Question

Methods section from Theuerkauf et al. 2017 (modified for length) Density-dependent role of an invasive marsh grass, Phragmites australis, on ecosystem service provision.

We assessed the density-dependent role of Phragmites on ecosystem service provision at Currituck Banks and Kitty Hawk Woods Reserves, which are two Reserves within the NCNERR located in Currituck Sound, North Carolina

We quantified the density-dependent role of Phragmites on the following ecosystem service response variables: (i) shoreline change rates … To do so, we sampled 9 randomly selected marsh sites within Kitty Hawk Woods Reserve (3 sites within Low, Medium, and High Phragmites Density treatment categories, described below; Fig 1B), and 6 randomly selected sites within Currituck Banks Reserve

We installed shoreline position benchmarks to quantify marsh shoreline change rates ... In May 2015, we installed between 3–5 iron-rebar stake pairs by driving two stakes (9.5 mm diameter, 1.22 m length) ~ 1 m into the ground at each site for each Phragmites Density treatment in both Reserves. We determined the number of shoreline position benchmarks assigned to a site based on the shoreline length of a given site, with the longest shoreline lengths receiving 5 pairs of equally spaced (~ 15 m apart) rebar stakes, and the shortest receiving 3 pairs of equally spaced rebar stakes. The first rebar stake was installed approximately 2 m soundward of the shoreline. The second rebar stake was installed perpendicular to the shoreline from the first rebar approximately 1 m landward of the first Phragmites or Spartina plants. Care was taken to ensure minimal impact and damage to marsh plants in the area of the shoreline position benchmarks. The survey tape was pulled taut between the two rebar stakes, and the distance from the inmarsh stake to the marsh edge (i.e., the interface between the vegetated marsh surface and shallow open water) was measured to establish a shoreline distance baseline. One year later, in May 2016, we returned to the sites to repeat the measurements from the in-marsh stake to the marsh edge to determine shoreline changes (i.e., landward (negative) or soundward (positive)) in the marsh edge measured as m yr-1. We compared these rates of shoreline change with historical rates of shoreline change estimated from aerial imagery collected for these sites during 1996 and 2012 at Kitty Hawk Woods and 2003 and 2012 at Currituck Banks … Historical shoreline changes were measured by digitizing the shoreline within ArcGIS software and using the measurement tool to quantify shoreline change at each of the shoreline position benchmark sites monitored in our study. We divided the distance change between shoreline position at t1 versus shore- line position at t2 by the number of years between the two shorelines to determine an annual rate in m yr-1.

We compared mean shoreline change rates (m yr-1) between Reserves, Phragmites Density treatments, and their interaction using a two-way ANOVA, and subsequently conducted one-way ANOVA for comparisons within the individual factors … Where appropriate, comparisons among treatments within a factor were conducted with a Tukey-Kramer multiple comparisons test.

1) What was this experiement about in various details

a) What was the hypothesis

b) What was the independent variable

c) What was the dependent variable

d) What controls treatments did they use in the experiment

Answer 1

1) What was this experiment about in various details
This experiment was about the density-dependent role of Phragmites australis, an invasive marsh grass. The shorelines of two reserves kitty Hawk woods and Currituck Banks. The researchers installed rebar stakes and measured the distance from the in-marsh stake to the marsh edge to determine shoreline changes (i.e., landward (negative) or soundward (positive). Then using controls they measured how much shorline has changed and how it is affected by density of the marsh grass. They used statistical tools to determine the signfincance of the data.

a) What was the hypothesis
The invasive marsh grass affects the shoreline in density-dependent fashion.

b) What was the independent variable
The density of Phragmites australis - High, Low, and medium density treatments.

c) What was the dependent variable
Changes in shoreline in both the reserves in terms of an annual rate of m per year.

d) What controls treatments did they use in the experiment
The historical shorelines measures were taken as control. The shoreline changes estimated from aerial imagery during 1996-2012 at Kitty Hawk woods and from 2003-2012 at Currituck Banks.