Studies On Mechanisms Of Species Coexistence In A Quercus Liaotungensis Forest In Northern China

Species coexistence, a key question in community ecology of plants, means the abundance or the number of species occurring in a certain time at a given community, which is determined by the processes of the evolutionary, historical and ecological scale. So far, there exist many theories explaining the mechanisms of species coexistence at certain levels and under particular conditions, including species pool hypothesis, regeneration niche theory, competition theory, and unified neutral theory. All these theories are not incompatible, but complementary. In this dissertation, in order to elucidate the mechanisms of tree species coexistence in the temperate deciduous forests in Dongling Mountains in northern China, we focused on four aspects: 1) spatial pattern analysis; 2) the role of competition in tree species coexistence; 3) the demography of seedlings of trees in a 5 ha plot of Quercus liaotungensis and Betula dahurica forest; and 4) demography and dynamics of seedling banks in three different stands of Q. liaotungensis forests (secondary oak forest, young oak forest, shrub oak forest). The results were as following.In the 5 ha plot, the two dominant species, Q. liaotungensis and B. dahurica accounted for ca. 68.69% of the total basal area and 52.71% of total density of individual trees ≥ 4 cm in DBH in 2000. Q. liaotungensis, Populus davidiana and Acer mono exhibited remarkably inverse J-shaped DBH distributions, whereas B. dahurica, B. platyphylla and Salix caprea had unimodal DBH distributions.Second order analysis based on Ripley's K-function was used to characterize the spatial patterns and spatial associations of the three species, Q. liaotungensis, B. dahurica and A. mono, at different growth stages (adult, sapling, seedling). Seedlings, saplings and adults of all three species exhibited significantly clumped distributions at most spatial scales. Q. liaotungensis seedlings and saplings were positively associated with conspecific adult trees, negatively associated with B. dahurica adult trees, andspatially independent of dead trees, suggesting that seed dispersal and vegetative regeneration influence the spatial patterning of Q. liaotungensis trees. B. dahurica seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales but negatively associated with live and dead trees of other species, indicating sprouting as an important mechanism of reproduction. The strong clustering of A. mono seedlings and saplings could be linked to their dispersal properties associated with the random interception and accumulation of seeds by nearby neighboring vegetation. Positive correlations between A.mono saplings and adults at relatively large scales suggested similar habitat preference. Negative associations between adult trees of B. dahurica and Q. liaotungensis suggested that interspecific competition might be important at local scales (<5 m).Based on the diffusion model and the growth dynamics model, the growth dynamics and mode of competition among adult trees ≥ 4 cm in diameter at breast height (DBH) of six abundant tree species were investigated. One-sided interspecific competition was detected in some species combinations on the scale of the 5 ha study plot, i.e. from S. caprea to B. platyphylla and to B. dahurica, from B. dahurica to Q. liaotungensis, from Q. liaotungensis to A. mono, and from A. mono. to P. davidiana, mainly from large individuals in the canopy layer to the smaller ones in the understory. Symmetric competition is only found between Q. liaotungensis and A. mono. No intraspecifc competition was detected in all the species. However, considering the straight line G (t, x) -D(t,x) relationship and relatively low mortality of trees largerthan 4 cm in DBH, we speculated that asymmetric interspecific competition could not be strong as a structuring force of the tree community.The seedlings and saplings of A. mono, Q. liaotungensis, T. mandshurica and P. davidiana dominated the understory of the forest, with high densities and occurrence frequencies. Th...