Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Common names\nSubspecies | Pacific\n(critchfieldiana) | Columbia\n(ponderosa) | Rocky Mountains\n(scopulorum) | Southwestern\n(brachyptera) | Central High Plains\n(readiana) |
| --- | --- | --- | --- | --- | --- |
| Years needles remain green | 3.9±0.25, N=30 | 4.7±0.14, N=50 | 5.7±0.28, N=23 | 4.3±0.18, N=24 | 4.7±0.18, N=5 |
| Foliage length on branch, cm | 25.1±2.4, N=30 | 26.2±2.2, N=50 | 21.1±1.7, N=23 | 21.8±2.7, N=24 | 42.2±6.7, N=5 |
| Needle length, cm | 19.8±0.44, N=30 | 16.8±0.29, N=48 | 11.2±0.27, N=23 | 14.7±0.45, N=24 | 15.6±0.57, N=5 |
| Needles per fascicle | 3.0±0.00, N=30 | 3.0±0.00, N=48 | 2.6±0.06, N=23 | 3.0±0.03, N=24 | 2.4±0.11, N=5 |
| Needle thickness | 45.9±0.49, N=30 | 47.8±0.51, N=48 | 46.4±0.68, N=23 | 44.8±0.87, N=24 | 49.7±0.61, N=5 |
| Branches per whorl | 4.4±0.13, N=30 | 3.7±0.11, N=50 | 3.0±0.17, N=23 | 3.4±0.25, N=23 | 2.3±0.11, N=5 |
| Branch angle ° from vert. | 56±1.8, N=30 | 51±1.7, N=50 | 50±2.3, N=23 | 48±3.1, N=24 | 36±1.9, N=5 |
| Seed cones length, mm | 101.4±2.48, N=25 | 88.7±1.24, N=36 | 70.7±2.20, N=22 | 74.9±2.51, N=20 | 71.1±2.46, N=5 |
| Seed cones width, mm | 77.1±1.35, N=25 | 71.6±0.73, N=36 | 61.5±1.08, N=22 | 62.6±1.77, N=20 | 63.3±2.18, N=5 |
| Seed cone form W/L | 0.80±0.03, N=25 | 0.84±0.03, N=36 | 0.90±0.02, N=22 | 0.86±0.02, N=20 | 0.90±0.03, N=5 |
| Seed length, mm | 7.5±0.08, N=23 | 7.6±0.16, N=14 | 6.3±0.09, N=17 | 6.4±0.18, N=16 | 7.0±0.12, N=5 |
| Seed width, mm | 4.9±0.05, N=23 | 4.9±0.08, N=14 | 4.1±0.05, N=17 | 4.3±0.09, N=16 | 4.5±0.10, N=5 |
| Seed + wing length, mm | 32.3±0.58, N=23 | 24.8±0.62, N=14 | 22.9±0.63, N=17 | 23.3±0.68, N=15 | 23.1±0.78, N=5 |
| Mature cone color | apple green to yellow green | green & red-brown to dk. purple | green & red-brown to dk. purple |  | green & red-brown to dk. purple |
Question:
how many additional years will the rocky mountains (scopulorum) subspecies of p. ponderosa needles remain green compared to pacific (critchfieldiana)?
Answer:
1.8 years