Stages Of Stand Development Research Articles

Changes in carbon stocks according to stand development stages in oriental beech forests in the Marmara Region of Türkiye.

This study was conducted to determine the changes in carbon stocks of oriental beech (Fagus orientalis) according to stand development stage in the Marmara Region of Türkiye. For this purpose, sample plots were taken from a total of 32 areas encompassing four stand development stages (young, middle age, mature and overmature stand). The diameter at breast height and height of all trees in the sample plots were measured, and only three dominant trees's ages per plot were determined. Aboveground carbon stock was calculated using equations developed for beech forests, while the coefficients in the Agriculture, Forestry and Other Land Use guide were used to determine belowground carbon stocks. A soil pit was dug in each plot and soil samples were taken at different depths (0-10, 10-30, 30-60, 60-100cm). In addition, litters were sampled from four different 25 × 25cm sections in each plot, and then the physical and chemical properties of the soil and litters were analysed. The variations in carbon stocks in above- and below-ground tree mass, litter and soil, and in ecosystem carbon stocks according to development stage were examined by analysis of variance and Duncan test, and the relationships between the carbon stocks were investigated by correlation analysis. Aboveground (AG) and belowground (BG) tree, soil and ecosystem carbon stocks showed significant differences between the four stand development stages (P < 0.05), but not the litter carbon stocks (P > 0.05). AG and BG tree and ecosystem carbon stocks increased with progressive stand development stages, while the soil carbon stock was the highest at the young stage. These findings will contribute to the preparation of forest management plans and the national greenhouse gas inventory.

Chronic anthropogenic disturbance mediates the biodiversity‐productivity relationship across stand ages in a large temperate forest region

Abstract Temperate forests, especially those in the densely populated regions of the world, are experiencing increasing levels of habitat degradation and biological impoverishment due to subtle but pervasive chronic anthropogenic disturbances including frequent and continuous grazing and extraction of non‐timber forest products. However, the effects of these subtle, chronic disturbances on the biodiversity‐productivity relationship have rarely been examined especially in forests at different development stages. Accordingly, this study explores how chronic anthropogenic disturbance affects the relationship between tree species diversity and forest productivity at different stand development stages in a large temperate forest region. We used the human footprint index as a proxy for chronic human disturbance. Hierarchical Bayesian models were employed to assess the effects of chronic human disturbance on the relationship between tree diversity and forest productivity across different stand age. Several measures of diversity were employed, including taxonomic, functional and phylogenetic diversity. Forest productivity consistently increased with taxonomic, functional and phylogenetic biodiversity; these biodiversity facets were the main drivers of forest productivity compared to stand age, chronic human disturbance and climate. However, the magnitude at which productivity increases with the increments of taxonomic and functional diversity diminishes with the increasing chronic disturbance, especially in younger stands. The effects of phylogenetic diversity on productivity did not vary with chronic disturbance, regardless of stand age. Synthesis and applications: Chronic human disturbance in a large temperate forest region reduces the increase in community productivity due to different facets of biodiversity, especially in young forests. The evidence suggests that the mitigation of chronic human disturbance and the conservation of biodiversity will be effective in sustaining essential ecosystem functions.

The Effects of Stand Development Stages on Soil Carbon and Nitrogen Stocks in Black Pine, Scots Pine and Fir Stands in Türkiye

