One summer, the Oregon forests experience a drought. The forest’s mosses are shriveled and dormant. In italicized sections that mimic the voice of journal entries, Kimmerer reveals that she is in Oregon to be with her dying grandfather. She is waiting for her daughter Linden’s plane to touch down. Linden has been away at college for her freshman year, and Kimmerer desperately wishes she could turn back time and have her daughter’s childhood back. Returning to her discussion of the mosses, she claims that they are free from “the pain of change” because they accept waiting and “surrender to the ways of rain” (35).

Mosses have no roots to rely on to gather water from the soil; they are dependent on rain and condensation. Mosses are adapted to survive periods of drought, however, because they are poikilohydric plants. Unlike most higher plants, mosses cannot regulate their own internal moisture levels: They swell up with water when it is plentiful, and they dry out almost completely during drought. When they are desiccated in this way, they can wait in a dormant state for rain to come again—unlike higher plants, which often die under such conditions. These periods of dormancy limit the growth of mosses, which cannot photosynthesize in their dried-out state.

The shapes and habits of mosses evolved to retain as much water as possible: They live in intertwined colonies that create a sponge-like effect to hold onto water, for instance, and their leaf shapes and spacings are optimized for preventing as much evaporation as possible. In this way, water and mosses are drawn together and create change in one another: “The shape of the water is changed by the moss and the moss is shaped by the water” (41).

In more journal-style passages, Kimmerer reveals that, in contrast to the mosses, she feels impatient and exposed to the pain of waiting. When Linden arrives, and Kimmerer sees how her daughter seems to be thriving as she grows and changes in the college environment, she stops wishing Linden were still a small child. Kimmerer feels herself expanding in Linden’s presence. She understands that the pain she feels in Linden’s absence is also an expression of fear of loss in general, and she sees how different she is from the patient mosses. She reflects that love between people leads to the same kind of shaping and expanding that occurs between water and moss.

Despite the strategies mosses have for retaining water, they often do become dried out and dormant. As they dry, they curl in on themselves and shrink. After the secretion and storing of an enzyme that will later allow them to repair themselves, their essential functions pause. In more italicized passages, Kimmerer shares images of her grandfather in his hospital bed, his body failing, and then of the women of her family gathered together for her grandfather’s burial. When rain finally comes to Oregon again, the communal nature of the mosses allows them to efficiently trap water. They quickly rebound, and Kimmerer hurries outside to watch their renewal happen.

In the Adirondacks, Kimmerer visits Aimee, a researcher studying the role mosses play in ecological succession. Aimee is working at an abandoned mining site, where plants struggle to survive on the dry, disrupted land. She has discovered that in some spots, flowers have taken hold—and that these spots are covered with Polytrichum moss. Together, Kimmerer and Aimee are trying to discover whether the mosses or the flowers were the first to spring up, and why. This will tell them something about succession—the process through which early species create favorable conditions for the growth of later species in a given area. They examine the moss growing under some small tents Aimee has set up and find that it is softer and greener than the unshaded mosses. The unshaded ground is crusted with microbes that are taking advantage of the shade offered by the mosses. The mosses are also helping prevent erosion in the dry soil. Not only do their rhizoids bind the dust together, but the mosses contribute organic matter that sifts down into the soil and helps to trap water, gradually changing the nature of the soil.

Aimee places brightly colored beads the size of plant seeds on various surfaces and tracks them over time. She finds that the ones on bare soil blow away. They stay in place the best where there is Polytrichum moss. Next, she releases real seeds and tracks their germination rates. Once she has established that they germinate best in the areas of moss, she and Kimmerer design an experiment to see whether any kind of protective shelter will perform the same function or if there is something special about the moss itself. They place pieces of carpet that mimic the structure of different mosses on the bare ground and sow seeds on both the carpet and the actual Polytrichum moss. They find that the living surface of the moss is a far better host to the seeds, which sprout there much more successfully. Through experiments like this, Kimmerer has come to see moss as integral to “binding up the wounds of the land” in disturbed sites like the abandoned mine (50).

