A Height Threshold Redefines Functional Communities: Structural Transition Between Shrublands and Alpine Forests of Polylepis tarapacana in the Argentine Altiplano. P.9–29

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https://doi.org/10.37482/0536-1036-2026-3-9-29

Abstract

The high-Andean forests of Polylepis tarapacana at the global treeline form a structural continuum between shrublands and forests, complicating their functional classification. This study evaluates whether a discrete height threshold – Mean Dominant Height ≥ 2 m – defines a genuine ecological transition between these formations in the Argentine Altiplano, aiming to validate this threshold, identify its predictors, and assess its consequences for the ground-layer vegetation. Ninety-six forest inventory plots were analyzed and classified as “Forest” (mean dominant height ≥ 2 m) or “Shrubland” (mean dominant height < 2 m). Structural variables (basal area, density, diameter distribution), proportions of life forms (arborescent, dwarf tree, shrub, brousse tigrée), allometric parameters, and ground cover composition were compared. Analyses included Principal Component Analysis, non-parametric tests, logistic regression models, and indicator species analysis. The 2 m threshold discriminated two clearly distinct communities. “Forests” (19.4 % of plots) exhibited greater basal area (2.8 times higher), diameter diversity, structural complexity, and a higher proportion of arborescent life forms. They showed a more efficient height- diameter relationship and a distinctive ground cover with greater cover of cushion plants and specialist indicator species (e.g., Senecio nutans). “Shrublands” were dominated by juvenile individuals, shrubby forms, and heliophytic perennial shrubs. The probability of achieving a forest state was positively predicted by the presence of arborescent forms and a favorable substrate (Favorable Substrate Index). The mean dominant height ≥ 2 m threshold constitutes a quantifiable ecological tipping point separating distinct successional and functional states in Polylepis tarapacana. This structural criterion synthesizes profound changes in community architecture, microclimate, and associated biotic assemblages. The findings provide a robust framework for the operational classification, monitoring, and priority conservation of these vulnerable alpine ecosystems, moving beyond purely morphological definitions towards a characterization based on ecological functionality.

Acknowledgments: We thank those researchers who, for years, questioned whether Polylepis tarapacana formations could be called forests, preferring terms like “forestlands” or “shrublands”. Their persistent skepticism challenged us to write this. Thanks to them, we now have clear, height-based criteria aligned with the UN definition. We are grateful for their opposition; it pushed us to do better. We also thank Argentina’s public, free, and co-governed university system. Despite devastating defunding and difficult times, we published this work through collective effort. This paper proves that public university researchers do not give up.

Authors

Juan Manuel Cellini¹, Doctor of Natural Sciences, Assoс. Prof.; ResearcherID: PCU-0716-2025, ORCID: https://orcid.org/0000-0002-7870-5751
Federica Germann^1*, Postgraduate Student, Research Scientist; ResearcherID: PDW-2782-2025, ORCID: https://orcid.org/0009-0005-5837-2266
Victoria Lien López^1,2, Doctor of Agriculture and Forestry, Postdoctoral Research Scientist, Assoc. Prof.; ResearcherID: PDW-2312-2025, ORCID: https://orcid.org/0000-0002-0035-7435
Rocio Lara Arcidiacono³, Postgraduate Student, Research Scientist; ORCID: https://orcid.org/0009-0002-0807-7152
Julián Rodríguez Souilla³, Doctor of Agriculture and Forestry Sciences, Postdoctoral Research Scientist; ResearcherID: PDW-2127-2025, ORCID: https://orcid.org/0000-0001-8772-2310

Affiliation

¹Universidad Nacional de La Plata, Facultad de Ciencias Agrarias y Forestales (UNLP), Laboratorio de Investigaciones en Madera (LIMAD), Diagonal 113 # 469, La Plata, Provincia de Buenos Aires, Argentina, 1900; JMC@agro.unlp.edu.ar, Federica.Germann@agro.unlp.edu.ar*, Victoria.Lopez@agro.unlp.edu.ar
²Centro Científico Tecnológico La Plata (CCT), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Calle 8 # 1467, La Plata, Provincia de Buenos Aires, Argentina, 1900; Victoria.Lopez@agro.unlp.edu.ar
³Centro Austral de Investigaciones Científicas (CADIC-CONICET), Bernardo Houssay # 200, Ushuaia, Tierra del Fuego, Argentina, 9410; RocioArcidiacono@conicet.gov.ar,
J.Rodriguez@conicet.gov.ar

Keywords

Polylepis tarapacana, treeline, structural threshold, mean dominant height, high-Andean forests, functional classification, alpine ecosystems, Argentine Altiplano

For citation

Cellini J.M., Germann F., López V.L., Arcidiacono R.L., Rodriguez Souilla J. A Height Threshold Redefines Functional Communities: Structural Transition Between Shrublands and Alpine Forests of Polylepis tarapacana in the Argentine Altiplano. Lesnoy Zhurnal = Russian Forestry Journal, 2026, no. 3, pp. 9–29. (In Russ.). https://doi.org/10.37482/0536-1036-2026-3-9-29

References

1. Assmann E. The Principles of Forest Yield Study: Studies in the Organic Production, Structure, Increment, and Yield of Forest Stands. Oxford, Pergamon Press, 1970. 506 p.

