Xiuhai Zhao

Tree growth and regeneration dynamics at a mountain ecotone on Changbai Mountain, northeastern China: Which factors control species distributions?

Abstract: n To improve our understanding of climate-driven long-term dynamics of eastern Asian mountain forests, we used field surveys and dendrochronological techniques to examine regeneration density, growth rate of mature trees, and growth sensitivity to climate of 3 common coniferous tree species at their respective altitudinal distribution limits on Changbai Mountain, northeastern China. The studied species were Manchurian fir (Abies nephrolepis, distributed between 780 and 1750 m asl), Korean pine (Pinus koraiensis, 780 and 1300 m asl), and Jezo spruce (Picea jezoensis var. komarovii, 1000 and 1750 m asl). Regeneration densities did not differ significantly among the elevations except for Jezo spruce, which showed a significantly lower regeneration density at 1000 m asl as compared to 1300 and 1750 m asl. All 3 species showed a significantly higher basal area increment (BAI) at the middle part of their distribution ranges than at their limits. The growth of Manchurian fir and Jezo spruce exhibited higher sensitivity to precipitation than to temperature at their lower distribution limits, and the inverse pattern was observed at the upper limit. In all cases the correlations between growth and the respective climate variable were positive, except for the correlation between Jezo spruce growth and precipitation. Growth of Korean pine was positively correlated with spring temperature and summer moisture at its lower distribution limit and with summer temperature at its upper limit. Our study suggests that elevational limits of forest vegetation were likely constrained by climate factors affecting growth of dominant species rather than those controlling regeneration density.

Seedling density dependence regulated by population density and habitat filtering: Evidence from a mixed primary broad-leaved Korean pine forest in Northeastern China

Key messageThe effects of distance dependence, negative density dependence (NDD), phylogenetic density dependence, and habitat filtering were integrated to provide additional evidence in temperate forest tree seedling survival. The main focus of this study was to explore how population density and habitat filtering regulate NDD. An approach involving four classes of population density and three classes of soil moisture was tested, including the effect of habitat variables to more accurately evaluate the underlying ecological processes affecting the density dependence of seedlings.ContextNDD is an important mechanism for the maintenance of species diversity across multiple life stages, particularly during seedling recruitment. By regulating specific population structures to maintain species diversity, the effects of density dependence and distance dependence are sometimes difficult to distinguish. Nevertheless, the contribution of NDD to community assembly, relative to other processes such as habitat filtering, remains a subject of debate. Recently, it has been reported that seedling survivals are also negatively correlated with phylogenetic relatedness between neighbors and focal individuals. This effect is known as phylogenetic negative density dependence (PNDD). However, another opposite effect known as phylogenetic positive density dependence (PPDD) has also been reported to exist.AimsThe objectives of this study are to examine the following: (i) how population density affects negative density dependence (NDD); (ii) how habitat filtering regulates the NDD; (iii) whether more evidence can be found for PNDD or PPDD and why; and (iv) whether the intensity of negative density dependence is affected by the distance between parent trees and seedlings.MethodsThe study was conducted in a 20-ha primary mixed broad-leaved Korean pine forest in Changbai Mountain of China. We used generalized linear mixed models to analyze how the seedling survival of 23 woody plant species relates to neighborhoods and habitat variables. Four models were established with and without habitat variables, and two of the four models were used to test how different population densities of focal seedlings and different gradients of habitat variable regulated negative density dependence.ResultsThe following results were obtained: (1) the strongest conspecific negative density dependence (CNDD) was found within a radius of 15xa0m; (2) seedling survival were most strongly impacted by the density of conspecific seedling and adult neighbors in habitats with relatively low soil moisture; (3) the effect of seedling-seedling CNDD was especially significant, when densities ranged from 20 to 40xa0seedlings/4xa0m2, and (4) there were some evidences of phylogenetic positive density dependence (PPDD), and the effect of seedling-seedling PPDD was increasing with an increase in soil moisture.ConclusionOur results demonstrate that conspecific negative density dependence played an important role in seedling survival, which is closely related to habitat filtering and population density. However, we found some evidences of phylogenetic positive density dependence. We suggest that future studies of neighborhood density dependence should increase awareness of evolutionary relationships.

