查看更多>>摘要：? 2022 Elsevier B.V.In forest ecosystems, seedling dynamics play a critical role in understanding species coexistence and community assembly. Exploring the effects of key factors on seedling survival can therefore offer key insights into how they interact to affect seedling mortality in natural forests. Based on 5 years of woody seedling census data and tree census data from a 25-ha permanent forest plot in the subtropical-temperate transitional region in the Qinling Mountains of north-central China, we examined the effects of biotic neighborhood processes and habitat heterogeneity as well as their interactions on seedling mortality using survival data of 11,408 seedlings of 69 species (i.e., 30 tree species and 39 shrub species). The results showed that negative density-dependence (NDD) had significant effects on seedling dynamics and survival at community level. Both biotic and abiotic factors affected seedling survival at different ages, but the influence of negative density-dependence was much more significant, especially on the tree seedlings ≥ 5 years old. For the shrub seedlings, however, biotic factors had a larger effect on their survival than abiotic factors. Thus, we concluded that both habitat heterogeneity and negative density-dependent mortality shaped species coexistence at the seedling stage in the deciduous broad-leaved forest.
查看更多>>摘要：? 2022 The AuthorsForest thinning can significantly affect hydrological processes. However, these effects largely vary with forest types, climate, thinning intensity, and hydrological variables of interest. Understanding these effects and their variations can significantly support thinning treatments' design and selection to ensure desired hydrological benefits. In this global-level review paper, we report the first comprehensive meta-analysis on the effects of thinning on major hydrological processes with an emphasis on rainfall partitioning, soil moisture and evapotranspiration processes. The synthesized and reviewed studies encompass different biophysical conditions (climate and forest ecosystems), silvicultural systems, and time scales (from weeks to decades) across continents. The results showed a significant increase in net precipitation, soil moisture and tree-level water use after thinning (the effect sizes are 1.19, 1.14 and 1.56 relative to the value of the control, respectively), while decreases in stemflow and transpiration (the effect sizes of 0.42 and 0.6 relative to the value of the control, respectively). Thinning intensity of about 50% of the stand density is determined as the threshold at or over which hydrological processes are significantly affected. The duration of thinning effect can be set between 2.6 and 4.3 (throughfall) and 3.1–8.6 years (soil moisture and transpiration), asking for repeated thinning in order to effectively sustain these effects. These global averages can serve as benchmarks for assessment and comparisons, but the effects of thinning depend on local biophysical conditions and thinning treatments. The literature review on the rest of the studied hydrological variables suggests that thinning generally enhance runoff to increase water yield and groundwater recharge. Thinning can also have a positive or limited role in water use efficiency (WUE), but it mitigates the effects of drought through increasing WUE. Moderate adverse effects on water quality can be prevented by adequate forest managements to prevent soil degradation. Nevertheless, more researches at relatively less studied regions are needed to support a more robust analysis of these reviewed hydrological variables. The management implications of the synthesized and reviewed results are suggested and discussed within the context of climate change.
查看更多>>摘要：? 2022 Elsevier B.V.Translocating topsoil from an appropriate donor forest is a promising strategy to restore seriously degraded sites. However, some dominant or constructive species did not survive due to plant stress in the seedling stage, which ultimately led to a poor community structure and low similarity between new communities and donor forest. In this study, we replaced the topsoil of karst rocky desertification with forest topsoil and imposed different shading and watering treatments following quadratic saturation D-optimum design. Richness, abundance, height and base diameter of woody species (trees + shrubs) were measured yearly to construct mathematical equation between them and shade degrees (SD) and water quantity (WQ) by using multiple stepwise regression. Results displayed a positive linear relationship between richness of woody species and SD at the second year of topsoil translocation, which changed to a parabolic relationship at the fifth year with a maximum 30.8 species when SD was 37.5 %. The positive linear relationship between density of woody species, shrubs and trees and SD at the second year transformed into a parabolic relationship at the fifth year, and density reached maximum 6.3, 3.7 and 3.8 seedlings/m2 when SD were 41.7, 38.9 and 45.0%, respectively. In contrast, the density of Paliurus orientalis and Sophora viciifolia turned into a negative linear relationship with SD at the fifth year. Moreover, although the effect of SD and WQ on height of woody species increased over time, shading inhibited base diameter of shrubs and height of Quercus cocciferoides, Sapium sebiferum and Fraxinus malacophylla at the fifth year. We concluded that no-shading and heavy shading reduced species diversity, and light to moderate shading should be recommended in first 2–3 years after topsoil translocation to enhance woody species survival and accelerate similar forest community establishment providing guidance for the management, regeneration and restoration of native forest in semi-arid areas.
