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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. [ABSTRACT FROM AUTHOR]

Tropical rainforests harbor a high diversity of tree species, offering a potentially rich array of timber (TFP) and non-timber (NTFP) forest products. The supply of such products has been commonly evaluated at the local (plot) scale; however, little is known about how their availability and diversity change at the landscape scale, particularly in heterogeneous environments. This information is critical in designing landscape forest management programs. Here, we assess the extent to which the frequency, abundance, diversity, composition and productivity (aboveground biomass) of tree assemblages with potential forest products (PFPs) change across three landscape units (LUs) that differ in soil and topographic conditions. The study was carried out in a well-conserved old-growth tropical rainforest in southeastern Mexico. Three plots (0.5 ha each) were established per LU, in which all trees ≥ 10 cm were inventoried, taxonomically identified and assigned to eight forest product categories. General linear models, multiple regression and ordination analysis (CCA) were used to assess structural and compositional changes in the tree assemblages supplying different PFPs among LUs and along soil physicochemical gradients. More than half (94 species, 57%) of the total number of identified species (165) had one or more PFPs, mostly related to timber products. Ordination analysis showed that the abundance of species with different PFPs has a heterogeneous distribution among LUs, mostly related to changes in soil nitrogen, pH and aluminum saturation. Variation among LUs in terms of tree biomass was strongly driven by soil available phosphorus and soil physiological depth. Each LU had a different potential to provide forest products, producing a diverse mosaic of PFPs within the landscape. Decisions concerning sustainable forest management should consider such variability in the availability and diversity of forest products across landscapes, as well as the environmental factors that govern this spatial variation. [ABSTRACT FROM AUTHOR]

Protected areas (PAs) are essential for biodiversity conservation, but their restrictive policies could accentuate poverty. Such a possibility may occur with the more restrictive PAs (e.g., national parks), which prioritize conservation while limiting the use of natural resources. However, less restrictive PAs, such as biosphere reserves, which allow the sustainable use of natural resources, may be better at alleviating poverty. However, such permissibility may reduce the effectiveness of preventing deforestation. Here, we assessed this conservation-development tradeoff by testing changes in marginalization (an indicator of poverty) and forest loss between two contrasting PAs management scheme types (MST, national parks and biosphere reserves) in Mexico. We quantified forest loss inside PAs and unprotected areas during the 2000–2019 period. Also, we contrasted marginalization changes during the 2000–2020 period between municipalities included in PAs (n = 288) and municipalities not directly influenced by PAs (n = 1615). Using a matching analysis approach, we tested for differences in forest loss and marginalization between protected and unprotected areas and between MST, in all cases controlling for the potential effects of confounding factors (e.g., slope, altitude, distance to cities, economic sector). We also evaluated potential conservation-development trade-offs resulting from the interaction of MST with the biophysical-socioeconomic context. PAs did not accentuate marginalization comparing unprotected areas. After matching, both national parks and biosphere reserves showed similar average changes in marginalization and forest loss probability. However, national parks showed higher marginalization than biosphere reserves in areas far from cities and sites with poor agriculture suitability, probably because restrictive policies in such adverse contexts might work against the development of the local communities. Also, national parks showed higher forest loss than biosphere reserves in areas suitable for agriculture. Our results suggest that, in the Mexican protected areas system, the interaction between MST and biophysical-socioeconomic contexts may lead to conservation-development tradeoffs. The more restrictive MST does not provide greater protection to the forest than the less restrictive MST and, under certain biophysical conditions, may reduce the capability of communities to cope with poverty. [Display omitted] • Protected areas by itself do not reinforce poverty of neighbor communities. • National parks are as efficient as biosphere reserves to prevent forest loss. • Poor agriculture suitability is associated with higher poverty in national parks. • Conservation-development trade-offs in protected areas depend on their context. • Under some context conservation and poverty alleviation can be compatible goals in protected areas. [ABSTRACT FROM AUTHOR]

