Stem respiration (
R
s
) plays a vital role in ecosystem carbon cycling. However, the measured efflux on the stem surface (
E
s
) is not always
in situ R
s
but only part of it. A previously proposed ...mass balance framework (MBF) attempted to explore the multiple partitioning pathways of
R
s
, including sap-flow-transported and internal storage of
R
s,
in addition to
E
s
. This study proposed stem photosynthesis as an additional partitioning pathway to the MBF. Correspondingly, a double-chamber apparatus was designed and applied on newly sprouted Moso bamboo (
Phyllostachys edulis
) in leafless and leaved stages.
R
s
of newly sprouted bamboo were twice as high in the leafless stage (7.41 ± 2.66 μmol m
−2
s
−1
) than in the leaved stage (3.47 ± 2.43 μmol m
−2
s
−1
).
E
s
accounted for ~80% of
R
s,
while sap flow may take away ~2% of
R
s
in both leafless and leaved stages. Culm photosynthesis accounted for ~9% and 13% of
R
s
, respectively. Carbon sequestration from culm photosynthesis accounted for approximately 2% of the aboveground bamboo biomass in the leafless stage. High culm photosynthesis but low sap flow during the leafless stage and vice versa during the leaved stage make bamboo an outstanding choice for exploring the MBF.
Late spring frost plays a major role in the structure and function of forest ecosystems with potential consequences on species distribution at both local and regional scales. Paradoxically, in a ...warmer world the incidence and impact of frost is increasing because of earlier leaf unfolding and flowering as a response to warmer temperatures. In this regard, European Beech (Fagus sylvatica L.), a native tree species widely distributed in European forests, is considered particularly sensitive to changes in spring temperature regimes associated with climate change and thus especially subject to the risk of frost damage. Although several studies concerning F. sylvatica frost damage have been conducted in northern and central Europe, no extensive studies are available for the southern part of its range, i.e. central and southern Italy as well as Greece.
In this paper the effect of a late spring frost occurring at the end of April 2016 is extensively documented with high spatial detail all along the Apennine Chain through satellite image data. Three different remote-sensing greenness indexes, namely the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and the greenness index (GI) derived from Landsat-8 satellite images acquired from May to July in the years 2014, 2015, and 2016 at a spatial resolution of 30 m, were used to gauge the spatial response of common beech forests to this late frost event with relation to latitude, altitude and slope exposure. Frost damage was evaluated as a difference (Δ) of NDVI, GI and EVI between the mean of years 2014 and 2015 (i.e. MRY, mean of reference years), and 2016 (i.e. FEY, frost reference year). The three satellite remote-sensing indexes were efficient at detecting leaf damage with detailed spatial resolution and proved consistent with one another.
The greatest damage occurred in the middle altitudinal range between 1500 and 1700 m a.s.l. with a decreasing trend toward both lower and higher elevations due to warmer temperatures below, and delayed phenology above. Exposure also influenced frost injury, with south-facing slopes of the mountain more damaged than the north. This difference was due to earlier spring leaf phenology of southern beech trees in response to a greater heat sum in the warm weeks preceding. Less damage in the northern Apennines is consistent with the spatial extent of minimum freezing temperatures. To sum up, frost damage is strongly related to site-specific conditions, i.e. on the one hand to minimum temperatures, and on the other to the phenological stage of the trees involving both altitude and exposure. Hence focusing on detailed sub-regional studies can be helpful for predicting future consequences of climate change on forests.
•Spring frost canopy damage of European beech in Apennines is related to site-specific conditions.•Damage severity depends by freezing temperatures coupled with phenological stage.•Frost damage is greater in the southern aspect and at the middle belts rather than at higher ones.•NDVI, EVI and GI are efficient to detect leaf damage with detailed spatial resolution.
