DOI: 10.5061/dryad.dr7sqvb42
title: Data from: strawberry guava invasion of a Hawaiian rainforest: changing population pattern

description: Strawberry guava (waiawī, Psidium cattleyanum O. Deg., Myrtaceae) is a
 small tree invasive on oceanic islands where it may alter forest ecosystem
 processes and community structure. To better understand the dynamics of
 its invasion in Hawaiian rainforests in anticipation of the release of a
 biocontrol agent, we measured growth and abundance of vertical stems
 &gt;= 0.5 cm DBH for 16 years (2005-2020) in an intact
 Metrosideros-Cibotium rainforest on windward Hawai'i Island.
 Specifically, we compared the growth and abundance of both shoots
 (originating from seed or from the root mat) and sprouts (originating
 above ground from established stems) in four replicate study sites. Mean
 stem density increased from 9562 stems/ha in 2005 to 26,595 stems/ha in
 2020, the majority of which were stems &lt; 2 cm DBH. Mean annual
 rates of population growth (lambda) varied between 1.03 and 1.17. Early in
 the invasion, both density and per capita recruitment of shoots was
 greater than that of sprouts, but as overall stem density increased over
 time, sprout abundance and recruitment came to surpass that of shoots.
 Relative growth rates among small stems &lt; 2 cm DBH declined over
 time for both shoots and sprouts, but relative growth rates of sprouts
 were consistently greater than that of shoots after the first 3 years. The
 capacity of strawberry guava to recruit from both rooted shoots and
 vegetative sprouts contributes to the facility with which it can invade
 intact rainforest, persist in the forest understory, and respond to canopy
 opening. Strawberry guava thus poses a considerable risk of stand
 replacement for Hawaiian rainforests. Stand management will require
 perpetual efforts of guava control at high priority sites as extreme
 weather events associated with climate change bring canopy-opening events
 due to storms, drought and pathogens.
description: Sites: We measured guava stem diameters
 annually between 2005 and 2020 at each of four replicate study plots
 selected to represent early stages of strawberry guava invasions in intact
 <em>Metrosideros-Cibotium</em> rainforest on windward
 Hawai'i Island (Juvik and Juvik 1998). Wet forests in Hawai'i
 are high priority conservation areas because of the biological diversity
 they harbor and their importance in the water economy of the islands
 (Jacobi and Warshauer 1992, Tunison 1992). Our study plots were
 established in the following conservation areas: Kahauale'a Natural
 Area Reserve (KAH, 19<sup>o</sup>10'N,
 155<sup>o</sup>10'W), Pu'u Maka'ala Natural
 Area Reserve (MAK, 19<sup>o</sup>34'N,
 155<sup>o</sup>11'W), Ola'a Forest Reserve (OLA,
 19<sup>o</sup>27'N,
 155<sup>o</sup>11'W), and Upper Waiakea Forest Reserve
 (WAI, 19<sup>o</sup>35'N,
 155<sup>o</sup>12'W).  All sites are at approximately 900
 m elevation and distances between sites are 2 to 17 km. Estimated annual
 rainfall is 3000-4000 mm at OLA and KAH and 4000-5000 mm at WAI and MAK
 (Giambelluca et al. 1996). Projected mean annual temperature based on
 adiabatic lapse rates is 17-17.5° C for the elevation range of the four
 study sites (Giambelluca and Schroeder 1998). All sites are on relatively
 young tholeiitic basalt lava flows that formed 200-1500 years BP (Wolfe
 and Morris 1996). The forests resemble native lowland (100-1200m
 elevation) wet forests with an 'ōhi'a lehua
 (<em>Metrosideros polymorpha </em>Gaud) overstory and an
 understory dominated by tree fern hāpu'u
 (<em>Cibotium</em> spp.) as described by Gagne and Cuddihy
 (1999) and Juvik and Juvik (1998). All areas are under conservation
 protection by the State of Hawai'i.
