There are 261 species of vascular plants in the Form. Quercus mongolica that located in the flo... more There are 261 species of vascular plants in the Form. Quercus mongolica that located in the floristic region of NE. China. The temperate florstic elements are 47 47% of the total elements. The E. Asia elements are 42 02%. The endemic floristic elements to China are 10 51%, in which the cosmopolitan floristic elements are not included. The distribution types of all genera in the Forma Quercus mongolica are analysed. The temperate distribution types of genera are 90 3%. The florstic elements of the tree layer, shrub layex, herbaseous layer and liana are also analysed.
Diversity of Quercus mongolica communities was investigated in 13 sites across northeastern China... more Diversity of Quercus mongolica communities was investigated in 13 sites across northeastern China which differed in latitude, altitude and longitude. Field investigations were conducted. Measurements were conducted from the north edge of Q. mongolica range (Huma, Heilongjiang Province) to the south end (Baishilazi, Liaoning Province). The geographic position (including latitude, longitude and altitude) of each site was recorded, and plants in the tree layer (including all mature trees, saplings and seedlings), the shrub layer and the herb layer were sampled using plots measuring 20m×20m, 10m×10m and 10m×10m, respectively. Species richness, Pielou′s index of evenness, the probability of species encounter, as well as Shannon-Wiener and Gini diversity indices were calculated for each plot in each site. Relationships between species richness or the diversity indices and the environmental factors (such as latitude, longitude and altitude) for the whole fields and different structural groups were analyzed. We found that the spatial distribution of species richness and species diversity of Q.mongolica communities showed great heterogeneity in different sites, to the extent that species richness and species diversity of some plots within sites differed. This indicates that these diversity indices may be affected not only by latitude and altitude, but also by topographical factors such as slope, soil, age of communities and disturbance.The correlation and regression analysis showed that species richness significantly related to altitude and latitude, decreasing as altitude and latitude increased. Additionally, patterns of plant species richness differed between plants structural groups. Woody species richness related closely and negatively with latitude, as did herb species richness with altitude. No significant relationship was found between woody species richness and altitude or between herb species richness and latitude. Taken together, this suggests that the species richness of vascular plants may more closely relate to altitude than to latitude. Neither the Gini diversity index, Shannon-Weiner diversity index and nor PIE closely correlated with latitude, longitude or altitude. Altitude and latitude are indirect environmental variables indicative of average temperature, and can drive gradients in species richness. Different patterns of species richness along these environmental gradients exist for different structural groups perhaps due to the fact that woody plant distribution is sensitive to large-scale environmental factors such as latitude, while the distribution of herbaceous plants is sensitive to local-scale environmental factors such as altitude.CCA ordination among diversity indices and environmental factors also support above conclusions.
Determining the patterns and drivers of the small‐scale species–area relationship (SAR) is crucia... more Determining the patterns and drivers of the small‐scale species–area relationship (SAR) is crucial for improving our understanding of community assembly and biodiversity patterns. Niche‐based and stochastic processes are two principal categories of mechanisms potentially driving SARs. However, their relative importance has rarely been quantified rigorously owing to scale dependence and the simplified niche volumes often used. In a fully mapped, 24‐hm2 plot of a typical subtropical forest, we built the SARs and well‐defined niche hyper‐volumes of a broad range of environmental variables at scales of 10–70 m (cell sizes). We then simulated passive sampling and partitioned the variances of the SAR slopes to disentangle these two contrasting mechanisms. We found that the small‐scale SAR best followed a power‐law relationship, consistent with large‐scale SARs. The SAR slope declined with increasing scale; it was lower than expected under passive sampling at scales below 30 m and higher at larger scales. Environmental niches explained more (39%–64%) of the slope at larger scales, exceeding 50% at scales >30 m, and these niches always captured the majority of the structured slopes. Environmental position (environmental mean values) effects were steady in absolute strength across scales and explained most (98%–68%) of the niche effect, but this proportion decreased with increasing scale. The effect of environmental heterogeneity increased with spatial scales, starting to rise at the 30 m scale after controlling for environmental position. Excluding soil properties from analyses strongly reduced these niche effects, highlighting the importance of soils for structuring the small‐scale SAR. There was also substantial stochasticity in the SAR slopes, which was only partially explained by passive sampling. Synthesis. Our results show that the small‐scale SAR in the studied subtropical forest follows a power law, exhibits a scale shift in SAR slope at 30 m, and is strongly shaped by niche effects that are dominated by environmental position relative to heterogeneity. However, soil heterogeneity controls the increase in niche effect and the shift in the SAR slope with increasing spatial scales. Hence, edaphic factors can be responsible for scale dependence in small‐scale SARs, thereby linking small‐scale and large‐scale SARs.
