Evergreen Conifer Research Articles

Monitoring Individual Tree Phenology in a Multi-Species Forest Using High Resolution UAV Images

Monitoring tree phenology is important for understanding ecosystem functioning and for assessing ecosystem responses to climate change. Satellite imagery offers open-access global coverage but is restricted to forest-level analyses, due to its coarse spatial resolution. Unmanned aerial vehicle (UAV) imagery can monitor phenology at the individual tree level by utilizing a centimeter-scale resolution. Two research objectives were identified for this study: (1) to derive phenological metrics at the individual tree level, using various vegetation indices (VIs); and (2) to assess the accuracy of automatic crown delineation in a diverse ecosystem. To achieve this, fourteen multi-spectral UAV flights were performed, and the ability of the normalized difference vegetation index (NDVI), enhanced vegetation index 2 (EVI2), optimized soil-adjusted vegetation index (OSAVI), and chlorophyll index red-edge (CIre) to model seasonal phenology was assessed. A double logistic model was fitted on the VI observations for each individual tree, to derive the start of season (SOS) and end of season (EOS). Individual tree crowns were delineated automatically using marker-controlled watershed segmentation (MCWS), and the treetops were identified using a local maximum filter (LMF). Overall, the automatic segmentation performed well (F-score: 0.79, IoU: 0.58), with higher accuracies in single-species areas, while it underperformed in complex mixed forest structures. All VIs captured a strong seasonal signal for the deciduous trees and derived SOS and EOS estimates consistent with literature and ground observations. General phenological patterns included an early silver birch SOS, a quick beech budburst, and large within-species phenology variations for oak trees. Seasonal VI variation for coniferous evergreen trees was limited, and the resulting phenology estimates proved unreliable. In conclusion, these findings emphasize the capabilities of UAV imagery for individual tree crown phenology monitoring. However, they also show the difficulty of monitoring evergreen phenology with the commonly-used VIs and stress the need for further investigations.

Mapping the Late Miocene Pyrenean Forests of the La Cerdanya Basin, Spain

The Late Miocene palaeofloras of the La Cerdanya Basin represent a unique look into the Pyrenean Miocene forested areas of the Iberian Peninsula at a time when the European warm and humid climate was experiencing progressive cooling and aridification. Macrofossils (leaves, seeds, fruits and cones) and miospores from several outcrops revealed the composition and abundances of the different plant species present in the area during the Tortonian and early Messinian geological stages (ca. 11.1–5.7 Ma). These fossils were found in the sediment deposits of an ancient lake system situated in the southwestern part of the basin. Previous studies indicated the presence of highly diversified mixed mesophytic forests with broadleaved evergreen and deciduous trees and conifers. However, the spatial structure and distribution of these forest types remains unknown. In the present work, the biomization method was used to infer the different late Miocene vegetation types from the basin. The extent of these vegetation types was calculated using a methodology for mapping vegetation units from fossil and biome data. While previous attempts at mapping Miocene vegetation units had a broad geographical scale, the present work aimed to map the extent of the vegetation units at a small scale, recreating local and specific vegetation changes in an abrupt basin. Results showed similarly high scores between for four biome types, which represent the different types of vegetation that coexisted in the basin during the Tortonian and the early Messinian: warm-temperate evergreen broadleaf and mixed woodlands (WTEM biome), temperate deciduous forests (TEDE) and cool conifer forests (COMX and COEG). Their extent was depicted in two vegetation maps, which account for differences in palaeoaltitude and palaeoclimate. These forests occupied different vegetation belts, which shifted upwards and downwards with climatic variations and the progressive uplift of the Pyrenees during the late Miocene. Azonal riparian forests and wetland vegetation occupied the more humid areas in the centre of the basin. Nonetheless, dry conditions during the early Messinian and decrease in the lake area degraded the wetland environments, which were partially replaced by broadleaved evergreen mixed woodlands.

