Relationship Between Soil Texture and Altitude in Three Conifer Communities at Lupine Meadows, Grand Teton National Park, Wyoming

Relationship Between Soil Texture and Altitude in Three Conifer Communities at Lupine Meadows, Grand Teton National Park, Wyoming

Melba Nuzen

Scripps Ranch High School, July 2017

Abstract: Though they are very different, abiotic and biotic factors are often involved  in intricate relationships; their interaction form the basis of many ecological communities. For example, previous studies suggest a relationship between soil texture and granularity and the flora that occupies it. Factors such as moisture retention and nutrient retention can be affected by different types of soil, and consequently hinder or help the growth of vegetation. To further study this relationship, particularly in forest biomes, this study examined abiotic soil and biotic conifer species. Samples of topsoil were collected from three conifer communities — Lodgepole Pine (Pinus contorta var. latifolia), Subalpine Fir (Abies lasiocarpa), and Whitebark Pine (Pinus albicaulis) — all of which grow at varying altitudes: the Lodgepole Pine generally grows at the lowest elevation out of the three species, and Whitebark Pine at the highest. Samples were collected along the Lupine Meadows Trail near Grand Teton in Grand Teton National Park, Wyoming during the summer of 2017. In each conifer stand, 25 grams of soil were collected and the ribbon test was used to determine soil texture. Ten ribbon tests were conducted along a 30 meter transect in each community for a total of 30 samples, ten from each conifer community. Although initial research suggested that increasing elevation correlates with coarser soil texture, the results from this study revealed the opposite. As elevation increased, data indicated that soil texture transitioned from being relatively coarse to fine (P < .005). Despite this contradiction, future research in this field can help further define the relationship between soil, flora, and possible human impact on these organisms.

Keywords: Soil texture, conifer communities, Jackson Hole, Grand Teton National Park

---

1 Introduction:

This study was conducted to further investigate the relationship between abiotic and biotic factors, specifically in the Jackson Hole area. Because of the interdependent nature of biotic and abiotic factors, there are many ecological connections that involve all three forest types of Lodgepole Pine, Subalpine Fir, and Whitebark Pine with the environment they thrive in. This relationship, which is only a small part of the larger ecosystem that includes abiotic and biotic elements interacting in tandem, sparked an interest in connections and broader understandings of the surrounding world.

Though all three trees are conifers, they thrive at different mountainous altitudes. The Lodgepole Pine grows at lower elevations, starting at around 6,000 feet above sea level, and the Whitebark Pine at higher elevations beginning at around 9,000 feet above sea level [1]. As the species differ in elevation growth, initial research suggests the species also differ in the type of soils they thrive in.

Previous research indicates that the Subalpine Fir thrives in medium texture soils, while Whitebark Pine lives in coarser soils [1, 2]. In turn, this suggests that coarser textured soils should be found at higher elevations since the Whitebark Pine grows at higher elevations. This conclusion is also supported logically: rain and other water run-off typically deposit heavier sediment first at higher elevations, leaving finer nutrients and minerals to trickle down and fall out later at lower elevations. Additionally, finer soils generally retain less moisture and more nutrients: rainfall and water in areas of fine soil are not absorbed as well as they are in larger, coarser soils, and consequently evaporate faster in finer soil [3]. The Lodgepole, which grows at lower elevations, is normally the first to regrow after forest fires [4]. This supports this study’s hypothesis that lower elevations with finer soils may possibly offer more nutrients for the Lodgepole to regrow quickly.

In this study, soil texture refers to the size of soil particles. Soil as a whole is composed of three main particles: sand, silt, and clay. The smallest and finest of these particles is clay, and the largest and coarsest is sand [5]. The amount of sand, silt, and clay found in any particular sample of soil determines the specific type of soil texture. See Figure 3 for more details.

