DOI: 10.5061/dryad.xsj3tx9g7
title: Pinus kesiya invasions in Tapia woodland Madagascar

description: Pinus species are among the highly invasive species which have spread
 outside their plantation area after their introduction in the Southern
 Hemisphere. The case of Pinus kesiya invasion is observed in the high
 plateau of Madagascar, inside the sclerophyll Tapia woodland which is
 dominated by the endemic Uapaca bojeri tree species. The analysis of this
 invasion was carried out using 375 plots of 100 m2 each in Tapia woodland.
 Data on the vegetation structure, the plot characteristics and the
 propagule pressure were collected. We recorded a total of 740 pines
 distributed in 29.8% of the plots. The generalized linear model revealed
 that the diminution in frequency of the dominant species Uapaca bojeri
 with the increasing degree of disturbance of the fragment led to the
 vulnerability of the Tapia woodland to the abundance of pine. The factors
 explaining pine occurrence varied according to the pine life-stage. In the
 seedling stage, the distance of the plot from the propagule source
 combined with the longitudinal position of the plot explained 18% of the
 pine invasion success. In the sapling and adult stages, the vegetation
 structure was the main important factor (22% and 11% of variation
 explained). The frequency of U. bojeri and the degree of disturbance were
 the most important factors characterizing this vegetation structure. Based
 on these results, a strategy to control pine invasion in the Tapia
 woodland may focus on enrichment with U. bojeri and limitation of the
 plantation of P. kesiya in proximity.
description: Data were collected throught inventory. In total, we have
 surveyed 375 plots of 100m2 each where woody species have been inventoried
 (counted, specified). Pinus kesiya was defined according to three
 different life-stages: seedlings (0 &lt; DBH ≤ 1 cm), saplings (1
 &lt; DBH &lt; 5 cm) and adults (DBH ≥ 5 cm)
description: To quantify the local dominance of  U. bojeri, we calculated the
 density (‘D’ in trees. ha−1),  the frequency (‘f’ in % trees. ha-1), and
 the basal area (‘G’ in m2. ha-1) of the species considering all trees
 above 1 cm DBH. We characterized the local community diversity by its
 species richness ‘S’, the Shannon-Weaver diversity index ‘H’, and Pielou’s
 evenness index ‘R’ (R = H / Hʹmax where Hʹmax = Log(S)). Two classes of
 plot disturbance degree (‘disturb’) were defined following  Rakotondrasoa
 et al. (2013) by hierarchical clustering based on the following stand
 variables (DBH &gt; 1 cm) calculating with all surveyed species at
 plot level:  tree mean diameter (d in cm), tree mean height (h in m), tree
 density (D tot), tree basal area (G tot), species richness (S). The cover
 of vegetation strata – litter, herbaceous, shrubs – was estimated using a
 categorical ordered scale (Calviño-Cancela and Van Etten 2018) from 1 to
 3: 1: [0–40%]; 2: ]40–70%]; 3: ]70–100%]. Topographic variables were
 recorded using a GPS unit for elevation, a clinometer for slope and visual
 observation for topographic position.  The topography was classified using two ordered
 factors following Randriambanona et al. (2019) (i) topographic position
 (Top-1: valley bottom, Top-2: middle slope, Top-3: upper slope), (ii)
 slope values (“low” &lt; 8°, 8° ≤ “middle” &lt; 20° and, “high” ≥
 20°). The position of the plot along the transect (pl_1: 10 m, pl_2: 30m,
 pl_3: 50 m) was used as an additional explanatory variable to account for
 edge effects. The geographical coordinates (‘latitude’ and ‘longitude’)
 were also included in order to account for a potential spatial structure
 in the response variables. To
 estimate the propagule pressure effect, two variables were defined. We
 first extensively mapped the majority of Pinus seed sources in the
 area. Firstly, we have calculated the distance from each plot to all the
 propagule sources. We have selected the nearest distance which is supposed
 to be the potential source and named the distance between the plot and the
 source ‘source distance. Secondly, the number of seed sources or ‘Source
 density’ in the surroundings, i.e. 500 meters around each plot, was
 considered.