Ever-wet Forests Research Articles

Flower production decreases with warmer and more humid atmospheric conditions in a western Amazonian forest.

Climate models predict that everwet western Amazonian forests will face warmer and wetter atmospheric conditions, and increased cloud cover. It remains unclear how these changes will impact plant reproductive performance, such as flowering, which plays a central role in sustaining food webs and forest regeneration. Warmer and wetter nights may cause reduced flower production, via increased dark respiration rates or alteration in the reliability of flowering cue-based processes. Additionally, more persistent cloud cover should reduce the amounts of solar irradiance, which could limit flower production. We tested whether interannual variation in flower production has changed in response to fluctuations in irradiance, rainfall, temperature, and relative humidity over 18 yrs in an everwet forest in Ecuador. Analyses of 184 plant species showed that flower production declined as nighttime temperature and relative humidity increased, suggesting that warmer nights and greater atmospheric water saturation negatively impacted reproduction. Species varied in their flowering responses to climatic variables but this variation was not explained by life form or phylogeny. Our results shed light on how plant communities will respond to climatic changes in this everwet region, in which the impacts of these changes have been poorly studied compared with more seasonal Neotropical areas.

The challenge of the enigmatic tricolporate tropical pollen type: A case study from Sulawesi, Indonesia

Any palynologist who has worked in the tropics has undoubtedly dealt with the frustration of trying to classify small, tricolporate pollen into meaningful taxonomic groups. While this is not a significant issue where coarse-scale identifications represent similar habitat indicators or "unknown" types are rare, it poses a problem when one of these "unknowns" overwhelm the record. This is the case with unknown “type 69” – a small, tricolporate pollen grain encountered within a 60,000-year sediment sequence from Lake Towuti in Sulawesi, Indonesia. This type comprises up to 35% of the pollen count for some Last Glacial Maximum (LGM) samples (highlighting its climatic sensitivity) but could not be identified by experts in the field. This study thus aimed to compare the metrics of “type 69” with reference pollen from Sulawesi to aid with its identification. In doing so, we present a pollen atlas of 63 maritime southeast Asian pollen types. Our results show that “type 69” aligns with metrics taken from Saurauia pollen. While detailed ecological data on Saurauia species in Sulawesi are lacking, they appear to favor higher elevations and riverbank settings, and are post-disturbance colonizers. Proliferation of this pollen type during the LGM is therefore linked to a combination of downslope range expansion of Saurauia species under a cooler climate and potentially, out competition of upland everwet forest taxa. This study demonstrates an approach to managing important unknown fossil pollen types in tropical records and, through the ensuing pollen atlas, provides a tool for progressing palynology in southeast Asia.

Drought and the interannual variability of stem growth in an aseasonal, everwet forest

AbstractLinking drought to the timing of physiological processes governing tree growth remains one limitation in forecasting climate change effects on tropical trees. Using dendrometers, we measured fine‐scale growth for 96 trees of 25 species from 2013 to 2016 in an everwet forest in Puerto Rico. Rainfall over this time span varied, including an unusual, severe El Niño drought in 2015. We assessed how growing season onset, median day, conclusion, and length varied with absolute growth rate and tree size over time. Stem growth was seasonal, beginning in February, peaking in July, and ending in November. Species growth rates varied between 0 and 8 mm/year and correlated weakly with specific leaf area, leaf phosphorus, and leaf nitrogen, and to a lesser degree with wood specific gravity and plant height. Drought and tree growth were decoupled, and drought lengthened and increased variation in growing season length. During the 2015 drought, many trees terminated growth early but did not necessarily grow less. In the year following drought, trees grew more over a shorter growing season, with many smaller trees showing a post‐drought increase in growth. We attribute the increased growth of smaller trees to release from light limitation as the canopy thinned because of the drought, and less inferred hydraulic stress than larger trees during drought. Soil type accounted for interannual and interspecific differences, with the finest Zarzal clays reducing tree growth. We conclude that drought affects the phenological timing of tree growth and favors the post‐drought growth of smaller, sub‐canopy trees in this everwet forest.Abstract in Spanish is available with online material.

Phenology of a dipterocarp forest with seasonal drought: Insights into the origin of general flowering

Abstract Our understanding of the factors that shape reproductive phenology in Southeast Asian tropical forests comes almost exclusively from studies of everwet, general flowering (GF) forests. Therefore, we examined the phenology of an evergreen dipterocarp forest in a climate exhibiting seasonal drought in Southeast Asia, with the aim of evaluating what evidence it brings to bear on the hypothesis that reproductive phenology in contemporary dipterocarp forests is the product of evolutionarily conserved responses to seasonal drought. We hypothesized that (1) dipterocarp forests that experience seasonal drought would exhibit annual reproduction and seasonality similar to that of forests with similar climates in other parts of the world, (2) within species, flowering frequency would be climate‐dependent, not a fixed trait, and (3) climatic events that cue flowering in everwet forests would also cue flowering in seasonally dry forests. From 2001 to 2009, we monitored flowering and fruiting monthly for 1,344 trees (>300 spp.) in a forest in Khao Chong (KC), Thailand that experiences an annual 2–4 month dry season, assessing frequency, duration, seasonality and synchrony of reproduction. We also examined phenological records for trees in three dipterocarp‐dominated forests in everwet climates. Reproductive phenology of the KC forest was more similar to tropical forests with similar rainfall seasonality in other parts of the world than it was to dipterocarp‐dominated forests in everwet regions of Southeast Asia. The forest exhibited annual reproduction, with peak flowering occurring at the end of the dry season and peak fruiting occurring early in the wet season. Approximately half of all species and individuals reproduced annually, including several species that are known to exhibit “general flowering” in everwet climates. Short dry spells appeared to cue flowering for early flowering species, while later flowering species may have responded to either low precipitation or temperature, consistent with data from everwet forests. GF behaviour also showed significant phylogenetic signal. Synthesis. Our results support the hypothesis that the phenological behaviour of both seasonal and everwet dipterocarp forests may have initially evolved in response to seasonal drought and that the general flowering phenomenon is a product of evolutionary conservatism.