All three of the conifer species provide valuable habitats and food sources for many animals - including Clark’s Nutcracker, a keystone species in the Greater Yellowstone Area - and protect soil from erosion with their root systems. However, the conifers and soils are at risk from human interference, particularly from outbreaks of blister rust and mountain pine beetle for the Whitebark. For these reasons, studies related to all these forest types, and specifically what textures of soil they thrive on, are crucial in understanding and preserving ecosystems surrounding Jackson Hole.

2 Materials and Methods:

Three sites were chosen within close proximity, along the Lupine Meadows Trailhead in Grand Teton National Park, Wyoming.

Figure 1: Sample Collection Sites at Various Elevations

2.1 Site Characteristics

Over the course of two days, samples from the three sites were collected: Subalpine on the first day and Whitebark and Lodgepole on the second. For consistency, each site was chosen within 100 yards from the trail, and a 30 meter transect was drawn perpendicular to the trail. All sample sites were located on North-facing aspects — the aspect of a slope indicates the way the slope faces. North-facing aspects in the Northern hemisphere generally receive less sun and retain more moisture [6]. Because of this, vegetation growing on North-facing aspects in the Northern hemisphere typically thrives much better than South-facing vegetation.

2.2 Sampling Protocol

After arriving at each conifer stand, transects were drawn perpendicular to the trail, and ten samples were collected along the transect at three meter intervals. For each sample, 25 grams of soil were collected from four inches below the surface of the earth. Each hole was dug with a metal spoon and, after organic material was removed, the soil was weighed with a portable hanging scale to keep the samples as consistent as possible.

To determine the soil texture of the different communities, the ribbon test was performed. Other procedures such as sifting require heavier equipment and drying the soil. Thus, in the interest of time, the ribbon test was chosen for convenience and practicality.

Though subjective, the ribbon test is often used estimate soil texture, as affirmed by Colorado State University, the US Department of Agriculture, and the University of Michigan [5, 7, 8].

Figure 2: Ribbon Test

After collecting 25 grams of soil, the sample was placed into the palm of the hand, and water was added until the soil reached a smooth, plastic consistency similar to dough. Then, the soil was rolled into a ribbon shape, placed between the thumb and forefinger, and pushed by the thumb over the forefinger. The soil broke with its own weight, and the length of the ribbon broken off was measured. The generic soil type was determined by the length of the ribbon that broke off. The ribbon test key indicates the category of soil texture collected. Finally, to further specify the texture of the sample, more water was added to a small pinch of the sample soil, and the soil was placed back into the palm. The coarseness of the soil was determined by the tester’s touch. Together, the length of the ribbon and the texture of the soil in the palm determined the type of soil [5].

3 Results:

A total of 30 samples were collected at the three conifer communities. The raw data can be seen in Tables 1, 2, and 3:

Figure 3: Soil Texture Spectrum

4 Analysis and Conclusion:

4.1 Statistical Analysis

Initially, the P-values generated by a two-factor ANOVA indicated that there was no correlation between data. However, a chi-square with two factors through RStudio produced a P-value of .0049.

With a P-Value of .00049, the null hypothesis was rejected. In comparison to the standard P-Value of .05, there is a statistically significant difference between the soil textures of the three tree stands.

The two factors considered were vegetation type — either Whitebark, Subalpine Fir, or Lodgepole — and soil texture. Soil textures were further simplified into three categories: fine, medium-coarse, or coarse. Whereas in the ANOVA the three sites were viewed as three samples, in the chi-square, the data was considered as 30 separate samples.

Figure 4 indicates the visual representation of the RStudio chi-square: each block — coarse, medium, or fine — indicates the percent composition within each community. For example, more than half of the Lodgepole soil consists of coarse soil.

4.2 Discussion and Further Studies

The data gathered disproved both the proposed alternate and null hypothesis. Instead of soil transitioning from coarse- to fine-textured from high elevations to lower elevations, the opposite was found. This means that, based on collected data, soil texture actually changes from fine to coarse from high to low elevations, contradicting previous research conducted.

