Grant Cottam

SOME SAMPLING CHARACTERISTICS OF A POPULATION OF RANDOMLY DISPERSED INDIVIDUALS

As our knowledge of plant communities increases, greater emphasis is being placed on the methods used to measure the characteristics of these communities. Succeeding decades have shown a trend toward the use of quantitative methods, with purely descriptive studies becoming less common. One reason for the use of quantitative techniques is that the resulting data are not tinged by the subjective bias of the investigator. The results are presumed to represent the vegetation as it actually exists; any other investigator should be able to employ the same methods in the same communities and secure approximately the same data. If such is not the case, the so called quantitative methods are worse than valueless, since they lend an aura of false accuracy that may be very misleading. To make certain that his results are reproducible, the worker must be sure that his sample is adequate, that the location of his sample has been made without bias, and that the limitations of his method are understood. The student of plant communities is concerned with the distribution of objects in space. His first problem is the determination of the kinds of plants present and their relative numbers. Since it is usually impossible to examine all of the plants present, he confines himself to some kind of a sample of the vegetation. This may be in the form of area samples. as quadrats or belt transects; line samples, as in

The successional status of a southern Wisconsin oak woods

We examined the applicability of concepts of succession to 27 yr of tree growth and demographic data from an oak woods. From 1956 to 1983 tree population dynamics in Noe Woods, a black oak—white oak woods in southern Wisconsin, were heavily influenced by oak wilt disease. Between 15 and 20% of the black oaks, many of them large, died in each 5—yr period; much of this mortality was due to wilt. White oak increased in basal area but declined slowly in numbers. Regeneration was dominated by black cherry, boxelder, and American elm; these species are either short—lived and small—statured or threatened by disease, and are, the therefore, unlikely to form a new canopy. None of the species in the woods seems capable of filling the role of a self—replacing climax species in the classical sense. We hypothesize that the absence of a climax species in Noe Woods and other areas of the prairie—forest transition is due to the changed disturbance regime. Decreased fire frequency has created an unprecedented opportunity for shade—tolerant species in dry woods. This opportunity has apparently been met by expansion of shade—tolerant native species from other habitats, invasion of exotic species, and increased abundance of some short—lived and small—statured native species.

Community Dynamics on An Artificial Prairie

The changes occurring on the J. T. Curtis Prairie, an artificial prairie in the University of Wisconsin Arboretum, were studied by means of four surveys spaced at 5—year intervals. Frequency data from more than 650 meter—square quadrats with known locations were obtained at each survey. Five stands, delimited on the basis of their compositional index (CI) as determined by indicator species, were compared with native prairies having similar CI values by means of species lists and sum frequency of the species. When prairie species only are considered, some artificially established stands are as similar to native stands as native stands is the presence of large numbers of non—prairie species. The artificial stands have much larger species lists and higher sum frequencies than native prairies. The results indicate that the Curtis Prairie is becoming very similar to native prairies in numbers and species of prairie plants, and that the non—prairie species are materially reduced in importance.

Some Sampling Characteristics of a Series of Aggregated Populations

Leverett, F. and F. W. Sardeson. 1932. Quaternary geology of Minnesota and parts of adjacent states. U. S. Dept. Interior, Geol. Surv. Prof. Paper 161. Moss, E. H. 1955. The vegetation of Alberta. Bot. Rev. 21: 493-567. Oosting, H. J. and W. D. Billings. 1951. A comparison of virgin spruce-fir forest in the northern and southern Appalachian system. Ecology 32: 84-103. Reichelderfer, F. W. et al. 1941. Climate and man. U. S. Dept. Agr. Yearbook.

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. Coles 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.

Some Autecological Studies of the Lonicera X Bella Complex

Lonicera X bella is an introduced, aggressive hybrid shrub that occurs in Wisconsin and much of central and eastern North America. Both parent species occur in a wide variety of habitats in their native ranges, as does this hybrid in North America. Ordination, by principal components analysis, indicated that the dimension of maximum morphological variability is that which best separates the parent species. Physiological tests and transplant gardens revealed no evidence of ecotypic differentiation in the populations studied. Selection for heterosis is suggested by certain morphological characteristics of the hybrids, by the high freqency of hybrid individuals that are intermediate to the parents, and by the ecological behavior of this shrub. See full-text article at JSTOR

Influence of Temperature on the Dormancy of Some Spring Emphemerals

The effect of temperature on the breaking of dormancy was examined in five species of spring ephemerals, Claytonia virginica, Erythronium albidum, E. americanum, Dicentra cucullaria, and D. canadensis. All species except Claytonia required cold treatment to imitate growth. Dormancy was not broken in D. canadensis under the experimental conditions. Generally, with increasing lengths of cold treatment, the time for subsequent emergence decreased, the time the plants remained green decreased, and up to a point, the size of the resulting plants increased. See full-text article at JSTOR