Aboveground Net Primary Production - MCSE

Overview

Above ground net primary production (ANPP) is measured in the MCSE ecosystems that range from annual crops to deciduous forest. Biomass sampling is conducted pre-harvest at peak annual biomass: for herbaceous plants this generally means at physiological maturity for annuals, prior to soil incorporation for cover crops, pre-senescence for perennials, and pre-harvest for alfalfa. Biomass sampling occurs at multiple stations in each treatment replicate, but the sampling protocol differs depending on the dominant plants in each treatment.

For treatments with herbaceous plant communities, all plants rooted within the boundary of a sampling quadrat are hand-clipped at ground level (or just above the crown of perennial grasses) and sorted to species, either directly in the field while being clipped or later in the lab for samples stored at 4° C. Each species is placed in its own labeled paper bag or envelope depending on quantity of plant material. Plants are identified to species based on Gleason and Cronquist (1991) and Voss (1972, 1985, and 2012) and verified with the KBS plant reference collection. Species are given codes typically consisting of the first three letters of the genus and first 2 letters of the species for herbaceous species or the first 3 letters for woody species (see datatable KBS019-000). When biomass samples are not separated by species or when live plant fragments cannot be identified to species, plants and/or fragments are combined and labeled as “unsorted”. After all standing plant material is removed from within the quadrat, the dead plant material remaining on the soil surface is collected and labeled as “surface litter”. Surface litter likely represents previous year’s growth and is not included in the current year’s ANPP. All bags and envelopes containing plant material are dried at 60° C for 48 h and weighed. Plant material is removed from envelopes and 2# bags for weighing. For 5# bags or larger, 10 paper bags of each size used are placed in the oven along with plant material; the average dry weight of the bag size used is subtracted from the total weight of plant samples to determine the plant biomass.

The area sampled is typically 1 m2, but the dimensions of the sampling quadrat varies with treatment. For annual cropping treatments (T1-T4), the dimensions vary depending on row spacing of the crop (see Table 1). For T6, T7, and SF (successional field), the quadrat is 0.5 by 2.0 m (1m2); for T8 it is 0.5 by 0.5 m (0.25 m2). Quadrats are oriented with the long side in an east–west direction. This orientation is perpendicular to crop rows in planted systems, thus both row and inter-row plant communities are included in the sampled area.

Tree biomass in the poplar and forest systems is estimated using allometric equations based on annual measurements of stem diameter. In T5 (Poplar), biomass estimates are derived from measurements of basal diameter using an allometric relationship derived from destructive sampling. In the DF (Deciduous Forest) and CF (Coniferous Forest) treatments, woody annual growth is estimated by changes in stem diameter at breast height using species specific allometric equations in Tritton and Hornbeck (1982). Tree diameters are measured in the winter and the same trees are measured every year. Tree leaf production is measured using litter traps placed on the forest floor. Leaf litter is processed as above for plant samples.

Plant samples are finely ground after drying and weighing, and a portion of the ground sample is archived. See datatable KBS052-001 for a listing of archived plant material from the MCSE.

Details for ANPP Estimates:

Treatments 1, 2: Conventional and No-Till with Corn/Soybean/Wheat Rotation

ANPP (T1 and T2) = crop biomass + noncrop biomass

Plants are hand harvested within a 1 m2 quadrat (see Table 1 for dimensions) at each of the five sampling stations per treatment replicate at the following times:

• Corn: harvest (mid-October)

• Soybean: harvest (late September)

• Wheat: kernel entering dough stage (early July)

Table 1. Row spacing since 2009 (see ag log for previous years at https://aglog.kbs.msu.edu/observations/)
| Crop | Treatment | Row spacing | Quadrat dimensions |
| Corn | T1-T4 | 30 inch | 1.5 m x 0.65 m |
| Soybeans | T1-T3 | 15 inch | 1.5 m x 0.65 m |
| Soybeans | T4 | 30 inch | 1.5 m x 0.65 m |
| Wheat | T1-T4 | 7.5 inch | 2.0 m x 0.5 m |

Before clipping, the number of rooted crop stems within the sampling frame are counted. Clipped plant samples are sorted to species either in the field or are stored at 4° C until sorted in the lab, oven dried at 60° C, and the biomass of crop and individual noncrop species recorded. Crop samples are then threshed (Almaco corn or small grain thresher) to separate the seed from shoots (stover). Seeds are again dried at 60° C and the biomass recorded. Seed and stover samples are combined by type across sampling stations for each treatment replicate; subsamples of the seed and stover composited samples are then ground and archived for future analyses.

