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Question: How does the diversity of successional forests evolve with stand age, and to what extent do permanent plots validate the previously studied successional patterns of tree diversity and composition observed through chronosequences? To evaluate the role of successional forests as reservoirs for many species, it is essential to examine how biodiversity recovers with the age of the stand. We studied patterns of taxonomic and functional diversity, as well as species composition during forest succession, by combining chronosequences and permanent plot monitoring. Location: Subtropical montane forests in NW Argentina. Methods: We used data from two chronosequences of plots monitored for 30 years in lower and upper montane forests dominated by native trees (LMF‐Native and UMF‐Native), and one chronosequence of plots dominated by the exotic tree Ligustrum lucidum, monitored for 10 years in low montane forests (LMF‐Invaded). We analyzed changes in taxonomic (species richness, Shannon diversity, Simpson diversity) and functional diversity, as well as composition with forest age. Results: Taxonomic and functional diversity increased between 30 and 70 years of succession in LMF‐Native and UMF‐Native. Successional LMF‐Native forests reached the diversity of mature forests earlier than UMF‐Native. In LMF‐Invaded, taxonomic and functional diversity decreased in the same period because of the increasing dominance of the exotic species Ligustrum lucidum. In non‐invaded chronosequences (LMF‐Native and UMF‐Native) we observed a convergence towards the composition of mature forests; however, each successional forest kept its identity for 30 years. Conclusions: Diversity and composition followed different successional trajectories depending on the type of forest. We found that successional patterns, such as changes in taxonomic and functional diversity, predicted with the chronosequence approach, were confirmed with data from plot monitoring. The effects of pre‐abandonment conditions persist in the diversity and composition of successional forests monitored between 10 and 30 years. [ABSTRACT FROM AUTHOR]

Patterns of species diversity have been associated with changes in climate across latitude and elevation. However, the ecological and evolutionary mechanisms underlying these relationships are still actively debated. Here, we present a complementary view of the well-known tropical niche conservatism (TNC) hypothesis, termed the multiple zones of origin (MZO) hypothesis, to explore mechanisms underlying latitudinal and elevational gradients of phylogenetic diversity in tree communities. The TNC hypothesis posits that most lineages originate in warmer, wetter, and less seasonal environments in the tropics and rarely colonize colder, drier, and more seasonal environments outside of the tropical lowlands, leading to higher phylogenetic diversity at lower latitudes and elevations. In contrast, the MZO hypothesis posits that lineages also originate in temperate environments and readily colonize similar environments in the tropical highlands, leading to lower phylogenetic diversity at lower latitudes and elevations. We tested these phylogenetic predictions using a combination of computer simulations and empirical analyses of tree communities in 245 forest plots located in six countries across the tropical and subtropical Andes. We estimated the phylogenetic diversity for each plot and regressed it against elevation and latitude. Our simulated and empirical results provide strong support for the MZO hypothesis. Phylogenetic diversity among co-occurring tree species increased with both latitude and elevation, suggesting an important influence on the historical dispersal of lineages with temperate origins into the tropical highlands. The mixing of different floras was likely favored by the formation of climatically suitable corridors for plant migration due to the Andean uplift. Accounting for the evolutionary history of plant communities helps to advance our knowledge of the drivers of tree community assembly along complex climatic gradients, and thus their likely responses to modern anthropogenic climate change. [ABSTRACT FROM AUTHOR]