The influence of stand development stages on soil organic carbon (SOC) and total nitrogen (TN) stocks was examined in black pine (Pinus nigra Arnold.), Scots pine (Pinus sylvestris L.), and Kazdağı fir (Abies nordmanniana subsp. equi-trojanı (Aschers. &amp;amp; Sint. ex Boiss) Coode et Cullen), differing in the mean tree diameters in which reproduction stages (RS)=&amp;lt;8 cm, sapling or pole stages (SPS)= 8-19.9 cm, large pole stages (LPS)= 20-35.9 cm, and medium wood stages (MWS)=36-51.9 cm in three tree species located in northwestern Turkey. A total of 216 soil samples were collected and analyzed for pH, organic matter, bulk density, maximum water holding capacity, carbon, and nitrogen concentrations, and the SOC and TN stocks were calculated. SOC and TN stocks varied significantly among the four stand development stage classes. The SOC stock at 0-30 cm increased significantly due to an increase in the diameter of black stands (BPLPS and BPMWS). SOC stocks in all stand development stages peaked in the large pole (44.94 Mg/ha) and declined as the sapling or pole (37.71 Mg/ha) was replaced by medium wood stands (30.17 Mg/ha), and a low point (27.94 Mg/ha) was found in the reproduction stages of stand development for Scots pine. The TN stock at a soil depth of 0-30 cm ranged from 1.66 to 6.46 Mg/ha. The highest TN stock was observed in the SPSPS (6.46 Mg/ha) and FirRS (5.48 Mg/ha), and the lowest was observed in the BPLPS (1.66 Mg/ha) stands. The results illustrate that soil was the main storage of C and N in all different stand development stages of tree species.

Fungal community dynamics in coarse woody debris across decay stage, tree species, and stand development stage in northern boreal forests

Fungi are primary agents of coarse woody debris (CWD) decay in boreal forests, playing an essential role in nutrient cycling and carbon storage. We compared fungal community assemblages using alpha and beta diversity metrics, and physical and chemical properties of CWD across three tree species (trembling aspen [ Populus tremuloides], black spruce [ Picea mariana], and jack pine [ Pinus banksiana]), five decay classes, and two stand development stages, differing in time since stand replacing disturbance in Ontario’s boreal forest region. We sampled 180 individual CWD logs from 6 independent stands, with 3 replicates per each species × decay class combination at each site. Using high-throughput sequencing of marker DNA, we found that fungal community structure significantly differed across tree species, decay stage, and stand age. Fungal diversity was highest in decay class 4 CWD. We found that Mn and K concentrations, total carbon, C/N ratio, N/P ratio, and moisture content were important predictors of fungal composition across CWD species and/or decay stage. This study suggests that forest management guidelines that consider both deadwood quantity and quality will support a broader range of fungal species and communities through post-disturbance stand development.

All boreal forest successional stages needed to maintain the full suite of soil biodiversity, community composition, and function following wildfire

Wildfire is a natural disturbance in boreal forest systems that has been predicted to increase in frequency, intensity, and extent due to climate change. Most studies tend to assess the recovery of one component of the community at a time but here we use DNA metabarcoding to simultaneously monitor soil bacteria, fungi, and arthropods along an 85-year chronosequence following wildfire in jack pine-dominated ecosites. We describe soil successional and community assembly processes to better inform sustainable forest management practices. Soil taxa showed different recovery trajectories following wildfire. Bacteria shared a large core community across stand development stages (~ 95–97% of their unique sequences) and appeared to recover relatively quickly by crown closure. By comparison fungi and arthropods shared smaller core communities (64–77% and 68–69%, respectively) and each stage appeared to support unique biodiversity. We show the importance of maintaining a mosaic ecosystem that represents each stand development stage to maintain the full suite of biodiversity in soils following wildfire, especially for fungi and arthropods. These results will provide a useful baseline for comparison when assessing the effects of human disturbance such as harvest or for assessing the effects of more frequent wildfire events due to climate change.

Exploring the effects of various rotation lengths on the ecosystem services within a multiple-use management framework

