Mixed Pine Forest Research Articles

Regeneration patterns of key pine species in a mixed-pine forest indicate a positive effect of variable retention harvesting and an increase in recruitment with time

BackgroundMany fire-dependent forests have experienced significant declines in species, structural, and functional diversity. These changes are attributed in part to traditional management approaches that were dominated by even-aged regeneration methods such as clearcutting. Variable retention harvesting (VRH) is an ecologically based forestry practice that involves retention of some mature overstory trees and other biological structures in the postharvest stand to emulate the effects of natural disturbance events. In this study, we examined the effect of a VRH treatment on recruitment of historically dominant pine species and understory vegetation two- and six years after its implementation in a naturally regenerated mixed pine forest in the Upper Peninsula of Michigan, USA.ResultsWe found greater regeneration of red pine (Pinus resinosa L.) and eastern white pine (Pinus strobus L.) in VRH stands compared to the unharvested controls. Although red pine recruitment was very low during the first 2 years, both species increased significantly from year two to year six. Recruitment responses for the two species did not differ significantly between the aggregated and dispersed retention treatments. We also found high recruitment of deciduous tree species, consisting primarily of sprouts, and red pine exhibited a negative correlation with these sprouts. Treatment, time, and the interaction of treatment and time were significant factors in red pine recruitment. Time had a strong effect on the understory vegetation, with significant decreases in shrubs and ferns over time.ConclusionsThe results suggest that VRH enhanced recruitment of red pine and eastern white pine and that this recruitment increased with time. We identify competition from sprouts and unfavorable seedbed conditions as the main factors that limited recruitment of red pine during the first 2 years. To reduce competing vegetation and improve seedbed conditions, we suggest following the VRH with a prescribed fire, mechanically removing sprouts, and implementing herbicide treatments. At a time when changes in global climate exacerbates the effects of traditional drivers of forest degradation, and with the need to maintain biodiversity, new ecologically based forest practices such VRH have the potential to facilitate regeneration of native trees and enhance the resilience of many fire-dependent forests.

Can mixed pine forests conserve understory richness by improving the establishment of understory species typical of native oak forests?

A positive effect of mixed pine forests ( Pinus sylvestris L. and Pinus pinaster Ait.) on the understory richness and tree regeneration was observed with respect to monospecific stands. Understory species typical of the native Pyrenean oak forests in the Iberian Peninsula contribute to maintaining high understory richness in such mixed pine forests. The influence of stands characteristics on the understory in mixtures that combine coniferous tree species of the same genus deserves more study since they are frequent in Spain. To assess the effect of mixed versus monospecific stands of Pinus sylvestris L. and Pinus pinaster Ait. on the main tree species regeneration and understory species composition. Tree regeneration and understory species composition were inventoried in eighteen forest plots (6 triplets) in North-Central Spain. Each triplet consisted of two plots dominated either by Scots pine or Maritime pine and one mixed plot that contained both species. The basal area (%) of both Pinus species was the only characteristic of the stands that significantly influenced the understory composition and tree regeneration. Characteristic species of humid and temperate zones, including P. sylvestris regeneration, dominated in Scots pine stands, and typical species of well-drained Mediterranean areas, including P. pinaster regeneration, dominated in Maritime pine stands. In mixed stands, the highest regeneration of the native Pyrenean oak with respect to monospecific stands was accompanied by understory species typical of native oak forests that share the same regeneration niche. Mixed pine forests allow the development of understory species better than monospecific forests.

Succession of a broad-leaved Korean pine mixed forest: Functional plant trait composition

Abstracts A longstanding goal of ecology and conservation biology is to understand the climatic and biological controls of forest succession. However, the patterns and mechanisms that guide forest succession, especially within broad-leaved forests, remain unclear. We collected leaf traits and abiotic data across a 200-year chronosequence within a broad-leaved Korean pine forest in northeastern China. We focused on five key leaf traits related to resource acquisition and competition by quantifying the community-weighted trait distributions for specific leaf area (SLA), leaf dry matter concentration (LDMC), leaf nitrogen content (Nmass (g/kg)), leaf phosphorus content (Pmass (g/kg)) and the ratio of nitrogen content to phosphorus content (Nmass/Pmass). We also studied how these traits respond to changing environmental variables (climatic, soil and topographical) during succession. Redundancy analysis was used to examine the importance of the environmental variables in shaping the successional variation in plant traits. Our results revealed the following. Older forests differed significantly from younger forests in species composition and trait distribution. For example, SLA, leaf N and P content and the N/P ratio tended to increase and then decrease throughout the community during forest succession (p