Permanent forest plots are sampling areas where tree identity, abundance and size are recorded periodically, in order to study how forests change with climate, natural disturbances, uses and management. So far, patterns of change observed with permanent plots in Argentina have been local or regional. To promote scientific collaborations between different research groups within and among regions of Argentina, we created the Network of Permanent Plots of Native Argentinian Forests (RAPP), which includes the regions of Bosques Andino-Patagónicos, Chaco Seco, Chaco Húmedo, Monte de Sierras y Bolsones, Monte de Llanuras y Mesetas, Selva Paranaense and Yungas. Here we synthesize and characterize the information of 317 permanent plots (328.9 ha) included in the RAPP, describing their geographic distribution, objectives, main methodological aspects, and characteristics of the forests where they are established (e.g., disturbance, land tenure, structure, species richness), and after that, discuss the complementarity between the RAPP and the national inventories of native forests. Permanent plots are established over a wide range of latitude (22.02-54.89° S) and elevation (19 a 2304 m a. s. l.), but they are mainly concentrated in Subtropics (Chaco Seco, Chaco Húmedo, Selva Paranaense, and Yungas) and in Bosques Andino-Patagónicos. In all plots, trees are taxonomically identified and different dasometric variables are remeasured, which are the basis for potential collaborations to answer ecological questions at a larger scale. We hope to continue incorporating working groups in the RAPP and encouraging the establishment of plots, mainly in regions with a low number of permanent plots such as Monte, Espinal, and Delta e Islas del Paraná. The goal is that the RAPP advances in the long-term study of all native forests in Argentina, achieving a greater national cover and more interactions among research teams. [ABSTRACT FROM AUTHOR]

Our knowledge about the structure and function of Andean forests at regional scales remains limited. Current initiatives to study forests over continental or global scales still have important geographical gaps, particularly in regions such as the tropical and subtropical Andes. In this study, we assessed patterns of structure and tree species diversity along ~ 4000 km of latitude and ~ 4000 m of elevation range in Andean forests. We used the Andean Forest Network (Red de Bosques Andinos, https://redbosques.condesan.org/) database which, at present, includes 491 forest plots (totaling 156.3 ha, ranging from 0.01 to 6 ha) representing a total of 86,964 identified tree stems ≥ 10 cm diameter at breast height belonging to 2341 identified species, 584 genera and 133 botanical families. Tree stem density and basal area increases with elevation while species richness decreases. Stem density and species richness both decrease with latitude. Subtropical forests have distinct tree species composition compared to those in the tropical region. In addition, floristic similarity of subtropical plots is between 13 to 16% while similarity between tropical forest plots is between 3% to 9%. Overall, plots ~ 0.5-ha or larger may be preferred for describing patterns at regional scales in order to avoid plot size effects. We highlight the need to promote collaboration and capacity building among researchers in the Andean region (i.e., South-South cooperation) in order to generate and synthesize information at regional scale. [ABSTRACT FROM AUTHOR]

Altitudinal gradients are associated with climatic gradients that promote species diversity. This study describes the composition, diversity and structure of trees along an altitudinal gradient in subtropical mountain forests (Yungas) in Serranías de Zapla, Jujuy province, Argentina. Three 1-ha plots at 1150 m, 1600 m and 2050 m above sea level were established. Each plot was subdivided into 25 subplots, where all trees ≥10 cm of diameter at breast height (dbh) were measured and identified as for species; number of species, diversity, and density of individuals, basal area, and dominance of individuals per species among elevations were compared. The effect of distance on species turnover was analyzed, and the relations between abundance of individuals per species and frequency of species occurrence was evaluated. We sampled 1375 individuals belonging to 46 species. A significant turnover in species composition along the gradient was found: only three species were present at all elevations, and most species (29) were found at a single altitude. Species richness and diversity decreased with altitude, density of individuals showed no clear pattern, basal area peaked at 1600 m, and dominance was more pronounced at higher altitudes. Low Montane Forest (1150 m) and High Montane Forest (2050 m) were clearly different in terms of species composition. Species similarity was negatively associated with distance within each altitudinal level. Abundance of individuals per species was positively associated with frequency of species occurrence. This study confirms the community organization of tree species in altitudinal ecological levels determined by environmental variables in Yungas forests, and emphasizes the importance of local factors in determining the diversity, composition and structure of these communities. [ABSTRACT FROM AUTHOR]