<p>Extreme climatic events such as droughts threaten forests and their clim... more <p>Extreme climatic events such as droughts threaten forests and their climate mitigation potential globally. Stability, the ability of forests to maintain functioning in periods of stress, is therefore expected to be a primary focus of forest management in the 21st century. A key management strategy suggested for enhancing stability may be to increase tree species richness in secondary and plantation forests. Here, we aim to understand the drivers that may promote forest stability in mixed-species tree communities. We use structural equation models to explain how tree species richness, asynchronous species dynamics and diversity in hydraulic traits affect the stability of yearly forest productivity along an experimentally manipulated biodiversity gradient ranging from monocultures up to mixtures of 24 tree species. Tree species richness improved stability by increasing species asynchrony. That is, at higher species richness, inter-annual variation in productivity among tree species buffered the community against stress-related productivity declines. This effect was mediated by diversity in species’ hydraulic traits in relation to drought tolerance and stomatal control within the community, but not by the community-weighted means of these hydraulic traits. The examined hydraulic traits may be used to select suitable tree species and design mixtures that stabilize productivity in an increasingly variable climate through diverse response strategies, while excluding those that would succumb to drought or competition. The identified mechanisms by which tree species richness stabilizes forest productivity emphasize the importance of hydraulically diverse, mixed-species forests to adapt to climate change.</p>
There are 261 species of vascular plants in the Form. Quercus mongolica that located in the flo... more There are 261 species of vascular plants in the Form. Quercus mongolica that located in the floristic region of NE. China. The temperate florstic elements are 47 47% of the total elements. The E. Asia elements are 42 02%. The endemic floristic elements to China are 10 51%, in which the cosmopolitan floristic elements are not included. The distribution types of all genera in the Forma Quercus mongolica are analysed. The temperate distribution types of genera are 90 3%. The florstic elements of the tree layer, shrub layex, herbaseous layer and liana are also analysed.
Diversity of Quercus mongolica communities was investigated in 13 sites across northeastern China... more Diversity of Quercus mongolica communities was investigated in 13 sites across northeastern China which differed in latitude, altitude and longitude. Field investigations were conducted. Measurements were conducted from the north edge of Q. mongolica range (Huma, Heilongjiang Province) to the south end (Baishilazi, Liaoning Province). The geographic position (including latitude, longitude and altitude) of each site was recorded, and plants in the tree layer (including all mature trees, saplings and seedlings), the shrub layer and the herb layer were sampled using plots measuring 20m×20m, 10m×10m and 10m×10m, respectively. Species richness, Pielou′s index of evenness, the probability of species encounter, as well as Shannon-Wiener and Gini diversity indices were calculated for each plot in each site. Relationships between species richness or the diversity indices and the environmental factors (such as latitude, longitude and altitude) for the whole fields and different structural groups were analyzed. We found that the spatial distribution of species richness and species diversity of Q.mongolica communities showed great heterogeneity in different sites, to the extent that species richness and species diversity of some plots within sites differed. This indicates that these diversity indices may be affected not only by latitude and altitude, but also by topographical factors such as slope, soil, age of communities and disturbance.The correlation and regression analysis showed that species richness significantly related to altitude and latitude, decreasing as altitude and latitude increased. Additionally, patterns of plant species richness differed between plants structural groups. Woody species richness related closely and negatively with latitude, as did herb species richness with altitude. No significant relationship was found between woody species richness and altitude or between herb species richness and latitude. Taken together, this suggests that the species richness of vascular plants may more closely relate to altitude than to latitude. Neither the Gini diversity index, Shannon-Weiner diversity index and nor PIE closely correlated with latitude, longitude or altitude. Altitude and latitude are indirect environmental variables indicative of average temperature, and can drive gradients in species richness. Different patterns of species richness along these environmental gradients exist for different structural groups perhaps due to the fact that woody plant distribution is sensitive to large-scale environmental factors such as latitude, while the distribution of herbaceous plants is sensitive to local-scale environmental factors such as altitude.CCA ordination among diversity indices and environmental factors also support above conclusions.