 Species: Strawberry guava (waiawī,
 <em>Psidium cattleyanum</em> O. Deg.) is a small tree, 2-8 m
 tall. The yellow-fruited form (<em>P. cattleyanum</em>
 f<em>. lucidum</em>), dominant in the forests studied here, is
 one of three forms common across Hawai'i (Wagner et al. 1999)
 occurring in similar habitats. Strawberry guava produces 2-3 cm diameter
 berries with multiple 5 mm long seeds (Wagner et al. 1999) via both sexual
 reproduction and apomixis. In the wet forests of Hawai'i, seeds
 germinate within a year and do not accumulate in a soil seed bank (Uowolo
 and Denslow 2008). In Hawai'i seeds are dispersed by birds, rodents,
 and pigs as well as humans.   Strawberry guava also
 reproduces vegetatively from both above-ground stems and from the root
 mat. For the purposes of this study, sprouts are defined as arising
 above-ground from established leaning or vertical stems. Such sprouts may
 overtake a leaning mother stem, obscuring the origin of older stems.
 Alternatively rooted shoots may arise via seed germination or directly
 from the root mat.  In this study we measured and tracked vertical stems
 standing more than 45 degrees from horizontal and greater than 0.5 cm at
 breast height (1.37 m, DBH). The population thus contained both shoots,
 apparently originating from seed or roots, and sprouts, originating as
 branches from older shoots or sprouts. We were unable to distinguish root
 sprouts from seedlings non-destructively and thus identified stems with an
 obvious above-ground connection to a mother stem as sprouts; shoots
 arising from the soil with no obvious above-ground connection to an
 existing stem were assumed to have originated from seeds or roots.
 Huenneke and Vitousek (1990), working in forests in the same area found
 that the proportion of rooted stems arising from seeds versus from roots
 varied widely. Thus, our study population is narrowly defined as vertical
 stems arising directly from the soil (shoots) or vegetatively from
 previously established stems (sprouts); leaning stems were
 excluded. Surveys: At the start of
 the study (2005) all four sites had established populations of strawberry
 guava with a range of stem diameters represented. With one exception
 (OLA), we established one 0.25 ha plot at each site.  The study plot at
 OLA, with an initially higher-density guava population, was 0.15 ha. All
 vertical stems at least 2 cm DBH were tagged in each plot and their
 diameters measured. In addition, we tagged and measured all vertical stems
 &gt;= 0.5 cm DBH and &lt; 2 cm DBH in a stratified random set of 5
 x 5 m subplots at each site (KAH: 6 subplots; MAK: 5 subplots; OLA: 5
 subplots; WAI: 11 subplots). Diameter was re-measured annually, and new
 recruits tagged. Stems dying and leaning to less than 45 deg from
 horizontal were noted and not included in the study population going
 forward. The population of strawberry guava at each site reported here
 thus comprised only vertical stems.
  Analyses: We calculated basal area and yearly
 relative growth rates (RGR=log (BA <sub>t+1</sub>/BA
 <sub>t</sub>) based on basal area for individual stems.
 Density (stems/ha) was calculated from sample plots to allow comparisons
 among sites with different sample areas; estimates of total population
 density was based on the sum of the density of stems &gt;=2 cm DBH
 from the entire plot plus the estimate of density of small stems
 (&gt;=0.5 cm DBH and &lt; 2cm DBH) from the subplots. Thus, total
 estimated density comprised all vertical stems &gt;=0.5 cm DBH for
 each site. Total basal area per hectare was calculated similarly. Lambda
 (N(t+1)/ N(t)) was calculated from total population densities. To better
 understand the pattern differences in shoots and sprouts, we focused on
 sources of variation among small stems &lt; 2 cm DBH, which comprised
 the majority of the population. <em>Per capita</em> annual
 recruitment and <em>per capita</em> stem death plus initial
 leaning of stems were calculated for both shoots and sprouts as a function
 of the total number of stems of all sizes present in the previous year at
 each site. To determine whether lambda varied over
 time, we used linear mixed effects models using the lme() function in the
 nlme package (Pinheiro et al. 2023) in R (R Core Team, 2022). Year coded
 as a factor) was the fixed effect and site was the random effect. We
 accounted for temporal autocorrelation using AR1() auto correlation
 structure. We used a likelihood ratio test to assess whether the random
 effect of site was significant. To determine how shoots and sprouts
 differed over time in their densities, relative abundances, total basal
 area per ha, relative growth rates of stems &lt; 2cm DBH,
 <em>per capita </em>recruitment, and <em>per
 capita</em> dying/leaning, we used linear mixed effects models using
 the lme() function in the nlme package.. For all models, we included stem
 type (shoot, sprout), year, and the stem type x year interaction as fixed
 effects (with year coded as a factor) and site as a random effect.
