DOI: 10.5061/dryad.jq2bvq8p1
title: Contrasting impacts of climbing plants on host tree reproduction in a drought-stressed forest

description: The uploaded dataset contains all the data to run the analyses and figures
 of the publication "Contrasting impacts of climbing plants on host
 tree reproduction in a drought-stressed forest". Climbing plants, or
 climbers, are known to negatively affect the survival and reproduction of
 tropical and temperate humid forest trees through competition and
 structural parasitism. These impacts are attributed to their growth
 strategy, which relies on other plants for mechanical support and allows
 them to divert resources away from structural investment toward vegetative
 and reproductive functions. Such negative interactions may ultimately
 influence the composition and dynamics of plant and animal communities
 around them. Effects of climbers on hosts may differ in drought-stressed
 systems because investments in foliage and reproductive structures could
 favor facilitative interactions, such as abiotic stress amelioration
 through shading or pollinator attraction through synchronous flowering.
 Knowledge of climber-host interactions in Mediterranean and
 drought-stressed forests in general is limited. To test the hypothesis
 that climbers can facilitate host reproduction via synchronous flowering
 in a drought-stressed Mediterranean forest, we assessed the effects of
 climber cover on the probability of flowering, fruiting, and final fruit
 set of Crataegus aronia, a common insect-pollinated tree. Overall, climber
 cover was negatively related to flowering probability but positively
 related to fruiting probability and final fruit set. These effects
 differed between climbers with distinct flowering phenology relative to
 the host. Non-co-flowering climber effects on flowering probability were
 negative. However, co-flowering climber effects on fruiting probability
 and final fruit set were positive. These positive effects on C. aronia are
 in stark contrast with pervasive negative effects of lianas in tropical
 moist forests. The differing effects of climbers with distinct phenology
 suggest involvement of pollinator attraction. Although limited to the
 studied tree species in a Mediterranean forest, the documented positive
 effects of climbers in this drought-stressed forest and their relation
 with synchronous flowering highlight the need for trait-based analyses of
 climber –host interactions across systems, particularly to expand our
 understanding of their ecological roles under varied climate conditions.
description: We conducted a foot survey of an area of approximately 88,000
 square meters in the south-eastern part of the reserve to map potential
 <em>Crataegus aronia</em> individuals. We visited the research
 site weekly, starting a couple of weeks before the known flowering time of
 <em>C. aronia</em>, and recorded the geographical locations of
 potential individuals using a smartphone GPS. We found a total of 162
 individuals throughout the survey and selected 123 individuals for
 sampling based on the following criteria: they were taller than 1.5 m
 (shorter individuals did not flower during the study regardless of the
 presence or absence of climbers, E. Fein <em>pers. obs.,</em>
 and were considered immature); they were free from infestation or
 overtopped by non-climbing plants; and they had at least one branch 50 cm
 or longer for quantifying flowering and fruiting. Measurements on selected
 trees were conducted from the onset of flowering. Individuals identified
 in the second census following the onset of flowering were included in the
 sample only if their peak flowering occurred after their initial census.
 All mapped individuals were assessed for the presence or absence of
 climbers. When climbers were present, each climber species was identified,
 and its respective cover on the host tree crown was visually estimated.
 Cover estimates were recorded separately for each climber species as the
 percentage of the total tree crown volume occupied, enabling analyses
 incorporating differences in species flowering phenology (described in the
 <em>Data analysis</em> section below). Host tree size was
 measured by the stem circumference at the base, as several individuals
 branched below the standard diameter at breast height.
