Understory Removal Research Articles

Managing both overstory and understory vegetation mitigates the impact of drought on soil nematode communities in a Mediterranean pine forest

Forest management strategies can effectively mitigate the impacts of drought on tree species, but their effects on soil fauna remain largely unexplored. Among soil organisms, soil nematodes can serve as valuable bioindicators to assess the impact of forest management on soil biodiversity and soil functioning. Consequently, we investigated two related questions in a Mediterranean Pinus halepensis Mill. forest located in southeastern France. First, how do soil nematodes respond to forest management practices? Second, can forest management practices help modulate the effects of Mediterranean summer drought on these soil organisms? We conducted a field experiment in which we explored the influence of two forest management techniques—tree thinning (intense, moderate, or absent) and understory removal (shrubs present or absent)—on soil nematodes before and after the summer drought. We found that only total and bacterivorous nematode abundances were positively influenced by the forest management practices. The highest values were observed under conditions of intense thinning combined with shrub presence, with an average of 97,509 individuals per kg of dry soil. In contrast, the abundances of all nematodes, with the exception of predaceous nematodes, were lower after the summer drought with a reduction ranging from −55 % to −82 %. Total, bacterivorous, and fungivorous nematode abundances were less negatively affected by the summer drought under conditions of moderate thinning when shrubs were present versus absent. More generally, we discovered that bacterivorous and fungivorous nematodes were particularly sensitive to the forest management practices and the summer drought. It is thus apparent that habitat alterations induced by forest management can strongly affect nematode community structure and could therefore prompt shifts in ecosystem functioning. Finally, this study highlights that, in forests, understory vegetation can have significant positive impacts on soil nematode populations when severe dry periods occur.

Effects of thinning and understory removal on soil phosphorus fractions in subtropical pine plantations.

Forest management changes the physical environments and nutrient dynamics and then regulates the forest productivity. Soil phosphorus (P) availability is critical for productivity in tropical and subtropical forests. However, it was still poorly understood how soil P content and fraction respond to various forest management practices in these regions. Here, we measured the soil total P, available P, and Hedley's P fractions, including inorganic and organic P (Pi and Po), in subtropical pine plantations treated with understory removal (UR), non-dominant species thinning (NDST) and dominant species thinning (DST) after nine years. Compared to plantations without management (CK), treatments such as UR, NDST, and DST decreased soil total P at 0-10 cm and soil available P at 0-10 cm and 10-20 cm. Increases in resin-Pi, NaOH-Pi, and C.HCl-Pi resulted in a higher total Pi in 0-10 cm (p < 0.05) in treated plots (UR, NDST, and DST) than in CK plots. UR, NDST, and DST treatments increased NaHCO3-Po and NaOH-Po (p < 0.05) but decreased C.HCl-Po at a depth of 0-10 cm. Regardless of management treatments, soil total P, available P, and P fractions in 0-10 cm showed higher contents than those in 10-20 cm. There were positive relationships between total P and total Po (p < 0.01) and between available P and total Pi. There were also positive relationships between total P, available P, NaHCO3-Pi, and NaOH-Pi (p < 0.05). In conclusion, forest management such as UR, NDST, and DST decreased soil total P and available P, and transforming soil P fractions to available P will meet the P demand following management in the pine plantations of subtropical China.

Short-term effects of understory removal on understory diversity and biomass of temperate forests in northeast China

