Lower Middle Mountain - USLMM001
Additional Site Information

Rosalind Wu, S. Brinton, D. Vega, Peter Z. Fulé, Julie E. Korb

Dating Method: Crossdated

Sample Storage Location: San Juan National Forest, Durango, CO
(contact Rosalind Wu) 

Reference: Fulé P.Z., J.E. Korb, and R. Wu. 2009. Changes in forest structure 
of a mixed conifer forest, southwestern Colorado, USA. Forest Ecology and 
Management 258:1200.1210. DOI:10.1016/j.foreco.2009.06.015.    

Abstract: We selected a warm/dry mixed conifer forest (ponderosa pine, white 
fir, Douglas-fir, and aspen) in southwestern Colorado to reconstruct historical 
conditions of fire regime and forest structure in preparation for an experiment 
in ecological restoration. Although mixed conifer forests are of high 
ecological and social value in the Southwest, they have been less studied than 
ponderosa pine forests.  Fire-scar analysis on a 150-ha area showed recurring 
fires at mean intervals of 24 years (all fires with minimum of 2 sample trees 
scarred) to 32 years (fire scarring 25% or more of sample trees) from the 16th
century until the abrupt cessation of fire after 1868, concurrent with European 
settlement. There was no evidence in age or species-specific data of severe 
burning at the scale of the study blocks (approximately 200 ha). The forest 
remained unharvested throughout most of the 20th century, until a cut in the 
early 1990s removed approximately equal basal areas of ponderosa pine and white 
fir. Forest structure had already changed substantially, however. Total basal 
area increased from an average of 11 m^2 ha^-1 in 1870 to 27 m^2 ha^-1 in 2003, 
despite harvesting of at least 8.4 m^2 ha^-1. Ponderosa pine declined from
representing nearly two-thirds of basal area in 1870 to one-third in 2003. The 
other species increased dramatically, especially white fir, which went from 12% 
to 35% of basal area and dominated stand density with an average of 392 trees 
ha^-1. Total tree density increased from 142 trees ha^-1 in 1870 to 677 trees 
ha^-1 in 2003. The ecological changes that occurred here since the 19th century 
have been in exactly the opposite direction considering the warm, fire-favoring 
climate expected in the 21st century.  If warm/dry mixed conifer forests of 
southern Colorado are to have a reasonable chance for persistence under the 
future climate regime, restoring conditions more similar to the frequently 
burned, open forests of the past is likely to be a useful starting point.

Fire History Graphs: Fire History Graphs illustrate specific years when 
fires occurred and how many trees were scarred. They are available in both 
PDF and PNG formats. The graphs consist of 2 parts, both of which show the 
X axis (time line) at the bottom with the earliest year of information on 
the left and the latest on the right.
The Fire Index Plot is the topmost plot, and shows two variables: sample 
depth (the number of recording trees in each year) as a blue line along 
the left Y axis, compared with the percent trees scarred shown as gray bars 
along the right Y axis.
Below, the Fire Chronology Plot consists of horizontal lines representing
injuries by year on individual sampled trees. Symbols are overlain that 
denote the years containing the dendrochronologically-dated fire scars or
injuries. The sample ID of each tree is displayed to the right of each
line. The Composite Axis below represents the composite information from
all individual series. The symbols used to represent the fire scars or
injuries, and the filters used to determine the composite information,
are shown in the legend.
These graphs were created using the Fire History Analysis and Exploration
System (FHAES). See http://frames.nbii.gov/fhaes/ for more information.