The hidden world of soil seed banks may help restore Western rangelands

Chihuahuan Desert Rangeland in New Mexico

By Joseph Knelman

Though rangelands have long supported ranching and wildlife in the West, many people may better recognize these landscapes as the blurred backdrop to audiobook-fueled road trips than as dynamic ecosystems.  Recently, however, rangelands have gained visibility for their superblooms.  In 2019, rangelands of Southern California drew crowds of 50,000-100,000 visitors on single weekends to witness carpets of poppy wildflowers so dense that the hillsides appeared to be burning in orange flowery flames.

Such superblooms are a manifestation of a soil seed bank, plant-deposited seeds that hang out in soils for several to hundreds of years, waiting for the right conditions to germinate and grow.

For Dr. Akasha Faist, Assistant Professor of Rangeland Sciences at New Mexico State University, the rare floral effulgence of superblooms is not only a moment of natural beauty, but also “a good litmus for what’s in the seed bank.”  Dr. Faist and her team are working to uncover what is in rangeland seed banks and how these seeds can be conjured into action to help restore degraded sites.  New understandings from her lab and collaborators’ research offer a natural solution for restoring and managing economically and ecologically important rangelands that constitute around 30% of land in the US.

Arid and semi-arid rangelands are the focus of seed bank research by Dr. Faist and Kirsten Romig. Kirsten is a range technician with the USDA Agricultural Research Service at the Jornada Experimental Range, and she is conducting her Ph.D. research in the Faist lab. In pursuit of soil seed banks, Faist, Romig, and collaborators sample multiple vegetation and soil types in New Mexican rangelands. Here, the processes of drought, overgrazing, or shrub invasion can irretrievably disrupt the delicate balance of the desert ecosystems meaning they can no longer productively support livestock, wildlife, or water and carbon dynamics. 

Faist and Romig find hope in the top few inches of sandy loam soil that they scoop into paper bags and transport back to the greenhouse for closer examination.  In these soils, through greenhouse emergence trials, they will find viable seeds that ancestral plants have left behind for uncertain times. Like the human-made seed bank vaults that store seeds to protect agricultural resources in the case of catastrophe, soil seed banks are nature’s insurance against harsh conditions and unfavorable years. 

If vegetation is lost because of extreme drought, fire, or the like, the seed bank can restore plant communities when conditions are once again favorable, thus ensuring a functioning, vibrant ecosystem over time; life in the wake of petrichor and ash.  Fortunately for rangeland ecologists looking to unlock seed banks as a tool for land management in drylands, plants that typify the aboveground aesthetic of these rangelands invest mightily in seeds and the dry desert soils are especially conducive to long-term seed storage.

Faist and Romig’s research addresses two primary questions: What seeds are out there in rangeland soil seed banks?; and, how might they be coaxed into action to restore a healthy, productive rangeland?

In a first step to use seed banks to restore healthy rangelands, Faist and Romig are taking an inventory of seed banks, mapping out what seeds different soils contain. The lab has found previously undocumented biodiversity lurking just inches below our feet.  In a recent study led by Romig at  the JER, the team sampled soils across the ~190,000 acre site.  Romig watered 258 soil samples in the greenhouse to reveal what seeds were cached within.  “When I first started watering soils in the greenhouse [seed germination] was almost immediate, like a carpet of seedlings. I had to scramble to get extra people to help me count these seedlings,” Romig described.  “[The experiment] lasted for 2 years and in the second year we were still getting new plant species coming up, also species that had not been found on the range.” 

Seed bank experiment

The study revealed that even when rangelands are degraded aboveground, the seedbank contains immense biodiversity, including plant species that were not known to exist in these locations.  “The seeds belowground are from past time, and [Romig] found a number of species that have rarely if ever been seen in the aboveground vegetation,”  said Faist of the work.

Knowledge of which seeds are in various soils can supplement existing management techniques including seeding -- adding seeds to landscapes.  This longstanding management technique to restore plant communities can be costly and difficult at large scales.  Complementing seeding with the existing seed bank can extend the scale of restoration efforts and reduce costs.  “If we are going to be putting all this work out there putting seeds in the system, then let's think critically about what seeds we need to put out,” Faist said. 

In addition, plants in the seed bank may harbor important adaptations to local conditions that allow the plant to grow even under stressful conditions of the desert southwest. Using DNA analysis, Romig is examining Mesa Dropseed grass populations in the Jornada range to identify potential varieties of this species that may prove “optimal for reseeding mixture” for restoration in the area.

As a next step, the Faist lab is working on the task of summoning existing seed banks into action. “Sometimes a site can be degraded in the plants that are aboveground, but belowground it has a huge suite of species that can actually help; so, what we need to do to release that seed bank is something we think a lot about,” explained Faist.  The lab has tested how additions of water or physical manipulation of the soil may help spur the seed bank into action.  The team is now triangulating on the perfect recipe of conditions to wake up seeds from dormancy.  Recent work has found that patterns of wetting and drying the soil is part of the puzzle in successfully breaking seed dormancy, likely simulating important natural cues for seeds.  Such research will be key for unlocking the power of seed banks in land management.

Overall, as scientists and land managers better characterize seed banks and learn how they can be spurred into action, this untapped natural resource of rangeland soils could become an effective tool to maintain productive landscapes. For top-of-mind issues in the American west -- livestock, water, and wildlife -- Faist and Romig see seed banks as increasingly playing a role in the conversation.

Seed banks may also offer an essential tool for ensuring the resiliency and health of rangeland ecosystems with changing climate.  Increased climate variability, such as in the frequency or severity of droughts, only further entwines seed banks with the future of rangelands. “From a seed bank perspective, those species that can wait out those longer droughts -- when the big rain events do come — may have a better chance in this variable system,” said Faist.

Even having run numerous seedbank experiments with hundreds of samples, Faist and Romig still feel the enchantment of seeing soil-concealed seeds come to life.  With the appropriate conditions multitudes of seeds may awaken, bringing life back to a rangeland otherwise choked out by drought, fire, or overgrazing.  While seed banks offer a practical, natural solution to assist in rangeland management, they also remind us all -- from ecologists, to ranchers, to vacationers -- of the wonder of nature in our everyday lives, even just beneath our feet.  “Things are more dynamic than we know,” Dr. Faist said, “and I love it!