What can ants tell us about restoration?

            As human worldwide human activities continue to develop natural lands for human use, conservation programs to conserve natural areas and mitigate development through restoration efforts are becoming increasingly common. In order to evaluate the success of these restoration efforts, scientists have applied a wide variety of techniques to measure the diversity of species occurring in restored areas. Many of these techniques focus on the use of bioindicators – certain organisms whose presence is highly correlated to the quality of the restored habitat. These species – or groups of closely related species – tend to require that specific natural resources are present in their environment, and, if restoration actions successfully increase the amount of these resources that are available, then the bioindicator will also become increasingly common. By focusing on organisms known to be useful bioindicators, studies surveying restored areas can reduce the effort required to determine the success of these restoration projects, allowing more efficient and informative monitoring programs.

Figure 1. Camponotus americanus, a member of Subordinate Camponotini, and a species that might occur in similarly conducted samples in the American Midwest. Photo from http://bugguide.net/node/view/328928/bgpage

            Previous studies throughout tropical rainforest and arid regions in northern Australia have found that ants are one such group of bioindicator; Gollan et al. (2011) show that these same methods can also be applied to temperate regions as well. In this study, the researchers selected 12 sites from within a temperate river catchment within a grassland area of southeast Australia. The chosen sites differed in the amount and type of vegetation present, and they were classified into four classes: mature woodlands, older revegetation (7-10 years post-restoration), young revegetation (less than 3 years post-restoration), and unplanted grassland. In each site, the researchers sampled insects using pitfall traps, designed to contain and collect any insects that stumble into them. After classifying the sampled ants according to morphospecies, which group together difficult to distinguish species with similar ecological functions, the researchers compared the number of species present in each of the four classes of site vegetation. Though they identified more than 20,000 ants from 68 different species, Gollan et al. (2011) found that the collection of ant species present at a site varied more within each vegetation class than between sites of different vegetation classes, showing that analyzing ant communities as a whole does not provide much information on the quality of the restored area. However, when they limited their analyses to certain functional groups – groups of morphospecies lumped together by shared interspecific interactions and food sources – they found that different functional groups responded in vastly different ways to habitat quality. In particular, one group known as Subordinate Camponotini, was common in mature woodlands, moderately present in revegetated areas, and absent in unplanted grasslands, as it likely responds to the availability of its food sources in the different types of vegetation.

            Despite being shown to be valid bioindicators in a wide range of habitats, analyses of habitat quality through measurement of ant communities has seen limited use in the United States. In proposed research, I am interested in exploring the applicability of this system in riparian areas here in the Midwest. In addition to the effects of agriculture, many rivers in the Midwest have been channelized, and these various control methods have resulted in substantial changes to the flooding patterns these rivers have experienced. As periodic disturbance by flooding is key to maintaining the health of riparian areas, human-induced modifications to flooding history may have had widespread impact on the communities of these riparian areas. In my proposed project, I will sample ants in riparian areas with different flooding histories and compare these communities using the methods of Gollan et al (2011). By looking at diversity of different functional groups, as well as overall diversity, I aim to identify the effects that changes to the flooding regime of rivers in the American Midwest has on the quality of adjacent riparian areas.

Reference:

Gollan, J., L. Lobry de Bruyn, N. Reid, D. Smith, & L. Wilkie. 2011. Can ants be used as ecological indicators of restoration progress in dynamic environments? A case study in a revegetated riparian zone. Ecological Indicators 11: 1517-1525. 

Between the Cracks: Plant Diversity, Abundance, and Root Health in Paved Areas

"Why doesn't Grinnell have more sidewalks?" students at Grinnell College frequently question while navigating the town. Although paved areas create smooth paths, pavement often creates problems for the surrounding ecological community. While ecological concerns likely did not cause lack of sidewalks in Grinnell, the effect on the surrounding ecological community might be a positive benefit. For instance, pavement decreases the filtration of storm water that would otherwise percolate through the soil. Additionally, paved surfaces reduce gas exchange between the soil and the air. This air exchange may be important for plants to maintain healthy root systems. Some companies marketed paved surfaces with permeable properties because of the negative environmental impacts of paved surfaces. These permeable surfaces allow for greater gas exchange and water filtration. The authors of the paper thought that these properties of permeable pavement might lead to healthier plant root systems for mature Sweetgum trees (Figure 1).

Figure 1. A mature American Sweetgum tree, Liquidambar styraciflua (Arbor Day Foundation).

This paper studies Sweetgum trees to determine the effects of pervious and impervious pavement on their root structure. The scientists created a mini underground laboratory with windows into the soil profile in order to study Sweetgum root structure. They found that pervious pavement did not positively affect any of their measures of Sweetgum performance in comparison to impervious pavement or no pavement at all (Figure 2). 

Figure 2. Mean cumulative (a) new root production, (b) dead root length production and (c) net root length production per cm² tube window until 80 cm depth through time. Open symbols are root production in plots with no pavement (control), black symbols are root production in plots with impervious pavement, and grey symbols are root production in plots with pervious pavement

However, the researchers found that the diameter of the tree trunks were unaffected by pavement installation. The researchers concluded that the negative effects of pavement on Sweetgum root performance likely result from both types of pavements’ prevention of gas exchange between the soil and surrounding air.

The Sweetgum article considers potential factors that may affect my group’s results for our project on the cracks between bricks. Besides crack width and the differences between edge and inner cracks, the differences in soil-air gas exchange could play a role in the performance of plants living in brick crack communities. Additionally, these plants may be nurtured by storm water lacking filtration. In the paper, the authors studied the root systems of ornamental trees. In contrast, my group will only identify the presence and abundance of shoots that arrived on their own (Figure 3). 

 

Figure 3. Different species of plants observed to grow in the cracks of the Noyce Courtyard, my group's experimental site.

My group will not study the root system, which might limit us from observing the negative effects of pavement. The work on pavement and Sweetgum trees shows that the choice to pave and the type of material used tangibly affects surrounding plants. Rather than asking about the effect of different types of concrete on root systems, my group is studying pavement structure by asking how different crack widths affect the diversity and abundance of plant communities.

References

Arbor Day Foundation. 2016. American Sweetgum. Liquidambar styraciflua.

Volder, A., B. Viswanathan, and W.T. Watson. 2014. Pervious and impervious pavement reduce production and decrease lifespan of fine roots of mature Sweetgum trees. Urban Ecology 17: 445-453.