Forest Ecosystem Processes Research Articles

The Role of Regional Ecological Assessment in Quantifying Ecosystem Services for Forest Management

Regional ecological assessments evaluate sustainability as an interaction among ecosystem services and stressors across changing landscapes. Using ecological assessments to inform ecosystem management activities relies on assessing functional linkages between ecosystem processes and ecosystem services, because ecosystem processes are the primary targets of ecosystem management. We undertook a review of regional ecological assessments in the Appalachian region of the United States to examine how forest-based ecosystem services, forest ecosystem processes, and their linkages are quantified. To provide context, we first give an overview of common ecological assessment frameworks, including risk, vulnerability, resilience, and indicator-based approaches. Assessments tended to target either ecosystem-level properties thought to be important for ecosystem service sustainability, or else to target specific ecosystem services or stressors. Forest ecosystem-level assessment most often relied on specific indicators for system properties such as integrity or health, but how those properties or their indicators were related to ecosystem services was typically not quantified. Individual ecosystem services were frequently assessed in terms of risk and vulnerability to specific external stressors, but linkages to ecosystem processes, and potential tradeoffs among ecosystem services, were infrequently quantified. Integrated system-level assessment and ecosystem service assessment can improve support for ecosystem management by advancing our understanding of dependencies on the ecosystem processes that are modified through management. Models that evaluate ecosystem services and underlying processes in a systems context offer one approach to do so.

Soil properties and microbial community in the rhizosphere of Populus alba var. pyramidalis along a chronosequence

By maintaining soil structure and quality, soil microbial communities usually play important role in many forest ecosystem processes, including ecological succession. Understanding changes in the microbial communities of areas afforested with stands of different ages is of interest in ecology. Populus alba var. pyramidalis Bunge has been widely planted in Northwest China for ecological restoration. Rhizospheric soil samples were collected from 4-, 9-, 15-, 25- and 30-year-old plantations of P. alba to measure soil characteristics and soil microbial community diversity using Illumina MiSeq sequencing. The soil nutrition concentration and enzymatic activities decreased with depth of soil layer increased. In terms of stand age, alkaline phosphatase and dehydrogenase and the contents of nitrate N, available P and soil organic content (SOC) increased gradually. According to Illumina MiSeq sequencing results, the fungal and bacterial community structure varied with stand age, and diversity of fungi was less than bacteria. With increasing stand age, fungal community diversity indexes first increased and then decreased, peaked at 25y or 30y. RDA results suggested that soil available P and nitrate N were the most important factors governing fungal community structure, while available P contributed significantly to the variance of the bacterial community. Structural equation modelling (SEM) results indicated soil available P, nitrate N and SOC contents largely explained the shift in the microbial community structure along the cultivation chronosequence, and soil enzyme activities were related with changes in microbial community. Our results illustrated that the successional changes in microbial communities in the P. alba plantations can largely be attributed to changes in soil nutrition level along the chronosequence.

Predicting the responses of subalpine forest landscape dynamics to climate change on the eastern Tibetan Plateau.

Subalpine vegetation across the Tibetan Plateau is globally one of the most sensitive to climate change. However, the potential landscape-scale effects of climate change on subalpine forest dynamics remain largely unexplored. Here, we used a forest landscape model (LANDIS-II) coupled with a forest ecosystem process model (PnET-II) to simulate forest dynamics under future climate change in Jiuzhaigou National Nature Reserve in the eastern subalpine region of the Tibetan Plateau. We examined changes in the composition, distribution and aboveground biomass of cold temperate coniferous forests, temperate coniferous forests, deciduous broad-leaved forests and redwood forest under four climate change scenarios (RCP2.6, RCP4.5, RCP8.5 and the current climate) from 2016 to 2096. Our model predicts that by 2096, (i) cold temperate coniferous forests will expand and increase by 7.92%, 8.18%, 8.65% and 7.02% under current climate, RCP2.6, RCP4.5 and RCP8.5scenarios, respectively; (ii) distribution of forests as a whole shows upward elevational range shift, especially under RCP8.5scenario and (iii) total aboveground biomass slowly increases at first and then decreases to 12%-16% of current distribution under RCPs. These results show that climate change can be expected to significantly influence forest composition, distribution and aboveground biomass in the subalpine forests of eastern Tibetan Plateau. This study is the first to simulate forest dynamics at the landscape scale in subalpine areas of the Tibetan Plateau, which provides an important step in developing more effective strategies of forest management for expected climate change, not only in China but also around the world.