In tropical forests, leaf phenology-particularly the pronounced dry-season green-up-strongly regulates biogeochemical cycles of carbon and water fluxes. However, uncertainties remain in the ...understanding of tropical forest leaf phenology at different spatial scales. Phenocams accurately characterize leaf phenology at the crown and ecosystem scales but are limited to a few sites and time spans of a few years. Time-series satellite observations might fill this gap, but the commonly used satellites (e.g. MODIS, Landsat and Sentinel-2) have resolutions too coarse to characterize single crowns. To resolve this observational challenge, we used the PlanetScope constellation with a 3m resolution and near daily nadir-view coverage. We first developed a rigorous method to cross-calibrate PlanetScope surface reflectance using daily BRDF-adjusted MODIS as the reference. We then used linear spectral unmixing of calibrated PlanetScope to obtain dry-season change in the fractional cover of green vegetation (GV) and non-photosynthetic vegetation (NPV) at the PlanetScope pixel level. We used the Central Amazon Tapajos National Forest k67 site, as all necessary data (from field to phenocam and satellite observations) was available. For this proof of concept, we chose a set of 22 dates of PlanetScope measurements in 2018 and 16 in 2019, all from the six drier months of the year to provide the highest possible cloud-free temporal resolution. Our results show that MODIS-calibrated dry-season PlanetScope data (1) accurately assessed seasonal changes in ecosystem-scale and crown-scale spectral reflectance; (2) detected an increase in ecosystem-scale GV fraction (and a decrease in NPV fraction) from June to November of both years, consistent with local phenocam observations with R2 around 0.8; and (3) monitored large seasonal trend variability in crown-scale NPV fraction. Finally, our results highlight the potential of integrating multi-scale satellite observations to extend fine-scale leaf phenology monitoring beyond the spatial limits of phenocams.
It is still unknown whether the previous summer season drought and fertilization will affect the winter non-structural carbohydrate (NSC) reserves, spring leaf development, and mortality of trees in ...the next year. We, therefore, conducted an experiment with
Quercus pubescens
(downy oaks) saplings grown under four drought levels from field capacity (well-watered; ~25% volumetric water content) to wilting point (extreme drought; ~6%), in combination with two fertilizer treatments (0 vs. 50 kg/ha/year blended) for one growing season to answer this question. We measured the pre- and post-winter NSC, and calculated the over-winter NSC consumption in storage tissues (i.e. shoots and roots) following drought and fertilization treatment, and recorded the spring leaf phenology, leaf biomass, and mortality next year. The results showed that, irrespective of drought intensity, carbon reserves were abundant in storage tissues, especially in roots. Extreme drought did not significantly alter NSC levels in tissues, but delayed the spring leaf expansion and reduced the leaf biomass. Previous season fertilization promoted shoot NSC use in extreme drought-stressed saplings over winter (showing reduced carbon reserves in shoots after winter), but it also showed positive effects on survival next year. We conclude that: (1) drought-stressed downy oak saplings seem to be able to maintain sufficient mobile carbohydrates for survival, (2) fertilization can alleviate the negative effects of extreme drought on survival and recovery growth of tree saplings.
•We proposed a practical method to estimate the seasonal variations of LAI in mixed evergreen–deciduous forests.•We assessed the accuracy of optical methods to estimate the seasonal changes of ...LAI.•We evaluated the relative contributions of different sources of errors to optical LAI measurements.
Leaf area index (LAI), a critical parameter used in process models for estimating vegetation growth, can be measured through litterfall collection, which is usually referred to as a direct method. This method has been demonstrated to be applicable to deciduous forests, but few studies have used this method for estimating seasonal variations of LAI in mixed evergreen–deciduous forests. In this study, we proposed a practical method to estimate the seasonal variation of LAI directly by combining leaf emergent seasonality and litterfall collection (defined as LAIdir) in a mixed broadleaved-Korean pine (Pinus koraiensis) forest (BK), a Korean pine plantation (KP), a spruce–fir valley forest (SV), and a secondary birch (Betula platyphylla) forest (SB). In this direct method, the seasonal variation of LAI in a mixed forest can be quantified by tracking leaf growth and fall patterns throughout the growing season for each major evergreen and deciduous species. Using the LAIdir as a reference, we validated optical LAI (effective LAI, Le) measurements through a digital hemispherical photography (DHP) and the LAI-2000 instrument. We also explored the contribution of major sources of errors to optical LAI, including woody-to-total area ratio (α), clumping index (ΩE), needle-to-shoot area ratio (γE) and automatic exposure (E). We determined that DHP Le significantly (P<0.05) underestimated LAIdir from May to November by 48–64% in BK, KP and SV but overestimated LAIdir by 7% on average in SB. Similarly, LAI-2000 Le also significantly (P<0.05) underestimated LAIdir by an average of 27–35% in BK, KP and SV but overestimated LAIdir by 22% on average in SB. The relative contribution of E to the error in DHP Le is larger than other factors, and the γE was the largest relative contributor to the underestimation of LAI by LAI-2000. The results from our study demonstrate that seasonal variations of LAI in mixed evergreen–deciduous forests can be optically estimated with high accuracy (85% for DHP and 91% for LAI-2000), as long as accurate corrections are made to the various factors mentioned above. These close agreements between direct and optical LAI results also suggest that the direct method developed in this study is useful for tracking the seasonal variation of LAI in mixed forests.