 Additionally, for the relative growth rate model we included a random
 effect of a stem ID nested within site. All models accounted for temporal
 autocorrelation using AR1() autocorrelation structure. When needed, we
 also accounted for heteroscedasticity by fitting different variances for
 each stem type in each year using varIdent(). Type III ANOVAs were run on
 the models to test significance of fixed effects. <em>Post
 hoc</em> tests were used to test for the difference between stem
 types in each year using the multcomp package (Hothorn et al. 2008).
 Marginal means and standard errors for plotting relative growth rates were
 calculated using the emmeans package (Lenth 2023). ANOVA results are
 provided in the figure captions. In addition, we
 estimated the ages of shoots in the population based on annual basal area
 increments. For this estimate we pooled data from the shoots at all four
 study sites under the assumption that the sites were samples of a
 forest-wide population of strawberry guava. Only shoot growth was used in
 this estimate because sprout growth is in part dependent on the mother
 stem. Shoot growth rates vary as a function of their DBH as well as a
 function of light availability and other microsite characteristics; thus,
 we used four estimates of annual growth increment to provide a range of
 age estimates. Excluding stems with zero or negative relative growth
 rates, we estimated smallest, largest, mean and median basal area
 increments of shoots in 1 cm DBH size-classes using data for the year
 2019-2020. For the few stems larger than 12 cm DBH we pooled data for all
 remaining large stems to estimate the increment. For each 1 cm growth ring
 and estimated annual basal area increment, we calculated the number of
 years a stem would take to reach the next size class. The total lapsed
 time to pass through size class 1 (0.5-2 cm DBH) through size class 21
 (20-21 cm DBH) was an estimate of the years elapsed between the smallest
 and largest shoot size.
description: # Strawberry guava invasion of a Hawaiian rainforest: Changing population
 pattern
 [https://doi.org/10.5061/dryad.dr7sqvb42](https://doi.org/10.5061/dryad.dr7sqvb42) This file provides information on the contents of the file “Psicat Demog 2005-2020 values 20231203.csv”. It is intended to accompany the manuscript titled “Strawberry guava invasion of a Hawaiian rainforest: Changing population pattern” authored by J. S. Denslow, M. T. Johnson, N. L. Chaney, E. C. Farrer. C. C. Horvitz, E. R. Nussbaum, and A. L. Uowolo which appears In the journal *Biotropica*. Please see the “Methods” section of that paper for more detail. The file provides diameter at breast height (DBH, 1.37 m) of vertical strawberry guava (*Psidium cattleyanum* O. Deg. f. *lucidum*) stems measured annually (2005-2020) at 4 study sites in rainforest on windward Hawai'i Island. KAH: Kahauale'a Natural Area Reserve MAK: Puu Maka'ala Natural Area Reserve OLA: Ola'a Forest Reserve WAI: Upper Waiakea Forest Reserve The file provides information on identity of the site, sub-plot identifiers, the tag number of the stem, the type of stem (shoot, sprout), the approximate date of the annual measurement of the site, the diameter of the stem (cm) at breast height (1.37 m) and the status of the stem at the time of measurement. Calculated values for basal area and relative growth rate are also included where available. This information can be used to compare shoots and sprouts with respect to density, stem growth, frequency of leaning or dying, recruitment rate as well as to describe the overall growth and size distribution of the whole population. ## Description of the data and file structure The data file is a spreadsheet with 87 columns and 5847 rows.  The first 7 columns provide information on the site, location within the site, tag numbers and stem type. For each measurement date there follow 5 columns providing sampling date, dbh, basal area, relative growth rate, an stem status of a tagged stem. Focal species: *Psidium cattleyanum O. Deg. f* lucidum. (strawberry guava, waiawī) Four replicate plots were established to describe the growth of a strawberry guava population in a lowland *Metrosideros-Cibotium* rainforest on windward Hawaii Island, Hawaii, USA. One plot was established in each reserve. Distances between study sites ranged from 2 to 17 km. See Methods for site descriptions. Site:                 KAH Kahauale’a Natural Area Reserve; 19o10'N. 155o10'W                 MAK Pu’u Maka’ala Natural Area Reserve; 19o34'N, 155o11'W                 OLA Ola’a Forest Reserve, 19o27'N, 155o11'W                 WAI Upper Waiakea Forest Reserve, 19o35'N, 155o12'W In calculating densities of stems &gt;= 2 cm dbh, the following plot areas apply by site code: KAH Kahauale’a Natural Area Reserve, 0.25 ha plot                 MAK Pu’u Maka’ala Natural Area Reserve, 0.25 ha plot                 OLA Ola’a Forest Reserve, 0.15 ha plot                 WAI Upper Waiakea Forest Reserve, 0.25 ha plot Row, Col: To facilitate annual measurements, each plot was gridded into 5x5m subplots, numbered in the lower left corner in the field.  