Forest Diversity and Structure in the Amazonian Mountain Ranges of Southeastern Ecuador

Ángel Benítez,Wilson Quizhpe,Isau Huamantupa,Jesús Muñoz,Klever Cuenca,Omar Cabrera,Hernán Uvidia

doi:10.3390/d11100196

Abstract

We analyze the structure of diameter, richness, and diversity of the forests in the upper limit of the great Amazon basin located in the Ecuadorian territory of the Cordilleras del Cóndor and Cutucú. Our hypothesis was that the forests of the eastern mountain ranges are not homogeneous, but rather present differences in their structure, richness, and floristic diversity. Our main objective was to classify the types of forests based on the characteristics of the diameter structure and the species composition of the Amazonian forests of the eastern mountain ranges in southern Ecuador, and we determined the influence of critical edaphic, environmental, and geomorphological factors, For this we installed eight permanent plots of one hectare in homogeneous and well preserved forest stands, four plots in the province of Zamora Chinchipe and four in the province of Morona Santiago. We identified and measured all trees >10 cm at chest height and for each plot, soil samples, as well as environmental and slope data were taken. We performed an non-metric multidimensional scaling analysis (NMDS) analysis to evaluate changes in climatic and geomorphological gradients, and used the CCA analysis to assess the relationship between the composition of the species at the plot level and the edapho-climatic variables. Finally, we modeled the change in diversity ad species (Fisher’s alpha) in relation to climatic, altitudinal, and geomorphological gradients using a GLM. We determined the existence of two different types of forest, the first called Terra Firme, characterized by the presence of a greater number of species and individuals per plot as compared to the second type of forest called Tepuy or Sandstone forest. Species richness was negatively correlated with the phosphorus content of the soil and the pH, annual average temperature, annual rainfall, and altitude. Terra Firme forests, settled in more stable and nutrient-rich climatic areas, were more diverse and Sandstone forests are poor in nutrients and develop in areas with greater seasonality.

Highlights

Ecuador is considered one of the 17 mega-diverse countries of the world [1]; the diversity of plants throughout its territory being a consequence of distribution patterns and geodynamic processes which have been studied during the last decades
The most diverse family is Fabaceae with 51 species and it is the one that contributes in both types of forest, with the largest number of species, followed by Rubiaceae 40 ssp. (7.7%), Euphorbiaceae and Lauraceae with 36 ssp. (7%), Moraceae with 27 ssp. (5.2%), Sapotaceae with 19 ssp. (3.7%), Clusiaceae and Melastomataceae with 18 ssp. (3.5%), Myristicaceae with 15 ssp. (2.9%), Burseraceae and Cecropiaceae with 14 ssp (2.7%), Annonaceae and Myrtaceae with 13 ssp. (2.5%), and Flacourtiaceae
Our results show that the forests from the Cóndor and Cutucú mountain ranges group into two distinct forest types, the Terra Firme forest and the Sandstone or Tepuy forest, and the differentiation is due to climatic, environmental, topographic, and edaphic factors

Summary

Introduction

Ecuador is considered one of the 17 mega-diverse countries of the world [1]; the diversity of plants throughout its territory being a consequence of distribution patterns and geodynamic processes which have been studied during the last decades. The forests of the Ecuadorian Amazon have undergone high rates of deforestation and fragmentation [5], which modifies environmental conditions at local and regional levels (higher temperatures, changes in precipitation regimes, and increased CO2 concentrations) These ecosystems are home to one of the highest concentrations of vascular plant species [6], but most studies are limited to the floristic diversity of these ecosystems [7,8], without relating this richness and diversity to environmental, geomorphological factors, and soil [9], nor with altitude patterns and specific edaphic-environmental factors such as precipitation, seasonality, soil fertility, and topography [10,11,12].

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