Summary
There is a long‐standing idea that the timing of leaf production in seasonally cold climates is linked to xylem anatomy, specifically vessel diameter because of the hydraulic requirements of ...expanding leaves.
We tested for a relationship between the timing of leaf out and vessel diameter in 220 plants in three common gardens accounting for species’ phylogenetic relationships. We investigated how vessel diameter related to wood porosity, plant height and leaf length. We also used dye perfusion tests to determine whether plants relied on xylem produced during the previous growing season at the time of leaf out.
In all three gardens, there was later leaf out in species with wider vessels. Ring‐porous species had the widest vessels, exhibited latest leaf out and relied less on xylem made during the previous growing season than diffuse‐porous species. Wood anatomy and leaf phenology did not exhibit a phylogenetic signal.
The timing of leaf out is correlated with wood anatomy across species regardless of species’ geographic origin and phylogenetic relationships. This correlation could be a result of developmental and physiological links between leaves and wood or tied to a larger safety efficiency trade‐off.
See also the Commentary on this article by Olson, 235: 815–820.
Vegetation green leaf phenology directly impacts gross primary productivity (GPP) of terrestrial ecosystems. Satellite observations of land surface phenology (LSP) provide an important means to ...monitor the key timing of vegetation green leaf development. However, differences between satellite‐derived LSP proxies and in situ measurements of GPP make it difficult to quantify the impact of climate‐induced changes in green leaf phenology on annual GPP. Here, we used 1,110 site‐years of GPP measurements from eddy‐covariance towers in association with time series of satellite LSP observations from 2000 to 2014 to show that while satellite LSP explains a large proportion of variation in annual GPP, changes in green‐leaf‐based growing season length (GSL, leaf development period from spring to autumn) had less impact on annual GPP by ∼30% than GSL changes in GPP‐based photosynthetic duration. Further, maximum leaf greenness explained substantially more variance in annual GPP than green leaf GSL, highlighting the role of future vegetation greening trends on large‐scale carbon budgets. Site‐level variability contributes a substantial proportion of annual GPP variance in the model based on LSP metrics, suggesting the importance of local environmental factors altering regional GPP. We conclude that satellite LSP‐based inferences regarding large‐scale dynamics in GPP need to consider changes in both green leaf GSL and maximum greenness.
Plain Language Summary
The ongoing global trends of vegetation green leaf phenology and physiology caused by climate change have drawn great attention in the climate science community as they significantly impact carbon cycle dynamics. By analyzing field‐measured vegetation productivity data from an extensive global eddy covariance flux data set and the corresponding satellite remote sensing observations, we found that changes in green leaf growing season length (GSL) had less impact on annual vegetation productivity by ∼30% than that in photosynthetic duration. Further, maximum leaf greenness affects vegetation productivity more than observed green leaf GSL, highlighting the role of future vegetation greening trends on large‐scale carbon budgets. We conclude that inferences regarding large‐scale dynamics in vegetation productivity based on satellite observations need to consider changes in both green leaf GSL and maximum greenness.
Key Points
Changes in green leaf growing season length (GSL) had less impact on vegetation productivity by ∼30% than changes in photosynthetic duration
Maximum leaf greenness affects vegetation productivity more than green leaf GSL
Studies of large‐scale vegetation productivity need to consider changes in both green leaf GSL and maximum greenness
The interest in tree phenology monitoring is increasing because this trait is a robust indicator of the impacts of climate change on natural and managed ecosystems. Different approaches to monitor ...phenology at different spatial scales, from in situ monitoring to remote sensing, are used to investigate spring and/or autumn phenological changes. In Mediterranean area, most of phenological changes occur during cloudy periods (spring and autumn), leading to a loss of information also for very high temporal resolution satellites. Instead, cloud-uninfluenced sensors, such as radar sensors, can allow to bypass this problem and produce a temporally continuous coverage.