Addressing the spatio-temporal dynamics of forest development under different management scenarios with varying rotation lengths is a challenge in forest management planning. This research aims to forecast forest development and assess the relative consequences of varying rotation lengths on several ecosystem services such as wood production, habitat for biodiversity, carbon sequestration, water provision, soil protection and cultural values. Forest development is simulated with the ETCAP model to examine the long-term effects of various rotation lengths with silvicultural prescriptions on the ecosystem services. Bürücek forest planning unit is used as a case study area with 10,711 ha forests in upper Mediterranean region of Turkey. Shorter rotation lengths are considered one of the main mitigation measures to climate changes in forestry; however, lead to the increased harvest level, net present value, ground water and soil loss, and reductions in the largest stand volume, understory, basal area, carbon storage and the cultural values with less regulated forest structure. The management scenarios with longer rotation lengths, however, have highlighted improvements in the carbon storage, larger standing volume, mean stand age, basal area and cultural values, and reductions in the mean harvest volume, net present value, ground water and soil loss due to larger-even distribution of tree sizes and stand development stages. An aspiration for a higher level of provisioning services for economic motivations may need to be discarded for the sake of enhancing the capacity of forest ecosystems to sequester more carbon and provide better habitat condition for biodiversity conservation with a careful design and selection of rotation lengths. Overall, the choice of optimal rotation length is highly dependent on a desired set of management objectives and target forest structure driven mostly by management interventions with the appropriate type and level of ecosystem services, provided that a thorough understanding of forest dynamics is achieved by considering both risks and uncertainties associated with natural disturbances and socio-economic conditions.

Looking for a magic island in the sea of agriculture: factors affecting forest patch attractiveness for wild boar in human-dominated landscape

Landscape fragmentation carries the risk of habitat loss for many animal species. This may include wild boars, which are one of the main culprits of conflicts with humans, while isolated patches of forest (forest islands) scattered in the agricultural landscape may affect its ecology and the pressure on the crops. This study aimed to understand the importance of small forest islands located in a human-dominated agricultural landscape in the ecology of wild boar. It explores what features, both of the interior and exterior of the islands, influence their use. The study area covered approximately 220,000 ha of northern Poland, where wild boar use of 200 islands distributed across the agricultural landscape was investigated. For this purpose, the method of counting pellet groups was applied on transects of a total length of 51.6 km. In order to compare the use of islands with compact forest complexes, 84 km of transects were made in the latter, divided into developmental stages and forest type. Among the features of the interior of the islands, increasing cover conditions and the main species of trees (pine, spruce and alder) had a positive influence on the wild boar use. The utilization also depended on the presence of human settlements, other islands, and the type of agricultural crop around the island. When comparing island use to compact forest complexes, islands were used more often than forest regeneration sites and mature stands, but less often than pre-thickets. For the 25% most frequently used by wild boar, islands were more attractive than virtually all stand development stages in compact forest complexes. Due to the cover conditions provided, the occurrence of islands in the agricultural space enables wild boars to use areas more distant from compact forest complexes. This may cause the spread of damage caused by wild boars in the fields, but on the other hand it may reduce the pressure on agricultural areas in the immediate vicinity of compact forest complexes. Intensification of hunting pressure in the vicinity of islands with specific characteristics e.g. good cover conditions, considerable distance from human settlements) will increase the effectiveness of wild boar population control in the agricultural landscape and will have a limiting effect on the damage caused by this species in the fields.

SAPSIZ MEŞENİN (Quercus petrea (Matt.) Liebl) TOPRAK ORGANİK KARBON VE AZOT STOKLARI ÜZERİNDE GELİŞİM ÇAĞLARININ ETKİSİ: TAŞKÖPRÜ, KASTAMONU ÖRNEĞİ

This study aimed to determine the effects of four different development stages of sessile oak (Quercus petrea (Matt.) Liebl) stands on soil organic carbon (SOC) and total nitrogen (TN) stocks in northwest Turkey. According to the diameter at breast height (dbh), sessile oak stands were classified into four development stages namely: a development stage (&amp;lt;8cm), b development stage (8 to 19.9 cm), c development stage (20 to 35.9 cm) and d development stage (36 to 51.9 cm). Soil samples were taken from three different soil depths (0-10, 10-20, and 20-30 cm). Total 72 soil samples were collected from all development stages. Forest floor litters were also sampled from each development stage. Results showed that soil organic carbon varied significantly between the four development stages (R2=0.714, p=0.000) with the highest stocks under the d development stage (55.0 Mg ha-1) and the lowest under the b development stage (10.6 Mg ha-1). Total N stock was highest under the a development stage (3.39 Mg ha-1), whereas it was lowest under the b development stage (1.18 Mg ha-1). About 71% of SOC was deposited in the upper 30 cm of the soil. The forest floor litter also varied between the four development stages with the highest values under the b development stage and the lowest under the a development stage. As a result, the results of the study indicated that sessile oaks can play a significant role in storing organic carbon and nitrogen in the soil. On the other hand, amounts of SOC and TN stocks can be significantly varied according to stand development stages.

