Forest Regeneration Dynamics Research Articles

Forest characteristics and population structure of a threatened palm tree Caryota obtusa in the karst forest ecosystem of Yunnan, China

Abstract Caryota obtusa of Arecaceae is a fascinating palm tree native to southwestern China, India, Myanmar, Thailand, Laos and Vietnam. It is an economically important and threatened species and appears as a canopy dominant in some karst areas in Yunnan. We aim to clarify the forest structure, species diversity, population status and regeneration dynamics of C. obtusa in the karst forest ecosystem of Yunnan, China. We established 56 vegetation plots dominated by C. obtusa in 10 counties of southern Yunnan. Based on the plot data, we analyzed the community stratification, floristic composition and C. obtusa’s population structure. We used questionnaires to interview local people and recorded the human activity history in C. obtusa-dominated forests. Caryota obtusa palm forests were distributed on limestone mountain slopes and gullies. There were seven forest community types. The stratification of each community included arborous layer, shrub layer and understory. The communities had rich species composition. For all the plots as a whole of each community type, Shannon–Wiener diversity index of either woody or herbaceous species ranged from 2.1 to 3.8. The diameter at breast height (DBH)-class frequency distribution of C. obtusa was a multimodal type. The regeneration was sporadic and dependent on intermediate natural disturbances. In the current population structure, a number of C. obtusa trees with small DBHs consisted mainly of the forest communities with no or a slight degree of human disturbances. Intensive human activities terribly hindered recruitment of C. obtuse, followed by the medium intensity of human activities.

Density-related effect of red deer browsing on palatable and unpalatable tree species and forest regeneration dynamics

Large herbivores play a key role in terrestrial ecosystems, and their populations alter the plant composition in many ecosystems. One example is deer, whose populations in the Northern Hemisphere have increased over the last decades. This has resulted in increased browsing pressure on saplings and, as a consequence, has hampered forest regeneration in some areas. Such herbivore-induced changes in the regeneration of forest stands have changed their composition and biodiversity. Although there is an established link between the deer population density and the level of damage caused by browsing, the question remains open: What is the effect of increasing deer density over years on the regeneration of palatable and less browsing-resistant tree species? In this study, we investigated the relationships between the regeneration dynamics of five tree species (European beech Fagus sylvatica, silver fir Abies alba, sycamore Acer pseudoplatanus, hornbeam Carpinus betulus, and oak Quercus spp.) and browsing pressure in two years with low and high red deer (Cervus elaphus) density and at similar roe deer (Capreolus capreolus) density. We set up experimental plots in Roztocze National Park (central-eastern Poland), a protected area where natural predators of deer are constantly present. In addition to deer density, we analysed parameters that may affect browsing intensity: height of saplings, forage availability (sapling density), sapling diversity and light intensity (canopy openness). We found that increasing red deer density significantly increased browsing on all tree species, with saplings taller than 50 cm being under the strongest pressure. Moreover, higher deer density altered deer forage selection – it increased their selection for unpalatable European beech and decreased for highly preferred sycamore. Additionally, more species-diverse patches and closed canopy attracted deer and increased the probability of browsing on saplings. Contrary to our predictions, sapling density decreased browsing intensity. The study confirms that high ungulate density has significant effects on tree recruitment and may alter tree species composition of the forest stand. We provide clear evidence that deer herbivory plays a crucial role in tree regeneration in top-down processes in natural ecosystems.

Modeling tolerant hardwood sapling density and occurrence probability in the Acadian forests of New Brunswick, Canada: Results 14 years after harvesting

Natural forest regeneration after natural or anthropogenic disturbance is difficult to predict given its high variability. The process is poorly documented for commercial northern hardwood species in the Acadian forest of eastern Canada. Our objective was to identify the silvicultural, environmental, and ecological factors that best explain the variability in sapling density and occurrence of two commercial tolerant hardwood species in New Brunswick: American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.). Forty-three permanent sample plots were established in 2002 and measured before harvesting in 2004. Sapling density and occurrence were measured 14 years after harvesting. The results showed that the interactions between the species and the residual merchantable basal area and between the species and the percent of hardwoods in the original stand best explained the sapling density and occurrence variation of tolerant hardwoods. The sapling density of sugar maple increased with increasing merchantable residual basal area. However, the effect of this variable was not significant for the density of American beech saplings. The density and occurrence of tolerant hardwood saplings both increased along with the percent of hardwoods in the original stand. These results provide an improved understanding about tolerant hardwood regeneration dynamics in New Brunswick forests.