2. Ball M.C. The Role of Photoinhibition During Tree Seedling Establishment at Low Temperatures. Photoinhibition of Photosynthesis from Molecular Mechanisms to the Field. Ed. by N.R. Baker, J.R. Bowyer. Oxford, BIOS Scientific Publishers, 1994, pp. 365–376.

3. Boza Espinoza T.E., Kessler M. A Monograph of the Genus Polylepis (Rosaceae). PhytoKeys, 2022, iss. 203, pp. 1–274. https://doi.org/10.3897/phytokeys.203.83529

4. Brooker R.W., Maestre F.T., Callaway R.M., Lortie C.L., Cavieres L.A., Kunst- ler G. et al. Facilitation in Plant Communities: The Past, the Present, and the Future. Journal of Ecology, 2008, vol. 96, iss. 1, pp. 18–34. https://doi.org/10.1111/j.1365-2745.2007.01295.x

5. Carilla J., Halloy S., Cuello S., Grau A., Malizia A., Cuesta F. Vegetation Trends over Eleven Years on Mountain Summits in NW Argentina. Ecology and Evolution, 2018, vol. 8, iss. 23, pp. 11554–11567. https://doi.org/10.1002/ece3.4602

6. Cierjacks A., Rühr N.K., Wesche K., Hensen I. Effects of Altitude and Livestock on the Regeneration of Two Tree Line Forming Polylepis Species in Ecuador. Plant Ecology, 2008, vol. 194, pp. 207–221. https://doi.org/10.1007/s11258-007-9285-x

7. Dufrene M., Legendre P. Species Assemblages and Indicator Species: The Need for a Flexible Asymmetrical Approach. Ecological Monographs, 1997, vol. 67, no. 3, pp. 345–366. https://doi.org/10.2307/2963459

8. Efron B., Tibshirani R.J. An Introduction to the Bootstrap. New York, Chapman & Hall, 1993. 436 p. https://doi.org/10.1007/978-1-4899-4541-9

9. Franco P., Cáceres C., Navarro M., Jove C., Ignacio J., Oyague E. Bosques de Polylepis tarapacana en la cuenca Maure, extremo Sur del Perú. Oportunidades para su Conservación. Estudios Geográficos, 2021, vol. 82, no. 290, art. e059. (In Span.). https://doi.org/10.3989/estgeogr.202071.071

10. García-Plazaola J.I., Rojas R., Christie D.A., Coopman R.E. Photosynthetic Responses of Trees in High-Elevation Forests: Comparing Evergreen Species Along an Elevation Gradient in the Central Andes. AoB PLANTS, 2015, vol. 7, art. plv058. https://doi.org/10.1093/aobpla/plv058

11. Garreaud R., Vuille M., Clement A.C. The Climate of the Altiplano: Observed Current Conditions and Mechanisms of Past Changes. Palaeogeography, Palaeoclimatology, Palaeoecology, 2003, vol. 194, iss. 1-3, pp. 5–22. https://doi.org/10.1016/S0031-0182(03)00269-4

12. Germino M.J., Smith W.K., Resor A.C. Conifer Seedling Distribution and Survival in an Alpine-Treeline Ecotone. Plant Ecology, 2002, vol. 162, pp. 157–168. https://doi.org/10.1023/A:1020385320738

13. Giberti G.C. Herbal Folk Medicine in Northwestern Argentina: Compositae. Journal of Ethnopharmacology, 1983, vol. 7, iss. 3, pp. 321–341. https://doi.org/10.1016/0378-8741(83)90006-5

14. Gilliam F.S. The Ecological Significance of the Herbaceous Layer in Temperate Forest Ecosystems. BioScience, 2007, vol. 57(10), pp. 845–858. https://doi.org/10.1641/B571007

15. Gini C. Variabilità e Mutabilità. Memorie di Metodologica Statistica. Ed. by E. Pizetti, T. Salvemini. Rome, Libreria Eredi Virgilio Veschi, 1912. (In It.).

