Aboveground Net Primary Productivity Protocol

Overview

Above ground net primary productivity (ANPP) is measured at the KBS LTER in habitats ranging from annual cropping systems to deciduous forests. The diverse plant communities in these habitats require different harvest and/or sampling methods. All measurements are taken pre-harvest at peak annual biomass for major community components. This generally means physiological maturity for annuals and pre-senescence for perennials; most treatments are thus sampled at least twice per year depending on the life history of community components (e.g. corn vs. winter annuals in Treatment 1) and on agronomic harvest frequency (e.g. 3-4 times per year for alfalfa). If possible, biomass samples are taken from each of the five sampling stations within a plot, although labor, weather, and time constraints may alter the number of sampling stations for a given harvest.

For Treatments 1, 2, 3, 4, 6, 7 and SF (successional field) ANPP is assessed by harvesting all the above ground portion of plants that are rooted within the bounds of the harvest quadrat. The quadrat size totals 1 m 2 but the dimensions vary depending on the crop row spacing in the annual systems (T1-4) and are described in Table 1. The quadrat size for T5-SF is 0.5 by 2.0 m (1m 2 ). Quadrats are oriented with the long side in an east – west direction. This direction is perpendicular to the crop rows (in planted systems) and allows for assessment of both the row and interrow plant communities. All plants within the quadrat are clipped at ground level, bagged, and stored at 4 degrees C until botanical separations are performed. Harvested plants are separated by species and identified using the five-letter Bayer code system (Weed Science, 1984). Six letter codes are used for woody species, using the first three letters of both genus and species to create the code. In some cases plants are composited into crop and non dominant plant component. Crops are further separated into seed and stover. Plants are dried at 60 degrees C for a minimum of 48 hours and dry weights recorded along with the date of harvest, field replicate, treatment, sampling station and species code.

In Treatment 5 (poplar plantation) biomass estimates are derived from measurements of basal diameter using an allometric relationship between diameter and biomass determined from a subset of trees harvested prior to leaf drop. In the DF (deciduous forest) and CF (conifer forest) wood annual growth is estimated by changes in stem diameter using an allometric equation available in Tritton and Hornbeck (1982). Leaf production in sites with trees is estimated with two 0.8 × 1.2 m litter traps placed on the forest floor of each site.

Details for the ANPP estimates for all treatments are provided below.

Treatment 1: Conventional tillage

Corn / Soybean / Wheat rotation.
h4. Crop

plants are hand harvested using a 1 m 2 quadrat (see Table 1) at each of the five sampling stations at physiological maturity of the crop:

• Corn : black layer (early September).
• Soybeans : pre-leaf drop (early September).
• Wheat: kernel entering dough stage (mid-July).

Plant tissue is dried and the total biomass of the plot is recorded. The tissue is then threshed (Almaco corn or small grain thresher) to separate the seed from stover. Seed biomass is recorded and moisture sub samples are taken using a Burrows Digital Moisture Computer 700. Seed and stover tissue sub samples are collected, combined by tissue type over stations, and archived for further analysis.

• Calculate the mean total, seed and stover biomass per plot on a dry weight basis.
• Report for ANPP: mean total biomass (g/m2 /y) and standard error (SE) with n=6 reps (blocks).

Non dominant plant biomass

Plants are hand harvested using a 1 m 2 quadrat at each of the five sampling stations at physiological maturity of the non dominant plant biomass community. Since this treatment is plowed annually each spring, the dominant non dominant plant biomass have a summer annual life history and mature (set seed) in mid-August. Botanical separations are performed by species by station, dried, and the dry biomass for each species at each station is obtained.

• Calculate the sum of the total non dominant plant biomass (over species) at each station; calculate the mean total non dominant plant biomass per plot.
• Report for ANPP : mean total non dominant plant biomass (g/m2/y), SE, with n=6 reps (blocks).

Total

sum each plot crop and non dominant plant biomass.

• Report mean total biomass (g/m2) and SE with n=6 reps (blocks).

Treatment 2: No tillage

Corn / Soybean / Wheat rotation
h4. Crop

Identical to Treatment 1

Non dominant plant biomass

Identical to Treatment 1 in harvest methods. The majority of non dominant plant biomass in the no till system have perennial life histories and mature at a variety of times, with most maturing in the late summer (mid-August). The few winter annual and biennial non dominant plant biomass that are present in the spring are killed/suppressed with a preplant treatment of glyphosate and are not harvested prior to herbicide application.

• Calculate the sum of the total non dominant plant biomass (over species) at each station; calculate the mean total non dominant plant biomass per plot.
• Report for ANPP : mean total non dominant plant biomass (g/m2/y), SE, with n=6 reps (blocks).

Total

sum each plot crop and non dominant plant biomass.

