Some Soil Microbes Don’t Mind Our Camping Trips

In many places in the United States, the beginning of October marks the end of the camping season, but here in Southern California the heat is becoming more bearable and camping season is in full swing. In general, camping is considered a low impact activity. It doesn’t require flying to another state, staying in a swanky hotel, and the overall carbon footprint of a camping trip is low. In 2020, the amount of people camping on our public lands has skyrocketed as COVID-19 prevents us from jet setting around the world. But have you ever considered what impact camping has on the soil?

Think about it: you drive to a campsite, tramp around the soil, hammer in the stakes for the tent, and walk around the site enjoying the views. If you are camping in a campground, the soil endures the same treatment day after day. 

Healthy soil microbes are important for a variety of reasons. They can store carbon and reduce the impacts of climate change. They provide nutrients such as nitrogen for plants. Essentially, a healthy soil leads to a healthy ecosystem. Can camping change the health of the soil microbes?

Well it’s 2020 and we all need some good news. 

Camping can lead to a variety of disturbances such as trampling, soil compaction, and damage to the plant life. These disturbances may impact the microbes and other organisms living below the soil surface. Image Source: Microbes by Alice Noir from the Noun Project.

In a new study, from Cornell University and the University of Arizona, Kariuki and colleagues found that the soil microbes in the Southern Arizona mountains are resistant to seasonal camping! When an ecosystem is resistant to a disturbance it means that once disturbed, it can recover to the pre-disturbance state. 

To understand the resistance of soil microbes to camping, the researchers studied campsites in the Santa Rita Mountains in Southeastern Arizona where over 100 established campsites exist. Between 2013 and 2015, the researchers installed fences around four campsites to limit the disturbance. Since the campsites in this area are primarily used on a seasonal basis between September and December and sites are heavily used during this period, they were classified as having low frequency but high intensity disturbance. They also included active campsites, unfenced and undisturbed control areas where camping is not present, in this study. 

Within each site, they measured the total cover of the plants and collected soil samples from open spaces and from below the most common tree in the area, Prosopis . Trees are not the most dominant vegetation in the area but the researchers hypothesized that the presence of the tree may create more fertile and healthy soil. 

The Santa Rita Mountains in Southeastern Arizona are a semi-arid ecosystem that receives most of its moisture during the summer monsoon season. Image Source: Wikimedia Commons

$1LENCE D00600D at English Wikipedia, CC BY-SA 3.0, via Wikimedia Commons

There were no differences in soil microbial response to camping between the active campsites and undisturbed areas. Interestingly, the researchers found that plant cover did not differ between the campsites, nor did the soil water content. The dissolved organic carbon and total dissolved nitrogen, both measurements of soil nutrients, were elevated in samples from below the tree canopy but were unaffected by camping disturbance. Enzyme activity, which is important in determining how active the microbes are, did not differ between camping disturbances nor was it affected by the tree cover but was correlated with the soil moisture content. Microbial biomass, the measure of how many microbes are in the soil, was greater under the tree but did not differ between the camping treatments. 

So can my conscience be at rest when I go camping next weekend?

Prosopis velutina, or velvet mesquite, is the tree species in this study. It creates islands of fertility in the soil below its canopy. Image Source: Wikimedia Commons

Adbar, CC BY-SA 3.0, via Wikimedia Commons

The short answer is yes! The long answer is yes with a caveat. If I am camping in the Santa Rita Mountains then the soil is resistant. This means that my presence will not significantly alter the natural microbial ecosystem. In the Santa Rita Mountains many of the soil properties and the plant cover were unaffected by the disturbance of camping, indicating this ecosystem may be resistant to this type of disturbance. However, the authors mention previous studies in wetter, temperate systems such as North Carolina or Ontario that show that camping has a negative effect on plant cover, although they did not specifically address the effect on soil microbes.

The researchers propose a variety of reasons to explain this resistance in the Santa Rita Mountains. 

First, Santa Rita is accustomed to long periods without water with sudden bursts of moisture during the monsoon season. This creates an ecosystem full of plants, animals, and even soil microbes that are used to adapting to constantly changing conditions. These adaptations may help plants withstand the tampling of campers as they walk around their sites. Additionally, the vegetation cover at these sites is low to begin with so there are just less plants to trample and the period of the year when there are no campers may allow the ecosystem to recover. 

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Most of the moisture in this ecosystem comes from the monsoon, pictured here. The seasonal pulses of water most likely has a greater effect on the soil microbes than seasonal camping. Image Source: Wikimedia Commons

Nicholas Hartmann, CC BY-SA 4.0, via Wikimedia Commons

The seasonal nature of the campers in this area may also help the soil maintain their functioning because there are long periods of time throughout the year when they are not disturbed. In semi-arid and arid ecosystems such as the Santa Rita Mountains, water is the most common stressor, not human tampling, therefore the functioning of the soil microbes is likely more dependent on the seasonal pulses of water rather than the seasonal nature tourism. 

The researchers determined that the soil below the tree, Prosopis, is benefiting from a fertility island formed by the tree. Litter, carbon, and nitrogen were greater under trees than in open spaces which indicates the tree is creating pockets of soil fertility, likely due to the ability of Prosopis to increase soil moisture. 

All in all, this study demonstrates that the soil microbial communities are resistant to camping and the presence of Prosopis helps support the microbial communities by augmenting water, carbon, and nitrogen. 

Biological soil crusts are common in semi-arid ecosystems and are a sensitive soil community that is not resistant to camping. Please avoid camping on them. Photo by author.

So next time you go camping in the Arizona mountains, or possibly in other semi-arid ecosystems, set your mind at ease knowing the soil microbes and plants will recover from your visit. But please, be careful where you put your tent or camper and ensure you are not camping directly on top of any plants or delicate soil communities. 

Citation: Kariuki, S., R.E. Gallery, J.P. Sparks, R. Gimblett, M.P. McClaran. Soil microbial activity is resistant to recreational camping disturbance in a Prosopis dominated semiarid savanna. 2020. Applied Soil Ecology 147: 103424.

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Brianne Palmer

I am a PhD candidate at San Diego State University and the University of California, Davis studying how biological soil crusts respond and recover from fire. Most of my research is in coastal grasslands and sage scrub. We use DNA and field measurements to understand how cyanobacteria within biological soil crusts help ecosystems recover after low severity fires. I am also involved with local K-12 outreach within the Greater San Diego Metro Area.

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