Spatio-temporal Distribution Patterns And Dynamics Of Two Species Of Abies In Different Climatic Zones

The spatial distribution patterns of species can reflect the basic characteristics of populations,the interactions between species,and the relationships between species and environment.The formation of the spatial patterns of species is closely related to various ecological processes.Currently,the point pattern analysis is widely applied as an efficient tool to characterize the distribution patterns of species.In this study,we focused on the Abies georgei var.smithii population in the Sygera mountains and the Abies fargesii Franch.population in the Qinling Mountains.We established a 1-ha(100 m × 100 m)sampling plot in each of the two study sites.Within each plot,all fir individuals with tree height > 2 m were tagged,geo-referenced,and recorded(including tree age,diameter at breast height,and crown size).The diameter class structure of population was analyzed based on the distribution of diameter classes,and the spatial pattern of population was analyzed by employing the point pattern analysis.To explore the spatiotemporal distribution patterns and temporal dynamics of two species of Abies population and compare the differences and similarities of the research results.Our results showed that:(1)For the community of A.georgei var.smithii: The diameter class distribution of A.georgei var.smithii was inverted “J” shape,indicating that the community had a stable structure and good natural regeneration.The adults were almost randomly distributed at all periods and all scales;the juveniles showed aggregations at a small scale(2 m)in each period after 1891,with successive aggregations at the scale of 1-41 m from 1981 to 2012;and the seedlings showed aggregations at small scales(1-2 m)from 1861 to 1920,with the largest range of scales(1-35 m,41 m,and 48m)of aggregations observed in 1951-1980.In all the five periods,there was almost no association or only positive association between trees at different age groups.The association between adults and juveniles shifted from no association to positive association at all scales over time;the association of adults-seedlings shifted from no association at all scales to positive association at medium and large scales(32-35 m,44 m,and 49 m)and then back to no association at all scales over time;the seedlingsjuveniles association shifted from no association at all scales to positive association at small scale(8 m)and then positive association at small and medium scales(1-30 m)over time.Overall,there was a suppressive effect of adults on juveniles at small scales while a facilitative effect at larger scales.The number of seedlings in the sampling plot increased substantially from 1951 to 1980,and the number of saplings also increased in the following 30 years since the seedlings grew up,which in part increased the competition in the fir stand.In general,there was an intraspecific promoting effect in the community of A.georgei var.smithii during its succession.(2)For the community of A.fargesii Franch.: The diameter class distribution of A.fargesii Franch.was “unimodal” shape,with a small number of seedlings and a large number of middle-and old-aged individuals,making it a declining population.The distribution of adults was basically random over a 150-year period,with occasional aggregations occurring at small scales(7 m and 13 m);the saplings showed aggregation distributions at small scales(2 m,4 m,and 7 m)at almost all periods except from 1921 to 1950,and then showed random distributions as the scale increased;and the seedlings were largely distributed randomly,with aggregations occurring at small scales from1921 to 1950.The adults and saplings were negative associated at small scales(1 m and 3 m)during 1861-1890 while positively associated at 3 m and 17 m during 1891-1920,and then shifted to no association as the scale increased.Moreover,there were negative associations of adults and saplings between 1921 and 2008 at medium and large scales(24 m,36 m,and 50 m);the adults and seedlings exhibited negative associations at large scales(20 m and 35 m),positive associations at medium scales(13m and 19 m),and negative associations at small scales(11 m,18 m,and19 m)over time;however,the saplings and seedlings showed no significant associations between each other at all scales over time.Generally,the spatial associations among the age groups were basically non-associated or negatively associated,and there was a competition effect in the community of A.fargesii Franch.in the Qinling Mountains.(3)By comparing the historical changes of the spatio-temporal distribution patterns of two species of Abies in the plateau climate zone and the temperate climate zone,we found that: In the temporal scale,warming since 1950 significantly promoted the regeneration of both Abies populations.According to the results of spatial distribution pattern,low temperature stress on the plateau and different biological characteristics of the two Abies species may be the important factors for the different.According to the results of spatial correlation,The correlation between adult and young Abies was consistent with the Janzen-Connell hypothesis of the two Abies species.The two populations had intraspecific promoting and competitive effects respectively.The reason was closely related to the effect of understory shrub layer density on seedling regeneration.This study revealing the population dynamics of the two species of Abies,which has certain theoretical and practical significance for the protection and sustainable management of the regional zonal tree species.