The Effect of Repeated Prescribed Burning on Soil Properties: A Review

Prescribed burning is a tool that is frequently used for various land management objectives, mainly related to reduction of hazardous forest fuels, habitat management and ecological restoration. Given the crucial role of soil in forest ecosystem processes and functions, assessing the effects of prescribed burning on soil is particularly relevant. This study reviews research on the impacts of repeated prescribed burning on the physical, chemical and biological properties of soil. The available information shows that the effects are highly variable, rather inconsistent and generally minor for most of the soil characteristics studied, while a number of soil properties show contrasting responses. On the other hand, ecosystem characteristics, differences in fire severity, frequency of application and the cumulative effect of treatment repetition over time, have possibly made it more difficult to find a more common response in soil attributes. Our study has also revealed some limitations of previous research that may have contributed to this result, including a limited number of long-term studies, conducted at a few experimental sites, and in a limited number of forest ecosystems. Research issues concerning the effects of prescribed fire on soil are presented. The need to integrate such research into a broader interdisciplinary framework, encompassing the role of the fire regime on ecosystem functions and processes, is also highlighted.

Soil physico-chemical properties have a greater effect on soil fungi than host species in Mediterranean pure and mixed pine forests

Soil fungi are fundamental drivers of forest ecosystem processes. Soil physico-chemical parameters and vegetation features such as host type or stand structure can affect soil fungal communities. However, there is a lack of comprehensive studies describing the relative importance of niche processes (soil physico-chemistry and forest structural drivers) versus neutral processes (geographical distance) driving soil fungal community assemblages, especially in less-studied drought-prone ecosystems such as Mediterranean forests. In this study, we performed Pacific Biosciences sequencing of internal transcribed spacer 2 amplicons to characterize the soil fungal community composition and diversity of 42 forests dominated by either pure Pinus nigra, Pinus halepensis or Pinus sylvestris or a P. nigra–P. halepensis or P. nigra–P. sylvestris mixture. Our specific aims were to identify and disentangle the relative importance of the main soil characteristics and the spatial and forest structural factors that accounted for the greatest proportion of fungal community variation along a regional gradient in the Mediterranean Pre-Pyrenees. Soil parameters accounted for the greatest significant proportion of the total variance in the overall fungal community (25%), in the mycorrhizal (23%) and saprotrophic (22%) communities, while geographical distance accounted for 14% of the variance in the overall fungal community, 7% in the mycorrhizal and 22% in the saprotrophic communities. Conversely, forest structure did not significantly affect the soil fungal community, as fungal composition and diversity did not differ significantly among the pine hosts. Moreover, pH, followed by P and the C:N ratio explained the largest differences in the composition of the overall fungal community and in the mycorrhizal fungal community. By contrast, the largest proportion of differences in saprotrophic composition were explained by geographical distance, closely followed by the C:N ratio and N. Our results show that, in these Mediterranean pine forests, soil parameters are the most important driving forces shaping soil fungal communities at the regional scale given that ectomycorrhizal and saprotrophic fungi were more influenced by soil physico-chemical parameters or geographical distance than by Pinus species or forest structural variables. Finally, P content in soils also emerged as a significant factor driving differences in mycorrhizal communities.

