Seasonally dry tropical forests (SDTF) are located in regions with alternating wet and dry seasons, with dry seasons that last several months or more. By the end of the 21st century, climate models ...predict substantial changes in rainfall regimes across these regions, but little is known about how individuals, species, and communities in SDTF will cope with the hotter, drier conditions predicted by climate models. In this review, we explore different rainfall scenarios that may result in ecological drought in SDTF through the lens of two alternative hypotheses: 1) these forests will be sensitive to drought because they are already limited by water and close to climatic thresholds, or 2) they will be resistant/resilient to intra- and inter-annual changes in rainfall because they are adapted to predictable, seasonal drought. In our review of literature that spans microbial to ecosystem processes, a majority of the available studies suggests that increasing frequency and intensity of droughts in SDTF will likely alter species distributions and ecosystem processes. Though we conclude that SDTF will be sensitive to altered rainfall regimes, many gaps in the literature remain. Future research should focus on geographically comparative studies and well-replicated drought experiments that can provide empirical evidence to improve simulation models used to forecast SDTF responses to future climate change at coarser spatial and temporal scales.
Seasonally tropical dry forests (SDTFs) in the American tropics are a highly diverse yet poorly understood and endangered ecosystem scattered from Northern Mexico to Southern Argentina. One floristic ...element of the STDFs is the genus Magoniella (Polygonaceae), which includes two liana species, M. laurifolia and M. obidensis , which have winged fruits and are distributed from Costa Rica to Southern Brazil. In a field expedition to the SDTFs of the Colombian Caribbean in 2015, morphologically distinctive individuals of Magoniella were found. In this study, we investigated the species boundaries within Magoniella and determined the phylogenetic position of these morphologically distinctive individuals in the tribe Triplaridae. We compiled morphological trait data across 19 specimens of both species and produced newly sequenced nuclear–plastid DNA data for M. obidensis . Morphometric analyses revealed significant differences in fruit length and perianth size among individuals from the Colombian Caribbean compared to M. obidensis and bract length when compared to M. laurifolia . Maximum likelihood analysis of non-conflicting nuclear and plastid datasets placed the Colombian Caribbean individuals as sister to M. obidensis with maximum statistical support. Additionally, pairwise sequence comparisons of the nuclear ribosomal ITS and the lfy2i loci consistently showed 15-point mutations (10 transitions, five transversions) and six 2 bp-long substitutions that differ between M. obidensis and the Colombian Caribbean individuals. Our morphological and molecular evidence thus suggests that the Colombian Caribbean individuals of Magoniella represent a divergent population from M. laurifolia and M. obidensis , which we describe and illustrate as a new species, M. chersina . Additionally, we provide nomenclatural updates for M. laurifolia and M. obidensis . This study highlights the power of combining morphological and molecular evidence in documenting and naming plant diversity.
Extreme drought events have negative effects on forest diversity and functioning. At the species level, however, these effects are still unclear, as species vary in their response to drought through ...specific functional trait combinations. We used long‐term demographic records of 21,821 trees and extensive databases of traits to understand the responses of 338 tropical dry forests tree species to ENSO2015, the driest event in decades in Northern South America. Functional differences between species were related to the hydraulic safety‐efficiency trade‐off, but unexpectedly, dominant species were characterised by high investment in leaf and wood tissues regardless of their leaf phenological habit. Despite broad functional trait combinations, tree mortality was more widespread in the functional space than tree growth, where less adapted species showed more negative net biomass balances. Our results suggest that if dry conditions increase in this ecosystem, ecological functionality and biomass gain would be reduced.
Extreme drought events have negative effects on forest diversity and functioning. We used long‐term demographic records of 21,821 trees and extensive databases of traits to understand the responses of 338 tropical dry forests tree species to an extreme. Our results indicate that irrespective of the drought adaptations, most trees will be negatively affected under drier scenarios predicted for tropical dry forests.
Fire causes dramatic short-term changes in vegetation and ecosystem function, and may promote rapid vegetation change by creating recruitment opportunities. Climate warming likely will increase the ...frequency of wildfire in the Arctic, where it is not common now. In 2007, the unusually severe Anaktuvuk River fire burned 1039 km2 of tundra on Alaska's North Slope. Four years later, we harvested plant biomass and soils across a gradient of burn severity, to assess recovery. In burned areas, above-ground net primary productivity of vascular plants equalled that in unburned areas, though total live biomass was less. Graminoid biomass had recovered to unburned levels, but shrubs had not. Virtually all vascular plant biomass had resprouted from surviving underground parts; no non-native species were seen. However, bryophytes were mostly disturbance-adapted species, and non-vascular biomass had recovered less than vascular plant biomass. Soil nitrogen availability did not differ between burned and unburned sites. Graminoids showed allocation changes consistent with nitrogen stress. These patterns are similar to those seen following other, smaller tundra fires. Soil nitrogen limitation and the persistence of resprouters will likely lead to recovery of mixed shrub–sedge tussock tundra, unless permafrost thaws, as climate warms, more extensively than has yet occurred.