Secondary Forests and Agrarian Transitions: Insights from Nepal and Peru

We provide an analytical contrast of the dynamics of secondary forest regeneration in Nepal and Peru framed by a set of common themes: land access, boundaries, territories, and rights, seemingly more secure in Nepal than Peru; processes of agrarian change and their consequences for forest-agriculture interactions and the role of secondary forest in the landscape, more marked in Peru, where San Martín is experiencing apparent agricultural intensification, than in Nepal; and finally processes of social differentiation that have consequences for different social groups, livelihood construction and their engagement with trees, common to both countries. These themes address the broader issue of the necessary conditions for secondary forest regeneration and the extent to which the rights and livelihood benefits of those actively managing it are secured.

Sustainable Management of Montane Forest and Landscape Tranformation Within the Oku Highlands of Cameroon

The setbacks of deforestation over the years have given light to awareness on the importance of regeneration. The benefits of forest regeneration are numerous both to the environment and man. The main objectives of this study were to assess forest regeneration dynamics and its implication on landscape projection in Oku. This study adopted both primary and secondary methods of data acquisition. This involved the administration of questionnaires, field visits, focus group discussions, observation and key informant interviews. This was practicable based on the accessibility and the potentials of the study area. In addition, satellite images of the study area were exploited to portray the rate of deforestation over the years and extent of tree planting within the area. Collected data was expected to enhance an understanding of endeavours of the local population to protect and regenerate exploited areas. The study found out that the local population are conscious, appreciative and encourage forest regeneration activities. Questionnaire exploitation revealed that 91% of the population plant trees in their farms. These trees range from soil fertilizer species, fruit trees and suitable trees for wood carving. The study equally revealed that 80% of local NGOs present within the matrix area are involved in forest regeneration. As a result of this, the cumulating local efforts of forest revival respects mitigation designed on climate change. The fact that local communities accept the canons of forest regeneration is of maximum importance in guaranteeing environmental benefits.

Chuva de sementes como indicador ambiental de áreas em processo de restauração ecológica do Mato Grosso do Sul

A chuva de sementes (CS) é caracterizada pela chegada de propágulos ao solo, advindos por mecanismos de dispersão e é essencial para a dinâmica da regeneração natural de florestas. O objetivo deste trabalho foi avaliar a CS como indicador de três áreas em processo de restauração do Mato Grosso do Sul, Ivinhema 12 anos (IV-12), Jateí 13 anos (JA-13) e Caarapó 16 anos de plantio (CA-16). Foram instalados aleatoriamente 15 coletores de 0,64 m² em cada uma das áreas e o material coletado mensalmente de maio/2015 a janeiro/2016. Foram calculados os índices de Shannon (H’) e Equabilidade de Pielou (J’) e as sementes classificadas quanto à síndrome de dispersão, hábito e classe sucessional das sementes de espécies arbóreas. Foi identificado o total de 47.124 propágulos nas três áreas. Para CA-16 foram amostradas 27.033 sementes, 29 famílias, 39 gêneros e 41 espécies. JA-13 obteve 8.056 sementes, 22 famílias, 32 gêneros e 33 espécies. A área IV-12 resultou em 12.035 sementes, 13 famílias, 21 gêneros e 22 espécies. Das 61 espécies encontradas para as três áreas, 88,5% são de hábito arbóreo. Referente à síndrome de dispersão, a maioria são zoocóricas, com destaque para IV-12 com 93,7%, sendo que 40,9% são alóctones. Quanto à classificação sucessional, as pioneiras foram destaque, principalmente para IV-12 (91,7%). A CS pode ser considerada um bom indicador para a avaliação da integridade ambiental de áreas em restauração por fornecer subsídios para compreensão da manutenção dos processos ecológicos, visto que nas áreas avaliadas, a maioria das sementes foi de espécies zoocóricas, com expressiva contribuição de espécies alóctones, demonstrando a existência de uma fauna dispersora facilitadora da sucessão florestal.

Driving factors of conifer regeneration dynamics in eastern Canadian boreal old-growth forests.

