Trees can be classified according to many vital strategies, although these categories do not respond to genetically related groups in all cases.
Botany is a branch of biology that does not usually receive much attention, because trees and plants cannot move or interact with humans in the same way that higher vertebrates do. However, plants are just as important as any other living being when it comes to building an ecosystem (if not more).
According to the research The biomass distribution on Earth, published in the journal PNAS, plants contribute 80% of the organic matter in the form of carbon present on Earth, or what is the same, 450 gigatons. We are not so surprised by this figure when, for example, we know that trees have existed for 370 million years and today there are 3 billion of them scattered around the planet.
Since the origin of the kingdom Plantae, plants have colonized all spaces, from water (where their ancestors appeared) to all terrestrial environments with conditions compatible with life. Trees, as a polyphyletic group, have not been left behind: more than 60,000 species are estimated within this group. If you want to know more about the types of trees and their characteristics, keep reading.
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What is a tree?
A tree is a woody-stemmed plant that branches at a certain height from the ground. The limit of what constitutes a tree or not is very diffuse, because depending on the source you can establish a limit in one meter, two, three and so on up to six. In addition to its height, a tree must branch at a certain height from the ground, thus generating a crown well differentiated from the rest of the stem and root structure.
At the evolutionary level, it should be noted that a tree is not a genus, family or taxon as such. It is a polyphyletic group, that is, it is not based on categorization by a common ancestor among all its representatives. The pines are of the class Coniferae and the almond trees are of the class Magnoliopsida, but both are considered trees. This grouping only has an informative utility, since it does not include phylogenetically related species necessarily.
Trees produce oxygen and absorb carbon dioxide, so they are necessary for maintaining the cycle of organic matter, but also to reduce the ecological footprint of human populations. A person needs between 7,200 and 8,600 liters of oxygen every day, which is equivalent to the activity of 22 trees in 24 hours. Without the world’s forests, all ecosystems would collapse and humans would have no chance of survival.
How are trees classified?
As we have said before, the boundary between tree, shrub and plant is very diffuse. For example, the species Hibiscus rosa-sinensis grows between 2 and 5 meters in height: is this a bush or a very very small tree? Depending on where the boundary is set, different types of trees may or may not also be encompassed within this space. Next, we tell you the 5 types of trees that we find interesting to comment, although they do not follow a strict botanical classification. Don’t miss them.
1. Trees/shrubs
The key difference between a tree and a shrub is the branching of the stem. In a tree, this cleavage of the trunk is carried out at a certain height from the ground, while in bushes it occurs at the base. Hibiscus, hydrangea, lavender, gardenia and many other vegetables are considered shrubs: as they branch from the base, there is no doubt.
However, species such as Hibiscus rosa-sinensis or Rhus typhina have such a low height (usually less than 6 meters) that they are rarely considered as trees, but they are also not shrubs due to their branching pattern. Therefore, they remain in a terminological limbo and it is the author of the writing who must choose in which category to put these and other species of very small size.
2. Deciduous trees
Deciduous (or deciduous) trees are those thatlose all their leaves at certain times of the year. The loss of foliage is an adaptive process that these species have adopted in places with extreme climates, since they are able to save energy at times when light and nutrients are scarce. The fewer leaves they have to nourish, the more they can save on a metabolic level.
The leaves of deciduous trees are large and flat, attached to the branches through a special stem, known as petiole. This dense, branching foliage “wide” usually gives deciduous trees a bushy appearance, although that’s not always the case. As not all species belong to the same genus, within this functional group there is a lot of diversity.
It is common for leaf structures to fall in autumn and winter, but this is not always the case: sometimes, some tree species lose foliage at times when the pollination peak is higher, as insects are more attracted to flowers when there are no structures to prevent their detection.
3. Evergreens
The term evergreen exemplifies the opposite case to the previous one. On this occasion, the leaves remain on the tree or shrub throughout the year, despite times of water or thermal stress. Within this group, a series of different genera and families are included, including:
- Most species of conifers: from pines to spruces, almost all members of the class Pinopsida are evergreen.
- The oldest gymnosperms at the evolutionary level also tend to the evergreen strategy. The Cycas are a clear example of this.
- Most gymnosperms live in environments free of freezing periods, such as eucalyptus and tropical trees.
We tend to think of pines and other conifers when talking about evergreens, but a lot of broad-crowned angiosperms are also perennial: as long as the right climatic conditions are present, preserving the leaves is a more viable strategy at the evolutionary level.
4. Fruit trees
As was the case in the category of trees/shrubs, in this case a typical classification is not followed. Many species of trees produce fruits that enclose their seeds, but we only conceive as fruit trees those that report some nutritional benefit to humans.
In this section, banana, apple, lemon, orange and many others may come to mind. The fruits are essential at an evolutionary level for many plant species, because their sweet taste and attractive aroma allows these trees to use vertebrates as a vehicle for dispersal: when a herbivore eats a whole orange, it can excrete the seeds ingested hundreds of meters away from the tree and thus disperse the genome of the individual. otherwise immobile.
5. Ornamental trees
Again, this arbitrary category only refers to a criterion based on the usefulness of the tree for the human being. Ornamental trees are those aesthetically strikingor pleasing to the eye that, above all, thanks to their flowers fill the parks and gardens of the world with color. A clear example within this group is the almond tree, although any tree with striking flowers can fall without problem in this category.
Summary
As you can see, tree types are catalogued by a very superficial criterion, which does not go beyond the external characteristics of the tree or adaptive traits very widespread among taxa (such as being deciduous or perennial). In the end, the importance of this categorization in botany is practically nil, because the essential thing when categorizing a group of living beings is always genetics.
In any case, this classification is excellent at an informative level and to establish certain generalities. For example, now you know that a broad-crowned tree that lives in Ecuador will surely be perennial because its environment allows it, beyond the image of the evergreen that is in the general culture (pines and related). In nature, nothing is as it seems.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.