Nondestructive Estimation of Net Primary Production in Urban Rain Gardens

1
Non-destructive Estimation of Net Primary
Production in Urban Rain Gardens
M. R. Johnston and N. J. Balster, Department of
Soil Science, University of WI, 1525 Observatory
Drive, Madison, WI 53706
Introduction
Methods
Preliminary Results
Harvesting one replicate of each prairie species
a month after planting plugs provided preliminary
relationships among biomass, LAI, and canopy
height. Here, we show initial data for the 19
species of prairie planted in experimental rain
gardens, labeled as in Table 1. We harvested a
sample plant for each shrub species at time of
planting, but preliminary data on shrubs are not
presented here.
Design Plastic pots (open cylinders, diameter 36
cm and height 92 cm) were filled with a mix of
topsoil, sand, and compost. Planting took place
in late June, 2006. There are three replicate
pots per species of prairie (Table 1) and shrub
(Table 2). Prairie monocultures were planted
with four individuals per pot, using second-year
plugs (Prairie Nursery, Brodhead, WI). Shrubs
were planted one individual per pot, using mature
potted plants (Watts Landscaping Service,
Madison, WI). All plants are growing under field
conditions with minimal irrigation. The pots are
located near experimental rain gardens on the
west side of Madison, WI.
Rain gardens installed within the urban landscape
have included various vegetation types, such as a
wet-mesic prairie or typical landscaping shrubs.
We evaluate the performance of rain gardens by
estimating plant productivity and light
interception for each vegetation type. We seek
simple predictors of biomass for each vegetation
type using dimensional analyses. Most of the
species of shrub planted in the rain gardens have
allometric equations derived from physical
dimensions such as stem diameter and crown area.
These allometries estimate aboveground biomass
(Smith and Brand, 1983 Golubiewski, 2006),
whereas estimates of belowground biomass are
lacking. Similarly, the 19 species of prairie
plants included in this study are commonly
planted within raingardens, yet these species
lack allometric equations for estimating biomass.
In the past, studies have approximated
belowground production beneath prairie vegetation
from aboveground growth (Reich et al., 2003), or
have emphasized differences in productivity at a
landscape scale (Knapp et al., 1993). By
destructive sampling, we will establish
allometric equations between total, aboveground,
and belowground biomass for each species of shrub
and wet-mesic prairie vegetation. Moreover, we
will regress plant biomass to a suite of physical
measurements, including stem diameter, plant
height, crown area, and canopy height. Since we
can easily measure indirect leaf area index (LAI)
in the rain gardens (with a light attenuation
probe), we will measure LAI as another possible
predictor of biomass. For each species of prairie
and shrub, we will relate plant aboveground
biomass to indirect LAI (Turner et al., 2004),
asking also whether indirect LAI correlates best
with leaf biomass or total aboveground biomass
(i.e., some of the prairie species have
photosynthetic stems). Through these
species-specific allometries, we will be able to
estimate aboveground, and thus belowground,
biomass for a community of species.
Total aboveground biomass was positively related
to indirect LAI (Figure 1). In general,
aboveground biomass and canopy characteristics
seemed to change LAI. For example, Baptisia and
Carex (numbers 4 and 6) grew very little
aboveground since planting, Monarda (12)
developed a tall, open canopy, and Boltonia and
Solidago (5 and 18) established dense canopies.
Aboveground biomass also related well with canopy
height for the 19 prairie species (Figure 2). We
checked whether LAI measured with an optical
light attenuation probe represented actual LAI
when calculated from leaf biomass (Figure 3).
Although we will establish this relationship on a
species-basis, combined data from all 19 species
supports measuring indirect LAI in rain gardens
as a surrogate for direct LAI. Note that direct
LAI calculated for Solidago (number 18) is high
because this species grew the most leaf biomass
at time of harvest (Figure 2).
Prairie plants one month after planting, in July
2006. The fourth pot of each species was
harvested for biomass.
Shrubs one month after planting, in July 2006.
Measurement Record physical plant measurements,
including heights, canopy volume, and basal stem
diameters. Compute specific leaf area (SLA) from
dry leaf mass (60 C for 48 hours) and a leaf
area meter with transparent conveyor belt (LiCor
LI-3000). Measure SLA by species three times
over the season, using 6 leaves per prairie
species and 9 leaves per shrub. Measure indirect
leaf area index (LAI) at the soil surface every
two weeks (LiCor LI-2000) beneath prairie
vegetation.