16. Hertel D., Wesche K. Tropical Moist Polylepis Stands at the Treeline in East Bolivia: The Effect of Elevation on Stand Microclimate and Above- and Below-Ground Patterns. Trees, 2008, vol. 22, pp. 303–315. https://doi.org/10.1007/s00468-007-0185-4

17. Hoch G., Körner C. The Carbon Charging of Pines at the Climatic Treeline: A Global Comparison. Oecologia, 2003, vol. 135(1), pp. 10–21. https://doi.org/10.1007/s00442-002-1154-7

18. Hoch G., Körner C. Growth, Demography and Carbon Relations of Polylepis Trees at the World’s Highest Treeline. Functional Ecology, 2005, vol. 19, iss. 6, pp. 941–951. https://doi.org/10.1111/j.1365-2435.2005.01040.x

19. Kessler M. Bosques de Polylepis. Botánica Económica de los Andes Centrales. Ed. by R.M. Moraes, B. Øllgaard, L.P. Kvist, F. Borchsenius, H. Balslev. La Paz, Universidad Mayor de San Andrés, 2006, pp. 110–120. (In Span.).

20. Kessler M., Toivonen J.M., Sylvester S.P., Kluge J., Hertel D. Elevational Patterns of Polylepis Tree Height (Rosaceae) in the High Andes of Peru: Role of Human Impact and Climatic Conditions. Frontiers in Plant Science, 2014, vol. 5, art. 194. https://doi.org/10.3389/fpls.2014.00194

21. Kharuk V.I., Petrov I.A., Im S.T., Golyukov A.S., Dvinskaya M.L., Shushpanov A.S. Tree Clusters Migration into Alpine Tundra, Siberia. Journal of Mountain Science, 2022, vol. 19, iss. 12, pp. 3426–3440. https://doi.org/10.1007/s11629-022-7555-7

22. Körner C. A Re-Assessment of High Elevation Treeline Positions and Their Explanation. Oecologia, 1998, vol. 115, pp. 445–459. https://doi.org/10.1007/s004420050540

23. Körner C. Alpine Plant Life: Functional Plant Ecology of High Mountain Ecosystems. Berlin, Springer, 2003. 349 p. https://doi.org/10.1007/978-3-642-18970-8

24. Körner C., Paulsen J. A World-Wide Study of High Altitude Treeline Temperatures. Journal of Biogeography, 2004, vol. 31, iss. 5, pp. 713–732. https://doi.org/10.1111/j.1365-2699.2003.01043.x

25. Levene H. Robust Tests for Equality of Variances. Contributions to Probability and Statistics: Essays in Honor of Harold Hotelling. Ed. by I. Olkin, S.G. Ghurye, W. Hoeffding, W.G. Madow, H.B. Mann. Stanford, CA, Stanford University Press, 1960, pp. 278–292.

26. López V.L., Bottan L., Martínez Pastur G., Lencinas M.V., Cuyckens G.A.E., Cellini J.M. Characterization of Polylepis tarapacana Life Forms in the Highest-Elevation Altiplano in South America: Influence of the Topography, Climate and Human Uses. Plants, 2023, vol. 12, art. 1806. https://doi.org/10.3390/plants12091806

27. López V.L., Cellini J.M. Plantas medicinales asociadas a bosques de Polylepis tarapacana del altiplano jujeño: Riqueza y cobertura en gradientes geográficos, topográficos y de estructura forestal. Ecología Austral, 2022, vol. 32, no. 3, pp. 894–907. (In Span.). https://doi.org/10.25260/EA.22.32.3.0.1905

28. López V.L., Cellini J.M., Cuyckens G.A.E. Influencia del micrositio y el ambiente en la instalación de Polylepis tarapacana en los Altos Andes. Neotropical Biodiversity, 2021, vol. 7(1), pp. 135–145. (In Span.). https://doi.org/10.1080/23766808.2021.1902251

29. López V.L., Huertas Herrera A., Rosas Y.M., Cellini J.M. Optimal Environmental Drivers of High-Mountains Forest: Polylepis tarapacana Cover Evaluation in Their Southernmost Distribution Range of the Andes. Trees, Forests and People, 2022, vol. 9, art. 100321. https://doi.org/10.1016/j.tfp.2022.100321

30. López V.L., Martínez Pastur G., Cellini J.M. Forest and Shrubland Structure of Polylepis tarapacana in Topographic and Substrate Gradients Across the Argentine Altiplano. New Zealand Journal of Forestry Science, 2025, vol. 55. https://doi.org/10.33494/nzjfs552025x319x

31. Mann H.B., Whitney D.R. On a Test of Whether One of Two Random Variables is Stochastically Larger than the Other. The Annals of Mathematical Statistics, 1947, vol. 18, no. 1, pp. 50–60. https://doi.org/10.1214/aoms/1177730491

