Expansion of pinyon-juniper woodlands into neighboring shrublands and grasslands can have detrimental impacts to species that prefer treeless areas, while infilling changes the structure of woodland stands and can have negative effects on species that prefer lower stem densities.
One species with a close ecological relationship to pinyon pine is the pinyon jay. Pinyon jays consume large quantities of pinyon pine seeds when they become available in late summer-early autumn. When seeds are plentiful, individual jays will cache thousands of them for use in the winter and spring nesting season. Many of these seeds are not recovered and, depending on where they were placed, will germinate and contribute to expansion into new areas or infilling of existing stands.
Surprisingly, this intelligent, social bird has seen a steady decline in their range wide population during the same period of contemporary woodland expansion. To gain a better understanding of how pinyon jays use the woodland, how they select cache sites, and thus how they might they facilitate the expansion and infill of pinyon pine stands, we used U.S. Forest Service Forest Inventory and Analysis techniques to describe where jays cached pinyon pine seeds and what structural features appear to be important for cache site selection.
Pinyon jays choose areas of low canopy cover, low shrub cover, low slope and high grass cover for caching seeds.
Many of the jays in our study preferred a large fire scar for caching seeds, flying up to 22 km from their roosts to place seeds there.
Cache areas were often near the ecotone between shrubland and woodland, which would facilitate expansion of the woodland edge over time.
Cache sites did not include areas with even moderate canopy cover, suggesting pinyon jays do not contribute to infilling processes as much as they do expansion.
Pushing boundaries: new directions in inventory techniques and applications: Forest Inventory and Analysis (FIA) symposium 2015
Stanton, Sharon M.; Christensen, Glenn A.; 2016