Trees: The Pros, the Cons, and the Amazing Facts.

Tree planting got quite a buzz. It has been widely promoted as one of the simplest and most straightforward ways to address climate change. “A billion trees” (or two) feels both inspirational and achievable. Yet like anything called “simple”, it has its share of skeptics. Those skeptics make some very good points.

Thanks to those criticisms, enough information exists to distinguish sustainable tree planting efforts from ones than mostly generate buzz and fizzle out. We explain why and how the Corcovado Foundation does tree planting right. After all, when done right, such projects go beyond capturing carbon into supporting resilient and beautiful forests full of life.

This is a long post in 3 parts:

Part 1: Reforestation in general, why, pros, and cons.

Part 2: Corcovado Foundation's approach to reforestation and community engagement

Part 3: Seven fascinating tree species planted and how they support tropical ecosystems

Part 1. Why plant trees.

Carbon feels like a dirty word these days. Ironically, it also happens to be the fundamental building block of all life on Earth. And likely, all life in the Universe - barring some very inventive science fiction. The problem is not with carbon itself. The problem is that due to industrial activity, our atmosphere has been accumulating too much of it (specifically, one of its many forms, CO2 or carbon dioxide).

So the next time somebody wonders how there can be too much of a good thing, point them to carbon. You could use Venus as an example, with its 96% CO2 atmosphere and the surface temperatures hot enough to melt lead.

Plants are a natural way to store and capture carbon. Their bright green color is beautiful. It is also functional: It comes from the tiny living chemical factories (called chloroplasts) inside plant cells that absorb light and allow photosynthesis to happen. Photosynthesis is a chemical process that converts CO2 into digestible sugars for plants using water and sunlight. They take in the C = carbon and release the O2 = oxygen for the rest of us.

The bigger the plant, the more carbon it absorbs as it actively grows. And trees are some of the biggest plants we have. Which is why scientists estimate that planting a billion trees could store 1-2 megatons of carbon each year - same as taking 600,000 cars off the road. For example, every year, a tree bigger than 75 cm in diameter can absorb over 4 times more carbon than a tree smaller than 45 cm in diameter. Tropical trees are some of the biggest trees on Earth, many of them supported by enormous buttress roots around the trunk: This trunk/buttress complex on mature trees routinely reaches several meters in diameter.

It is also far cheaper to plant trees than to build industrial carbon capture facilities. As result, there has been tremendous excitement about tree planting – as one of many tools in the climate adaptation toolbox.

Trees and the ecosystem

Beyond carbon capture, the role that trees play in the overall ecosystem deserves a whole book. The tropical rainforest has several layers. Canopy is where most flowers and fruits grow, and therefore where many mammals and birds come to eat, sleep, and play. The ground layer is dark with little sunlight. Yet that brown surface of shallow soil, fallen leaves, tree roots, and fungi is what nourishes the entire world above it. Insects are present throughout every level.

Trees are the sources of shelter, food, nutrient exchange, and physical stability across the entire ecosystem… and yet this description barely even begins to give them justice. Tree species’ descriptions in part 3 provide some fascinating examples of their relationship with the rest of the rainforest.

Concerns about planting efforts.

Tree planting provides quick publicity. A quick way to feel good and to gather attention. Unfortunately, there is also increasing number of reports that many such mass planting efforts do not work as expected. That is, improvements in tree cover or carbon uptake end up being a fraction of what was expected and hoped for.

Reforestation efforts fail for many reasons and in many ways.

Some fail entirely. Planting at a wrong time, so there is not enough rainfall, means they may simply die within the first year - or even within several months. Perhaps, the name is the problem: We do, after all, talk about “planting” trees - and not about “growing” them to maturity.

