Mining plant phenology records from Kanazawa, Japan in the 1807-1838 Kakuson Diary.

Mining the various records of plant phenology before the era of modern weather observations is an important but challenging task. We mined descriptions of plant phenology in Kanazawa, Japan, during the first half of the nineteenth century in the Kakuson Diary. We retrieved records of full bloom of 28 plant species, appearance of 31 seasonal foods, and peak leaf colouring. In particular, we found more than 10 years of records of plum, peach, cherry blossoms, udo, and bamboo shoots in spring; watermelon in summer; and persimmon, chestnut, and peak leaf colouring in autumn. The records suggest that spring phenology during 1807 to 1838 was later and autumn phenology was earlier than now. Despite spatio-temporal uncertainty in records in old diaries, we need to mine records of plant phenology in more old diaries and publish them in English.

How did the characteristics of the growing season change during the past 100 years at a steep river basin in Japan?

The effects of climate change on plant phenological events such as flowering, leaf flush, and leaf fall may be greater in steep river basins than at the horizontal scale of countries and continents. This possibility is due to the effect of temperature on plant phenology and the difference between vertical and horizontal gradients in temperature sensitivities. We calculated the dates of the start (SGS) and end of the growing season (EGS) in a steep river basin located in a mountainous region of central Japan over a century timescale by using a degree-day phenological model based on long-term, continuous, in situ observations. We assessed the generality and representativeness of the modelled SGS and EGS dates by using phenological events, live camera images taken at multiple points in the basin, and satellite observations made at a fine spatial resolution. The sensitivity of the modelled SGS and EGS dates to elevation changed from 3.29 days (100 m)-1 (-5.48 days °C-1) and -2.89 days (100 m)-1 (4.81 days °C-1), respectively, in 1900 to 2.85 days (100 m)-1 (-4.75 days °C-1) and -2.84 day (100 m)-1 (4.73 day °C-1) in 2019. The long-term trend of the sensitivity of the modelled SGS date to elevation was -0.0037 day year-1 per 100 m, but the analogous trend in the case of the modelled EGS date was not significant. Despite the need for further studies to improve the generality and representativeness of the model, the development of degree-day phenology models in multiple, steep river basins will deepen our ecological understanding of the sensitivity of plant phenology to climate change.

Estimating spatial variation in the effects of climate change on the net primary production of Japanese cedar plantations based on modeled carbon dynamics.

Spatiotemporal prediction of the response of planted forests to a changing climate is increasingly important for the sustainable management of forest ecosystems. In this study, we present a methodology for estimating spatially varying productivity in a planted forest and changes in productivity with a changing climate in Japan, with a focus on Japanese cedar (Cryptomeria japonica D. Don) as a representative tree species of this region. The process-based model Biome-BGC was parameterized using a plant trait database for Japanese cedar and a Bayesian optimization scheme. To compare productivity under historical (1996-2000) and future (2096-2100) climatic conditions, the climate scenarios of two representative concentration pathways (i.e., RCP2.6 and RCP8.5) were used in five global climate models (GCMs) with approximately 1-km resolution. The seasonality of modeled fluxes, namely gross primary production, ecosystem respiration, net ecosystem exchange, and soil respiration, improved after two steps of parameterization. The estimated net primary production (NPP) of stands aged 36-40 years under the historical climatic conditions of the five GCMs was 0.77 ± 0.10 kgC m-2 year-1 (mean ± standard deviation), in accordance with the geographical distribution of forest NPP estimated in previous studies. Under the RCP2.6 and RCP8.5 scenarios, the mean NPP of the five GCMs increased by 0.04 ± 0.07 and 0.14 ± 0.11 kgC m-2 year-1, respectively. The increases in annual NPP were small in the southwestern region because of the decreases in summer NPP and the small increases in winter NPP under the RCP2.6 and RCP8.5 scenarios, respectively. Under the RCP2.6 scenario, Japanese cedar was at risk in the southwestern region, in accordance with previous studies, and monitoring and silvicultural practices should be modified accordingly.

Does global warming decrease the correlation between cherry blossom flowering date and latitude in Japan?