How Is Bark Absorbability and Wettability Related to Stemflow Yield? Observations From Isolated Trees in the Brazilian Cerrado

Few investigations have examined the structural controls of bark on its water storage and influence on stemflow, despite the bark being considered a critical component that determines the time and magnitude of this process. This study seeks to answer the question: Do bark water absorbability and wettability estimates correlate with stemflow yield? We hypothesized that (1) the absorbability and wettability are correlated, that is, greater water absorbability implies greater wettability, and (2) high rates of bark water absorbability and wettability has a strong and negative correlation with stemflow generation. Stemflow yield (Sy) was monitored over 12 months for 31 trees, representing 9 species common to the Brazilian savanna ecosystem known as Cerrado. Bark absorbability, per unit dry weight, changes over time of the water absorbability (BWA - by submersion methodology), bark drying (BWD), bark absorbability rate (BWArate), bark drying rate (BWDrate), and wettability (initial contact angle – CAin and CA rate - CArate) were determined under laboratory conditions. As insoluble lignin may also act to alter bark water storage dynamics, for each species, the bark insoluble lignin content was characterized. Stemflow variability was significant across the study species. Funneling ratios (FR) indicates that all species’ canopies diverted enough rainfall as stemflow to concentrate rainwaters at the surface around their stem bases (FR > 1). Differences in bark water absorbability were notable some of tree species. A decrease in the CA value as a function of time was not observed for all barks, which in association with stemflow yields, allowed a novel classification method of wettability, based on CAin and it’s rate of change: highly wettable (CAin ≤ 75.3° and CArate ≥ 0.26°h–1) and non-wettable (CAin ≥ 93.5° and CArate ≤ 0.13°h–1). So, only from the wettability classification could be observed that the non-wettable bark species presented higher Sy, FR, BWA, and BWArate than highly wettable bark species. The stemflow from species with highly wettable bark had a strong and positive correlation with BWA. On the other hand, non-wettable bark stemflow yield has a strongly and negative correlation with FR, CAin, and BWArate. Thus, bark wettability properties showed to deserves special attention. This novel classification of bark wettability had a substantial effect on stemflow yield comprehension and proved to be an important variable to link laboratory and field investigation for understanding the stemflow yield. These findings will improve our understanding of the stemflow dynamics, water balance and the ecohydrology processes of forest ecosystems.

Ecosystem age-class dynamics and distribution in the LPJ-wsl v2.0 global ecosystem model

Abstract. Forest ecosystem processes follow classic responses with age, peaking production around canopy closure and declining thereafter. Although age dynamics might be more dominant in certain regions over others, demographic effects on net primary production (NPP) and heterotrophic respiration (Rh) are bound to exist. Yet, explicit representation of ecosystem demography is notably absent in many global ecosystem models. This is concerning because the global community relies on these models to regularly update our collective understanding of the global carbon cycle. This paper aims to present the technical developments of a computationally efficient approach for representing age-class dynamics within a global ecosystem model, the Lund–Potsdam–Jena – Wald, Schnee, Landschaft version 2.0 (LPJ-wsl v2.0) dynamic global vegetation model and to determine if explicit representation of demography influenced ecosystem stocks and fluxes at global scales or at the level of a grid cell. The modeled age classes are initially created by simulated fire and prescribed wood harvesting or abandonment of managed land, otherwise aging naturally until an additional disturbance is simulated or prescribed. In this paper, we show that the age module can capture classic demographic patterns in stem density and tree height compared to inventory data, and that simulated patterns of ecosystem function follow classic responses with age. We also present two scientific applications of the model to assess the modeled age-class distribution over time and to determine the demographic effect on ecosystem fluxes relative to climate. Simulations show that, between 1860 and 2016, zonal age distribution on Earth was driven predominately by fire, causing a 45- to 60-year difference in ages between older boreal (50–90∘ N) and younger tropical (23∘ S–23∘ N) ecosystems. Between simulation years 1860 and 2016, land-use change and land management were responsible for a decrease in zonal age by −6 years in boreal and by −21 years in both temperate (23–50∘ N) and tropical latitudes, with the anthropogenic effect on zonal age distribution increasing over time. A statistical model helped to reduce LPJ-wsl v2.0 complexity by predicting per-grid-cell annual NPP and Rh fluxes by three terms: precipitation, temperature, and age class; at global scales, R2 was between 0.95 and 0.98. As determined by the statistical model, the demographic effect on ecosystem function was often less than 0.10 kg C m−2 yr−1 but as high as 0.60 kg C m−2 yr−1 where the effect was greatest. In the eastern forests of North America, the simulated demographic effect was of similar magnitude, or greater than, the effects of climate; simulated demographic effects were similarly important in large regions of every vegetated continent. Simulated spatial datasets are provided for global ecosystem ages and the estimated coefficients for effects of precipitation, temperature and demography on ecosystem function. The discussion focuses on our finding of an increasing role of demography in the global carbon cycle, the effect of demography on relaxation times (resilience) following a disturbance event and its implications at global scales, and a finding of a 40 Pg C increase in biomass turnover when including age dynamics at global scales. Whereas time is the only mechanism that increases ecosystem age, any additional disturbance not explicitly modeled will decrease age. The LPJ-wsl v2.0 age module represents another step forward towards understanding the role of demography in global ecosystems.