Others fail partially. A plantation of monoculture trees, after all, fits the definition of tree planting. The most puzzling notion is counting timber plantations – those explicitly designed to be cut down eventually – as part of carbon offsets. Yet some offset markets include such projects because the harvesting is deferred or reduced relative to standard practices. While there may be some merit to such practices as a harm reduction, they do contribute to the carbon offset market failure. However, even when monocultures are planted to endure, they are still vulnerable to disease and support little wildlife.

If the local communities were not properly involved or consulted, the projects may backfire in several ways. Farm animals may destroy the saplings. Local landowners may have no incentives to continue protecting the young and vulnerable forests. In some cases worldwide, local communities even destroyed new plantings, cutting them for firewood or burning them to restore grazing land. And if the needs and rights of local communities were neglected or trampled over by projects organizers, this reaction is understandable. One could even argue they were entitled to this kind of resistance.

Part 2. Corcovado Foundation: Doing tree planting right.

The critical coverage of tree planting projects is an excellent resource. It identifies best practices that lead to sustainable long-term results. In a nutshell, these practices are as follows:

“Instead of focusing on planting huge numbers of trees, experts told Vox, we should focus on growing trees for the long haul, protecting and restoring ecosystems beyond just forests, and empowering the local communities that are best positioned to care for them”.

This is great news because it is exactly how Corcovado Foundation works. For this particular project, the focus is on restoring forests. Yet only because in this area of Costa Rica, the Osa Peninsula, tropical rainforests were the original ecosystem.

How reforestation works

The trees have been selected and planted strategically. Planting takes place from May to September, to take full advantage of the rainy season which ends at the end of November. They have been monitored monthly since they were planted in 2021.

The initial push focused on trees that are most resilient to sun and poor soils, to start creating a canopy to allow other plants to regrow.

Long-term reforestation usually takes advantage of the so-called pioneer species: Hardy enough to survive in barren environments, grow fast, and reproduce easily (without being invasive). Once pioneers take hold, they provide a richer environment for other plants, insects, birds, and animals to thrive. After these trees have grown, other trees may be planted. Trees that mimic the natural ecosystem that was there once before.

Corcovado Foundation was able to source a wide variety of trees, to at least somewhat approach the immense diversity of tropical forests. From the 2050 initial saplings, around 1000 were donated by Osa Conservation, and others were purchased from local plantations. Over 50 tree species were represented. Some species numbered in hundreds of saplings while others were just several trees each.

After all, the network of planted trees is only the first step. Then, as animals and birds come in, they bring more seeds with them. It’s the old-fashioned kind of planting: Seeds pass undigested through their stomachs and get dumped onto the ground together with some ready-made fertilizer.

This way, the initial reforestation effort effectively kick-starts and turbocharges a natural regrowth process, allowing it to happen faster.

Some biologists say there is no point to bother with any tree planting, just let nature take its course. And in cases where diversity is not actively promoted, that may be true. At the same time, we are learning that many Indigenous people actively managed their forests. Such managed areas attracted more pollinators, animals, and even a wider variety of plants than their entirely natural surrounding forests. And while we still have much to learn from the wisdom and experience of these Indigenous forest stewards, the same logic applies here. The logic of giving a helping hand to the tree species that are extra effective at providing shelter and food to a variety of wildlife.

Engaging the community

The outcomes recorded by Corcovado Foundation have been almost a case study in the importance of community engagement and support. The reforestation activities have been taking place on 3 private farms and one large government-controlled area.

For the 1000 trees donated by Osa Conservation, Corcovado Foundation had the funding to pay farmers to look after the trees. As a result, 97.7% have survived and established.

Yet without such funding, it varied widely. Where the owners were on board but couldn’t devote any time, the survival rate was 48%. With aware and committed owners who were able to care for the saplings, it was 67%. Some of these rates were lower than hoped for due to out-of-control events, such as a river overflowing and neighbors’ herbicide use.

Overall, Corcovado Foundation has been working with the local communities for 25 years. Much of their work explicitly focuses on ensuring buy-in for environmental projects. The key to such buy-in has been helping communities earn income through ecotourism or conservation activities.