Synchronous Changes of GPP and Solar-Induced Chlorophyll Fluorescence in a Subtropical Evergreen Coniferous Forest.

Using in situ near-surface observations of solar-induced chlorophyll fluorescence (SIF) and gross primary productivity (GPP) of a subtropical evergreen coniferous forest in southern China, this study analyzed the dynamics of SIF, GPP and their environmental responses, and explored the potential of SIF in characterizing the variation of GPP. The results showed that SIF and GPP have similar diurnal and seasonal variation and both reach the highest value in summer, indicating that the SIF can be applied to indicate the seasonal variation of GPP for the subtropical evergreen co-niferous. With the increase in temporal scale, the correlation between SIF and GPP becomes more linear. The diurnal variations of both SIF and GPP were characterized by photosynthetically active radiation (PAR), the seasonal variations of SIF and GPP were influenced by air temperature (Ta) and PAR. Probably due to the absent of drought stress during the study period, no significant correlation was detected between soil water content (SWC) and either SIF or GPP. With the in-crease in Ta, PAR or SWC, the linear correlation between the SIF and GPP gradually decreased, and when Ta or PAR was relatively higher, the correlation between SIF and GPP become weakly. Further research is still needed to illustrate the relationship between SIF and GPP under drought condition which occurred frequently in this region based on longer observation.

Dataset for "Incorporating leaf chlorophyll content and leaf age into a two-leaf terrestrial biosphere model for estimating carbon and water fluxes at a subtropical evergreen conifer forest"

Dataset for "Incorporating leaf chlorophyll content and leaf age into a two-leaf terrestrial biosphere model for estimating carbon and water fluxes at a subtropical evergreen conifer forest"

Mineral Nutrient Uptake, Accumulation, and Distribution in Cunninghamia lanceolata in Response to Drought Stress.

Mineral accumulation in plants under drought stress is essential for drought tolerance. The distribution, survival, and growth of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.), an evergreen conifer, can be affected by climate change, particularly seasonal precipitation and drought. Hence, we designed a drought pot experiment, using 1-year-old Chinese fir plantlets, to evaluate drought effects under simulated mild drought, moderate drought, and severe drought, which corresponds to 60%, 50%, and 40% of soil field maximum moisture capacity, respectively. A treatment of 80% of soil field maximum moisture capacity was used as control. Effects of drought stress on mineral uptake, accumulation, and distribution in Chinese fir organs were determined under different drought stress regimes for 0-45 days. Severe drought stress significantly increased phosphorous (P) and potassium (K) uptake at 15, 30 and 45 days, respectively, within fine (diameter < 2 mm), moderate (diameter 2-5 mm), and large (diameter 5-10 mm) roots. Drought stress decreased magnesium (Mg) and manganese (Mn) uptake by fine roots and increased iron (Fe) uptake in fine and moderate roots but decreased Fe uptake in large roots. Severe drought stress increased P, K, calcium (Ca), Fe, sodium (Na), and aluminum (Al) accumulation in leaves after 45 days and increased Mg and Mn accumulation after 15 days. In stems, severe drought stress increased P, K, Ca, Fe, and Al in the phloem, and P, K, Mg, Na, and Al in the xylem. In branches, P, K, Ca, Fe, and Al concentrations increased in the phloem, and P, Mg, and Mn concentrations increased in the xylem under severe drought stress. Taken together, plants develop strategies to alleviate the adverse effects of drought stress, such as promoting the accumulation of P and K in most organs, regulating minerals concentration in the phloem and xylem, to prevent the occurrence of xylem embolism. The important roles of minerals in response to drought stress should be further evaluated.