In this paper, we analyzed the spring phenology of two European beech (Fagus sylvatica L.) populations, located at different latitudes in Mediterranean area. Weekly in situ monitoring of leaf-out has been correlated with data collected by Synthetic Aperture Radar. Spring phenological phases were monitored in situ following a modified BBCH-code with a 5-scores scale (from 1 - buds closed and covered by scales, to 5 - leaf completely unfolded). The score 3 (young leaves starting to emerge from the bud) was considered the bud break. Different site conditions based on aspect (northern and southern) and altitudinal gradient (high and low altitude) have been considered. The aim was to test and implement a new methodology able to decrease the frequency of the field sampling, using remote data, to extend more detailed information on geographical scale, and to reconstruct past phenology.
Results showed a statistically significant different length of the vegetative spring period, spanning from dormant buds, up to leaves completely unfolded, between sites. Through Synthetic Aperture Radar estimation, this study demonstrates that leaf-out can be monitored with an extreme accuracy. The phenophase score 4 and 5 estimation showed the best performance (RMSE < of 4 days), phenophases score 2 and 3 showed promising performances (4 days < RMSE <5 days), while phenophases score 1 seems to be not easily detectable, although it can be extrapolated with an RMSE <6 days.
This radar approach fixes the cloud problem typical of multispectral approach and very frequent in phenophase change periods in Mediterranean climate. This study promotes the proposed remote sensing approach as a very useful tool to monitor growing season starting in remote areas, helping to reduce in situ observations and allowing past phenology reconstruction.
•Sentinel-1 proved to be an operative monitoring tool for beech leaf phenology.•Beech leaf emerging and unfolding were the best detected phenophases.•Phenophases detecting errors ranged between 3 and 5 days.•A human assisted was the best performing approach.•Lower altitudinal belts were synchronised due to similar ecological condition.
•The space-time distribution of rainfall influenced the vegetative phenophases.•The reproductive phenophases showed few space-time variations.•Seed harvesting should be undertaken in November, before ...dispersal.•Plant height, associated with more developed soils, affected leaf production.•Smaller stem diameters produced a greater number of buds and flowers.
The scarcity of phenological studies based on different populations of tropical forest trees limits seed management and collection for reforestation efforts. Precipitation is the primary factor driving tropical plant phenology in seasonal environments, although other environmental variables and plant traits may be associated. We examined the seasonality, synchrony, and intensities of the vegetative and reproductive phenophases of four populations of Handroanthus spongiosus, an endangered species, under similar climate regimes in a seasonally dry tropical forest, in northeastern Brazil. We expected to observe some divergence in the phenologies of the populations related to distinct functional traits selected for by differences in rainfall and soil properties. Mature trees (n = 87) were monitored during a three-year period. Seasonality was examined using circular statistics, and the influences of environmental variables on phenophases were investigated using generalized additive models. Variations in intensities and activity indices were identified among the different populations. Vegetative phenophases were seasonal, driven by precipitation and photoperiod, with leaf longevity of up to 7 months; budding peaked in February-March, while leaf fall peaked in April and October. The reproductive phenophases were found to be seasonal, during the rainy season (November to April), influenced by temperature and photoperiod. The slight divergences noted among the phenological behaviors of the populations were related to distinct functional traits (e.g., tree height, stem diameter) selected for by differences in certain environmental variables (rainfall volumes and soil properties). Given ongoing global climate changes, increases in leaf fall and reductions of flowering intensity, as verified here, will likely be observed.
