Reforesting with Figs

 Benjamin E. Smith is a Ph.D. student at George Washington University. He recently completed a field ecology course with the Organization for Tropical Studies in Costa Rica, where he worked with CCSD scientist Leighton Reid. When he’s not coring fig trees in Costa Rica, Benjamin studies plant-herbivore interactions in American chestnut.

It was my recent privilege to spend a week at Las Cruces Biological Station in Costa Rica where I learned about some amazing properties of fig trees.

The genus Ficus contains over 800 species, which can be found in the tropical to warm temperate regions throughout the world. Where they occur, figs are vital components of their local ecosystems because they provide high quality fruits for many animals. Animals attracted by the delicious figs often carry other plants’ seeds in their digestive tracks and subsequently deposit them below the fruiting fig tree. This can lead to patches of forest with especially high plant diversity.

Two individuals of Ficus obtusifolia demonstrating the strangler lifestyle (left) and the free-standing lifestyle (right). The individual on the left has overtaken one host tree and is reaching out to claim another. The individual on the right was planted (either by humans or birds) in a fence row.

Some fig species have the ability to resprout roots, branches, and leaves from broken limbs – an adaptation that would be useful in an ecosystem with frequent disturbances, like hurricanes or landslides. Rural people have been utilizing this incredible feat of nature to create living fences for hundreds of years; they simply cut branches from a tree and plant them. Plant a large enough branch, and you’ve got an instant tree.

Instant fruiting trees could be a practical tool for ecological restoration, and there is currently an experiment underway to test this idea. But not all fig species can resprout from cuttings, so in order for this tool to be useful outside of southern Costa Rica, it would be helpful to know which species will resprout and which will not.

A healthy cutting of Ficus colubrinae. This instant tree was planted in May 2015.

Does wood density predict resprouting in figs?

We sought a way to determine whether a particular fig species would be able to resprout from a limb cutting before actually cutting apart large trees. This would mean only trees whose cuttings will survive would be used and trees that can’t resprout could be left undamaged.

We believed that wood density would be a good measure to figure this out. Wood density can tell you a lot about a tree’s life history strategy. Is it a hard tree that will resist snapping in a stiff breeze? Or is it a softer tree that might break, but then resprout?

To test this, we took core samples from seven fig species and headed to the lab. After a couple days of measurements, we had our data.

(A) OTS student Orlando Acevedo Charry extracts a core from a Ficus colubrinae. (B) Cores were cut into small pieces. We measured the mass of the water that each segment displaced to determine the wood’s green volume. (C) Next, samples were placed in a drying oven at 106° C for 24 hours. Finally, we measured the mass of the dried samples and divided by the green volume to determine wood density.

The fig species we tested turned out to have pretty similar wood densities. Also, the slight variations in wood density did not correlate with trees’ resprouting abilities. This initially came as a big disappointment, but after taking a second look at our data we started to see a trend that may actually be much cooler.

Wood density was a poor predictor of resprouting capacity (measured by tallying fig cuttings that were planted in April-May 2015; Left), but strangler figs in the subgenus Urostigma performed much better than two free-standing species in subgenus Pharmacosycea.

Fig species come in a variety of forms. Some are rather conventional free-standing trees that grow from the ground up, but others start as seedlings high in the canopy of another tree and send roots down to the ground, gradually strangling their host. Still others are shrubs, climbers, and epiphytes. We found that stakes cut from strangling figs, the ones that initially rely on a host tree, were much more likely to resprout than stakes cut from free-standing fig species. If this holds true, no measurements will be needed in the future. People around the world may be able to tell if a tree will likely sprout from a cutting just by the way it grows.

Monitoring epiphyte colonization in Costa Rican forest restoration

Leighton Reid and Miguel Chaves are investigating how tropical forest restoration influences plant diversity. Leighton is a postdoctoral fellow in the Center for Conservation and Sustainable Development. Miguel is a doctoral student at University of Missouri Saint Louis.

Epiphytes are plants that live non-parasitically on other plants. That is, they grow on the trunk or branches of another plant (often a tree) without extracting nutrients from it, as mistletoes do. In Missouri, one example is the resurrection fern (Pleopeltis polypodioides), an epiphyte famous for its ability to re-green after lengthy desiccation.

In tropical forests, epiphytes are much more diverse. Science writers commonly use the word “festooned” to describe the profuse growth of aroids, bromeliads, ferns, and especially orchids on tropical trees. In certain places, epiphytes can make up as much as 50% of a forest’s vascular plant species.

We were curious about how ecological restoration influences epiphyte communities, so over the summer Miguel Chaves worked with local conservationist Juan Abel Rosales and botanist Federico Oviedo to survey the vascular epiphyte composition and abundance on 1086 trees growing in thirteen restoration sites in southern Costa Rica. They found about one hundred species, several of which are depicted below.

This fall, we are analyzing these data to learn about how tree planting influences epiphyte community assembly compared to natural forest regeneration. In particular, we hope to shed light on two questions:

(1) To what degree does tree planting facilitate epiphyte recovery?

(2) At what spatial scale does local forest restoration interact with landscape context to influence epiphyte recolonization?

The base of this poro tree (Erythrina poeppigiana) has sufficient ferns to warrant the descriptor “festooned”. Ferns visible in this photograph include: Niphidium crassifolium, Serpocaulon fraxinifolium, Serpocaulon dissimile and Polypodium dulce.

A showy orchid (Dichaea cryptarrhena) hangs from a mossy bed below two bromeliads.

