Geographical and climatic limits of needle types of one‐ and two‐needled pinyon pines

Abstract

AimThe geographical extent and climatic tolerances of one- and two-needled pinyon pines (Pinus subsect. Cembroides) are the focus of questions in taxonomy, palaeoclimatology and modelling of future distributions. The identification of these pines, traditionally classified by one- versus two-needled fascicles, is complicated by populations with both one- and two-needled fascicles on the same tree, and the description of two more recently described one-needled varieties: the fallax-type and californiarum-type. Because previous studies have suggested correlations between needle anatomy and climate, including anatomical plasticity reflecting annual precipitation, we approached this study at the level of the anatomy of individual pine needles rather than species.LocationWestern North America.MethodsWe synthesized available and new data from field and herbarium collections of needles to compile maps of their current distributions across western North America. Annual frequencies of needle types were compared with local precipitation histories for some stands. Historical North American climates were modelled on a c. 1-km grid using monthly temperature and precipitation values. A geospatial model (ClimLim), which analyses the effect of climate-modulated physiological and ecosystem processes, was used to rank the importance of seasonal climate variables in limiting the distributions of anatomical needle types.ResultsThe pinyon needles were classified into four distinct types based upon the number of needles per fascicle, needle thickness and the number of stomatal rows and resin canals. The individual needles fit well into four categories of needle types, whereas some trees exhibit a mixture of two needle types. Trees from central Arizona containing a mixture of Pinus edulis and fallax-type needles increased their percentage of fallax-type needles following dry years. All four needle types occupy broader geographical regions with distinctive precipitation regimes. Pinus monophylla and californiarum-type needles occur in regions with high winter precipitation. Pinus edulis and fallax-type needles are found in regions with high monsoon precipitation. Areas supporting californiarum-type and fallax-type needle distributions are additionally characterized by a more extreme May–June drought.Main conclusionsThese pinyon needle types seem to reflect the amount and seasonality of precipitation. The single needle fascicle characterizing the fallax type may be an adaptation to early summer or periodic drought, while the single needle of Pinus monophylla may be an adaptation to summer–autumn drought. Although the needles fit into four distinct categories, the parent trees are sometimes less easily classified, especially near their ancestral Pleistocene ranges in the Mojave and northern Sonoran deserts. The abundance of trees with both one- and two-needled fascicles in the zones between P. monophylla, P. edulis and fallax-type populations suggest that needle fascicle number is an unreliable characteristic for species classification. Di...

A long‐term vegetation history of the Mojave–Colorado desert ecotone at Joshua Tree National Park

“…Pinus californiarum, the most common pinyon in the middens and the one present at JTNP today, is characterised by fascicles with a single stout (1.2-1.6 mm in diameter) needle with thickened sclerophyll layers and the presence of 8-16 resin canals and 13-18 stomatal lines. In contrast, the other single-needled pinyon in the region, Pinus monophylla (single-leaf pinyon), has 2-7 resin canals and 17-30 stomatal lines (Bailey, 1987;Cole et al, 2008). Pinus juarezensis (Sierra Juárez pinyon) is a five-needled pinyon that occurs from the San Jacinto Mountains of southern California, 50 km southwest of JTNP, into the Sierra Juarez and Sierra San Pedro Martir of Baja California.…”

Vegetation Response to Early Holocene Warming as an Analog for Current and Future Changes

“…The slowcolonizing species abundant today probably experienced a population bottleneck at the time but have successfully re-expanded since. This is the case for the pinyon pines in western North America (Cole et al 2008b) and the oak species in Europe (Dumolin-Lapégue et al 1997).…”

Long‐term survivorship of single‐needle pinyon (Pinus monophylla) in mixed‐conifer ecosystems of the Great Basin, USA

“…These ecosystems are characterized by the presence of two main pinyon species, namely Colorado pinyon (Pinus edulis Engelm.) in the American Southwest (mostly Arizona, New Mexico, Colorado, and Utah), where it covers more than 20 million ha (Cole et al 2008), and single-needle pinyon (Pinus monophylla Torr. & Frém.)…”