Abstract: Leaves of the long-lived Dioon merolae have been harvested intensively for decades (possibly for centuries) for ceremonial purposes by Zoque and mestizo groups inhabiting the Central Depression of Chiapas, Mexico. Over a period of four years, we evaluated vital rates (stem growth, leaf production, reproductive performance, and survival) and projected population growth rates in three populations (250 plants each, divided into eight size classes: new germinants, seedlings, saplings (S1, S2), and adults, A1–A4) with different leaf harvesting histories: non-defoliated by humans for at least 55 years (or very old harvest), defoliated annually until 15 years ago (recovering from harvest), and defoliated annually for at least the past 25 years (currently being harvested intensely). Population structure was affected by leaf harvest history. Stem growth was negatively affected by the annual harvest of leaves in size classes from seedlings up to A4 (ANOVA, P <0.003); fewer leaves were produced by seedlings, saplings and adults at the annually harvested site (ANOVA, P <0.027). Survival was high at all sites across all size classes; in the annually harvested site, A4 plants showed a decrease in survival (one dead out of four plants). Sex ratio of adults that produced cones during the four years of study was 61% males to 39% females. At the non-defoliated site, adult classes A2 and A4 produced >80% of the cones; no cones were produced by the A3 and A4 adult size classes at the annually harvested site. Asymptotic estimates of population growth indicated growing populations (λ ≥1); the highest mean values of finite population growth rate were obtained in the non-harvested site (λ =1.0202). Elasticity analysis with population projection matrices indicated that stasis (L, 9–38%) was the component that most contributed to λ, followed by growth (G, 1.2–2.9%), and fecundity (F, 0.2–1.1%). We observed detrimental effects on several vital rates due to continued long-term defoliation, although population growth parameters do not currently suggest a decreased trend as a result of the annual harvest of leaves. The duration of this study of a very long-lived plant species suggests caution when setting levels and frequency of leaf harvest. The results help pinpoint practical recommendations that could be implemented in a sustainable management plan for this species, particularly to increase seed production in the annually harvested site, and recruitment of new germinants and seedlings at all sites. However, sound practices will need to consider the interests of involved stakeholders (landowners, pilgrims, conservation organizations and authorities) to effectively reduce anthropogenic pressure on this endangered species. [Copyright &y& Elsevier]

The Selva El Ocote Biosphere Reserve is located within the Mesoamerican biodiversity hotspot for global conservation. The area, poorly known relative to other humid tropical areas within Mexico, shows a mosaic of several types of forests, contains over 2000 species of vascular plants and 97 species of mammals, and plays a key role within Mexican tropical forests. We analyze the process of land-use/land-cover change (LUCC) within a 5755km2 area which includes the reserve. Viability of conservation of the area was assessed by an integrated multi-temporal analysis of the LUCC process. Three cartographical data bases – from 1986, 1995 and 2000 – were used to assess rates and trends in LUCC for seven land cover types: agriculture/pasture (A/P); four types of second-growth forest (SGF); and two types of mature forest (tropical and temperate). Even when taking into account pathways of regeneration, results show a fast net loss of primary and secondary forests, primarily due to the establishment of A/P. For the entire area of study, the annual deforestation rate of tropical mature forests was 1.2% during the period 1986–1995, increasing to 6.8% for the period 1995–2000. For both periods, the annual deforestation rate was appreciably lower within the reserve (0.21% and 2.54%) than outside it (2.15% and 12.4%). The annual rate of conversion of tropical SGF to A/P was 1% during the first period and increased sixfold for the second period. Three future scenarios on forest cover were constructed using a Markovian model and annualizing LUCC transition matrices. Results show that between 29% and 86% of remaining forest may be lost within the next 23 years. Urgent action is necessary to reduce loss of biodiversity within this region. Particular attention must be paid to tropical SGF, which are rapidly being deforested. [Copyright &y& Elsevier]

Discusses the natural growth conditions that maximize height growth after transplantation from a nursery in a Mexican rainforest. Significance of multiple regression analysis in analyzing the plant growth; Effect of light on various species.