IntroductionUnderstory removal is a traditional practice in forest management to reduce fire risk and promote seedling regeneration. However, its effect on understory diversity, biomass and soil nutrients in temperate forest ecosystems is less known, which limits our assessment of the effectiveness of understory vegetation management.MethodsWe quantified the composition of the understory species, their diversity, and the biomass of the understory and factors driving changes in these parameters in primary mixed broad-leaved Pinus koraiensis forest (BKF), secondary Betula platyphylla forest (BF), and Larix gmelinii plantation (LF) in northeast China after a 5-year understory removal.ResultsAfter understory removal, the number of shrub and herb species in BKF and LF decreased, while the number of shrub species in BF increased significantly and that of herb species decreased; the species with strong light preference, Equisetum hyemale, Impatiens noli-tangere, and Filipendula Palmata, were dominant in the herb layer of the three forest types; Shannon–Wiener diversity, Pielou evenness, and Simpson diversity of the herb layer in LF increased significantly (P &amp;lt; 0.05), while those of the shrub and herb layers in BF and LF showed no significant changes (P &amp;gt; 0.05). The total understory biomass of understory of BKF and LF decreased by 0.94 t·hm−2 and 1.32 t·hm−2, respectively, while that of BF increased by 1.31 t·hm−2; soil NH4+-N and total phosphorus (TP) were the key factors regulating understory vegetation diversity and biomass, respectively.ConclusionThese results suggest that understory removal is a beneficial management strategy for increasing shrub biomass and diversity in secondary forests, while it should be avoided in primary forests and plantations to prevent the reduction of understory plant diversity and soil nutrient loss.

Linkages among leaf nutrient concentration, resorption efficiency, litter decomposition and their stoichiometry to canopy nitrogen addition and understory removal in subtropical plantation

BackgroundThe prevalence of understory removal and anthropogenic nitrogen (N) deposition has significantly altered the ecological processes of forest ecosystems at both regional and global scales. However, it remains a pressing challenge to understand how N deposition and understory removal affect leaf nutrient dynamics, nutrient resorption, litter decomposition, and their linkages for better managing forest ecosystems under nutrient imbalances induced by N enrichment. To address this research gap, a field manipulation experiment was carried out in a subtropical Cunninghamia lanceolata plantation with four treatments including: control (CK), canopy N addition (CN), understory removal (UR), and canopy N addition plus understory removal (CN × UR). Green and senesced leaf N and phosphorus (P) concentrations, N and P resorption efficiencies, litter decomposition, and their correlations were measured.ResultsThe results revealed that the average N concentrations of green early and late leaves in UR were increased by 6.61 and 18.89% compared to CK. UR had the highest whereas CN had the lowest P concentrations in green leaves across the two sampling seasons. Following this, UR, leaf type, season, and their interactions significantly affected leaf N, P, and N:P (P < 0.05). The highest leaf N resorption (32.68%) and P resorption efficiencies (63.96%) were recorded in UR. Litter decomposition was significantly retarded in UR (P < 0.01) relative to CN. The regression analysis demonstrated that leaf nutrient status was significantly interconnected with leaf nutrient resorption efficiencies. In addition, leaf nutrient dynamics were strongly correlated with litter nutrients, indicating that both were coupled.ConclusionThese findings can deepen our knowledge of biogeochemical cycling and reveal contrasting nutrient-acquisition strategies on N and P limitation in response to UR and CN. Considering the P limitation, it is important to note that P was resorbed more efficiently, illustrating a remarkable nutrient preservation approach for nutrient-limitations. Resorption may be a crucial mechanism for keeping nutrients in these forests, so better understory management practices are required to prevent reliance on external nutrient pools. Overall, this study sheds meaningful insights into the ability of forest adaptation in response to global climatic change.

Canopy nitrogen addition and understory removal destabilize the microbial community in a subtropical Chinese fir plantation

Subtropical Chinese fir plantations have been experiencing increased nitrogen deposition and understory management because of human activities. Nevertheless, effect of increased nitrogen deposition and understory removal in the plantations on microbial community stability and the resulting consequences for ecosystem functioning is still unclear. We carried out a 5-year experiment of canopy nitrogen addition (2.5 g N m−2 year−1), understory removal, and their combination to assess their influences on microbial community stability and functional potentials in a subtropical Chinese fir plantation. Nitrogen addition, understory removal, and their combination reduced soil bacterial diversity (OUT richness, Inverse Simpson index, Shannon index, and phylogenetic diversity) by 11–18%, 15–24%, and 19–31%; reduced fungal diversity indexes by 3–5%, 5–6%, and 5–7%, respectively. We found that environmental filtering and interspecific interactions together determined changes in bacterial community stability, while changes in fungal community stability were mainly caused by environmental filtering. Fungi were more stable than bacteria under disturbances, possibly from having a more stable network structure. Furthermore, we found that microbial community stability was linked to changes in microbial community functional potentials. Importantly, we observed synergistic interactions between understory removal and nitrogen addition on bacterial diversity, network structure, and community stability. These findings suggest that understory plants play a significant role in promoting soil microbial community stability in subtropical Chinese fir plantations and help to mitigate the negative impacts of nitrogen addition. Hence, it is crucial to retain understory vegetation as important components of subtropical plantations.

