The Correlation of Species and Habitat Factors in a Xerothermic Oak Forest (Orno‐Quercetum) Stand

Abstract

AbstractThe investigations of the authors were made in the Buda Hills, in a stand of calciphilous oak forest (Orno‐Quercetum), a Submediterranean xerothermic forest association frequent in the Transdanubian part of the Hungarian Central Range. Subdividing the 1024 m2 sample plot into 64 portions, the cover values of the dominant‐ and frequent species were noted; in the same system holes were dug in the ground and 7 physical soil factors studied in all of the soil layers. Considering these factors (together with tree‐ and shrub cover) as independent ones affecting the species, correlations were calculated between them and the several species. Diverging from preceding studies, not merely first grade (linear) but also quadratic (parabolic), square root, exponential, and logarithmic models were also applied.Some significant correlations may be pointed out among the results. The connection between Vicia sparsiflora and pH is considerable and demonstrable by several methods: related probably to the pH requirement of nitrogen‐fixing bacteria symbiotic with the plant. In the case of Lithospermum purpureo‐coeruleum, it is not the pH but the nutrient demand wich appears to be the regulating factors: as shown by its close correlation with humus and potassium. On the other hand, the close correlation between Quercus pubescens and humus may result from the inverse relation between humus and soil depth, indicating the significance of topographic effects. Humus plays a role in the appearance of Oryzopsis virescens but also in that of Euphorbia cyparissias; this latter is decisively influenced also by light conditions.Results can, however, be evaluated also methodically. Accordingly, the linear model presents in some cases a good description of the interrelationships, whereas the parabolic approach is better in a great number of other cases; this indicates that in these ones not all regions of the connection is of the same character and that in our ecosystem one has to consider, in several cases, minimum and maximum effects and the subsequent alteration of the direction of relationship. As for the other types of connection, one has to take into account the exponential in some cases.