查看更多>>摘要：? 2022 Elsevier B.V.Many dry conifer forests in the western United States were historically adapted to frequent low-to-moderate severity fires, but are increasingly susceptible to large, stand-replacing wildfires due to dramatically altered stand conditions and changing climate. The historic tree spatial patterns of mature stands in fire-adapted forests – individual trees, clumps of trees, and openings (ICO) – are associated with heightened resistance and resilience to fire. How this pattern develops over time, however, is not well understood and could help inform reforestation practices better designed to increase fire resistance in developing stands. We investigated growth rates and spatial patterns among regenerating trees in mixed-conifer forests with restored fire regimes in California's Sierra Nevada. We compared average stocking densities across tree species, size classes, shrub cover, and fire histories. We also examined the effects of microsite topography on spatial patterning of these juvenile trees, and the effects of clump patterning, local stem density and adjacent shrubs on tree growth rates. We found that the majority (75%) of sampled stems were found in clumps. Our mixed-effect models indicated that for trees growing within clumps, increased crowding slowed tree growth, as expected. Surprisingly, however, compared with individual trees growing outside clumps, trees growing within clumps grew significantly faster. Shrub cover in proximity to juvenile trees did not have a consistent impact across our models, but was associated with increased annual height growth. Additionally, plots with high shrub cover had higher stocking rates among the tallest regenerating stems (height > 137 cm). Our findings indicate that clumped spatial patterns of natural tree recruitment may favor the establishment and early growth of regenerating conifers in active-fire forests. While our study focused only on the early stages (<30 years old) of regeneration, our results contrast with common reforestation strategies favoring regular, widely-spaced plantings and aggressive shrub reduction. Our research suggests we need a better understanding of how heterogeneity in the spatial patterns of juvenile trees and shrubs may enhance the resilience of regenerating stands as they mature.
Tattersall Smith C.Briggs R.D.Stupak I.Barusco B....
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查看更多>>摘要：? 2022 Elsevier B.V.Intensive harvesting of forest biomass for bioenergy has the potential to degrade forest soils and productivity if ecosystem carbon and other nutrients are depleted faster than replenished naturally or by management inputs. Climate change mitigation potential associated with bioenergy may be threatened if forest management operations reduce soil carbon stocks. Research reported here was initiated in 1979 to determine the effects of whole-tree harvesting on long-term site productivity and ecosystem carbon and nutrient pools and fluxes in a northeastern North American temperate balsam fir-red spruce forest. A sequence of harvesting and silvicultural treatments were applied from 1981 to 1993 using a paired-watershed experimental design. Treatments included whole-tree clearcutting, stem-only harvesting, simulated by return of chipped or lopped delimbing residue, conifer release by applying herbicide, and pre-commercial thinning and fertilizer application. Quantitative samples of the forest floor were excavated in 2016. Quantitative soil pits were sampled in 2017 to a depth of 50 cm below the forest floor, where possible; the basal till subsoil was sampled to a depth of 100 cm with an auger. Forest floor samples were analyzed for total carbon, nitrogen, phosphorus, potassium, calcium, magnesium and aluminum. Organic and mineral soil layer samples from the quantitative pits were analyzed for pH, short and long-lived soil carbon via 13C cross polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR), total carbon and nitrogen and extractable phosphorus, potassium, calcium, magnesium and aluminum. Forest floor carbon and nitrogen on whole-tree harvested plots 35 years after harvest were about 50% of the amount on the unharvested watershed. Stem-only harvesting partially mitigated the reduction, and gross losses were apparently offset by increases in the mineral soil solum to depth 50 cm, suggesting that downward translocation of soil organic matter was a significant ecosystem process during the 35 years since harvest. Accumulated forest floor and mineral soil stock of total carbon and nitrogen and extractable nutrients to depth 100 cm did not differ significantly between the harvested and unharvested watershed. A corresponding similarity in mineral soil pools of extractable phosphorus and non-acid cations in the two watersheds suggests that inputs from atmospheric deposition, primary and secondary mineral weathering, organic matter mineralization and litterfall balanced exports including leaching and plant uptake. Ecosystem stocks of extractable phosphorus, base cations, and total organic carbon and nitrogen were maintained 35 years after whole-tree harvesting of a primary spruce-fir forest.