 During 10 weekly censuses conducted between March and May 2023,
 the number of flowers and fruits found** on a single branch per tree was
 recorded. For each tree, the branch with the highest number of flowers in
 the first census was selected for all subsequent counts. These weekly
 censuses allowed us to determine, with a week-level resolution, the timing
 of peak flowering and final ripe fruit production, which were used to
 estimate fruit set as detailed in the <em>Data analysis</em>
 section. Censused branches were marked with a plastic or metal tags
 secured with metal wire. Counts were performed on the distal 50 cm of each
 branch, including any daughter branches. Flower counts included all flower
 buds and open flowers with petals. Fruit counts included all swollen
 ovaries and fully ripe fruits. Additionally, the orientation of the branch
 relative to the cardinal points and the branch circumference 50 cm from
 its distal end were recorded. We assessed the effect of
 climber load on <em>C. aronia</em> reproduction by modeling
 the probability of flowering, the probability of fruiting, and the final
 fruit set as a function of the hosts’ climber load. Climber load was
 calculated as the sum of the individual cover percentages estimated
 separately for each climber species present on the host crown, which
 occasionally resulted in climber load, or total climber cover, exceeding
 100% due to overlapping layers of climbers. <em>Crataegus
 aronia</em> individuals were classified as flowering if they had at
 least one flower recorded in any census. Individuals were classified as
 fruiting if they had ripe fruits at the final census. Because we did not
 track the fate of individual flowers, final fruit set was estimated as the
 ratio of the final count of ripe fruits to the maximum number of flowers
 recorded on sampled branches across all censuses (Giménez‐Benavides et
 al., 2007; Rominger et al., 2021). All censused trees were included in the
 analysis of effects on flowering. For fruiting effects, only trees that
 produced flowers (n=68) were included. This excludes trees unable to
 produce fruits and provide information on the effects of climbers on
 fruiting success. The individual probability of
 flowering and fruiting were modeled as binary responses (success or
 failure to produce flowers or fruits) using a Bernoulli generalized linear
 model (GLM) with a binomial family distribution. The final fruit set was
 modeled with a binomial GLM, with the response variable representing the
 tree’s fruiting success as the proportion of flowers developing into ripe
 fruits. Two sets of models were used to analyze the effect of climber load
 on each response variable. One set examined the effects of total climber
 cover, representing the sum of the cover of all climber species, while the
 other set differentiated between climber cover with distinct flowering
 phenologies, i.e., co-flowering and non-co-flowering climber cover. We
 defined climbers as co-flowering when they have some temporal overlap in
 flowering with the host tree, and as non-co-flowering when there is no
 such overlap. From the total of 123 trees sampled, 70 were hosting vines;
 26 of these individuals hosted the co-flowering vine species
 <em>Rubia tenuifolia, Galium aparine, Lonicera etrusca, Prasium
 majus</em> and <em>Ephedra foeminea</em> and 66
 individuals hosted the non-co-flowering <em>Asparagus
 aphyllus</em>. From the 68 flowering trees, 30 were hosting vines;
 11 trees hosted the co-flowering vine species <em>Rubia tenuifolia ,
 Galium aparine, Prasium majus</em> and <em>Ephedra
 foeminea</em> and 30 trees hosted the non co-flowering
 <em>Asparagus aphyllus</em>. Single trees hosted different
 combinations of climber species. Each set of models
 included all possible combinations of the climber cover variable(s) of
 interest and covariates measured to account for their potential effects on
 host tree reproductive responses. For the flowering model, control
 covariates included the host tree’s stem circumference. For the fruiting
 model, covariates included the host tree’s stem circumference, branch
 circumference, branch orientation, flowering time, and maximum flower
 count. The fruit set model used the same covariates as the fruiting model,
 excluding the maximum flower count.
description: # Contrasting impacts of climbing plants on host tree reproduction in a
 drought-stressed forest Dataset DOI:
 [10.5061/dryad.jq2bvq8p1](10.5061/dryad.jq2bvq8p1) ## Description of the
 data and file structure We describe and quantify the effect of climbing
 plants on host reproduction by evaluating flower and fruit production of
 *Crataegus aronia*, a common tree species in Mediterranean Israel. We
 assessed the effects of climber cover on the host probability of
 flowering, fruiting, and final fruit set. Climber cover was negatively
 related to the host's flowering probability but positively related to
 the host's fruiting probability and final fruit set. These effects
 depended on whether the climbers flowered simultaneously with the host.