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• Ecological filters differentially affect seedlings and resprouts along succession. • Abiotic filters predominantly select for legume species. • Biotic filters on resprouts generate high clade diversity. • Secondary forests are similar to old-growth forest after 15 years of succession. • Understanding differential operation of filters during succession informs forest management. Abiotic and biotic filters may play differential roles in the plant community organization along forest succession in abandoned fields. However, little is known about how life stage-specific filters influence species replacement during succession. We approach this issue by analyzing changes in community attributes (abundance, species density, species diversity, species composition) and the phylogenetic structure of shrubs and trees at different life stages during the old-field succession of a seasonally tropical dry forest (TDF) in Western Mexico. We raised two main questions: (1) How different are the trajectories of change in community attributes and phylogenetic structure along succession for shrub and tree species at different life-stages? (2) Do different stage-specific trajectories result from differential filtering mechanisms? We used a chronosequence of abandoned pastures and forest sites, classified in five successional categories (with three sites each): Pasture (< 1.5 years fallow age), Early (3.5–5.5 y), Mid (6–8 y), Advanced (13–15 y), and Old-Growth Forest. Identity and abundance of species were recorded at five life stages: seeds in the top soil layer, seedlings (plants emerged from seeds, 10–100 cm height), resprouts (plants emerging from buds in roots or stumps, 10–100 cm height), juvenile [shrubs and trees > 100 cm height and < 2.5 cm diameter at breast height (DBH)], adults (shrubs and trees with DBH ≥ 2.5 cm). Additionally, we quantified the phylogenetic mean parwise distance (MPD) among species, and analyzed the phylogenetic community structure, for each successional category and life stage. We found that early in succession the resprout stage was more abundant and diverse than the seedling stage, while the inverse occurred late in succession. Along the first 15 years of succession, the seedling stage showed a clumped phylogenetic structure (with a strong dominance of legume species), while the resprout stage tended to have an overdispersed one (with species from a wide range of clades). Also, community attributes of the juvenile and adult stages approached those of the old-growth forest, and in both stages the phylogenetic structure changed from clustered to random. Overall, our results suggest that the assembly of shrub and trees communities along succession resulted from a combination of abiotic filtering processes, operating mostly on seedlings (selecting primarily legume drought-tolerant species), and biotic filtering processes, operating mostly in resprouts (generating a taxonomic and phylogenetically diverse regenerative pool). The implications of these results for the management of secondary TDF in human modified landscapes are discussed. [ABSTRACT FROM AUTHOR]

A major challenge in tropical human-modified landscapes (HMLs) is meeting the ever-growing demand for agricultural products while conserving biodiversity and ecosystem services provided by forest ecosystems. Within this challenge, a major issue is the understanding of the forest potential to naturally regenerate in abandoned agricultural fields. To assess such potential, it is necessary to know the diversity of agricultural land uses in the landscape, quantify the ecological disturbance inflicted by such uses, and evaluate forest regeneration as a function of disturbance both at the field and landscape levels. Our previous work has shown that in abandoned fields the abundance and species diversity of regenerating rain forest trees decline as disturbance level increases. Here we aimed to achieve the following: 1) to quantify the diversity of agricultural land uses in HMLs; 2) to assess ecological disturbance regimes caused by different agricultural land uses, at the field and landscape scales; and 3) to identify groups of agricultural land uses with contrasting effects for forest regeneration at the landscape level. We approach these issues by using a case study of HMLs in a southeastern region of Mexico, which are representative of landscapes in the agricultural frontier in the Neotropics. We interviewed 68 landowners to gather information on agricultural land uses and management of 156 fields. Based on this information, we quantified an ecological disturbance regime associated with each field considering the following: field size (in hectares), duration of agricultural use (in years), and land-use disturbance severity (i.e. frequency or magnitude of fire, agrochemicals, machinery, grazing or removal of tree cover). By integrating disturbance inflicted by different land uses and the proportion of the landscape covered by each land use, we constructed a landscape ecological disturbance index. Finally, by using this index and data gathered from nine landscapes (3 × 3 km each), we tested the hypothesis that structural attributes (abundance, biomass, and species diversity of trees) of regenerating forests decrease as agriculture disturbances increase in the landscape. There was a high inequality in the proportion of land allocated to the 13 recorded agricultural land uses, with cattle pastures representing ca. 90% of total agricultural land. There was a wide disturbance gradient, ranging from land uses with high (e.g. cattle pastures) to low disturbance (e.g. coffee and cocoa plantations). Three major groups of land uses with contrasting disturbance regimes were detected: 1) agroforestry systems, characterized by small size, low to intermediate duration, and low disturbance severity; 2) monocultures, typically small size, long duration, and medium to high disturbance severity; and 3) extensive farming, large size, short to intermediate duration, and high disturbance severity. Biomass and species diversity of regenerating forests consistently reduced with increasing levels of agriculture disturbance in the landscape. We conclude that positive balances between biodiversity conservation and agricultural production in HMLs will depend on establishing agricultural land uses that inflict low disturbance regimes (such as agroforestry systems) embedded in a matrix of old-growth forest and long-lasting second-growth forests. Our results may inform farmers, policy makers and land managers about HMLs where agricultural production and conservation of biodiversity and ecosystem services can be conciliated. [ABSTRACT FROM AUTHOR]