Effects of thinning and understory removal on water use efficiency of Pinus massoniana: evidence from photosynthetic capacity and stable carbon isotope analyses

Effects of thinning and understory removal on water use efficiency of Pinus massoniana: evidence from photosynthetic capacity and stable carbon isotope analyses

Niches, interspecific associations, and community stability of main understory regeneration species after understory removal in temperate forests.

Understory removal is frequently used to relieve the renewal pressure on trees and promote the growth capability of trees for maintaining community stability, while the lack of previous study on temperate forests limits our assessment of the effectiveness of this essential management measurement. In this study, we calculated the niche characteristics and interspecific association of main understory species and community stability in temperate forests [original broad-leaved Korean pine forest (BKF), Betula platyphylla secondary forest (BF), and Larix gmelinii plantation (LF)] after understory removal for characterizing the resource utilization capacity of the regeneration trees. During the restoration stage, the niche breadth of understory plants with similar habits varied across stands and layers; regeneration tree species with heliophile and semishade occupied a larger niche in BKF and LF, while it was the opposite in LF. Niche overlap among heliophile regeneration trees increased in both BKF and BF, but not in LF. The interspecific association among main species revealed that the distribution of each species was independent and the interspecific association was loose and it varied in different forests and different light-demanding species with regeneration trees. The stability of shrub communities in BF and LF improved whereas that of BKF declined, while that of the herb communities of corresponding forests showed the opposite state. Our study demonstrated that the effectiveness of understory removal depends on species' ecological habits, which enhances the renewal and resource utilization capacity of regeneration tree species in temperate forests and shrub community stability in BF and LF.

Understory vegetation removal significantly affected soil biogeochemical properties in forest ecosystems

Understory vegetation plays a crucial role in mediating the natural development of forest ecosystems. The removal of understory vegetation, as a common forest management practice, may have a significant impact on soil properties. However, a global perspective on how understory removal might affect soil biogeochemical properties is still lacking. To fill this knowledge gap, we performed a meta-analysis with 2059 observations collected from 71 peer reviewed publications to evaluate the effects of understory vegetation removal on soil carbon (C), nitrogen (N), phosphorus (P), potassium (K), and microbial biomass. We found that (1) removal of the understory significantly increased soil nitrates (NO3−) concentration by 6.5 %, but decreased the stocks of C and N, the concentrations of N, available K (AK) and microbial biomass C (MBC), and fine root biomass by 19.4, 15.1, 7.9, 19.9, 13.5 and 32.2%, respectively; (2) mycorrhizal association significantly mediated understory removal effects on soil organic C (SOC) and dissolved organic C (DOC) concentrations, and soil pH, while canopy type had a significant impact on the effects of understory removal on soil K, AK, NO3−, MBC concentrations, C:N ratio, and soil pH; (3) soil depth had a negative impact on the effects of understory removal on SOC, AK, ammonium nitrogen (NH4+) concentrations, and soil moisture; and (4) mycorrhizal association, soil depth, slope, forest stand age, elevation, and MAT were the most important moderator variables. Our results suggest that the removal of understory vegetation generally have negative effects on soil biogeochemical properties, and that managing understory vegetation is important for promoting the healthy development of forest ecosystems.

Effects of fertilisation and understory removal on aboveground and belowground carbon stocks in wet and dry moorlands in south-western France

Effects of fertilisation and understory removal on aboveground and belowground carbon stocks in wet and dry moorlands in south-western France

Altered energy dynamics of multitrophic groups modify the patterns of soil CO2 emissions in planted forest

