GRADUATE STUDENT

Jimena Forero

by Suzanna Engman

Dioecious trees have separate sexes. In other words, some trees are female and others are male. In the plant world this is a rare occurrence. About ninety percent of all plants are hermaphrodites, which means both male and female functions occur in a single flower. Five percent are monoecious, which means that an individual has both sexual functions, but they occur in unisexual or separated flowers in a single plant. And five percent of all plants are dioecious.

Dioecious trees may have an evolutionarily advantage that provides them with a stronger survival strategy than hermaphrodite or monoecious trees, says graduate student Jimena Forero. She is studying three dioecious trees in the Luquillo Forest Dynamics Plot (LFDP) and analyzing some of the plant data collected by the Long-Term Ecological Research program since 1990 for her master’s thesis.

“I’m using the data of growth and recruitment in the LFDP to describe some aspects of the demography of three species and their spatial distribution in the LFDP. The specific questions I want to answer are: What is the proportion of the sexes in the populations? Are there differences between the size class distributions of males and females? Do males grow faster than females? Are the sexes spatially segregated, or do they occur in different microhabitats? These are classical questions about dioecious plants whose answers will help us understand how the breeding systems of plants have evolved.”

Forero chose three tree species to study: the Tabanuco tree (Dacryodes excelsa), a climax species that grows slowly and is abundant in the LFDP; Tetragastris balsamifera, another climax species, but less common; and Cecropia schereberiana, an abundant pioneer tree that grows quickly and plays an important role in the recovery of the forest after hurricanes.

Forero points out that the biggest questions in plant ecology are why biodiversity in the tropics is so high, and what favors and maintains this biodiversity.

Currently, biodiversity loss is faster than ever before in human history, and although species extinction is a natural process of evolution, human activity has increased the extinction rate by at least 100 times, according to World Conservation Union. The human activities that most affect biodiversity are land use changes, climate change, invasive species, and pollution. Biodiversity loss can affect food and drug availability and access to clean water and raw materials.

Forero says that a paradigm shift in values may be necessary to reverse biodiversity loss. “We maybe have to change our way of thinking that only things that are important and useful for humans are important for the world.”

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