Nutrient cycling in Nothofagus pumilio forests along an altitudinal gradient in Tierra del Fuego, Argentina

Nothofagus pumilio (lenga) forests form monocultures from sea level to timberline in Tierra de Fuego, Argentina. Past studies suggested that the life form change from erect forest to krummholz had advantages to forest function. Aboveground net primary productivity (NPP) and organic matter production per unit leaf area and growing season day were higher in krummholz than in adjacent short erect forests at lower elevation. We compared tall erect, short erect, and krummholz lenga stands in terms of the concentration, accumulation, fluxes, turnover, and use-efficiency of nutrients (N, P, K, Ca, and Mg) along an elevation gradient (220-640 m) in Tierra del Fuego (Valle de Andorra, 54°9′S, 68°2′W). With few exceptions, patterns of decreasing values of nutrient concentration, nutrient stock, nutrient flux, and nutrient turnover reversed at the krummholz, which had higher values of these parameters than an adjacent short erect forest at lower elevation. Nutrient cycles accelerated at the krummholz but nutrient use-efficiency of organic matter production and nutrient return to the forest floor decreased. Several functional attributes of krummholz support the notion that this life form has functional advantages at timberline. For example: (1) a shift towards fast turnover compartments for nutrient storage; (2) a switch from high storage of nutrients in stemwood biomass to nutrient storage in branch biomass; (3) faster rates of internal nutrient transfer (recycling and retention); (4) greater dependence on biotic recycling of nutrients; (5) morphological characteristics associated with leaf size, leaf duration, number of leaves, and leaf area to sapwood area ratio. Nutrient cycling attributes measured in Tierra del Fuego span values reported for forests across temperate and boreal latitudes, with krummholz and tall erect forests representing either the low or the high values. Lenga krummholz is different from coniferous krummholz in North America's tundra in that lenga appears to be a nutrient-rich forest that acts as a nutrient sink, while coniferous krummholz scavenge for nutrients on tundra soils and reduce their nutrient pools.