Soil microbes and fauna as key components of belowground food webs play important roles in energy flux and carbon cycling in terrestrial ecosystems. However, it remains unclear whether forestry management regimes alter the energetic structure of soil food webs and thereby reshape the patterns of soil CO2 emissions in planted forest. Here, we tested the effects of legume (Cassia alata) addition, understory removal, understory removal with legume addition and all plants removal on energy fluxes through soil food webs and soil CO2 flux in the wet and dry seasons. We show that soil heterotrophic respiration contributed 36.9–57.8% of total CO2 flux in the soil. In the dry season, C. alata addition increased soil heterotrophic respiration by 24.6% and 57.3%, respectively, when compared with the control and understory removal treatment. Compared with the understory removal treatment, the total energy flux across the whole food web increased with legume addition (i.e., C. alata addition and understory removal with C. alata addition). Legume addition supported a high proportion of energy flux through herbivorous nematodes, whereas understory vegetation removal supported a high proportion of energy flux through microbivorous nematodes. Less energy fluxes were transferred from basal resources to fungivorous mites and collembolans compared with microbivorous and herbivorous nematodes. The total soil CO2 flux was positively correlated with metabolic rates of herbivorous and omnivorous-predatory nematodes, and energy fluxes through multitrophic groups. Taken together, legume addition and understory vegetation removal modify the patterns of soil CO2 emissions via changing nematode metabolic rates and re-shaping the energetic structure of soil food webs.

Responses of natural and artificial pin oak (Quercus palustris) reproduction to a sequence of silvicultural release treatments in bottomland hardwood forests in southern Missouri

Developing competitive oak advance reproduction prior to canopy disturbance is understood to be important for oak regeneration success. In the early 2000s, a study was installed in southeastern Missouri to examine the effects of midstory and understory release on natural and artificial sources of pin oak (Quercus palustris Muenchh.) advance reproduction. The findings obtained three years after midstory and understory release indicated photosynthetically active radiation increased from 3 to 15 % and a corresponding increase in density of pin oak reproduction as well as the survival and growth of both natural and artificial pin oak reproduction compared to control. In 2010, eight years after the midstory and understory was removed, three different overstory harvests were applied to release the established pin oak advance reproduction. Here, we investigated the effects of the midstory and understory removal and the subsequent overstory harvests on underplanted and naturally regenerated oak advance reproduction. We also tested effects of a later midstory release on the density of natural pin oak advance reproduction. Results indicate that the survival of bareroot pin oak seedlings increased with increasing initial basal diameter. The survival of Root Production Method (RPM®) container pin oak seedlings, however, was not dependent on the size at the time of planting. The early understory removal with triclopyr herbicide was ineffective in ensuring survival of planted pin oak seedlings. Shelterwood increased the growth of oak advance reproduction but did not eliminate competition from other species. A late release also failed to increase the growth of oak advance reproduction. Given shelterwood also favored oak competitors in our study, multiple applications of midstory and understory competition control treatments following the shelterwood treatment will be imperative for successful oak regeneration.

Soil bacterial community is more sensitive than fungal community to canopy nitrogen deposition and understory removal in a Chinese fir plantation.

Soil microorganisms are key regulators for plant growth and ecosystem health of forest ecosystem. Although previous research has demonstrated that soil microorganisms are greatly affected by understory nitrogen (N) addition, little is known about the effects of canopy N addition (CNA) and understory management on soil microorganisms in forests. In this study, we conducted a full designed field experiment with four treatments: CNA (25 kg N ha–1 year–1), understory removal (UR), canopy N addition, and understory removal (CNAUR) (25 kg N ha–1 year–1), and control in a Chinese fir plantation. High-throughput sequencing and qPCR techniques were used to determine the abundance, diversity, and composition of bacterial and fungal communities in three soil layers. Our results showed that CNA increased bacterial diversity in the 10–20 cm soil layer but decreased bacterial abundance in the 20–40 cm soil layer and fungal diversity in the 0–10 cm soil layer. UR increased bacterial abundance only in the 20–40 cm soil layer. CNA, not UR significantly altered the compositions of soil bacterial and fungal community compositions, especially in the 0–20 cm soil layer. CNA sharply reduced the relative abundance of copiotrophic taxa (i.e., taxa in the bacterial phylum Proteobacteria and the orders Eurotiales and Helotiales in the fungal phylum Ascomycota) but increased the relative abundance of oligotrophic taxa (i.e., in the bacterial phylum Verrucomicrobia). RDA analysis revealed that soil pH, DON, and DOC were the main factors associated with the variation in bacterial and fungal communities. Our findings suggest that short-term CNA changes both soil bacterial and fungal communities, with stronger responses in the surface and middle soil than in the deep soil layer, and that UR may enhance this effect on the soil bacterial abundance. This study improves our understanding of soil microorganisms in plantations managed with understory removal and that experience increases in N deposition.

