Global Patterns in Net Primary Production Allocation Regulated by Environmental Conditions and Forest Stand Age: A Model‐Data Comparison

Xia, Jiangzhou; Yuan, Wenping; Lienert, Sebastian; Joos, Fortunat; Ciais, Philippe; Viovy, Nicolas; Wang, Ying‐ping; Wang, Xufeng; Zhang, Haicheng; Yang, Chongming; Tian, Xiangjun

doi:10.1029/2018jg004777

Cited by 36 publications

(33 citation statements)

References 127 publications

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“…However, a saturation rather than an increase of C veg in aging forest was captured by these models (Figure 6). Such a saturation pattern is consistent with the modeling results in a recent study, which found that the allocations ratios among leaves, woods, and roots only change in young forests (Xia et al, 2019). It also should be noted that some vegetation processes and environmental factors can influence the C allocation patterns.…”

Section: Discussionsupporting

confidence: 91%

Nonlinear Increase of Vegetation Carbon Storage in Aging Forests and Its Implications for Earth System Models

Zhu

Xia

2020

J Adv Model Earth Syst

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Vegetation carbon stock (C veg) in global forests, which is important for C cycle-climate feedbacks, commonly increases with forest age. Due to the allometric growth of plants, the nonlinear increase in C veg with woody fraction (f w) is expected across space. However, it remains unclear whether such a nonlinear relationship between C veg and f w can be constrained by observations and further used to benchmark Earth system models (ESMs). Here, based on the in situ measurements at 1,145 forest sites, we found that the nonlinear relationship between C veg and f w followed an exponential equation (i.e., C veg ¼ be a • f w). Then, we showed that such an exponential dependence of C veg on f w also exists in ESMs of CMIP5 and CMIP6 (all P < 0.01), even though age-dependent processes have not been incorporated in most models. However, the exponential C veg-f w relationship varied greatly among the models, and the coefficient b was systematically lower in the ESMs (0.08 ± 0.11; mean ± SD) than the observations (0.28). Based on a compiled forest age data set, we further found that the observed nonlinear increase of C veg with forest age across the Northern Hemisphere (>30°N) was not captured by ESMs. These findings reveal a high disagreement on the spatially nonlinear relationship between vegetation carbon stock and woody fraction in current ESMs. The exponential relationship based on observations provides one useful benchmark for ESMs when they implement the age-dependent processes in the future. Plain Language Summary Forest age plays an important role in vegetation carbon stock (C veg) predictions. This study detects a nonlinear increase of C veg with woody fraction (f w) in aging forests across 1,145 in situ observations. The nonlinear C veg-f w relationship was then used to benchmark the age impacts on C veg predictions in Earth system models (ESMs). Combined with a global forest age data set, we show that current ESMs divergently represent the relationship between C veg and forest age. Our study suggests that the C veg-f w relationship could be one useful benchmark for evaluating ESMs.

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Section: Discussionsupporting

confidence: 91%

Nonlinear Increase of Vegetation Carbon Storage in Aging Forests and Its Implications for Earth System Models

Zhu

Xia

2020

J Adv Model Earth Syst

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“…This approximation reflects the overall turnover times of all plant carbon pools (including above and below ground). Nevertheless, the turnover times of different living plant tissues (e.g., leaves, roots and wood) vary greatly, and allocation patterns differ in time and space (Hofhansl et al., 2015; Xia et al., 2019). Thus, it is useful to compute the carbon allocation and turnover time of individual pools separately.…”