Calculations

• For crops, express whole crop biomass and seed biomass as g/m2. Subtract the seed biomass from the whole crop biomass at each station to estimate stover biomass.
• For noncrops, express the biomass of each species and the total biomass of all noncrop species in the sampling quadrat as g/m2.
• For ANPP of T1 or T2, first find the average total biomass (whole crop plus noncrop biomass) for each treatment replicate (n=5 sampling stations). Then determine the mean total biomass accumulated (g/m2/y) and standard error for the treatment (n=6 replicates).

Treatments 3, 4: Reduced Input and Biologically Based with Corn/Cover crop (CC)/Soybean/Wheat/CC Rotation

ANPP (T3 and T4) = crop biomass + noncrop biomass + cover crop biomass + noncover crop biomass

Crop and noncrop biomass are determined at the same time and with the same methods as above for T1 and T2. Cover crops are sampled just prior (0-2 days) to plowing under in preparation for planting of the annual crop and may or may not be physiologically mature when sampled. Plants are hand harvested, typically mid- to late May, within a 0.5 by 2.0 m quadrat at each of the five sampling stations per treatment replicate. Samples are sorted to species (cover crop and individual noncover crop species), oven dried at 60° C, and the biomass of each species recorded.

Calculations

• For crops, express whole crop biomass and seed biomass as g/m2. Subtract the seed biomass from the whole crop biomass at each station to estimate stover biomass.
• For cover crops, express cover crop biomass as g/m2.
• For noncrop and noncover crop biomasses, express the biomass of each species in the sampling quadrat and the total biomass of all noncrop and noncover crop species, respectively, as g/m2.
• For ANPP of T3 or T4, first find the average total of crop, noncrop, cover crop, plus noncover crop biomass for each treatment replicate (n=5 sampling stations). Then determine the mean total biomass accumulated (g/m2/y) and standard error for the treatment (n=6 replicates).

Treatment 5: Poplar (short-rotation 7-10 year cycle)

ANPP (T5) = woody growth increment + leaf biomass + understory biomass

The Poplar treatment is managed as a short-rotation woody biomass system with coppicing or replanting after harvest. The woody growth increment of poplars is derived from allometric equations in between harvests.

For allometry, the stem (basal) diameter at 15 cm above ground level is measured with calipers on 10 randomly selected trees in each treatment replicate, typically in December. The biomass of each tree is determined using allometric equations derived from destructive sampling where one tree per replicate is clear cut, weighed whole, then chipped in a wood chipper. A subsample of the chipped tree is weighed fresh, dried in at 60° C, and weighed again to develop a fresh weight to dry weight conversion factor for whole trees. Regression analysis is conducted to develop the best predictor of dry tree biomass based on stem diameter. Dried biomass per tree is converted to biomass per m2 based on the planting density of trees. For the 1989 planting this density is 1 tree per 2 m2; for the 2008 planting it is 1 tree per 3.6 m2.

Poplar leaf biomass is estimated by collecting poplar leaves as they drop throughout leaf fall (typically late July through mid-November). Leaves are collected in 0.8 × 1.2 m wooden litter traps (size designed to fit within or between poplar rows). Two traps are placed in each replicate plot prior to leaf fall in late July. Leaves within the traps are collected throughout leaf fall (weekly through 2014, every other week starting 2015), oven dried at 60° C, and weighed. Litter samples are composited by replicate over the fall season, and subsamples are ground and archived at the end of each fall season.

Understory biomass is estimated by hand-harvesting plants within two 0.8 × 1.2 m quadrats per replicate in late July, using the litter traps described above. Traps are placed predetermined distance and direction from a selected station flag with the long edge running in both a North-South (NS) and East-West (EW) direction; after sampling, traps are left in place for leaf litter collection. Plant samples are sorted to species, oven dried at 60° C, and the weight of each species recorded. They are then composited by plot and subsamples are ground and archived for analysis. An understory of Festuca rubra (red fescue) was planted in 1990 to reduce erosion, but after the 2008 harvest plots were left to colonize naturally. During this time fescue was ground and archived separately.

Calculations

For allometry of poplar biomass, convert stem diameter to woody biomass using the following allometric equations based on destructive sampling:

DN34 (eugenii): Populus nigra x P. deltoids hybrid (before 2008):

biomass (in grams) = 10^ (-1.195 + 2.505 * log(diam.))

NM-6: Populus. nigra x Populs maximowiczii (after 2008):

biomass (in grams) = 10^(-0.713 + 2.367 * log(diam.))

