'Secondary hemiepiphytes' - A concept under scrutiny

• Applicant: Professor Dr. Gerhard Zotz
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403244543

Tropical plant biodiversity is not only impressive in terms of species numbers, but also in terms of structural and life form diversity. Much of the complexity and diversity of a tropical forest is due to the occurrence of life forms that are quite rare or even altogether absent in temperate forests, e.g. vascular epiphytes, strangling or non-strangling hemiepiphytes, or woody and non-woody climbing plants, but the ecology of these groups is still little understood. A case in point are so-called ‘secondary hemiepiphytes’ (SH), plants defined by germination on the ground, ascent on tree trunks and dieback of the lower portion of the stem leading to severance of all connections with the ground. Although modern text books on tropical forest ecology typically describe SH as one of five mechanically dependent plant groups, the concept of ‘secondary hemiepiphyte’ is almost entirely based on anecdotal evidence. The few published experimental reports and own preliminary data suggest that plants categorized as SH do not lose connection with the soil, but rather that adventitious roots replace stems as water conducting systems. This could simply be a consequence of hydraulic limitations in climbers that lack secondary growth: almost all so-called SH are monocots. The proposed study will now rigorously address a problem that has been neglected both by liana researchers and epiphyte researchers. Based on a solid quantitative spatio-temporal analysis of SH communities in two tropical forests with a thorough census of root connections, we will investigate germination, establishment, and important functional aspects of SHs as compared to ‘normal’ vines and epiphytes. If we can show that all studied SH continuously depend on soil root contact, the entire notion of SH is probably blurs biological reality and the term secondary hemi-‘epiphyte’ is an unnecessary and even misleading misnomer. Alternatively, validating Kress´ notion for at least a few species would be evidence for an exciting facet of plant growth strategies.

• DFG Programme: Research Grants