• Report mean total biomass (g/m2) and SE with n=6 reps (blocks).

Treatment 3: Low Chemical Input / Annual tillage

Corn / Legume cover (LC) / Soybean / Wheat / LC rotation
h4. Crop

Identical to Treatment 1
h4. Non dominant plant biomass

Identical to Treatment 1
Legume Cover Crop (LC)

plants are hand harvested using a 1 m 2 quadrat at each of the five sampling stations just prior to plowing and planting of the annual crop. The LC has often not reached physiological maturity by this time (typically mid- to late-May). Non dominant plant biomass is separated from LC for separate analysis (below).

• Calculate the mean total LC biomass per plot on a dry weight basis.
• Report for ANPP: mean total biomass (g/m2/y) and standard error (SE) with n=6 reps (blocks).

LC Non dominant plant biomass

Non dominant plant biomass associated with the legume cover in early spring have winter annual, biennial or perennial life histories. Botanical separations are performed by species by station, dried, and the dry biomass for each species at each station is obtained.

• Calculate the sum of the total non dominant plant biomass (over species) at each station; calculate the mean total non dominant plant biomass per plot.
• Report for ANPP : mean total non dominant plant biomass (g/m 2 /y), SE, with n=6 reps (blocks).

Total

sum each plot crop, non dominant plant biomass, LC, and LC non dominant plant biomass.

• Report mean total biomass (g/m 2 ) and SE with n=6 reps (blocks).

Treatment 4: Zero Chemical Input / Annual tillage

Corn / Legume cover (LC) / Soybean / Wheat / LC rotation
h4. Crop, Non dominant plant biomass, LC, and LC non dominant plant biomass and Total

Identical to Treatment 3

Table 1.

Crop	Treatment	Row spacing (in)	Quadrat dimensions
Corn	T1-T4	30 inch	1.5 m x 0.65 m
Soybeans	T1-T2	7.5 inch	2.0 m x 0.5 m
Soybeans	T3-T4	30 inch	1.5 m x 0.65 m
Wheat	T1-T4	7.5 inch	2.0 m x 0.5 m

Treatment 5

Populus Plantation. Poplar trees with grass cover crop
h4. Crop

poplar woody biomass has been estimated using a regression equation developed from a destructive harvest each fall prior to fall leaf drop. Historically basal tree diameter squared has been the best predictor of total tree biomass.

• Allometric measures of basal tree diameter (mm) at 15 cm above the soil surface are taken in late August . The measurements are made on a subset of 28 flagged trees near sample station 3 (a four row by seven tree matrix) in the 2 × 1 m density plots . Data for rep, tree #, diameter (mm) are entered into a poplar allometric spreadsheet. A histogram of tree diameter is generated to establish the range of diameters and to develop size classes used in the destructive harvest to follow. The regression equation developed in the destructive harvest is used in conjunction with the diameter measures to estimate the biomass of each of the 28 flagged trees per plot.

• To develop the regression equation, we annually harvest 12 trees chosen to encompass a proportional representation of trees in each diameter size class. Trees are harvested from all plots but rep 3, which had poor initial stand establishment . Trees are cut at 10 cm above the ground. Measurements include the dry weight of leaves, branches, and trunk separately; basal diameter (mm), total tree height (m), and leader height for each year’s growth.

• Separate regressions are developed to relate tree height, tree diameter, and basal area to total tree mass and to woody tree mass (branches and stems only).

• Mean woody tree biomass (kg/tree) is converted to mean woody areal extent on the basis of 0.5 trees per m 2 .

The 2 × 1m density trees are a matrix of 86 trees (EW) by 27 trees (NS) within a 88.3 by 53.2 m area = 2322 trees/ 4697.56 m 2 = 0.49 trees/m 2

• Calculate woody growth increment: The difference of the mean woody tree biomass between successive growing seasons (g/m 2 /y) for each plot

Regression Equations for Estimated Woody Biomass

The following predictive equations for poplar woody or total biomass have been generated using the destructive harvest technique. Reported are equations pertaining to the main site 2 × 1 m spacing, however equations specific to tree density spacings and non dominant plant biomass/non dominant plant biomass free growth may be available from the investigating lab for that season. Diameter is measured as mm from 15 cm from the ground unless specified otherwise. Trees were planted as 25 cm cuttings in 1989.

