The ability of dry forests to deliver ecosystem services of both local and global relevance depends on the capacity of those forests to recover from constant disturbances in human-modified ...landscapes. Here we examine the effects posed by biomass, chronic human disturbances and aridity on the recovery of reproductive functional diversity by edible fruit plant assemblages following slash-and-burn agriculture in a Caatinga dry forest, in northeastern Brazil. The edible fruit plant assemblages were described across 24 forest stands, including regenerating stands of varying age (4 to 50 yr old) and old-growth stands, adopting a large set of reproductive traits as floral sizes, reproductive systems, and pollination systems. Such a chronosequence covered a gradient relative to aboveground biomass, aridity, and chronic anthropogenic disturbances (CAD). We observed that edible fruit plant assemblages across both regenerating and old-growth forest stands exhibited similar taxonomic diversity scores. This pattern is also figured in the recovery of reproductive traits, which is relatively fast as regenerating forest scores are generally similar or higher to those in old-growth forests. Generally, regenerating forest stands support more specialized reproductive traits and strategies than old-growth forest stands e.g., edible fruit plants with very large flowers (>30 mm), specialized pollination systems, large fruits (>1.5 ≤3.0 mm), and medium-sized seeds (>0.6 ≤1.5 cm). However, the functional diversity of specialist reproductive traits decreased with increases in the levels of biomass and aridity, isolated, but was also impacted by the interactive effect. Considering the effects of biomass, CAD or aridity individually, we observed that biomass itself was responsible for most of the effects (42.8%), while 52.3% of the reproductive traits were negatively affected by CAD or aridity, which seems to be a major force against the recovery.
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•Secondary forests harbor similar abundance of edible fruit plants as mature forests.•Aridity reduces the species richness of edible fruit plant assemblages.•Secondary forests harbor more specialized traits and strategies than mature forests.•The successional trajectory goes from specialized to generalist traits.•Aridity act as a strong environmental filter against regeneration.
Earth system models must predict forest responses to global change in order to simulate future global climate, hydrology, and ecosystem dynamics. These models are increasingly adopting vegetation ...demographic approaches that explicitly represent tree growth, mortality, and recruitment, enabling advances in the projection of forest vulnerability and resilience, as well as evaluation with field data. To date, simulation of regeneration processes has received far less attention than simulation of processes that affect growth and mortality, in spite of their critical role maintaining forest structure, facilitating turnover in forest composition over space and time, enabling recovery from disturbance, and regulating climate-driven range shifts. Here, our critical review of regeneration process representations within current Earth system vegetation demographic models reveals the need to improve parameter values and algorithms for reproductive allocation, dispersal, seed survival and germination, environmental filtering in the seedling layer, and tree regeneration strategies adapted to wind, fire, and anthropogenic disturbance regimes. These improvements require synthesis of existing data, specific field data-collection protocols, and novel model algorithms compatible with global-scale simulations. Vegetation demographic models offer the opportunity to more fully integrate ecological understanding into Earth system prediction; regeneration processes need to be a critical part of the effort.
Applying arginine-phosphate (AP) to tree seedlings at planting is a novel silvicultural practice in Northern Europe to improve the success of forest regeneration. We present three case-studies of the ...potential advantages of adding AP at planting on the establishment and damage susceptibility of seedlings in pure and mixed plantings of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) H. Karst. ) and silver birch (Betula pendula Roth) over two years in the field. Location of study sites were in southern (S), northeastern (NE) and northwestern (NW) Sweden. The main agents of damage were pine weevil (Hylobius abietis L.) on conifers at the south site, browsing of birch at all sites and browsing/other top damage to conifers at the north sites. The effect of adding AP varied between the sites. It was positive for survival of pine at site S, despite considerable damage by pine weevil. However, at the S site more of the surviving spruce and birch were browsed when treated with AP. At the NE site AP-treatment had positive effects on conifer growth. At the NW site adding AP positively affected survival and growth of all three species, and AP-treated seedlings of all species were less browsed than untreated seedlings. AP treatment presents a potential tool to improve the success of forest regeneration, especially when establishing pine stands in south Sweden.