Cultural services in arid landscapes. A comparative study based on people’s perception, southeast of Iran

Cultural ecosystem services (CESs) are powerful motivators for stakeholders and managers to preserve valuable landscapes. There is little information about CESs and their spatial distribution in arid lands. It is necessary to identify the most important social-ecological drivers of CESs supply to improve coldspot areas in this regard. Seven cultural ecosystem services were quantified based on people’s perception across eight different arid landscapes, in southeast of Iran. A questionnaire was prepared based on landscape photography to interview people using non-proportional quota sampling. Using hotspot analysis, the spatial distribution of cultural services was then examined. CESs’ hotspots were often dispersed in the semi-arid regions (95% of hotspots), whereas coldspots were often dispersed in arid regions (73% of coldspots). The landscape condition, landscape type, and plant traits were the most important ecological drivers of CESs supply (p < 0.05), showing priority regions for conservation or restoration. Woodlands were more successful in providing CESs than rangelands. The two woodland landscapes, i.e., scale-leaved evergreen coniferous and deciduous broad-leaved trees had the most potential for providing CESs. The lowland mixed halophyte shrubs-annual species landscape had the least potential for CESs supply. The education and income (p < 0.05) were the main social drivers of CESs provision, which are effective for restoration of areas with the risk of CESs loss. Our findings provide useful information for planners and managers to understand the potential of different landscapes in providing multiple CESs and to relate them to conservation/restoration plans.

Influence of phenology on waveform features in deciduous and coniferous trees in airborne LiDAR

Information on forest structure is vital for sustainable forest management. Currently, airborne LiDAR remote sensing has been well established as an effective tool to characterize the structure of canopies and forest inventory variables. Radiometry and geometry are highly intertwined in LiDAR remote sensing of forest vegetation and phenology influences the geometric-optical properties of deciduous and evergreen trees causing seasonal variation in LiDAR observations. This variation may be considered as a nuisance or exploited in for example tree species identification. Airborne LiDAR data are also influenced by sensor functioning, acquisition settings, scan geometry and the atmosphere. Reliable estimation of subtle phenological effects calls for data in which the impact of the external factors is minimal. We experimented with such data and explored LIDAR waveforms (WFs) in boreal trees in winter, early summer and late summer. Our objectives were to i) assess the match of the multitemporal LiDAR data for observing true changes in vegetation; ii) quantify the influence of phenology in deciduous and evergreen trees; iii) study the effect of varying scan zenith angle (SZA) and canopy age on WF features in different phenostates; iv) assess the temporal feature correlation in individual living and dead standing trees. A WF-recording pulsed LiDAR sensor unit operating at the wavelength of 1550 nm was used in repeated acquisitions. WF attributes such as energy, peak amplitude and echo width were derived for each pulse and were localized vertically to crown, understory and ground components. Silver and downy birch, black alder, European aspen, Siberian larch, Scots pine, Norway spruce and dead standing spruce formed our strata. Results showed that phenology caused more variation in WF features of deciduous trees compared to evergreen conifers. Deciduous trees displayed substantial between-species variation that was linked with differences in branching pattern, leaf orientation and bark reflectance. Pine displayed a possible winter-early summer anomaly in canopy backscattering that may be linked with changes in foliage clumping or with the role of stamens in early summer trees. Trees displayed positive temporal correlation in WF features and correlations were the strongest in evergreen and deciduous conifers and decreased with time. SZA had minor influence on WF features whereas age exercised a strong effect on many features with parallel variation between species and phenostates. Structural changes following death, i.e. ‘aging’ changed the geometric WF features of dead standing trees. Our results provide new insights for enhancing tree species identification by using WF LiDAR and for LiDAR time-series analysis of vegetation.