Old-growth forests play a major role in conserving biodiversity, protecting water resources, and sequestrating carbon, as well as serving as indispensable resources for indigenous societies. Novel silvicultural practices must be developed to emulate the natural dynamics and structural attributes of old-growth forests and preserve the ecosystem services provided by these boreal ecosystems. The success of these forest management strategies depends on developing an accurate understanding of natural regeneration dynamics. Our goal was therefore to identify the main patterns and drivers involved in the regeneration dynamics of old-growth forests with a focus on boreal stands dominated by black spruce (Picea mariana (L.) Mill.) and balsam fir (Abies balsamea (L.) Mill.) in eastern Canada. We sampled 71 stands in a 2 200 km2 study area located within Quebec's boreal region. For each stand, we noted tree regeneration (seedlings and saplings), structural attributes (diameter distribution, deadwood volume, etc.), and abiotic (slope and soil) factors. The presence of seed-trees located nearby and slopes having moderate to high angles most influenced balsam fir regeneration. In contrast, the indirect indices of recent secondary disturbances (e.g., insect outbreaks or windthrows) and topographic constraints (slope and drainage) most influenced black spruce regeneration. We propose that black spruce regeneration dynamics can be separated into distinct phases: (i) layering within the understory, (ii) seedling growth when gaps open in the canopy, (iii) gradual canopy closure, and (iv) production of new layers once the canopy is closed. These dynamics are not observed in paludified stands or stands where balsam fir is more competitive than black spruce. Overall, this research helps explain the complexity of old-growth forest dynamics, where many ecological factors interact at multiple temporal and spatial scales. This study also improves our understanding of ecological processes within primary old-growth forests and identifies the key factors to consider when ensuring the sustainable management of old-growth boreal stands.

Species richness, forest types and regeneration of Schima in the subtropical forest ecosystem of Yunnan, southwestern China

BackgroundSchima genus of Theaceae is confined to subtropics and tropics of South, East and Southeast Asia. Thirteen species of Schima are distributed in subtropical China. Many of them appear as dominant canopy species in the subtropical forests. To date, Schima species richness distribution patterns of China have remained unknown. Meanwhile, there has been a longtime debate as to whether forests dominated by Schima species are early or late successional forests. We aim to clarify Schima species richness patterns and these species’ roles in the forest succession and regeneration dynamics of the subtropical ecosystem in Yunnan Province, China.MethodWe mapped Schima species richness distribution patterns in China. Based on 71 vegetation plots, we analyzed forest characteristics, population structure, and regeneration dynamics of Schima species in Yunnan.ResultsYunnan was found to harbor the greatest richness and the highest rarity-weighted richness of Schima species in the subtropical regions of China. We classified five primary and six secondary forest types containing Schima species as one of dominants. Yunnan had the high floristic diversity and varying stand structure of forests containing Schima species. The Schima species studied generally had a sporadic regeneration type and a long life-span. Four species (Schima argentea, Schima villosa, Schima sinensis, Schima sericans) were shade-intolerant. But three species (Schima noronhae, Schima khasiana and Schima wallichii) were considered as bi-modal type species having shade-intolerant and shade-tolerant traits. Schima noronhae was seen to be a top dominant in late successional forests, while S. wallichii was found as a top-dominant in early or middle or late successional forests. S. khasiana, Schima villosa, Schima sinensis usually appeared as a top dominant in early or middle successional secondary forests, though they also presented as a second dominant in late-successional forests. Schima argentea and Schima sericans dominated only in the early or middle/seral successional forests. Schima species’ regeneration establishment depended mainly on forest canopy gap formation through moderate human and natural disturbances.ConclusionsYunnan has high species richness and rarity-weighted richness of Schima. Both moderate human and natural disturbances have provided regeneration niches for Schima species. Some of the Schima species studied as a second dominant (rare as the top-dominant) present in the late-successional forests. Some of them are more often as the top-dominant in early or middle successional forests, where as time goes by the dominance of Schima species would be replaced by their associated dominant taxa such as Castanopsis species.

