Publication Date

2012-11-21

Availability

Open access

Embargo Period

2012-11-21

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biology (Arts and Sciences)

Date of Defense

2011-11-14

First Committee Member

Guillermo Goldsteim

Second Committee Member

David P. Janos

Third Committee Member

Carol Horvitz

Fourth Committee Member

Stefan Schnitzer

Abstract

Lianas is a term that identifies vines that produce secondary wood tissue and whose distribution is mostly restricted to the tropics. They usually start their lifecycle as seedlings in the forest understory an after a period of time they climb to the canopy forest supported by the surrounding vegetation. The seedling itself is an important stage on the plant’s life cycle; in this stage plants are susceptible to high mortality rates due to biotic or abiotic factors, such as predation, diseases, drought or flooding. Depending on the survival at this stage, they can extend their habitat range and colonize new environments, but failure to do so can decrease their natural habitat range. Liana seedlings can be classified in two separated functional groups: freestanding seedlings: the ones that can grow without a mechanical support and can remain as small woody plants for a relatively long period of time and support-seekers seedlings: the seedlings that reach for a host to climb on earlier in their life cycle. Until now little is known about the ecological or the physiological differences or similitudes between this two different functional groups. My main objective in this work was to evaluate the distribution and density of liana seedlings in general and of this two functional groups, first at regional scale using a series of plots across a rainfall gradients and different types of soil, then evaluate the population trends of liana seedlings at local scale using a series of datasets from the 50 hectare plot located in Barro Colorado Island in the Gatun Lake of the Panama Canal. The data sets consist on a series of seedling censuses from 2001 to 2004, soil data for all the 50 hectare and canopy forest census for the same period of time. Finally I have studied the physiology and life history traits of each group, comparing traits such as relative growth rates, stem diameter, leaf area and leaf mass per area, hydraulic architecture, and photosynthetic rates in plants with similar age. At regional scale liana seedlings were more abundant in sites that have limestone soil, independently of the rainfall pattern. But laterite soil sites in contrast had higher diversity of liana seedlings. Freestanding liana seedlings were more abundant in wet sites than in dry sites, while the support-seekers liana seedlings were more abundant in drier sites than in wet areas. On a smaller scale at the 50 hectare plot I observed that liana seedlings were increasing in population size together with shrub seedlings, meanwhile tree seedlings were decreasing in number. Out of the two liana seedling functional groups, freestanding and support-seekers, the support-seekers contribute more to this trend in liana population changes because they had a higher rate of yearly increase. Neither soil nutrients nor gap opening showed a strong effect over changes in population trends. Experiments determining the differences in life history and physiological traits between the two functional groups, freestanding versus support-seekers liana seedlings using eight different species of liana, showed that although the groups do differ in traits such as leaf area, leaf mas per area, stem diameter, relative growth rate, specific and leaf specific hydraulic conductance, and electron transport rate, the freestanding seedlings seems to be en general more closely related in those characteristics, while the support-seekers, seems to have some characteristics in common between them and also some in common with freestanding seedlings Overall these two groups of seedlings seems to have different distributions patterns at regional scale, different population patterns at local scale, but the physiological and life traits characteristics seems to overlap in some species. Perhaps we can view these groups as either two complete separate functional groups with some species more closely related to each other in terms of life history and physiological traits or as a gradient of characteristics in which each species is located in a different position along a continuum of life history and physiological characteristics.

Keywords

Liana physiology; seedling ecology; tropical ecology; rainfall gradient

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