Persistent anthropogenic legacies structure depth dependence of regenerating rooting systems and their functions

Biotically-mediated weathering helps to shape Earth’s surface. For example, plants expend carbon (C) to mobilize nutrients in forms whose relative abundances vary with depth. It thus is likely that trees’ nutrient acquisition strategies—their investment in rooting systems and exudates—may function differently following disturbance-induced changes in depth of rooting zones and soil nutrient stocks. These changes may persist across centuries. We test the hypothesis that plant C allocation for nutrient acquisition is depth dependent as a function of rooting system development and relative abundances of organic vs. mineral nutrient stocks. We further posit that patterns of belowground C allocation to nutrient acquisition reveal anthropogenic signatures through many decades of forest regeneration. To test this idea, we examined fine root abundances and rooting system C in organic acid exudates and exo-enzymes in tandem with depth distributions of organically- and mineral-bound P stocks. Our design permitted us to estimate C tradeoffs between organic vs. mineral nutrient benefits in paired forests with many similar aboveground traits but different ages: post-agricultural mixed-pine forests and older reference hardwoods. Fine roots were more abundant throughout the upper 2 m in reference forest soils than in regenerating stands. Rooting systems in all forests exhibited depth-dependent C allocations to nutrient acquisition reflecting relative abundances of organic vs. mineral bound P stocks. Further, organic vs. mineral stocks underwent redistribution with historic land use, producing distinct ecosystem nutritional economies. In reference forests, rooting systems are allocating C to relatively deep fine roots and low-C exudation strategies that can increase mobility of mineral-bound P stocks. Regenerating forests exhibit relatively shallower fine root distributions and more diverse exudation strategies reflecting more variable nutrient stocks. We observed these disparities in rooting systems’ depth and nutritional mechanisms even though the regenerating forests have attained aboveground biomass stocks similar to those in reference hardwood forests. These distinctions offer plausible belowground mechanisms for observations of continued C sink strength in relatively old forests, and have implications for soil C fates and soil development on timescales relevant to human lifetimes. As such, depth-dependent nutrient returns on plant C investments represent a subtle but consequential signal of the Anthropocene.

长白山阔叶红松林乔木幼苗组成及多度格局的影响因素

长白山阔叶红松林乔木幼苗组成及多度格局的影响因素

Impact of stand characteristics on litterfall production and its decomposition in chir pine mixed Banj Oak forests in the Central Himalaya

Litterfall and its decomposition is a fundamental process that regulates the nutrient cycle in the forest ecosystems. This study was conducted in four chir pine (Pinus roxburghii) mixed banj oak (Quercus leucotrichophora) forests in the central Himalaya. Ten 50×50 cm litter traps were randomly placed in each site to collect the litterfall on monthly basis. Litter packets of 10×10 cm were kept randomly in each site to measure the decomposition rate of banj oak and chir pine leaf litter. The litterfall was found maximum in summer season followed by rainy and winter in all the sites. The values were found to be increasing with the stand characteristics and found highest in Hathikhan B (3.85 Mg ha−1) and lowest in Toli (1.73 Mg ha−1). Leaf litter percentage decreased with increasing stand characteristics whereas wood litter followed the opposite pattern. Litter decomposition was found faster in banj oak leaf litter than chir pine leaf litter. Decay constant was also found higher for banj oak whereas half-life was greater for chir pine leaf litter. Decomposition rate was unaffected by stand characteristics indicating that stand density and basal area do not affect the degradation process. Thus stand characteristics is a good indicator for litterfall production for a chir pine mixed banj oak forest.

Tigers, pine nuts and logging

The temperate mixed pine and deciduous forests in the Far East of Russia are home to an extraordinary variety of plants and animals. They are a part of the Amur Basin and are of considerable economic importance to the local population. They also help protect the global climate. Non-sustainable use, illegal logging and forest fires are all endangering these forests. As acts of human interference intensify, the degree of biodiversity in the forests lessens, as does the amount of carbon that they store. The ecological, environmental and social contribution made by these forests must be maintained. However, Russia’s forestry industry has been undermined, and is in need of reform.