Mapping Growing Stem Volume Using Dual-Polarization GaoFen-3 SAR Images in Evergreen Coniferous Forests

Unaffected by cloud cover and solar illumination, synthetic aperture radar (SAR) images have great capability to map forest growing stem volume (GSV) in complex biophysical environments. Up to now, c-band dual-polarization Gaofen-3 (GF-3) SAR images, acquired by the first Chinese civilian satellite equipped with multi-polarized modes, are rarely applied in mapping forest GSV. To evaluate the capability of dual-polarization GF-3 SAR images in mapping forest GSV, several proposed derived features were initially extracted by mathematical operations and applied to obtain optimal feature sets by different feature sorting methods and feature selection methods. Then, the maps of GSV in an evergreen coniferous forest were inverted by various machine learning algorithms and stacking ensemble learning methods with different strategies. The results implied that backscattering coefficients and partially proposed derived features showed high sensitivity to the forest GSV, and the saturation phenomenon also obviously occurred once the forest GSV was larger than 300 m3/ha. Furthermore, the results showed that the accuracy of the mapped GSV was significantly improved using the stacking ensemble learning methods. Using various optimal feature sets and base models (MLR, KNN, SVM, and RF), the rRMSE values mainly ranged from 30% to 40%. After using the stacking ensemble learning methods, the values of rRMSE ranged from 16.71% to 20.51%. This confirmed that dual-polarization GF-3 images have great potential to map forest GSV in evergreen coniferous forests.

Estimation of spatio-temporal distribution of 137Cs concentrations in litter layer of forest ecosystems in Fukushima using FoRothCs model

The nuclear power plant accident in Fukushima had led to pollution of forest ecosystems with 137Cs in 2011. In this study, we simulated the spatiotemporal distribution of 137Cs concentrations of litter layer in the contaminated forest ecosystems in two decades from 2011, which is one of the key environmental components of 137Cs migration in the environment due to the high bioavailability of 137Cs in the litter. Our simulations showed that 137Cs deposition is the most important factor in the degree of contamination of the litter layer but vegetation type (evergreen coniferous/deciduous broadleaf) and mean annual temperature are also important for changes over time. Deciduous broadleaf trees had higher initial concentrations in the litter layer due to the direct initial deposition on the forest floor. However, the concentrations remained higher than those in evergreen conifers after 10 years due to redistribution of 137Cs by vegetation. Moreover, areas with lower average annual temperatures and lower litter decomposition activity retained higher 137Cs concentrations in the litter layer. The results of the spatiotemporal distribution estimation of the radioecological model suggest that, in addition to 137Cs deposition, elevation and vegetation distribution should also be considered in the long-term management of contaminated watersheds, which can be informative in identifying hotspots of 137Cs contamination on a long-term scale.

Screening and characterization of paclitaxel-producing fungus \(\textit{Talaromyces wortmannii}\) WQF18 isolated from \(\textit{Cephalotaxus mannii }\)Hook. f..

Cephalotaxus mannii Hook. f. is a rare evergreen conifer native listed in the International Union for Conservation of Nature (IUCN) Red List, which is utilized for leukemia treatment. Although endophytic fungi from C. mannii was reported before, their cytotoxic property has not been revealed yet. In the present study, a total of 7 endophytic fungi were isolated from C. mannii collected in Ha Giang province, Vietnam, among which the isolate WQF18 was active against 5 tested pathogens with inhibition zones ranging from 18.0 ± 0.7 to 25.0 ± 0.4 mm. In addition, only ethyl acetate extract of isolate WQF18 showed cytotoxicity on A549 and MCF7 cell lines with IC50 values of 69.6 ± 2.3 µg/mL and 78.6 ± 1.6 µg/mL, respectively. PCR-based molecular screening revealed that the positive hits for both 10-deacetylbaccatin III-10-O-acetyl transferase (dbat) and taxadiene synthase (ts) genes involved in paclitaxel biosynthesis were only observed in the WQF18 isolate. Based on morphological and molecular identification, the WQF18 isolate was identified as Talaromyces wortmannii WQF18. The presence of paclitaxel in T. wortmannii WQF18 was further confirmed by dbat sequence alignment, phenotypic, and HPLC-DAD analysis. To the best of our knowledge, this is the first report demonstrating the paclitaxel-producing capability of endophytic fungi from C. mannii. These findings provide a new platform for deciphering paclitaxel biosynthesis of endophytic fungi from non-Taxus plants and further paclitaxel production.