Contrasting Effect of Thinning and Understory Removal on Soil Microbial Communities in a Subtropical Moso Bamboo Plantation

Thinning and understory clearance are among the two most popular forest management practices carried out to improve stand productivity in subtropical plantations. Unfortunately, studies have not fully explored the single and combination effect of thinning and understory clearance on soil microbial properties. By conducting a field manipulation experiment in a subtropical moso bamboo (Phyllostachys edulis) plantation in Southern China, we assessed the effects of thinning, understory clearance, and their combination on soil microbial phospholipid fatty acids (PLFAs) three years after treatments were first applied. We also examined the changes in soil properties after thinning and/or understory clearance. Thinning decreased soil fungal and bacterial PLFAs, and consequently soil total microbial PLFAs due to the increased soil NH4+-N, and NO3−N concentrations. Understory clearance decreased soil pH and soil water content resulting in increased soil fungal PLFAs and the ratio of soil fungal to bacterial (F:B). In addition, thinning and understory clearance caused apparent interactive effects on soil total microbial PLFAs and bacterial PLFAs, and the negative influence of thinning on soil total microbial and bacterial PLFAs were partly compensated by understory clearance. These results suggest the contrasting and interactive effect of thinning and understory clearance should be considered to assess the changes of soil microbial community and ecological processes in subtropical moso bamboo (Phyllostachys edulis) plantations in southern China.

A meta-analysis of understory plant removal impacts on soil properties in forest ecosystems

Understory plants have an important role in regulating various functions and processes in forest ecosystems. However, the overall consequences of understory plant losses on soil properties remain unclear. Here, we used a meta-analysis to determine overall trends in soil organic carbon, total nitrogen and microorganism following understory removal experiments in forest ecosystems of China. Sites with removed understories exhibited significant increases in soil temperature and decreases in soil organic carbon, total nitrogen, soil water content, pH, and microbial biomass. Fungi responded more quickly to plant removal than bacteria. Negative effects were increased with treatment duration and were stronger in broad-leaved forests than in coniferous forests. The responses of soil water, nutrient content, and microbial community composition to understory plant removal diminished as mean annual temperature and precipitation decreased. Our study showed that the effects of understory plant removal on soil properties varied among experimental durations, ecosystem types, and environmental factors (i.e., mean annual temperature, mean annual precipitation, and latitude). These results indicate that understory plants help in sustaining soil organic carbon, total nitrogen, and microbial activities in forest ecosystems. Our findings suggest that understory plants should be maintained to support the health of forest ecosystems.

Understory plant removal counteracts tree thinning effect on soil respiration in a temperate forest.

Elucidating the response mechanism of soil respiration (Rs) to silvicultural practices is pivotal to evaluating the effects of management practices on soil carbon cycling in planted forest ecosystems. However, as common management practices, how thinning, understory plant removal, and their interactions affect Rs and its autotrophic and heterotrophic components (Ra and Rh) remains unclear. Therefore, we investigated Rs, Ra and Rh by the trenching method from 2011 to 2015 in a Pinus tabuliformis plantation in northern China, subjecting to four treatments (intact control plots [CK], thinning [T], understory removal [UR], and thinning with understory removal [TUR]). Mean annual Rs was significantly increased by thinning (by 15.3%), whereas decreased by UR (by 17.4%), compared with CK. These variations in Rs were mainly attributed to changes in Ra. The increments of Ra were caused by the enhanced growth of fine root biomass after thinning. However, UR led to lower Ra compared with CK (p < .05), indicating that understory growth is inadequate to compensate for the decreased respiring root biomass induced by understory removal. Rs was unchanged between TUR and the intact control plot due to the opposite effects of thinning and UR on the Ra. Changes in Rh exhibited no significant differences among the treatments, partly because of the stable microbial biomass carbon (MBC) and forest floor mass (litter and fine woody debris). No interaction effect between thinning and understory removal was detected on Rs, Ra, and Rh. The lowest temperature sensitivity (Q10 ) value of Ra was found in CK. This study highlights the necessity of incorporating understory plant effects on soil CO2 efflux in assessing forest management practices on soil carbon cycling.

