Spatial and Temporal Variation in Primary Forest Growth in the Northern Daxing’an Mountains Based on Tree-Ring and NDVI Data

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Spatial and Temporal Variation in Primary Forest Growth in the Northern Daxing’an Mountains Based on Tree-Ring and NDVI Data


The results of spatial analyses indicate that in addition to the effect of large-scale climate change on tree growth, microclimatic differences at microtopographical scales can affect spatial variation in tree growth [24,28,29]. The results of this study revealed differences in the growth decline of both P. sylvestris var. mongolica and L. gmelinii at different elevations. The results of the spatial analysis showed that elevation had the greatest relative effect on forest degradation. The intensity of the decline in both species increased with elevation within the same periods. This might stem from the fact that temperature plays a major role in affecting the total growth rate early and late in the growing season [67]. As the temperature decreases with altitude, the growth period of trees starts later, and the growth rate decreases when the growing season is shorter [27]. That is, global warming has not altered changes in P. sylvestris var. mongolica growth with elevation. Although cold temperature limitations at higher elevations may have been mitigated, poorer soil nutrient and moisture conditions will still limit tree growth. The radial growth of P. sylvestris var. mongolica became more strongly correlated with the vegetation index as elevation increased. Therefore, spatial analyses can be conducted on the radial growth of P. sylvestris var. mongolica at high altitudes. Patterns in the radial growth in L. gmelinii at different elevations were consistent with those of P. sylvestris var. mongolica. However, this trend was not observed in the performance of the mid-elevation L. gmelinii sample site (LG-B), which was less correlated with the vegetation index. This stems from the fact that the trees in the LG-B sample site are much older, especially at high altitude; these trees are thus more susceptible to environmental stresses and have lower cambium activity compared with younger trees, which are prone to having narrow or missing tree rings [34]. Topography and slope orientation affect the distribution of water, nutrients, and heat in the region. Southward-facing sunny slopes experience higher intensities of solar radiation and more sunshine hours. This leads to high evapotranspiration and greater soil weathering, which leaves the soil devoid of organic matter and susceptible to moisture limitation [29]. P. sylvestris var. mongolica and L. gmelinii are shade-tolerant and moisture-loving species [68], and south-facing slopes are likely to exacerbate the adverse effects of drought. The relative effect of slope is 7.08%. Soils on steep slopes are more susceptible to erosion and water loss, and this results in a low nutrient content and water deficits [29]. This is similar to the effects of elevation and slope orientation on growth observed in other studies of tree rings. For example, Kermavnar et al. [25] conducted isotopic studies of Fagus sylvatica and found that trees growing on southwestern slopes experienced greater environmental stress compared with trees on slopes with different orientations, and this was attributed to differences in the strength of water evapotranspiration on slopes of different orientations. Kooch et al. [69] explored the effects of soil conditions and altitude on silvicultural systems, and high altitude had an adverse effect on soil function and fertility. Overall, topography affects the distribution of environmental factors, and the responses of trees to environmental factors vary among regions. Thus, the climatic environment of the region has a strong effect on the topographic patterns of recession. Climatic and environmental factors require consideration when analyzing the effects of topographic factors on tree growth.

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