In Japan, the geographical distribution of the first date of flowering (FFD) of Yoshino cherry trees (Cerasus ×yedoensis) in 2020, a year when temperatures were mild during the previous December and March, was different from the average FFD, which progresses northward along a latitudinal gradient. We hypothesized that global warming may have changed the average geographical pattern of the FFD. To test this hypothesis, we examined the relationship between the observed FFD and latitude at 42 sites during the period 1953-2020. We found that the correlation between FFD and latitude had decreased since 1980. This decrease may have been caused by a rise of temperatures in winter that delayed dormancy release and the subsequent FFD in areas where the annual mean temperature is high. Our results suggest that the correlation between FFD and latitude will decrease further as the climate warms in the future.

Peak autumn leaf colouring along latitudinal and elevational gradients in Japan evaluated with online phenological data.

We evaluated the spatial characteristics of the first day of peak leaf colouring (PLCstart) and their relationships with air temperature along latitudinal and elevational gradients in Japan from 2015 to 2017. Leaf colouring information collected from more than 740 sites via citizen science was analysed, representing elevations from 0 to 2800 m and latitudes from 32°N to 44°N. We found that locations with earlier PLCstart dates (day of year 265-294) displayed steeper slopes in elevation per degree of latitude than locations with later PLCstart dates (day of year 295-314). This statistically significant result indicates that the influence of elevation on PLCstart (vertical gradient) weakened as the leaf colouring season progressed in Japan. In addition to these spatial characteristics, the PLCstart and the warmth index (based on monthly mean air temperature) showed significant linear correlations for latitudinal and elevational gradients. This result suggests that the sensitivity of PLCstart to air temperature, as manifested in both latitudinal and elevational gradients, is constant. This study suggests that online phenological data may provide more accurate results for a regional scale (100-1000 km) than the datasets used by previous studies.

Cultural ecosystem services provided by flowering of cherry trees under climate change: a case study of the relationship between the periods of flowering and festivals.

In Japan, cherry blossoms are an important tourism resource and provide many cultural ecosystem service benefits. Under future warming conditions, we will require adaptions such as changing the timing of flower festivals to account for changes in the flowering phenology. In this study, we evaluated the coincidence between the flowering phenology of cherry blossoms and the associated festival periods in two Japanese cities under past, recent, and future climate conditions. We examined the situation in Shinhidaka, where the flower festival period changes every year, and Takayama, where the festival period is fixed to coincide with a shrine's annual spring festival. Currently, the average dates of beginning of flowering (more than four or five flowers open in an index tree; ~BBCH60) and full bloom (equal to or more than 80% of flowers open in an index tree; after BBCH65) in Shinhidaka (day of year (DOY) 126 and 130) are later than the long national holiday of Golden Week (DOY 119 to 125). The respective dates in Takayama (DOY 106 and 111, respectively) are later than the local a festival period (DOY 104 and 105). Under a scenario of 1.0 to 2.0 °C warming, the full blooming dates in Shinhidaka will coincide with Golden Week, whereas under 1.0 to 1.5 °C warming, the full blooming dates in Takayama will coincide with the spring festival period. Thus, moderate warming may increase the value of cherry blossoms to the tourism industry. Under more than 3.5 °C warming in Shinhidaka and 2.5 °C warming in Takayama, however, cherry blossoms will have already dropped by Golden Week and the spring festival period, respectively, suggesting that greater warming may decrease the value of this tourism resource.

Current and future carbon budget at Takayama site, Japan, evaluated by a regional climate model and a process-based terrestrial ecosystem model.

Accurate projection of carbon budget in forest ecosystems under future climate and atmospheric carbon dioxide (CO2) concentration is important to evaluate the function of terrestrial ecosystems, which serve as a major sink of atmospheric CO2. In this study, we examined the effects of spatial resolution of meteorological data on the accuracies of ecosystem model simulation for canopy phenology and carbon budget such as gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) of a deciduous forest in Japan. Then, we simulated the future (around 2085) changes in canopy phenology and carbon budget of the forest by incorporating high-resolution meteorological data downscaled by a regional climate model. The ecosystem model overestimated GPP and ER when we inputted low-resolution data, which have warming biases over mountainous landscape. But, it reproduced canopy phenology and carbon budget well, when we inputted high-resolution data. Under the future climate, earlier leaf expansion and delayed leaf fall by about 10 days compared with the present state was simulated, and also, GPP, ER and NEP were estimated to increase by 25.2%, 23.7% and 35.4%, respectively. Sensitivity analysis showed that the increase of NEP in June and October would be mainly caused by rising temperature, whereas that in July and August would be largely attributable to CO2 fertilization. This study suggests that the downscaling of future climate data enable us to project more reliable carbon budget of forest ecosystem in mountainous landscape than the low-resolution simulation due to the better predictions of leaf expansion and shedding.