Vegetation Monitoring and Post-Fire Recovery: A Case Study in the Centre Inland of Portugal

Wildfires are a major environmental issue that have an impact on land degradation. Remote sensing spectral indices provide valuable information for short-term mitigation and rehabilitation after wildfires. A study area in the Centre inland of Portugal occupied with Maritime pine and Eucalypts forests and affected by wildfires in 2003, 2017 and 2020 was used. The aims of the study were twofold: (1) to compute the Normalized Difference Vegetation Index (NDVI) and with forest inventory data derivate a Maritime pine production model, differentiate evergreen coniferous forests (e.g., Maritime pine), evergreen broadleaved forests (e.g., Eucalypts), and shrubland, and monitor vegetation and its post-fire recovery; and (2) to compute the Normalized Burn Ratio (NBR) difference between pre-fire and post-fire dates for burn severity levels assessment. The plots of a previous forest inventory were used to follow the NDVI values in 2007 and from 2020 to 2022. An aerial coverage in 2007 and the Sentinel-2 imagery in 2020–2022 were used. Linear models fitted maritime pine production with the transformed NDVI by age, showing a fitting efficiency of 60%. The stratification of cover types by stand development stage and fire occurrence was possible using the NDVI time curve, which also showed the impact of fire and of low precipitation. Cover types were ranked by decreasing NDVI values as follows: mature Eucalypts plantations, young Maritime pine regeneration, mature Maritime pine, young Eucalypts plantations, Strawberry tree shrubland, Eucalypts plantations post-fire, Maritime pine post-fire, tall shrubland, and short shrubland. Vegetation post-fire recovery was lower in higher burn severity level areas. Maritime pine areas have lost their natural regeneration capability due to the wildfires’ short cycles. Spectral indices were effective tools to differentiate cover types and assist in the evaluation of forest and shrubland conditions.

Stand development stages and recruitment patterns influence fine-scale spatial genetic structure in two Patagonian Nothofagus species

Key messageNothofagus alpina (Poepp. et Endl.) Oerst. and Nothofagus obliqua (Mirb.) Oerst forests have strong fine-scale spatial genetic structures. The intensity of genetic structure patterns differed according to species, stand development stages, life stages, and spatial arrangement of regeneration groups. This data becomes useful for forest management as it provides an understanding of how populations evolve as well as of the consequences of disturbances and enables the establishment of sampling strategies.ContextThe understanding of fine-scale spatial genetic structure in natural populations is useful for forest management. Although Nothofagus alpina (Poepp. et Endl.) Oerst. and N. obliqua (Mirb.) are important species of the Patagonian forest, little is known about the genetic structure of their populations.AimsThe main objectives were to investigate the differences in fine-scale spatial genetic structure among mature tree populations of both species considering two stands at different development stages. Genetic structure was also evaluated among life stages and spatial distribution groups of regeneration within the old-growth stand.MethodsGenetic structure was examined by microsatellite DNA analysis of regeneration and mature tree populations of both species (around 1300 individuals). Gene dispersal distance was additionally estimated.ResultsIn both stands and species, strong fine-scale spatial genetic structure and short dispersal distance were found. This pattern was stronger in the early successional forest, in N. obliqua populations, in earlier life stages, and in scattered regeneration.ConclusionStand development stages and recruitment patterns influence the fine-scale spatial genetic structure of both Nothofagus species. However, the genetic structure also differs between species.

