In 1874 British Columbia began a policy of extinguishing all fires not beyond the available suppression resources (Parminter, 1975). In southeastern BC, this coincides with the onset of mining, timber harvesting, and railway construction, which all contributed to a strengthened fire exclusion effort (Egan, 1998). Prior to this, frequent anthropogenic and natural fire -- with anthropogenic fire playing a critical role -- characterized the fire regime in the low, dry portions of study area (Barrett and Arno, 1982). Frequent low intensity and severity fire maintained open stands or grassland, which in turn provided high quality ungulate graze and other benefits. With fire-exclusion, Douglas fir was able to fill in stands of once-open Ponderosa Pine, and to begin the process of converting grasslands to forests. At the beginning of the restoration project, it was estimated that of 250,000 hectares of grassland within the British Columbian trench, 3,000 hectares per year were being encroached upon by forest (Egan, 1998). Since 1950, approximately half of what was grassland has been converted to forest (Gayton, 2013). Beyond simply creating a more densely forested landscape, altering the natural disturbance cycle creates less frequent but more severe fires, which affects everything from soil structure to the safety of human communities (Agee, 1993).
In addition to the direct implications of increased tree density caused by fire-exclusion, either continued exclusion or ecosystem restoration work might affect the establishment and success of invasive species. This, coupled with climate change forecasted to produce warmer, drier and longer summers (Pacific Climate Information Consortium, n.d.), creates uncertain trends for ecosystems. For example, it is almost certain that the changing climate, combined with the presence of invasive species, will create novel plant community assemblages, as different species adapt to change at different rates. These two drivers, climate change and invasive species, make the onset of novel assemblages of species likely. Invasive species currently present in the area, such as cheatgrass (Bromus tectorum), may increase, while those which are currently at there northern limit in Washington and Oregon species may expand further northward with warmer and drier climate (eg. Taeniatherum caput-medusae, Eremopyrum triticeum, and Bromus madritensis) (Gayton 2013).
Another means of "changing nature" invokes several meanings of the term: restorationists may be prescribing treatments by based on inaccurate or incomplete understandings of the area's biogeoclimatic zones and disturbance regimes. The disturbance regime for valley bottoms in British Columbia's dry interior have long been considered NDT 4, characterized by frequent, low-intensity and low-severity fires which maintain grassland or open forest. However, a growing body of research suggests that mixed-severity regimes would better describe most areas in the region (eg. Heyerdahl et al., 2011; Klenner et al, 2008; Kubian, 2013; Marcoux et al., 2013), with occasional high-severity fires. Current prescriptions focus exclusively on low-severity fire, which may limit the likelihood of achieving historically fidelity with ecosystems that experienced a range of disturbance types.
While the current models for describing ecosystems and their disturbance regimes may not be accurate due to an inadequate understanding of historical ecosystem processes, they may be made even less accurate by a changing climate conditions and an increase in invasive species. The potential for fundamentally altered ecosystems and disturbance regimes, beyond a simple shift from one of the described categories to another (i.e. Ponderosa Pine Biogeoclimatic Zone to Bunchgrass Biogeoclimatic Zone or Natural Disturbance Type 3 to NDT4), is possible. Cheatgrass is an example of an invasive species which has the potential to cause such an alteration. Cheatgrass invasion can shift the fire regime towards more frequent fire (Zouhar, 2003), but it can also alter plant communities by altering microbiota and nutrient availability. For example, nitrogen availability is diminished by the presence of cheatgrass, which can alter plant community structure beyond what cheatgrass directly displaces (Evans et al., 2001). The creation of positive feedbacks, such as the increasing fire frequency/decreasing nitrogen noted in cheatgrass invasions, has the potential to move ecosystems well outside their normal range of variability.
Rocky Mountain Trench Blueprint for Action 2013, retrieved from http://trencher.com/images/uploads/Blueprint2013_summaryweb.pdf