First surveying of forest canopy epiphytes in Honduras (Biodiverstity Science Newsletter)
The first investigation into epiphyte diversity, distribution and biomass on large canopy trees in Honduras, carried out between June and August 2012 in Cusuco National Park, has begun to reveal just how diverse these communities are: there are more than 100 different epiphyte species found within a small area, and an individual branch may be harbouring as many as 15 different species of epiphyte.
Film of amazing epiphytes in the canopy of Cusuco National Park, in the Merenden Cloud Forset, Honduras. Filmed by Canopy Access, Operation Wallecea Honduras.
Lack of research
Canopy epiphytes – plants that grow on other plants – are a very diverse group and contribute substantially to the diversity within a forest. It has been estimated that approximately 10% of all global plants are epiphytes and that in many instances they exceed the vascular plant diversity at ground level.
The biomass of epiphytes can sometimes exceed the above leaf biomass of the host tree. These epiphytes from the family Bromeliaceae often form gigantic ‘mats’ 40 + m above the forest floor. Picture taken by Sven Batke
Due to the challenges of studying the canopy, epiphytes have mostly been neglected in general vegetation surveys and it has only recently been recognised how important epiphytes really are. In Honduras for example, no investigations of canopy epiphytes had been undertaken to date, leaving the upper forest strata largely unexplored.
In an attempt to widen our knowledge on epiphytes in Honduras, a small team set out to Cusuco National Park in Honduras. The aims of the project are/were: i) to assess the vascular epiphyte diversity and abundance within the park and along an altitudinal gradient; ii) to assess the response of epiphytes to hurricanes along a newly developed hurricane index gradient; and iii) to assess the role of host tree specificity to epiphytes.
Cusuco is located in the North-West of the country, near the border with Guatemala. Cusuco is remarkable for its unique flora and fauna. Much of the park is Pinus spp. dominated tropical mountain cloud forest, with moist broadleaved and dwarf forest at higher elevations. The moisture supplied by the clouds and rain make this forest an excellent habitat for epiphytes.
During the 2012 summer season six plots were sampled near two of Cusuco’s easterly camps, namely Base Camp and Cantiles (Figure 1). The locations of the plots were standardised using results from a previous developed hurricane impact model and a contour map of the park.
Using rope access methods, the team surveyed 30 large trees (28-56 metres high), gathering data from 647 branches and collecting over 200 plant specimens, within the first of the three planned summer seasons (see Table 1 below).
Within each tree the investigators recorded the position and size of every epiphyte and additionally recorded microclimatic (temperature and humidity) and micro-architectural (branch aspect, inclination, texture etc) habitat differences.
Watch video footage of the survey here.
Although many of the specimens are still pending further identification and verification, it is already clear how great the epiphyte diversity and abundance in Cusuco is. The 100+ of epiphyte species identified so far, including climbers, stranglers and hemi-epiphytes, can be placed within 34 different families and 64 different genera. The most diverse families were Orchidaceae, Bromeliaceae, Polypodiaceae, Araceae, Ericaceae, Piperaceae, Dryopteridaceae, Clusiaceae and Araliaceae.
Challenges and further work
Fast and safe canopy access is of fundamental importance. Because the steep terrain in Cusuco hampers forest travel, the scientists typically had only 5-6 hours of sampling time a day, and merely rigging a tree could take a couple of hours.
Sven Batke taking notes on top of a 54.5 m tree. Sudden storms mean that the climber needs to be prepared for a swift descent. Picture taken by Nickolas Hill
There are three major problems associated with this kind of work in Cusuco. First, it is often difficult to see from below what lies above; second, tree limbs vary unpredictably in their strength (and therefore in their ability to support a climber); and third, within-canopy encounters with aggressive social insects such as wasps, bees and ants were a constant danger.
To reduce the risk to the climber, the surveyors used ‘Ground Based Rescue Systems’ that meant the climber could be lowered by a ground crew in case of an emergency. To roam through the three-dimensional canopy, however, prusik-systems are employed that allow the climber to access the upper and outer parts of the canopy.
The aims over the next 2-3 years are to undertake further work into the fascinating vertiginous world of epiphytes in Cusuco and to support the ongoing conservation efforts within the park. This is more important than ever, given the recent increase in logging activities within the park’s core zone.
- Sven Batke, Trinity College Dublin