Identifying and evaluating the effects of forest community composition on western larch (Larix occidentalis) growth and development

Authors' Names

Christian M. Mercado, University of Montana, MissoulaFollow

Presentation Type

Poster Presentation

Category

STEM (science, technology, engineering, mathematics)

Abstract/Artist Statement

Western larch (Larix occidentalis) is an important tree species that is exclusive to the inland northwest region of North America; however, projected climate conditions may have a profound impact on its ability to grow within this region in the future. Predictive models are commonly used by land managers and scientists to evaluate how forests in this region will grow under various conditions and how management activities today will affect these forests in the future. Such models typically assume that a species’ growth attributes are independent of community species composition; however, a growing body of evidence suggests that the mixing of species traits within forest communities can alter how trees grow and develop. Western larch forests are typically composed of various species, not just larch, so uncovering how species-mixing impacts the growth of western larch can aid in elucidating and managing larch’s future outcomes. This research aims to identify and evaluate if and how western larch growth varies across community species composition using a unique long-term forest inventory data set that is distributed across forest lands in Montana and Idaho.

I aim to determine whether community species composition has an impact on western larch basal area increment (BAI), by first developing and validating a statistical model that accounts for variables known to impact larch growth. Variables like tree size, competitive position, stand density, and site productivity are already known to provide important information in describing a tree’s BAI. Second, I will develop and apply quantifiable measures of species-mixing based on physiological and competitive characteristics, such as shade tolerance. Third, I will incorporate these metrics into the model, comparing each metric’s marginal influence on tree growth. Through this framework, and by implementing a novel measure of community species composition, I will determine how western larch’s growth varies across the variety of communities where it is found.

To date, there has not been a study that specifically addresses how western larch grows relative to local community physiological variability, and specifically, shade tolerance has not yet been used to characterize forest tree growth in this region. If community species composition significantly impacts western larch growth, then managers would have access to more accurate depictions of future forest development, better informing how this unique species can be sustainably managed and preserved.

Mentor Name

David Affleck

Personal Statement

How can we manage forests in such a way that is beneficial to sustaining the future of our planet? This is one of the fundamental questions that drives how forest ecological research is driven today. There is no simple answer to this question, however, various lines of research aim to better understand how climate change will impact the world around us. My name is Christian Mercado and I am a second-year master’s student studying forestry in the Affleck lab at the University of Montana. My primary research goal is to better describe how trees grow and develop over time, and in turn, aid in informing how land management decisions are made. I am also profoundly interested in studying how statistical methods can be implemented and improved in an ecological setting to aid in the conservation and preservation of forests. Millions of acres of forest lands are threatened not only by unexpected extreme events like wildfires, droughts, and floods, but also by the lack of long-term data to inform how forests grow and change over time. Since trees and forests are so complex, and take centuries to grow, develop, and change, a fundamental issue in understanding how to manage forests is that various assumptions must be made about how altering a forest ecosystem now will impact the very same ecosystem in the near, middle, and long-term futures. Numerous mathematical models are used to help land-managers understand how forests change over time. These models often consider the size of trees, density of trees in an area, and competition between trees in a given area as strong predictors of how trees grow. In my research, I am considering how the addition of a new variable, species-mixing, will alter the relationship between these variables, specifically for western larch, which grows with many different species in the interior northwest. Species-mixing is a term to characterize how different species interact with one another in a community. There is a growing body of evidence which suggests that the level of species-mixing that occurs in a forest ecosystem has a great impact on how the trees within the system grow. However, the identity and physical placement of different tree species has not yet been considered as an important variable in modelling tree growth within forests in the interior northwest region of North America. I am using a large, long-term data set to inform my research through developing and evaluating statistical models. If my research provides compelling evidence that species-mixing impacts western larch growth, then management decisions made over the millions of acres that these trees occupy, can be better informed to a higher degree of accuracy. This can have long-term impacts on how carbon, lumber supply, fire, and various other values are managed in the near and long-term future.