Early Regeneration Dynamics of Pure Black Spruce and Aspen Forests after Wildfire in Boreal Alberta, Canada

Research Highlights: Black spruce (Picea mariana Mill.) and trembling aspen (Populus tremuloides Michx.) both regenerated vigorously after wildfire. However, pure semi-upland black spruce stands are at increasing risk of changing successional trajectories, due to greater aspen recruitment. Background and Objectives: Black spruce and aspen are found across the boreal forest with black spruce dominating lowlands and aspen being common in uplands. Both species are well adapted to wildfire with black spruce holding an aerial seedbank while aspen reproduce rapidly via root suckering. In the summer of 2016, the Horse River wildfire burned 589,617 hectares of northern Alberta’s boreal forest. Methods: We assessed early regeneration dynamics of both pure aspen and pure black spruce forests. For black spruce, 12 plots were established in both bog and semi-upland habitats to assess seedling regeneration and seedbed availability. For aspen, 12 plots were established in each of the low, moderate, and high burn severities, as well as 5 unburned plots. Results: Post-fire black spruce regeneration densities did not differ between bog and semi-upland habitats, but were positively correlated with forb cover and charred organic matter seedbeds. Aspen regeneration within pure black sprue stands was substantial, particularly in semi-upland habitats, indicating a potential shift in successional trajectory. Fire severity did not significantly affect aspen regeneration in pure aspen stands, but regeneration density in all severity types was >90,000 stems ha−1. Aspen regeneration densities were negatively related to post-fire forb and shrub cover, likely due to competition and cooler soil temperature.

Impact of pathogenic fungi, herbivores and predators on secondary succession of tropical rainforest vegetation

Abstract There is growing evidence that top–down biotic factors play an important role in plant community dynamics and are able to maintain the high plant diversity of primary tropical forests. However, the top–down impact by herbivores on the accumulation of plant biomass, richness and the community assembly process remains poorly known for the initial stages of secondary ecological succession. Here we test the top–down effects of natural enemies on the biomass, richness, diversity, community composition, trait dynamics and randomness during the assembly process on an early successional community in a lowland tropical forest in Papua New Guinea. We initiated secondary succession on 36 vegetation plots (5 × 5 m) organized in six blocks. After 1 year we evaluated successional community characteristics in each block containing a control plot and five treatment plots: experimentally excluding (a) insects by insecticides, (b) fungal pathogens by fungicides, (c) vertebrate predators and ants with exclosures and traps and experimentally adding (d) low and (e) high levels of a generalist herbivore species. Insects were responsible for increased plant diversity, shifts in plant community composition and a decrease in community weighted mean of leaf dry matter content. The lack of herbivores resulted in a diversifying effect but did not affect plant biomass and stem density. No other treatment had a significant effect on plant diversity during succession. The highest level of artificially increased herbivore density reduced plant biomass, while the fungicide treatment decreased stem density of woody plants. Using a null model approach, we showed that the removal of insects and their vertebrate predators increased randomness during the community assembly processes for woody plants, whilst the same effect was not found for the removal of fungi or elevated herbivore abundances. Synthesis. Early rainforest succession was not entirely plant driven. During the early succession of lowland tropical forest, insect herbivores enhanced plant diversity and caused shifts in community structure by promoting species with acquisitive leaf traits. As expected, the early successional communities were highly variable, but insects and vertebrate predators reduced randomness during the assembly process. Insect and vertebrate communities can thus impact the regeneration dynamics of tropical forests. In contrast, fungal pathogens were less important in maintaining high diversity of successional communities in our system.

Drivers of forest regeneration patterns in drought prone mixed-species forests in the Northern Calcareous Alps