Relative importance of tree species richness, tree functional type, and microenvironment for soil macrofauna communities in European forests.

Soil fauna communities are major drivers of many forest ecosystem processes. Tree species diversity and composition shape soil fauna communities, but their relationships are poorly understood, notably whether or not soil fauna diversity depends on tree species diversity. Here, we characterized soil macrofauna communities from forests composed of either one or three tree species, located in four different climate zones and growing on different soil types. Using multivariate analysis and model averaging we investigated the relative importance of tree species richness, tree functional type (deciduous vs. evergreen), litter quality, microhabitat and microclimatic characteristics as drivers of soil macrofauna community composition and structure. We found that macrofauna communities in mixed forest stands were represented by a higher number of broad taxonomic groups that were more diverse and more evenly represented. We also observed a switch from earthworm-dominated to predator-dominated communities with increasing evergreen proportion in forest stands, which we interpreted as a result of a lower litter quality and a higher forest floor mass. Finally, canopy openness was positively related to detritivore abundance and biomass, leading to higher predator species richness and diversity probably through trophic cascade effects. Interestingly, considering different levels of taxonomic resolution in the analyses highlighted different facets of macrofauna response to tree species richness, likely a result of both different ecological niche range and methodological constraints. Overall, our study supports the positive effects of tree species richness on macrofauna diversity and abundance through multiple changes in resource quality and availability, microhabitat, and microclimate modifications.

High‐frequency monitoring of hydrological and biogeochemical fluxes in forested catchments of southern Chile

AbstractThe variability of rainfall‐dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet‐temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad‐leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old‐growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad‐leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history.

Exploring the stemflow dynamics and driving factors at both inter‐ and intra‐event scales in a typical subtropical deciduous forest

AbstractNumerous efforts have been made to understand stemflow dynamics under different types of vegetation at the inter‐event scale, but few studies have explored the stemflow characteristics and corresponding influencing factors at the intra‐event scale. An in‐depth investigation of the inter‐ and intra‐event dynamics of stemflow is important for understanding the ecohydrological processes in forest ecosystems. In this study, stemflow volume (FV), stemflow funnelling ratio (FR), and stemflow ratio (F%) from Quercus acutissima and Broussonetia papyrifera trees were measured at both inter‐ and intra‐event scales in a subtropical deciduous forest, and the driving factors, including tree species and meteorological factors were further explored. Specifically, the FV, FR and F% of Q. acutissima (52.3 L, 47.2, 9.6%) were lower than those of B. papyrifera (85.1 L, 91.2, 12.4%). The effect of tree species on FV and F% was more obvious under low intensity rainfall types. At the inter‐event scale, FV had a strong positive linear correlation with rainfall amount (GP) and event duration (DE) for both tree species, whereas FR and F% had a positive logarithmic correlation with GP and DE only under high‐intensity, short‐duration rainfall type. FR and F% were mainly affected by wind speed and the maximum 30‐min rainfall intensity under low‐intensity, long‐duration rainfall type. At the intra‐event scale, for both tree species, the mean lag time between the start of rainfall and stemflow was the shortest under high‐intensity, short‐duration rainfall type, while the mean duration and amount of stemflow after rain cessation were the greatest under high‐amount, long‐duration rainfall type. The relationship between stemflow intensity and rainfall intensity at the 5‐min interval scale also depended greatly on rainfall type. These findings can help clarify stemflow dynamics and driving factors at both inter‐ and intra‐event scales, and also provide abundant data and parameters for ecohydrological simulations in subtropical forests.

