Monitoring pinyon-juniper cover and aboveground biomass across the Great Basin
Reference
Filippelli, S. K., M. J. Falkowski, A. T. Hudak, P. A. Fekety, J. C. Vogeler, A. H. Khalyani, B. M. Rau, and E. K. Strand. 2020. Monitoring pinyon-juniper cover and aboveground biomass across the Great Basin. Environmental Research Letters 15:11 025004.
Location
Pinyon and juniper woodlands in the Great Basin and Columbia Basin occupied primarily by Utah juniper (Juniperus osteosperma), western juniper (J. occidentals), and singleleaf pinyon (Pinus monophylla).
Description of Site
A wide range of ecological sites occupied by pre- and post-settlement singleleaf pinyon and/or juniper (Juniperus spp.) communities with <1% to >20% tree cover.
Inventory
Time Period – 2000 to 2016; Measurements – changes in canopy cover and biomass during the 16 year period.
Findings
The authors concluded: “Even after 150 years of prior encroachment, PJ is continuing to replace sagebrush and grasslands with 4,600 km² (1,776 mile²) of new ‘forest’ (i.e. >10%tree cover) between 2000 and 2016 despite some loss of forest from management and various disturbances.” The majority of increased biomass (80%) occurred as infilling in existing PJ woodlands (stands with >10% canopy cover). Woodland reduction during this period of 8 Tg was not enough to offset estimated increases of 17.9 Tg. These results suggest that the known consequences of encroachment such as reduced water availability, impacts to biodiversity, and risk of severe wildfire may have been increasing across the region in recent years despite the actions of sagebrush steppe restoration initiatives.
Comments
Many dendrochronology studies show rates of woodland expansion have declined during the second half of the 20th Century but also show infill and encroachment into non-woodland communities is still occurring. The majority of increased biomass has occurred as infill in stands with greater than 10% tree cover. Infill into pre- and post-settlement woodlands were not separated. However, other studies have reported infill to be widely occurring in both, resulting in significant changes in stand structure, composition, biodiversity in addition to ecological processes in both post- and pre-settlement woodlands. (see Miller et al. 2008 and 2019).
In comparison, Reinhardt, Fillippelli et al. 2019 reported a 1.6% reduction in PJ cover. However, this worked evaluated a different time period comparing 2011-2013 to 2015-2017 and evaluated areas within the range of greater sage-grouse (Centrocercus urophasianus) (areas in the two studies similar but not identical).