An evaluation of Illinois grassland restoration success based on ecosystem function

Background/Question/Methods

Grasslands in Illinois have declined rapidly since European settlement due primarily to conversion of land for agricultural use. Grassland ecosystems perform vital ecosystem functions including carbon sequestration, erosion control, water filtration, and act as reservoirs of genetic diversity. Due to the importance of grassland ecosystem functions, grassland restoration projects have become more common. The majority of the efforts to evaluate grassland restorations focus solely on species composition. The recovery of ecosystem functions should also be used as a measure of success for grassland restorations. The aim of this study is to determine if grassland ecosystem functions are regained in restored grasslands by measuring soil bulk density (BD), aboveground net primary productivity (ANPP), nitrogen availability and soil organic carbon (SOC) along a chronosequence of restored grasslands managed by The Nature Institute in Godfrey, IL (38.92^o N, -90.22^o W). Grasslands used in this study were 1, 4, 10, 12, and 25 years old. Biomass and soil sampling was organized along a 50 m transect at each site.  Peak standing crop was harvested in October and November 2012 from 20 0.25 m² quadrats placed at random along the transect. Biomass could not be collected from the 1 year old site. Three 20 cm soil cores were taken from each quadrat and split into 0-10 cm and 10-20 cm sections; samples from each combination of plot and depth were bulked.  Ten BD cores were taken from random points along the 50 m transect at each site.

Results/Conclusions

BD ranged from 1.16 in year 25 to 1.24 in year 1. Linear regression showed a weak pattern of declining BD over time (p = 0.057). ANOVA showed significant differences in total aboveground biomass production in sites of different ages (p < 0.001).  As expected, the 10 and 12 year old sites were similar in biomass production, but it is interesting to note that year 4 biomass was not different from the 25 year-old site (Tukey’s HSD). It was expected that the 4 year restoration would have the lowest level of biomass production.  These two sites contained similar proportions of grasses and forbs. These preliminary data show that soil structure changes fairly quickly over time.  Further analysis of the soil properties of these sites will include soil organic matter, pH, pore space, and nitrogen availability.