The Herbaceous Layer as a Filter Determining Spatial Pattern in Forest Tree Regeneration

Abstract Although small in stature and seemingly ephemeral in nature, herbaceous understory communities have the potential to exert a strong influence on the dynamics of forest tree regeneration. Through study of fern-dominated understory communities in central Massachusetts mixed-deciduous forests, we have found that this understory stratum can act as a selective fitter of tree seedling species in their earliest life stages. All trees, first as seeds, must penetrate this layer to reach the forest floor and then germinate and grow under the “canopy” of the herbaceous stratum. The microenvironment at and near the forest floor is dictated largely by the nearby herbs and shrubs above. Tree seedlings that are able to germinate, survive, and grow in this environment will ultimately emerge from this stratum and become potential successors to the forest canopy. Tree seedling species performance may vary considerably under the particular rigors of a well-developed understory, and it is this variability that enables the understory to fiter tree seedlings.