Radial growth response of trees to seasonal soil humidity in a subtropical forest

Tree growth is the most important factor in determining the carbon sequestration processes of forest ecosystems. However, the growth phenology (seasonal growth pattern) and responses of tree growth to climatic variables vary considerably among different species, especially between deciduous and evergreen species. Thus, it is crucial to explore the seasonal growth patterns of different tree species in relation to climate to better understand the responses of tree physiology to climate changes, especially in mixed-species forest stands. In this study, we monitored the daily basal area increments of 220 individuals belonging to 15 common broadleaved tree species, nine deciduous and six evergreen species, in mixed-species experimental stands in subtropical China and analysed the relationships between radial stem growth and seasonal climate at a high-temporal resolution. We fitted daily increments of stem diameters with four frequently used nonlinear models and chose the best model for each species. The results showed that the evergreen trees grew faster than the deciduous trees, both annually and within the growing season. The tested nonlinear models (Korf, Weibull, logistic and Gompertz) produced good fits for the growth patterns of all species. Overall, the evergreen species began stem growth earlier and finished later during the growing season than that of the deciduous species. Within the growing season, the radial growth of trees in mixed stands containing both types of species was strongly positively correlated with humidity. In spring, increases in both temperature and moisture increased the daily relative basal area increment of all species. Maximum growth rates occurred when the soil water content reached its highest level and gradually decreased when the soil water content decreased. In summer, high temperatures combined with low amounts of precipitation led to heat-induced summer drought, to which the evergreen trees appeared to be more tolerant than the deciduous trees, which was reflected in the reduced stem growth of the latter. These results indicate the different climate-dependent seasonal growth strategies of evergreen and deciduous trees related to the trade-off described by the leaf economics spectrum, i.e., short-lived leaves with higher assimilation rates in deciduous and longer-lived leaves with a greater drought tolerance in evergreen species.

Effects of forest gap disturbance on forest ecosystem.

Forest gap disturbance has important consequences on plant species assemblage, stand structure and ecosystem functions of forests via changing micro-scale heterogeneity and community succession. Here, we reviwed research progress in the effects of forest gap disturbance on forest ecosystem. The effects of forest gap disturbance on plant species assemblage was analyzed based on the intrinsic biological characteristics and external environmental factors. The effects of forest gap disturbance on stand structure was discussed from the perspectives of texture and architecture of plant community. Forest gap disturbance effect on forest ecosystem functions was reviewed. After analyzing the theoretical shortcomings and the key bottleneck of forest ecosystem management practices, the following research directions were proposed, including the methods of determining threshold of forest gap, the mechanism of canopy closure, the effect of forest gap disturbance on forest ecosystem processes, and the relationship between forest gap disturbance and forest productivity. The advantage of forest gap disturbance in accelerating plant species regeneration and structure complexities could provide scientific evidence for enhancing the quality of low yield and low function plantations in China.

Oak decaying wood harbors taxonomically and functionally different bacterial communities in sapwood and heartwood

Wood decay is an important process in forest ecosystems, which relies on wood chemical properties and the action of a complex community of decomposers. While the important role of fungi in this process is recognized, our knowledge concerning the colonization of decaying wood by bacteria, their relative distribution as well as their potential functional roles remain under-investigated. In this context, our aim was to characterize how the bacterial communities are structured at both taxonomic and functional levels along the soil-wood continuum, using oak discs positioned on the forest floor for nine months. Using a combination of culture-dependent and -independent methods associated to a physical measure of wood decay, we evidenced that at the middle stage of decay investigated, the heartwood- and sapwood-inhabiting bacterial communities significantly differed from one another in term of richness and taxonomic composition, but also from those of the bulk soil. The functional screening revealed low metabolic potentials and a higher frequency of cellulose decomposing bacteria in wood than in the bulk soil, suggesting an adaptation of these communities to this habitat and to the physical-chemical conditions occurring in decaying wood. Together, our data evidence that the colonization of decaying wood by bacteria is based on a deterministic process linking extrinsic and intrinsic factors.