A New Nearctic Species of Diadocidia Ruthe Fungus Gnat (Diptera: Diadocidiidae)

A new species of Diadocidia Ruthe fungus gnat was discovered in a mixed pine and hardwood forest in the eastern Lower Peninsula of Michigan. Diadocidia longivena Taber is the fourth species recorded from North America and the first new species of the genus described from the Nearctic in 63 years. The fly belongs to subgenus Adidocidia Laŝtovka and Matile, as do both of its congeners that were described in North America.

Pine Forests in Moscow Region: History and Perspectives of Preservation

Features of the structure and composition of forests with admixture of pine (Pinus sylvestris) were studied in central, northern, and western parts of Moscow region, a central part of the East European plain. Pine stands and mixed pine and spruce forests comprise around 16% of the total area of woodlands within the studied territory. This study addressed a possibility of conservation of indigenous pine communities in Moscow region and considered landscape conditions where it could most likely occur. In order to assess the prospects for pine regeneration in various types of communities, the dynamics of its coenopopulations was analyzed. It was found that various types of pine communities are associated with relief parameters (altitudes, slopes, varying curvatures, and lighting) and localization in physical–geographical provinces. The spatial structure of groups of pine forest associations was characterized using landscape and ecological metrics. These data improve the understanding of the phytocoenotic structure of pine communities. Their composition is indicative of succession stage (1), domain-specific features of vegetation cover of the region (2), and associations with landscape elements (3). Pathways of secondary successions on watershed surfaces involve active demutation of spruce forests and, in some cases, mixed woods. This will limit the occurrence of pine and pine–spruce communities in Moscow region after several decades. Only a small part of pine forests will remain on steep river banks.

The temperature and length for the release of primary and induction of secondary physiological dormancy in Korean pine (Pinus koraiensis Sieb. et Zucc.) seeds

Primary physiological dormancy and secondary physiological dormancy of Korean pine seeds restrict the regeneration of broad-leaved Korean pine (Pinus koraiensis) mixed forest. Dry and imbibed seeds were stratified at 1 °C and 5 °C for 1, 2, 4 and 6 months. Germination percentage, mean germination time (MGT) and germination rate index (GRI) were measured to determine the optimal low temperature and its duration for the release of primary physiological dormancy. Once primary physiological dormancy was released through cold stratification, seeds were stored in an environment in which the temperature progressively increased from 5 to 25 °C. After one month of storage at each storage temperature, the germination percentage, MGT and GRI were measured to determine the threshold temperature for the induction of secondary physiological dormancy. Both dry and imbibed seeds not only exhibited a high germination percentage (approximately 80%) but also germinated rapidly (MGT and GRI were 17 days and 2.36, respectively) after 6 months of storage at either 1 °C or 5 °C. The germination percentage of cold stratified seeds gradually decreased from 78% (5 °C) to 72% (10 °C), 55% (15 °C), 10% (20 °C) and 8% (25 °C). The results of this study suggest that stratifying seeds at 1 °C or 5 °C for 6 months releases primary physiological dormancy. The induction of secondary physiological dormancy occurs at temperatures above 15 °C.

Microbial community structure and the relationship with soil carbon and nitrogen in an original Korean pine forest of Changbai Mountain, China

