Pinus kesiya invasions in Tapia woodland Madagascar

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.

松属（Pinus）物种是极具入侵性的物种之一，它们在被引入南半球后，已从原有种植区域向外扩散。目前已在马达加斯加高原的硬叶Tapia林地中观测到思茅松（Pinus kesiya）的入侵现象，该林地以特有物种博杰乌桕（Uapaca bojeri）为优势种。本次针对该入侵事件的分析，在Tapia林地内布设了375块面积为100平方米的样地，采集了植被结构、样地特征以及传播体压力（propagule pressure）相关数据。本次调查共记录到740株松树，分布于29.8%的样地中。广义线性模型（generalized linear model）分析结果显示，随着生境片段化干扰程度的加剧，优势种博杰乌桕的频度下降，使得Tapia林地更容易受到松树大量入侵的影响。影响松树定植的因子会随松树的生活史阶段发生变化：在幼苗阶段，样地距传播体源的距离与样地的经度位置共同解释了18%的松树入侵成功率；在幼树与成树阶段，植被结构为主要影响因子，分别解释了22%与11%的变异量。博杰乌桕的频度与干扰程度是表征该植被结构的核心因子。基于上述结果，针对Tapia林地的松树入侵防控策略可聚焦于补植博杰乌桕，以及限制在邻近区域种植思茅松。