Large trees are surrounded by more heterospecific neighboring trees in Korean pine broad-leaved natural forests

Hongxiang Wang,Yanbo Hu,Hui Peng,Zhonghua Zhao,Gangying Hui

doi:10.1038/s41598-018-27140-7

Abstract

Negative conspecific density dependence is one of the principal mechanisms affecting plant performance and community spatial patterns. Although many studies identified the prevalence of density dependent effects in various vegetation types by analyzing conspecific spatial dispersal patterns (spatial patterning) of forest trees, interactions between individuals and heterospecific neighboring trees caused by density-dependent effects are often neglected. The effects of negative density dependence lead us to expect that neighbourhood species segregation would increase with increasing tree size and that larger trees would be surrounded by more heterospecific neighbours than would smaller trees. We studied four mapped 1-Ha plots on Changbaishan Mountain in North-eastern China and used marked point pattern analysis to explore whether trees of different sizes exhibited differences in neighbourhood species segregation; we also determined whether larger trees were more likely to have heterospecific neighbours than smaller trees were. Our results show that bigger trees generally have higher species mingling levels. Neighborhood species segregation ranged from lower than expected levels to random or nearly random patterns at small scales as tree size classes increased under heterogeneous Poisson null model tests. This study provides some evidence in support of negative density dependent effects in temperate forests.

Highlights

In the time since Janzen[1] and Connell[2] described the impairing performance of conspecific neighbors in forest communities due to host-specific pathogens, herbivores, seed predators and intraspecific competition, negative conspecific density dependence has become recognised as important in the maintenance of species diversity
If density dependence is in play, intraspecific aggregation emphasises intra- rather than interspecific competition; heterospecific trees may enjoy recruitment and survival advantages when growing among cohorts of conspecific trees, and the numbers of other species may increase as conspecific tree size increases
Assuming that density-dependent effects are important in the maintenance of species segregation patterns, we would expect that small trees would exhibit low-level neighbourhood species mingling patterns and that neighbourhood heterogeneity would rise around large focal trees

Summary

Introduction

In the time since Janzen[1] and Connell[2] described the impairing performance of conspecific neighbors in forest communities due to host-specific pathogens, herbivores, seed predators and intraspecific competition, negative conspecific density dependence has become recognised as important in the maintenance of species diversity. One involves monitoring the growth and mortality of a particular species as well as the development of its seedlings (because trees are more sensitive to competition during early life stages)[8,9,10,11] This approach may be insufficient because the reactions of trees to density-dependent effects may not be readily detectable over short time intervals[12], and seedling mortality can vary with environmental heterogeneity and large scale natural disturbances such as droughts and floods. Gaps caused by mortality of conspecific trees may be colonised by new heterospecific neighbours that may enjoy survival advantages when robust intraspecific competition is in play Such an effect cannot be detected by comparing the unmarked spatial distribution patterns of the various life stages of conspecific trees. If both the nearest-neighbour and second-order approaches to neighbourhood species mingling are employed, detailed patterns emerge

Methods

Results

Conclusion