Deforestation of old-growth forests (OGF) is a significant driver of biodiversity loss, particularly impacting rare species. However, the threat to dominant species is usually overlooked, given their relatively high abundance. Therefore, assessing the impact of forest loss on dominant species is imperative, mainly because they play critical roles in the structure, functioning, and ecosystem services. In particular, identifying the amount of OGF required to avoid local extinction and conserve dominant species in human modified landscapes is critically needed. Furthermore, as dominant species may regenerate in secondary forests (SF), growing in abandoned fields, assessing whether SF may buffer species' local extinction is also needed. We addressed these issues by analyzing demographic changes of four canopy dominant tree species across twenty 1-km2 landscapes encompassing the whole deforestation gradient (0 to ~100% OGF and SF cover) in the Lacandon rainforest, Mexico. Non-linear modeling identified local extinction thresholds at 25–35% OGF cover, below which tree density (DBH ≥ 5 cm) and regeneration potential (juvenile/adult ratio) of all species sharply declined. Deforestation also increased the spacing of remaining trees and reduced tree size. Thus, we propose that ≥40% OGF cover be retained in the landscape to be conservative. SF were too young (<30 years fallow age) and perishable to sustain viable populations of our dominant species. Because the remaining OGF in the study region is within the estimated extinction thresholds, we urge the adoption of land uses promoting high-quality landscape matrices suitable for the conservation of dominant species and associated biodiversity. Local extinction threshold for Ampelocera hottlei , one of the four dominant-canopy tropical rainforest species studied in human modified landscapes in the Lacandon tropical rainforest region, southern Mexico. Left: old-growth forest cover threshold (vertical dashed line, confidence interval indicated by grey area) required for avoiding local extinction in the landscape. Right: total (old-growth plus secondary) forest cover required for avoiding local extinction in the landscape. Continuous lines are trajectories of change in population density (trees ≥ 5 cm DBH) as a function of the percentage forest cover in the landscape, as predicted by non-linear modeling. Note that when secondary forest is included, more forest is required for avoiding extinction. [Display omitted] • Dominant trees play key roles in the structure and function of forest ecosystems. • Extinction thresholds of dominant trees occurred at 35% old-growth forest cover. • Spacing and aggregation of trees increased exponentially as deforestation enhanced. • Young secondary forest (<30 years) does not buffer extinction thresholds. • Conserving dominant trees needs at least 40% old-growth forest embedded in high-quality matrices. [ABSTRACT FROM AUTHOR]

With the decreasing affordability of protecting large blocks of pristine tropical forests, ecologists have staked their hopes on the management of human-modified landscapes (HMLs) to conserve tropical biodiversity. Here, we examine key forces affecting the dynamics of HMLs, and propose a framework connecting human disturbances, land use, and prospects for both tropical biodiversity and ecosystem services. We question the forest transition as a worldwide source of new secondary forest; the role played by regenerating (secondary) forest for biodiversity conservation, and the resilience of HMLs. We then offer a conceptual model describing potential successional trajectories among four major landscape types (natural, conservation, functional, and degraded) and highlight the potential implications of our model in terms of research agendas and conservation planning. [Copyright &y& Elsevier]

Abstract: Functional diversity (FD) ‘those components of biodiversity that influence how an ecosystem operates or functions’ is a promising tool to assess the effect of biodiversity loss on ecosystem functioning. FD has received ample theoretical attention, but empirical studies are limited. We evaluate changes in species richness and FD during tropical secondary forest succession after shifting cultivation in Mexico. We also test whether species richness is a good predictor of FD. FD was calculated based on a combination of nine functional traits, and based on two individual traits important for primary production (specific leaf area) and carbon sequestration (wood density). Stand basal area was a good predictor of successional changes in diversity and FD, in contrast to fallow age. Incidence-based FD indices increased logarithmically with stand basal area, but FD weighted by species’ importance values lacked pattern with succession. Species richness and diversity are strong predictors of FD when all traits were considered; linear relationships indicate that all species are equally functionally complementary, suggesting there is little functional redundancy. In contrast, when FD was calculated for individual traits and weighted for abundances, species richness may underestimate FD. Selection of functional trait(s) critically determines FD, with large consequences for studies relating biodiversity to ecosystem functioning. Careful consideration of the traits required to capture the ecosystem process of interest is thus essential. [Copyright &y& Elsevier]