Yet something else has been bearing fruit too. Environmental education has been a core Corcovado Foundation’s activity in the Osa Peninsula since 2003. This particular ongoing reforestation project started in 2021. In total, about 120 people took part. Yet the core group consisted of approximately 50 volunteers doing the hard work of planting and monitoring the trees. Most are locals. Young people in their late teens and twenties. The new generation – those who want to make a difference.

We spent about 2 hours planting trees with them. Just a tiny taste of what that is like. The hillside was steep. The grass was slippery. The sun was hot. It was hard work, just in those 2 hours. And these guys have been doing it for many weeks! Yet the sense of cheerfulness and collegiality among them was irresistible.

“What else is there to do here?”, some of them laughed. A point that highlights how limited rural opportunities are. And how even hard manual labor becomes a way to connect with each other and to find meaning.

Part 3. The amazing incredible trees.

This section covers a small selection of the most prominent and fascinating trees that were planted.

Cecropia

Cecropia is a perfect pioneer species. Not only is it only resilient and fast-growing, but its succulent juicy fruit is loved by many animals. It is a favorite of bats, squirrel monkeys, and multiple birds.

Cecropia leaves and buds attract three-toed sloths. Many tropical plants protect themselves from being eaten by producing toxins that repeal insects. Leaf-eating mammals are not big fans of those toxins either. In contrast, cecropia uses very few such chemical weapons, so sloths have reliable access to soft digestible leaves. (Note though that while cecropia has a great role in reforestation and canopy connectivity projects, sloths need far more than that to thrive).

Why doesn’t it defend itself through chemical weapons? Because instead, cecropia has an army. And this army does a great job keeping most other herbivores away. Azteca ants, numerous and aggressive, reside inside cecropia trees, in an amazing symbiotic relationship. Cecropia evolved hollow stems that are easy for ants to colonize without harming the plant, and even provide a little buffet for their tenants. In return for housing and food, the ants protect their landlord from threats, and deposit their waste as fertilizer.

At the time of writing, I have not yet found a satisfactory explanation for why and how sloths are able to feed on cecropia leaves despite these fiercely protective ants. Birds and even squirrel monkeys chasing fruit - well, one can just imagine them moving fast. That definitely wouldn’t work for sloths. Encyclopedia Britannica states that “ants do not seem concerned with the main leaf surfaces or external wood surfaces”. However, Azteca ants sometimes quickly swarm to the sites of external damage (such as what sloths do with their claws) and repair it. Perhaps, some or many cecropia plants remain ant-free. There may need to be follow up, exploring other mysteries of cecropia that emerged researching this article…

Guaba

My namesake, “Inga”, refers to a family of small tropical trees and shrubs. In tropical forests, “small” means they reach a mere 9 meters in height. In Costa Rica, several of them share the common name Guaba (not to be confused with ‘guava”), or the ice-cream bean.

This whole tree family produces seeds in "bean-like" pods. These pods have white-ish edible sweet pulp, whose flavour reportedly resembles vanilla ice-cream. The pulp is rich in minerals and calories, and the tree can produce fruits almost all year long. This winning combination attracts multiple mammals and birds.

Guaba’s blooms may be infrequent yet apparently, their leaves also produce nectar. Which makes it a magnet for multiple insects, including ants and their protection. Looking at both Cecropia and Inga species make you wonder just how many other tropical plants have developed similar relationships. Although apparently, not all ants remain faithful: Some of them betray Guaba and allow a certain type of caterpillar in, one that produces even sweeter nectar that the tree.

What makes the Guaba trees even more important, is their role in soil restoration. Nitrogen is an essential ingredient that all plants require to survive. Yet most plants simply consume nitrogen, thus having to rely on however much is available. It is one of the reasons conventional farmers have to use industrial fertilizer. Or in Central America, they still often resort to slash and burn practices, restoring soil fertility through a layer of ash.

