The shape of things to come: woodland herb niche contraction begins during recruitment in mesic forest microhabitat

Natural abundance is shaped by the abiotic requirements and biotic interactions that shape a species' niche, yet these influences are rarely decoupled. Moreover, most plant mortality occurs during early life stages, making seed recruitment critical in structuring plant populations. We find that natural abundance of two woodland herbs, Hexastylis arifolia and Hepatica nobilis , peaks at intermediate resource levels, a pattern probably formed by concurrent abiotic and biotic interactions. To determine how this abundance patterning reflects intrinsic physiological optima and extrinsic biotic interactions, we translocate adults and seeds to novel locations across experimentally extended abiotic gradients. These experiments indicate that the plant distributions probably reflect biotic interactions as much as physiological requirements, and that adult abundance provides a poor indication of the underlying niche requirements. The positive response exhibited by adult transplants in the wettest conditions is offset by increased fungal attack on buried seeds consistent with peak natural abundance where soil moisture is intermediate. This contraction of niche space is best described by Connell's model—species are limited by physiological tolerances where resources are low and biotic interactions where resources are high.

Deep complex morphophysiological dormancy in Sanicula europaea (Apiaceae) fits a recurring pattern of dormancy types in genera with an Arcto-Tertiary distribution

Genus Sanicula encompasses about 40 species, mainly from temperate deciduous forests and exhibiting an Arcto-Tertiary relict distribution. It has previously been shown that stasis in physiological traits, such as seed dormancy, can occur in genera with an Arcto-Tertiary disjunct distribution. The aim of this study was to determine the requirements for dormancy break and seed germination in the Eurasian woodland herb Sanicula europaea L. Comparing our results with other Apiaceae in a phylogenetic and biogeographic framework enables us to determine whether stasis in seed dormancy has occurred in Sanicula. Experiments under natural conditions showed that the embryo elongates within the seed during winter, when temperatures are low. Seeds of S. europaea germinated immediately after growth of the embryo was completed, and seedlings subsequently emerged when temperatures had risen in spring. A series of tests under temperature-controlled conditions revealed that growth of the embryo and physiological dormancy break occur simultaneously at low temperatures (5 °C), irrespective of a pre-treatment at high temperatures. These results contrast with the dormancy traits of several eastern North American Sanicula species, which presumably require a high temperature pre-treatment before chilling becomes effective. This geographical distribution pattern of seed dormancy traits has also been established independently in several other Arcto-Tertiary relict genera.

Effects of Forest Cover on Fruit Set in the Woodland Herb, Maianthemum canadense (Liliaceae)

Animal pollination has been recognized as an essential ecosystem function that is potentially under various environmental stresses. We investigated the landscape effects of forest cover at multiple spatial scales on the sexual reproductive success of a common woodland herb in North America, Maianthemum canadense. This species is a self-incompatible species and pollinated by insects requiring natural landscapes. Nine populations were selected in deciduous forests within agricultural fields of southern Ontario, Canada. We investigated whether fruiting success decreases as forest cover surrounding the plant populations increases at the landscape scale. Forest cover was quantified by the proportion of forest within six different radii from 250 to 1500 m. Analyses showed relationships with the proportion of forest at 750- and 1000-m radii and fruiting success in populations of M. canadense. These findings suggest potential local extirpation of M. canadense and indicate that forest loss can negatively impact on even some common woodland herbs.

Density-dependent hoarding by rodents contributes to large variation in seed mass of the woodland herb Symplocarpus renifolius

We analyzed effects of seed-hoarding by rodents on the variation in seed mass and seed success for a perennial forest undergrowth plant — Symplocarpus renifolius Schott ex Miquel — in Hokkaido, northern Japan. Although density of rodents differed greatly between seasons, more rodents were always captured in mesic Sasa sp. patches with dense foliage than in wet Lysichiton sp. patches. In the season with fewer rodents, they cached seeds close to the original places irrespective of vegetation, while in the season with abundant rodents, they transported seeds further and cached seeds disproportionately in Lysichiton patches. Seeds missed by rodents were larger than seeds that were eaten or that survived. Sasa patches are more suitable for seedlings to establish and a size advantage was observed there, but even small seeds could establish in Lysichiton patches, although seedling success was lower. We concluded that maternal plants of Symplocarpus renifolius increase their reproductive success by having small to middle-sized seeds transported to suitable sites while offering larger seeds as rewards to the transporters. Since the variation in seed mass was not correlated with the biomass per seed of the maternal plant, the large variation in seed mass is considered to have evolved through the density-dependent hoarding by rodents.