Tropical dry forests (TDFs) have been defined as a single biome occurring mostly in the lowlands where there is a marked period of drought during the year. In the Neotropics, dry forests occur across ...contrasting biogeographical regions that contain high beta diversity and endemism, but also strong anthropogenic pressures that threaten their biodiversity and ecological integrity. In Colombia, TDFs occur across six regions with contrasting soils, climate, and anthropogenic pressures, therefore being ideal for studying how these variables relate to dry forest species composition, successional stage and conservation status. Here, we explore the variation in climate and soil conditions, floristic composition, forest fragment size and shape, successional stage and anthropogenic pressures in 571 dry forest fragments across Colombia. We found that TDFs should not be classified solely on rainfall seasonality, as high variation in precipitation and temperature were correlated with soil characteristics. In fact, based on environmental factors and floristic composition, the dry forests of Colombia are clustered in three distinctive groups, with high species turnover across and within regions, as reported for other TDF regions of the Neotropics. Widely distributed TDF species were found to be generalists favored by forest disturbance and the early successional stages of dry forests. On the other hand, TDF fragments were not only small in size, but highly irregular in shape in all regions, and comprising mostly early and intermediate successional stages, with very little mature forest left at the national level. At all sites, we detected at least seven anthropogenic disturbances with agriculture, cattle ranching and human infrastructure being the most pressing disturbances throughout the country. Thus, although environmental factors and floristic composition of dry forests vary across regions at the national level, dry forests are equally threatened by deforestation, degradation and anthropogenic pressures all over the country, making TDFs a top priority for conservation in Colombia.
Thaw of ice-rich permafrost soils on sloping terrain can trigger erosional disturbance events that displace large volumes of soil and sediment, kill and damage plants, and initiate secondary ...succession. We examined how retrogressive thaw slumps (RTS), a common form of thermo-erosional disturbance in arctic tundra, affected the local loss and re-accumulation of carbon (C) and nitrogen (N) pools in organic and surface mineral soil horizons of 18 slumps within six spatially independent sites in arctic Alaska. RTS displaced 3 kg C and 0.2 kg N per m2 from the soil organic horizon but did not alter pools of C and N in the top 15 cm of the mineral horizon. Surface soil C pools re-accumulated rapidly (32 ± 10 g C m−2 yr−1) through the first 60 years of succession, reaching levels similar to undisturbed tundra 40-64 years after disturbance. Average N re-accumulation rates (2.2 ± 1.1 g N m−2 yr−1) were much higher than expected from atmospheric deposition and biological N fixation. Finally, plant community dominance shifted from graminoids to tall deciduous shrubs, which are likely to promote higher primary productivity, biomass accumulation, and rates of nutrient cycling.
•Natural vegetation hold larger biomass and carbon stocks per area than agrosystems.•Agricultural lands (oil palm plantations) can sequester large carbon stocks.•Conservation of natural land near ...agrosystems is critical for climate mitigation.
Agricultural lands occupy 38% of global land surface and are expected to grow significantly in the next years, increasing the need for more sustainable practices, as well as better informed conservation practices of natural ecosystems. Carbon stocks are important estimates for the assessment of potential emissions caused by deforestation, and therefore widely used in strategies to mitigate climate change in agroforestry systems. Although research on biomass and carbon accumulation in agricultural lands is well documented, comparisons with adjacent natural forest areas are uncommon, mainly in tropical regions. Here, we used forest inventory data and allometric models to estimate biomass and carbon stocks of natural vegetation types (gallery forest-GF, morichal-MOR, and savanna-SAV) and oil palm (Elaeis guineensis) crops in the Orinoquía bioregion, in Eastern Colombia. We found that natural forests (GF and MOR) hold 542.45 Mg ha−1 of aboveground biomass, whereas oil palm plantations store 284.87 Mg ha−1. Morichal vegetation, commonly known as peat swamp forests, accumulated the highest aboveground biomass and carbon per hectare among all vegetation types (natural and agricultural), with an estimate of 402.76 Mg ha−1. Thus, although oil palm crops are great reservoirs of biomass and carbon at the landscape level, it is the combination of natural and agricultural lands which assure highest carbon sequestration in the study area. These results highlight the importance of preserving natural areas in agricultural landscapes for climate mitigation and conservation of biodiversity, which may jointly benefit plantations sustainable development.
Previous studies have shown that environmental conditions and plant attributes determine biomass stocks and productivity across multiple tropical forests. However, it is less clear how these factors ...act at local scales. We evaluated how the spatial variation of soil resource availability (soil nutrient and water content) and plant functional traits determine species biomass stocks and productivity in a Colombian tropical dry forest, based on spatially explicit soil sampling and an intensive plant trait characterization of 89 species in three 1-ha permanent plots with similar climate and floristic composition. Within each plot, we measured nine soil variables and ten functional traits and quantified forest biomass stocks and productivity for 10,161 individual trees in a period of 3 years. The soil resources where species were located and their functional traits had coordinated effects on the spatial distribution of forest biomass stocks across the plots. The highest biomass stocks were concentrated on nutrient-rich soils with low water availability and were dominated by conservative species with dense tissues and low hydraulic failure risk, probably because they are able to better cope with water limitation. Most of the remaining forest biomass stocks were found in nutrient-poor soils with high water availability and were dominated by acquisitive species. Sites with nutrient-rich soils and low water availability increased biomass survival but also mortality; however, the presence of conservative species in these sites also increased biomass survival, decreased mortality, and led to biomass accumulation, probably because their strong and hydraulically secure tissues are able to deal with water limitation for nutrient absorption during dry seasons. Interestingly, soil resources and functional traits had no effects on biomass recruitment. We conclude that strong coordinated effects of soil resources and functional traits determine local biomass processes of tropical dry forests with a central role of conservative trait species types, whereby these species promote community assembly and functioning but are also vulnerable to potential changes in water availability. Thus, conservation and restoration actions should pay special attention to soil and plant functional trait trade-offs to improve management practices in these threatened forests.