Contrasting interactions of remnant spruce trees with indigenous broadleaves in a partially converted stand from a former plantation

Although important for both restoration and conservation provisions, little is known of the multispecific tree interactions involved in secondary spruce-broadleaf stands undergoing natural conversion from conifer monospecific plantations. We aimed to identify signals of such interactions in a partially converted, 60-year-old stand located in the Eastern Carpathians (northern Romania) and composed of sycamore, ash, maple, and wych elm (hereinafter, SAE), beech and remnant spruce trees.The position and size of all standing tree species individuals at least 1.50 m tall were measured within a 1.5 ha plot. Bivariate spatial pattern analysis, hierarchical Strauss models, and generalised linear squares regression were used for estimating tree neighbourhood interaction and interference.At fine scales, the beech sapling distribution was closely described through opposite models of attraction or inhibition with respect to spruce and SAE trees, respectively. The repulsion detected within the 3 m neighbourhood between SAE and spruce trees translated also in a significant inhibition process. This was in accordance with the negative effect of the nearest spruce on SAE tree growth. The significant segregation and spatial dissociation between beech and SAE trees was very likely related to the negative effect of neighbouring beech veterans on SAE tree diameter. Negative effects on spruce tree growth were only detected through interference with the nearest beech tree.In the given context of site conditions and stand development stage, the observed spatial interdependence and interference patterns were probably determined, to a large extent, by the intense interspecific competition for below-ground resources and light. The remnant spruce trees can act as both growth promoter and inhibitor in relation to the neighbouring beech and SAE trees, respectively. The spruce trees slow down the natural conversion to a mixed SAE stand by contributing to beech dominance, but that will eventually lead through negative feedback to the gradual exclusion of spruce.

Fruit characteristics, defoliation, forest floor and soil properties of sweet chestnut (Castanea sativa Mill.) forests in İstanbul-Turkey

The defoliation and fruit characteristics of natural Castanea sativa Mill. forests were annually monitored between 2014 and 2016 in İstanbul, Turkey. The soil and forest floor properties were also investigated and evaluated according to the stand development stages. Comparisons were made with ANOVA and Tukey HSD tests; the relationship between fruit yield and the properties of the soil and forest floor were tested with correlation analysis; and allometric regression models were developed for fruit yield with DBH (diameter at breast height) and (DBH)2H. The total mass was 509-652 g/m2, N mass was 7.67-9.70 g/m2 and C mass was between 165.75 g/m2 and 183.28 g/m2 in the forest floor in the development stages. The soil texture was loam-clay loam, soil C concentration was between 0.3% and 1.92%, N concentration was 0.08-0.32%, the EC was very low (33-84 μS/cm), and the pH was acidic (5 pH). The properties of the forest floor and soil were not significantly different from the development stages. The defoliation rates increased significantly every year in each development stage. The fruit yield was between 183.51 kg/ha and 298.27 kg/ha, and fruit was not detected in the smallest development stage (SDF). The fruit yields were quite low in comparison with other natural C. sativa forests. However, in each year in the study period, fruit yields were negatively correlated with mass and C and N content and positively correlated with N concentration in the H layer of the forest floor. There was not a significant difference in fruit yield over the years, and it had a low relation with DBH and (DBH)2H (R2 = 0.34 and R2 = 0.23, respectively). The fruits? characteristics significantly fluctuated over the years. As a result, low fruit yield and low relationships with properties of the forest floor and soil might be attributed to the former coppice management and possible health problems.

Dependência, pressão e recuperação de recursos florestais no Parque Nacional do Limpopo (Moçambique)