Yet some plants are the so-called “nitrogen fixers”. They develop a symbiotic relationship with bacteria in their roots, where the bacteria extracts nitrogen from the atmosphere and provides it to the host. Bacteria gets plant-produced sugar in return (remember, that photosynthesis is how plants turn CO2’s carbon into sugars for their own nutrition?).

A family large number of plant species are nitrogen fixers - effectively, all legumes (e.g., beans, soybeans, peanuts). The Inga trees appear capable of teamwork, forming a relationship with both nitrogen-fixing bacteria and mycorrhizal fungi that recycles phosphorus. This ability to extract both essential nutrients is far more rare. Over time, as leaves and branches fall and decompose, these nutrients also become available to the trees’ neighbors. Inga trees are famous for being tolerant of the worst quality soils. This is likely why then can thrive in such environments.

There seems to be increasing attention to the use of Inga species in regenerative agriculture across Central America, as a way to improve soil fertility, control weeds, and produce edible fruit for human and animal use.

Guanacaste

There are plenty of excellent articles about the Guanacaste tree already. What makes it a good reforestation candidate is how fast it grows to immense size (80-100 feet tall, with a trunk up to 3.5 m or 11 ft in diameter), tolerates poor soils, and provides shady relief for wildlife under its vast canopy.

Pouteria Sapota

It is truly remarkable how many amazing fruits are out there across Central and South America. This one is a glorious, oversized berry (4-10 inches large), with succulent orange flesh. Apparently, it is delicious raw yet can also be fried “like bacon”. I would really like to know now what is tastes like fried. Why “like bacon”?…

It is also remarkable what information is and isn’t available in English. If mature trees may bear 200 to 500 fruit per year, each weighing up to a kilo - it must also be beloved by much wildlife. Yet while you can read about a dozen of various human uses (including food, medicinal, and cosmetic) – good luck finding any information about its role in the original ecosystem. Except in scientific articles.

Turns out, large fruits appeal to large mammals. Specifically, there is evidence that tapir, peccary, coati, and pacas come pick the fallen fruit off the ground. Additionally, puteria trees are not very common in the jungle and their fruits are remarkably high in protein – at 25% of the dry weight! All this makes them an amazing choice to support returning mammal population.

Dipteryx panamensis, or Almendro de montaña

The Mountain Almond is not an easy tree to find information about in English. It is remarkable for the number of animals that depend on it: 60 species of birds, mammals, and insects; including primates, parrots, toucans, orioles, agutis, and bats. Pollination alone is performed by 12 various species of bees.

Schizolobium parahyba, or Gallinazo

Some trees grow fast. And then there is this guy: Three meters – 9 feet – a year! Reaching up to 40 meters tall, with large nectar-producing blooms from October through December.

(Although apparently, the world record for growth is held by Paulownia tomentosa, appropriately named the empress tree. It can grow 20 feet = 6 meters tall in its first year)

Brosimum (utile, alicastrum), or Cow Tree, or Vaco

Brosimum utile brings a whole new game to plant-based milks. Viscous white fluid seeps through cuts in its leathery bark. This liquid contains 5 to 7% protein and has a long history of use by Indigenous Central and South Americans as food and medicine.

While the Vaco tree sap is renown among humans, it is not clear whether wildlife interacts with it. Anecdotally, some Costa Rican nature guides reported seeing opportunistic use by mammals, such as rubbing against tree bark where it has been cut. Potentially, as a relief from parasites or other discomfort, given its analgesic properties.

However, their fruits and seeds are rich in oil. Which makes them a common food for many animals, including macaws and spider monkeys. Another brosimum species – alicastrum, or breadnut – is also known for its highly nutritious seeds, eaten by agoutis, pacas, monkeys, and bats.

If you have any tree facts to add, share your tips or experiences - or something that surprised you from this article, or to simply geek out about how amazing nature is, let's do that in comments!

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