Mitsuru Hirota

Aim: Assessing species range shifts and subsequent thermophilization—the increasing dominance of warm‐adapted species in communities—is critical for understanding ecological responses to climate change. Because systematic monitoring data for assessing thermophilization are limited geographically, temporally, and taxonomically, the use of occurrence data has been attempted. Although occurrence data have enabled important discoveries in studies evaluating the impact of climate change‐induced range shifts on community responses, two major biases—Spatiotemporal Variation of Observation Effort (STVOE) and the Truncation Effect—hinder their full potential. This study introduces the Community Change Detection Model (CCDM), a novel statistical framework designed to address these biases and accurately measure the thermophilization rate using large‐scale occurrence data. Innovation: CCDM is a simple method based on multiple regression, yet it is the first method to simultaneously correct for the various degrees of STVOE and the truncation effect, enabling reliable thermophilization rate estimation from biased occurrence data. Validated through simulations and an empirical application to Japanese vascular plants, CCDM surpasses previous approaches, enabling the use of large amounts of occurrence data that had previously been restricted. Main Conclusions: Applying CCDM to Japan's vascular plant communities from 1900 to 2024 revealed consistent thermophilization with acceleration since 1985, though it lagged behind regional warming rates, leading to the development of a climatic debt. Our analysis enabled this discovery by utilising occurrence data from historical warming periods, which is largely inaccessible through systematic monitoring. Furthermore, CCDM demonstrated robust performance in estimating thermophilization rates under various bias conditions in the simulation, indicating its high general applicability. CCDM unlocks the potential of historical occurrence data, offering unprecedented insights into climate change impacts across under‐monitored regions, periods, and taxa.

The increase in forest wood biomass is an important carbon sink in the biogeochemical carbon cycle. The effect of forest succession on carbon sequestration is essential for predicting the impact of future global warming. However, there are limited studies considering the temporal changes of net primary production (NPP) with secondary succession in cool-temperate forests based on long-term data. Therefore, we monitored changes in forest structures over 23 years in a cool-temperate secondary forest (Takayama Forest), which is dominated by Quercus crispula, Betula ermanii, and B. platyphylla var. japonica, to determine how individual stem growth and wood NPP changes with succession and thereby affect biomass accumulation. For Q. crispula and B. ermanii, the population size reduction (71% and 66% of the initial number, respectively) exhibited density-dependent mortality in the self-thinning process. Conversely, B. platyphylla var. japonica decreased from 125 to 51 stems ha⁻¹, or a reduced to 41%, due to interspecific competition and/or short longevity of the species. The individual stem growth of the smaller shaded trees was suppressed, and the mean individual biomass did not increase notably with decreasing density compared to that of Q. crispula and B. ermanii. The aboveground wood NPP for this forest averaged 2.44 Mg ha⁻¹ year⁻¹ over 23 years and exhibited no significant temporal trend. The increased mean individual stem growth of Q. crispula and B. ermanii with decreasing density compensated for the total wood NPP. As a result, the aboveground biomass of the forest increased by 21% over 23 years from 132.4 to 160.2 Mg ha⁻¹, and the rate of biomass accumulation increased with decreasing mortality. It is unlikely that the wood NPP of these pioneer secondary forests will decrease with forest development after canopy closure because the individual stem growth of the long-lived pioneers, such as Q. crispula and B. ermanii, is maintained for extended durations.

As plant distribution and performance are determined by both environmental and genetic factors, clarifying the contribution of these two factors is a key for understanding plant adaptation and predicting their distribution under ongoing global warming. Betula ermanii is an ideal species for such research because of its wide distribution across diverse environments. Stomatal density and size are crucial traits that plants undergo changes in to adapt to different environments as these traits directly influence plant photosynthesis and transpiration. In this study, we conducted a multi‐location common garden experiment using B. ermanii to (1) clarify the contribution of both environmental and genetic factors to the variation in stomatal density and size of B. ermanii, (2) demonstrate the differences in the plasticity of stomatal density and size among B. ermanii populations, and (3) understand how stomatal density and size of B. ermanii would respond to increased temperature and changing precipitation patterns. Genetic factors played a more significant role in stomatal size than environmental factors, suggesting that B. ermanii struggles to adjust its stomatal size in response to a changing environment. Our results also revealed a positive correlation between stomatal size plasticity and original habitat suitability, indicating that in B. ermanii populations in harsh environments exhibit lower adaptability to environmental shifts. Although stomatal density and size of B. ermanii showed the significant responses to increased temperature and shifting precipitation patterns, the response ranges of stomatal density and size to the environmental factors varied among populations. Our findings highlighted the interplay between genetic and environmental factors in determining the intraspecific variation in stomatal density and size in B. ermanii. This indicated that certain populations of B. ermanii exhibit limited stomatal plasticity and adaptability, which could directly affect photosynthesis and transpiration, suggesting potential population‐specific fitness implications for B. ermanii under future climate change.

Long‐term monitoring of forest tree communities is a basis for elucidating forest structure and dynamics and for evaluating ecosystem functions such as primary production. Because global climate change is changing forest ecosystems from the local to the global scale, it is essential to document long‐term monitoring data of forests to examine the temporal and geographical trends of forest changes. We report monitoring data of 45 forest plots (average area 0.69 ha; range 0.0325–6.25 ha) at 27 sites in Japan. These plots are situated within 32.38° N to 43.36° N and at elevations ranging from 8 to 2453 m above sea level. The forest plots include both old‐growth and secondary forests, and cover various forest biomes, such as warm‐temperate evergreen forests, temperate deciduous broadleaved forests, and boreal or sub‐alpine coniferous forests. In each plot, all living trees and lianas larger than a certain minimum size (typically 15 cm stem girth at breast height) were repeatedly measured and survival and recruitment of stems were recorded over 5–40 years (average 17.3 years). The data are presented in the format used by the Monitoring Sites 1000 Project in Japan (Ishihara et al. 2011, Ecological Research , 26 , 1007–1008) and in the sample‐based Darwin Core format. This dataset expands existing open monitoring data for Japanese forests and thereby facilitates further meta‐analysis of forest community structures and changes in relation to climate change and other drivers. The complete data set for this abstract is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2024-03.1/jalter-en .

Soil respiration (R_s) consists of autotrophic (R_a) and heterotrophic (R_h) respiration, and the metabolic responses of R_a and R_h are supposedly affected by environmental factors. Our hypothesis was that the contribution of R_a and R_h would be affected by seasons. To characterize seasonal patterns of R_s, sap flow (as an indicator of photosynthetic activity), and environmental factors, we continuously measured temporal variation in R_s using an automated opening and closing chamber system in a cool temperate forest. R_s had counterclockwise hysteresis (R_s: spring < autumn) with soil temperature at a depth of 5 cm. Daily maximum R_s had a significant positive relationship with daily maximum sap flow over three seasons, and daily maximum sap flow was lower in autumn than in spring (R_a: spring > autumn). The amount of leaf litterfall increased significantly from August to October; the high R_s in autumn would be due to an increase in R_h (R_h: spring < autumn). These results suggest that R_a contributes more in spring than in autumn, and the contribution of R_h is high from summer through autumn.