In temperate mountain forests of Northern Calcareous Alps, shallow soils, in combination with steep slopes and high radiation input on sun-exposed slopes, imply severe conditions for tree regeneration. Considering the remarkable trend of temperature increase and related climatic extremes in the Greater Alpine Area, it is likely that conditions for successful regeneration further deteriorate at these sites. Hence, investigating the relation of regeneration patterns to site conditions is crucial for recent and future forest management. Spatial point process models are appropriate tools to test the effect of environmental covariates in plant pattern generation. By applying these methods, we aim at identifying driving factors of forest regeneration dynamics of Fagus sylvatica, Abies alba and Picea abies. We used tree regeneration data from two sample sites along transects from closed canopy to forest gaps of natural origin. A set of spatially continuous explanatory variables (light environment, rock outcrops, microrelief, distance to mature trees, estimated seed density and presence of already established saplings) were generated. We fitted nonstationary parametric intensity functions with Poisson point process models and Thomas cluster point process models. The first and second order processes were analysed with pair correlation summary statistics. Interactions between regeneration patterns of different species and height classes were assessed with cross-pair correlation summary statistics. Successful germination and growth, at least at some microsites, is possible for any of the investigated species when ungulate browsing is prevented by fencing. Light is the most important environmental factor for describing the regeneration patterns. As higher shading has a positive influence, it is apparently not a limiting resource but rather a proxy for other, latent unfavourable conditions like drying of seedbeds. We thus propose to limit canopy opening sizes to a maximum of 10–12 m. No indications of seed limitation as a cause for regeneration failure of any of the main tree species were detected. Conditions for A. alba seedlings and partly also for P. abies seedlings are more favourable under the canopy of F. sylvatica than under the canopies of conspecifics or the other conifer species. Therefore, we conclude that at our study sites with the current species mixture, at least for the two conifer species, safe microsites are more important than seed availability. With increasing height of P. abies, the spatial segregation of small A. alba and F. sylvatica seedlings became stronger, indicating that competition for resources becomes more dominant and determinant for species coexistence.

Neighborhood effects explain increasing asynchronous seedling survival in a subtropical forest

Biotic interactions play a critical role in mediating community responses to temporal environmental variation, but the importance of these effects relative to the direct effects of environmental change remains poorly understood, particularly in diverse forest communities. Here we combine a neighborhood modeling approach with insights from coexistence theory to assess the effects of temporal variation in species interactions and environmental conditions (e.g., precipitation, temperature, and understory light availability) on seedling survival over nine census years in a subtropical forest. We find significant temporal shifts in the magnitude of neighborhood effects on both community-wide and species-level seedling survival (statistically significant random effects of neighborhood × year and neighborhood × species × year interactions). These results are consistent with the idea that environmental change will play a fundamental role on forest regeneration dynamics by altering biotic interactions at the neighborhood scale. Moreover, differences among species in response to neighbors over time contribute to a pattern of temporal decoupling of seedling survival between species, which can help to promote diversity in certain contexts. In separate analyses of multiple regression on distance matrices (MRM), altered interactions with neighbors are much stronger predictors of asynchronousseedling survival among species than the pure effects of climate and plant functional traits, explaining twice as much variation (43.9% vs. 22.2%). In sum, these results reveal that divergent species responses to interannual environmental variability detected are driven primarily by indirect effects mediated by changing biotic environments. This highlights the importance of including indirect effects from local biotic (neighborhood) interactions in forecasts of forest community responses to global change.

The loss of functional diversity: A detrimental influence of landscape‐scale deforestation on tree reproductive traits

Abstract Agricultural activities such as crop production and cattle ranching are rapidly replacing forests worldwide, especially in the tropics. Resulting forest loss can adversely affect biodiversity in many ways, including trajectories of community reassembly, community composition, forest structural profiles and taxonomic diversity. Yet, effects of forest loss on specific ecosystem functions remain limited. Processes closely linked with tree reproduction, such as pollination and seed dispersal are of paramount importance for many ecological functions in tropical forests. Disruption in these processes is known to delay or change forest regeneration, diversity and structural dynamics. To explore how reproductive and dispersal traits are being altered by landscape‐scale deforestation, we surveyed and compiled trait data for tree communities in 20 tropical Atlantic rainforest remnants in northeastern Brazil, across a gradient of deforested landscapes, each retaining 3%–93% forest cover. The functional richness of reproductive plant attributes decreased as the amount of forest cover decreased, while divergence increased along the same gradient. Loss of forest cover disproportionately affected certain dispersal and reproductive attributes, with most heavily impacted functional attributes including: brief flowering duration, hermaphrodite sexual system, and zoochoric dispersal mode. We identified a clear threshold at 25–30% of forest cover, below which, reproductive attributes disappeared more quickly than expect from forest remnants. Synthesis. Deforestation may impair tree community functional diversity, particularly by decreasing the number of functions. Under scenarios of extensive deforestation, changes to reproductive and dispersal trait profile of forest communities suggest that profound modifications in the availability of floral and seed resources are likely to be substantial. Such extensive changes to food supply of pollinating and dispersing animals suggest carry‐over effects to the fauna of these important forest systems.