32. Martínez Pastur G., Amoroso M.M., Baldi G., Barrera M.D., Brown A.D., Chauchard L.M., et al. ¿Qué es un bosque nativo en la Argentina? Marco conceptual para una correcta definición de acuerdo con las políticas institucionales nacionales y el conocimiento científico disponible. Ecología Austral, 2023, vol. 33(1), pp. 152–169. (In Span.). https://doi.org/10.25260/EA.23.33.1.0.2040

33. Oehlert G.W. A Note on the Delta Method. The American Statistician, 1992, vol. 46(1), pp. 27–29. https://doi.org/10.1080/00031305.1992.1047842

34. Ramsay P.M., Oxley E.R.B. The Growth Form Composition of Plant Communities in the Ecuadorian Páramos. Plant Ecology, 1997, vol. 131, pp. 173–192. https://doi.org/10.1023/A:1009796224479

35. Renison D., Cuyckens G.A.E., Pacheco S., Guzmán G.F., Grau H.R., Marcora P., et al. Distribución y estado de conservación de las poblaciones de árboles y arbustos del género Polylepis (Rosaceae) en las montañas de Argentina. Ecología Austral, 2013, vol. 23(1), pp. 27–36. (In Span.). https://doi.org/10.25260/EA.13.23.1.0.1189

36. Rojas R., Flexas J., Coopman R.E. Particularities of the Highest Elevation Treeline in the World: Polylepis tarapacana Phil. as a Model to Study Ecophysiological Adaptations to Extreme Environments. Flora, 2022, vol. 292, art. 152076. https://doi.org/10.1016/j.flora.2022.152076

37. Shannon C.E. A Mathematical Theory of Communication. Bell System Technical Journal, 1948, vol. 27, iss. 3, pp. 379–423. https://doi.org/10.1002/j.1538-7305.1948.tb01338.x

38. Shapiro S.S., Wilk M.B. An Analysis of Variance Test for Normality (Complete Samples). Biometrika, 1965, vol. 52, iss. 3-4, pp. 591–611. https://doi.org/10.1093/biomet/52.3-4.591

39. Simpson E.H. Measurement of Diversity. Nature, 1949, vol. 163, iss. 4148, art. 688. https://doi.org/10.1038/163688a0

40. Soliveres S., Maestre F.T. Plant–Plant Interactions, Environmental Gradients and Plant Diversity: A Global Synthesis of Community-Level Studies. Perspectives in Plant Ecology, Evolution and Systematics, 2014, vol. 16, iss. 4, pp. 154–163. https://doi.org/10.1016/j.ppees.2014.04.001

41. Soliveres S., Maestre F.T., Berdugo M., Allan E. A Missing Link Between Facilitation and Plant Species Coexistence: Nurses Benefit Generally Rare Species More than Common Ones. Journal of Ecology, 2015, vol. 103, iss. 5, pp. 1183–1189. https://doi.org/10.1111/1365-2745.12447

42. Spearman C. The Proof and Measurement of Association Between Two Things. The American Journal of Psychology, 1904, vol. 15, no. 1, pp. 72–101. https://doi.org/10.2307/1412159

43. Staudhammer C.L., LeMay V.M. Introduction and Evaluation of Possible Indices of Stand Structural Diversity. Canadian Journal of Forest Research, 2001, vol. 31(7), pp. 1105–1115. https://doi.org/10.1139/x01-033

44. Toivonen J.M., Horna V., Kessler M., Ruokolainen K., Hertel D. Interspecific Variation in Functional Traits in Relation to Species Climatic Niche Optima in Andean Polylepis (Rosaceae) Tree Species: Evidence for Climatic Adaptations. Functional Plant Biology, 2014, vol. 41, iss. 3, pp. 301–312. https://doi.org/10.1071/FP13210

45. United Nations Framework Convention on Climate Change (UNFCCC). Report of the Conference of the Parties on its Seventh Session, Held at Marrakesh from 29 October to 10 November 2001. FCCC/CP/2001/13/Add.1. United Nations, 2002. 69 p. Available at: https://unfccc.int/resource/docs/cop7/13a01.pdf (accessed 17.12.25).

46. Wilcoxon F. Individual Comparisons by Ranking Methods. Biometrics Bulletin, 1945, vol. 1, no. 6, pp. 80–83. https://doi.org/10.2307/3001968

47. Wilks S.S. Certain Generalizations in the Analysis of Variance. Biometrika, 1932, vol. 24, iss. 3/4, pp. 471–494. https://doi.org/10.1093/biomet/24.3-4.471

48. Yates F. Contingency Tables Involving Small Numbers and the χ² Test. Journal of the Royal Statistical Society, 1934, vol. 1, iss. 2, pp. 217–235. https://doi.org/10.2307/2983604