•Seed viability decreases after fire, while seed density remained constant.•The diversity of seeds also decreases after fire, especially the rare species.•β-diversity between plots drops after fire, ...especially its turnover component.•This farming method limits the forest’s regenerative potential.
Forest ecosystems are increasingly threatened by unsustainable agricultural practices, especially by those that damage their regenerative potential. This can be the case of slash-and-burn agriculture – a farming method that can negatively impact the soil seed bank, potentially limiting the resilience of forest ecosystems. To test this hypothesis, and thus look for management practices aimed at enhancing forest recovery, we examined the impact of fire throughout an experiment of slash-and-burn agriculture on the soil seed bank of woody plants in the Caatinga tropical dry forest, northeast Brazil. We compared seed damage and viability, and the structure (seed density and diversity) and composition (taxonomic and functional) of seed bank assemblages before and after fire. We found a significant decrease in the frequency and proportion of intact (undamaged) seeds after fire, and a 3.6-fold decrease in the proportion of viable seeds. While seed density remained constant, species diversity drastically decreased after fire, especially the number of rare species. The compositional dissimilarity (β-diversity) between plots also dropped after fire, particularly its turnover component, thus causing the homogenization of seed assemblages across space. The functional composition of seed assemblages was also altered, with the relative frequency of shrub species increasing after fire, especially species with fleshy fruits and biotic dispersal. Taken together, our findings highlight the low resistance of the soil seed bank to this common farming method in tropical dry forests. Therefore, the recovery of this and potentially of other species-rich tropical forests exposed to slash-and-burn agriculture cannot rest on the soil seed bank, but on other processes such as seed dispersal and resprouting – an interesting avenue for future research.
•Ecosystem-based management aims to mimic natural variability in managed forests.•High densities of ungulates in some areas are unrepresentative of past abundance.•Direct and indirect effects of ...browsing hinder achievement of several objectives.•Ungulates should be considered when planning and establishing management objectives.
Forest management can enhance the ecosystem services forests provide, but it can also alter the capacity of forests to provide those services in the future. Ecosystem-based management has been widely implemented to mitigate the deterioration of forest ecosystems by reducing dissimilarities between managed and natural forests. Ecosystem-based management objectives generally aim to maintain community composition, stand structure, ecosystem functions and services. Heavy browsing pressure by ungulates at densities unrepresentative of past abundance could interfere with these objectives by chronically and selectively browsing tree regeneration following logging.
Using a browsing exclusion experiment, we investigated how the effects of different moose browsing pressures on tree regeneration could interfere with ecosystem management objectives in boreal forests of Quebec, Canada. Management objectives in this region include, among others, reaching targeted coniferous trees densities for commercial harvest, favouring the conservation of birches (Betula spp.) to maintain soil quality and conserving fruit-bearing trees due to their ecological significance for biodiversity. We used path analyses to differentiate direct and indirect effects of moose on seedling density and mixed models to investigate how browsing affected sapling recruitment and whether resulting densities are compatible with ecosystem management objectives.
By directly reducing the overall sapling density, moose browsing indirectly increased seedlings densities of all deciduous species. This indirect effect increased with browsing pressure and favoured raspberry cover, which was positively or negatively linked to seedling density, depending on tree species. Moderate and heavier browsing pressures reduced coniferous sapling density below the ecosystem management target. Moose suppressed birch saplings so that the minimal target of 50 birches ha−1 was not met under heavier browsing pressure. Sapling density of fruit-bearing trees was low under all browsing pressures when compared to exclosures.
Policy implications
Heavy moose browsing is preventing the achievement of ecosystem management objectives in our study area. Positive indirect effects on seedling densities suggest that reducing moose density could allow released seedlings to replenish the sapling layer, but we discuss why this would not guarantee reaching ecosystem management objectives. To help forest managers evaluate and respond to challenges posed by high ungulate densities, we suggest incorporating browsing inventories in national forest surveys to monitor this chronic disturbance and modulate decisions for forest ecosystem management.
•Heavily visited forests are at great risk of Phytophthora invasion.•Chestnut and beech recreational forests are often host to exotic Phytophthora.•Phytophthora invasion is linked to high defoliation ...and low regeneration of trees.