Prescribed fire and other fuel-reduction treatments alter ground spider assemblages in a Southern Appalachian hardwood forest

Prescribed burns and understory thinnings are forest management practices aimed at reducing fuel loads to lessen wildfire threat in the Southern Appalachians, USA. Spiders play a critical role in forest ecosystems by controlling insect populations and providing an important food source for vertebrates. We used pitfall and colored pan traps to investigate how abundance, species richness, and diversity of spiders differed among three fuel reduction treatments administered repeatedly over a 15-year period and untreated controls. Additionally, we examined how spiders responded to one round (before and after) of fuel reduction treatments. We established treatments within the 15-year period as follows: mechanical understory removal (twice; M), prescribed burning (four times; B), mechanical understory removal followed one year later by high-severity prescribed burns and three subsequent burns (MB), and untreated controls (C). Our study period (2014–2016) occurred after multiple prescribed burns and two rounds of mechanical understory removal had occurred. Salticidae and Lycosidae were the two most commonly collected spider families in Southern Appalachian hardwood forests. Generally, we found increased spider abundances within all fuel-reduction treatments compared to controls. Individual spider families and species showed variable responses to treatments, but abundance of several spider families was greater in one or more fuel-reduction treatments than in controls. Additionally, abundance of several spider families and hunting/web building guilds (webs built for hunting purposes or defense) exhibited yearly differences to the last round of fuel-reduction treatments. Overall, our results suggest that changes in the overstory and understory of a forest are important drivers of regional spider abundance and assemblages, and forest management practices that modify forest structure can dramatically alter spider abundance and richness, usually in a positive manner.

Understory vegetation interacts with nitrogen addition to affect soil phosphorus transformations in a nutrient-poor Pinus sylvestris var. mongolica plantation

Globally increasing atmospheric nitrogen (N) deposition has aggravated phosphorus (P) limitation in many forests around the world. However, how N deposition affects soil P transformations and what is the role of understory vegetation in regulating these N deposition impacts are largely unknown. Here, we examined soil P transformation characteristics (P fractions, adsorption capacity, and related soil physicochemical properties) in a nutrient-poor Mongolian pine (Pinus sylvestris var. mongolica) plantation that has been subjected to six years of N addition and understory removal treatments in northern China. Nitrogen addition alone significantly elevated labile and moderately labile organic P concentrations by 1.2 times and 24.1%, but decreased labile inorganic P and occluded P concentrations by 42.8% and 41.5%. Nitrogen addition elevated maximum P adsorption capacity, but did not affect maximum buffer capacity. Understory removal alone significantly reduced occluded P concentration by 38.6% but did not affect other P fractions. There were significantly negative interactions between understory removal and N addition on labile inorganic P, all organic P fractions and occluded P concentrations, as N addition effects on these variables were non-significant when the understory vegetation was removed. These results indicate that N addition depressed mineralization of organic P, but accelerated solubilization of occluded P, and these N addition effects were alleviated by understory removal. Significantly positive correlations between soil pH, microbial biomass and P fractions suggest that reduction in soil pH and microbial biomass are largely responsible for the variation in soil P fractions. These findings greatly improve our understanding of the consequences of N addition on soil organic and inorganic P transformations and the role of understory vegetation in affecting the responses of soil P transformation to N deposition.

