**3. Results**

#### *3.1. Model Calibration and Validation*

Our simulated results indicated that the initialized forest composition constructed from the observed data from year 2000 adequately represented the forest landscape (stand density: R<sup>2</sup> = 0.821, Pearson correlation test: *p* < 0.01; basal area: R<sup>2</sup> = 0.804, *p* < 0.01) (Figure 3a,b). The simulated stand density and basal area were close to the observed forest inventory data at year 2010 (stand density: R<sup>2</sup> = 0.803, *p* < 0.01; basal area: R<sup>2</sup> = 0.832, *p* < 0.01) (Figure 3c,d). Thus, we accepted the calibrated results for further calculation.

**Figure 3.** Scatter plot showing the relation between simulated and observed data for stand density (**<sup>a</sup>**,**<sup>c</sup>**); and basal area (**b**,**d**) at year 2000 and 2010, respectively (Pearson correlation test: *p* < 0.01).

The results showed that the post-fire stand density increased during the first 10 years (up to 17,295 trees/ha) and then decreased to 4725 trees/ha after 25 years (Figure 4a). The increasing trend was largely attributed to forest fires removing many trees causing the release of growing space for pioneer species to establish. After year 10, these post-fire stands reached the self-thinning stage, and began to reduce individual trees in the following years. The post-fire basal area showed an increasing trend throughout the observed 25 years (Figure 4b). The simulated trends in both stand density, basal area and aboveground biomasses closely followed trends in the field sample data (Figures 4 and 5).

**Figure 4.** Comparison between observed and simulated stand density (**a**) and basal area (**b**) in burned areas in relation to post-fire year.

**Figure 5.** Comparison between simulated data and observed field aboveground biomass, published data from plot surveys in the study area.

#### *3.2. Ecological Resiliencies Response to Climate Change and Fire Regimes at Landscape Scale*

Our results showed that under current climate conditions, ecological resilience was affected by forest fire regimes (Figure 6a). The forest ecological resilience was greatest under the CF2 scenario followed by the CF1 and CF3 scenarios. Under the current fire regimes (CF1), the ecological resilience increased rapidly from the simulated years 50 to 80, then decreased until year 160, and then increased slightly to year 300. The ecological resilience decreased significantly under the CF3 scenario in the first 160 years compared to the CF1 scenario. However, the ecological resilience under CF1 scenario coincided with the CF3 scenario from year 170 to 270.

The trajectories of forest ecological resilience varied among climate change and fire regime scenarios (Figure 6b). Under B1F1, B1F2, and A2F1 scenarios, the ecological resilience dynamics had a similar trend for the whole simulation period. The curves of these three scenarios fluctuated in the first 50 years and peaked at year 80, then decreased until year 160, and then increased to year 300 gradually. The calculated forest ecological resilience was highest under the B1F2 scenario across all simulated

periods, followed by B1F1, A2F1, and A2F3 scenarios. Moreover, the ecological resilience under the A2F3 scenario was visibly lowest among these scenarios until year 210.

**Figure 6.** Changes in ecological resilience at the landscape level under different simulated scenarios. (**a**) current climate condition with different fire occurrence (CF1, CF2, and CF3); and (**b**) climate change scenarios with different fire occurrences (B1F1, B1F2, A2F1, and A2F3).

#### *3.3. Effects of Fire Regimes, Climate Change on Ecological Resilience*

The effects of forest fire on ecological resilience varied among the three fire occurrence scenarios across the three simulated periods (Figure 7). Compared to the CF1 scenario, no significant difference was found between the short and medium term interval (*p* > 0.05) under CF2 scenario, while the ecological resilience under the CF2 scenario differed significantly from CF1 scenario during long-term interval (*p* < 0.05). However, the ANOVA tests demonstrated that the simulated ecological resilience under CF3 scenario for both short and medium term interval differed significantly from CF1 scenario (*p* < 0.05), and no significant difference existed in the long term interval (150–300 year).

The ecological resilience was substantially higher under the CF2 scenario than the CF1 scenario (Figure 7). Our results showed that the increase in ecological resilience under CF2 scenario was 17.5%, 12.4%, and 43.2% greater than that in CF1 scenario across the entire simulated periods, respectively. Under CF3 scenario, the largest reduction in ecological resilience occurred in the short and medium term interval, and was 24.6% and 34.3% lower than that in the CF1 scenario. However, the average value of ecological resilience under CF3 scenario was similar in the long-term period.

**Figure 7.** Multiple comparison of three fire scenarios effects on ecological resilience at different simulated periods. Small letters indicated significant differences among scenarios at 0.05 level. CF1, CF2, and CF3: different fire occurrence scenarios.