Abstract: The phylogenetic structure of communities can reveal forces shaping community assembly, but the vast majority of work on phylogenetic community structure has been conducted in mature ecosystems. Here, we present an analysis of the phylogenetic structure of three Neotropical rain forest communities undergoing succession. In each site, the net relatedness of the community is initially high and consistently declines during succession. This pattern is evident both when comparing plots of different age classes and when comparing stem size classes within each plot: the oldest plots and the youngest stem cohorts, representing the most advanced stages of succession, have the lowest relatedness. Our results suggest that succession leaves a distinct signature in the phylogenetic structure of communities, which may reflect an increasing role of biotic interactions in community assembly during succession. We discuss theoretical explanations for the decline in community phylogenetic relatedness during succession, and suggest directions for future study. [Copyright &y& Elsevier]

Abstract: Several studies have proposed a group of morpho-functional traits as determinants of the ecological strategy of species. Among these, four morpho-functional traits are considered to be relevant in determining a plant''s ecological strategy: specific leaf area (SLA), height at maturity (Hmax), wood density (WD), and seed mass (SM). We examined the variation of these traits and attempted to identify functional groups among 33 tree species with different biogeographical affinities from a montane cloud forest. Covariation among the four traits was examined using Principal Component Analysis (PCA) and species clustering. Bivariate trait relationships were evaluated through two methods: cross-species correlations, and evolutionary divergence correlations using phylogenetically independent contrasts (PICs). Correlations between attributes were overall weak, the most obvious ones being between Hmax and SM, and between Hmax and WD; this latter trait pair was also correlated in PICs. In both analyses SLA was unrelated to all other traits. In the PCA ordination the first two axes explained 66.9% of the between-species variation. Despite a largely continuous between-species variation, species clustering allowed differentiation of two main groups. Observed trait correlations were consistent with those reported for other floras, with the important exception of the independent behaviour of SLA. This study indicates a variety of comparable successful life history strategies among the studied species. The effect of phylogeny in trait covariation was unimportant, in fact, a mixture of clades was represented in several groups among the species they contained, suggesting among-lineage convergence. [Copyright &y& Elsevier]

• Phylogenetic structure was clustered but tended to random as succession advanced. • Fabales determined the phylogenetic clustering mainly in first years of succession. • Effects of global climatic change on Fabales could impact the plant community dynamic. • Severe drought could increase phylogenetic distance and phylodiversity on dead component. • Abiotic and stochastic processes could be major mechanisms in our successional system. Phylogenetic analysis of plant communities is useful for inferring ecological mechanisms driving forest succession. However, such analysis has scarcely been undertaken in tropical dry environments, especially for the dynamics of demographic components (i.e., recruited, surviving and dead plants) affecting the successional process. Here, we combine chronosequence and dynamic data to study the role of habitat filtering and limiting similarity in the old-field succession of a seasonal tropical dry forest subjected to strong climatic events (e.g., the El Niño Southern Oscillation (ENSO) and heavy rains). We documented successional changes in the phylogenetic structure and phylodiversity of regenerative communities (shrubs and trees ≤ 1 m in height), assessed phylogenetic changes in demographic components during succession, and explored the effects of interannual rainfall variation on such changes. Over five years, we monitored the dynamics of regenerative plant communities in a chronosequence of nine abandoned pastures (fallow age of 0–12 years) and three old-growth sites. For each year and site, we quantified changes in the standardized mean phylogenetic distance (MPD.OBS.Z) and phylodiversity (PD) of entire regenerative communities and recruited, surviving and dead plants. For each phylogenetic metric and demographic component, we assessed the effect of successional age, time (years), and interannual rainfall variation. Large variation in MPD.OBS.Z and PD was observed among sites and years, especially in the recently abandoned pastures. Overall, the phylogenetic community structure was clustered early in succession and became more random as succession advanced. Species from the order Fabales made especially strong contributions to the phylogenetic clustering, especially during the first years of succession. In dead plants, the MPD.OBS.Z and PD increased in the drier year due to the high mortality of plants from several clades (orders). The high prevalence of clustered and random phylogenetic structure suggests that abiotic filtering and stochastic processes are major structuring mechanisms in this successional system. Due the strong contribution of Fabales in the phylogenetic structure of regenerative communities of tropical dry forest, the effects of strong climatic events (e.g., ENSO) on Fabales could influence the old-field succession of tropical dry forests. [ABSTRACT FROM AUTHOR]