• Express woody biomass on an areal basis (g/m2) by adjusting for plant density, as given above, and determine the average biomass per replicate. Calculate the average annual woody growth increment per replicate as the difference in average tree biomass between successive growing seasons (g/m2/y) and determine the mean annual woody growth increment (g/m2/y) and standard error for the treatment (n=6 replicates).
• For leaf biomass, calculate the sum of leaf litter collected over the fall season for each trap in the replicate, then determine the average cumulative leaf litter per m2 for each replicate (g/m2/y, n=2 litter traps).
• For annual poplar production, determine the sum of annual woody growth increment (g/m2/y) and leaf biomass (g/m2/y) for each replicate, then calculate the mean annual production and standard error for the treatment (n=6 replicates).
• For understory biomass, sum the biomass of all species in the sampling quadrat, then determine the average understory biomass per m2 for each replicate (g/m2, n=2 quadrats).
• For ANPP of T5, sum the annual woody growth increment, leaf biomass and understory biomass for each replicate then determine the mean total biomass accumulated (g/m2/y) and standard error for the treatment (n=6 replicates).

Treatment 6: Switchgrass (since 2019; Alfalfa through 2017)

For Switchgrass:

ANPP (T6) = plant biomass (sum of all species)

For Switchgrass: plant biomass is hand harvested within a 0.5 × 2.0 m quadrat at each of the five sampling stations at physiological maturity, typically in August or early September. Samples are sorted to species by station, oven dried at 60° C, and the biomass of each species recorded. Switchgrass and a composited sample of the remaining species are ground and archived for analyses.

Calculations

• Calculate the total biomass of all plant species at each station; then determine the average total plant biomass for each replicate (g/m2, n=5 stations).
• For ANPP of T6, determine the mean total plant biomass accumulated (g/m2/y) and standard error for the treatment (n=6 replicates).

For Alfalfa (5-6 year rotation with winter wheat as 1 year break crop):

ANPP (T6) = crop biomass (sum of all harvests) + noncrop biomass (sum of all harvests)

Crop (alfalfa) and noncrop (weeds) biomass is hand harvested within a 0.5 × 2.0 m quadrat at each of the five sampling stations per replicate just prior to agronomic harvest (one-tenth bloom); harvests typically occur 3 to 4 times per year from late May through mid-October. Samples are sorted to species (crop and individual noncrop species), oven dried at 60° C, and the biomass of each species recorded. Noncrop species are combined into a composite sample; subsamples are ground and archived for future analyses.

Sampling of winter wheat during the break year between alfalfa replanting follows the same timing and methods as described above for Treatments 1 and 2.

Calculations

• For alfalfa, calculate the average crop biomass (g/m2) by harvest date and the average total crop biomass (g/m2) for each replicate over the growing season (n=5 sampling stations).
• For noncrops, express the biomass of each noncrop species in the sample by harvest date and the total biomass of all noncrop species for each replicate as g/m2.
• For ANPP of T6, first find the average total biomass (seasonal crop plus noncrop biomass) for each replicate (n=5 sampling stations). Then determine the mean total biomass accumulated (g/m2/y) and standard error for the treatment (n=6 replicates).

Treatment 7: Early Successional Community (with annual spring burn)

ANPP (T7) = plant biomass (sum of all species)

Plant biomass is hand harvested within a 0.5 × 2.0 m quadrat at each of the five sampling stations at physiological maturity of the dominant plant community, typically in early August. Samples are sorted to species by station, oven dried at 60° C, and the biomass of each species recorded. Subsamples of the top 3 dominant species, by weight, and a composited sample of the remaining species are ground and archived for analyses.

Calculations

• Calculate the total biomass of all plant species at each station; then determine the average total plant biomass for each replicate (g/m2, n=5 stations).
• For ANPP of T7, determine the mean total plant biomass accumulated (g/m2/y) and standard error for the treatment (n=6 replicates).

Treatment 8: Mown Grassland (Never-Tilled) Community (with annual fall mowing)

ANPP (T8) = plant biomass (sum of all species)

Plants are hand harvested within a 0.5 × 0.5 m quadrat at each of the five sampling stations per replicate. The harvested area is less than other treatments because of the smaller plot size. The dominant species have primarily perennial life histories and mature over the summer: cool season grasses (e.g. Bromus sp.) and late season perennials (e.g. Solidago sp.) are dominants, and a harvest in early August allows for reasonable assessment of both community types. Samples are sorted to species by station, oven dried at 60° C, and the biomass of each species recorded. Subsamples of the top 3 dominant species, by weight, and a composited sample of the remaining species are ground and archived for analyses.

Calculations

• Calculate the sum of plant biomass of all species at each station; then determine the average total plant biomass per quadrat (g/m2, n=5 stations).
• For ANPP of T8, determine the mean total plant biomass accumulated (g/m2/y) and standard error for the treatment (n=4 replicates).

