Spatial Relationships of Mesic Forest Herbs in Southern Wisconsin

Species distributions and their interrelationships within the herbaceous stratum of 10 southern Wisconsin maple—basswood (Acer saccharum—Tilia americana) stands were studied. Frequency data were collected in each stand within a belt transect which consisted of 500 contiguous square—foot quadrats. Aggregation and association characteristics of individual species in these stands were compared. A D/d index was calculated by dividing the actual density (D) (each occupied quadrat as considered to be an individual) by expected density (d). Run—gap index values were determined by obtaining the average frequency within the 5—ft segments considered to be within aggregates and dividing by the average frequency within those 5—ft segments considered to be within gaps between aggregates. The larger the D/d and run—gap values, the greater the intensity of aggregation within the stand. Generally, these two indices were found to be higly correlated. All species examined were aggregated at the level tested. Cole's index of association values were calculated from the 1—square—foot quadrat data. Those species combinations with significant association value as determined by a chi—square test were used for further analysis. The highly negative associations indicate either dissimilar habitat requirements or a high degree of competition which leads to the exclusion of one species. The highly positive associations indicate which species require a similar habitat, but do not compete directly.