Litter removal exerts greater effects on soil microbial community than understory removal in a subtropical-warm temperate climate transitional forest

Litter and understory play important roles in maintaining structure and functions of belowground ecosystems in forests. However, how litter and understory affect soil microbial community is unclear. As part of a three-year (2016–2018) manipulative experiment, this study was designed to evaluate the effects of litter and/or understory removal on soil microbial community in a coniferous-broadleaved mixed forest of the subtropical-warm temperate transition zone in Central China. The results showed that soil moisture, NO3−-N, NH4+-N, and dissolved organic carbon were decreased under litter removal, but remained unchanged under understory removal. Total, bacteria, and actinomycetes PLFAs were significantly reduced by 11.2%, 16.3%, and 11.0% under litter removal, and by 10.1%, 13.3%, and 12.5% under understory removal, respectively. Both litter and understory removal suppressed network complexity of soil microbial community, but litter removal showed much stronger impacts on the biomass (−14.9 mg kg−1 vs. −10.9 mg kg−1) and composition (−7.77% vs. −2.89%) of bacteria (including gram-positive and gram-negative bacteria) as well as fungi to bacteria ratio than understory removal. Changes of soil NH4+-N and moisture might be primarily responsible for the inhibitory effects of litter removal on soil gram-positive and gram-negative bacterial biomass, respectively. Our findings highlight the contrasting responses of soil microbial community to litter and understory removal and would facilitate the mechanistic understanding of these two management practices on belowground ecology in climate transitional forests.

Effects of understory removal and thinning on water uptake patterns in Pinus massoniana Lamb. plantations: Evidence from stable isotope analysis

Understanding the dynamic relationships between water uptake patterns and forest management in plantations is important for predicting the impacts of climate change and tailoring forest restoration to mitigate potential impacts. However, the water uptake patterns of overstory trees and associated drivers in plantations with different management practices are poorly understood. In this study, analyses of stable isotopes (δ2H and δ18O), in addition to a MixSIAR model, were applied to assess the water uptake patterns of Pinus massoniana Lamb. under four forest management measures (no thinning: NTN; understory removal: USR; light-intensity thinning: LIT; and heavy-intensity thinning: HIT) under three rainfall events (8.9 mm, 13.3 mm and 67.7 mm) in the Three Gorges Reservoir Area in China. A random forest model and variation partitioning analysis were further used to identify the effects of tree and soil properties on the water uptake patterns of overstory trees. The results indicated that P. massoniana in the NTN and USR stands mainly derived water from deep soil, whereas P. massoniana in the HIT stand absorbed more water from surface soil. P. massoniana in the LIT stand consistently used deep soil water after 8.9 mm of rainfall, and preferred to use shallow soil water after 67.7 mm of rainfall. This result suggested that P. massoniana in the LIT stand has a more competitive advantage over that in the HIT stand through consistent uptake of deep soil water following light rainfall; however, this strategy is more conducive to avoid excessive consumption of deep soil water than the strategies used in the NTN and USR stands as it allows the extraction of shallow soil water following heavy rainfall. The different water uptake patterns of P. massoniana among the four treatments were mainly attributed to differences in tree properties, including leaf biomass, fine-root biomass density, and leaf water potential. Overall, light-intensity thinning may be a suitable forest management practice to optimize the water use strategies of P. massoniana to cope with the changes in precipitation pattern.

Effects of understory removal and litter addition on leaf and twig decomposition in a subtropical Chinese fir plantation

AbstractSubtropical plantations have been undergoing understory removal and increased plant litter inputs due to global change and anthropogenic activities. However, how understory removal and increased litter inputs affect litter decomposition is still unclear in these plantations. Using a field manipulation experiment, we assessed the effects of understory removal and litter addition on decomposition rates of leaf litter, twig litter, and mixed leaf and twig litter over 16 months of incubation in a subtropical Chinese fir (Cunninghamia lanceolata) plantation in southern China. We also examined the changes in soil chemical properties and fungal and bacterial phospholipid fatty acids (PLFAs) after understory removal and litter addition. Litter decomposition rates were inhibited by understory removal due to the decreased fungal PLFAs and the associated declines in the ratio of fungal to bacterial biomass. Litter addition also retarded litter decomposition rates, despite the increases in soil NH4+‐N concentration and fungal PLFAs. However, both litter decomposition rates and soil microbial PLFAs remained unchanged in the presence of both understory removal and litter addition. In all treatments, mixed leaf and twig litter produced additive effects on litter decomposition rates. These results suggest that understory removal and litter addition interact to affect litter decomposition dynamics and highlight that litter mixture decomposition rates could be easily predicted from component litter in subtropical Chinese fir plantations of southern China.