Table 1. Prairie Mix Species List No. Scientific
Name Common Name  1 Andropogon geradii Big
bluestem 2 Asclepias incarnata Red
milkweed 3 Aster novae-angliae New England
aster 4 Baptisia bracteata Cream
indigo 5 Boltonia asteroides False aster 6 Carex
vulpinoidea Fox sedge 7 Echinacea pallida Pale
purple coneflower 8 Echinacea purpurea Purple
coneflower 9 Eupatorium perfoliatum Boneset 10 Hel
ianthus occidentalis Ox-eye sunflower 11 Liatris
pycnostachya Prairie blazing star 12 Monarda
fistulosa Bergamot 13 Panicum virgatum Switch
grass 14 Parthenium integrifolium Wild
quinine 15 Penstemon calycosus Longsepal
beardtongue 16 Ratibida pinnata Yellow
coneflower 17 Rudbeckia hirta Black-eyed
susan 18 Solidago rigida Stiff
goldenrod 19 Veronicastrum virginicum Culver's
root
Figure 1. Total aboveground biomass (g) and
optical leaf area index (LAI) for the 19 prairie
species harvested one month after planting.
Harvest We will harvest all shrubs at the end of
the growing season (October, 2007). Each species
of prairie vegetation will be considered
independently to account for the seasonal range
in peak productivity (harvested before, during,
and after flowering). Clip aboveground biomass
and separate into leaves, stems, fruit, flowers.
Hand sort and rinse live roots from soil
carefully excavated from pot. Hand sort roots and
separate them into two groups roots which were
part of the original plug and roots new since
planting. Dropped leaves from all pots will be
collected every week and factored into the
biomass summations.
The Next Step
Beginning in the spring of 2007, we will monitor
changes in the physical dimensions, LAI, and
productivity for each species of prairie and
shrub. We will harvest all plants to capture
their peak productivity and build allometric
equations for each species. These measurements,
excepting harvest, will be repeated in the
experimental rain gardens. We will select the
best predictors of biomass for each species by
generating sets of equations. We will apply these
relationships to approximate aboveground and
belowground productivity in the experimental rain
gardens, where destructive sampling is not
preferable. Finally, rain garden performance may
be evaluated as a function of differing
vegetation types.
Figure 2. Aboveground biomass and canopy height
for the 19 species of prairie harvested one month
after planting.
Objectives
Table 2. Shrub Species List Scientific
Name Common Name   Cornus sericea
isanti Red-twig dogwood Ilex
verticillata Winter berry Prunus
aroniamelanocarpa Black chokeberry Salix purpurea
gracilis Dwarf arctic willow Viburnum
trilobum American cranberry Viburnum
dentatum Arrowwood viburnum
Establish allometric equations for aboveground,
belowground, and total biomass by species. Apply
these allometric equations for each species to
prairie and shrub vegetative communities in rain
gardens.
References Knapp, A. K., J. T. Fahnestock, S. P.
Hamburg, L. B. Statland, T. R. Seastedt, and D.
S. Schimel. 1993. Landscape patterns in
soil-plant water relations and primary production
in tallgrass prairie. Ecology 74549-560. Reich,
P. B., C. Bushena, M. G. Tjoelker, K. Wrage, J.
Knops, D. Tilman, and J. L. Machado. 2003.
Variation in growth rate and ecophysiology among
34 grassland and savanna species under
contrasting N supply a test of functional group
differences. New Phytologist 157617-631. Smith,
W. B., and G. J. Brand. 1983. Allometric biomass
equations for 98 species of herbs, shrubs, and
small trees. Research Note NC-299, North Central
Forest Experimental Station, USDA Forest Service,
St. Paul, Minnesota, USA. Turner, M. G., D. B.
Tinker, W. H. Romme, D. M. Kashian, and C. M.
Litton. 2004. Landscape patterns of sapling
density, leaf area, and aboveground net primary
production in postfire lodgepole pine forests,
Yellowstone National Park (USA). Ecosystems 7
751-775.
Hand-sorting belowground biomass one month after
planting.
Measuring aboveground biomass one month after
planting, Aster sp.
Figure 3. Leaf area index (LAI) by direct
calculation and optical light attenuation probe
for the 19 prairie species harvested one month
after planting.