Determining the patterns and drivers of the small‐scale species–area relationship (SAR) is crucia... more Determining the patterns and drivers of the small‐scale species–area relationship (SAR) is crucial for improving our understanding of community assembly and biodiversity patterns. Niche‐based and stochastic processes are two principal categories of mechanisms potentially driving SARs. However, their relative importance has rarely been quantified rigorously owing to scale dependence and the simplified niche volumes often used. In a fully mapped, 24‐hm2 plot of a typical subtropical forest, we built the SARs and well‐defined niche hyper‐volumes of a broad range of environmental variables at scales of 10–70 m (cell sizes). We then simulated passive sampling and partitioned the variances of the SAR slopes to disentangle these two contrasting mechanisms. We found that the small‐scale SAR best followed a power‐law relationship, consistent with large‐scale SARs. The SAR slope declined with increasing scale; it was lower than expected under passive sampling at scales below 30 m and higher at larger scales. Environmental niches explained more (39%–64%) of the slope at larger scales, exceeding 50% at scales >30 m, and these niches always captured the majority of the structured slopes. Environmental position (environmental mean values) effects were steady in absolute strength across scales and explained most (98%–68%) of the niche effect, but this proportion decreased with increasing scale. The effect of environmental heterogeneity increased with spatial scales, starting to rise at the 30 m scale after controlling for environmental position. Excluding soil properties from analyses strongly reduced these niche effects, highlighting the importance of soils for structuring the small‐scale SAR. There was also substantial stochasticity in the SAR slopes, which was only partially explained by passive sampling. Synthesis. Our results show that the small‐scale SAR in the studied subtropical forest follows a power law, exhibits a scale shift in SAR slope at 30 m, and is strongly shaped by niche effects that are dominated by environmental position relative to heterogeneity. However, soil heterogeneity controls the increase in niche effect and the shift in the SAR slope with increasing spatial scales. Hence, edaphic factors can be responsible for scale dependence in small‐scale SARs, thereby linking small‐scale and large‐scale SARs.
<p>Extreme climatic events such as droughts threaten forests and their clim... more <p>Extreme climatic events such as droughts threaten forests and their climate mitigation potential globally. Stability, the ability of forests to maintain functioning in periods of stress, is therefore expected to be a primary focus of forest management in the 21st century. A key management strategy suggested for enhancing stability may be to increase tree species richness in secondary and plantation forests. Here, we aim to understand the drivers that may promote forest stability in mixed-species tree communities. We use structural equation models to explain how tree species richness, asynchronous species dynamics and diversity in hydraulic traits affect the stability of yearly forest productivity along an experimentally manipulated biodiversity gradient ranging from monocultures up to mixtures of 24 tree species. Tree species richness improved stability by increasing species asynchrony. That is, at higher species richness, inter-annual variation in productivity among tree species buffered the community against stress-related productivity declines. This effect was mediated by diversity in species’ hydraulic traits in relation to drought tolerance and stomatal control within the community, but not by the community-weighted means of these hydraulic traits. The examined hydraulic traits may be used to select suitable tree species and design mixtures that stabilize productivity in an increasingly variable climate through diverse response strategies, while excluding those that would succumb to drought or competition. The identified mechanisms by which tree species richness stabilizes forest productivity emphasize the importance of hydraulically diverse, mixed-species forests to adapt to climate change.</p>
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