Figure 4: Soil Texture of Conifers (Visual Representation of RStudio)

Since the Whitebark Pine grows at high elevations, and has the least exposure to water, it has the most exposure to erosion, which could significantly reduce the particle size of the soil and explain the results of this study.

Although trees and soil are delicately connected, their relationship is affected by many other additional factors, which were not studied in this research project. With time constraints and limited equipment, this study only briefly addresses the complex relationship between soil texture and tree communities. Additional factors, such as soil moisture, pH, and slope, would almost certainly have an effect on the texture of soil found in different stands. For example, the transect drawn in the Subalpine community was drawn along a very steep slope: the beginning of the transect was 42 feet higher than the end of the transect, but this elevation change was not taken into consideration during data analysis.

In retrospect, there are several factors that could be improved for further studies. Firstly, due to time constraints, only one sample could be taken at each tree community. Had more data been collected, the data would have been more reliable. For example, the Lodgepole stand site was close to a stream, which mostly likely affected data due to the alluvial fan. In regards to consistency of sampling, as mentioned before, the slopes of the sites were varied. The samples themselves were collected only four inches from the surface of the earth; topsoil can be easily affected by weather, wildlife, and other factors. With more efficient equipment and more time, soil from deeper horizons can be collected for a more holistic study.

Human error also played a role in the research. Because of time limitations, the ribbon test was conducted by different students along the transect simultaneously. The subjectivity of the ribbon tests leaves room for error, possibly affecting the identification of soil textures.

Regardless, the null hypothesis was rejected: specific trees require specific kinds of soil. This information is crucial in human understanding of ecosystem fragility and ecosystem stability, especially when discussing trees as important as Lodgepole Pines, Subalpine Firs, and Whitebark Pines.

As mentioned before, these conifers play crucial roles in their forest ecosystems. They provide shelter and food for dozens of fauna and stabilize the community around them. For future studies, forest impact on other factors, such as the keystone species Clark’s Nutcracker, grizzly bears, or soil itself would prove interesting for further research.

As human influence spreads across the globe, even the smallest contributions can affect the interconnected systems already in place. This only reinforces the idea that every action has a consequence, and emphasizes the need for careful attention to human actions and further investigation in this subject.

5 Acknowledgements:

Many thanks to Teton Science Schools (TSS) for providing transportation, equipment, and references; to Roland Aranda, Anna Langlois, Victoria Lara, and Naomi Schulberg for help with sample collection and peer-editing; to the graduate students Clare Gunshenan and Peggie dePasquale for supervision and statistics guidance; to Grand Teton National Park; and to the Elementary Institute of Science of San Diego for a summer scholarship to attend TSS and make this research possible.

6 References:

1. Watts, T., & Watts, B. (2008). Rocky Mountain tree finder: a pocket manual for identifying Rocky Mountain trees. Rochester, NY: Nature Study Guild.
2. Arno, S. F., & Hoff, R. J. (1989, June). Silvics of Whitebark Pine (Pinus albicaulis. Retrieved July 10, 2017.
3. University of Hawai'i. (2007). Soil Texture and Soil Structure. Retrieved July 10, 2017.
4. Government of British Columbia. (n.d.). Lodgepole pine. Retrieved July 13, 2017, from https://www.for.gov.bc.ca/hfd/library/documents/treebook/lodgepolepine.htm
5. Colorado Master Gardener Program. (2015). The Size of Sand, Silt, and Clay [Chart]. In Estimating Soil Texture (Vol. 214, pp. 214-1-214-5). Colorado : Colorado State University.
6. National Avalanche Center. (n.d.). Aspect. Retrieved July 15, 2017, from http://www.fsavalanche.org/aspect/
7. Thien, S. J. (1979). Natural Resources Conservation Service. Retrieved August 13, 2017, from https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/edu/?cid=nrcs142p2_054311
8. University of Michigan. (2003). A Guide for Preparing Soil Profile Descriptions. Retrieved July 16, 2017, from http://www.umich.edu/~nre430/PDF/Soil_Profile_Descriptions.pdf