Treatment SF: Mid-Successional Community (cropland abandoned in 1950-1960)

ANPP (TSF) = plant biomass (sum of all species) + leaf litter biomass

Herbaceous plants are harvested in the same manner as Treatment 7; samples may include small woody species that can be clipped with a shears. TSF sites are in varying stages of succession and may contain larger trees and shrubs, however woody biomass is not included in ANPP estimates. Leaf litter is collected in five 0.5 × 0.95 m litter traps (made from plastic barrels cut lengthwise and secured in a wooden cradle) placed on the forest floor in each replicate prior to leaf fall. Litter is collected (weekly through 2014, every other week starting 2015), oven dried at 60° C, and the biomass recorded. Litter samples are composited by replicate over the fall season (early September through mid-December), and subsamples are ground and archived at the end of each fall season.

Calculations

• Calculate the summed biomass of all plant species at each station; then determine the average summed biomass for the replicate (g/m2, n=5 stations).
• Calculate the sum of litter trap biomass collected over the fall season by station, then determine the average cumulative litter trap biomass for each replicate (in g/m2, n=5 litter traps).
• For ANPP of TSF, first determine the total plant biomass by adding the average summed plant biomass (g/m2) and the average cumulative litter trap biomass (g/m2) for each site; then determine the mean total plant biomass accumulated (g/m2/y) and standard error for the treatment (n=3 replicates).

Treatments DF and CF: Deciduous and Conifer Forests

ANPP (TDF or TCF) = woody growth increment (sum of all trees in quadrat) + leaf litter biomass

Annual growth of deciduous and coniferous trees is estimated by monitoring changes in stem diameter for all trees within each treatment replicate that are greater than 5 cm dbh (diameter at breast height). Stem diameters are measured in the winter with dbh tape at 4 points on the stem that are determined by hanging a measuring chain from a nail permanently installed in each tree trunk 5 feet from the ground. The average of the 4 diameter measurements is used to estimate individual tree biomass based on allometric equations available in Tritton and Hornbeck (1982):

Example equations:

Species	Equation	applies within diameter range:
Acer rubrum	wt (lb)=2.0772(dbh)^2.5080	2-20 in
Acer saccharum	wt (lb)=2.4439(dbh)^2.5735	2-20 in
Carya glabra	wt (lb)=2.034(dbh)^2.6349	2-20 in
Fraxinus americana	wt (lb)=2.3626(dbh)^2.6174	2-20 in
Prunus serotina	wt (lb)=1.8082(dbh)^2.6174	2-20 in
Quercus alba	wt (lb)=1.5647(dbh)^2.6887	2-20 in
Quercus rubra	wt (lb)=2.4601(dbh)^2.4572	2-20 in
Picea abies	ln wt=0.8079+2.3316*(ln dbh)	1-26 in
Pinus resinosa	ln wt=0.7157+2.3865*(ln dbh)	1-20 in
Pinus strobus	ln wt=0.4080+2.4490*(ln dbh)	1-26 in
Prunus serotina	wt(lb) 1.8082 * (dbh)^2.6174	2-20 in

Herbs and shrubs are a minor part of these communities and are not sampled; shrub leaf litter (if any) is included in leaf litter estimates. Leaf litter is collected in five 0.5 × 0.95 m litter traps (made from plastic barrels cut lengthwise and secured in a wooden cradle) placed on the forest floor of each treatment replicate prior to leaf fall. Litter is collected (weekly through 2014, every other week starting 2015), oven dried at 60° C, and the biomass recorded. Litter samples are composited by treatment replicate over the fall season (early September through mid-December), and subsamples are ground and archived at the end of each fall season.

Calculations

• Calculate woody growth increment as the difference in individual tree biomass between successive growing seasons, sum the biomass increase across all trees in the treatment replicate, and determine the total woody growth increment increase on an areal basis (g/m2).
• Calculate the sum of litter trap biomass collected over the growing season for each trap, then determine the average cumulative litter trap biomass for each replicate (g/m2, n=5 litter traps).
• For ANPP of TDF or TCF, first determine the total plant biomass as the sum of the woody growth increment (g/m2) and the average cumulative litter trap biomass (g/m2) for each replicate, then determine the mean total plant biomass accumulated (g/m2/y) and standard error for the treatment (n=3 replicates).

References:

Gleason, H.A. and A. Cronquist. 1991. Manual of vascular plants of Northeastern United States and adjacent Canada. New York Botanical Garden, Bronx NY.

Tritton, L.M. and J.W. Hornbeck. 1982. Biomass equations for major tree species of the Northeast. Broomall, PA: Northeast. For. Exp. Stn.; USDA For. Serv. Gen. Tech. Rep. NE-69.

Voss, E. G. 1972. Michigan Flora. Part I. Gymnosperms and monocots. Cranbrook Institute of Science and University of Michigan Herbarium.

Voss, E. G. 1985. Michigan Flora. Part II. Dicots (Sauruvaceae – Cornaceae). Cranbrook Institute of Science Bulletin 59 and University of Michigan Herbarium.

Voss, E.G. 2012. Field manual of Michigan flora. Sixth edition. University of Michigan Press, Ann Arbor MI.