## 4 Results
### Spatio-Temporal Distribution  
From 2001 to 2020, the NPP of the alpine meadow was significantly higher than that of the alpine steppe, and the inter-annual fluctuation of the alpine meadow was smaller than that of the alpine steppe. The annual average NPP of the alpine meadow was 82.5 gCm\({}^{-2}\)yr\({}^{-1}\), ranging from 60.1 gCm\({}^{-2}\)yr\({}^{-1}\) to 105.6 gCm\({}^{-2}\)yr\({}^{-1}\), and the coefficient of variation (CV) was 13.2%. The annual average NPP of the alpine steppe was 41.1 gCm\({}^{-2}\)yr\({}^{-1}\), ranging from 26.4 gCm\({}^{-2}\)yr\({}^{-1}\) to 56.7 gCm\({}^{-2}\)yr\({}^{-1}\), and the CV was 17.6%. Further, the spatial heterogeneity of the alpine steppe was significantly higher than that of the alpine meadow. The average CV of the alpine steppe was 82.4%, ranging from 67.8% to 88.6%. The average CV of the alpine meadow was 43.7%, ranging from 41.8% to 50.6% (Figure 3). The NPP in the TRH region showed an increasing trend in the time series, and the rate of increase in the alpine steppe was slightly higher than that in the alpine meadow. In 2000, the estimated NPP of the alpine meadow was 60.8 gCm\({}^{-2}\)yr\({}^{-1}\). By 2020, the estimated NPP of the alpine meadow was 93.6 gCm\({}^{-2}\)yr\({}^{-1}\), with an average annual increase rate of 1.64 gCm\({}^{-2}\)yr\({}^{-1}\) (\(p<0.05\)). In 2000, the estimated NPP of the alpine steppe was 37.0 gCm\({}^{-2}\)yr\({}^{-1}\), and by 2020, the estimated NPP of the alpine steppe was 61.5 gCm\({}^{-2}\)yr\({}^{-1}\), with an average annual increase rate of 1.72 gCm\({}^{-2}\)yr\({}^{-1}\) (\(p<0.05\)). To illustrate the spatial distribution of the estimated NPP, this paper performed the average NPP of the whole TRH region from 2001 to 2020 (Figure 4a). To illustrate the spatial distribution trend of the estimated NPP, this paper calculated the average NPP and standard deviation values along the latitude and longitude (Figure 4(a1,a2)). To illustrate the distribution gathering area of the estimated NPP, this paper plotted the area within each basic unit with 20 gCm\({}^{-2}\)yr\({}^{-1}\) as the step size (Figure 4(a3)). To view the changing trend of the NPP in the past 20 years pixel by pixel, the changing trend of the estimated time series NPP was drawn by combining the senSlope and MK (Figure 4b). At the same time, to explore whether the changing trend is persistent, this paper drew the changing character of the estimated time series NPP based on the change trend map and combined it with the Hurst index (Figure 4c). The estimated NPP had a large spatial difference. The minimum NPP value was 0.10 gCm\({}^{-2}\)yr\({}^{-1}\), the maximum NPP value was 287.6 gCm\({}^{-2}\)yr\({}^{-1}\), and the average NPP value was 77.0 gCm\({}^{-2}\)yr\({}^{-1}\) (Figure 4a). With 20 gCm\({}^{-2}\)yr\({}^{-1}\) as the step size, after dividing the whole TRH region into eight classes, there was little area difference within each basic  
Figure 3: The net primary productivity of the alpine meadow and alpine steppe from 2001 to 2020.  
unit. The largest area was the second class, with an area of 6.9 \(\times\) 10\({}^{4}\) km\({}^{2}\), accounting for 17.85%; the smallest area was the seventh class, with an area of 3.1 \(\times\) 10\({}^{4}\) km\({}^{2}\), accounting for 8.18%. The remaining six classes had a little area difference, ranging from 4.0 \(\times\) 10\({}^{4}\) km\({}^{2}\) to 5.6 \(\times\) 10\({}^{4}\) km\({}^{2}\). Within each class, there was a dominant land use type. The first class was mainly distributed in the westernmost part of the TRH region, which was mainly occupied by alpine vegetation (Circles av1, av2, av3, and av4 in Figure 4a). The second and third classes were mainly distributed in the midwest, north, and northeast, which were mainly occupied by alpine steppe (Circles as1., as2., and as3 in Figure 4a). The fifth to seventh classes were mainly distributed in the central, southern, and southeast, which were dominated by alpine meadows (Circles am1. and am2. in Figure 4a).