Palmetto data
Study sites
Flatwood and scrubby flatwood habitats were selected in Archbold's
West Section in 1981. Flatwood sites included Ridge Road, WSP1 and
WS30 and were compared to scrubby flatwoods sites Ridge Road, WSP2 and
Copse Road. The West Section of Archbold had not burned within the
last decade, but historically had experienced a more natural fire
return interval (5 - 20 years). All other sites are on Archbold's Red
Hill in either sand pine scrub or sandhill, and had been fire
suppressed, with the last known fire occurring in 1927. These latter
two habitats fall in either Control management units or Experimental
Burn management units. At the time this study was initiated, the fire
management plan for Red Hill included restoring fire in some
management units (Experimental Burn) while leaving others long
unburned as reference sites (Controls). Experimental manipulations of
clipping and fertilizing took place in sand pine scrub control
management units.
The sandhill control site was roller chopped in 2013 as part of a
sandhill restoration effort, dislodging aluminum stakes so they could
not be matched up with their respective palmetto. Therefore, data were
not collected in 2017.
A wildfire in May 2013 burned several of our study plants in both
sandhill and sand pine scrub. Notes of whether or not the plant burned
were recorded as comments in 2017. Because this was a wildfire, a plow
was used to contain the escape and subsequently plowed through and
killed 53 of our plants (31 S. repens and 22 S. etonia). These notes
were also recorded in 2017. By 2017, out of 940 palmettos, 168 (17.9%)
had died or were lost from the study but only 15 (1.6%) were not human
induced. All others were mowed or plowed or died from some other
human-induced management activity.
Plant selection
Plants of S. repens and S. etonia >30 cm in height (S. repens
<30 cm in height were excluded as these do not flower) were
selected in pairs to minimize microsite differences. We selected
individuals of the least dominant species first and then found the
closest pair of the more common species. Dominance varied by habitat
and management unit. Each palmetto was marked with an aluminum angle
stake with an attached aluminum number either pop-riveted or wired to
the aluminum stake. Stakes were driven into the ground adjacent to the
palmetto. For S. repens, the stake was driven next to the rhizome
because rhizomes grow horizontally and thus move spatially. To avoid
confusion of which palmetto the stake was marking, notes were taken on
the S. repens' direction of rhizome growth. Stakes were always placed
alongside the rhizome and never "in front" of the rhizome's
growth path. During the 2017 census, we moved a number of S. repens
stakes closer to their growing apex to avoid future confusion. Since
S. etonia doesn't move spatially, stake position relative to apex
location was not an issue.
Clipping and Fertilizing Experiment
This experiment was designed to examine what triggers post-fire
flowering responses in palmettos. Treatments included: (1) Clipping to
removing all leaves and their petioles to simulate leaf loss by fire
(we took care to not physically damage the unfolded leaf), (2)
Fertilizing to simulate enhanced nutrient availability following fire,
and (3) applying both the clipping and fertilizing treatments to
individuals.
Control plants for this study were the nearby sand pine scrub control
plants that were established in 1985. We first numbered 300 aluminum
stakes using 150 S. repens and S. etonia each (stakes 501-650 were
used for S. repens and stakes 651-800 were used for S. etonia). Next,
we randomly assigned each numbered stake within a species to the
clipping, fertilizing, or both treatment (N=50 for each treatment).
Palmettos were selected regardless of size so both small and large are
represented.
We mixed 80 lbs. of commercial Palm Fertilizer (10-5-5) and 40 lbs. of
Dolomite lime to make 120 lbs. of fertilizer/lime mix. This was added
at a rate of 1 cup/fertilizer treatment palmetto or approximately 1/4
lb. (actual 156.6 g) of mix per treated palmetto. This mix was
scattered evenly under the crown of the palmetto. Fertilized plants
were well separated spatially from unfertilized plants.
Several stakes and/or number tags were replaced during the 2017 census
because the tags and/or stakes had melted during a May 2013 escaped
sand pine scrub fire. Damage to stakes and mortality to palmettos
occurred primarily where downed sand pines burned creating higher
temperatures for longer periods.
Seedling plant selection
For seedlings, we used a 2-m wide belt transect running through the
WSP1 flatwoods marked palmetto area and a second 2-m wide belt
transect near the WSP2 scrubby flatwoods. We marked every putative
palmetto seedling we could locate using a wire flag inserted through
the hole of a metal number tag that laid on the surface of the ground.