Influence of urbanisation on the phenology of evergreen coniferous and deciduous broadleaf trees in Madrid (Spain)

Plant phenology plays a crucial role in terrestrial ecosystems and is a key indicator of ecological changes. It is influenced by alterations in meteorological conditions at micro- and mesoscale in cities as a result of urbanisation and the intensification of anthropogenic activities. One example is the urban heat island (UHI), i.e. the increase in temperature in city cores compared to their surroundings. In this study, we used plant phenological data from the High-Resolution Vegetation Phenology and Productivity dataset of the Copernicus Land Monitoring Service to explore the relationship between urbanisation intensity (i.e., proportion of built-up area) and the phenology and productivity of broadleaf deciduous and evergreen coniferous trees in the city of Madrid and its surroundings, one of the largest metropolitan areas in Europe. We found the average start of season date advanced by 0.79–11.79 days in broadleaf deciduous trees in highly urbanised areas, and was delayed by 5.77–9.16 days in evergreen coniferous trees. Although differences were also observed for the end and length of the growing season, these patterns showed great interannual variability. Both broadleaf deciduous and evergreen coniferous trees were most productive in highly urbanised areas. Although previous studies have explored the response of different land-cover types to urbanisation, to our knowledge, none have looked at this relationship at a fine spatial scale in a Mediterranean city with different vegetation functional groups. The analysis of more specific classes of vegetation enables a better understanding of the phenological response of vegetation to urbanisation intensity.

Leaf-branch vulnerability segmentation occurs all year round for three temperate evergreen tree species

Vulnerability segmentation (VS) and Hydraulic segmentation (HS) hypotheses propose higher hydraulic resistance and vulnerability to embolism in leaves than in branches, respectively. The VS and HS are suggested as an acclimation strategy of trees to drought stress, but whether they occur during freezing stress has rarely been explored. We measured the leaf and branch hydraulic traits of three temperate evergreen tree species [Picea koraiensis (Korean spruce), Pinus koraiensis (Korean pine), and Pinus sylvestris var. mongolica (Mongolian pine)] during four seasons (winter, spring, summer, and autumn) across the year. We assessed the applicability of VS and HS all year round, particularly in winter. The water potential at which leaf hydraulic conductance lost 50% (P50L), was more negative in winter than in summer, while higher leaf mass per area was obtained in winter. These results suggest that these species invest more carbon into leaf (including hydraulic systems) to acclimate to winter frost drought. Leaf and branch hydraulic conductance (KmL and KmB) were lower, and the percentage loss of branch hydraulic conductance (PLCB) was higher in spring than in autumn. These results were probably because of more freeze-thaw cycles in spring (69 cycles) than in autumn (37 cycles). The water potential at which branch hydraulic conductance lost 50%, P50B, was more negative than P50L across the year. The values of VS (P50L minus P50B) were positive, i.e. leaf was more vulnerable than the branch in all species and across seasons, with higher values occurring in spring or autumn. However, KmL positively correlated with KmB, suggesting hydraulic coordination between leaf and branch, but did not support HS. Our findings indicate that leaf-branch vulnerability segmentation can occur all year round, including freezing stress, to protect branches from hydraulic failure in temperate evergreen conifers.