BackgroundThe broad-leaved Korean pine mixed forest is an important and typical component of a global temperate forest. Soil microbes are the main driver of biogeochemical cycling in this forest ecosystem and have complex interactions with carbon (C) and nitrogen (N) components in the soil.ResultsWe investigated the vertical soil microbial community structure in a primary Korean pine-broadleaved mixed forest in Changbai Mountain (from 699 to 1177 m) and analyzed the relationship between the microbial community and both C and N components in the soil. The results showed that the total phospholipid fatty acid (PLFA) of soil microbes and Gram-negative bacteria (G-), Gram-positive bacteria (G+), fungi (F), arbuscular mycorrhizal fungi (AMF), and Actinomycetes varied significantly (p < 0.05) at different sites (elevations). The ratio of fungal PLFAs to bacterial PLFAs (F/B) was higher at site H1, and H2. The relationship between microbial community composition and geographic distance did not show a distance-decay pattern. The coefficients of variation for bacteria were maximum among different sites (elevations). Total soil organic carbon (TOC), total nitrogen (TN), soil water content (W), and the ratio of breast-height basal area of coniferous trees to that of broad-leaved tree species (RBA) were the main contributors to the variation observed in each subgroup of microbial PLFAs. The structure equation model showed that TOC had a significant direct effect on bacterial biomass and an indirect effect upon bacterial and fungal biomass via soil readily oxidized organic carbon (ROC). No significant relationship was observed between soil N fraction and the biomass of fungi and bacteria.ConclusionThe total PLFAs (tPLFA) and PLFAs of soil microbes, including G-, G+, F, AMF, and Actinomycetes, were significantly affected by elevation. Bacteria were more sensitive to changes in elevation than other microbes. Environmental heterogeneity was the main factor affecting the geographical distribution pattern of microbial community structure. TOC, TN, W and RBA were the main driving factors for the change in soil microbial biomass. C fraction was the main factor affecting the biomass of fungi and bacteria and ROC was one of the main sources of the microbial-derived C pool.

Effects of freeze-thaw and soil moisture on content and spectral structure properties of dissolved organic matter in forest soil leachates.

The contents and stability of soil dissolved organic matter (DOM) can affect key processes of soil carbon and nitrogen cycle. The responses of DOM content and its spectral structure pro-perties in forest soils to climate change remain unclear. We collected soil samples from two temperate forests, i.e., the broadleaf and Korean pine mixed forest (BKPF) and adjacent secondary white birch forest (WBF), in Changbai Mountains, northeastern China. Using a combination of three-dimensional fluorescence spectrum and parallel factor analysis, a simulated freeze-thaw experiment was conducted in the laboratory. We examined the effects of freeze-thaw intensity, freeze-thaw cycle and their interaction on the content, components and spectral properties of DOM leached from the two forest surface soils with different moisture levels. The results showed that DOM content and components of soil leachates varied with forest types, soil moisture, freeze-thaw intensity and freeze-thaw cycle. The DOM content in the leachates was lowest at medium moisture level and was significantly affected by the high freeze-thaw intensity. In addition, the DOM content increased first and then decreased with the increases of freeze-thaw cycles. Three fluorescence components of DOM in the forest soil leachates were identified as humic acid-like DOM, fulvic acid-like DOM and protein-like DOM. The DOM components of BKPF soil leachates were mainly consisted of fulvic acid-like substances with a high humification index. However, the DOM from WBF soil leachates was dominated by humic acid-like substances with low stability, and the three fluorescence components were significantly affected by the freeze-thaw intensity. Results from the redundancy analysis showed that under the experimental conditions, forest type played a leading role in changing DOM properties. The DOM content and its three fluorescence intensities of WBF soil leachates were higher than those of BKPF. Soil moisture significantly affected the aromaticity of DOM in the forest soil leachates, and the DOM aromaticity of soil leachates from the two forest stands ranked as medium moisture > high moisture > low moisture. With the increases of freeze-thaw intensity, the DOM aromaticity of BKPF soil leachates significantly decreased. Furthermore, the increases of freeze-thaw cycles significantly increased the humification degree of DOM in the forest soil leachates. Therefore, upon different freeze-thaw disturbance, the DOM content and bioavailability of soil leachates with low moisture tended to increase, particularly in the WBF soil leachates, which may result in an increased lea-ching of DOM in temperate forest soils during spring freeze-thaw periods. The results provide a refe-rence for further investigating DOM turnover in temperate forest soils during spring freeze-thaw periods.

