ISM Research Memorandum
No. 1058
Title:
- A forest herb, Pertya rigidula, lives more than 200 years: inference from 11-year monitoring and growth model
Author(s):
- Kawarasaki, Satoko/Transdisciplinary Research Integration Center, Aikawa, Shin-ichi/Forestry and Forest Products Research Institute, Kato, Masako/Tokyo Metropolitan University, Suzuki, Kazuo/Tokyo Metropolitan University, Suzuki, Jun-ichiro/Tokyo Metropolitan University, Hara, Toshihiko/ Institute of Low Temperature Science, Hokkaido University, Hori, Yoshimichi/Ibaraki University, Shimatani, K., Ichiro/The Institute of Statistical Mathematics
Key words:
- first flowering year, individual growth model, life expectancy, life history, long-term monitoring, perennial herb, shade tolerance, survival analysis
Abstract:
- 1. Forest herbs are long lived and often show retrogression or stasis in growth, which prevents us from estimating longevity. Based on 11-year population monitoring data, we carried out survival analysis, identified the growth pattern of each plant, and constructed an individual growth model from seedling to flowering for the long-lived forest herb Pertya rigidula.
- 2. Survival analysis revealed that smaller plants tended to die sooner. For example, 28% of plants with a total plant leaf area (TLA) < 10 cm2 were expected to survive for the next 5 years and survivors had a life expectancy of 6.3 years. 94% of plants that possessed a TLA > 640 cm2 and a flowering possibility were expected to survive and had a life expectancy of about 80 years.
- 3. One-third of 210 plants that survived over 10 years showed progressive growth. The others showed stasis or retrogression.
- 4. Assuming logistic growth curves from seedling to flowering, we tested the fit of individual data to growth models. A moderate growth curve had a relatively large number of well-fitted data points. Data of a very slow growth were less well-fitted, while rapid growth exhibited a fewer number of fitted points. Combining the results of life expectation, we inferred that plants with an approximate TLA of 100 cm2 acquired a tolerance that enabled them to withstand stasis/retrogression over 10 years. The first flowering year ranged from 25 to 160 years. We estimated a potential longevity of P. rigidula that ranged from 100 to 260 years, which represents one of the longest estimates of longevity. This estimate could be longer if retrogression and/or stasis occur during the lifetime of the individual.
- 5. Synthesis. The 11-year monitoring period of this study was much shorter than the potential longevity of the plant under investigation. However, survival analysis and the individual growth model allowed us to estimate the very long longevity of a long-lived forest herb and reveal its shade-tolerant life history.