Tree decline caused by exotic Phytophthora pathogens is a serious issue affecting forests around the world. The presence of Phytophthora has been reported in heavily visited natural forests; however, whether recreational forests are at higher risk of being attacked by Phytophthora than non-recreational forests has yet to be explored. In this study, we sampled soil from 44 forests in Catalonia (NE Spain) with high or low recreational use that were dominated by chestnut (Castanea sativa), beech (Fagus sylvatica) or cork oak (Quercus suber). A systematic soil sampling of 277 plots in stands of different tree species, predominantly Pinus and Quercus spp., was also conducted across Catalonia to compare soils of recreational forests with high and low recreational use with the baseline incidence of Phytophthora in the region. The putative impacts of the presence of Phytophthora in recreational areas were assessed by measuring tree defoliation and regeneration, and by performing pathogenicity trials using Phytophthora isolates from soil and root samples to inoculate seedlings of tree species growing in the region. The incidence of native and invasive Phytophthora species was higher in chestnut, beech and cork oak forests than in forests of other tree species. For chestnut and beech forests, we found that the likelihood of finding an invasive Phytophthora in forests with high recreational use was more than three times higher than in forests with low recreational use (76% vs 21%, respectively). No differences were observed in cork oak forests. In plots with invasive Phytophthora species, beech exhibited higher defoliation levels than in plots without Phytophthora. The presence of both native and invasive Phytophthora species was associated with lower chestnut and cork oak regeneration. Our data indicate that Phytophthora is widespread in some forests used for recreation and seems to be associated with defoliation and low regeneration. However, the primary mechanism explaining the high prevalence of Phytophthora in recreational areas remains unclear. Disturbance, soil movement due to construction, or visitors moving inoculum within and across sites could be studied as possible contributing factors to establish effective management actions.
Tree fecundity and recruitment have not yet been quantified at scales needed to anticipate biogeographic shifts in response to climate change. By separating their responses, this study shows ...coherence across species and communities, offering the strongest support to date that migration is in progress with regional limitations on rates. The southeastern continent emerges as a fecundity hotspot, but it is situated south of population centers where high seed production could contribute to poleward population spread. By contrast, seedling success is highest in the West and North, serving to partially offset limited seed production near poleward frontiers. The evidence of fecundity and recruitment control on tree migration can inform conservation planning for the expected long-term disequilibrium between climate and forest distribution.
•Natural regeneration of peatswamp forest on degraded peatlands is driven by distance to forest, mammal and bird dispersal.•Regeneration occurred in clusters of young trees at distances up to 2 km ...from the forest.•Forest burnt in 1997 had higher species diversity and trees per plot than intact forest.•Natural regeneration could restore degraded peatlands surrounding remnant forest patches up to 500 m from natural forest.
Restoration of peat swamp forest (PSF) on degraded Southeast Asian peatlands could reduce global carbon emissions and biodiversity loss. However, multiple ecological barriers are believed to hinder natural regeneration of native trees on degraded peatland and make restoration expensive. We evaluated if natural PSF regeneration occurs and what factors may influence it on eight different land use and land cover (LULC) classes with different types of disturbance, including drainage and fire, in a retired Acacia crassicarpa Benth. (Acacia) plantation landscape. The study involved 42 plots inside five PSF LULCs – intact, logged, burnt (1997, 2015), remnant and 212 plots at distances up to 2 km from the PSF edge in three Acacia plantation LULCs – unharvested, harvested, and burnt. The number of species per plot were similar between intact PSF (25 ± 6 (SD) per 20 m × 10 m plot), logged forest (30 ± 6) and 1997 burnt forest (30 ± 13) but lower in 2015 burnt forest (11 ± 10) and remnant forest (18 ± 11). Regeneration away from the PSF across all degraded LULCs varied from fern dominated areas with no regeneration to clusters with high stem densities. The plantation LULCs, unharvested (94 species) and harvested Acacia (71 species), had similar overall species diversity after 3–4 years of regeneration to the intact and logged PSF (90 species). In unharvested Acacia, total species diversity, species per plot and stem density decreased with distance from forest edge (1–300 m – 87 species; 9 ± 6 (SD) species per 20 m × 10 m plot; 1,056 stems/ha; 301–500 m – 33; 5 ± 2; 511 and >500 m – 38; 6 ± 3; 683). In harvested Acacia, there was low plot species diversity irrespective of distance from the forest (1–300 m – 51; 4 ± 2; 578; 301–500 m – 17; 4 ± 2; 1,100; >500 m – 48; 4 ± 2; 780). Factors which may influence regeneration differed between different LULCs, but there was a clear influence of distance from forest edge and dispersal mechanism – i.e. whether a tree was bird or mammal dispersed and the interaction between these two factors. While our study suggests that if not further disturbed by logging, drainage and/or fire, degraded PSF could regenerate naturally to a similar species diversity as intact PSF, the lower levels of natural regeneration further away from the forest may warrant selective planting of species which do not disperse over long distances. More study is needed on the factors facilitating natural regeneration, whether it leads to restoration of PSF ecosystem functioning and the role of Acacia as a potential regeneration catalyst.
