A thin autumn mist drifts low across New Hampshire’s White Mountains, yet the laser-bright scarlet of sugar maple leaves still glows beneath the valley’s canopy. Inside each fading blade, microscopic conveyor belts are hard at work, packing away nitrogen (N) and carbon (C) atoms before the leaf’s final descent—an act as ordinary as litterfall and as astonishing as a cargo ship docking inside a cell. If you could lean close enough, the rustle would sound like warehouse doors gliding shut for winter.
Foliar resorption of beech and maple along an elevation gradient in a northern hardwood forest by Timothy J. Fahey, Natalie L. Cleavitt, Pamela H. Templer, Peter M. Groffman, Amey S. Bailey, Stephen B. Caron, and Geoffrey Wilson renders those invisible mechanics visible. Published in Forest Ecosystems (Vol. 13, 2025), the study decodes how two stalwart species—American beech (Fagus grandifolia) and sugar maple (Acer saccharum)—tune their internal recycling systems along a 400-meter climb at Hubbard Brook Experimental Forest (HBEF). The authors collected sunlit branches, sifted litter through nylon screens, and probed soils whose sandy-loam particle might span half a millimeter—roughly the breadth of a human eyelash.
HBEF has long served as a planetary archive. In 1963 the U.S. Forest Service began gauging every raindrop in this 3,160-hectare watershed; by 1970 Gene Likens and colleagues discovered acid rain here, spurring the Clean Air Act Amendments of 1990. Those amendments throttled atmospheric nitrogen deposition throughout the northeastern United States, courting a new era of what ecologists call N oligotrophication—a drift toward nutrient scarcity. Fahey’s team asked whether beech and maple compensate by squeezing more N back into stems and roots before the leaves fall.
Their first metric, NRP (nitrogen-resorption proficiency), simply measures how little N remains in litter; lower litter N means sharper proficiency. “Foliar N resorption proficiency (NRP) increased significantly at lower elevations for both sugar maple and American beech, the dominant species in these forests,” report the authors. Imagine the difference this way: a sugar maple at 395 meters repackages enough N to trim its leaf litter concentration to 0.63 percent—about the weight fraction of vanilla in an ice-cream pint—while its cousin at 780 meters leaves a thicker nutrient footprint.
Efficiency tells another tale. NRE (nitrogen-resorption efficiency) is the percentage of N withdrawn. “Foliar N resorption efficiency (NRE) also decreased with increasing elevation, but only in one year,” observe the authors, hinting at weather’s caprice. In 2021, a 6-day-longer autumn gave both species extra time to shuttle proteins into woody vaults. By 2022, a shorter senescence curtailed the process, underscoring that climate’s tempo matters as much as its temperature.
Soil chemistry threaded through every measurement. HBEF’s higher plots hold more nitrate (NO₃⁻, a nitrogen atom bonded with three oxygens) because colder winters slow root uptake and microbial transformations. Yet, paradoxically, leaves resorbed less there. “Both species exhibited strong negative relationships between NRP and soil N availability,” write the authors. An abundance of soil N apparently lulls the trees into relaxed housekeeping, a botanical version of cheap energy discouraging conservation.
Species identity also stamped the results. Beech leaves—each about the size of a metro ticket—lost 35 percent of their carbon mass during senescence, compared with maple’s 13 percent. That lost carbon is not wasted; it shuttles with amino acids into perennial tissues, fueling next spring’s flush. “Both species also exhibited strong correlations between resorption efficiency of N and C, but resorption of both elements was much greater for beech than sugar maple, suggesting contrasting mechanisms of nutrient conservation between these two widespread species,” say the authors.
Hard numbers accentuate the comparison. The team computed a mass-loss correction factor (MLCF) to account for tissue shrinkage: beech scored 0.64, maple 0.86. Translated, a beech leaf the mass of a postage stamp relinquishes roughly one-third of its bulk during resorption, whereas maple yields only one-eighth. That disparity may arise from their mycorrhizal alliances—beech partners with ectomycorrhizal fungi (EM) that demand generous carbon subsidies, prompting higher internal recycling; maple relies on arbuscular mycorrhizae (AM), cheaper to feed.
The broader chronicle stretches back to HBEF’s seed traps, which have tallied mast years since 1993. In 2023 both species unleashed bumper crops—an echo of evolutionary strategy linking nutrient hoarding to reproduction. Historical foliar data show maple’s N content climbing steadily with altitude for three decades, while beech holds steady—a divergence the new study reinforces.
Resorption also converses with policy. After four decades of declining nitrogen pollution, soils at lower elevations now supply less inorganic N, and trees answer by tightening their loops. “Thus, we anticipate that with climate warming and decreasing N inputs, northern hardwood forests can be expected to exhibit stronger N conservation via foliar resorption,” caution the authors. If litter C:N ratios widen, microbial decomposers may immobilize nitrogen longer, slowing its return to roots and reshaping forest productivity under future CO₂-rich skies.
Forest ecologists once pictured nutrients descending lazily each autumn like coins tossed from a balcony. Fahey’s elevation transect reveals something craftier: a species-specific calculus in which every amino acid is negotiated, packed, and stored—an anticipatory dance that feels, in its precision, almost extraterrestrial. As climate and deposition regimes tilt, these living algorithms adjust, making the canopy not merely a palette of pigments but a dynamic, self-programming archive of elemental economy.
Fahey, T. J., Cleavitt, N. L., Templer, P. H., Groffman, P. M., Bailey, A. S., Caron, S. B., & Wilson, G. (2025). Foliar resorption of beech and maple along an elevation gradient in a northern hardwood forest. Forest Ecosystems, 13, 100304. https://doi.org/10.1016/j.fecs.2025.100304