Understanding the factors influencing tree productivity is central to forest ecology. However, the relative contributions of neighborhood interactions, tree species diversity, and tree size to larch (Larix principis-rupprechtii) productivity require further study. Three plots in the Guandi Mountains, Shanxi Province, were set up for each of the following forest types: natural pure larch forest (PL), mixed larch and birch (Betula platyphylla) forest (LB), and mixed larch and spruce (Picea asperata) forest (LS). Based on the tree size-stratified sampling method, a total of 318 tree core samples were collected. A linear mixed model was used to analyze the effects of tree size, dominance, mixing, and neighborhood competition on larch productivity. Birch and spruce promoted larch growth at the stand and individual tree levels, and birch exhibited a more significant facilitating effect. Intraspecific competition was the main factor affecting larch growth. When the intensity of competition among trees was low, the basal area increment (BAI) of larch in the mixed forests was higher than that in the pure forest. However, with increasing competition, the BAI of larch was lower in the mixed forests than in the pure forest. Factors including tree size, dominance, and mingling were positively correlated with the BAI of larch. With increasing tree size, the BAI of larch was higher in the mixed forests than in the pure forest and higher in LB than in LS. When the dominance was less than 0.5, the BAI of larch was higher in the pure forest than in the mixed forests and higher in LS than in LB. With increasing dominance, the BAI of larch was higher in the mixed forests than in the pure forest. The BAI of larch increased with an increasing mixing degree in the mixed forests, and the increasing trend of BAI was larger in LB than in LS. Larch productivity was influenced mainly by neighborhood interactions and stand structure. Improving neighborhood tree diversity and increasing the large tree proportion and dominance of larch will be helpful for improving larch productivity in mixed forests.

Larix principis-rupprechtii Mayr (larch) is a native conifer species in North China, and also a major silvicultural and timber species in the region. Climate change has led to a change in its suitable distribution area. However, the dominant factors affecting changes in its suitable distribution and migration trends are not clear. In this study, based on forest resource inventory data and bioclimatic data in Hebei and Shanxi provinces, China, we built an ensemble model based on seven algorithms to simulate the larch’s potential suitable distribution areas under three shared socioeconomic pathways (SSPs: SSP1-2.6, SSP2-4.5, and SSP5-8.5) for the current and future (2021–2040, 2041–2060 and 2080–2100). The results revealed that: (1) ensemble models significantly improved the predictive accuracy (ROC = 0.95, TSS = 0.81, KAPPA = 0.65); (2) the current potentially suitable distribution area was concentrated in the Bashang Plateau and the northwestern mountain range of the study area. Among them, 12.38% were highly suitable distribution areas, 12.67% were moderately suitable distribution areas, and 12.01% were lowly suitable distribution areas; (3) the main climatic factors affecting larch distribution were mean temperature of driest quarter, mean diurnal range, precipitation of warmest quarter, and temperature annual range; (4) under different future climate scenarios, the contraction of the suitable distribution area of larch increased significantly with increasing SSP radiation intensity. By 2100, the suitable distribution area of larch was expected to decrease by 26.5% under SSP1-2.6, 57.9% under SSP2-4.5, and 75.7% under SSP5-8.5 scenarios; (5) from 2021 to 2100, the different suitable distribution areas of larch showed a trend of migration to the northeast. Under the SSP5-8.5 scenario, the migration distance of different suitable distribution areas was the largest, in which the high suitable distribution area migrated 232.60 km, the middle suitable distribution area migrated 206.75 km, and the low suitable distribution area migrated 163.43 km. The results revealed the impact of climate change on the larch distribution, which provided a scientific basis for making forest management decisions.

Larix principis-rupprechtii Mayr (larch) is one of the main afforestation and timber production species used in North China. Climate change has led to a change in its suitable distribution and growth. However, the impact of climate change on its growth suitability is not clear. In this study, using forest resource inventory data and spatially continuous environmental factor data (temperature, precipitation, topography, and soil) in Hebei and Shanxi Provinces, China, the random forest model (RF) was used to simulate the larch site index (SI) and growth suitability under three shared socioeconomic pathways (SSPs: SSP1-2.6, SSP2-4.5, and SSP5-8.5) for the current and future (2021–2040, 2041–2060 and 2080–2100). The results revealed that (1) RF had excellent performance in predicting the regional SI (R2 = 0.73, MAE = 0.93 m, RMSE = 1.35 m); (2) the main factors affecting the productivity of larch were the mean temperature of the warmest quarter (BIO10), elevation (ELEV), mean diurnal range (BIO2), and annual precipitation (BIO12); and (3) larch currently had a higher SI in the Bashang areas and in the high-altitude mountains. The areas characterized as unsuitable, poorly suitable, moderately suitable, and highly suitable accounted for 15.45%, 42.12%, 31.94%, and 10.49% of the total area, respectively. (4) Future climate warming had an obvious inhibitory effect on the SI, and the effect strengthened with increasing radiation intensity and year. (5) The moderately suitable and highly suitable areas of larch growth showed a downward trend under future climate scenarios. By the end of this century, the suitable growth areas would decrease by 14.14% under SSP1-2.6, 15.17% under SSP2-4.5, and 19.35% under SSP5-8.5. The results revealed the impact of climate change on larch growth suitability, which can provide a scientific basis for larch forest management.

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