## 4 Discussion
### Impact of Sampling Interval on FRP Estimates  
The timing of sampling considerably affected FRP in the both methods (Figure 4). Estimates of FRP based on T1 and T2 obtained in the first half year were higher than those from other sampling periods for either method (Figure 4). This variation was caused by a rapid increase in fine root biomass and fine root necromass between T1 and T2 (Figure 2a). [PERSON] and [PERSON] [38] reported a rapid increase in fine root biomass inside the ingrowth cores during the first year after installation but not during the second year of installation, in a _Cryptomeria japonica_ forest in Japan. The authors examined the anatomical characteristics of the fine roots and found that the ratio of short-lived fine roots was higher in the first year and lower in the second year. A rapid increase in fine root biomass was also observed in a Eucalyptus plantation in Brazil [13]. The authors found that the specific root length sampled from the ingrowth cores after 2 months of installation (60.3 m g\({}^{-1}\)) was about three times higher than that in undisturbed soils (21.7 m g\({}^{-1}\)). Consequently, the authors suggested that a substantial proportion of fine roots found in ingrowth cores had a longevity of less than three months. Therefore, the characteristics of fine root biomass that grows in a short period after installation differ to those outside the cores. In comparison, previous studies of temperate and boreal forests have reported low fine root production using ingrowth cores over a short time period [7; 26]. For example, fine root production in the first three months was much lower than that incubated for 12 months in an oak woodland in California [39]. The authors suggested that disturbance effects, such as low newly colonizing root systems, cause the slower growth documented during short-term measurements. [PERSON] et al. [6] found that FRP estimated following 2 years of ingrowth cores was still lower than that estimated by minirizotrons because of the slow rates of root recolonization in the root-free cores for aspen, jack pine and black spruce forests. Although it is not known why different responses were observed in previous studies, fine root growth characteristics might be different between inside and outside the cores during the first year after installation. We observed lower fine root biomass and higher fine root necromass at T4 compared to that recorded outside the cores (Figure 2b). Consequently, the ratio of fine root biomass to fine root necromass at T4 (1.47 \(\pm\) 0.28) did not reach the ratio recorded outside the cores (3.47 \(\pm\) 0.42, Figure 3). The ratio in the boreal forest was 6.16 during the first year of ingrowth cores and 1.05 during the second year of ingrowth cores, which was comparable to that recorded outside (0.94, [7]). No noticeable differences in fine root necromass were recorded inside the ingrowth cores after 1, 2 and 3 months of installation in Eucalyptus plantations in Brazil [13]. Compared to these studies, the ratio of live fine roots to necromass in the ingrowth cores of the current study was very low. A rapid increase in short-lived fine roots appeared to occur during the first half of the year, after which many roots might have died over a short period. The high fine root necromass production during the first half of the year produced a lower ratio of fine root biomass to fine root necromass than that recorded by previous studies. Even though the response of roots to the installation of the cores differed across studies, the FRP estimate following 6-months of core installation might not be representative. There was little seasonality in temperature and rainfall in the study forest [25]; therefore, there was no clear seasonal variation in litterfall, flowering and stem growth [40; 41]. Although these results imply no seasonality in root growth, [PERSON] et al. [5] reported that fine root production increased during relatively wet periods and decreased during relatively dry periods in a tropical rainforest in Borneo.