Year	Equation	r^2	Lab
1989	Not applicable (whole tree harvests)	NA	Core
1990	wdbmass (Kg/tree) = 0.0054 (diam mm 2 ) + 168.5	0.98	Gross (updated 3/31/95 sjh)
1991	wdbmass(Kg/tree) = 0.09 (diam 2 cm) – 0.6	0.925	Pregitzer/ Maas thesis
1991	totbmass(Kg/tree) = 0.099 (diam 2 cm) – 0.667	0.93	Pregitzer/ Maas thesis
1992	wdbmass(Kg/tree) = 0.00935 (diam mm 2 ) -491.07 totbmass(Kg/tree) = .01086 (diam mm 2 ) – 816.96	0.95	Core/Halstead
1993	wdbmass(Kg/tree) = .0011 (diam mm 2 ) – 0.829 totbmass(Kg/tree) = 0.0012 (diam mm 2 ) – 0.97	0.96	Core/Halstead
1994	Wdbmass (kg/tree) = 0.00139 (diam mm 2 ) -1.867	0.92	Core/Halstead	Does not work for trees with diam < 37.66 mm
1995	Wdbmass (kg/tree) = 0.00205 (diam mm 2 ) – 3.366	0.983	Core/Halstead
1996	Wdbmass (kg/tree) = 0.0022 (diam mm 2 ) – 5.844	0.929	Core/Halstead	Drought year- high tree mortality
1997	Wdbmass (g/tree) = 1.5784 (diam mm 2 ) + 187.853 Note units are in Grams per tree!	0.853	Core/Halstead
1998	Wdbmass (kg/tree) = 0.0016 (diam mm 2 ) – 0.276	0.975	Core/Halstead

Leaf

Poplar leaves drop throughout the growing season. Leaf litter is collected in 0.8 × 1.2 m wooden litter trap frames (size was designed to fit within or between poplar rows ) . Two traps are placed in each plot following leaf emergence in late May. Leaves within the traps are collected throughout the season, dried, weighed, and archived for tissue analysis.

• Calculate the mean litter biomass (g/m 2 ) per plot per collection date.
• Report for ANPP: Mean seasonal (sum over dates) litter drop (g/m 2 /y), n=6 reps (blocks).

Total Crop ( Populus ) ANPP:

• Calculate on a per plot basis the sum of woody growth increment and leaf fall by plot, SE, and n=6 reps (blocks).
• Report for ANPP the mean sum, SE, and n=6 reps (blocks).

Grass cover (since 1990)

grass Festuca rubra (red fescue) is hand harvested from two 0.8 × 1.2 m stations per plot in late May at fescue anthesis (reproductive maturity) . (Litter traps [above] are placed on the harvested area). Botanical separations are not performed since the grass is essentially a monoculture, however a large majority of the collected grass is standing litter and not fresh tissue.

• Calculate the mean fescue biomass (g/m 2 ) per plot.
• Report for ANPP: Mean fescue biomass (g/m 2 ), SE, and n=6 reps.

Non dominant plant biomass (prior to 1990)

Non dominant plant biomass in the poplar understory were most prevalent before the establishment of the grass cover crop (fall 1990); there are very few species now. A separate harvest has not been taken for non dominant plant biomass since 1992 . Prior to 1993, non dominant plant biomass was assessed as for Treatment 1. The non dominant plant biomass community in the 2 × 1 m density micro plots without fescue, contains a number of perennial species including Trifolium and Hypericum sp.

• Calculate the mean non dominant plant biomass (g/m 2 ) per plot.
• Report for ANPP (prior to 1993) mean non dominant plant biomass (g/m 2 ), SE, and n=6 reps (blocks).

Total ANPP

• Calculate on a per plot basis the sum of total Populus ANPP (woody growth increment + leaf fall), grass cover, and non dominant plant biomass.
• Report for ANPP the mean sum, SE, and n=6 reps (blocks).

Treatment 6

Continuous Alfalfa
h4. Crop

alfalfa is hand harvested using a 0.5 × 2.0 m quadrat at each of the five sampling stations at one-tenth bloom (just prior to agronomic harvest) 4 times per year: late May, early July, mid-August and mid-October or 4 weeks following a killing frost. Alfalfa is separated from non dominant plant biomass prior to drying.

• Calculate the mean biomass (g/m 2 ) per plot by harvest date and the total seasonal biomass (g/m 2 ) per plot.
• Report for ANPP : Mean seasonal biomass (g/m 2 /y), SE, and n=6 reps (blocks)

Non dominant plant biomass

non dominant plant biomass is collected from the crop sample noted above . Botanical separations are performed by species by station, dried, and the dry biomass for each species at each station is obtained.

• Calculate the sum of the total non dominant plant biomass (over species) at each station for each harvest date; the mean total non dominant plant biomass per plot (g/m 2 ) by harvest date; and the total seasonal non dominant plant biomass per plot (over harvest dates).
• Report for ANPP : mean total seasonal non dominant plant biomass (g/m 2 /y), SE, with n=6 reps (blocks).

