Concern over the die-off of trees during the 1950’s drought in the Chisos Mountains prompted the establishment of 11 monitoring plots in the pinon-juniper woodlands in 1955. Today, concern focuses on the risk of uncharacteristically severe wildfires resulting from past decades of fire suppression. These long-term plots in Big Bend National Parks provide a unique opportunity to examine woodland and forest dynamics in the absence of many anthropogenic influences.
The original investigators used 30-foot radius (9.14 m) semi-circular plots which were permanently located with steel stakes. In 1955, a plane table was used to map the stem location of all woody species (including seedlings). The location of dead trees was also mapped and identified to species, when possible. Tree diameters and heights were also recorded and each plot was also photographed. Plots were relocated and re-mapped using a staff-compass and measuring tape in October 2008. Permanent stakes were missing from many plots, but the tree maps allowed accurate relocation of the plots.
Results/Conclusions
Seedlings and saplings were uncommon in 1955 but abundant in 2008. The lack of seedlings in 1955 may have been a result of the severe 1950’s drought. From 1955 to 2008, little recruitment into larger tree size classes was observed. Tree establishment may be episodic. However, competition with herbaceous species following removal of domestic livestock from the Chisos Mountains in the 1930’s may also be limiting tree establishment. Overall, results suggest that relatively little change has occurred over the last half century. Major die-off of trees was not observed on these plots nor over most of the higher elevation woodlands of the Chisos Mountains following the 1950’s drought. Since then, neither understory regeneration nor substantial increases in tree density have occurred.
