As a research ecologist, I've spent much of my career trying to understand the complex interactions that shape our planet's ecosystems. For nearly three decades, a question has lingered in my mind: How does the conversion of native perennial shrublands to invasive annual grasslands impact the storage of carbon in our soils? This isn't just an academic curiosity; it's a question with profound implications for how we manage our lands in the face of a changing climate.

The research journey that led to our recent publication in Communications Earth & Environment, a Nature Portfolio journal, began with recognizing that the existing scientific literature on this topic was incomplete. Many previous studies only scratched the surface – literally! They only sampled soil down to 30 centimeters or less, neglecting the deeper depths where significant carbon storage can occur, particularly in dryland systems. This realization sparked a collaboration with my USGS colleagues, Dr. Toby Maxwell, a soil biogeochemist, and Samuel Price, an ecologist and GIS specialist.

Our research took a significant leap forward when we partnered with Dr. Harry Quicke, North America Solutions Development Manager for Environmental Science U.S. LLC, doing business as Envu.Dr. Quicke and his Envu colleagues recognized the importance of our research question and provided the financial backing we needed to conduct a truly comprehensive two-year study. This partnership allowed us to address the limitations of past research and pursue a more rigorous approach.

Digging Deep, Unveiling a Hidden Carbon Story

We embarked on an ambitious field campaign, carefully selecting study sites across three distinct ecoregions in the western United States. We wanted to ensure that our comparisons between invaded and uninvaded grasslands were as controlled and precise as possible. And, critically, we dug deeper – sampling soil cores down to a full meter. This involved collecting and analyzing over 1,000 soil samples, a testament to the dedication of our field team.

Think of it this way: Imagine trying to assess the wealth of people in a community by only looking at the money they have in their checking accounts. You'd be missing a big part of the picture – their savings accounts, retirement funds, and other assets. Similarly, previous studies that only sampled near the soil surface or that didn’t consider microsite variability could not accurately account for the impact of invasive grasses on soil carbon storage.

Our findings, published in the paper “Annual grass invasions and wildfire deplete ecosystem carbon storage by >50% to resistant base levels,” were eye-opening. We discovered that the conversion of deep-rooted perennial shrublands to shallow-rooted annual invasive grasslands resulted in a substantial reduction of soil carbon – between 42% and 49%.

Why This Matters for a Changing Climate

Our research underscores the vulnerability of soil carbon in rangelands. Globally, vast areas of native shrublands have already succumbed to grass invasion, and this process continues at an alarming pace. The loss of soil carbon from these lands represents a significant release of carbon dioxide into the atmosphere, contributing to the very problem we're trying to solve – climate change.

The good news is that our research also points toward solutions. As Dr. Maxwell eloquently stated in our paper, "Maintaining intact sagebrush-steppe by protecting against the annual grass-fire cycle appears to be a highly effective 'nature-based' solution to the global greenhouse gas problem, stabilizing soil carbon at magnitudes relevant to the global carbon cycle."

Prioritizing the protection of intact native perennial systems is critical for preventing further soil carbon loss and mitigating the impacts of climate change. Our findings have important implications for land management agencies tasked with safeguarding our public lands. Proactive land management strategies thatprotect native shrublands from annual grass invasion could keep existing carbon stores secure. Such actions not only avoid soil carbon losses, but also provide a host of other benefits, including improved wildlife habitat, increased forage production and reduced wildfire frequency.

Our collaboration with Envu was instrumental in making this research possible. Their financial support allowed us to pursue a level of scientific rigor that was previously unattainable. This type of partnership between industry and academia is critical for addressing complex environmental challenges.

This research is just the beginning. We are currently engaged in Phase 2 of this project, which involves a more extensive sampling effort across a broader geographic range. With continued support and collaboration, we can further refine our understanding of carbon dynamics in rangelands and develop effective strategies for managing these vital ecosystems for a more sustainable future.