Forest vegetation monitoring at Indiana Dunes National Lakeshore

Sanders, Suzanne; Grochowski, Jessica

A comprehensive, long-term forest monitoring program was established at Indiana Dunes National Lakeshore in 2007, when 20 plots were installed. In 2012, we resampled these 20 plots and installed an additional 30, bringing the total to 50. Collectively, these plots spanned five forest types: black oak, upland oak, mesic, wet mesic, and modified successional. In general, black oak forests were healthy, largely due to prescribed burns in this forest type. Although 8.1% of the species located in black oak forest plots were non-native, these were largely naturalized and non-invasive species. In modified successional forests, a mean of 11.9 species per plot were not native. These plots were largely located near the Calumet Bike Trail and other areas of disturbance. The non-native species also reflect land use history, as many plots in this forest type are located on previously farmed land, or former homesteads. Upland oak forests, like black oak forests, were generally healthy. Mesic forests had the lowest percentage of invasive species (4.5%), although this forest type seems to be the most threatened. Many of the plots were invaded by bittersweet. Mesic forests are further threatened by the emerald ash borer (EAB), since green ash was, and still is, a large component of this forest type. Infestation by EAB, which feeds on the phloem and kills the tree within four years of initial attack, results in large amounts of coarse woody material and large canopy gaps. This facilitates further colonization by bittersweet, and other invasive species preferentially located in areas of high light. Forest change between time periods (2007-2012) was largely explained by stand aging. In black oak forests, change was largely related to time-since-burn. The density of live trees decreased by 166 trees/ha, while standing dead tree density increased by 170 trees/ha. Basal area of living trees differed little between years, although basal area of standing dead trees doubled between the two sampling periods. In mesic forests, the dynamics of ash are an important component of change. Although ash is more common in mesic forests than any of the other types, collectively ash species represent only 11.7% of the density and 6.12% of the basal area within this forest type. It does not appear that changes in mesic forests are entirely a reflection of ash demographics in response to EAB. The drop in density coupled with increased basal area is a pattern commonly observed when stands become composed of multiple cohorts, as is happening in mesic forests. The demographic patterns observed in modified successional forests reflect the relatively young age of these stands. Senescence of large trees will leave gaps that lead to recruitment of new cohorts. Park managers at INDU face tough challenges as the problems posing the greatest threats are generally beyond their control. We recommend that managers identify these areas and prioritize a limited number for intensive exotic species monitoring and management. With the impending loss of ash, early detection of exotic species attempting to occupy the vacant niche will be paramount.

Forest vegetation monitoring at Indiana Dunes National Lakeshore

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