Over the (range) edge:: a 45-year transplant experiment with the perennial forest herb Hyacinthoides non-scripta

Most experimental populations of perennial forest herbs have been monitored for only a few years and thus only apply to germination and early seedling survival. Moreover, there is a lack of long-term, quantitative data on the rates of spread of populations. We report the results of a cross-range-edge transplant experiment established in 1960 with the perennial forest herb Hyacinthoides non-scripta. We evaluated determinants of survival/extinction, performance and migration distances and patterns of 27 transplanted populations after a period of 45 growing seasons. Of 27 experimental populations of Hyacinthoides non-scripta implanted in 1960, 11 (41%) were still found in 2005-06. Population survival was independent of soil type and changes in the vegetation layer. In contrast, physical disturbance of the soil and major changes in the tree layer as a result of forest management were the main determinants of population extinction. Current population surface areas ranged from 0.23 to 26.23 m(2). Plant height, leaf length, number of flowers and seed size were generally lower in the introduced populations than in the source populations. However, densities and proportions of non-flowering adults were higher, especially in the larger populations. This suggests that these populations are still expanding with more but younger, and thus smaller, individuals. Observed migration rates were very low, ranging from 0.006 my(-1) to 0.06 my(-1). Migration occurred by the establishment of isolated individuals, which were later absorbed by the advancing wave of the main population. The spread projected for the largest population in the next 45 years is only 14 m for the main population front and 42 m for the furthest individual. Our results may be representative of population spread for slow dispersing forest plant species after occasional long-distance dispersal events across a range edge. However, the slow rates of spread indicate that, even if such events occur, it can take a very long time to establish viable population sizes.