Decadal Changes in a Tropical Montane Cloud Forest in the Northern Andes Restricted; Files Only

Abstract

Tropical montane cloud forests harbor an exceptional portion of global biodiversity relative to their land mass. However, they are extremely susceptible to the rapid shifts of environmental factors due to climate change along elevational gradients. Climate change and other disturbances are causing shifts in environmental factors that force species to migrate upwards or risk extirpation, yet long-term monitoring of community level changes remains limited. This study aims to enhance the understanding of these climate-driven changes by continuing a study done in 2014 in a Tropical montane cloud forest in the Northern Andes of Ecuador to address the following questions: Is there evidence that forest types are shifting in elevation over time? How have dominant species in each forest type changed over the last ten years? How has tree abundance and diversity changed in the last ten years? Findings reveal evidence suggesting a shift of homogenization, specifically in mid-elevation forests. The composition of these communities are reducing in ecological uniqueness over time. Mid-elevation forests also revealed the highest change in dominant species composition compared to low and high elevation forest types, highlighting its ecological sensitivity. Tree abundance showed a shifting relationship with elevation throughout time with a positive slope, indicating increasing abundance throughout elevation and time. Species richness resulted in being stable throughout elevation and time, while Simpson’s index revealed to have a shifting relationship with elevation throughout time with a negative slope, suggesting shifting species evenness rather than species composition. These findings highlight the early changes in tropical montane cloud forests. However, interpretations may be limited by the lack of environmental variables included in the analyses, disproportion of sampling efforts with high elevation plots, a lack of demographic statistics such as mortality and turnover rates, and a short time span within analyses.

Table of Contents

Table of Contents

Introduction ..........................................................................................................................................1

Methods .................................................................................................................................................4

Study Site ................................................................................................................................4

Data Collection ......................................................................................................................5

Data Analysis .........................................................................................................................6

Data Wrangling .....................................................................................................................6

Forest Composition and Structure .....................................................................................7

Species Dominance and Stand Volume ............................................................................8

Tree Abundance and Diversity ...........................................................................................9

Tree Abundance .....................................................................................................10

Richness ...................................................................................................................10

Simpson’s Index .....................................................................................................10

Results ....................................................................................................................................................11

Table 1......................................................................................................................................12

Changes in Community Structure .......................................................................................12

Communities in 2014 .............................................................................................12

Figure 1 .......................................................................................13

Communities in 2024 ..............................................................................................14

Figure 2 .....................................................................................................................14

Composition ............................................................................................................................15

Figure 3 ......................................................................................................................16

Abundance, Elevation and Time ..........................................................................................16

Figure 4 ......................................................................................................................17

Alpha Diversity, Elevation, and Time .................................................................................17

Beta Diversity, Elevation, and Time ...................................................................................18

Figure 5......................................................................................................................18

Discussion ..............................................................................................................................................19

Mid-elevational forest shifts toward homogenization .....................................................19

Changes in species dominance across different forest types ..........................................20

Low elevation forest (2437 - 2630 m) .................................................................20

Mid-elevation forest (2669 - 3250 m) ..................................................................21

High elevation forest (3288 - 3334 m) .................................................................22

Tree abundance increased with time and elevation ..........................................................22

Richness is stable despite elevation-specific shifts in species evenness .........................23

Limitations ..............................................................................................................................24

Future Directions ...................................................................................................................26

Conclusion ..............................................................................................................................27

Lit Cited .................................................................................................................................................29

About this Master's Thesis

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School	Laney Graduate School
Department	Environmental Sciences
Degree	M.S.
Submission	Master's Thesis
Language	English
Research Field	Biology, Ecology Environmental Sciences
Keyword	Tree Community Composition Tree Diversity Tree Community Structure Tropical Montane Cloud Forest Elevational gradient Tropical Andes
Committee Chair / Thesis Advisor	Emily Coffey, Emory University Lance Gunderson, Emory University
Committee Members	Loy Xingwen, Atlanta Botanical Garden Carolyn Keogh, Emory University

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