查看更多>>摘要：? 2022 Elsevier B.V.The replacement of natural areas with forestry plantations is a worldwide expanding process with direct consequences for biodiversity and ecosystem functionality. In the Mediterranean region, Eucalyptus spp. plantations are widespread, forming monospecific landscapes that in Portugal dominate most of its forested areas. The reduction in the availability of native habitats induces important challenges to native wildlife, namely changes in habitat use patterns and behavior. In this study, we evaluated the influence of Eucalyptus globulus exotic plantations on the occupancy patterns of the red fox (Vulpes vulpes L.), a mesocarnivore widely distributed in the Palearctic, and we examined potential drivers shaping those patterns. We conducted camera trapping surveys in Central Portugal (Southwestern Europe), in eight 16 km2 grids, and analyzed the resulting occurrence data accounting for imperfect detection. Our analysis revealed a preference of the red fox for native vegetation over non-native plantations and avoidance of areas with higher human disturbance. Our data suggest that the current structure of exotic plantations can have a negative impact on species occurrence, even for generalist and resilient species such as the red fox. By gaining insight into landscape structures that promotes fox occupancy, our research can contribute to the development and implementation of more integrative management measures aiming to promote the presence and conservation of mesocarnivores in Eucalyptus dominated landscapes while ensuring sustainable exploitation of these plantations.
查看更多>>摘要：? 2022 Elsevier B.V.Our understanding of how environmental heterogeneity shapes plant community dynamics is largely based on above-ground diversity despite the importance of seed banks as reservoirs of genetic and taxonomic diversity that buffer plant populations and influence vegetation following disturbance. Using a plant functional trait approach, this study examined the importance of fire-related germination cues and environmental determinants of plant community turnover in wet forests of south-eastern Australia – forests of both high conservation value and the focus of current timber harvesting. We surveyed extant vegetation, soil seed banks, forest structure and edaphic properties across 62 sites burnt in 1939 and not subsequently affected by wildfire or logging. A total of 46 families, and 99 species were identified in extant vegetation with 43 and 126 respectively in the soil seed bank, with only 32% of species co-occurring in both species’ pools. Despite historically long fire return intervals, the soil seed bank demonstrated a clear positive response to fire-related germination cues (heat in combination with smoke) that were concentrated in hard-seeded species dispersed by ants. Seeds from early successional species showed no response to fire cues, while species typical of the wetter margins of these forests were killed by high heat. The soil seed bank was dominated by species associated with early successional stages, consistent with the initial floristics model of succession. Woody species were largely restricted to extant vegetation and replacement is most likely to occur from future seed rain. Spatially structured environmental heterogeneity shaped plant turnover with the relative strength of environmental controls differing among functional types and pools of diversity. Differential response of the combined species pool relative to extant vegetation demonstrates that the soil seed bank provides a storage effect. Forest management practices that generate patchy and heterogenous environments, including the intensity of regeneration burns and density of overstorey species, will benefit biodiversity conservation through overstorey structural controls on resource availability and diversity of understorey vegetation, that is transferred to soil seed banks via tight abiotic controls and seed inputs.