When Kimmerer finally got the opportunity to travel to the Amazon rainforest, she found it teeming with life and yet strangely familiar. It felt to her like “walking through a moss” (52). The similarities between the microcosm of a moss and the rainforest are not just visual. Both contain a complex food web with carnivores, herbivores, and predators. Both exhibit nutrient cycling, mutualism, and competition. When she climbed into an observation platform in the canopy, she could see that the mosses along the tree branches, epiphytes themselves, also supported other epiphytic plants.

Even outside the rainforest, mosses commonly support epiphytes in the form of algae colonies, liverworts, and even other mosses. Miniscule invertebrates called rotifers may live in the tiny pools of water held in the curled leaves of mosses. The microcosm of a moss is stratified, just as the larger world of the rainforest is, into layers that support different species. A fine mist of debris constantly filters from the upper layer down into lower layers, similar to the way leaves, flowers, fruit, nuts, and other debris rain down from the rainforest canopy onto its floor. The organic debris accumulates and eventually provides anchorage for larger, rooted plants. A single gram of moss can play host to hundreds of thousands of other organisms. Kimmerer wishes that she could walk through a moss “forest” as easily as she once walked through the rainforest in Ecuador.

Because mosses are so hospitable to tiny creatures, many entomologists believe that moss mats may have provided habitat for the earliest evolution of insects. Even today, many insect species rely on the humid environment within mosses as a spot to lay eggs. Kimmerer describes some of the fauna that live among mosses, some feeding on the flora supported by moss and others preying on other tiny creatures. Just as birds and insects assist rainforest plants to reproduce by carrying pollen and other reproductive material from place to place, the microfauna within moss colonies can help moss sperm move from place to place. One species that Kimmerer has spent time observing in moss colonies is the tardigrade, an eight-legged micro-animal sometimes called the “waterbear.” This creature, she says, may be the species most dependent on the moss ecosystem. Tardigrades are so small that they can cross between plants on bridges of water. Like mosses, they shrink into a dormant and desiccated form when water runs out, and like mosses, they swell up and return to their active form when water is abundant again.

Kimmerer recalls a summer she spent as a graduate student working along the Kickapoo River in Wisconsin. She decided to study the striking pattern of stratification of the mosses living on the cliff walls that lined the river. With all of her gear tied down inside a canoe that floated beside her, she stood in the river and observed the way that each species seemed to have its own separate territory. She wondered what variable determined how high above the river each moss grew. The highest layer consisted not of moss, she realized, but of a liverwort called Conocephalum conicum. She used a voice recorder for data about the distribution of each species, and at night when she transcribed these tapes, she often found amusing unintended additions to her recitation of numbers: a conversation with canoers floating past, her own splashing and squealing as something in the water nibbled at her, and so on.

Kimmerer’s data disproved her initial hypothesis that some variation in temperature, humidity, light, or rock type was responsible for the stratification of plant life along the river cliffs. She wondered if the stratification was related to competition between species. She grew samples of the moss from the bottom layer—Fissidens—and the liverwort at the top—Conocephalum—next to one another in her lab. She found that the liverwort consistently overwhelmed the moss and realized that, for Fissidens, growing a significant distance from Conocephalum was adaptive. This made her wonder why Conocephalum did not simply colonize the entire rock face. She considered how periodic flooding might impact these species in different ways and designed an experiment to test how each species tolerated being submerged for long periods. This showed her that Conocephalum needed to stay high on the cliff face to avoid being submerged during a flood. Fissidens, by contrast, was extremely tolerant of being submerged, and this is why it dominated the space immediately above the water’s usual level.

Kimmerer next turned her attention to the many species that lived in the space between Fissidens and Conocephalum. None of these dominated space as clearly as did Conocephalum and Fissidens. Kimmerer explains that this illustrates the intermediate disturbance hypothesis: species variation is highest where disturbances—waves, floods, fire—is moderate. Where disturbance is constant or completely absent, monocultures are more frequent.