Section: Introductionmentioning

confidence: 99%

Variations of carbon allocation and turnover time across tropical forests

Yang

Ciais

Wang

et al. 2021

Global Ecol Biogeogr

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Aim The carbon sink in tropical forests is a highly uncertain component of the global carbon budget. An understanding of the processes controlling this sink requires better quantification of carbon allocation, stocks and turnover times. Location Tropical forests. Time period 2010–2017. Major taxa studied Tropical forest ecosystem. Methods We develop a novel data assimilation system using satellite‐based annual above‐ground biomass derived from L‐band vegetation optical depth with 25 km × 25 km grid spacing, together with leaf area, to constrain the 25 km × 25 km carbon allocation patterns of net primary productivity (NPP) into the wood, leaf and root pools, and their turnover times. Our average data‐driven estimates of these variables are broadly consistent with independent ground‐based estimates of NPP allocation and wood turnover from forest inventory plots. Results In tropical forest, on average, the NPP allocation into wood (0.30 ± 0.04) is significantly higher than that into leaves (0.24 ± 0.07). From the wet to dry tropics, forest NPP allocation into both wood and leaves declines slightly. The turnover times of forest leaf pools exhibit little spatial variation, whereas the turnover times of wood pools in Africa (median and interquartile range: 50.1‐4.0+5.5 years) are slightly longer than those in South America (48.2‐3.3+4.0 years) and Southeast Asia (48.3‐3.1+5.4 years). Our datasets reveal emergent trade‐offs across climatic and vegetation gradients between growth and life span/turnover for both wood and leaves. The spatial gradients of NPP allocation to wood/leaves are associated with canopy height, adjusted by climate condition and nutrient acquisition. The spatial gradients of wood and leaf turnover times are influenced mainly by climate and leaf characteristics. Main conclusions Our data‐driven estimates of carbon allocation and turnover times provide a basis for more detailed exploration of these mechanisms in field studies. This highlights that improved model representation of carbon allocation and turnover is necessary for more accurate prediction of future carbon dynamics.

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“…The IBIS model is responsible for modeling the photosynthates allocation to roots and the soil moisture in each soil layer on a daily time step (Foley et al, ; Yuan et al, ). The IBIS model uses the newly developed carbon allocation model to simulate carbon allocation to roots based on resource availability (i.e., radiation, soil moisture, and nitrogen) (Xia et al, ; Xia et al, ). Specifically, the IBIS model was updated to include 40 soil layers in the top 2‐m soil depth with a thickness of 5 cm and the soil moisture of each layer was modeled.…”

Section: Methods and Datamentioning

confidence: 99%

A Processes‐Based Dynamic Root Growth Model Integrated Into the Ecosystem Model

Lü

Yuan

Chen

2019

J Adv Model Earth Syst

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Plant roots play a critical role in regulating the uptake of soil water and nutrients. Shifts in root growth and biomass distribution resulting from climate change can impact ecosystem water and carbon cycling. Such interactions between root growth and ecosystem functioning have not been integrated into current terrestrial ecosystem models. Here a three-dimensional dynamic root model (DyRoot) was developed and implemented into the Integrated Biosphere Simulator (IBIS) ecosystem model for simulating root growth, architecture (i.e., fine and coarse roots), and distribution driven by soil water and nitrogen availabilities. Field root biomass observations were used for model calibration and validation. Results showed that DyRoot was able to simulate the root biomass distribution across five forest ecosystem types with good performance (R 2 = 0.79, P < 0.01). The validations of root distribution in three forest chronosequences suggested that DyRoot captured the changes in rooting depth with the increase in stand age. The sensitivity of simulated root distribution to soil water availability was compared against root biomass observations from two precipitation reduction experiments. Results indicated that DyRoot reasonably represented the decrease of root biomass in topsoil layers in response to the deficits of soil moisture simulated by (IBIS). The DyRoot model algorithm in this study has great implications for representing an optimized root distribution in ecosystem models, which can improve model performance by simulating the feedbacks of root evolution in response to climate change. Furthermore, allowing explicit root architecture in the DyRoot model also sheds light on depicting the responses of root traits to environmental changes.

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Global Patterns in Net Primary Production Allocation Regulated by Environmental Conditions and Forest Stand Age: A Model‐Data Comparison

Cited by 36 publications

References 127 publications

Nonlinear Increase of Vegetation Carbon Storage in Aging Forests and Its Implications for Earth System Models

Nonlinear Increase of Vegetation Carbon Storage in Aging Forests and Its Implications for Earth System Models

Variations of carbon allocation and turnover time across tropical forests

A Processes‐Based Dynamic Root Growth Model Integrated Into the Ecosystem Model

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