Revisiting Great Basin Bristlecone Pine (Pinus longaeva) in the Stansbury Mountains, Utah

Abstract. Great Basin bristlecone pine (Pinus longaeva D.K. Bailey) presence in the Stansbury Mountains of north-central Utah has been reported prior to the year 2020, but these reports lack adequate population characterization and the delineation of distinct stands of trees. In summer 2020, we identified and documented the presence of 5 separate stands of bristlecone pine in the Stansbury Mountains. These stands are removed from the nearest bristlecone populations in other mountain ranges by a distance of approximately 120 km; as such, they represent a unique outlier population of the species. We used GPS data to create a geographic information system (GIS) database delineating the 5 stands we identified, and we sampled tree age and size in one of the stands for comparison with other bristlecone pine populations in the Great Basin. We present here 2 hypotheses to explain the occurrence of bristlecone pine in the Stansbury Mountains: first, that this population is a relict from a time when bristlecone pine was widely distributed across the Great Basin; and second, that the species arrived in the range via long-distance dispersal mechanisms at some point during or after the Pleistocene/Holocene transition (ca. 12,000 14C YBP). Neotoma (woodrat) midden data suggest that bristlecone pine was absent or at least not widespread in the northern Bonneville Basin during the late Pleistocene, but midden data are sparse for the Stansbury Mountains and surrounding ranges. Additionally, we present possible migration pathways that the species could have taken to reach the Stansbury Mountains from the southern Bonneville Basin, where it was widespread during the late Pleistocene, using the largest extent of Lake Bonneville as a limiting boundary. Hypothesized migration vectors include windborne long-distance dispersal events or transport by granivorous birds. We also postulate that a small population of bristlecone pine may be present in the Oquirrh Mountains to the east of the Stansbury Mountains based upon the existence of similar habitat characteristics there, as well as our identification of a likely misdetermined 1964 voucher specimen from the Oquirrh Mountains that appears to be of bristlecone pine. Resumen. La presencia del pino longevo de la Gran Cuenca (Pinus longaeva D.K. Bailey) en las montañas Stansbury del centro-norte de Utah fue registrada antes del año 2020. No obstante, estos reportes carecen de caracterización adecuada de la población y delineación de distintos rodales de árboles. En el verano de 2020, identificamos y documentamos la presencia de cinco rodales separados de pino longevo en las montañas Stansbury. Estos rodales se encuentran alejados de las poblaciones de pinos longevos más cercanas en otras cadenas montañosas, a una distancia de aproximadamente 120 km, y como tales, representan una población atípica única de la especie. Usamos datos de GPS para crear una base de datos del sistema de información geográfica (SIG) que delinea los cinco rodales que identificamos, y tomamos muestras de la edad y el tamaño de los árboles en uno de los rodales para compararlos con otras poblaciones de pinos longevos en la Gran Cuenca. En este trabajo presentamos dos hipótesis para explicar la presencia del pino longevo en las montañas de Stansbury: (1) esta población es un relicto de la época en que el pino longevo se encontraba ampliamente distribuido en la Gran Cuenca, y (2) la especie llegó a la cordillera a través de mecanismos de dispersión de larga distancia (LDD, por sus siglas en inglés) en algún momento durante o después de la transición Pleistoceno/Holoceno (ca. 12,000 14C YBP). Las estadísticas de los yacimientos de neotoma (rata de bosque) sugieren que el pino longevo estaba ausente o al menos no estaba muy extendido en la cuenca del norte de Bonneville durante el Pleistoceno tardío, pero los datos de los yacimientos son escasos en las montañas Stansbury y las cordilleras circundantes. Adicionalmente, presentamos posibles rutas de migración que la especie podría haber tomado para llegar a las montañas Stansbury desde el sur de la cuenca de Bonneville, donde se encontraba muy extendida durante el Pleistoceno tardío, utilizando la mayor extensión del lago Bonneville como límite. Los vectores de migración hipotéticos incluyen eventos LDD transportados por el viento o por aves granívoras. También postulamos que una pequeña población de pino longevo podría estar presente en las Montañas Oquirrh al este de las Montañas Stansbury ya que el hábitat presenta características similares, así como, nuestra identificación de un espécimen de prueba de 1964 de las Montañas Oquirrh que probablemente no se describió correctamente y que parece ser de pino longevo.

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