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Abstract

Terrestrial ecosystems, and forests in particular, are important components of land processes because of their key role in reducing atmospheric greenhouse gas concentrations by storing a large amount of carbon in tree biomass and soils. Increasing attention is being paid to forestland area, which accounts for 30% of the total land surface and acts as the main C store in the Earth system. In their life cycle, plants uptake, process, allocate (i.e., the distribution of net primary production among the different plant organs), and remobilize the product of photosynthesis. The relative amount of above-and below-ground biomass partitioned among leaves, branches, stems, roots, non-structural pools, and reproductive tissues is a good indicator for forest productivity and reflects the material flow, the health, the wood quality, and the plant's survival strategies. How plants share their labile products across their compartments is not fixed, rather is influenced by plant size and likely varies over time, among species and growth environments, and is affected by natural and anthropogenic disturbances (e.g., forest management). Accordingly, the whole allocation process would be constrained under strong natural selection. Our understanding of the mechanisms governing these processes is, however, still patchy, with some processes and their responses to the environmental conditions much more well understood than others.
Editorial
Growth and Allocation of Woody Biomass in Forest Trees Based
on Environmental Conditions
Alessio Collalti 1, *,† , Luigi Todaro 2,*, and Angelo Rita 2, 3, *,†


Citation: Collalti, A.; Todaro, L.; Rita,
A. Growth and Allocation of Woody
Biomass in Forest Trees Based on
Environmental Conditions. Forests
2021,12, 154. https://doi.org/
10.3390/f12020154
Academic Editor: Timothy A. Martin
Received: 27 January 2021
Accepted: 28 January 2021
Published: 28 January 2021
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4.0/).
1Forest Modelling Lab., Institute for Agriculture and Forestry Systems in the Mediterranean,
National Research Council of Italy (CNR–ISAFOM), Via Madonna Alta 128, 06128 Perugia, PG, Italy
2School of Agricultural, Forestry, Food and Environmental Science (SAFE), University of Basilicata,
V.le dell’Ateneo Lucano 10, 85100 Potenza, PZ, Italy
3Department of Agricultural Sciences, University of Naples “Federico II”, Via Università100,
80055 Portici, NA, Italy
*Correspondence: alessio.collalti@cnr.it (A.C.); luigi.todaro@unibas.it (L.T.); angelo.rita@unibas.it (A.R.)
All authors contributed equally.
Terrestrial ecosystems, and forests in particular, are important components of land
processes because of their key role in reducing atmospheric greenhouse gas concentrations
by storing a large amount of carbon in tree biomass and soils. Increasing attention is
being paid to forestland area, which accounts for 30% of the total land surface and acts as
the main C store in the Earth system. In their life cycle, plants uptake, process, allocate
(i.e., the distribution of net primary production among the different plant organs), and
remobilize the product of photosynthesis. The relative amount of above- and below-
ground biomass partitioned among leaves, branches, stems, roots, non-structural pools,
and reproductive tissues is a good indicator for forest productivity and reflects the material
flow, the health, the wood quality, and the plant’s survival strategies. How plants share
their labile products across their compartments is not fixed, rather is influenced by plant
size and likely varies over time, among species and growth environments, and is affected by
natural and anthropogenic disturbances (e.g., forest management). Accordingly, the whole
allocation process would be constrained under strong natural selection. Our understanding
of the mechanisms governing these processes is, however, still patchy, with some processes
and their responses to the environmental conditions much more well understood than
others. Getting a qualitative/quantitative insight into the impact that the above-mentioned
factors have on tree growth and above- and below-ground biomass allocation is essential
both for understanding plant ecology and evolution and for developing environmental
policies and forest management practices to cope with climate change. In this regard, new
insights for Amazonian forests come from the modeling work of De Faria et al. [
1
], who
quantified the loss in above-ground biomass and the changes in recovery time (i.e., the
time required for a forest to return to its former or usual condition following a disturbance)
of forests affected by droughts, wildfire, and their combination. Their findings provide a
valuable gaze and alarming prevision on the impacts that climate change will likely have on
the Amazonian regions housing more than half of the world’s remaining rainforests in the
world. However, even European forests are likely to face an increasing number of extreme
events in the future. The work of Schäfer et al. [
2
] analyzed the effect of drought and
mixture of forest composition in a mature temperate forest of Norway spruce (Picea abies
(L.) Karst.) and European beech (Fagus sylvatica L.) located in southern Germany. They
reported differential allocation of tree biomass related to the drought condition period,
where trees prioritized the stem growth at the beginning of the growing season, and root
growth during the remaining growing season. Interestingly, spruces exhibited less tree
water deficit than beech trees, while mixture seems to enhance the water supply of spruce
trees, which should increase the stability of this species in a time of climatic warming.
