Attribute_Accuracy_Report:
Data accuracy was checked by comparing values against original data sheets. Attributes were spot checked and values were sorted to identify possible errors. For example, if data looked like a potential error, original data sheets were checked to confirm and fixed it if it was a data entry error. Additionally peer-review used sort functions in Excel to identify attributes, domains, and domain ranges. These were checked against metadata entries to ensure all definitions and levels were accounted for.
Attribute values fall within expected ranges. Blank cells may appear in some attributes when data were not available, see Completeness Report.
Blank cells appear in the dataset for data that were not obtained for a sample. Users are advised to read the rest of the metadata record carefully for additional details, particularly the Entity and Attribute definitions for specifics on the entity and data within those entities.
Methodology:
Methodology_Type: Field
Methodology_Description:
We sampled 21 sites spread across 3 transects bisecting the summer ranges of 3 arctic caribou herds (Western Arctic, Teshekpuk, and Central Arctic) over the years 2011 to 2014. Nine sites were spread over a 200-km transect along the Dalton Highway where central arctic caribou can be observed from spring to fall. Four sites were spread over a 175-km transect through the summer range of the Teshekpuk caribou herd. Seven sites were spread over a 160-km transect through the summer range of the western arctic caribou herd. One site on the western arctic transect (macroplot label "PA") burned early in the summer of 2013 and was sampled through 2014 in addition to an adjacent unburned site (macroplot label "PB"). Study sites were at least 1 km away from roads to avoid effects of dust and water runoff. Sites were classified into three ecoregions: Brooks Range, Arctic Foothills, and Coastal Plain. Samples of six preferred forage species (Carex aquatilis, Carex bigelowii, Eriophorum vaginatum, Pedicularis spp., Salix pulchra, and Salix richardsonii) were collected, when present, every two weeks from late May to late September. In addition, we collected samples of Betula nana in 2012 and 2013.
Methodology:
Methodology_Type: Field
Methodology_Description:
Forage plants were sampled for biomass and quality by mimicking caribou browsing and grazing, that is, for deciduous shrubs, easily accessible leaves and twigs were stripped off, while forbs and graminoids were clipped at ground level. Biomass was measured in 0.5 × 0.5 m quadrats at up to five locations within each site of 5 ha. Forage quality samples (20–100 g) were collected directly adjacent to biomass sites to preclude any effects of forage removal.
Methodology:
Methodology_Type: Lab
Methodology_Description:
Forage samples were transferred to pre-weighed paper bags and air-dried at ambient temperature (0-22°C) in the field and then air-dried to constant mass in a forced-air oven at 50-55°C when samples were returned to the laboratory, within 2-6 days of collection. Dried samples were ground through a #20 mesh (1.27 mm) in a Wiley mill or a centrifugal mill. Ground samples were dried to constant mass in a fan-forced oven at 50°C to determine dry matter. Dried samples were combusted in a muffle furnace at 500°C to measure mineral ash. The difference between dry matter and mineral ash was the estimate of organic matter. Total nitrogen and carbon were measured in dry samples by elemental analyzer (CNS2000, LECO, St Joseph MI).
Methodology:
Methodology_Type: Lab
Methodology_Description:
A subset of 696 samples (378 from Central Arctic Herd, 110 from Teshekpuk Lake Herd, 208 from Western Arctic Herd) were selected to represent plant emergence (peak nitrogen [N] content), peak abundance (peak biomass) and plant senescence (typically latest collection in the year) for each species at each site. Polyester bags (Ankom, Fairport NY) were used to extract plant cell walls as neutral detergent fiber (NDF) and acid detergent fiber (ADF). We assessed digestibility by an in vitro method using purified hemicellulases, cellulase and pepsin. Residues of in vitro digestion and acid detergent extraction were analyzed for to estimate the digestibility of N and the availability of N in plant cell contents respectively.
