Chapter 3 Intro

This study looks at interconnections between fire disturbances and montane wetlands to understand how wetlands affect vegetation recovery on post-fire landscapes. With wetlands in the Colorado Rockies serving as a vital ecosystem resource for biodiversity it is important to understand how these wetlands recover after disturbances. In recent years, the most drastic disturbances in the mountains of Colorado have been fires which can occur both naturally and by human incident. While it is a part of a natural process in the life cycle of forests, they have become increasingly frequent and severe due to drought and climate change impacting Colorado. When severe enough, they can drastically alter the landscape both in terms of land cover and hydrologic regimes. Specifically, they will drive fundamental changes in vegetation density, diversity, and ecosystem processes (Carlson et al., 2017). When looking at the impact of fires on wetlands the increased hydrologic connectivity and water content of soils means they are much less likely to suffer from severe burning, unlike non-wetland areas (Fairfax & Whittle, 2020). After major disturbances such as fires, vegetation is likely to reach new stages of steady state because of the new generations of vegetation. The wetlands of the Colorado Rockies form in valleys and slopes where the ground surface intersects or becomes close to the water table. The steep and variable topography of these areas mean that, generally, the wetlands are going to be constrained to small sizes (Cooper et al., 2017). The most common type of wetlands within these regions are riparian areas around ponds/rivers, freshwater emergent, and forested/shrub. In Colorado the main sources of water for these wetlands are often snowmelt, runoff, and underground springs. Due to the heightened hydrological activity, the soils and water tend to be nutrient rich, and the wetland will be responsible for greater biotic activity in vegetation. In turn this makes the wetlands more valuable to animals and humans because of the ecological services they provide (Fretwell et al., 1996). For these reasons, it is important to understand the role ecological disturbances such as fire play in affecting mountain wetlands and vice versa.

Using GIS tools such as the Normalized Difference Vegetation Index (NDVI) the relationship between fire disturbance and wetlands can be more easily understood. NDVI serves as a dimensionless index that indicates the difference between visible and near infrared reflectance of vegetation cover and helps to visualize how vegetation and its greenness changes over time. The study presented here analyzes how NDVI values vary across different wetland types and how they might influence the vegetation recovery rates. Along with the use of NDVI the Hayman fire, which occurred southwest of Denver in 2002, is used as a medium for looking at the effect of wetlands on post-fire vegetation recovery. Wtih the Hayman fire as a region of interest nine sites were chosen to study how their, and the surrounding areas, greenness changed post-fire.

library(png)

fire_wetland <- readPNG("Data/Hayman_PerimWetlands.png")

grid::grid.raster(fire_wetland)

grid::grid.text("Figure 1: Wetland locations within the Hayman Fire perimeter", x = 0.5, y = 0.1, 
                gp = grid::gpar(fontsize = 10, fontface = "bold"))

As vegetation recovers over time the NDVI values will approach similar, if not the same, levels of greenness as pre-fire. But the difference in the rates of recovery between wetland types and non-wetlands is the key point of interest here. The Hayman fire allows for over 20 years of data to analyze the patterns of NDVI values before and after the fire occurred. The variance in NDVI values indicates whether there is significant difference between the wetland types and their rates of recovery. Analysis of this change and recovery will shed light on the relationship wetlands have with the recovery of vegetation on the landscape around it.