Dendroclimatology and Woodland Dynamics on the Volcanic Badlands of Western New Mexico, U.S.A.

My dissertation research addressed woodland dynamics and dendroclimatology on the volcanic badlands of western New Mexico. The research was intended to complement previous studies by: (1) assessing vegetation structure and composition dynamics at El Malpais National Monument between 1948–2010 using repeat photography; (2) improving knowledge of the influence of climate and land use on vegetation dynamics at El Malpais National Monument; (3) providing a unique tree-ring data set from Rocky Mountain juniper growing on the malpais; (4) elucidating relationships between Pacific teleconnections and radial growth in Rocky Mountain juniper; and (5) improving understanding of the dynamic nature of climate in the Southwest. I used tree-ring data from the interior of the Bandera Lava Flow and repeat-photography sequences from a nearby location at the edge of the flow to assess vegetation changes at two ecologically different locations on the malpais. I concluded that noticeable vegetation changes occurred during the 20^th and early 21^st centuries at the periphery of the Bandera Lava Flow. Vegetation changes at the lava-substrate interface could be linked to human activity, resource management, and drought.

I also sampled Rocky Mountain junipers on a lava flow in Cibola National Forest to produce a multi-century tree-ring chronology. The data set is the first Rocky Mountain juniper chronology produced in New Mexico and is one of few conifer chronologies from the Southwest with a significant temperature-growth relationship. Dendroclimatic analyses identified growth relationships with monthly mean temperature, monthly total precipitation, monthly PDSI, and local water year precipitation. Trees appeared most sensitive to climate factors that influence and indicate moisture availability during dry periods of the growing season. Tree-ring data indicated positive relationships between SSTs in the El Niño 3.4 region of the central Pacific Ocean and Rocky Mountain junipers on the malpais. Positive PDO-growth relationships during the cool months prior to current growing season further suggest a link between SSTs in the Pacific Ocean and trees on the badlands. Positive relationships between monthly PNA index values and annual radial growth may result from the large distances between the malpais and PNA centers of activity.