Similarly, but in a Mediterranean context, Ogaya and Peñuelas [
3
] studied the growth and
Forests 2021,12, 154. https://doi.org/10.3390/f12020154 https://www.mdpi.com/journal/forests
Forests 2021,12, 154 2 of 4
the allocation in a Mediterranean holm oak (Quercus ilex L.) forest experimentally exposed
to partial rainfall exclusion during 21 consecutive years in the Prades holm oak forest, in
Catalonia, NE Spain. The authors aimed to study the effects of the expected decrease in
water availability in the Mediterranean in the following decades and found that allocation
in woody structures and total above-ground biomass were correlated with annual rainfall,
whereas canopy allocation and the ratio of wood/canopy allocation were not dependent
on rainfall. Their results highlight that water deficits characterized by lower soil moisture
and higher atmospheric aridity are leading to several changes in the ecosystem functioning
of the Mediterranean forests, causing a strong decrease in the capacity of these forests to
mitigate climate change because of the high decrease in wood growth and suggesting that
progressive substitution of the species most sensitive to water scarcity by other species
more adapted to drought is expected, transforming the current Mediterranean forest. In
the context of climate change, the effect of increasing temperature on tree phenology
and growth, even including biomass partitioning, is also the focus of the work of Mura
and colleagues [
4
]. Mura et al. analyzed, under field conditions in managed Norway
spruce plots regenerating after clearcuts in central Norway, whether the trees growing
at different elevations invest similarly in their various organs. They found that different
local environmental conditions affect both the growth rate and phenology but the biomass
partitioning among different parts of the tree remains essentially unchanged, giving support
to the hypothesis that maintaining specific allometric trajectories is fundamental for tree
functioning. High temperatures in warm months were also found to be a key environmental
factor for the net primary productivity (NPP) in Pinus massoniana (Lamb.), a major planted
tree species in southern China due to its important role in the development of forestry both
for economic and ecological benefit. Huang et al. [
5
] established a large biomass database
for P. massoniana including stems, branches, leaves roots, above-ground organs, and entire
tree, thanks to published literature, to find out potential geographical trends in NPP for each
tree compartment and their influencing factors in carbon allocation. Huang et al. found that
the NPP of tree components showed no clear relationships with longitude and elevation, but
a statistically significant inverse relationship with latitude, but with different sensitivities
to environmental conditions, mostly temperature, and stand variables. Temperature and
precipitation are also the focus for the transcontinental work of Usoltsev et al. [
6
] based on
a database of 413 sample plots for stand biomass, ranging from France to Japan to southern
China, for the genus Populus spp, which is overall the most widely cultivated fast-growing
tree species in the middle latitude plain. They found significant changes in the structure
of the forest stand biomass (stems, above- and below-ground biomass). However, while
a positive and statistically significant relationship with winter temperature emerged for
all components of the biomass, a less clear relationship with the precipitation was found.
Poplar plantations are also the focus of the work led by Zhang and colleagues [
7
]. The
authors, based on a field trial established in 2007 in Sihong forest farm, Jiangsu Province
(China), in order to understand the response of growth, biomass production, carbon storage,
planting spacing, and their interaction, they destructively harvested 24 sample trees for
biomass measurements and stem analyses. Not surprisingly, they found that biomass
production and carbon storage for the single tree of three clones was enhanced as planting
spacing increased, with carbon concentration decreasing from stem to leaves. With these
data, Zhang et al. established a Chapman–Richards empirical model for predicting tree
volume growth for Chinese poplar clones. With the aim to quantify total tree biomass
and its allocation to components in common aspen (Populus tremula L.), at both the tree
and stand levels, in the forested mountainous area in central Slovakia, Konôpka et al. [
8
]
measured, through destructive sampling, leaves, branches, stem, and roots. By these
measurements, the authors derived allometric biomass models with stem base diameter
as an independent variable for individual tree components. Moreover, biomass stock of
the woody parts and foliage, as well as the leaf area index, were modeled using mean
stand diameter as an independent variable, showing that foliage contribution to total tree
biomass decreased with tree size.
Forests 2021,12, 154 3 of 4
Ritchie et al.’s [
9
] work evaluate the tree growth and total above-ground productivity
(even including shrubs) of a twelve-year-old ponderosa pine (Pinus ponderosa (Lawson and
C. Lawson)) plantation under three separate treatments representing a range of manage-
ment intensities in the southern Cascade Range in northeastern California subjected to
wildfire events. The authors found a significant effect of the manual grubbing release from
shrub competition on tree growth when compared with the no release control and that
the total above-ground biomass or carbon was only marginally influenced because shrub
biomass dominated both sets of plots in this young plantation. Their results show that a
broader tradeoff for controlling competing shrubs between using herbicides and grubbing
or other means should be evaluated if biomass production or carbon sequestration is one
of the goals of prevention or for a post-fire reforestation program.
A novel approach, aiming at comparing structural carbon allocation to tree growth
and to the climate in a dendrochronological analysis, is presented in Ivanusic et al. [
10
]
for hybrid white spruce (Picea glauca (Moench)
×
engelmannii (Parry)) grown in British
Columbia, Canada. With this new approach, the authors found significant differences
between the percent structural carbon of wood in individual natural and planted stands.
