Objective

The Great Basin National Park located in east-central Nevada (see http://www.nps.gov/grba) is one of many island mountain massifs in the arid Great Basin, with a maximum elevation of 13,063 feet at Wheeler Peak.  Precipitation rarely exceeds 10 inches/year and is evenly distributed across all months.  Because the park’s forest cover ranges from lower-forest border to upper-timberline, it supports nine arid-site conifer species at a number of elevations (see Table 1).  These species are certain to be drought-stressed on a routine basis.  This diversity of species and elevation range limits will allow us to determine if certain species/elevation combinations are optimal for detecting a WUE signal.  If a WUE signal can be found in any tree-ring series anywhere, it ought to be found in some or all of these arid-site conifers at Great Basin National Park.

Table 1.  Arid-site conifers growing in Great Basin National Park, with elevation ranges indicated (see http://www.nps.gov/grba/treesshrubs.htm).  These nine tree species have proven dendrochronological (i.e. cross-dating) potential, with Utah juniper probably being the most difficult species to cross-date in the group (see http://web.utk.edu/~grissino/species.htm).

Common Name

Scientific Name

Elev. (ft)

Utah juniper

 Juniperus osteosperma

3,000-8,000

Rocky Mt. Juniper

Juniperus scopulorum

3,000-8,000

Singleleaf pinyon pine

Pinus monophylla

5,000-9,000

Ponderosa pine

Pinus ponderosa

7,000-8,500

Douglas fir

Pseudotsuga menziesii

6,500-9,000

White fir

Abies concolor

7,000-9,500

Englemann spruce

Picea engelmannii

7,500-timberline

Limber pine

Pinus flexilis

8,000-timberline

Bristlecone pine

Pinus longaeva

9,000-11,500

If the WUE signal were obvious in tree-ring widths, it would have been easily found before.  Therefore, a very methodical sampling approach will be necessary.  This will involve sampling trees of a given species, with a 5mm diameter increment borer, at three points along the species’ elevation range:  lower-limit, mid-range, and upper-limit.  The actual location(s) of the species collections will be determined after consultation with on-site National Park Service officials.  However, care will be taken to keep as many site variables (e.g. slope aspect), as constant as possible.  At each sampling point, we will estimate stand density and composition using standard forest silvicultural methods.  Two cohorts of trees of a given species will be randomly sampled (20 trees/cohort) to test whether there is an age-related bias in drought sensitivity and WUE.  These cohorts will be roughly in the <100 and >100 year age classes, but will ultimately be selected by diameter class in the field. This design will provide a full sample of nine tree species by elevation and cohort for a total of 54 annual tree-ring chronologies for analysis.  This collection ought to provide an adequate basis for detecting a WUE signal if it exists.

Tent view of Mt. Wheeler, Great Basin National Park. (P.Fenwick, 2001)