The general perception is that forest resources exploitation can cause the degradation and loss of resources and biodiversity, promoted by landscape fragmentation and pressure over habitats. But such assumption might not be adjusted to situations where long term exploitation by traditional communities is based on management strategies adapted to recovery, adjusting pressure to kept resources available. In this work, we assess the recovery of the Mopane woodlands considering different land use practices and stand development stages on areas explored by local communities. In detail, we want to explore: i) changes on stem size across plant comunities dominated by Mopane (Kirk ex Benth ex J. Leonard); ii) relationships between the variation in stem size across communities and the associated land use practices and vegetation stand development stage. To answer those questions, an inventory was carried out to collect data from 50 temporary circular plots of different sizes spatially nested, covering four stand development stages. Each nested circular plot was composed of a large plot (0.02 ha), an intermediate plot (0.04 ha), and an inner plot (0.01 ha) for counting stems of different DBH. Data was analysed using Excel, Two-Way Indicator Species Analysis (TWINSPAN) and CANOCO, and several parametric and non-parametric tests. TWINSPAN analysis, using stem counts, grouped the 1746 stems from 29 species (with Mopane as one species) into 5 communities and 10 sub-communities, based on indicator species and eigenvalues (level of stability). This study was carried out in the Limpopo National Park (LNP), in Mozambique, a conservation area established in 2001 and part of the Great Limpopo Transfrontier Park (GLTP) since 2002. Acording to the results, population structure (size class distribution of trees) of Mopane communities showed variation related to stand development stage, as expected. The initial stages show good regeneration, indicating that recovery is not hampered by the exploitation regime in use, a critical aspect once ecosystem dynamics of Mopane woodland has a deep influence on the way that local communities manage harvesting of Mopane products for different uses, and traditional uses do also have influence on recovery dynamics. So, management of such resource is critical to ensure sustainable resource use and guarantee provision for future generations. For that, a zonation of Mopane woodlands within the Park, considering different land uses, might enhance a quick system recovery on specific areas and contribute to woodland productivity, good quality products and reduce used areas, promoting habitat conservation.

Height-diameter allometric equations of an emergent tree species from the Congo Basin

Reliable tree height-diameter (H-D) allometric equations are a key tool for the estimation of forest productivity and Above Ground Biomass (AGB). Most existing H-D allometric equations developed for the tropical region are based on large-scale multi-species datasets, and their use to derive information on productivity and AGB at the species level is prone to uncertainties. The single-species H-D allometric equations available are mainly focused on monocultures or stands with simple tree species mixtures and did not account for the site effects. Here we measured the height and diameter of 2,288 trees of the emergent tree species Pericopsis elata (Harms) Meeuwen in the Democratic Republic of the Congo (DRC) and in Cameroon. We first examined how accurate multispecies H-D allometric equations are in predicting the total height of P. elata. We then tested whether single-species H-D allometric equations vary between sites. We developed the first H-D allometric equation of P. elata and tested whether and how stand-level and environmental variables induce changes in H-D allometric relationship of P. elata at the regional level. We additionally evaluated whether tree-level variables are important at the local level where climate and stand development stage are expected to be less variable. We found that pantropical, regional and local H-D allometric equations significantly underestimate the total height of P. elata. The local multi-species H-D allometric equation developed for Yangambi showed the highest underestimation in all the studied sites. This result supports the need for an H-D allometric equation specific for P. elata. The species-level H-D allometric equation developed showed significant underestimations for trees from the disturbed and undisturbed forests in DRC, while overestimations were observed for similar sites in Cameroon. Using a mixed-effect H-D allometric equation, we showed that even within a single species, a substantial variation exists between sites. This variation showed to be driven by the differences in the maximum asymptotic height (Hmax) between sites. We found that P. elata trees are taller and attain higher Hmax in DRC than in Cameroon. The basal area showed to be a significant covariate accounting for the site effects at the regional-scale where climate variables showed minor effects. However, at the local-scale, none of climate or stand variables showed to be significant. Local-scale variation showed to be associated with differences in light availability, highlighting the potential of management options that shape the local environment in driving species productivity.