Native forest regeneration and vegetation dynamics in non-native Pinus patula tree plantations in Madagascar

Today, exotic invasive alien species are considered to be one of the greatest threats to biodiversity. However, not all exotic species cause negative consequences in the ecosystems in which they settle. In some cases, artificial plantations of exotic species can act as a catalyst for the regeneration of native species. In southern central Madagascar, which has been affected by diverse disturbances (cyclones, logging, cultivation), Pinus patula plantations have become environments conducive to the regeneration of native species. This study aims to assess the level of understory plant diversity in these artificial plantations, describe the vegetation dynamics, and examine the effects of agricultural practices and logging on vegetation diversity and structure. Floristic inventories and biomass measurements were made on three types of vegetation that have resulted from previous human-induced disturbance: (i) cassava crops established after pine logging; (ii) fallows corresponding to cassava crops left fallow for 1–2 years; and (iii) post-logging regrowth after pine logging 3–10 years previously. Botanical surveys were conducted on 205 10 × 10 m2 quadrats placed along 40 transects. A total of 125 species, 34 of which endemic, from 46 families were inventoried. The Shannon Weaver index H′ values were significantly different between post-logging regrowth (H′ = 4.01 ± 0.67), and cultivated fields (H′ = 1.46 ± 0.23) and fallows (H′ = 3.31 ± 0.78) (p < 0.001). Agricultural practices, such as tillage regime, number of crop-fallow cycles (>2 cycles) and number of fire occurrences (>4 fires) had a greater impact on the reconstitution of vegetation than environmental parameters such as slope and topographic position. The Shannon-Weaver diversity index (H′) and vegetation structure parameters (tree density, biomass) were inversely correlated with the intensity of disturbance linked to these agricultural practices. These results suggest that a low level of disturbance, such as that resulting from Pinus tree logging, can act as a catalyst for the establishment of native woodlands. Excessive disturbance from sylvicultural and agricultural practices, such as frequent burning, heavy tillage and high number of crop/fallow cycles, may hinder, but does not block, the establishment of native woodlands.

Are microbial activity and arbuscular mycorrhizal fungal community influenced by regeneration stages? A case study in Southern Brazil coastal Atlantic Rain Forest

Aiming to describe coastal Atlantic Rain Forest (ARF) regeneration dynamics, we evaluated attributes linked to soil biota and mycorrhizal symbiosis in two coastal ARF sites in Florianópolis, Southern Brazil. In each site, we selected forest transects in early regeneration (ER) and advanced regeneration (AR) stages, i.e., about 20 and 50 years without agricultural use, respectively. Soil total organic carbon (TOC) was higher in AR than in ER stage. Soil microbial biomass carbon (MBC) varied between sites and was higher in the AR than in the ER stage. Basal respiration and qCO2 rates differed between sites and were, respectively, higher and lower in advanced regeneration stage areas. Arbuscular mycorrhizal (AM) root colonization and AM fungal spore density were higher in the ER stage, with no difference between sites. Principal Component Analysis (PCA) for correlation between soil microbiological and chemical attributes showed that the variables with the most influence on sample separation for the first component were total spore number, soil MBC, root mycorrhizal colonization, and soil TOC. Soil pH, available P, and qCO2 had the highest influence on the second component. This analysis separated samples by regeneration stage, and sites differed only in AR stage. PCR-DGGE analysis on DNA extracted from soil samples showed that AMF community structure differed more between sites than between regeneration stages.

Forest Spectral Recovery and Regeneration Dynamics in Stand-Replacing Wildfires of Central Apennines Derived from Landsat Time Series