Quantifying heterogeneity in ecohydrological partitioning in urban green spaces through the integration of empirical and modelling approaches

Urban green spaces (UGS) can help mitigate hydrological impacts of urbanisation and climate change through precipitation infiltration, evapotranspiration and groundwater recharge. However, there is a need to understand how precipitation is partitioned by contrasting vegetation types in order to target UGS management for specific ecosystem services. We monitored, over one growing season, hydrometeorology, soil moisture, sapflux and isotopic variability of soil water under contrasting vegetation (evergreen shrub, evergreen conifer, grassland, larger and smaller deciduous trees), focussed around a 150-m transect of UGS in northern Scotland. We further used the data to develop a one-dimensional model, calibrated to soil moisture observations (KGE’s generally > 0.65), to estimate evapotranspiration and groundwater recharge. Our results evidenced clear inter-site differences, with grassland soils experiencing rapid drying at the start of summer, resulting in more fractionated soil water isotopes. Contrastingly, the larger deciduous site saw gradual drying, whilst deeper sandy upslope soils beneath the evergreen shrub drained rapidly. Soils beneath the denser canopied evergreen conifer were overall least responsive to precipitation. Modelled ecohydrological fluxes showed similar diversity, with median evapotranspiration estimates increasing in the order grassland (193 mm) < evergreen shrub (214 mm) < larger deciduous tree (224 mm) < evergreen conifer tree (265 mm). The evergreen shrub had similar estimated median transpiration totals as the larger deciduous tree (155 mm and 128 mm, respectively), though timing of water uptake was different. Median groundwater recharge was greatest beneath grassland (232 mm) and lowest beneath the evergreen conifer (128 mm). The study showed how integrating observational data and simple modelling can quantify heterogeneities in ecohydrological partitioning and help guide UGS management.

Interactive effects of elevated temperature and drought on plant carbon metabolism: A meta-analysis.

Elevated temperature (Te ) and drought often co-occur and interactively affect plant carbon (C) metabolism and thus the ecosystem C cycling; however, the magnitude of their interaction is unclear, making the projection of global change impacts challenging. Here, we compiled 107 journal articles in which temperature and water availability were jointly manipulated, and we performed a meta-analysis of interactive effects of Te and drought on leaf photosynthesis (Agrowth ) and respiration (Rgrowth ) at growth temperature, nonstructural carbohydrates and biomass of plants, and their dependencies on experimental and biological moderators (e.g., treatment intensity, plant functional type). Our results showed that, overall, there was no significant interaction of Te and drought on Agrowth . Te accelerated Rgrowth under well-watered conditions rather than under drought conditions. The Te × drought interaction on leaf soluble sugar and starch concentrations were neutral and negative, respectively. The effect of Te and drought on plant biomass displayed a negative interaction, with Te deteriorating the drought impacts. Drought induced an increase in root to shoot ratio at ambient temperature but not at Te . The magnitudes of Te and drought negatively modulated the Te × drought interactions on Agrowth . Root biomass of woody plants was more vulnerable to drought than that of herbaceous plants at ambient temperature, but this difference diminished at Te . Perennial herbs exhibited a stronger amplifying effect of Te on plant biomass in response to drought than did annual herbs. Te exacerbated the responses of Agrowth and stomatal conductance to drought for evergreen broadleaf trees rather than for deciduous broadleaf and evergreen coniferous trees. A negative Te × drought interaction on plant biomass was observed on species-level rather than on community-level. Collectively, our findings provide a mechanistic understanding of the interactive effects of Te and drought on plant C metabolism, which would improve the prediction of climate change impacts.

Linkage between Leaf–Litter–Soil, Microbial Resource Limitation, and Carbon-Use Efficiency in Successive Chinese Fir (Cunninghamia lanceolata) Plantations