The ecological resilience responses to three climatic scenarios differed among different land types (Figure 8). Results showed that the ecological resilience increased more sharply in the first 80 years (up to 0.919), then decreased until year 170, and then increased slightly to year 300, and the ecological resilience responded negatively to both B1, A2 climate scenarios after year 80 on the terrace land type (Figure 8a). On south-facing slopes, the ecological resilience decreased in the first 50 years, then increased slightly until year 80, and remained almost stable afterward under the CF1 and B1F1 scenarios. Ecological resilience under A2F1 scenario decreased by 61.5% in the first 130 years, and then generally increased to year 300 (Figure 8b). The curves of ecological resilience in north-facing land type responded to climate change similar to that on south-facing land types (Figure 8c). On the ridge top land type, the curves of ecological resilience under three climatic scenarios decreased sharply in the first 30 years, and then increased slightly afterward (Figure 8d). There was a slight increase of ecological resilience in B1F1 and A2F1 scenarios compared to the CF1 scenario after year 120 (Figure 8e).

**Figure 8.** Ecological resilience dynamics for different land types under three climatic simulated scenarios. CF1: current fire only scenario, and B1F1, A2F1: climate change only scenarios.

#### *3.4. The Interactive Effects of Fire Disturbance and Climate Change on Ecological Resilience*

There was no significant difference of ecological resilience on the terrace land type between CF1 and B1F2 scenarios during the simulated periods (*p* > 0.05, Figure 9); and ecological resilience on the terrace land type decreased by 1.7%, 5.9%, and 1.7% at the three simulated periods compared to the CF1 scenario. For the South-facing and North-facing land types, the ecological resilience did not differ significantly between CF1 and B1F2 scenarios for the short and medium-term interval (*p* > 0.05, Figure 9). However, ecological resilience differed significantly between the B1F2 scenario and the CF1 scenario for the long-term period (*p* < 0.05, Figure 9), where ecological resilience was 11.3% lower than that in CF1 scenario. On the ridge top land type, no significant difference was found between CF1 and B1F2 scenarios for the whole simulation periods, where ecological resilience was 14.1% higher, and 3.7% lower, respectively, than that in the CF1 scenario. The results showed that ecological resilience under the B1F2 scenario was significantly higher than that under CF1 scenario at landscape scale only for the long-term period (*p* < 0.05, Figure 9). The increase in ecological resilience at the landscape scale was 3.2%, 12.1%, and 29.6% greater than that in the CF1 scenario during the three simulated periods, respectively.

**Figure 9.** Ecological resiliencies of different land types for the three simulated scenarios: current fire only scenario (CF1); climate change induced-fire scenarios (B1F2, A2F3). Short term: 0–50 years, medium term: 50–150 years, and long term: 150–300 years; \* indicates that significant differences are detected between the CF1 scenario and a given scenario (*p* < 0.05).

Ecological resilience under the A2F3 scenario differed significantly on terrace, South-facing slope, and ridge top land types from CF1 scenario at medium and long-term periods (*p* < 0.05, Figure 9), and no significant differences were detected at short-term interval on those three land types. On North-facing slopes, the ecological resilience under A2F3 scenario differed significantly from CF1 scenario during the long-term period (*p* < 0.05, Figure 9), and the decrease in ecological resilience was 26.7%, 12.4%, and 12.3% lower than that in the CF1 scenario across the three simulated periods, respectively. Collectively, our results indicated that the B1F2 scenario did not affect ecological resilience across the short- to medium-term range, but with continuous climate and fire influence, it will significantly affect the ecological resilience at landscape level across the long-term range. Meanwhile, under the A2F3 scenario, forest ecological resilience could be recovered almost to its original state by 150 years simulation time.

#### *3.5. The Effects of Forest Management Schemes on Ecological Resilience*

Our results showed that forest managemen<sup>t</sup> schemes played a role in altering ecological resilience under the climate change scenarios in contrast to the no managemen<sup>t</sup> treatments (Figure 10). For the B1F2 scenario, ecological resilience decreased obviously under the eight harvesting and planting scenarios (Figure 10a). Under all simulated scenarios, ecological resilience initially fluctuated, then peaked at year 80, and then decreased until year 130, and increased gradually afterward. The curves of ecological resilience for the eight harvesting and planting scenarios were relatively lower than that under B1F2 scenario during most of the simulation periods. Generally, our results indicated that all eight harvesting and planting strategies did not affect ecological resilience at landscape scale under the B1F2 scenario during all simulation periods.

**Figure 10.** The ecological resilience simulated under different forest managemen<sup>t</sup> schemes at landscape scales under two climate change scenarios in comparison with no managemen<sup>t</sup> treatment (B1F2 and A2F3): (**a**) The ecological resilience affected by harvesting and planting in B1 climatic scenario; and (**b**) the ecological resilience affected by harvesting and planting in A2 climatic scenario.

For the A2F3 scenario, ecological resilience also varied among these eight harvesting and planting strategies across all simulation periods (Figure 10b). Ecological resilience decreased sharply under all the harvesting and planting scenarios in the first 20 years, and then fluctuated until year 220 and increased gradually afterward. The ecological resiliencies of eight harvesting and planting scenarios were higher than that under A2F3 scenario during the first 190 years simulation. Under A2F3H4P30, A2F3H4P40, and A2F3H4P50 scenarios, the ecological resiliencies were higher than that under the A2F3 scenario after year 240 (Figure 10b). Our results indicated that certain harvesting and planting strategies needed to be implemented under the A2F3 scenario, and only three of the eight harvesting and planting strategies affected the ecological resilience positively at the landscape level during the simulation periods except for simulated year 210 to 240.