Developing a new disturbance index for tracking gradual change of forest ecosystems in the hilly red soil region of southern China using dense Landsat time series

Gradual change is prevalent across the forest landscape and generates long-lasting effects for the landscape surface; thus, tracking long-term gradual change can effectively characterize forest change processes. The objective of this study was to establish a vegetation index for change monitoring so as to determine long-term gradual change processes of forest ecosystems in typical red soil areas. The study area was located in Hengyang City, Hunan Province, China. Landsat images, field survey, and auxiliary data were collected to devise a disturbance sensitive vegetation index (DSVI) as an indicator of forest change. Long-term (1985–2019) forest changes were detected using the LandTrendr algorithm on the Google Earth Engine (GEE), while three evaluation aspects of velocity, frequency, and variance were used to analyze the processes of forest gradual change in red soil regions. Results indicate that the DSVI is a suitable index for forest change detection due to its stronger sensitivity compared to other indexes. Further, it shows excellent change detection ability for different types of gradual changes, such as those caused by drought and significant soil erosion. Furthermore, 97.26% of the forests showed gradual change, and approximately 2/3 of monitored forests showed an increasing growth trend while 1/3 showed a decreasing trend. The dominant (28.33%) forest disturbance frequency indicated instability in red soil regions. Dispersion degree of forest variance was mainly low (48.46%) or medium (28.84%). This research establishes the DSVI as a promising method to track forest gradual change and contributes to a better understanding of gradual change processes of forest landscape over time.

Simulated atmospheric nitrogen deposition inhibited the leaf litter decomposition of Cinnamomum migao H. W. Li in Southwest China

Atmospheric nitrogen (N) deposition could affect various ecological processes in forest ecosystems, including plant litter decomposition and nutrient cycling. However, the mechanism of underlying litter decomposition and nutrient cycling of Cinnamomum migao under N deposition remains unclear. Therefore, we conducted a simulated N deposition experiment including four onsite treatments to assess the effects of N input on C. migao leaf litter decomposition, nutrient release, and soil enzyme activity. The results showed that simulated N deposition significantly increased the amount of total residual mass and lignin and cellulose, decreased the decomposition rate, and suppressed net nutrient release. N input increased C, N, and P ratios as decomposition progressed, and the proportion of mass remaining was positively correlated with the proportions of lignin and cellulose remaining at the later stage of decomposition. The differences in soil enzyme activity were primarily due to enzyme type and sampling time. We conclude that simulated N deposition significantly suppressed the leaf litter decomposition of C. migao by mainly altering the chemical properties and suppressing the decomposition of the organic matter in leaf litter. Lignin might have played an important role in the loss of leaf litter biomass at the later stage of decomposition.

Moderate swidden agriculture inside dense evergreen ombrophilous forests can sustain soil chemical properties over 10–15 year cycles within the Brazilian Atlantic Forest

