Transplanted bromeliads improve microclimate and facilitate arthropods in restored forests

Estefania Fernandez is a masters student at the University of Montpellier, France. She spent the past six months working with scientists in the Center for Conservation and Sustainable Development on a tropical forest restoration experiment in southern Costa Rica.

Costa Rica is one of the world’s most biodiverse countries, hosting 4% of flowering plant species in an area representing only 0.03% of the Earth’s terrestrial surface. With a large diversity of ecosystems, ranging from mangroves to cloud forests, Costa Rica hosts a unique family of (almost exclusively) Neotropical plants: the Bromeliaceae, commonly called bromeliads. With their colorful inflorescences and strikingly patterned leaves, numerous bromeliads are cultivated around the world for their ornamental value. Less is known, however, about their ecology in tropical ecosystems, particularly in regenerating forests.

Werauhia gladioliflora rosette, showing its overlapping leaves.

Many of the so-called “tank bromeliads” are epiphytes, meaning that they grow non-parasitically on other plants. These bromeliads have ample rosettes of overlapping leaves, capable of holding considerable amounts of water. These water tanks keep them hydrated, and plant detritus that accumulates in these structures also provides bromeliads with nutrients. Arthropods take refuge in bromeliad rosettes, and consequently these plants attract mammals and birds seeking prey. Mutualistic ants build their nests in bromeliad rhizospheres, or root zones, and frogs lay eggs in the tanks. When sufficiently numerous in tree canopies, bromeliads can stabilize local temperature and humidity.

Water stored inside a W. gladioliflora tank. (Photo courtesy of Dave Janas)

Despite these important ecological roles, vascular epiphytes like bromeliads are often scarce in regenerating tropical forests. Their recovery could be slowed by limited seed dispersal or by a lack of suitable recruitment sites. One way to overcome dispersal limitation is to transplant individuals. In our study area in southern Costa Rica, transplanting bromeliads is relatively simple because they are easily found on fallen tree branches in the old growth forest reserve at Las Cruces Biological Station. We hypothesized that transplanting bromeliads from the old growth forest into 10-year old forest restoration sites would buffer local temperatures and increase arthropod abundance and diversity compared to bare, control branches.

Measuring local temperature in a transplanted Aechmea dactylina.

To test our hypothesis, we transplanted 120 bromeliads into three restoration sites in southern Costa Rica. The restoration sites are part of the Islas Project, an NSF-funded restoration experiment led by Drs. Karen Holl and Rakan Zahawi. Bromeliads were sterilized and attached to tree branches in the restoration sites with twine. Each day, we measured the microsite temperature on branches with and without transplanted bromeliads, as well as ambient temperature in the nearby air. To characterize arthropod colonization, we extracted and identified arthropods (to order) from transplanted bromeliads after two and three weeks.

We found that transplanted bromeliads decreased local temperatures on tree branches, creating a less stressful microclimate for other organisms. Bromeliads also facilitated arthropods; transplanted bromeliads were quickly colonized, especially by ants. We also observed small frogs inside of some bromeliad tanks, but none on the bare branches where we did not transplant bromeliads.

We found this frog (Craugastor stejnegerianus) in a small Catopsis sessiliflora tank. (Photo courtesy of Dave Janas)

Our observations suggest that bromeliad transplantation can buffer microclimates and create useful structures for invertebrates. If so, this method could improve restoration outcomes for canopy flora and fauna. Given that this experiment was conducted over a single field season, it is still an open question whether transplanted bromeliads will survive over longer time periods. It will also be important to learn whether transplanted bromeliads will facilitate colonization by other epiphytic plants. We did find some evidence of this as ferns were already growing in several bromeliads’ rhizospheres after two months.

Can the Ozark chinquapin successfully re-colonize interior highland forests?

Jenn Rosen is an undergraduate at the University of Missouri – Saint Louis. This summer, she participated in the Missouri Botanical Garden’s Research Experience for Undergraduates (REU) program. She spent eight weeks working with scientists in the Center for Conservation and Sustainable Development. Here, Jenn writes about her field experiment at Shaw Nature Reserve.