Understory diversity are driven by resource availability rather than resource heterogeneity in subtropical forests

Understory vegetation accounts for most of the plant diversity, particularly in plantation forests, and contributes significantly to energy flows and nutrient cycling. However, we lack a mechanistic understanding of understory diversity associated with resource availability and heterogeneity across forest types over a wide range of stand development stages. We sampled the understory vegetation of Chinese fir plantations and natural secondary forests (4–40 years old) and used primary forests as a reference in subtropical China. The percent covers of all understory plant species were estimated at the shrub layer (height >1.3 m) and herb layer (≤1.3 m). We quantified understory light availability and heterogeneity, substrate diversity and soil nutrients and employed principal component analysis to reduce multiple physical and chemical soil properties to PC1 and PC2, with PC1 positively correlating with soil carbon and total nitrogen, and PC2 with available soil nitrogen and phosphorus. Structural equation modelling (SEM) was employed to test the direct and indirect influences of forest type, stand age, light availability and heterogeneity, substrate diversity and soil nutrients on the diversity of understory species. We found that shrub layer richness was higher in the secondary natural and primary forests than in the plantations, but plantations had higher bryophyte richness. Shrub cover was positively correlated with shrub richness and had a positive indirect effect on shrub richness but a negative indirect effect on herb richness via its effect on soil carbon and nitrogen. Stand age has a positive direct effect on bryophyte richness. There were strong positive correlations among the richness of understory layers and life forms. Our results suggest that physical and chemical soil properties, specifically soil nutrient availability, rather than light availability and heterogeneity or substrate diversity, were the main drivers that affected subtropical forests' understory richness.

Fire risk and severity decline with stand development in Tasmanian giant Eucalyptus forest

Forest fire risk, and how it changes over time, has important influences on forest dynamics. Two common models describing how fire risk changes with stand development, known as flammability functions, are (a) the ‘moisture model’, where fire risk initially increases, then decreases, as a stand develops after a fire, and (b) the ‘Olson model’, where fire risk increases asymptotically as a function of time since previous fire. These two flammability functions have both been used to describe the world’s tallest angiosperm forest, the Australian tall wet Eucalyptus forest (TWEF). It is unclear, however, which function is more appropriate for TWEF, as there are little empirical data describing fuels and microclimate, two important influences on fire risk and potential severity, across the long lifespan of these forests. Accordingly, we use a chronosequence of TWEF stands in southeast Tasmania, Australia, to see how fuels, microclimate, and resulting fire risk and potential fire severity changed amongst four stand-development stages ranging from regrowth to old forests. We measured fuel loads, understorey microclimate, and forest physiognomy. We then used these data with historical fire weather data and fire behaviour models to estimate how often low- and high-severity fire was possible historically. We also investigated if the severity of the previous disturbance influenced the likelihood of a subsequent high-severity fire. We found that, while fuel loads remained unchanged across the chronosequence, later development stages had a significantly moister understorey, an increased abundance of rainforest trees, and more vertically discontinuous fuels. These factors resulted in a significantly reduced fire risk, with high-severity fire much more likely in the early stages. Further, we found that stands that had been initiated by stand-replacing fire were more susceptible to subsequent high-severity fire than those that experienced non stand-replacing fire, due to a lack of a remaining mature canopy. We concluded that, unlike most other fire-dependent ecosystems where the Olson curve is an appropriate model, the flammability function in TWEF is best described by the moisture model. Our results indicate that TWEF is vulnerable to a ‘landscape trap’ effect, where intensive disturbance creates large areas of regrowth stands with increased risk of high-severity fire, which increases the likelihood of landscape-wide, demographic collapse. We suggest that fire and forest management incorporate techniques mimicking low-severity disturbances to create more resilient landscapes.

Assessing temporal response to biomass removal: A framework for investigating evolving constraints on boreal stand development