An inflorescence of Drymonia macrantha (Gesneriaceae).

Miguel and Juan Abel at work next to a particularly good-looking bromeliad (Guzmania zahnii). Photo by Karen Holl.

Plants that use other plants for support but also have roots in the ground are called “hemiepiphytes”.

These aroids (Monstera sp and Syngonium hastiferum) are secondary hemiepiphytes, that is, plants that begin life on the forest floor and climb upwards towards the light.

Many of the epiphytes that Miguel and Juan Abel observed were flowerless seedlings, like this Gongora armeniaca (Orchidaceae).

Drones can help monitor forest restoration

Leighton Reid is a postdoctoral fellow in the Center for Conservation and Sustainable Development.

Hexacopter flying over a restoration site. The red, digital camera is visible between the landing bars.

Monitoring restoration projects is important to demonstrate progress and learn what works and what doesn’t, but it can be time consuming and expensive. As such, restoration practitioners around the world are looking to automate tasks like monitoring, and one way this can be done is with unmanned aerial vehicles, or drones.

Over the past two years I’ve worked with a research team in southern Costa Rica to test how well drones can monitor tropical forest restoration. We used hexacopter drones: helicopter-like contraptions with six rotors. Each drone had a consumer-grade digital camera attached to the bottom. We flew the drones over thirteen restoration sites and then used Ecosynth computer software to stitch the images together and create three-dimensional models of the vegetation structure.

Drones accurately estimated forest structure

Drone-based measurements of canopy height closely matched our hard-won field measurements (but with less sweat and insect bites). The drone-based system also detected canopy gaps, predicted fruit-eating bird movements, and estimated above ground biomass. The ability to accurately assess above ground biomass is particularly important; it suggests that drones could be used to monitor carbon accumulation in regenerating forests.

Editors’ choice – a must read

Our research on drones and forest restoration was published this week in the journal Biological Conservation. The editors selected it as the must-read choice of the month, saying:

“The rapidly expanding use of unmanned vehicles to monitor vegetation and other aspects of biodiversity is an exciting development in conservation biology. This article also demonstrates that bird abundance can be estimated using data gathered by UAVs.”

The paper is freely available for download through August 27, 2015 at the publisher’s website.

Researchers Jonathan Dandois and Dana Nadwodny (University of Maryland Baltimore County) launch a drone at a site in Costa Rica [Photo courtesy of Karen Holl].

Talking Ecological Restoration on the Osa Peninsula, Costa Rica

Over the weekend, thirty scientists and land managers met in a rainforest clearing on Costa Rica’s Osa Peninsula. We discussed tropical, ecological restoration. Among the attendees were some of the luminaries of tropical biology and conservation. Expertise ranged from forestry to power grid infrastructure to loan financing to mangrove snails. Here are a few thoughts that I took from the gathering.

Red-lored Parrot (Amazona autumnalis) in a royal palm (Raphia taedigera)

Tropical forest restoration isn’t just tree planting. Planting trees is a standard restoration practice, but it can become impractical at the enormous spatial scales needed to preserve hundreds of thousands of organisms and their interactions. Moreover, forests are made of more than just trees; fruit-eating animals (like spider monkeys) and meat-eating animals (like jaguars) are vital for maintaining ecologically intact tropical forests. Even flies can do the grunt work of restoration.

Above: Spider monkeys (Ateles geoffroyi) drinking nectar from Ochroma pyramidale flowers. Spider monkeys also disperse tree seeds throughout the forest. One scientist at the workshop quipped that a lowland, Neotropical rainforest without spider monkeys has serious problems.

Restoration doesn’t happen without people. Knowing your neighbors can afford special opportunities. The longer that people have lived in a landscape, the richer their potential as informants and collaborators. Restoration gains ground when it provides things that people want, like clean water, wild nature, and jobs. Working with people in government could be the surest way to achieve restoration permanence.

Watch out for the trap of the ivory tower. Designing restoration experiments is intellectually satisfying, but to make a difference at a regional or global level, these ideas also need to be scaled up and implemented as land management practices. Ideally, restoration research is place-based; that is, it’s designed to meet the unique conservation challenges of its particular landscape using local resources.

-Leighton Reid

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Planning Fig Tree Planting in Costa Rica

In early December I spent 10 days in southern Costa Rica preparing sites for a tropical forest restoration experiment using fig trees. Figs are classic keystone species; that is, they have a large influence on their ecosystem relative to their abundance. Figs produce fruits that are eaten by many animals throughout the year. These animals disperse other plant species’ seeds below the figs’ crowns, and as a result, forests around fig trees often have diverse types of seedlings.

Ficus tonduzii – a fig species that we are using for an enrichment experiment.

An 8.5-yr old fig (Ficus americana) planted as a giant, 4-m long, vegetative cutting.

Some figs are also capable of resprouting from vegetative cuttings, meaning that one can cut branches from adult trees and plant them as though they were seedlings. If cuttings are taken from fruiting adult trees, the cuttings can even produce fruits in the first year after they are planted, potentially attracting seed-carrying animals.

On one humid night last week, I woke up at 2AM, my bed shaking from a nearby magnitude 6.6 earthquake. The next day a co-worker cut through his shin to the bone with a machete. It rained every day, but flowering corteza amarilla (Tabebuia ochracea) trees signified that the dry season is nearly here.

You can read more about tropical forest restoration research in Costa Rica in our latest paper on seed dispersal, or you can listen to a podcast from earlier this fall on Science Sort-Of.

-Leighton Reid

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