Methodology:
Methodology_Type: Lab
Methodology_Description:
Ground samples were treated with acetone to extract phenols for reaction with Folin-Ciocalteau reagent to assess the concentration of toxins. Ground samples of Salix were also extracted with methanol to measure protein-binding capacity of tannins. Initial tests of total starch in all species were negligible and were therefore discontinued. Finally, we analyzed 13C, 15N and 34S by isotope ratio mass spectrometry of whole plants and fiber extracts at peak plant abundance. Methods for mineral analysis were validated and executed at Texas A and M University by microwave digestion of forage samples in nitric acid. Acid digests were analyzed for calcium (Ca), phosphorus (P), iron (Fe), sodium (Na), potassium (K), magnesium (Mg), manganese (Mn), copper (Cu) and zinc (Zn) against certified standards. Mineral availability was assessed from difference in mineral content of whole samples and the residues of in vitro digestion in pure 1 NHCl solution at 37°C for 24 hours.
Methodology:
Methodology_Type: Field
Methodology_Description:
Soil samples were collected once per year in 5 locations at each sampling site. Available minerals in soils were assessed via Mehlich III extraction for Ca, P, Mg, Na, and K while Fe, Mn, Cu, and Zn were assessed via DPTA extractable minerals. Extracted soil mineral solutions were then measured by inductively coupled plasma mass spectrometry.
Process_Step:
Process_Description:
We measured the dry matter (DM), organic matter (OM), ash, total nitrogen (N) and total carbon (C) content in more than 1,100 forage samples with a forced air drying oven, muffle furnace or elemental analyzer (CNS2000; LECO, St. Joseph, Michigan, USA). Phenology curves of total N vs. ordinal day (OD) were established for each species x site x year combination, and we used these curves to select representative samples for further analysis from three key time periods: early season (peak N content), mid-season (peak biomass), and late season (last sampling date). These sample subsets (~700) were analyzed for neutral detergent fiber (total plant cell walls), acid detergen fiber (ADF), acid lignin, digestibility and mineral content. We measured digestibility (g digested/g whole) of dry matter by using an in vitro digestibility method with purified enzymes, which has been validated for caribou. Digestible N (g/100 g DM) was estimated as the difference between total N and the N retained in the residue from in vitro digestion. Similarly, available N was calculated as the difference between total N and the N retained in the ADF residue. Mineral availability was estimated as the proportional disappearance of total mineral content following in vitro digestion in acid. Gross energy content was determined using an adiabatic bomb calorimeter (Parr Instruments, Moline, Illinois, USA). Digestible energy content was calculated as the product of gross energy content and digestibility of DM. We measured total phenolic compounds by reaction of extracted phenolics with Folin-Ciocalteu reagent, which was expressed in gallic acid equivalents as a standard phenol (mg gallic acid/g DM).
Process_Date: Unknown
Process_Step:
Process_Description:
Residual fractions produced by extraction with detergent, enzymes or acid were normalized to the laboratory standard of ground alfalfa to correct for variation among batches associated with reagents, temperatures, durations and instruments. The available or digestible portion of dry mass and components of dry mass in the plant was calculated by difference, that is disappearance after extraction. For example, digestibility of dry mass with purified enzymes and acids in vitro (IV_digest) was calculated from the proportion of indigestible residue in the sample (IV_indigest): IV_digest = 1-IV_indigest. The digestibility of dry mass in vitro (IV_digest) was used to estimate digestibility in the animal (in sacco; IS_digest) by the equation from VanSomeren, et al. 2018: IS_digest = 0.87 * IV_digest + 0.22. We used the estimate of digestibility in the animal to calculate the digestible fraction of the gross energy content (dig_e) of the diet as dig_e = gross_energy * IS_digest.
Process_Date: Unknown
Process_Step:
Process_Description:
The nutrients contained in extracts were expressed on the basis of the whole sample. For example, the N held in the fiber fraction (adfn_dm) was a product of the proportion of fiber in the whole sample (i.e. adf) and the concentration of N in the fiber residue (adfn): adfn_dm = adfn * adf. Consequently, the N available (N_avail) to the animal was the difference between total N (total_n) and the fiber bound N (adfn_dm): N_avail = total_n - adfn_dm. Digestible N was the difference between total N (total_n) and the N retained in the extract from in vitro digestion (IV_indigest), which was expressed as a proportion of total N (i.e. digestibility). Similarly, availability of each mineral was calculated as the proportion of total mineral (XX_ppm) that was not retained on the indigestible acid extract (indigest_MA), which was a function of the mineral concentration on the residue (XX_ppm_r).
Process_Date: Unknown