Conservationists and ecologists have recently sought to restore an ecologically important tree, the Ozark chinquapin (Castanea ozarkensis), that became threatened not by the effects of clear-cutting, but instead due to an incurable parasitic fungus called chestnut blight (Chyphonectria parasitica). After devastating its cousin (American chestnut) in eastern forests, the fungal disease moved west and began infecting chinquapin trees in the Ozark and Ouachita Mountains. The blight is presumed to have been brought into the United States by accident in the early 1900s when Chinese chestnuts (C. mollissima) were imported into the country. What makes the Ozark chinquapin and the American chestnut so susceptible to the disease is that the fungus’ wind-borne ascospores can easily enter through small cavities in their bark where they then grow and spread to neighboring trees. The blight causes Ozark chinquapin trees to die back to the roots, from which multiple stems resprout to form a large shrub-like growth form. Once a widely dispersed canopy tree in upland Interior Highland forests, chinquapins declined in abundance and are now often found as multi-stemmed, blight-infected subcanopy shrubs.

Castanea ozarkensis seeds, with white radicles, from two maternal lines. One group’s seeds are twice the size of the others. Large seeds hold more resources, which can give seedlings a head start. But larger seeds also face a higher risk of being preyed upon by rodents.

Chinquapins were prized by many folks of the Ozarks for the nutrient-rich nuts they produced, and its rot-resistant woods were used to make furniture, railroad ties, and fence posts, among other products. Additionally, large mammals such as black bears were known to forage in the Ozarks in search for the nutritious nuts to help replenish their fat reserves for the upcoming breeding season. There is a collaborative effort among groups to restore the chinquapin throughout its’ former range once blight-resistant seeds become widely available, estimated to take approximately 20 – 30 years.

Once blight-resistant seed becomes available, understanding how chinquapin trees successfully regenerate in the wild will be the key to successfully restoring this species. Unfortunately, little is known about the ecology of the tree prior to blight infection. Like other nut-bearing trees in Ozark woodlands (e.g., oaks), we suspect that there may be several limiting factors to chinquapin seedling recruitment, such as seed predation, poor soil quality and/or poor light availability. In order to test these predictions, we planted 320 chinquapin seeds (from two distinct maternal origins from the wild) across ten experimental replicates at the Shaw Nature Reserve (Gray Summit, Missouri). The criteria for each replicate was that there had to be a shrub microhabitat, which was dominated by the common understory tree, eastern redbud (Cercis canadensis), and an open habitat, separated by at least three meters. Like other Ozark woodlands, prescribed fire is currently being used to restore woodlands at the Shaw Nature Reserve and will likely be a key component to successfully reintroducing chinquapins back into the wild. After enduring many scrapes and pricks from constructing mammal exclusion cages for half of the seeds, roughly two weeks after planting the seeds we had a bounty of little chinquapin seedlings emerge.

Castanea ozarkensis seedling, protected from marauding rodents by a wire cage.

We found that consumer treatment and microhabitat structure, as expected, influenced the rates of Ozark chinquapin seed emergence. Nearly all of the seeds that were exposed to small mammals were eaten or removed, even though seeds were buried a few centimeters in the soil. Interestingly, small mammals consumed seed at greater rates in shrub than open microhabitats. These results imply that understory vegetation structure determines where chinquapin seedlings can successfully recruit through its influence on small mammal behavior. Also, small mammals removed larger, and presumably more nutritious, seed at greater rates than smaller seed. Environmental factors, like light availability, did not affect seedling growth, but the short duration of the study may not have been adequate for the potential influence of these factors to become apparent.

A rodent successfully consumed this unprotected nut.

A thwarted attempt to breach a protective cage.

Our work contributes to a larger ongoing project by the Ozark Chinquapin Foundation to restore and conserve Ozark chinquapins. Given the high rates of seed removal, future restorationists will have to transplant chinquapin seedlings as opposed to seeds to successfully reestablish this species in the wild. However, once reintroduced seedlings grow to maturity and produce seed, our study suggests that microhabitat structure in Ozark woodlands will play a key role in determining the recruitment and growth rates of restored populations.