Productivity Estimations for Monospecific and Mixed Pine Forests along the Iberian Peninsula Aridity Gradient

National Forest Inventories (NFIs) are the primary source of information to fulfill international requirements, such as growing stock volume. However, NFI cycles may be “out of phase” in terms of the information required, so prediction techniques are needed. To disentangle the effects of climate and competition on stand productivity and to estimate the volume of stocks at national scale, it is important to recognize that growth and competition are species-specific and vary along climatic gradients. In this study, we estimate the productivity of five pine species (Pinus sylvestris, Pinus pinea, Pinus halepensis, Pinus nigra and Pinus pinaster), growing in monospecific stands or in mixtures along an aridity gradient in the Iberian Peninsula, based on Spanish NFI data. We study the stand volume growth efficiency (VGE), since it allows the comparison of volume growth in monospecific and mixed stands. The results reveal the importance of considering the aridity when assessing VGE. Moreover, it was found that, in general, admixture among pine species leads to modifications in the VGE, which can vary from negative to positive effects depending on species composition, and that this is always influenced by the aridity. Finally, we provide simple growth efficiency models for the studied pines species which are valid for both monospecific and mixed stands along the aridity gradient of the Iberian Peninsula.

Competition of key tree species with selective cutting at different intensities in broadleaved-korean pine mixed forest in the Changbai Mountain, China.

Selective cutting changes tree species composition and stand structure, modifies tree competition intensity in the stand, with consequences on tree growth and population dynamics. Key tree species play a crucial role in maintaining community structure and ecosystem function. To clarify the competitive characteristics of three key species (Pinus koraiensis, Tilia amurensis, and Fraxinus mandshurica, which accounted for about 70% of growing stock) of typical forest types in broadleaved-Korean pine mixed forest, Hegyi competition index was used in four permanent 1-hm2 plots, i.e. virgin forest (VF), low-intensity cutting forest (LCF), moderate-intensity cutting forest (MCF) and high-intensity cutting forest (HCF). Compared with VF, the stand density and mean DBH of big trees (DBH≥20 cm) significantly decreased in MCF and HCF, but the stand density of young trees (2 cm≤DBH<10 cm) increased, but no significant changes of stand or DBH in LCF. In all the four forest types, individual competition index (CI) of the three species decreased with increasing DBH. There was a power function relation between CI and DBH. CI curve turned to be gentle at DBH reaching 20 cm, and this rule was not affected by selective cutting. In VF, LCF and HCF, most of competition pressure of young trees of all key species derived from other tree species in secondary canopy or understory, but the competition pressure of small trees (10 cm≤DBH<20 cm) and big trees of P. koraiensis originated mainly from intra-species and other species in secondary canopy or understory. The competition stress of F. mandshurica was mainly affected by P. koraiensis and other species in secondary canopy or understory. T. amurensis was mainly affected by intra-species and P. koraiensis. Betula platyphylla contributed most of the competition stress (over 50%) to all three key species in HCF. Our results suggested that removing the trees which are in secondary canopy or understory but suppress the three key trees species intensively would be beneficial to the regeneration and growth of key species before tree DBH exceeds 20 cm. We proposed to regulate the density of key tree species in overstory to cultivate large diameter timber according to the competition among the key trees species. Once tree DBH exceeds 20 cm, tree growth would not be affected by competition. This study had guiding significance for the cultivation of key tree species and rapid recovery of natural forests after selective cutting.

Spatio-temporal dynamics of woody plants seed rains in broad-leaved Korean pine mixed forest in Changbai Mountains form 2006 to 2017, China.

Seeds are the basis for forest regeneration. To examine the composition and spatio-temporal dynamics of seed rains, a total of 150 seed traps of 0.5 m2 were installed in a 25 hm2 broad-leaved Korean pine (Pinus koraiensis) mixed forest plot in Changbai Mountains. With a total of 252 collections from May 2006 to September 2017, we collected 764299 mature and immature seeds which were belonged to 27 species, 17 genera, and 12 families. More than 90% of all collected seeds (704231 seeds) were from 13 canopy species. Seeds of four tree species, including Tilia amurensis, Fraxinus mandschurica, Acer mono, and Acer pseudo-sieboldianum could be collected every year from each trap. Mast-seeding was found in every canopy layer, but it happened one to two years earlier in the overstorey layer than midstorey and understorey layer. Almost all species produced seeds in autumn, with considerable spatiotemporal variation. Generally, the spatial variation of seeds was larger than temporal variation. Compared with annual variation coefficient of seeds in tropical forest of the Barro Colorado Island (BCI) and subtropical evergreen forest in the Gutianshan, annual variation coefficient of seeds in Changbai Mountains was higher, which supported the hypothesis that annual variation in seed rains would be lower in the tropics than that in higher latitudes.