Climatic Response of Betula ermanii Tree-ring Growth Along an Altitudinal Gradient on the Northern Slope of the Changbai Mountains

In order to explore climate-growth relationships at different elevations, tree-ring width chronologies of Betula ermanii were developed from three sampling sites on the northern slope of the Changbai Mountains, northeastern China. Monthly mean temperature and monthly total precipitation were used for the analysis. The study found more climatic signals revealed by statistical characteristics of the tree-ring chronologies in higher elevations. Response function analysis indicated that on the lower tree-line site(1 700 m a.s.l.), radial growth of Betula ermanii was negatively correlated with temperature of January, but positively correlated with precipitation of previous September(P 0.05). On the mid-elevation interior forest site(1 850 m a.s.l.), growth of Betula ermanii responded negatively to temperature of previous June and July(P 0.05). On the upper tree-line site(2 000 m a.s.l.), tree-ring growth of Betula ermanii was negatively correlated with temperature of March and previous July, but positively correlated with that of June and previous September(P 0.05). Besides, on upper tree line, growth of Betula ermanii benef ited from high level of precipitation during current June. Our results suggested that along the altitudinal gradient, Betula ermanii tree-ring growth responds differently to local climatic conditions. In general, the climatic sensitivity of Betula ermanii chronologies increases with the elevation. Fig 4, Tab 1, Ref 54

Relationship Between Climate and Tree-ring Chronology of Betula ermanii on Tree-line in North Slope of the Changbai Mountains

The tree-ring width chronologies were developed in north slope of the Changbai Mountains to analyze the Betula ermanii radial growth-climate relationships through dendrochronological methods including correlation and response analysis.The results showed that the radial growth of Betula ermanii exhibited a significantly nagative correlation with monthly temperature of both previous July and current March(P 0.05),a significantly positive correlation with monthly temperature of previous September and current July,and a significantly positive correlation with monthly total precipitation of previous June.Besides,the analysis of response toseasonally climatic factors showed that the tree-ring growth of B.ermanii had a significantly negative correlation with mean temperature of current spring(January to March),a significantly negative correlation with mean temperature of the period before current growth season(April and May),and a significantly positive correlation with mean maximum temperature of the period before current growth season.But it showed no significant correlation with seasonally precipitation.Furthermore,the regression model between tree-ring width index and climatic factors was established via multiple stepwise regression analysis and run under the scenario of climate warming.The results showed that the radial growth of B,ermanii on tree-line zone would decline by 14.8%.

The direct and indirect effect of fire on radial growth of Pinus koraiensis trees in a northern temperate forest of China

The long-term effects of fire on the radial growth of Korean pines (Pinus koraiensis) in Changbai Mountain is poorly understood. In order to quantify the impact of fire on the radial growth of Korean pines, we measured ring widths and developed two tree-ring chronologies from 21 burned Korean pine trees that were damaged by fire in 1857 as well as 30 control trees in the Changbai Mountain Nature Reserve, China. As expected, the growth rates of the burned trees were slower than those of the control trees in the first five years following the fire. However, beginning six years after the fire, the growth of the burned trees increased considerably, and this period of increased growth lasted 13 years, with moderate growth occurring throughout the 1866 to 1871 period. A difference in growth rates between burned and control tress was also observed for the 20 years since temperatures began markedly increasing in 1980. Burned trees tended to respond negatively to monthly minimum temperature, precipitation, and vapor pressure deficits (VPD), whereas the positive relationship between those factors and radial growth of control trees became stronger. In addition, the significantly negative effect of competition on radial growth was only observed among burned trees. These results demonstrated that the negative and direct effect of damage to physiological plant processes by fire only affected the years shortly after a fire occurred and then became obscured by its indirect effects, such as differential responses to climate and competition, which did persist for a long time. The indirect effect on radial growth over time could be explained by the variability in the relative strength of climatic responses and competition caused by fire.

Correlations Between Meteorological Factors and Tree-ring Width Index of Chinese Pine (Pinus tubulaeformis) in Hunshandake Sandy Area, China

To explore the radial growth of Chinese pine(Pinus tubulaeformis) with different diameter classes in response to meteorological factors,dendrochronological measurements were carried out to 20 large trees(LAG,mean diameter = 34.6 cm) and 20 small trees(SMA,mean diameter = 15.5 cm) of the species in Hunshandake sandy area,Inner Mongolia,China,and the correlations between the tree-ring chronology data and meteorological factors were studied.The results showed that the relationship between the mean sensitivity and DBH(diameter at breast height) was negatively correlated,while there existed similarities between the correlations of STD chronologies and the meteorological factors in that the STD chronologies were all positively correlated to the precipitation and spring temperatures,and negatively correlated to the summer temperatures.The STDs were positively correlated to the mean and maximum temperatures in January,February,September(P0.05);and negatively correlated to the mean and maximum temperatures in June but positively correlated to the minimum temperature of January,February,August and September(P0.05).They were positively correlated to the precipitation of October in the last year,and May and July of this year(P0.05).On the other hand,the SMAs were positively correlated to the precipitation in June and negatively correlated to the maximum temperature in July(P0.05).It was concluded that the differed correlations between the tree-ring chronologies and the meteorological factors among the trees of the different diameter classes should be taken into consideration indendrochronological studies.