Swidden agriculture as a production system has been practiced for thousands of years, based on ecological processes of forest ecosystems. While this cultivation system has often been framed as contributing to environmental degradation, it can also be argued to be compatible with sustainable agricultural practices. Its sustainability strongly depends on the length of the recovery period, the period of secondary forest succession, after swidden agriculture. In this study we focused on soil fertility maintenance and recovery during secondary succession after swidden agriculture, compared to old-growth forests. Smallholders practiced a moderate form of swidden agriculture, abandoned the production field after one or two production cycles, and returned to the field after 10–15 years. Sampling took place in two traditional communities situated in the southeast portion of the Atlantic Rainforest at São Paulo state, Brazil. Soil samples were collected from forest fragments belonging to seven different Caiçara families (descendants from Amerindians, African Brazilian and European colonizers). Our chronosequence spanned a period of sixty years, while the old-growth forests were 100 years old. In all 28 sites were sampled, of which 19 were from ombrophilous forests on clay and 9 from restinga vegetation on sandy soil. Soils were analyzed for texture, macro- and micronutrient availability, bulk density, pH and nitrogen and carbon stocks. Linear regression, with clay content and fallow period as main factors, showed that successional age of the forest stand had only a significant effect on pH and Mn. Clay content of the soil influenced availability of nutrient bases and the CEC. Other soil properties, including stocks of carbon and nitrogen were not influenced by fallow period. Our data indicate that swidden agriculture might not lose key soil nutrients over time and hence can be considered an ecologically sustainable system in the region, challenging the negative perception of swidden agriculture.

Stand age related dissimilarity in radial growth of a moisture-sensitive forest tree species is greater under a lower drought limitation

Although stand age has been shown to strongly affect forest ecosystem processes, little is known about the role that forest stand age plays in tree radial growth processes. The knowledge on geographical patterns of the stand age effect on radial growth along climatic gradients is also scarce. Based on dendrological methods and tree-ring cores from 2276 trees at 14 sampling plots, we confirmed that differences in stand age could result in radial growth dissimilarities of Qinghai spruce (Picea crassifolia Kom.), a moisture-sensitive forest tree species endemic to the Tibetan Plateau. However, the effect that stand age has on the radial growth of Qinghai spruce is not consistent. There is evident dissimilarity in the radial growth dynamics of Qinghai spruce from different-aged forest stands in semi-humid regions, but this dissimilarity is minimal in regions under higher drought limitation. Additionally, we observed significant negative correlations in temporal changes of growth concordance of Qinghai spruce from different-aged stands and regional moisture conditions at each study site. It can therefore be concluded that Qinghai spruce will exhibit greater stand age related growth dissimilarities under lower drought limitation. Findings from this study can improve our understanding of biogeographical patterns of moisture-sensitive tree growth that will be necessary to improve future projections of forest dynamics and to guide forest management under a changing climate.

Development and Performance Evaluation of a Very Low-Cost UAV-Lidar System for Forestry Applications

Accurate and repeated forest inventory data are critical to understand forest ecosystem processes and manage forest resources. In recent years, unmanned aerial vehicle (UAV)-borne light detection and ranging (lidar) systems have demonstrated effectiveness at deriving forest inventory attributes. However, their high cost has largely prevented them from being used in large-scale forest applications. Here, we developed a very low-cost UAV lidar system that integrates a recently emerged DJI Livox MID40 laser scanner (~$600 USD) and evaluated its capability in estimating both individual tree-level (i.e., tree height) and plot-level forest inventory attributes (i.e., canopy cover, gap fraction, and leaf area index (LAI)). Moreover, a comprehensive comparison was conducted between the developed DJI Livox system and four other UAV lidar systems equipped with high-end laser scanners (i.e., RIEGL VUX-1 UAV, RIEGL miniVUX-1 UAV, HESAI Pandar40, and Velodyne Puck LITE). Using these instruments, we surveyed a coniferous forest site and a broadleaved forest site, with tree densities ranging from 500 trees/ha to 3000 trees/ha, with 52 UAV flights at different flying height and speed combinations. The developed DJI Livox MID40 system effectively captured the upper canopy structure and terrain surface information at both forest sites. The estimated individual tree height was highly correlated with field measurements (coniferous site: R2 = 0.96, root mean squared error/RMSE = 0.59 m; broadleaved site: R2 = 0.70, RMSE = 1.63 m). The plot-level estimates of canopy cover, gap fraction, and LAI corresponded well with those derived from the high-end RIEGL VUX-1 UAV system but tended to have systematic biases in areas with medium to high canopy densities. Overall, the DJI Livox MID40 system performed comparably to the RIEGL miniVUX-1 UAV, HESAI Pandar40, and Velodyne Puck LITE systems in the coniferous site and to the Velodyne Puck LITE system in the broadleaved forest. Despite its apparent weaknesses of limited sensitivity to low-intensity returns and narrow field of view, we believe that the very low-cost system developed by this study can largely broaden the potential use of UAV lidar in forest inventory applications. This study also provides guidance for the selection of the appropriate UAV lidar system and flight specifications for forest research and management.

