DOI: 10.25338/b84h18
title: Researcher effects on the biological structure and edaphic conditions of field sites and implications for management

description: Field studies are necessary for understanding natural processes, but they
 can disturb the environment. Despite researchers acknowledging these
 effects, no studies have empirically tested the direct (e.g., harvesting
 plants) and indirect effects (i.e., trampling) of researcher activities on
 biological structure and edaphic conditions. We leveraged field studies in
 Alabama and California to monitor the recovery of tidal marshes following
 research activities. Researcher effects on animals, plants, and sediment
 conditions remained prevalent almost one year after the disturbance ended.
 For instance, trampled plots had 14-97% lower plant cover than undisturbed
 plots after &gt;10 months of recovery. Researcher effects also
 impacted plant composition, leading to increased subordinate species
 abundance. We encourage field researchers to adopt strategies that reduce
 their scientific footprints, including reducing field visits, limiting
 field team size, and considering ways to limit potential environmental
 impacts during study design.
description: Experimental design The study included four
 treatments: High Crab, Low Crab, Trampled, and Control (n = 5
 treatment<sup>-1</sup>) at constructed and natural marshes in
 both regions. The High Crab and Low Crab treatments were established in
 the footprints of the high-crab density and low-crab density cages,
 respectively, that were part of the original burrowing crab manipulative
 studies conducted at each site (Appendix S1). Thus, these plots had their
 crab communities modified, aboveground biomass harvested, rhizomes
 severed, and sediments cored as part of prior experiments (Appendix S1).
 Trampled plots were established in areas where researchers frequently
 walked to maintain the original caging studies. Controls were placed in
 nearby habitat that was previously undisturbed by researcher activities.
 Plots sizes were 0.7 x 0.7m (length x width) in CA and 0.5 x 0.5m in
 AL. Starting in February (AL: 2021; CA: 2019), we
 monitored crab burrow density, plant cover, and the mean height and stem
 density (AL: n ≤ 5 stems plot<sup>-1</sup>; CA: n ≤ 10 stems
 plot<sup>-1</sup>) of the dominant plant species (AL:
 needlerush; CA: Pacific cordgrass) in each marsh every-other month until
 September (CA) and October (AL). Additionally, in October in AL marshes,
 we collected one, 10-cm-deep sediment core using a Russian Peat corer
 (i.d. = 5cm) that we sub-sectioned in the field at 2.5cm intervals.
 Subsections were oven-dried at 60°C to a constant mass to obtain bulk
 density, and once dried, samples were ground with a mortar and pestle
 before being ashed in a muffle furnace (6h at 550°C) to estimate sediment
 organic matter (SOM) via loss on ignition. We also collected one,
 10-cm-deep sediment core using a t-corer (i.d. = 7.9cm) that we
 sub-sectioned in the field at 5 cm intervals to assess belowground biomass
 at the AL sites. Subsections were rinsed to remove sediment attached to
 belowground biomass, which was then dried at 60°C to a constant mass
 (Conner & Cherry 2015).
description: # Researcher effects on the biological structure and edaphic conditions of
 field sites and implications for management.
 [https://doi.org/10.5061/dryad.v15dv422w](https://doi.org/10.5061/dryad.v15dv422w) These data were collected to assess the impacts of researcher activities on tidal wetland structure. We used an observational study to track the recovery of four tidal marshes following the conclusion of a series of caging experiments assessing burrowing crab effects on marsh structure and functions. We show that researcher manipulations and trampling can result in disturbances that persist for up to 10 months after the initial caging study was complete. Date of data collection: Alabama: 02-10/2022; Southern California: 02-09/2019 Geographic location of data collection: Alabama: Fowl River Natural Marsh (AL-NAT; 30°22’02.5'' N, 88°09’37.2'' W) & Fowl River Constructed Marsh 1 (AL-CON; 30°22’02.3'' N, 88°09’06.8'' W) California: Kendall-Frost Marsh (CA-NAT; 32°47041.0'' N, 117°13046.4'' W) & San Dieguito Lagoon (CA-CON; 32°58047.0'' N, 117°14043.6'' W). Environmental/experimental conditions: Alabama: Our natural site was Fowl River Natural Marsh (AL-NAT; 30°22’02.5'' N, 88°09’37.2'' W) and our constructed site was Fowl River Constructed Marsh 1 (AL-CON; 30°22’02.3'' N, 88°09’06.8'' W). AL-CON was initially constructed in 1987 by harvesting pine savanna habitat and excavating topsoil down to a clay layer that