Review: advances in in situ and satellite phenological observations in Japan.

To accurately evaluate the responses of spatial and temporal variation of ecosystem functioning (evapotranspiration and photosynthesis) and services (regulating and cultural services) to the rapid changes caused by global warming, we depend on long-term, continuous, near-surface, and satellite remote sensing of phenology over wide areas. Here, we review such phenological studies in Japan and discuss our current knowledge, problems, and future developments. In contrast with North America and Europe, Japan has been able to evaluate plant phenology along vertical and horizontal gradients within a narrow area because of the country's high topographic relief. Phenological observation networks that support scientific studies and outreach activities have used near-surface tools such as digital cameras and spectral radiometers. Differences in phenology among ecosystems and tree species have been detected by analyzing the seasonal variation of red, green, and blue digital numbers (RGB values) extracted from phenological images, as well as spectral reflectance and vegetation indices. The relationships between seasonal variations in RGB-derived indices or spectral characteristics and the ecological and CO2 flux measurement data have been well validated. In contrast, insufficient satellite remote-sensing observations have been conducted because of the coarse spatial resolution of previous datasets, which could not detect the heterogeneous plant phenology that results from Japan's complex topography and vegetation. To improve Japanese phenological observations, multidisciplinary analysis and evaluation will be needed to link traditional phenological observations with "index trees," near-surface and satellite remote-sensing observations, "citizen science" (observations by citizens), and results published on the Internet.

Spatio-temporal distribution of the timing of start and end of growing season along vertical and horizontal gradients in Japan.

We detected the spatio-temporal variability in the timing of start (SGS) and end of growing season (EGS) in Japan from 2003 to 2012 by analyzing satellite-observed daily green-red vegetation index with a 500-m spatial resolution. We also examined the characteristics of SGS and EGS timing in deciduous broadleaf and needleleaf forests along vertical and horizontal gradients and then evaluated the relationship between their timing and daily mean air temperature. We found that for the timing of SGS and EGS, changes along the vertical gradient in deciduous broadleaf forest tended to be larger than those in deciduous needleleaf forest. For both forest types, changes along the vertical and horizontal gradients in the timing of EGS tended to be smaller than those of SGS. Finally, in both forest types, the sensitivity of the timing of EGS to air temperature was much less than that of SGS. These results suggest that the spatio-temporal variability in the timing of SGS and EGS detected by satellite data, which may be correlated with leaf traits, photosynthetic capacity, and environment conditions, provide useful ground-truthing information along vertical and horizontal gradients.

Carbon allocation in a Bornean tropical rainforest without dry seasons.

To clarify characteristics of carbon (C) allocation in a Bornean tropical rainforest without dry seasons, gross primary production (GPP) and C allocation, i.e., above-ground net primary production (ANPP), aboveground plant respiration (APR), and total below-ground carbon flux (TBCF) for the forest were examined and compared with those from Amazonian tropical rainforests with dry seasons. GPP (30.61 MgC ha(-1) year(-1), eddy covariance measurements; 34.40 MgC ha(-1) year(-1), biometric measurements) was comparable to those for Amazonian rainforests. ANPP (6.76 MgC ha(-1) year(-1)) was comparable to, and APR (8.01 MgC ha(-1) year(-1)) was slightly lower than, their respective values for Amazonian rainforests, even though aboveground biomass was greater at our site. TBCF (19.63 MgC ha(-1) year(-1)) was higher than those for Amazonian forests. The comparable ANPP and higher TBCF were unexpected, since higher water availability would suggest less fine root competition for water, giving higher ANPP and lower TBCF to GPP. Low nutrient availability may explain the comparable ANPP and higher TBCF. These data show that there are variations in C allocation patterns among mature tropical rainforests, and the variations cannot be explained solely by differences in soil water availability.