At WSP1, we marked 100 putative seedlings using numbers 1-100 and at
WSP2 we marked putative seedlings with numbers 101-188. At both sites,
we recorded which quadrats on the belt transect each putative seedling
occurred in.
Harvested palmetto plant selection
We destructively harvested 33 palmettos (17 S. repens and 16 S.
etonia) from three sites in 1985. Plants (5 of each species) were
harvested on 18 January 1985 on the southwest corner at the
intersection of Culvert and Ridge Road. A second harvest was made (5
S. repens and 6 S. etonia) on 21 January 1985 on the southwest corner
at the intersection of Ridge Road and North Seven Road. A final
harvest was made on 22 January 1985 (7 S. repens and 5 S. etonia) on
Red Hill in the sand pine scrub control area. Thirty-two palmettos
were used to develop biomass regression models (17 S. repens and 15 S.
etonia).
Data collection
Data were collected annually, starting in 1981 (or when plants were
initially marked) in January/February for all plants and sites. Data
collection included maximum standing height (cm), maximum canopy
length (cm), maximum canopy width (cm, perpendicular to the length),
number of green leaves and number of inflorescence scapes. In 1982,
the number of new leaves produced between annual censuses were counted
(the newest leaf of a given year was banded with a plastic-coated wire
so new leaves could be determined). For green leaves and new leaves, a
value of 0.5 was given if a new leaf had emerged and was free from the
apex but the leaf blade had not yet expanded. In 1990, we also began
to calculate leaf longevity, which is the working leaf life span, as
described by Corner (1966), Chazdon (1986), and Cunningham (1997).
This estimate is calculated by dividing the number of living, fully
expanded leaves in the crown by the number of new leaves produced
during that year. This leaf longevity measure does not include the
"nonworking" leaf development time before leaf expansion,
which according to Corner (1966) would roughly double the life spans
estimated.
Canopy cover for each palmetto was measured in January 1993 with a
densitometer pointed to the four cardinal directions, then averaged.
Biomass for each palmetto species was calculated for each year of
measurements using regression models developed from 32 destructively
harvested palmettos. Leaf longevity was also calculated by dividing
the number of living, fully expanded leaves in the crown by the number
of new leaves produced during that year.
For seedlings, starting in 1989, only height and maximum crown
diameter (cm) were recorded. In 1992, we started measuring the base of
the plants using calipers (cm). Data were collected continuously from
1989 through 1997, then again in 2001 and for a final census in 2008.
For harvested palmetto biomass, we took measures (in cm) at three
levels: whole plant, largest leaf and petiole of largest leaf. Height,
length and width were taken across the entire canopy and on the
single, largest leaf. Length and width of the petiole for the largest
leaf were also recorded. We also counted the number of green leaves
per plant. Data were collected on 33 individuals (17 S. repens and 16
S. etonia), but only 32 were used in developing biomass regressions
(17 S. repens and 15 S. etonia).
Biomass from the harvested palmettos is the estimated dry mass (g) of
each harvested palmetto. The regression models used for S. repens and
S. etonia were generated from 32 destructively harvested palmettos of
a wide range of sizes excavated from two scrubby flatwoods stands and
one sand pine scrub stand. Plants were measured for basal diameter,
crown height, crown maximum width, crown maximum width perpendicular
to the maximum width, number of living leaves, leaf-blade width and
length, and petiole length and width of the largest leaf, and number
of inflorescences. Palmettos were divided into leaf and stem (both
above- and below-ground), but roots were not harvested since they grow
to depths of several meters, making recovery of all root tissues
virtually impossible for fresh-mass determination. Subsamples of fresh
mass were oven dried at 80C to constant mass for estimation of dry
mass. The best regression models to estimate dry mass (g) are:
Serenoa repens dry mass = Exp (0.637LN (MINXX) +
2.3LN (GLVSXX) + 0.254
Sabal etonia dry mass = (10.71(MINXX)) +
(332.5(GLVSXX)) - 826.3
Where: MINXX = crown "minimum" in year XX and GLVSXX =
number of green living leaves in year XX.
The S. repens model for N = 17 had a r2 = 0.84, F =36.7, df = 2,14, P
< 0.001
The S. etonia model for N = 15 had a r2 =0.86, F = 38.2, df = 2,12, P
<0.001
Some biomass estimates are negative due to error in the regression
models (Abrahamson 1995). This mostly occurs for smaller plants. These
values have been retained and the data user may choose to include the
values, remove the values or modify the values with additional data
and a better fitting regression model.