Row and Column coordinates for each subplot are given. SapQuad: All vertical stems &gt;=2 cm dbh were sampled and measured in all subplots. In addition, vertical stems &gt;=0.5 cm to &lt;2cm dbh (saplings) were sampled in a stratified random selection of subplots. In column “SapQuad”, this subsample was coded “1”. The rest of the subplots were coded “0”. In calculating stem densities for each site the following sample areas apply for the sapling subplots:                 Stems &gt;= 0.5 cm to &lt;2 cm dbh by site                                 KAH       6 subplots, 0.015 ha total                                 MAK      5 subplots, 0.0125 ha                                 OLA        5 subplots, 0.0125 ha                                 WAI       11 subplots, 0.0275 Tag. Tag number given to each measured stem. Numbers are unique within a site but not among sites. NewTag. This number incorporates both a code for the site and the tag number to provide a unique code for each stem in the dataset. StemType. Stems are identified as shoots (SHT: originating from the soil and comprising both stems originating from seed and those originating from the root mat) or sprouts (SPR: originating above ground from an existing larger mother stem). All stems first tagged are vertical (greater than 45 degrees from horizontal). Other leaning and downed stems are also present but not included in this study. A stem subsequently leaning or dying is effectively removed from the data set by recording DBH as “NA”. The following columns are repeated for each measurement date: date2005, date2006, etc. Date of initial or remeasurement as a Julian date. For each site the date reported is the midpoint of the range of dates over which measurements were taken in a given year. dbh2005, dbh2006, etc. Diameter at breast height (1.37m above ground) measured with either calipers (small stems) or a dbh tape in a given year. NA = data not available due to stems not yet recruited or having died or leaned to less than 45 degrees above horizontal since last measured. ba05, ba06, etc. Basal area (cm2) at each year calculated for each stem from its dbh (ba=(dbh/2)2 *![](file:///C:/Users/jdens/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png)). NA = no data. rgr05, rgr06, rgr07, etc. Annual relative growth rate calculated as log (ba at time t+1/ba at time t). Relative growth rate is entered for year t+1 and represents growth over the preceding year. NA = no data. Relative growth rates were not calculated for 2005. test05, test06, etc.  A code describing the status of the stem in a particular year as follows:                 recruitsm = recruit this year into sapling subplot (&gt;=0.5 cm dbh); These stems are considered recruits to the population in subsequent analyses.                 recruitlg = recruit this year into non-sapling subplot (&gt;= 2 cm dbh); These stems are counted as part of the total population. Stems reaching 2 cm dbh in non-sapling subplots are not coded as recruitlg but are counted in the total population.                 unborn = stems that recruit in subsequent years but for which we have no prior data                 notlean = stems vertical (&gt;=45 degrees from the horizontal). This is a place holder. All measured stems are vertical.                 firstlean = stems leaning to &lt; 45 degrees from horizontal for the first time this year. Leaning stems are deleted from the population by replacing dbh with NA when they first lean and in subsequent years (stilllean)                 stilllean = stems originally measured as vertical, but subsequently leaning to &lt;= 45 degrees from horizontal. This is a place holder for stems removed from the population by recording NA as dbh for the year. Stems once leaning are assumed to remain below 45 degrees from horizontal.                 firstdead = stems initially recorded as dead in this year. Dead stems are deleted from the population by replacing dbh with NA when they are first recorded as dead and in subsequent years (stilldead).                 stilldead = stems dead but originally in the database as live vertical stems                 NA = none of these categories or missing information