Biometric-based estimation of net ecosystem production in a mature Japanese cedar (Cryptomeria japonica) plantation beneath a flux tower.

Quantification of carbon budgets and cycling in Japanese cedar (Cryptomeria japonica D. Don) plantations is essential for understanding forest functions in Japan because these plantations occupy about 20% of the total forested area. We conducted a biometric estimate of net ecosystem production (NEP) in a mature Japanese cedar plantation beneath a flux tower over a 4-year period. Net primary production (NPP) was 7.9 Mg C ha(-1) year(-1) and consisted mainly of tree biomass increment and aboveground litter production. Respiration was calculated as 6.8 (soil) and 3.3 (root) Mg C ha(-1) year(-1). Thus, NEP in the plantation was 4.3 Mg C ha(-1) year(-1). In agreement with the tower-based flux findings, this result suggests that the Japanese cedar plantation was a strong carbon sink. The biometric-based NEP was higher among most other types of Japanese forests studied. Carbon sequestration in the mature plantation was characterized by a larger increment in tree biomass and lower mortality than in natural forests. Land-use change from natural forest to Japanese cedar plantation might, therefore, stimulate carbon sequestration and change the carbon allocation of NPP from an increment in coarse woody debris to an increase in tree biomass.

Carbon dioxide exchange in a cool-temperate evergreen coniferous forest over complex topography in Japan during two years with contrasting climates.

We investigated carbon dioxide (CO(2)) exchange and its environmental response during two years with contrasting climate (2006 and 2007) in a cool-temperate mixed evergreen coniferous forest dominated by Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa). The study, which was conducted in a mountainous region of central Japan, used the eddy-covariance technique. Our results (crosschecked using the common u (*) approach and van Gorsel's alternative approach) showed that annual gross primary production (GPP) and ecosystem respiration (RE) were at least 6% higher in the dry year than in the wet year, whereas net ecosystem exchange (NEE) was similar in both years. Without soil water stress, strong light stress or seasonality of plant area index during most of the study period, the forest had high metabolic activity. GPP and RE differed greatly between the two years, especially in spring (April-May) and summer (July-September), respectively. The spring GPP difference (>20%) was influenced by different winter air temperatures and snow melt timing, which controlled photosynthetic capacity in spring, and by different spring light intensities. The annual NEE differed depending on the evaluation method used, but the mean 2-year NEE estimated by the u (*) threshold approach [-3.39 +/- 0.11 (SD) MgC ha(-1) year(-1)] appears more reasonable in comparison with results from other forests.

Effects of seasonal and interannual variations in leaf photosynthesis and canopy leaf area index on gross primary production of a cool-temperate deciduous broadleaf forest in Takayama, Japan.

Revealing the seasonal and interannual variations in forest canopy photosynthesis is a critical issue in understanding the ecological mechanisms underlying the dynamics of carbon dioxide exchange between the atmosphere and deciduous forests. This study examined the effects of temporal variations of canopy leaf area index (LAI) and leaf photosynthetic capacity [the maximum velocity of carboxylation (V (cmax))] on gross primary production (GPP) of a cool-temperate deciduous broadleaf forest for 5 years in Takayama AsiaFlux site, central Japan. We made two estimations to examine the effects of canopy properties on GPP; one is to incorporate the in situ observation of V (cmax) and LAI throughout the growing season, and another considers seasonality of LAI but constantly high V (cmax). The simulations indicated that variation in V (cmax) and LAI, especially in the leaf expansion period, had remarkable effects on GPP, and if V (cmax) was assumed constant GPP will be overestimated by 15%. Monthly examination of air temperature, radiation, LAI and GPP suggested that spring temperature could affect canopy phenology, and also that GPP in summer was determined mainly by incoming radiation. However, the consequences among these factors responsible for interannual changes of GPP are not straightforward since leaf expansion and senescence patterns and summer meteorological conditions influence GPP independently. This simulation based on in situ ecophysiological research suggests the importance of intensive consideration and understanding of the phenology of leaf photosynthetic capacity and LAI to analyze and predict carbon fixation in forest ecosystems.