Differences of leaf dark respiration and light inhibition between saplings and mature trees of Pinus koraiensis and Tilia amurensis.

Leaf dark respiration is an important component of carbon cycle. Understanding the differences of leaf dark respiration and light inhibition between saplings and mature trees is important for accurate estimation of ecosystem gross primary productivity (GPP). We meansured leaf dark respiration of saplings and mature trees of two dominant species (Pinus koraiensis and Tilia amurensis) in light and in darkness in the broadleaved-Korean pine mixed forest on Changbai Mountain. Differences of leaf dark respiration, light inhibition and leaf physiological and ecological parameters between saplings and mature trees were analyzed. The reason of differences on leaf dark respiration and the light inhibition were explored. The results showed that leaf dark respiration of saplings of two species under light was 6.8%-39.6% higher than that of mature trees in growing season. Light inhibition of leaf dark respiration in saplings was 2.5%-14.1% lower than in mature trees. The difference of light inhibition of leaf dark respiration between saplings and mature trees of P. koraiensis was higher than that of T. amurensis, with a maximum difference of 18.6%. The higher leaf dark respiration and lower light inhibition degree in saplings might result from the changes of max net photosynthesis rate, specific leaf area, and stomatal conductance, instead of leaf nitrogen content.

Effect of neighborhood competition on key tree species growth in broadleaved-Korean pine mixed forest in Changbai Mountain, China.

Competition is the main factor affecting the growth, morphology and death of trees in fore-sts. The analysis of individual competition can reflect the characteristics of interaction among individuals and their interaction ranges, which is important for reducing individual competition and promoting tree growth. To understand the effects of competition on tree growth in broad-leaved Korean pine forest, based on Hegyi single-tree competition index and neighborhood analysis method, we explored the neighborhood radius of competition for five key tree species, i.e. Pinus koraiensis, Tilia amurensis, Fraxinus mandshurica, Quercus mongolica and Ulmus japonica (80% of basal area at breast height in total), and analyzed the effects of competition on the growth and death of the key tree species. The results showed that the neighborhood radius of single-tree competition of four tree species, P. koraiensis, T. amurensis, F. mandshurica and Q. mongolica was 11 m, while that of U. pumila was 13 m. The single-tree competition intensity for all five key tree species was negatively correlated with the logarithm of its growth increment, and positively correlated with the size of individual trees. The relative importance of competition intensity on tree growth decreased with tree growth. Neighborhood competition significantly increased tree mortality. Our results revealed the effects of neighborhood competition on the growth and survival of the key tree species at different developmental stages in broad-leaved Korean pine forests in Changbai Mountain. The results are instructive to the adjustment of competitive environment and the improvement of productivity of key tree species in broad-leaved Korean pine forests.

Latitudinal pattern of soil lignin/cellulose content and the activity of their degrading enzymes across a temperate forest ecosystem

Temperate mixed forests, along with other high latitudinal ecosystems, are more vulnerable to global warming in comparison with warm sites, because of the slower carbon (C) turnover and higher soil organic carbon (SOC) accumulation. Lignin and cellulose are two major components of plant litter, and usually make contributions to the recalcitrant and labile SOC pool, respectively. Because the chemical composition of SOC plays key role in regulating the bioavailability of soil C pool, understanding the relationship between soil lignin or cellulose content and temperature are of great significance in evaluating the feedbacks between SOC pool and the future scenarios of global warming. The biological degradation of soil lignin or cellulose is mainly dependent on soil enzymatic activities, and thus, the response of ligninolytic and cellulolytic enzymes to increased temperature would determine C release under future warming scenarios. However, the responses of the soil lignin/cellulose content and the activity of cellulolytic and ligninolytic enzymes to increased mean annual temperature (MAT) have rarely been studied, and the factors driving these changes are not fully understood. Latitudinal gradients are often used for monitoring global-warming-related problems, because of its natural gradients of temperature. In this study, we demonstrate the latitudinal pattern of lignin/cellulose content and the activities of cellulose- and lignin- degrading enzymes in a temperate Broad-leaved Korean pine mixed forests distributed along a latitudinal gradient (with MAT ranging from −1.9 to 5.1 °C) in northeastern China. The linear mixed model revealed that soil lignin content was negatively correlated with MAT (Slope = −7.604, t = −2.608, P = 0.011), whereas soil cellulose content showed no response to increased MAT. The activity of soil polyphenol oxidase (PPO), one of the enzymes catalyze lignin decomposition, was higher in high-latitude sites, in contrast, the activity of the cellulase (CEL) complex was higher in low-latitude plots. Structural equation model (SEM) analysis indicates that MAT can directly influence soil lignin or cellulose content, and indirectly through changing NRCB, plant litter C/N, microbial biomass, and degrading enzymatic activities. The value of soil lignin/(lignin + cellulose) ratio and soil lignocellulose index (LCI, lignin/(lignin + holocellulose) ratio), varied between 0.8–0.9, and 0.6–0.8, respectively, indicating that the SOC pool in this temperate ecosystem is dominated by recalcitrant components. The negative correlations between MAT and LCI, soil lignin/(lignin + cellulose), and log (PPO + PER)/log(CEL) (Slope = −0.008, t = −2.363, P = 0.021; Slope = −0.004, t = −3.134, P = 0.003, and Slope = −0.057, t = −4.477, P < 0.001, respectively) suggested that the recalcitrance of SOC would decrease with elevated MAT. Thus, we propose the content and the proportion of recalcitrant carbon in soil organic matter will decrease under the projected global warming, and thus, the temperature sensitivity of SOC decomposition will accordingly to be predicted to decline. This may have consequences on SOC stability in this temperate forest ecosystem.

