Fire, Forest History, and Ecological Restoration of Ponderosa Pine Forests at Mount Rushmore, South Dakota

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1 Fire, Forest History, and Ecological Restoration of Ponderosa Pine Forests at Mount Rushmore, South Dakota Restoration uses the past not as a goal but as a reference point for the future...it is not to turn back the evolutionary clock, but to set it ticking again. (Don Falk 1990) Peter M. Brown 1 Cody Wienk 2 Amy Symstad Rocky Mountain Tree-Ring Research, 2901 Moore Lane, Ft. Collins, CO National Park Service, Northern Great Plains Ecoregion, Hot Springs, SD US Geological Survey, Northern Prairie Wildlife Research Center, Rapid City, SD Project Report March Introduction Evidence of past ecosystem patterns and processes provides answers for the what and why of ecological restoration efforts: what do we restore to, and why is it important to do so? Ecological restoration of degraded or altered Multiple fire scars are visible on this cross section cut from a snag (standing dead tree). A small portion of the sapwood is visible in the upper right of the photograph, making it possible to date the death of this tree to Sapwood decays fairly rapidly relative the heartwood, which is the darker colored portion of the wood that makes up most of the section. The sapwood had evidence of blue stain, a fungus introduced into the tree by bark beetles. This tree died from a beetle attack, not fire or timber harvest. ecosystems - such as those dominated by fire-adapted species like ponderosa pine (Pinus ponderosa) - requires historical data both to provide guidance for what to restore to, as well as justification for the return of an ecosystem to some semblance of its longer-term evolutionary trajectory. This latter point is especially true in areas such as National Parks or Monuments, where public focus on policy and planning decisions may be especially intense. A solid scientific foundation for why restoration or fuel treatments is needed is a critical concern in areas that may be subject to public scrutiny of land and natural resource management decisions and activities. Mount Rushmore National Memorial (MORU) in the Black Hills of South Dakota is one place where public scrutiny is high owing to both its large

2 numbers of annual visitors and its symbolism as a national icon. The Memorial is known worldwide for its massive sculpture of four of the United States most respected presidents, George Washington, Thomas Jefferson, Abraham Lincoln, and Theodore Roosevelt. However, Mount Rushmore itself where the sculpture is located is surrounded by continuous and often dense ponderosa pine forest. As in ponderosa pine forests across the western US, fire exclusion over the 20th century has resulted in changes in forest canopy structure, especially the formation of ladder fuels, that increase the likelihood of catastrophic crown fires. Increased tree density also has had cascading effects on related ecosystem processes, such as decreased understory species density and diversity because of less light penetration through the canopy and increased competition for soil water and nutrients with trees. Mount Rushmore is also relatively unique in the Black Hills in that it contains some of the largest and last contiguous stands of ponderosa pine that have not had any timber harvest. Intensive timber harvest began across the Black Hills with Euro-American settlement after gold was discovered in Already by the turn of the twentieth century much of the forest has been affected by harvest, and it is difficult to find any stands today that have not seen some level of cutting, often with multiple entries. Even parts of what is today encompassed by the Mount Rushmore Memorial had some timber harvest before the sculptures were started in 1927, mainly from mining activities that took place in the nearby town of Keystone. Our purposes with this study were to reconstruct historical fire regimes and stand structures at Mount Rushmore and to use simulation modeling to estimate changes in fire behavior from a historical forest in 1870 to the present. These data provide the basis to argue for restoration of historical forest structure and, more importantly, reintroduction of surface fires to restore this keystone ecosystem process to the Mount Rushmore landscape.

3 Methods and Results We placed a 500 m grid across the Memorial to locate sample plots (circles). We increased grid spacing to 250 m in the western half to increase data collection from unharvested stands to better characterize current stand structure including tree heights and crown base heights for later fire behavior modeling. We also collected additional firescarred trees outside of plots as they were encountered (stars). Both living and dead trees were collected from each plot, with a total of 1000 trees sampled across the 1238 acre Memorial. We also measured tree heights, canopy base heights, tree diameters, and mapped tree locations in all plots to determine stand densities and structural arrangements. All but a handful of trees sampled were ponderosa pine (the rest were burr oak and aspen). All trees were dendrochronologically crossdated to provide absolute dates for fire scars, tree recruitment events, and tree death dates. Evidence of fire in the form of catfaced trees, logs, and snags is common across the Mount Rushmore landscape.

4 Dates of tree recruitment (diamonds) and fire scars (triangles) summarized for each plot at Mount Rushmore. Closed triangles are fire-scar dates found on plot trees, open triangles are additional fire-scar dates found on trees collected from polygons placed around each grid point. Solid horizontal lines represent time spans of trees found within plots while dashed lines are additional time spans of polygon trees. Dates shown at bottom are those recorded in at least 25% of the plots or polygons. Note that no fire scars were recorded on any tree we sampled after 1893, which means that the fire-free period since that time is ~6.6 times as long as the mean fire interval in the historical record and ~3.4 times as long as the longest interval from 1706 to 1743.

5 Representative current conditions in a denser stand at Mount Rushmore. Average basal area over the whole area measured in 2005 was ft /ac (range 20 to 176 ft /ac); density in this stand is ft /ac. This stand is south of the main parking lot in an area that would be ideal for thinning and fire restoration, possibly as part of a natural history trail or demonstration area. Estimated scenario in stand of this density to moderately severe fire weather (a 90 th percentile weather event based on instrumental data). Note that all fire behavior is passive crown fire; even at this density active crown fire does not occur in the fire models However, tree mortality is estimated to be 100% due to crown torching coupled with surface fire burning through the understory. This is entirely due to the ladder fuels. Representative estimated historical conditions (in 1870) in an open stand at Mount Rushmore with basal area of 2 ~60 ft /ac. One- to 20-year old seedlings are present in this visualization; however, most of these seedlings would have been killed in the next fire under the historical fire frequency of about every 17 years (range 3 to 33 years) for the more widespread fires across the landscape.

6 Representative view of a stand on the south side of the Memorial that should be targeted for restoration. No harvest has occurred and all pre-settlement trees are in place. Thin-from-below should be used to remove all th 20 century regeneration. Note the cat-faced large ponderosa pine to the right; evidence of surface fire is prevalent throughout this area (and in fact throughout the Memorial). A dense stand of doghair trees in a plot just to the west of the one above. These trees all established after ~1890, the last extensive fire in the Memorial. They have grown up in a dense stand and are very suppressed; most of these trees are over 100 years old but only 3-5" in diameter and very susceptible to bending by snow loading as seen here. Another view of a cluster of older yellow-bark trees within a matrix of younger doghair trees. Reduction of the density and extent of the smaller trees will both reduce the potential for crown fire and restore light, nutrients, and water for understory plants.