During the 20th Century, pinyon+/-juniper woodland has expanded its distributional range and stand density in mid-elevation zones of Nevada and surrounding regions (Tausch et al. 1981; Miller and Rose, 1994, 1995). This change has occurred on large areas of public lands. The change is regarded by many stakeholders as a negative change, due to perceived reductions in abundance and quality of forage for cattle and sheep, reductions in habitat for desirable wildlife species, reduced groundwater flows in watersheds, increased threats of canopy-carried wildfire to private property and human lives, and increased threats of post-fire conversion to a cheatgrass-fire cycle (e.g. Miller and Wigand, 1994; Tausch 1999; Miller et al. 2005).
Control of further expansion and densification, and reversal of the 20th Century trend, is now a focus of management on public lands. The cause of the expansion and densification of woodlands is primarily ascribed to Euro-American fire suppression, through a combination of:
- direct fighting of wildfires throughout the 20th Century;
- the loss of native bunchgrasses and forbs due to intense cattle grazing, thereby removing fine fuels that enable wildfires to spread from ignition sources (Burkhardt and Tisdale 1976; Young and Evans 1981); and
- absence of traditional land burning practices by displaced Native American communities (Miller and Wigand, 1994).
Under this scenario, woodland stands comprised of individuals dating from the mid 19th Century or later are considered to be expansion and older woodland stands containing cohorts of individuals dating from the mid 19th Century or later are considered to be undergoing densification.
Thus it is concluded that management actions to clear expansion woodlands and thin densified woodlands will return Great Basin landscapes to their pre-grazing, pre-fire-suppression conditions and the landscapes will thereby be returned to both their historic range of variability and a healthier state from the perspective of stakeholder groups.
This rationale for clearing and thinning of pinyon+/-juniper woodlands assumes that 20th Century fire suppression (in the broad sense) is the only significant driver of the observed changes in woodland distribution and density. It assumes that at least two other processes did not significantly contribute woodland changes observed in the 20th Century:
- on-going global-scale environmental changes and
- tree harvesting during the early stages of Euro-American settlement.
This proposal focuses on testing the second assumption.
Mining booms in the second half of the 19th Century drove the settlement and establishment of many towns across Nevada. As coal did not become readily available until the end of the 19th Century, early mines, smelters and the households of those working in mines and smelters were dependent on timber and charcoal, primarily sourced from surrounding pinyon and juniper woodlands.
For example, Reno (1994) documented more than 500 charcoal platforms in the Robert Mountains, 30 miles northwest of the Eureka mining district to which the charcoal was delivered by railroad. Even if each platform were fired just once, a large amount of timber was harvested in this one mountain range and thus a large area of woodland was either clear-cut or thinned for larger trees.
Thus the distribution and/or density of woodland towards the end of the 19th Century is likely to have been less than in the early to mid 19th Century in districts servicing mining boom towns. In addition, subsequent reestablishment of trees following clear-cutting or selective felling of commercially viable trees from amongst non-commercial saplings would yield 21st Century stand structure comprising trees dating from no earlier than the mid 19th Century, the same stand structure currently interpreted as woodland expansion as a consequence of fire suppression alone.
There is indirect evidence for woodland sites being converted into sagebrush-bunchgrass communities through the administrative conversion of 19th Century mining-boom “timber ranches” (for charcoaling) into 20th Century “grazing ranches” (Reno 1994). There is also direct evidence for post-logging reestablishment sites, including:
- the widespread occurrence of old, axe-cut juniper stumps in woodland stands of younger trees and
- the stand-structure and fire-scar analysis of woodlands in the Shoshone Mountains by Bauer (2006).
Returning the effects of 19th Century mining booms to our understanding of Nevada landscapes may have significant impacts on the reality and limitations of the historic range of variability concept when applied to management of pinyon-juniper woodlands.
It may be invalid to reduce pinyon-juniper woodlands in some places where they have been viewed as encroaching because it is thought to be an artifact of human alteration of natural disturbance regimes. Contrary to the implications of the fire-suppression scenario, removal of trees in post-logging woodland reestablishment sites would actually take the landscape away from its historic range of variability, not towards it, if “historic” is truly intended to refer to pre-1849 rather than (say) 1890 conditions.
Furthermore, since remaining old growth may significantly underestimate the amount of land that has a natural woodland climax, some NRCS ecological site descriptions describing these lands as range sites may be wrong. Agencies might better focus range management where there is irrefutable evidence of range community types prior to the mining boom, and instead develop environmental services and alternative economic output from sites with natural woodland climax.
For pinyon-juniper management policy and implementation in Nevada to be more ecologically sound and responsive to multiple-user perspectives, agencies and other stakeholders urgently require a map of pre-1849 pinyon-juniper woodland distribution that is based upon multiple lines of evidence, not solely upon current stand structure.
In this project, such a map will be interpolated from spatially-explicit databases for two unexploited types of evidence in addition to stand structure:
- vegetation observations in 19th Century Mineral Survey records, and
- phytoliths from past vegetation still preserved in modern soils (as per Piperno 2006).
The data will then be analyzed to quantify the extent of late 19th Century mining impacts, the extent of post-logging woodland reestablishment sites that might have previously been misinterpreted as encroaching or densifying, and thus overall woodland historic range of variability.