Understanding post-fire regeneration dynamics is an important task for assessing the resilience of forests and to adequately guide post-disturbance management. The main goal of this research was to compare the ability of different Landsat-derived spectral vegetation indices (SVIs) to track post-fire recovery occurring in burned forests of the central Apennines (Italy) at different development stages. Normalized Difference Vegetation Index (NDVI), Normalized Difference Moisture Index (NDMI), Normalized Burn Ratio (NBR), Normalized Burn Ratio 2 (NBR2) and a novel index called Forest Recovery Index 2 (FRI2) were used to compute post-fire recovery metrics throughout 11 years (2008–2018). FRI2 achieved the highest significant correlation (Pearson’s r = 0.72) with tree canopy cover estimated by field sampling (year 2017). The Theil–Sen slope estimator of linear regression was employed to assess the rate of change and the direction of SVIs recovery metrics over time (2010–2018) and the Mann–Kendall test was used to evaluate the significance of the spectral trends. NDVI displayed the highest amount of recovered pixels (38%) after 11 years since fire occurrence, whereas the mean value of NDMI, NBR, NBR2, and FRI2 was about 27%. NDVI was more suitable for tracking early stages of the secondary succession, suggesting greater sensitivity toward non-arboreal vegetation development. Predicted spectral recovery timespans based on pixels with a statistically significant monotonic trend did not highlight noticeable differences among normalized SVIs, suggesting similar suitability for monitoring early to mid-stages of post-fire forest succession. FRI2 achieved reliable results in mid- to long-term forest recovery as it produced up to 50% longer periods of spectral recovery compared to normalized SVIs. Further research is needed to understand this modeling approach at advanced stages of post-fire forest recovery.

Regeneration for resilience framework to support regeneration decisions for species with populations at risk of extirpation by white pine blister rust

Natural forests are increasingly invaded by nonnative pests and pathogens that threaten host species with population extirpation and cascading ecological impacts. The regeneration for resilience (R4R) framework provides a decision structure to prioritize limited resources and utilize artificial and natural regeneration management to offer the best likelihood of success in positioning stands and landscapes to support multi-generational self-sustaining host populations in the presence of the nonnative invader by (1) increasing host population size to offset invader-caused mortality, (2) increasing the frequency of genetic resistance traits in host populations in habitats that enable their expression and durability to retard future mortality and facilitate population sustainability and recovery, and (3) maintain host genetic diversity, adaptive capacity, and population connectivity. This application is designed for conditions where the nonnative invader is expected to be a persistent threat, the host species naturally has some genetic resistance to the invasive species, and the forest host populations are integral to support valued ecosystem processes and services. The R4R framework has been developed for application in high elevation five-needle pine ecosystems of North America impacted and threatened by the nonnative pathogen Cronartium ribicola that causes the lethal disease white pine blister rust (WPBR). Several examples using the R4R framework to integrate information on current forest condition, WPBR risk or hazard, genetic resistance to WPBR, and host population dynamics and silvics to prioritize areas and design interventions are discussed. Effective management of forest regeneration dynamics can increase forest resilience and adaptive capacity to mitigate impacts of invasive species.

Effects of gap size and within-gap position on seedling growth and biomass allocation: Is the gap partitioning hypothesis applicable to the temperate secondary forest ecosystems in Northeast China?

Forest gaps can change stand structure and affect forest regeneration dynamics. The gap partitioning hypothesis claims that tree species would regenerate along gap environmental gradients owing to their different resource demands. However, many studies that examined this hypothesis in uncontrolled gap conditions have yielded inconsistent conclusions and there are limited studies testing the hypothesis taking into account biomass allocation. In this study, we examined the gap partitioning hypothesis in a temperate secondary forest ecosystem where gap formation drives forest regeneration. We created gaps with different sizes and planted two commercially important native tree species with contrasting shade tolerance in nine positions along four cardinal directions within the gaps. We found that shade tolerance was the main factor affecting seedling regeneration performance within gaps. For the light-demanding Manchurian walnut (Juglans mandshurica Maxim.), seedling growth varied significantly along the light intensity gradients, which indicated that seedlings could greatly benefit from high light areas within gaps, especially when the gap size increased. Seedling biomass in gap centers and transitions (54.0 g) were much higher than in gap edges (13.7 g) and forest understories (8.6 g). High light environments contributed to higher biomass allocation to the leaves and accelerated carbon assimilation. Low light conditions resulted in increasing proportions of stem biomass, which might promote seedling height growth, although the promotion effects were relatively limited. However, for the shade-tolerant Korean spruce (Picea koraiensis Nakai), little evidence of seedling divergence was found within gaps. Mostly, seedlings only showed growth and biomass allocation differences between gaps and forest understories. Korean spruce showed high adaptability to various gap environments and might be a generalist species rather than being limited to small gaps. The performance of Manchurian walnut strongly supported the gap partitioning hypothesis, but Korean spruce provided little evidence for gap partitioning. Therefore, planting scenarios in silvicultural practices could be suitably designed, with Manchurian walnut in high light gap areas and Korean spruce in most positions within gaps, during the early stage after competition elimination.