Treatment 7

Successional Community
h4. Crop

none
h4. Non dominant plant biomass

Plants are hand harvested using a 0.5 x2.0 m quadrat at each of the five sampling stations at physiological maturity of the majority of the non dominant plant biomass community. The dominant non dominant plant biomass have primarily biennial or perennial life histories; harvest in mid-July allows for assessment of the early season species (matured) and the late season species (in full vegetative growth but not physiologically mature) . Botanical separations are performed by species by station, dried, and the dry biomass for each species at each station is obtained.

• Calculate the sum of the total non dominant plant biomass (over species) at each station; and the mean total non dominant plant biomass per plot (g/m 2 ).
• Report for ANPP : mean total non dominant plant biomass (g/m 2 /y), SE, with n=6 reps (blocks).

Treatment 8

Never Tilled Community
h4. Crop

none
h4. Non dominant plant biomass

Plants are hand harvested using a 0.5 × 0.5 m quadrat at each of the five sampling stations. A reduced harvest area is used due to the limited size of the plots. The dominant plants have primarily perennial life histories and mature over a range of the summer months. Cool season grasses (e.g. Bromus sp.) and late season perennials (e.g. Solidago sp.) are dominants, and a harvest in mid July allows for reasonable assessment of both types of communities. Botanical separations are performed by species by station, dried, and the dry biomass for each species at each station is obtained.

• Calculate the sum of the total non dominant plant biomass (over species) at each station; the mean total non dominant plant biomass per plot (g/m 2 ).
• Calculate the sum of the total non dominant plant biomass (over species) at each station; the mean total non dominant plant biomass per plot (g/m 2 ).
• Report for ANPP : mean total non dominant plant biomass (g/m 2 /y), SE, with n=6 reps (blocks).

Treatment SF

Successional Community – Old Field for 20+ years
h4. Crop

No Crop
h4. Non dominant plant biomass

Identical to Treatment 7
h3. Treatment DF

Deciduous Forest Community
h4. Wood

Annual growth is estimated by changes in stem diameter for all trees within a 20 × 20 in area within each of the three DF stands. Stem diameters are measured in the fall with spring dendrometers (Cattelino et. al., 1986) permanently attached at breast height to all trees beginning in 1995 . Diameters are used to estimate individual tree mass based on allometric equations available in Tritton and Hornbeck (1982): DBH (diameter at breast height) tapes are also used in the spring and fall on all trees within the 400 m 2 plot area.

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

• Calculate woody growth increment as summed differences in individual tree masses between successive growing seasons or a per site basis.

Leaves

Leaf litter is collected in two 0.8 × 1.2 m litter traps placed on the forest floor prior to spring leafout. Traps are emptied biweekly(?), dried, and composited by plot over the season. A subsample is ground and archived at the end of each season.

• Calculate total seasonal leaf fall per site.

Total Tree ANPP

Sum of woody growth increment and total seasonal leaf fall (g/m2/y), SE, n=3 sites.

Herbs and shrubs

Herbs and shrubs are a minor part of these DF communities; shrub leaf litter (if any) is included in the leaf litter (above).

Treatment CF

Conifer Forest
h4. Wood

annual growth is estimated by changes in stem diameter for all trees within a 20 × 20 in area within each of the three DF stands. Stem diameters are measured in the fall with spring dendrometers (Cattelino et. al., 1986) permanently attached at breast height to all trees beginning in 1995 . Diameters are used to estimate individual tree mass based on allometric equations available in Tritton and Hornbeck (1982):

The following equations were used:

Species	Equation	applies within diameter range:
Picea abies	ln wt=0.8079+2.3316*(lndbh)	1-26 in
Pinus resinosa	ln wt=0.7157+2.3865*(lndbh)	1-20 in
Pinus strobus	ln wt=0.4080+2.4490*(lndbh)	1-26 in
Prunus serotina	wt(lb) 1.8082 * (dbh)^2.6174	2-20 in

Leaves

Leaf litter is collected in two 0.8 × 1.2 m litter traps placed on the forest floor prior to spring leafout. Traps are emptied biweekly(?), dried, and composited by plot over the season. A subsample is ground and archived at the end of each season.

• Calculate total seasonal leaf fall per site.

Total Tree ANPP

sum of woody growth increment and total seasonal leaf fall (g/m 2 /y), SE, n=3 sites.
Herbs and shrubs

Herbs and shrubs are a minor part of these CF communities; shrub leaf litter (if any) is included in the leaf litter (above).

Citations

Cattelino, P.J., C.A. Becker and L.G. Fuller . 1986. Construction and installation of homemade dendrometer bands. Northern J. Appl. Forestry 3(2):73-75.

Fuller, L.G., P.J. Cattelino, D.D. Reed . 1988. Correction equations for dendrometer band measurements of five hardwood species. Northern J. Appl. Forestry 5(2):111-113.

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.

Weed Science Society. 1984. Weed Science composite list of weeds. Weed Science Vol. 32 Supplement 2.