When I started my sabbatical, I told (almost promised) myself that I would write more reflective pieces about our nascent work on forest restoration in Costa Rica. After a month and half here I still haven’t done much to meet that goal. Today might be the day that pushes me into telling more forest stories. It’s Sunday and Julia and the kids went back to Boone earlier this week, so I have a bit of time to explore.
I’ve been working with colleagues to identify and document a set of experimental studies that were started in the 1980s and 90s on the use of native tree species for reforestation. At the time, there was limited reforestation happening in the country (there was much more deforestation). The little that was happening used primarily exotic species. A set of innovative studies were set up to assess a wide range of native species (and some exotics) for their ability to improve degraded soils, produce useful timber, and provide other ecosystem services. Many of those studies served their intended purpose and have been un(der) utilized for decades.
One of these studies was the Ensayos de Eliminación (Elimination Trials). Started in the late 1980s, it evaluated 84 native and exotic species on four different types of abandoned pastures within La Selva Biological Station. One of those sites was the Peje Annex – a cattle ranch that was acquired by the station in the 1980s as a buffer around the station and a broader biological corridor. The original forest was cut in the 1940s and grazed until the 1980s. After being planted in the late 80s, the trial was maintained for 3 years, re-measured again in 1996 and 2006, but generally forgotten.
The plantings in the Peje are some of the most forgotten. When this round of the Ensayos was planted, it was not an easy process. Eugenio Gonzalez tells stories about taking seedlings across Sarapiquí River by boat and lugging them up and down hills to plant.
Today I had the benefit of biking down the Sendero Tres Rios and hiking up the Sendero Ribereño – a much easier process. I had an idea of where the plots might be from an old hand drawn map and guidance from Eugenio. The hike to where I thought the plots would be started with a 1 km hike along the Peje River. On the other side of the river there is still a cattle ranch. Putting aside the significant problems with cattle ranching here, it is probably the most beautiful place I can imagine for a ranch. There are still trees in the pastures – some along the river, some as living fences, some as small fragments, and some as lone large trees.
A common large tree to find in pastures here is Dipteryx panamensis (almendro). Farmers often left almendro trees when clearing forest for pasture because they are so difficult to saw, without a carbide or diamond tip saw blade – which are only recent arrivals here. This turns out to be fortunate for the Great Green Macaw (Aru ambigua) which nests in the trees. In the picture of the pasture across the river, I believe that’s a lone Dipteryx in the field.
As I was walking toward the area where I thought some of the plots would be, I noticed the most impressive Dipteryx I’ve ever seen. The tree was easily 1.5 meters in diameter above its buttresses. It was maybe 40m high (I’m a bad judge) and towered over everything around it. Its roots snaked out noticeably for 10m and certainly continued much further unnoticed. It’s hard to know this tree’s real story. I want to be able to tell a version of Aldo Leopold’s “The Good Oak”, but I don’t know enough.
But I can imagine some possibilities. I’m guessing this tree stood much like the one pictured in the pasture across the river for decades – cows munching on grass around it. It almost certainly stood for many more decades (maybe centuries) before that in the middle of a dynamic forest – establishing itself as a seedling and waiting (and waiting and waiting) for a tree to fall and create a gap with more light. For the past four decades, with cattle no longer grazing, other trees have started to grow around this Dipteryx. The seeds for some of those trees were likely brought in by birds who came to perch in the Dipteryx and poop, puke, or just drop the other seeds. Without anthropomorphizing this epic tree, I find it hard not to think about its role in nurturing this new forest.
A number of animals eat the almendro seeds – often eating the fleshing pulp around the seed and later dispersing the hard seed elsewhere. Among these frugivores are bats and tapirs. I saw no bats and no tapirs on my walk, but there are signs that they are there.
As I walked further down the trail I noticed an amazing collection of Virola seeds (or at least parts of them). There are two species of Virola in the forest here – V. sebifera and V. koschnyi. They are impressive trees with straight trunks. They are locally called fruta dorada (the husk around the seed is golden) and more generally called wild nutmeg (although I wouldn’t add it to my apple pie).
The seeds are favorites of toucans and others. They have a thick (but not hard) shell and a seed that is surrounded by a fleshy aril. I think the aril is the real prize for most frugivores. The Virola seeds are quite distinctive, even without their red arils and nuts, so it isn’t uncommon to stumble across them in mature or secondary forests. However this was a pretty amazing collection of seed husks – thousands of them scattered under a very productive parent tree. It was also interesting to note what wasn’t there – the seeds themselves.
I managed to find one nut with an immature aril and a few small nuts, but most of the others were long gone. Was it toucans, the tapir, an occasional motmot? The literature suggests the Chestnut-mandibled toucan (Ramphastos ambiguus swainsonii) was the most likely disperser, but either way the seeds are long gone.
Back to my original goal – finding these forgotten plots planted more than three decades ago. Hiding between the STR and SR trails appear to be several of these experimental plots; another couple appear to be on the other side of the STR trail. Mortality over time, new regeneration of trees within the plots, and my limited tree identification skills make it hard to know for sure. But the hidden rows of trees and unlikely combinations species are a good starting point. The expert knowledge of colleagues Eugenio Gonzalez and Orlando Vargas will be the real test.
So why do I want to find these old plots anyway? They provided important information on survival, growth, and more decades ago – serving their intended purpose. But I think these trees and the forests they are becoming also hold important lessons about what happens in the future to plantations we plant now. Which ones will promote regeneration of native species? Which ones will be more resistant to the effects of higher temperatures and longer droughts triggered by climate change?