 Thus, while climber cover may decrease flowering, some climbers can also
 enhance fruiting, likely by attracting pollinators. Positive effects of
 climbing plants on host reproductive output contrast with numerous reports
 of negative effects in other biomes. ### Files and variables #### File:
 OIK-11340.R2_Rcode.R **Description:** R code file to recreate analyses and
 figures #### File: climbers_AAproject_R2.csv **Description:** Study
 dataset ##### Variables * tree_id: - tree I.D (unique identifier) * site:
 site name * date: the date of the first record * location: GPS coordinates
 of the tree location * stem_circ: stem circumference in cm * br_or: the
 orientation of the selected/sampled stem branch * br_circ: circumference
 in cm of the selected/sampled stem branch * ASAP_cover: *Asparagus
 aphyllus* cover of the host tree crown in percent of crown volume *
 RUTE_cover: *Rubia tenuifolia* cover (as above) * GAAP_cover: *Gallium
 aparine* cover (as above) * LOET_cover: *Lonicera etrusca* cover (as
 above) * PAMA_cover: *Prasium majus* cover (as above) * EPFO_cover:
 *Ephedra foeminea* cover (as above) * l_sum_cov: the sum of the different
 climber species cover on a single host tree * t0_flower: flower count on
 the selected branch on the initial (time 0) census * t1_flower: flower
 count on the selected branch 1 week after the initial census * t2_flower:
 flower count on the selected branch 2 weeks after the initial census *
 t2_fruit: fruit count on the selected branch 2 weeks after the initial
 census * t3_flower: flower count on the selected branch 3 weeks after the
 initial census * t3_fruit: fruit count on the selected branch 3 weeks
 after the initial census * t4_flower: flower count on the selected branch
 4 weeks after the initial census * t4_fruit: fruit count on the selected
 branch 4 weeks after the initial census * t5_flower: flower count on the
 selected branch 5 weeks after the initial census * t5_fruit: fruit count
 on the selected branch 5 weeks after the initial census * t6_flower:
 flower count on the selected branch 6 weeks after the initial census *
 t6_fruit: fruit count on the selected branch 6 weeks after the initial
 census * t7_fruit: fruit count on the selected branch 7 weeks after the
 initial census * t8_fruit: fruit count on the selected branch 8 weeks
 after the initial census * t9_fruit: fruit count on the selected branch 9
 weeks after the initial census * fl_t: flowering duration in weeks *
 max_fl: the maximum flower count during any of the censuses * max_fr: the
 maximum fruit count during any of the censuses * fl: indicates whether the
 tree flowered during any of the censuses (1) or not (0) * fr: indicates
 whether the tree carried fruits during any of the censuses (1) or not (0)
 * fr9: the fruit count on the last census, when fruits were fully ripe *
 CL_cov: the sum of the co-flowering climber species cover on a single tree
 *NA stands for not available datum. For the branch orientation and branch
 circumference variables, NAs occur for trees that did not flower. For the
 cover data, NA means no climbers of the given species were found in the
 host tree ## Code/software OIK-11340.R2_Rcode.R - is the R code file to
 run published analyses and figures. User instructions: Set the working
 directory to the location where the data file
 "climbers_AAproject_R2.csv" is located, then run the code. The
 code was written using R version 4.3.2. (R Core Team, 2023). The sets of
 models for each response variable were fitted using the “dredge” function
 from the ”MuMIn” R package (Barton, 2023). The goodness of fit for the
 selected models was evaluated by testing for deviations in residuals,
 under-/over-dispersion, and zero-inflation using the “DHARMa” package
 (Hartig, 2022). Results on the effects of climbers were visualized using
 the “effect_plot” function from the “jtools” package (Long, 2022).