An introduction to human impact indicators

Posted on by

The post provided by Jack Zinnen, Jeffrey W. Matthews & Greg Spyreas

The areas in North America (left) and Europe (right) where the three human impact indicator values are used. Adapted from Fig. 1 in the paper (Zinnen et al. 2021).

This Behind the paper post refers to the article Expert-based measures of human impact to vegetation by Jack Zinnen and colleagues, published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12523).

Species indicator values are tools used by ecologists to understand species, communities, and environmental conditions. These indicator values are numeric ratings that ecologists assign to species to represent species’ habitat requirements. Some indicator values have straightforward interpretations, for example, how much moisture or sunlight a particular plant species prefers. Others describe conditions that are more difficult to measure, such as the overall human impact to an environment. In our paper, we examined three different human impact indicators: coefficients of conservatism, naturalness indicator values, and hemeroby degrees (see maps above).

A crash course on the human impact indicator values

Coefficients of conservatism are used in North America as the backbone of “Floristic Quality” metrics; these metrics reflect a plant community’s resemblance to historical (i.e., pre-European colonization) conditions and its perceived conservation value. Hemeroby degrees, created in Finland and Germany, reflect the degree of influence humans had on forming a given plant community. Naturalness indicator values are very similar to coefficients of conservatism. However, they are specific to Hungary and reflect perceived ecosystem naturalness.

For each of these three indicator systems, experts assign each plant species a numeric, regionalized value to express its propensity to human-disturbed habitats (see the table below). High coefficients of conservatism or naturalness values represent species that are intolerant of human disturbance, whereas higher hemeroby values indicate disturbance-tolerant species. Using these simple interpretations, we see that sundew (Drosera rotundifolia) is indicative of ecosystems that are not disturbed by humans, whether in Europe or North America. In Europe, purple loosestrife’s (Lythrum salicaria) presence reflects more natural or pristine ecological conditions; conversely, in North America, it is weedy. Lastly, giant goldenrod (Solidago gigantea) tolerates human disturbance wherever it is found. Different botanical authorities created these three indicator systems independently, in different times and different parts of the world, but nevertheless, their shared focus on human impacts to plant community composition makes them conceptual cousins.

Human impact indicators with three example species. Expert values are presented for coefficients of conservatism (Illinois, USA), hemeroby degrees (Germany), and naturalness values (Hungary). Adapted from Table S1 in the original paper (Zinnen et al. 2021).

A continental rift of indicators

These indicator systems are surprisingly analogous. But, are their users aware of the analogous systems being used elsewhere, and is there any intellectual exchange occurring between them? To answer this, we conducted a bibliographic analysis of papers about these three indicator systems to determine the degree to which authors cited papers about the other systems (see the figure below). We found a continental rift among the users of these indicator systems, suggesting a lack of awareness among users. We argue that this lack of intellectual awareness holds back the development and application of all three systems, as each system has it strengths and weaknesses. Human impact indicators have proven highly useful for ecological management and science, and they will continue to expand in use and regional coverage. But each would benefit from study and cross-pollination by their conceptual cousins.

A bibliographic analysis of scientific papers using human impact indicators. Each circle is a paper, while color, lines, and distance between circles represent exchange. The left cluster are papers using coefficients of conservatism, whereas the right green cluster are papers about hemeroby degrees and naturalness values. Figure 2 from the original paper (Zinnen et al. 2021).

Brief personal summary: Jack Zinnen is a doctoral candidate at the University of Illinois at Urbana-Champaign in the Department of Natural Resources & Environmental Sciences. Jeffrey W. Matthews is an associate professor in the Department of Natural Resources & Environmental Sciences at the University of Illinois at Urbana-Champaign. Greg Spyreas is a research ecologist and botanist at the Illinois Natural History Survey. Their research interests include plant and community ecology, restoration ecology, and ecological indicators.