Chinese fir (Cunninghamia lanceolata) is a kind of evergreen coniferous tree species, the expansion of its pure forest area and multiple generations of continuous planting has led to a decline of stand quality and woodland fertility. To further investigate the relationship between leaf, litter, and soil stoichiometry, microbial community status, and microbial resource limitation of Chinese fir after continuous planting. We studied the C, N, and P stoichiometries of leaf, litter, and soil from successive rotations of Chinese fir plantations. In addition to this, soil microbial biomass C, N, and P, extracellular enzymes, as well as the soil microbial community composition, were determined. The continuous planting of Chinese fir significantly increased the leaf N and P contents and decreased the C content of litter, and the soil C:N and C:P ratios, thus leading to a soil stoichiometric imbalance. The continuous planting of Chinese fir plantations significantly increased the soil microbial biomass. Compared with the first-generation plantations, the N and P contents of the second- and third-generation plantations increased by 37.11%, 21.83% and 46.28%, 73.38%, respectively, thus alleviating the restriction of microbial N and P. Under continuous planting, the extracellular enzyme activities of N (NAG + LAP) and P (AP) were significantly decreased, and those of the second- and third-generation plantations were significantly decreased by 7.05%, 9.43% and 11.79%, 48.94%, respectively, compared with those of the first-generation plantations, resulting in an increase of 7.85 and 3.19% in carbon-use efficiency. The fungi:bacteria (F:B) ratio of the soil microbial community was elevated in successive plantations. The least squares pathway model (PLS-PM) indicated that the stoichiometric ratio of ecological enzymes had an indirect negative effect on CUE, and was the strongest predictor. This study showed that the successive plantation of Chinese fir resulted in a leaf, litter, and soil stoichiometric imbalance, further affecting community composition and resource limitation of soil microorganisms.

Microclimatic gradients cause phenological variations within temperate tree canopies in autumn but not in spring

Tree crowns experience strong vertical microclimatic gradients, particularly in light availability. Surprisingly, little is known about whether these gradients cause within-crown variation in leaf phenology and whether such variations represent different light-use strategies of sun- and shade leaves.In a temperate mixed forest at the Swiss Canopy Crane II site in Switzerland, we measured over three years the annual leaf phenology in the upper and lower crowns of mature trees from six broadleaved and three conifer species. We further recorded the microclimate (temperature, humidity, light) continuously in various positions within the canopy.We found microclimatic canopy gradients to be strongest during summer, but negligible in winter and spring, indicating that any phenological gradients in autumn, but not in spring, might be driven by microclimatic differences. Budbreak timing did not differ within the crowns of any of the broadleaved trees. However, in the three species with deeper crowns, leaf unfolding was up to 10 days faster in the lower crown but showed no difference in the more shallow-crowned species. Surprisingly, only the evergreen conifers Abies alba and Picea abies showed earlier bud break in the lower crowns. In autumn, senescence in all broadleaved species progressed from the upper crown downwards, resulting in up to two weeks longer vegetation seasons in the lower crown.With this first broad assessment of within-tree phenology, we show how microclimatic gradients and different light-use strategies lead to a considerable variability of within-crown phenological gradients. We interpret the faster leaf unfolding in the lower crown of three broadleaved species as a shade avoidance strategy, allowing shade branches to improve their C balance early in the season. In contrast, longer retention of lower leaves in autumn is unlikely to significantly improve the C balance, and more likely caused by higher summer temperature and irradiance in the upper leaves.

Reconstructing spatiotemporal dynamics of mixed conifer and broad‐leaved forests with a spatially explicit individual‐based dynamic vegetation model

AbstractA dynamic vegetation model was adapted to a mixed forest of deciduous broad‐leaved trees and evergreen conifers in Hokkaido, the northernmost main island of Japan, located within a transition zone between cool‐temperate and sub‐boreal forest ecosystems. In this forest, elevation and a terrestrial‐wetness index affect tree biomass and the percentage of conifers. We maximized agreement between this observed pattern and model output by calibrating parameters that control drought and excessive soil‐moisture tolerance, establishment rate, and background mortality rate. In the simulation, biomass increased as a single peak curve with simulation year, while the percentage of conifers increased until the end of 200 simulation years. The 75‐year simulated forest was most comparable to the adapted forest, consistent with the average frequency of catastrophic storm disturbances in Hokkaido. The model also reconstructed a reasonable succession pattern based on temperature and soil moisture. Therefore, the model mechanistically reconstructed the mixed forest via spatial niche segregation and succession after catastrophic disturbances. However, the model did not reconstruct the percentages of broad‐leaved trees and conifers of forests prior to the disturbance in independent validation plots, demonstrating that additional processes should be considered in future models.