查看更多>>摘要：? 2022 Elsevier B.V.Sewage sludge (SS) application to Eucalyptus urograndis plantations can result in wood yields rivalling those achieved when mineral fertilizers are used. While climatic conditions determine Eucalyptus growth and wood production, the use of fertilizers containing boron (B) can mitigate the impact of drought on Eucalyptus growth. We hypothesized that SS application supplemented with P and B would improve growth and wood production of Eucalyptus planted in the Cerrado region of Brazil. We evaluated wood production and the influence of two years of meteorological seasonality on trunk cross-sectional area (TCSA) growth of Eucalyptus planted on an infertile Oxisol treated with SS. The experiment was conducted on a 54-month-old Eucalyptus urograndis plantation. The treatments were: i) control; ii) two levels of mineral fertilization; iii) seven SS treatments with or without P and/or B. SS application, based on tree N requirement, supplemented with P, resulted in wood production like those produced under mineral fertilization. Within climate variables, rainfall, potential evapotranspiration, and minimum air temperature had the largest influence on Eucalyptus TCSA growth. There was lower accumulated TCSA growth in the cold and dry winter season compared to the hot and rainy summer. However, SS application supplemented with B promoted TCSA growth, enhancing Eucalyptus tolerance to drought periods. In summary, SS supplemented with P and B is a valuable option as an organomineral fertilization management in Eucalyptus plantations, as it improved trunk growth during drought periods as well as wood volume production.
查看更多>>摘要：? 2022 Elsevier B.V.Drought has been observed to decrease the accumulation of carbon (C) and nitrogen (N) in forest ecosystems. The microbial C use efficiency (CUE) and N use efficiency (NUE) are critical to elemental cycling in terrestrial ecosystems, which can be calculated by the C:N stoichiometry of soils, microbial biomass, and extracellular enzyme activities. However, little is known about how drought affects microbial CUE and NUE. We extracted soil samples at different depths (0–15 cm, 15–30 cm, and 30–45 cm) in forest stands that were subjected to 30% and 50% throughfall reduction manipulation experiments, in contrast to those obtained from stands that were left undisturbed from July 2019 to April 2020 in a poplar plantation of Eastern China. Under drought conditions, we found that the soil moisture, soil C:N ratio, and C- and N-acquiring enzyme activities decreased; however, the soil pH, microbial biomass C:N ratio, ecoenzymatic activity C:N ratio, and fungi:bacteria ratio increased. Microbial CUE and NUE, which were calculated based on these C:N stoichiometric ratios, also increased. These responses were similar at different soil depths across sampling dates. Our structural equation models indicated that drought-induced increases in CUE and NUE were driven by changes in the soil moisture, fungi:bacteria ratio, and ecoenzymatic activity C:N ratio. Our results suggested that decreases in soil moisture and increases in the ecoenzymatic activity C:N and fungi:bacteria ratios could stimulate microbial CUE and NUE.
查看更多>>摘要：? 2022 Elsevier B.V.Prescribed burning (PB) is increasingly recognised as a viable, cost-effective technique for reducing wildfire risk. Yet, quantification of the effect of PB on the reduction of wildfire extent in southern Europe is non-existent. We used 35 years of fire mapping data in Portugal to analyse wildfire regime metrics in nine landscapes before (1985–2004) and during (2005–2020), the period when systematic use of PB to reduce fuel load began. We employed robust linear mixed models and generalized linear mixed models to examine the role of annual wildfire extent drivers at landscape scales and quantified the effect of PB on the reduction of subsequent wildfire extent, i.e., leverage. We found evidence of larger wildfires during the PB era, suggesting that other influences are counteracting its putative effect. The most important variables explaining wildfire extent were fire weather and ignition density, with positive effect, and past wildfire and PB extent, with negative effect, corresponding to leverage. We obtained a total past fire (PB and wildfire) leverage of 0.28, i.e., approximately 4 ha of past fire decrease subsequent wildfire by 1 ha, increasing to 0.84 if only landscapes with high wildfire incidence are considered. The analyses failed to unequivocally identify a direct leverage effect of PB but a 1:5 return-for-effort is reasonable as a conservative estimate. Increasing the size of PB treatments and treatment effort in the landscape in combination with fire-modelling assisted planning would enhance PB leverage, making it more effective at reducing wildfire extent, rather than functioning only as a supplement to the effect of previous wildfires.
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