Using Hidden Markov Models for Land Surface Phenology: An Evaluation Across a Range of Land Cover Types in Southeast Spain

Land Surface Phenology (LSP) metrics are increasingly being used as indicators of climate change impacts in ecosystems. For this purpose, it is necessary to use methods that can be applied to large areas with different types of vegetation, including vulnerable semiarid ecosystems that exhibit high spatial variability and low signal-to-noise ratio in seasonality. In this work, we evaluated the use of hidden Markov models (HMM) to extract phenological parameters from Moderate Resolution Imaging Spectroradiometer (MODIS) derived Normalized Difference Vegetation Index (NDVI). We analyzed NDVI time-series data for the period 2000–2018 across a range of land cover types in Southeast Spain, including rice croplands, shrublands, mixed pine forests, and semiarid steppes. Start of Season (SOS) and End of Season (EOS) metrics derived from HMM were compared with those obtained using well-established smoothing methods. When a clear and consistent seasonal variation was present, as was the case in the rice croplands, and when adjusting average curves, the smoothing methods performed as well as expected, with HMM providing consistent results. When spatial variability was high and seasonality was less clearly defined, as in the semiarid shrublands and steppe, the performance of the smoothing methods degraded. In these cases, the results from HMM were also less consistent, yet they were able to provide pixel-wise estimations of the metrics even when comparison methods did not.

Seasonal dynamics of fine root respiration in the degraded and successional primary Korean pine forests in the Lesser Khingan mountains of Northern China

The broad-leaved and Korean pine mixed forests in the Liangshui National Natural Reserve, China, are important components of boreal forests in areas that are sensitive to global climate change. Respiration rates of excised roots were measured using an oxygen electrode (Hansatech Oxy-Lab 2, UK) to examine the variation in and identify the controlling factors of fine root respiration (Rr) during the growing period (May–October) in 2016. The relationships between Rr and biotic/abiotic factors [e.g., soil temperature, live fine root biomass (LFRB), and the soil carbon index] were subsequently analyzed. The results showed that Rr was significantly higher in the secondary broad-leaved forest (SF) than that in the primary Korean pine forest (PK) (p < 0.001); whereas soil carbon sequestration showed the opposite trend (p < 0.05). Rr tended to exponentially increase with soil temperature (p < 0.001) in both forest types. The Q10 value of the PK was significantly higher than that of the SF (p < 0.01). Pearson correlation and regression analyses revealed that Rr was significantly linearly correlated with LFRB, total soil organic carbon, soil soluble organic carbon, and soil microbial biomass carbon (p < 0.01). Stepwise regression was used to further explain that LFRB and soil microbial biomass carbon were the major contributors to changes in Rr (F = 53.97, p < 0.001, R2 = 0.75). The findings of the present study offer insights into the variability of the soil carbon sink function in the degraded and successional primary Korean pine forests.