Impacts of harvest intensity and soil disturbance on site productivity are likely to vary with stand development stage and interactive processes related to ecosystem function. On upland boreal sites, stand productivity may initially be constrained by microclimatic conditions. However, increasing nutrient demands and overstory light interception associated with canopy development may place progressively greater emphasis on nutrient availability, profile water storage capacity and asymmetric competition. We illustrate these effects using 20-yr post-harvest data from fourteen jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP) Long-term Soil Productivity (LTSP) installations in northern Ontario.Initial growth and ten-year survival were as great or greater without forest floors (NFF), but by year 15 dominant height increments were usually greater with intact forest floors (FF). Growing season frost occurrence and high vapor pressure deficits occurred more frequently with FF than NFF treatments during the initial stand establishment phase. Similarly, mean growing season soil temperatures were 2-5˚C warmer with NFF during this phase, with stand Leaf Area Index (LAI) values < 0.5. During the following Accelerated Growth phase, treatment differences in microclimate dissipated as LAI increased. Foliar N concentrations and N:P ratios, and soil net N mineralization were usually greater from an early age with FF, and often declined as canopy closure approached. Likewise, modelled site-level constraints related to soil water availability increased with stand development, peaking at LAI values associated with the stem exclusion stage. Placing post-harvest response (i.e., impacts of harvest intensity) in the context of relationships among stand structural development, changes in microclimate, and resource supply and demand should provide greater insights into longer-term effects of establishment practices.

Comparing airborne and spaceborne photon-counting LiDAR canopy structural estimates across different boreal forest types

The monitoring of forested ecosystems relies on an accurate description of forest structure. The Ice, Cloud and land Elevation Satellite-2 (ICESat-2), launched in September 2018, carries the Advanced Topographic Laser Altimeter System (ATLAS), a Light Detection and Ranging (LiDAR) instrument capable of detecting individual photons reflected back from vegetation canopy. ICESat-2 data is delivering global estimates of forest structure; however, analysis of the performance of ICESat-2 on-orbit data across a range of forest conditions remains limited. This study derives structural estimates of (i) canopy height, (ii) canopy cover and (iii) canopy height variability from ICESat-2 data acquired in snow-free and low atmospheric scattering conditions over different boreal forest structural types in Ontario, Canada. ICESat-2 structural estimates were derived from the Global Geolocated Photon Data (ATL03) and Land and Vegetation Height (ATL08) data products and compared against single-photon detection airborne LiDAR (Leica SPL100). An extensive network of ground plots were used to stratify the study area into three distinct forest structural groups, each resulting from different stand development stages. ICESat-2 and SPL100 estimates of canopy height were compared at the ATL03 photon level, whereas estimates of height variability and canopy cover were compared for spatial analysis units (AU; mean size = 1287 m2). ICESat-2 photons returned from the top of the canopy underestimated canopy height relative to SPL100 by an average of 2.3 m overall and corresponded most strongly to the 90th percentile (P90) of coincident airborne SPL100 returns (root mean square difference (RMSD) = 2.9 m and correlation coefficient (r) = 0.84). The lowest average underestimation of SPL P90 was observed in homogeneous stands that were relatively simple, and single-layered with a single dominant species (RMSD = 2.5 m, r = 0.84). We observed the least agreement of ICESat-2 and SPL forest structural metrics in over-mature stands with complex structure and greater variability in canopy heights (RMSD = 3.5 m, r = 0.64). For the AUs, the strength of the relationship between SPL100 and ICESat-2 canopy height percentiles increased with increasing height percentiles (e.g. P25 RMSD% = 77.8%; P95 RMSD% = 23.7%). ICESat-2 generally underestimated canopy height variability relative to the SPL100 data, with both data having similar absolute variability (standard deviation of canopy heights RMSD% = 26.8%, r = 0.75), but lower agreement in relative variability (coefficient of variation of canopy heights RMSD% = 33.9%, r = 0.45). Herein we propose the use of the vegetation fill index as a method to estimate canopy cover with ICESat-2. Comparison of SPL100 and ICESat-2 vegetation fill indices at the AU level resulted in strong agreement overall (RMSD% = 19.7%; r = 0.57). These observations and results contribute to the overall objective of building a comprehensive understanding of the performance of ICESat-2 for characterizing vegetation structure in boreal forest environments.

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.

Tree species composition and diversity in Miombo woodlands between co‐managed and government‐managed regimes, Malawi

Appendix A. Tree species names, families, species codes, and the number of stems per species recorded in each sampled forest reserve (FR) under co‐management (CM) and government management (GM) in Miombo woodland in Malawi.