intercepted the water table and was 0.27m above mean sea level (NAVD88 datum). The site was then planted with needlerush (Juncus roemerianus) and smooth cordgrass (Spartina alterniflora) in 1988. Today, both AL sites are almost entirely dominated by needlerush, although the subordinate species, Distichlis spicata, is also common at AL-NAT. Burrowing crabs, fiddler crabs (i.e., Minuca longisignalis, Minuca minax, Leptuca panacea, and Leptuca spinicarpa) and marsh crabs (Sesarma reticulatum) are common and have known effects on needlerush productivity and sediment conditions. Southern California: Our natural site was Kendall-Frost Marsh (CA-NAT; 32°47041.0'' N, 117°13046.4'' W) and our constructed site was San Dieguito Lagoon (CA-CON; 32°58047.0'' N, 117°14043.6'' W). CA-CON was initially constructed in 2006 and planted with Pacific cordgrass (Spartina foliosa) and pickleweed (Sarcocornia pacifica) in 2008, with subsequent grading and planting activities occurring from 2009-2022. At both sites, Pacific cordgrass dominates low-elevation habitat, pickleweed dominates high-elevation habitat, and mixtures of these species occur at intermediate elevations. Subordinate plants are more common at CA-NAT and include Salicornia bigelovii, Jaumea carnosa, Batis maritima, and Triglochin maritima. Burrowing crabs, including lined shore crabs (Pachygrapsus crassipes) and Mexican fiddler crabs (Leptuca crenulata), are abundant at CA-NAT and CA-CON and can influence plant community structure and edaphic conditions. Funding was provided by the University of Alabama’s Department of Biological Sciences. ## Description of the data and file structure DATA & FILE OVERVIEW File List: 1. ResearcherImpacts_Burrows&Plants_1: Impacts of researcher direct and indirect effects on burrowing crab density and plant community composition at the natural (NAT) marsh and constrcuted (CON) marsh in both Alabama and southern California. For Alabama marshes, bi-monthly data is included starting in February 2022 and continuing through October 2022. For southern California marshes, bi-monthly data is included starting in February 2019 and continuing through August 2019, with an additional final sampling timepoint in September 2019 (the end of the growing season). 2. ResearcherImpacts_BGB_1: Impacts of researcher direct and indirect effects on total belowground biomass at depths of 0-5 cm and 5-10 cm. These data were only collected at the natural (NAT) and constructed (CON) marshes in Alabama. 3. ResearcherImpacts_BD&OM_1: Impacts of researcher direct and indirect effects on sediment bulk density and organic matter content at depths of 0-2.5 cm, 2.5-5 cm, 5-7.5 cm, and 7.5-10 cm. These data were only collected at the natural (NAT) and constructed (CON) marshes in Alabama. 4. ResearcherImpacts_LRR_1: The Log Response Ratios (LRRs) calculated using OpenMee software showing the effect size of researcher direct and indirect effects on ecosystem attributes for all marshes in Alabama and southern California. LRRs were calculated using the data associated with the final timepoint in each region (i.e., October in Alabama, September in southern California). METHODOLOGICAL INFORMATION Methods for processing the data: 1. ResearcherImpacts_Burrows&Plants_1: "mean burrow diameter_cm" was calculated by taking the average diameter (cm) of up to five crab burrows per plot; "juro_mean stem height_cm" was calculated by taking the average height (cm) of up to five Juncus roemerianus stems; "spfo_mean stem height_cm" was calculated by taking the average height (cm) of up to ten Spartina foliosa stems. 2. ResearcherImpacts_BGB_1: "belowground biomass_kg/m3" is represented as the kg of belowground biomass per m3. 3. ResearcherImpacts_BD&OM_1: "bulk density_g/cm3" is the g of sediment per cm3. "sediment organic matter_%" is the percent of organic matter comprising the sample calculated via loss of ignition ((100-(Post Ignition Dry Mass/Pre Ignition Dry Mass))*100). 4. ResearcherImpacts_LRR_1: All LRR values were calculated using the mean, standard deviation (SD), and sample size (N) of the treatments (I.e., High Crab, Low Crab, & Trampled) relative to contols (I.e., Control) using OpenMee software (http://www.cebm.brown.edu/openmee/). The height and density of the dominant plant species (I.e., Juncus in Alabama, Spartina foliosa in southern California) were used to compare the effects of researcher activities on the dominant plant height and dominant stem density in each region. LRR values used for Belowground biomass, bulk density, and SOM (sediment organic matter) are based on averages across all depths samples (I.e., 0-5 & 5-10 cm for Belowground biomass and 