. Planting saplings during the middle of the dry season greatly increases the likelihood of transplant failure as roots cannot grow deep fast enough to survive a Maltese summer. In addition, be intensely sceptical of trees languishing in pots for long periods of time. These plants are babied at the landscape store and watered profusely. Over time, the majority of the roots can hit the outside of the container, making them “pot bound” as they circle the plant searching for nutrients. After it is replanted, the roots then have to deal with an alien, perhaps inhospitable soil right in the middle of construction season. If it does not die then, pot bound trees can grow circling roots that end up strangling the main trunk, killing it. These series of events are avoidable if ethical, professional arborists are involved in wide scale replanting efforts.
Selecting tree species should be done just as carefully as identifying the planting site. All other things being equal, lean on the plants which do better with longer periods of full sun and heat, as the climate of Malta will likely shift toward them in the coming decades. Take care not to choose invasive species; some are occasionally marketed in landscape catalogues. A myriad of problems tend to arise when a gardener purchases something that “looks good” and neglects to do any research, leading to a state or country-wide infestation that could last decades or maybe centuries in the worst cases.
Tree of heaven/xumakk falz (Ailanthus altissima) is one such plant that is somewhat remarkably invasive to both Malta and Minnesota. Quite an accomplishment for one species to deal with a Maltese summer as well as a Minnesotan winter, where the wind chill reached -48 degrees C this past January. Tree of heaven—or as some call it in the USA, “tree of hell”—originated in Asia, and was brought worldwide due to its unheard of fast growth, good shade potential, resistance to pollution, and its propensity to grow in a wide array of soils. However, this tree can also put out chemicals that inhibit the growth of other native plants in Malta. This survival strategy is called “allelopathy”. While not discovered in Malta as of this writing, tree of heaven is a favorite food of the spotted lanternfly (Lycorma delicatula), an invasive insect which is also known to devor grapes. In addition, there are reports which indicate Tree of Heaven can regrow vigorously after fires, outcompeting other native brush.
However, I can empathize with many Maltese. With such a high urban area in Malta, the removal of any tree, even an invasive
Tree of Heaven, can be upsetting. So if those are removed, for one reason or the other, communities should plant native or non-weedy species that are adapted to the area.
Finally, pressure your elected officials to care for trees properly after they plant them. Some knowledge and forethought beforehand could limit wasteful spending on future removal/replanting. These plants are not just a landscape fixture to be dug in and abandoned only to log a nice number on a promotional sheet. These trees are living organisms that must deal with the soil and climate given to them, as should we.