Abstract
Pinus leiophylla, or Chihuahua pine, (PILE) and P. ponderosa, or ponderosa pine, (PIPO) are two wide-ranging North American species with distributions that overlap in Arizona, USA. We compared the growth of fifty-eight trees from three study sites over an elevation gradient at the northernmost point of PILE occurrence. Because the PILE trees were growing at the extreme edge of the species´ range, we expected that PILE sensitivity to climate would be higher and growth performance would be reduced compared to PIPO. From 1918 to 2017, the study area became drier and warmer with precipitation declining by approximately 9% while temperature rose by approximately 5%. We found that PILE tree-ring indices were more sensitive in terms of average year-to-year percent variation than those of PIPO and had higher variability in tree-ring variation in the ten wettest vs. the ten driest years. But PILE displayed higher absolute diameter growth rates as measured by basal area index (BAI) and was less negatively correlated with warm monthly temperatures. Within species, low-elevation trees of both species tended to have greater sensitivity to climate over all variables assessed, but the differences were not statistically significant. The overall assessment of growth of paired trees of the two species showed the locally rare species PILE to perform approximately equally as well as the dominant species PIPO. Species migration is reshaping global forests but species found predominantly in Mexico with distributions coinciding closely with national boundaries have received insufficient research attention in the USA. We recommend cross-border, climate-focused, comprehensive studies on PILE and other species likely to migrate northward to provide critical information for conservation and management of forest resources.
Highlights
Interactions of anthropogenic climate change and disturbance have been shifting global vegetation patterns for decades with much greater changes expected in the near future
We evaluated changes in tree growth associated with drought (H5) for the five most severe drought years defined as the five lowest water years: 1928, 1955, 2000, 2002, and 2011
Despite endeavoring to closely match PILE and PIPO trees in the field, we found that the PILE trees averaged 10% larger in diameter but PIPO trees averaged about 11% taller
Summary
Interactions of anthropogenic climate change and disturbance have been shifting global vegetation patterns for decades with much greater changes expected in the near future. Examples of recent shifts include the upward movement of numerous species comprising plant communities on mountain ranges in desert (Brusca et al, 2013) and Mediterranean (Kelly and Goulden, 2008) ecosystems. Analysis of potential future climate conditions in British Columbia, for example, guided a common-garden experiment testing Pinus albicaulis planting up to 800 km NW of its current range (McLane and Aitken, 2012). Disturbance-mediated change associated with interactions between climate and wildfire or insect pathogens is likely to affect shifting distributions in variable ways (Waring et al, 2009; Campbell and Shinneman, 2017; Parks et al, 2019)
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