| Global climatic change challenges sustainable forest management and adaptive management decision is a key factor. Adaptive forest management needs modeling and predicting the effects of climatic change on forest growth and yield. As traditional forest growth models presume the site quality is constant, they can not be used to predict forest growth under climatic change. Thus, it is necessary to construct climate-sensitive forest growth models. In the present paper, a stand growth model system(CSSGM-larch) was constructed for larch plantations in northern and northeastern China based on 370 sample plots from the sixth, seventh and eighth Chinese national forest inventory data and 12 bioclimatic factors extracted from Climate AP. The model system is statistically reliable and biologically reasonable. CSSGM-larch was used to predict larch plantations growth during 2010-2099 under three future climate scenarios(RCP2.6, RCP4.5 and RCP8.5). The interaction of thinning and climatic change on the growth of larch plantations was also explored.(1) Regional height-diameter model for larch plantations was developed. Nonlinear least squares, mixed-effects model, quantile regression and generalized additive model were used to construct simple and generalized height-diameter models. Simple height-diameter model based on mixed-effects model performed best(For fitting data, adjust R squares Ra2=0.912, absolute bias MAB=0.801 m, relative absolute bias RMA=9.1 %, root mean square error RMSE=1.095 m; for validation data, MAB=0.736 m, RMA=8.6 %, RMSE=1.013 m). This model can be used to forecast tree height for larch plantations in northern and northeastern China.(2) Regional climate-sensitive dominant height model for larch plantations was constructed. We found that the relationship between mean warmest month temperature and dominant height was affected by summer precipitation, and summer precipitation was positive with the maximum of dominant height. Furthermore, the site index of each plot(base age is equal to 20 year) was calculated using the model. By modeling the response of site index to climatic change during 2010-2099, we found that site index became larger under future climate scenarios. Compared to current climate, the mean difference of site index of different climate scenarios were-0.093 m ~ 0.174 m(-1.40 % ~ 1.69 %) with the range from-0.554 m to 1.100 m(-9.19 % ~ 7.52 %).(3) Regional climate-sensitive stand tree number transfer model with thinning effect, and climate-sensitive stand basal area, volume and biomass models were constructed for larch plantations. The growth of larch plantations during 2010-2099 was simulated. The results showed that stand mortality, basal area and biomass decreased and stand volume increased under future climatic scenarios. Compared to current climate, the mean difference of stand mortality were-0.086 trees×hm-2×year-1 ~ 0.014 trees×hm-2×year-1(-0.87 % ~ 0.05 %) with the range from-3.497 trees×hm-2×year-1 to 3.053 trees×hm-2×year-1(-16.26 % ~ 15.04 %). The mean difference of stand basal area were-0.294 m2×hm-2 ~ 0.072 m2×hm-2(-1.98 % ~ 0.74 %) and it ranges from-5.766 m2×hm-2 to 4.534 m2×hm-2(-22.68 % ~ 21.22 %). The mean difference of stand volume were-2.390 m3×hm-2 ~ 1.807 m3×hm-2(-2.37 % ~ 1.44 %) and it ranges from-52.706 m3×hm-2 to 84.062 m3×hm-2(-26.63 % ~ 35.76 %). The mean difference of stand biomass were-1.896 t×hm-2 ~ 1.119 t×hm-2(-2.33 % ~ 0.97 %) and it ranges from-35.212 t×hm-2 to 44.878 t×hm-2(-25.79 % ~ 25.04 %).(4) Regional climate-sensitive stand growth model system(CSSGM-larch) based on mixed-effects model and simultaneous equations for larch plantations were constructed. Compared to seperate model, the model system considered the correlation of the residuals among different models. CSSGM-larch was used to model growth status of larch plantations under climatic change during 2010-2099. It was found that stand mortality and basal area decreased, and stand volume and biomass increased under future climatic scenarios, which means that climatic change retarded stand growth. The mean difference of stand mortality was-0.106 trees×hm-2×year-1 ~ 0.024 trees×hm-2×year-1(-2.04 % ~ 0.27 %) and it ranges from-48.338 trees×hm-2×year-1 to 42.046 trees×hm-2×year-1(-45.96 % ~ 68.01 %). The mean difference of stand basal area was-0.055 m2×hm-2 ~ 0.022 m2×hm-2(-0.36 % ~ 0.08 %) and it ranges from-1.016 m2×hm-2 to 0.865 m2×hm-2(-6.27 % ~ 5.67 %). The mean difference of stand volume was-0.778 m3×hm-2 ~ 1.267 m3×hm-2(-0.78 % ~ 0.57 %) and it ranges from-13.284 m3×hm-2 to 40.640 m3×hm-2(-10.41 % ~ 15.07 %). The mean difference of stand biomass was-0.825 t×hm-2 ~ 0.719 t×hm-2(-0.97 % ~ 0.33 %) and it ranges from-10.837 t×hm-2 to 18.064 t×hm-2(-11.85 % ~ 10.07 %).(5) Growth response to future climate change was analyzed by provinces, age classes and climate zones. The simualtion of either the induvidual models or model system showed that stand mortality, basal area, volume and biomass in Hebei and Inner Mongolia decreased under future climatic scenarios; stand mortality, basal area, volume and biomass in Beijing, Heilongjiang, Liaoning and Shanxi increased; stand mortality in Jilin decreased and stand basal area, volume and biomass in Jilin increased. For different age classes, stand mortality, basal area, volume and biomass in young forest; stand mortality, basal area and biomass in middle-aged forest decreased and stand volume in middle-aged forest increased; and stand mortality and basal area decreased and stand volume and biomass increased in pre-mature and mature forest. In different climatic zones, changes of stand mortality, basal area, volume and biomass in mid temperate zone were larger than those in cold temperate and warm temperate zones.(6) The growth of young and middle-aged larch plantations under different thinning intensities and climatic scenarios during 2010-2039 was simulated by using CSSGM-larch, and the interaction of thinning and climatic change was analyzed. The results showed 2 trends, one is that stand mortality decreased and stand basal area, volume and biomass increased with larger thinning intersity, the other one is that stand mortality increased and stand basal area, volume and biomass decreased with larger thinning intersity.(7) The study proved the potential of empirical growth models to forecast forest growth under future climatic change, and the conclusions above could be as a basis for adaptive management of larch plantations to climatic change in north and northeast China. |
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