•We studied tropical forest regeneration along an elevation and disturbance gradient.•We recorded and identified all saplings of woody plants in 65 plots of 100 m2 each.•Natural regeneration was ...shown in all vegetation zones and disturbance levels.•Sapling diversity and abundance was strongly driven by climate and land-use.•Our data serve as baseline for future monitoring of disturbance and climate change.
The continuous decline and degradation of tropical rainforests is currently mainly driven by land-use change. Over the long term, climate change will further exacerbate the situation for the remaining forests. To develop sustainable conservation strategies, we need to understand the natural forest-recovery potential after disturbance and the impact of climate on forest recovery. So far, little is known about regeneration of woody species in tropical landscapes, especially in tropical Africa. We investigated the regeneration of woody plant species in six natural and seven anthropogenically disturbed habitat types along a 3.6 km elevational gradient from savanna woodland to afro-alpine vegetation at Mt. Kilimanjaro, Tanzania. We recorded and identified all saplings of woody plants in a total of 65 plots, each measuring 100 m2. The total number of recorded sapling individuals amounts to 4,738 saplings from 110 species of 50 families. Along the elevational gradient, sapling numbers in natural plots showed a hump-shaped distribution peaking at mid elevation, where rainfall and overall woody biomass were highest, while species number and diversity of saplings were continuously decreasing with increasing elevation. The sapling layer in the savanna zone had three times as many species as the layer of adult trees and shrubs in the same plots, but the species composition of saplings differed strongly from the one of trees and shrubs, indicating strong spatial or temporal heterogeneity. Active agricultural plots at lower elevations also showed natural regeneration of woody species, even though numbers of sapling individuals and species were much lower than in natural low-elevation plots. Forests formerly disturbed by fire and logging showed either comparable or even increased numbers of sapling individuals and species than natural plots at the same elevation, indicating ongoing succession. Finding regeneration of woody species in all disturbed habitat types, even in agriculturally managed habitats, strongly suggests that natural regeneration is a very powerful tool to recover forest diversity after disturbances. Furthermore, our sapling dataset provides an important baseline for future monitoring of the consequences of climate and land-use change on regeneration.
Tropical secondary forests are increasingly important for carbon sequestration and biodiversity conservation worldwide; yet, we still cannot accurately predict community turnover during secondary ...succession. We propose that integrating niche differentiation and dispersal limitation will generate an improved theoretical explanation of tropical forest succession. The interaction between seed sources and dispersers regulates seed movement throughout succession, and recent technological advances in animal tracking and molecular analyses enable us to accurately monitor seed movement as never before. We propose a framework to bridge the gap between niche differentiation and dispersal limitation. The Source-Disperser Limitation Framework (SDLF) provides a way to better predict secondary tropical forest succession across gradients of landscape disturbance by integrating seed sources and frugivore behavior.
Current theories of tropical forest succession have focused on niche differentiation among plants but have not adequately addressed how dispersal limitation shapes succession.We describe dispersal limitation in terms of seed source and disperser limitation; these two factors determine the production of seeds throughout succession and the arrival of seeds to suitable recruitment sites.We present a framework to better understand how seed sources interact with animal abundance, behavior, and diet preferences across the landscape to determine seed movement and deposition during forest regeneration.Using technological advances in animal tracking and molecular tools, the proposed framework will improve models of tropical forest succession beyond niche differentiation.
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