Crna topola (Populus nigra L.) je jedna od najznačajnijih europskih vrsta drveća koja nastanjuje aluvijalna staništa uz obale velikih rijeka. U Bosni i Hercegovini postoji značajan neiskorišten ...zemljišni potencijal pogodan za reintrodukciju autohtonih crnih topola, kao i podizanje intenzivnih i ekstenzivnih nasada hibridnih i američkih crnih topola. Cilj ovoga istraživanja je utvrditi početak i završetak fenoloških faza listanja, kao i zimsko zadržavanje lista, što će pomoći pri selekciji pogodnih klonova autohtonih crnih topola za reintrodukciju na određenom lokalitetu i za određene mikroklimatske uvjete u svrhu očuvanja autohtonog genofonda, te klonova hibridnih topola za osnivanje plantaža u Bosni i Hercegovini. Istaživan je materijal 161 klona autohtonih crnih topola iz 26 populacija iz slivova 6 rijeka, te 11 klonova proizvodnih hibridnih topola (euro-američke ili kanadske) i američkih crnih topola. Klonovi se nalaze u klonskom arhivu u Žepču, koji je podignut 2006. godine. Promatrana je fenologija listanja i to od 14.3.- 22.4.2019. godine i to u šest fenoloških faza 0 - uspavani pupoljak, 1 – napukli pup, 2 – probijanje pupa, 3 – pup otvoren, listovi skupljeni, 4 – listovi se razdvajaju, 5 – listovi potpuno razvijeni). Zadržavanje lista praćeno je od 30.8.-4.11.2019. godine i ocjenjivano u tri kategorije: 1 - prisutni svi listovi na stablu, 2 - 50% listova je preostalo na stablu, 3 – nema preostalih listova na stablu. Efektivna duljina vegetacijske sezone definirana je kao vrijeme između pojavljivanja faze pucanja pupova (ocjena 3) i ocjena opadanja lišća 2 (tj. kada je 50% lišća ostalo na stablu). Analiza varijance pokazala je statistički značajne razlike između klonova iz različitih populacija za duljinu trajanja fenoloških faza listanja. Fenološka faza 1 (napukli pupovi) najranije se javila 14.3. a faza 5 (potpuno otvoreni listovi) najranije 8.4. Rezultati zadržavanja listova pokazuju da su 4.11. svi klonovi u klonskom arhivu odbacili list 100%. Najkraću efektivnu duljinu vegetacijskog perioda imali su klonovi populacije Bugojno (154 dana), a najdužu klonovi Populus boleana i Populus nigra var. italica te klonovi populacija Čapljina (sliv rijeke Neretve); Dobrinje, Visoko, Babina rijeka, Maglaj, Doboj (sliv rijeke Bosne); Kopači i Tegare (sliv rijeke Drine). Rezultati istraživanja su značajni za odabir klonova sa boljom prilagodbom na uvjete staništa, te obnovu i uporabu klonskog reprodukcijskog materijala crnih topola u Bosni i Hercegovini.
Black poplar (Populus nigra L.) is a species growing in flood forests and today it is one of the most endangered species in Europe. In Bosnia and Herzegovina, there is significant area of unused land suitable for the reintroduction of autochthonous black poplar and the establishment of intensive and extensive plantations of hybrid and American black poplar. This research aims to determine the beginning and the end of the phenological phases of leafing, as well as the winter retention of leaves, which will help in the selection of suitable clones for the establishment of plantations in Bosnia and Herzegovina. The material of 161 clones of autochthonous black poplars from 26 populations from the basins of 6 rivers, and 11 clones of production hybrid poplars (Euro-American or Canadian) and American black poplars was analyzed. The clones were located in the clonal archive in Žepče, which was established in 2006. Leafing phenology was observed from March 15 to April 22, 2019, and during six phenological phases: 0 - dormant bud, 1 - cracked bud, 2 - bud breaking through, 3 - bud open, leaves gathered, 4 - leaves separate, 5 - leaves fully developed. The retention of the leaves was monitored from August 30 to November 4, 2019, and evaluated in three categories: 1 - all leaves on the tree are present, 2 - 50% of the leaves are left on the tree, 3 - there are no leaves left on the tree. Analysis of variance showed statistically significant differences between clones from different populations for the duration of the leafing phenological phases. Phenological phase 1 (buds breaking through) occurred at the earliest on March 14 and phase 5 (fully open leaves) no earlier than April 8. The results of leaf retention show that on November 4 all clones in the clonal archive fully rejected the leaves. The shortest effective length of the vegetation period had the clones of the Bugojno population (154 days), and the longest the clones of Populus boleana and Populus nigra var. italica and clones of the Čapljina population (Neretva river basin). Dobrinje, Visoko, Babina Rijeka, Maglaj, Doboj (Bosna river basin), Kopači and Tegare (Drina river basin). The results of this research will be used in the selection of the most suitable clones for reintroduction in a specific locality and for specific microclimatic conditions, especially the occurrence of late spring and early autumn frosts, for the purpose of preserving the autochthonous gene pool, as well as clones of hybrid poplars for the establishment of clonal plantations. It is necessary to continue phenological research in the clonal test of autochthonous black poplars and hybrid poplars in Bosnia and Herzegovina, as well as to conduct research on growth properties in order to be able to compare the results of phenological research, i.e. the length of the growing season, as well as thickness and height growth.
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