The autumn sun climbs a hand-span above the White Mountains, gilding ridgelines the color of boiled sugar as samaras—those paired-wing sugar-maple seeds—spiral downward like pocket-size helicopters. Beneath them, four forest stands stretch north to south across New Hampshire, their canopies fluttering in shades from bronze to vermilion. To the casual hiker the scene seems perfectly stable. Look closer, though, and a quieter drama appears: young sugar-maple seedlings, each scarcely taller than a coffee mug, survive in some groves yet vanish in others. Their fate matters to everything from maple-syrup economies to nitrogen cycling, and it is that miniature drama that forest ecologist Natalie Cleavitt and colleagues set out to decode.
“Sugar maple seedling regeneration of a natural cohort across a latitudinal gradient in New Hampshire,” by Natalie L. Cleavitt, Carrie Deegan, Sarah Thorne, Ana Suppé, Kimberly L. Colson, and Wanda Rice, follows a single cohort of seedlings for five years across four sites—Monadnock, Yatsevitch, Sudrabin, and Kauffmann—spanning nearly one degree of latitude, a month of growing-season length, and a 200-meter rise in average snow depth. Their methods range from motion-triggered cameras that log deer visits to common-garden pots where soil microbes from each site contend under controlled light.
The puzzle is older than acid rain legislation. Since the 1970s foresters have watched sugar-maple (Acer saccharum) regeneration falter in parts of New England and Québec. Early blame fell on cation loss from acid precipitation; later studies implicated deer browse, American-beech thickets, and warming winters that steal insulating snow from fragile roots. Cleavitt’s project tests all three lines of thought in living seedlings rather than retrospective ring widths. As the authors write, “Sugar maple, an economically and ecologically important tree in the northern hardwood forest, has experienced regeneration failure that … has been variously attributed to soil acidification, impacts of climate change, and effects of species composition.”
One surprise emerges before the first sapling reaches ankle height: “Overall, sugar maple seedling survival was highest in the two sites with lower sugar maple abundance,” the authors report. Where adults dominate the canopy—more than 50 % basal-area share—the seedlings fare worst. That pattern echoes the Janzen–Connell framework, in which host-specific enemies concentrate under parent trees. Indeed, seedling leaves at Yatsevitch and Kauffmann showed twice the caterpillar and fungal damage of their counterparts at less maple-heavy stands. “Conspecific impacts on seedling survival were related to foliar pests and fungal pathogens rather than through soil feedbacks,” the authors conclude, undercutting the long-standing assumption that depleted calcium or excess aluminum is the primary villain.
The team’s common-garden experiment isolates soil chemistry from biotic attack. Seedlings planted in Yatsevitch’s calcium-rich loam grow fastest—even after that soil has been sterilized—while those in the poorer Monadnock substrate lag, their total biomass after three months no heavier than a standard #2 pencil. Yet the richest soil does not rescue field seedlings when leaf-eating insects thrive. The inference is stark: chemistry sets the stage, but biology writes the script. “Seedling leaf area, leaf damage, and site had the greatest contribution to seedling survival patterns,” the authors state, a finding that reframes foresters’ reliance on lime treatments alone.
Climate enters the story sideways. The northernmost Kauffmann site boasts snowpack deep enough—up to one meter, roughly a Labrador retriever’s shoulder—to shield roots from freeze-thaw shearing, yet it shows the lowest seedling survival. Longer snow cover shortens the photosynthetic season, yielding tiny leaves that gather less carbon before winter’s shutdown. In the study’s mast year, Kauffmann’s mature maples released 38 viable seeds for every new seedling—an efficient conversion—while Yatsevitch required 128. Seed rain, therefore, cannot offset high juvenile mortality where pests flourish.
History adds another layer. Calcium addition at Hubbard Brook Experimental Forest once seemed to promise a maple revival, but American beech quickly filled sapling gaps, shading out maple shoots. Cleavitt’s plots illustrate the same tension: beech saplings dominate two of four stands, converting light into an understory dusk that sugar-maple seedlings, calibrated to patchy sunlight, tolerate poorly. The new research positions stand diversity as both shield and scaffold. “These results lend support to other studies encouraging promotion of stand tree diversity and avoidance of monocultures,” the authors write—an ecological chorus growing since the 1990s push to convert single-species sugarbushes into mixed stands resilient to pests and drought.
Perhaps the most forward-looking twist comes from predator cameras. White-tailed deer, plentiful in the state’s fertile river valleys, browse sugar-maple seedlings preferentially. At Yatsevitch the lens captures repeated nighttime visits; seedling stems vanish between surveys. That pressure climbs as winters warm and deer overwinter farther north. Add climate-accelerated insect lifecycles, and the maple future resembles a finely tuned feedback machine sensitive to species mix, not merely temperature or pH.
Size helps translate the stakes. A mature sugar maple can exceed 30 meters—taller than a ten-story building—and store more than a metric tonne of carbon in wood and roots. Lose a cohort, and the gap opens wide enough to spin a carousel of hardwood replacements: beech, red maple, birch. Gain a cohort, and you anchor centuries of syrup harvests and autumn tourism. Cleavitt’s five-year window on saplings hardly settles centuries, yet it shifts the management lens from chemistry labs to community ecology.
The study’s practical epilogue feels almost science-fictional: foresters might seed focal predators of maple-specific caterpillars or engineer silvicultural mosaics that mimic old-growth heterogeneity, all to secure the crimson canopy that draws leaf-peepers each October. In a warming, browsing, fungus-threaded world, that mosaic may prove as valuable as calcium, and far harder to counterfeit.
Cleavitt, N. L., Deegan, C., Thorne, S., Suppé, A., Colson, K. L., & Rice, W. (2025). Sugar maple seedling regeneration of a natural cohort across a latitudinal gradient in New Hampshire. Canadian Journal of Forest Research, 55, Article e0314. https://doi.org/10.1139/cjfr-2024-0314