Effects of long-term inter-annual rainfall variation on the dynamics of regenerative communities during the old-field succession of a neotropical dry forest

Effects of long-term rainfall inter-annual variation on regeneration dynamics of tropical dry forests (TDF) are still poorly understood. Such understanding is particularly important to assess the regeneration potential of TDF in landscapes subjected to slash-and-burn farming management. Here, we studied from 2004 to 2016 the effects of inter-annual rainfall variation on the dynamics of regenerative communities of woody species during the old-field succession of a TDF in Western Mexico. Over the study period a severe drought, caused by an El Niño Southern Oscillation (ENSO) event in 2005, and two hurricanes (Jova, 2011, magnitude 2; Patricia, 2015, magnitude 4) were experienced. In 2004, we established a chronosequence of abandoned cattle pastures and old-growth forest sites, which were assigned to four successional categories, each one with three sites: Pasture (0–3 years fallow age), Early (3–5 years), Intermediate (8–12 years), and Old-Growth Forest (without any human disturbance). At each site, seedlings, saplings and resprouts 10–100 cm height of shrub and tree species were tagged, taxonomically identified, measured in height and monitored over 12 continuous year intervals. At each year, all new plants reaching 10 cm height were recorded and considered as recruits. Community rates (recruitment, relative growth rate in height, mortality, species gain and species loss) were calculated per year, considering all plants combined and separating shrub from tree species. All community rates varied notoriously in response to temporal rainfall variability, with almost null interaction with successional category. As expected, mortality and species loss rates declined as the amount of rainfall increased, especially when precipitation of the current and the previous year were taken into account; these rates peaked in the ENSO year and were still high in the following year. Unexpectedly, recruitment and species gain rates also declined with the increase in rainfall, especially with the amount of rainfall in the current year. Overall, community rates of tree species were more responsive than those of shrub species to temporal rainfall variation. The ENSO-related drought event produced a short and transient instability in the plant density and species density of regenerative communities. However, ENSO effects were smoothed out by subsequent rainy years, leading to a net increase in plant density and species density in all successional categories, especially in the younger one. Overall, our study shows that global (e.g. ENSO) and regional (e.g. storms, hurricanes) climate factors play a key role on forest succession, modulating the speed of the TDF regeneration dynamics. We conclude that low impact agricultural land use and the presence of good levels of remnant forest cover in the landscape confers a high potential for regeneration in abandoned agricultural fields, even under the impact of severe droughts and severe hurricanes.

High Mortality and Low Net Change in Live Woody Biomass of Karst Evergreen and Deciduous Broad-Leaved Mixed Forest in Southwestern China

Repeated observation based on large permanent monitoring plots is a key method for directly understanding forest regeneration dynamics. Karst forests grow slowly in adverse habitats and possess a special regeneration mode. However, no data can support these properties because no repeated observations have been performed. The mortality, recruitment, and net change in live woody biomass (NPPlw) of a karst evergreen and deciduous broad-leaved mixed forest in Central Guizhou Province, Southwestern China, were studied on the basis of a short-term continuous monitoring (3 years) of a 2 ha plot. The species richness of individuals with a diameter at breast height (DBH) ≥ 1 cm decreased from 66 to 58 during the study period. Eight species disappeared, and no new species appeared. The individual number declined from 16,821 to 15,003 because most species indicated more deaths than recruitments. Trees presented the lowest mortality rate, and shrubs presented the highest recruitment rate among the species. Individual death number decreased with the increase in DBH classes. The estimated aboveground NPPlw was 8.41 t ha−1 year−1. The survivors, recruitments, and deaths contributed 10.88, 0.11, and −2.58 t ha−1 year−1, respectively. Trees (8.37 t ha−1 year−1), rather than shrubs (0.04 t ha−1 year−1) and lianas (−0.004 t ha−1 year−1), were the major contributors. The karst forest presented higher mortality and lower NPPlw than nonkarst forests in subtropical China and in the world.