The germination rate of creosote (Larrea tridentata) on the Sevilleta appears to be very low. During the early years of the LTER project it was attempted to quantify such germination through the use of seedling plots which were monitored on a bi-annual basis (spring and fall). During the period from 1989 through 1992 there were no creosote seedling that germinated on the monitoring plots. In 1999 a rather sizeable population of small seedlings was observed in one quite localized area in the vicinity of Five Points. This rather large number of individuals in one very limited area raised several questions:1. When did this small community of individuals germinate- the supposition is that they had all germinated at the same time.2. What conditions existed in this particular location which allowed such prolific germination when there was no indication of virtually any other germination in this vicinty.3. The most immediate question was whether these seedlings would survive through the impending La Nina winter, spring and summer as many of the individuals did not appear to be very "healthy." To help answer these questions it was decided to begin a "small" monitoring project. All of the individuals in this small area thatappeared to be of the same age were marked with posts, located with GPS, measured (height) and photographed. This initial survey included 78 individuals. The population was resurveyed in August, 2000 and it was discovered that: 1. Many individuals were missed in the initial survey; 2. Most of the individuals (72 of 78) had survived the intervening 9 months; and 3. The average individual growth during this period was 1.4 cm. It is planned that this population will continue to be monitored (probably on an annual basis) to track survival and growth rate of these individuals.
Experimental Design: There has been little recent germination of creosote in the Five Points area. However, the discovery of a patch of relatively new seedlings in one localized area in Nov. 1999 prompted the initiation of this sampling. Continued measurement through time provides growth rates that can then be correlated with meteorological conditions.
Data Collection: Seedlings were marked by pounding galvanized pipes (about 1 m long) into the soil about 6" south of the seedlings. In some cases a single pipe was used to mark more than one seedling. Pipe numbers were written with black magic marker near the top of the pipe. Seedling numbers were written near ground level so they could be seen when photographed. Each pipe was GPS'd.
The height of each seedling was measured to the nearest mm. Measuring was done from the soil surface to a plane even with the top of the tallest leaves. Each seedling was photographed and a meter stick was laid horizontally on the ground (parallel to the plane of the photograph) against the corresponding pipe for scale. In some cases, multiple seedlings were included in one photograph. Arrows on the pipe indicated designated seedlings. These photos were taken with slide film and are currently in the possession of Doug Moore.
The initial cohort of seedlings from 1999 were remeasured on Aug 23, 2000 and seedlings 79-101 added to the data set. At that time, more seedlings were discovered. Seedlings 102-175 were measured on Sep 18, 2000.
Beginning in 2001, two diameters of the crown were measured; the first at the widest point and the second perpendicular to the first.
Between 2001 and 2004, the permenant marker that had been used to mark each pipe faded to the point that they could no longer be read. In 2004, numbered aluminum tags were attached to the pipes with wire but the numbers of the pipes and the corresponding samples no longer designate the same individual as prior to 2004.
Also, note the effect of the unprecedented freeze event of early 2011.
11/01/09 (JMM) Metadata updated and compiled from 1999 to 2009 data.
01/29/09 (YX) Metadata updated and compiled from 1999 to 2008 data.
01/28/2009 (YX) 99-2008 dataset was checked for errors and missing data.
Additional Information on the personnel associated with the Data Collection / Data Processing
Joy Francis, a post-doc with Jim Gosz, was instrumental in setting up this study.
1. Initiated - November 11, 1999, and Resurvey - August 23, 2000. 2. Marked missed seedlings - September 18, 2000. 3. Measured 1-79 - October 9, 2001-measured both height and 2 diameters. 4. Measured 129 - Dec.13, 2004 - Measured both height and 2 diameters. 5. Measured 1-129 - Sept. 22, 2005 - Measured both height and 2 diameters. 2006-2008 measured 1-129 for both height and 2 diameters.