We conducted a historical (40 y) floristic assessment of a small (4 km²) park in eastern Canada (Bonaventure Island National Park, Quebec) to evaluate whether small protected areas located in rural landscapes suffer declines in vascular plant populations. We hypothesized that the limited park access (an island accessible only by boat) has a greater influence than the size of the park per se on the preservation of the integrity of the flora. The island flora just before the creation of the protected area (1971) was compared to the flora surveyed during 2 consecutive summers (2007–2008). Of the 358 taxa that were identified before 1971, only 21 (6% of the total) were not found in 2007–2008; of these 21, all but 1 were native taxa, and 17 are likely extirpated, which represents a “natural” extirpation rate of about 1 taxon every 2 or 3 y. Twenty-four taxa found in 2007–2008 were apparently not present before 1971, 14 native taxa and 10 exotic taxa. This represents an introduction rate of 1 native and 1 exotic species every 2 or 3 y. The creation of the protected area did not totally prevent the extinction of native plants or the introduction of exotic species, but the island lost very few species during recent decades, at least compared to small urban parks where historical floristic assessments have been conducted. These urban parks were visited much more frequently than the island, which probably accounts for most of the differences. Strict regulations for visiting the island are apparently an excellent tool for preventing plant introduction (or extirpation), although they are by no means a barrier against the most invasive species.