A New Approach to Monitor Soil Microbial Driven C/N Ratio in Temperate Evergreen Coniferous Forests Managed via Sentinel-2 Spectral Imagery

Forests are key ecosystems for climate change mitigation, playing a pivotal role in C and N land sequestering and storage. However, the sustainable management of forests is challenging for foresters who need continuous and reliable information on the status of soil conditions. Yet, the monitoring of soils in temperate evergreen forests, via satellite data, is jeopardized by the year round prevailing heavily dense canopy. In this study, the Sentinel-2 spectral imagery derived normalized difference vegetation index (NDVI), proved to be a reliable tool to determine the C/N ratio in two managed pine-dominated forests, in southern Poland. Results showed a strong negative correlation between NDVI values and the on-site C/N ratios measured at the upper soil horizons in 100 and 99 randomly distributed sampling points across the Kup (r2 = −0.8019) and Koniecpol (r2 = −0.7281) forests. This indicates the feasibility of using the NDVI to predict the microbial driven soil C/N ratio in evergreen forests, and to foresee alterations in the vegetation patterns elicited by microbial hindering soil abiotic or biotic factors. Spatial/temporal variations in C/N ratio also provide information on C and N soil dynamics and land ecosystem function in a changing climate.

Landscape gradient of autumn photosynthetic decline in Abies sachalinensis seedlings

Understanding what environmental factors are genetically linked to a phenological event is critical for predicting responses to climate change. Photosynthetic phenology often varies among a species of evergreen conifers due to local adaptation. However, few empirical studies have revealed relevant relationships between climatic factors in provenance environments and photosynthetic phenology. This study evaluated the effects of environmental conditions of the growing site and seed source provenance on the seasonal changes in maximal photochemical quantum yield of photosystem II (Fv/Fm) in a common garden experiment with 2-year-old seedlings of Sakhalin fir (Abies sachalinensis), a representative species with local adaptation, from four seed source provenances. A logistic model was constructed to explain the seasonal variation of Fv/Fm from July to October and the relationships between the estimated model parameters and representative factors featuring provenance environments were evaluated. The landscape gradient of the detected model parameters responsible for the provenance environments was visualized in a map of the distribution area. The lowest temperature was the most plausible factor in the growing environment to explain the seasonal changes of Fv/Fm. Among the representative meteorological factors of provenance environments, the lowest temperatures in July showed significant relationships with two model parameters, explaining the lower limit of Fv/Fm and the higher sensitivity of autumn Fv/Fm decline. The estimated spatial maps of model parameters consistently showed that the higher the lowest temperature in July in the provenance environment, the lower the Fv/Fm in October and the greater the decrease in the autumn Fv/Fm decline. Therefore, the lowest summer temperature could be associated with the local adaptation of autumn photosynthetic phenology in A. sachalinensis.

Biological characteristics of Diplodia sapinea f. sp. cupressi infecting Cupressus sempervirens L. in Tunisia

Cupressus sempervirens L. (Italian cypress), is a Mediterranean evergreen coniferous tree. Due to its ecological values, this cypress has been used in forest protection against desertification and soil conservation. Last decades, cypress dieback has been commonly observed in Tunisian forests. Symptoms of shoot dieback, necrosis, twig blight, and trunk cankers have been observed on cypress trees in Bou Chrik (Nabeul) region. The causal agent was identified as Diplodia pinea f. sp. cupressi. The mycelial growth rate of the fungus was evaluated by using four different media culture at 25 °C and at seven temperatures ranging from (5 °C to 35 °C) on PDA medium. The results showed that the species was able to grow in a range of temperatures ranging from 20 to 25 °C and showed a higher growth rate on PDA medium. A pathogenicity test was conducted on C. sempervirens seedlings, and the aggressiveness of the fungus was approved.