Biogeography of the Pastaza Watershed


What this book is about....

( Table of Contents follows below.)

        The mountains surrounding the Rio Pastaza don't look very different from the other mountains of eastern Ecuador, but they turn out to be full of unique plant species that grow nowhere else in the world. In fact there are more species unique to the upper Pastaza watershed than there are to the famous Galapagos Islands! About a quarter of these unique species have been discovered in the last five years by my students and myself, and the list is growing rapidly. This book describes the complex flora of the region, with particular emphasis on the distributions of these unique species. This is the first time that plant distributions have been carefully mapped over a large and complicated area in the eastern Andes, and the patterns that are emerging from this mapping project shed new light on the nature of plant endemism and the mechanisms of plant evolution in the Andes.

     The book consists of an overview chapter, followed by chapters on each of the distinct floristic zones of the Pastaza watershed. Each zone has a set of unique species endemic to it, and these are described and discussed at the end of each chapter. The book concludes with chapters on the relationships between this flora and the floras of other regions, the priority areas for the conservation of the endemic plants of the region, and the theoretical implications of the discoveries described here.

To view a chapter, click on the Contents item below. Each chapter opens in its own browser window. Close it to return to this contents page.

It will be some time before I get all this on line, however.



     Table of Contents

Note: The Chapters are still under construction and only a few are on line.

1. Overview

    A general description of the region and its floristic divisions.

The Upper Pastaza Watershed is shown here in a composite image consisting of a false-color elevation map superimposed on a satellite radar image.


2. Floristic Zones:

A. Lower eastern slopes of the Amazonian foothills

   This zone is extremely diverse but very poorly explored. The trees here are tall and straight, and the forest interior is dark and wet. Epiphytes are abundant, and orchid endemism is higher than one would expect. The Masdevallia at left is just one of several newly discovered orchids apparently endemic to this zone.



B. Upper slopes of the Amazonian foothills

The first foothills facing the Amazon are called the Cordillera Abitagua (north of the Pastaza) and the El Encanto mountain chains (south of the Pastaza). This is the wettest zone of the region. It is extremely rich in endemic species, including some that were discovered 150 years ago by Richard Spruce and never seen again. Orchids of the genus Lepanthes are diverse here, perhaps more diverse than in any other place of its size on earth. Many of the orchids, such as theLepanthes at left (which I have named Lepanthes spruceana), are new to science. The highest peaks of this zone have still not been explored, nor even visually mapped, because of the ever-present fog and difficult topography.




C. The Rio Topo/ Rio Las Estancias valleys

      The broad flat valley of the Rio Topo, and its smaller counterpart on the other side of the Rio Pastaza, supports a humid subtropical forest with a surprising number of endemic species of trees, shrubs, herbs, and even an endemic liverwort discovered by Spruce in 1857 and not seen again until Dr Gradstein, Dr. Noske, and myself recently rediscovered it. The number of orchid species endemic to this zone is less than the number endemic to Zone B, but there are still quite a few. This zone is severely threatened by deforestation and hydroelectric projects.


D. The upper Pastaza valley and its tributary valleys

     The forests here are mostly gone. Still, there are some interesting species in this zone, including the endemic tree Zapoteca aculeata, and an endemic amaryllis, Phaedranassa tungurahuae.


E. Semi-arid scrub between Baños and Ambato

    It is surprising to find desert-like conditions so close to wet cloud forest, but both are consequences of the strong interaction of topography and wind in the Pastaza valley. There are few plants endemic to this zone, but it has some very interesting orchids in spite of the dry climate. One of the most spectacular (though not endemic to the region) is Phragmipedium lindenii, which I have painted at left. Among the special plants of the zone are several rare, threatened amaryllis relatives.




F. The Cerro Hermoso-Mayordomo chain and the mountains above the Rio Cristal

    This zone includes the high Llanganates mountains, famous as the supposed burial ground of the treasure of Atahualpa, the last Inca king. The middle and high elevation forests of this zone are rich in endemic orchids, all discovered in the last four years. The genera with the most endemic species are Lepanthes (of course) and Teagueia, but there is also a new Maxillaria, a new Epidendrum, and a new Ponthieva. Most of this zone is almost impossible to reach because of the rugged terrain.  





 G. The Añangu and Cerro Negro mountain chains

      These mountains are remarkable for their endemic Teagueia species (Orchidaceae). In the last year we have discovered around 14 new species of Teagueia in this zone. See Teagueia Explosion! for the full story. There are also a few newly discovered endemic Lepanthes species, but in general the number of endemic orchids is not as high as in the previous zones.



H. Volcan Tungurahua and the mountains above Leito

     The upper slopes of Volcan Tungurahua are unlikely to have unique species, because of periodic violent eruptions. The middle elevations have several apparently-endemic orchids, though I suspect that these will eventually turn up on other neighboring mountains.


3. Relationships with Other Regions

    The flora of the Pastaza watershed is compared to that of neighboring regions to the north and south.

4. Conservation Priorities in the Region

     Where are the most important places to protect here?

5. Implications for Evolutionary Theory

     What do these distribution patterns teach us about the process of speciation in the Andes?



Biogeography of the Pastaza Watershed