Tree planting can be complicated. Like ordering food at a restaurant for 17 people with differing needs, tastes and seating preferences, there are a lot of factors to consider and understanding them isn’t always easy. We cannot think of singular trees, we need to think in tree communities when we are planting. For a lovely well-rounded social meal, we don’t want clones of the same person over and over again. A mixture of different people is ideal. Imagine a restaurant with a sharing menu, we want to order a variety, and not have everyone ordering the same thing. If everyone just wanted to eat olives, that wouldn’t utilize the restaurant’s offerings.
We aim for the same on a planting site. Our tree community needs to work together to share the nutrients and support each other to have their best chance at survival. Different trees, different needs. Much like the diversity of trees and plants, a diverse group of people with different skillsets, attributes and needs accomplish more in life than a single clone. For people to survive we need to eat, to thrive we need to eat well; trees need the correct nutrients in the same way. Balance is imperative; if everyone at the restaurant constantly ordered one dish in low supply, the restaurant would eventually run out. Soil is similar. As we often plant in areas with degraded land, this can be difficult and makes ensuring that we know the science behind which trees can thrive where essential.
There is no one size fits all when it comes to trees, they are living beings and therefore need to be planted with consideration. However, one universal rule is to understand which trees are native to which habitats and plant accordingly. Some trees thrive in the cold, some in the heat. As humans, we have created sovereign borders for every piece of land we have titled a country, but trees don’t follow our rules. They are native to certain habitats, rather than adhering to all of our geographical borders. Habitats can be categorized by features, such as how much water is available and what kind of terrain they are, as well as localized climates. The term “habitat-specific” was coined to describe that different species of trees have certain specific habitats in which they are delighted to grow. If we ignore their preferences, by planting in regions where they would not naturally be, we make them non-native and potentially invasive.
If humans ignore these needs, we can disturb natural ecosystems, giving certain species room to take over which can have drastic effects on some of the more vulnerable species. In some cases, these can turn into what we call “invasive species”. Going back to our restaurant analogy, that would be the one greedy person who has no consideration for the others, eating everything and leaving some to go hungry. An invasive species is a species that can threaten native biological diversity, displaying weed-like characteristics with prolific reproductive spreading through seeds or vegetatively. Non-native species can be especially problematic if they become invasive. We have all heard about invasive animals, like the rabbit and camel in Australia, but invasive trees can be equally as damaging.
An example is the Norwegian Maple in the USA, making its way from Europe to America as ornamental species. They are fast-growing and produce an abundance of winged seeds that travel by wind and germinate at a rapid pace. As a non-native species in North America, they invade woodlands and out-compete the native sugar maple as they are more tolerant to shaded areas. They also reduce the diversity of wildflowers due to their dense canopy. This is just one of many examples, displaying that non-native invasive species can be incredibly destructive and ruin the natural balance of an ecosystem.
Another way in which planting can be problematic is monocropping, referring to the planting of a single crop or species over and over again. Again, monocropping can happen with both native and non-native species, and either way the practice is potentially damaging. This is sometimes seen as an attractive “quick fix” in reforestation, as fast-growing trees that are planted together are easier and more efficient to plant, and can be more predictable. When selling carbon credits, this also appears to be preferable to more slow-paced planting, as the speed at which they sequester carbon means more credits can be sold. Sounds too good to be true? That’s because it is.
Monocropping uses one fast-growing species to maximize CO2 drawdown from the air. This is not a resilient choice if that species is taken out by varying conditions, such as a bug or changing weather conditions. It is much better to have a mix of different species with different needs to ensure long-term survival and CO2 drawdown. Monocropping can be detrimental to long-term ecosystem restoration and sustaining a healthy soil ecology. Specifically, one species that has the same “diet” will compete over the same set of nutrients, which will result in a one-sided extraction of soil nutrients and attract opportunistic parasites and microorganisms. Fragile species, that is to say, those less able to compete with the more dominant species, can be eliminated from regions and eventually, the soil depletion can mean that the land is no longer able to support the plantation. Additionally, when nature restoration is the aim, it is important to give nature a hand and increase the restoration pace by optimizing complementary species, ensuring not to put all of the eggs in one basket. This means that if there are difficult, unpredictable conditions, more species are likely to survive if they need different conditions to grow.
It is important to note that there are some instances where non-native planting is necessary. As the climate changes, certain species will no longer thrive in their natural ecosystems. In these cases, we can use assisted migration. It is important that this is researched thoroughly. If we take one final visit to our restaurant, imagine the chefs are running out of one ingredient, they will have to change their menu. If their menu changes, it is pretty likely that the customers will change too. This is characterized by the effects a changing climate has on habitats, like changing water supplies and different migratory animals. To adapt to this, research on new planting practices is essential. This research will first look at an intraspecific level, in which the genetic diversity within one species varies, and then an interspecific level, looking at the genetic differences amongst different species. This allows us to see which species will cope with these changes best.
Often the most beautiful and simple dishes take an immense amount of time and training to prepare and the same goes for planting trees. Species planted must be thought through carefully and researched, whenever possible, native species must take center stage so we can create thriving forests with a vast range of species naturally regenerating biodiversity. Tree planting is a science that only gets more complicated as we try to plant in areas with degraded land. To do it successfully, we must make sure we meticulously research and understand the area we are planting in, and what it is the trees we are planting need to thrive.