0-2.5, 2.5-5, 5-7.5, and 7.5-10 cm for bulk density and SOM). DATA-SPECIFIC INFORMATION FOR: ResearcherImpacts_Burrows&Plants_1 Number of variables: 18 Number of cases/rows: 401 Missing data codes: na Specialized formats or other abbreviations used: juro- Juncus roemerianus; disp- Distichlis spicata; spfo- Spartina foliosa; sapa- Sarcocornia pacifica; sabi- Salicornia bigelovii Variable List: "region"- the region (alabama or southern califonia) where the data were collected "marsh"- the type of marsh [natural (nat) or constructed (con)] "plot"- code associated with individual replicates "treatment"- the researcher activity treatment (i.e., high crab, low crab, trampled, and control). "month"- the month the data were collected. "year"- the year the data were collected. "burrow density_1m2"- the density of burrowing crab burrows per m2 "mean burrow diameter_cm"- the mean diameter (cm) of up to five crab burrows per plot. "cover_juro_%"- the percent cover of Juncus roemerianus. "cover_disp_%"- the percent cover of Distichlis spicata. "cover_spfo_%"- the percent cover of Spartina foliosa. "cover_sapa_%"- the percent cover of Sarcocornia pacifica. "cover_sabi_%"- the percent cover of Salicornia bigelovii. "cover_allspp_%"- the percent cover of all plant species. "juro_mean stem height_cm"- the mean stem height (cm) of up to five Juncus roemerianus stems per plot. "juro_stem density_0.25m2"- the density of Juncus roemerianus stems. "spfo_mean stem height_cm"- the mean stem height (cm) of up to ten Spartina foliosa stems per plot. "spfo_stem density_0.49m2"- the density of Spartina foliosa stems. DATA-SPECIFIC INFORMATION FOR: ResearcherImpacts_BGB_1 Number of variables: 7 Number of cases/rows: 81 Missing data codes: na Variable List: "region"- the region (alabama or southern califonia) where the data were collected "marsh"- the type of marsh [natural (nat) or constructed (con)] "plot"- code associated with individual replicates "treatment"- the researcher activity treatment (i.e., high crab, low crab, trampled, and control). "month"- the month the data were collected. "depth_cm"- the depth of the belowground biomass sample (either 0-5 cm or 5-10 cm). "belowground biomass_kg/m3"- the total kg of belowground plant biomass per m3. DATA-SPECIFIC INFORMATION FOR: ResearcherImpacts_BD&OM_1 Number of variables: 8 Number of cases/rows: 161 Missing data codes: na Variable List: "region"- the region (alabama or southern califonia) where the data were collected "marsh"- the type of marsh [natural (nat) or constructed (con)] "plot"- code associated with individual replicates "treatment"- the researcher activity treatment (i.e., high crab, low crab, trampled, and control). "month"- the month the data were collected. "depth_cm"- the depth of the sediment sample; 0-2.5 cm, 2.5-5 cm, 5-7.5 cm, or 7.5-10 cm. "bulk density_g/cm3"- the bulk density (grams per cm3) of sediments. "sediment organic matter_%"- the organic matter content (%) of sediments. DATA-SPECIFIC INFORMATION FOR: ResearcherImpacts_LRR_1 Number of variables: 13 Number of cases/rows: 67 Missing data codes: na Specialized formats or other abbreviations used: LRR: Log response ratio; SD: Standard deviation; N: Sample size Variable List: "Code"- a numberical code assigned to each row "Variable"- the response variable associated with the log response ratio (e.g., crab burrow density, total plant cover (%)). "Region"- the region associated with the data-- either Alabama or southern California. "Site"- the specific marsh-- either natural (NAT) or constructed (CON)-- associated with the data. "Treatment"- the researcher activity impacting the variable-- burrowing crab manipulations (i.e., High Crab and Low Crab treatments) or researcher trampling. "Treatment mean"- the mean value of the Variable in the relative Treatment group. "Treatment SD"- the standard deviation of the Variable in the relative Treatment group. "Treatment N"- the sample size of the Variable in the relative Treatment group. "Control mean"- the mean value of the Variable in the relative Control group. "Control SD"- the standard deviation of the Variable in the relative Control group. "Control N"- the sample size of the Variable in the relative Control group. "LRR"- the calculated log response ratio for each Treatment and Variable across all sites. Positive values indicate treatments increase the Variable, negative values indicate treatments decrease the Variable. "Var(LRR)"- the variation associated with the log response ratio for each Treatment and Variable across all sites. ## Sharing/Access information Licenses/restrictions placed on the data: None ## Code/Software No special software required.