Declines in pinyon pine cone production associated with regional warming

Authors: REDMOND, MIRANDA - University Of Colorado; Forcella, Frank; BARGER, NICHOLE - University Of Colorado

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2012
Publication Date: 12/27/2012
Citation: Redmond, M.D., Forcella, F., Barger, N.N. 2012. Declines in pinyon pine cone production associated with regional warming. Ecosphere. 3(12). Available: http://www.esajournals.org/doi/full/10.1890/ES12-00306.1.

Interpretive Summary: Pinyon pine of the Southwest is America’s only commercial source of edible pine seeds. These seeds were dietary staples of indigenous Americans in bygone eras. Nowadays, they are sold as a novelty item rather than as a staple food. However, pinyon seeds continue to be important resources for wildlife, and the trees themselves are key components of the Southwest’s vegetation and landscapes. The cones in which the seeds are produced are initiated two years prior to seed maturity, and the environmental stimulus for cone initiation is unseasonably low temperatures during late summer. Consequently, cones are not produced regularly (that is, annually or every other year). Instead, the cones are produced episodically, and often in massive quantities, whenever abnormally low temperatures occurred two years earlier. Episodic reproduction is known as “masting behavior” and “mast crops” in ecological jargon. In this project, we asked the following question: As climate in the Southwest changes (warms) over time, will cone production in pinyon pine decline? To answer this question we compared two ten-year sequences of cone production in nine pinyon woodlands scattered throughout New Mexico and extending into western Oklahoma. The first sequence was from 1969 to 1978, and the second sequence was from 2003 to 2012. Official long-term weather stations were located near each of these woodlands. The frequency of mast crops was less for the more recent time frame (2003-12) than for the former (1969-78), and the cause may be increased late summer temperatures. Additionally, the amount of cones produced during the mast years in the more recent time frame (2003-12) was less than the former (1969-78), and the cause appeared to be increased growing season temperatures. In other words, temperatures were higher during the past decade compared to three decades previously, and these hotter conditions likely inhibited cone initiation. These results suggest that those who gather pinyon seeds for woodland regeneration (USFS managers, etc.), culinary purposes (hobbyists), or survival (wildlife) face greater difficulties today than in the past, and they likely will endure even greater troubles in the future.

Technical Abstract: Global climate change is expected to produce large shifts in vegetation distribution and already has increased tree mortality, altering forest structure. However, long-term shifts will be dependent on the ability of species to regenerate under a novel climate. Few studies have examined the impact of climate change on the reproductive output of long-lived "masting" species, or species characterized by episodic reproductive events. Here, we show that seed cone production among pinyon pine (Pinus edulis), a masting species, has declined by 33% from the 1970s to the 2000s in revisited stands throughout New Mexico and northwestern Oklahoma. Declines in seed cone production were greatest in areas with larger increases in growing season temperatures prior to cone initiation, suggesting seed production may be an important bottleneck for pinyon pine regeneration with changing climate. The full geographic and taxonomic extents of these declines are unknown and require further investigation.