Invader, encroacher, or does it matter? Ecological and psychological influences on beliefs about unwanted conifers
Woody plant encroachment is of concern because of its consequences for the ecosystems being encroached upon. Because the causes of encroachment are typically of anthropogenic origin – for example, non-native plant invasion, wildfire suppression, or livestock grazing – cessation or reversal of encroachment processes will require interventions not only in ecological processes but also social processes. However, accomplishing the latter requires that humans agree to changes in behavior. Achieving such agreement is more likely if we first try to understand how people perceive the changes that currently are ongoing. My research group has studied citizen perceptions of conifer encroachment into sagebrush-dominated shrub-steppe. In 2006, we surveyed 1,345 randomly selected households in the three largest urban centers in the Great Basin (Boise, Reno, Salt Lake City) and in six rural counties, then were able to resurvey 698 of those individuals in 2010. Questions asked about knowledge and beliefs regarding various potential threats to sagebrush ecosystems including juniper and pinyon pine encroachment, as well as about acceptability of management approaches to reduce encroachment. In 2008 we surveyed 237 randomly selected households in the northern Rockies region of the U.S., again asking beliefs about encroachment and management options. In the latter survey we also randomly assigned each survey to one of three categories: one framed the study as being about conifer “encroachment,” one about conifer “expansion” and one about conifer “invasion.”
In the Great Basin, respondents were significantly more likely to believe juniper encroachment poses a problem than pinyon pine encroachment, and also much more likely to say they didn’t know if pinyon pine encroachment poses a threat to sagebrush. There was a significant increase in the proportion of respondents seeing juniper encroachment as a threat between 2006 and 2010. However, increased perception of the threat was not closely associated with an increase in support for practices land managers use to halt or reverse conifer encroachment. In the Northern Rockies study, Douglas-fir and ponderosa pine encroachment were generally not understood to be a threat to sagebrush systems. We found relatively low levels of support for removing encroaching tree species. Respondents also indicated they would rather look at a forested landscape than a sagebrush-dominated landscape. Characterizing the process as invasion rather than encroachment did not have a strong influence on responses. Results suggest that knowledge about conifer encroachment processes does not necessarily lead to support for removing them.