Some significant relationships were found between percent carbon, ring widths, early
wood, late wood, and the cell wall thickness and density values. Carbon accumulation in
planted stands and natural stands was found in some cases to correlate with increasing
temperatures where warmer late-season conditions appear to enhance growth and carbon
accumulation in these sites.
The below-ground biomass, especially fine roots, and the relationship with forest
structure in a mature European beech forest in central Italy is the core of the analyses
presented by D’Andrea et al. [
11
]. The authors investigated the spatial variability of fine
root production, soil CO
2
efflux, forest structural traits, and their reciprocal interactions and
found, unexpectedly, that, in the year of study (2007–2008), fine root production resulted
in the main component of NPP explaining about 70% of the spatial variability of soil
respiration. The authors also found that fine root production was strictly driven by leaf
area index and soil water content, suggesting close interactions between forest structure
and functional forest characteristics to optimize carbon source–sink relationships.
Migolet and colleagues [
12
] implemented local and regional methods for estimating
palm biomass in a mature plantation, using destructive sampling in the Congo Basin (West
Equatorial Africa). Using data from eighteen 35-year-old oil palms in a plantation located
in Makouké, central Gabon, they derived allometric equations for estimating stem, leaf,
and total above-ground biomass. With a comparison with existing allometric models
for oil palms generated elsewhere, the authors showed that their site-level model was a
better predictor.
The current Special Issue groups a selection of works representing the most recent
advances and insights linking growth and carbon allocation with, among others, environ-
mental forcing, forest structure, and potential wood supply, including soil characteristics.
We hope that new further research and scientific questions may come about in the near
future by reading this collection of papers. We would like to thank the authors for their
invaluable efforts and also the reviewers and the editorial board who helped us in signifi-
cantly improving the quality of each of the published papers.
Funding: This research received no external funding.
Conflicts of Interest: The authors declare no conflict of interest.
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... In the past four decades, substantial effort has been made to develop biomass estimation models, converting tree biometric measurements into biomass values (Jiang and Wang, 2017;Collalti et al., 2021). It has been proven that these biomass models can provide accurate and reliable estimations for the biomass of forest ecosystems (Zolkos et al., 2013;Meng et al., 2019). ...
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Understanding the spatial variation of forest productivity and its driving factors on a large regional scale can help reveal the response mechanism of tree growth to climate change, and is an important prerequisite for efficient forest management and studying regional and global carbon cycles. Pinus massoniana Lamb. is a major planted tree species in southern China, playing an important role in the development of forestry due to its high economic and ecological benefits. Here, we establish a biomass database for P. massoniana, including stems, branches, leaves, roots, aboveground organs and total tree, by collecting the published literature, to increase our understanding of net primary productivity (NPP) geographical trends for each tree component and their influencing factors across the entire geographical distribution of the species in southern China. P. massoniana NPP ranges from 1.04 to 13.13 Mg·ha−1·year−1, with a mean value of 5.65 Mg·ha−1·year−1. The NPP of both tree components (i.e., stem, branch, leaf, root, aboveground organs, and total tree) show no clear relationships with longitude and elevation, but an inverse relationship with latitude (p < 0.01). Linear mixed-effects models (LMMs) are employed to analyze the effect of environmental factors and stand characteristics on P. massoniana NPP. LMM results reveal that the NPP of different tree components have different sensitivities to environmental and stand variables. Appropriate temperature and soil nutrients (particularly soil available phosphorus) are beneficial to biomass accumulation of this species. It is worth noting that the high temperature in July and August (HTWM) is a significant climate stressor across the species geographical distribution and is not restricted to marginal populations in the low latitude area. Temperature was a key environmental factor behind the inverse latitudinal trends of P. massoniana NPP, because it showed a higher sensitivity than other factors. In the context of climate warming and nitrogen (N) deposition, the inhibition effect caused by high temperatures and the lack or imbalance of soil nutrients, particularly soil phosphorus, should be paid more attention in the future. These findings advance our understanding about the factors influencing the productivity of each P. massoniana tree component across the full geographical distribution of the species, and are therefore valuable for forecasting climate-induced variation in forest productivity.
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The tree belowground compartment, especially fine roots, plays a relevant role in the forest ecosystem carbon (C) cycle, contributing largely to soil CO2 efflux (SR) and to net primary production (NPP). Beyond the well-known role of environmental drivers on fine root production (FRP) and SR, other determinants such as forest structure are still poorly understood. We investigated spatial variability of FRP, SR, forest structural traits, and their reciprocal interactions in a mature beech forest in the Mediterranean mountains. In the year of study, FRP resulted in the main component of NPP and explained about 70% of spatial variability of SR. Moreover, FRP was strictly driven by leaf area index (LAI) and soil water content (SWC). These results suggest a framework of close interactions between structural and functional forest features at the local scale to optimize C source-sink relationships under climate variability in a Mediterranean mature beech forest.