Soil biota response to experimental rainfall reduction depends on the dominant tree species in mature northern Mediterranean forests

Soil organisms play a major role on litter decomposition process and nutrient cycling in forest ecosystems. These organisms are extremely sensitive to environmental conditions such as soil temperature and moisture conditions which control their demographic parameters and activity. The ongoing climate change can therefore directly affect soil biota communities and the processes they drive. Besides, climate change can also indirectly affect soil biota by altering tree functional traits (e.g., N, Ca, Mg, water holding capacity) with cascading effects on the litter quality. The aim of this study was to determine the relative effects of increased drought and litter type on microbial biomass (bacteria and fungi) and mesofauna abundance (Collembola and Acari) in three experimental sites representative of the three main forests encountered in the northern part of the Mediterranean Basin (dominated by either Quercus pubescens, Quercus ilex or Pinus halepensis) where rainfall exclusion experiments were taking place. At each site, and in each precipitation treatment (natural and amplified drought plots), we collected and transplanted foliage litters (i.e., species × drought level). After two years, we reported a litter species effect: Q. pubescens litter presented consistently the higher abundance of all soil biota groups compared to Q. ilex and P. halepensis litters in each forest. Surprisingly, despite that the amplified drought treatment induced a modification of the litter quality, we did not reported an indirect reduced precipitation effect on soil biota parameters. While Oribatid Acari abundance decreased with amplified drought in all three forest types, the direct effects on the other soil biota groups were forest-dependent. In P. halepensis forest, amplified drought resulted in higher bacterial and fungal biomasses but lower Collembola abundance. In Q. ilex forest both Collembola and predatory Acari abundances decreased with amplified drought. In addition, the positive relationships between Collembola and Oribatida abundances and litter mass loss disappeared under amplified drought conditions in both Q. ilex and P. halepensis forests. These results suggest a key role played by Ca, Mg, specific leaf area (SLA) and water holding capacity (WHC) as drivers of soil biota parameters. Finally, the study highlights that within the same Mediterranean region, climate change could differently alter the soil organisms inhabiting the litter layer and their contributions to the decomposition process depending on the tree species and soil biota group considered.

Change in root-associated fungal communities affects soil enzymatic activities during Pinus massoniana forest development in subtropical China

Root-associated fungal communities play a key role in plant productivity and soil processes in forest ecosystems. However, how diversity and composition of root-associated fungi change with forest development and their linkage with soil enzyme activities remain largely unknown. We characterized the root-associated fungal communities, plant and soil properties, and extracellular enzyme activities along a chronosequence spanning young (15 years old) to over-mature (63 years old) Pinus massoniana forest development stages. Our results showed that P. massoniana roots harbored diverse root-associated fungal communities and they varied with forest development. Near-mature (36 years old) forest stands had the lowest alpha-diversity but higher relative abundances of ericoid mycorrhizal and activities of enzymes involved in C, N and P acquisition. The relative abundances of ectomycorrhizal fungi and endophyte were higher in middle-age (24 years old) and mature stands (45 years old), whereas the relative abundance of ericoid mycorrhizal fungi was highest in the near-mature stand. Soil pH, soil C:P and N:P ratios were important factors shaping the diversity and composition of root-associated fungal communities. Structural equation modeling indicated that changes in the community composition, but not richness of root-associated fungi, had significant correlations with soil enzymatic C:N and N:P stoichiometry. In conclusion, this study suggests that different stand development stages exhibit distinct diversity and composition of root-associated fungal communities, which affecting soil functions in terms of enzymatic activity.