Nuclear DNA based species delineations ofCoccusscale insects in symbiosis with plants and ants, and the role of plant epicuticular wax in structuring associations

We undertook phylogenetic analysis of nuclear DNA to elucidate species boundaries in the symbiotic Coccus scale insects associated with mutualistic Crematogaster ants and Macaranga plants occurring in the ever-wet forests of Southeast Asia. The coccid specimens clustered into ten lineages, each corresponding to a morphospecies assignment. The lineage identified as C. secretus was separated from the Main Clade by an outgroup. We also examined all pairwise associations among the three symbiont guilds to understand how patterns of association were structured. The analyses revealed that each ant, plant or coccid operational (taxonomic) unit often associated with multiple O(T)Us of each of the other two guilds. However, where testing was feasible, a ‘preference’ for one or sometimes two partner O(T)Us of each guild was often detected. Mutual ‘preferences’ or ‘avoidances’ were relatively common among the symbionts, and no conflicts of interest were apparent. The network of preferred partners among all three guilds showed compartmentalization structured by the presence/absence of plant epicuticular wax, suggesting that this feature plays a fundamental role in how the symbionts select partners that best serve their needs. To a lesser degree, the network was also structured by whether the host plant stems were ant-excavated or hollowed naturally.

Fire as a selective force in a Bornean tropical everwet forest

Tree species rarely exposed to burning, like in everwet tropical forests, are unlikely to be fire adapted. Therefore, one could hypothesize that these species are affected equally by burning and that tree abundance changes are linked solely to fire behavior. Alternatively, if species do react differentially to burning, abundance changes should be linked to tree habitat preference and morphology. Using tree inventories from old-growth and adjacent burned Bornean forest in combination with a database on tree morphology and habitat preference, we test these alternative hypotheses by (1) determining whether species specific abundance changes after fire differ significantly from equal change, and (2) whether observed abundance changes are linked to species morphology and habitat preference. We found that of 196 species tested, 125 species showed an abundance change significantly different from that expected under our null model of equal change. These abundance changes were significantly linked to both tree morphology and habitat preference. Abundance declines were associated with slope or ridge preference, thin barks, and limited seed dormancy. Abundance increases were associated with high light preference, small adult stature, light wood, large leaves, small seeds and long seed dormancy. While species habitat preference and morphology explained observed abundance increases well, abundance declines were only weakly associated with them (R(2) ~ 0.09). This suggests that most tree mortality was random and everwet tropical tree species are poorly fire adapted. As fire frequencies are increasing in the everwet tropics, this might eventually result in permanently altered species compositions and even species extinctions.

The geography of diversification in mutualistic ants: a gene's‐eye view into the Neogene history of Sundaland rain forests

We investigate the geographical and historical context of diversification in a complex of mutualistic Crematogaster ants living in Macaranga trees in the equatorial rain forests of Southeast Asia. Using mitochondrial DNA from 433 ant colonies collected from 32 locations spanning Borneo, Malaya and Sumatra, we infer branching relationships, patterns of genetic diversity and population history. We reconstruct a time frame for the ants' diversification and demographic expansions, and identify areas that might have been refugia or centres of diversification. Seventeen operational lineages are identified, most of which can be distinguished by host preference and geographical range. The ants first diversified 16-20 Ma, not long after the onset of the everwet forests in Sundaland, and achieved most of their taxonomic diversity during the Pliocene. Pleistocene demographic expansions are inferred for several of the younger lineages. Phylogenetic relationships suggest a Bornean cradle and major axis of diversification. Taxonomic diversity tends to be associated with mountain ranges; in Borneo, it is greatest in the Crocker Range of Sabah and concentrated also in other parts of the northern northwest coast. Within-lineage genetic diversity in Malaya and Sumatra tends to also coincide with mountain ranges. A series of disjunct and restricted distributions spanning northern northwest Borneo and the major mountain ranges of Malaya and Sumatra, seen in three pairs of sister lineages, further suggests that these regions were rain-forest refuges during drier climatic phases of the Pleistocene. Results are discussed in the context of the history of Sundaland's rain forests.

An Overview on the Conservation Status Of Mersawa (Anisoptera costata Korth.) in Java

Anisoptera costata Korth., which has a commercial name of mersawa grows and proliferates naturally, often gregarious, in semi-evergreen dipterocarp forest and evergreen forest in areas with seasonal climate and rare but widespread in lowland everwet forest from sea level up to 700 m in continental S.E. Asia, Malay Peninsula, Borneo, Sumatra, and Java (Ashton, 1982). In Java, it has been recorded to occur only in Banten (Backer & Bakhuizen van den Brink,1963) and in Leuweung Sancang Nature Reserve (LSNR) (Kalima, 2006)

An Interdisciplinary Research Initiative Towards Sustainable Management of Forest Resources in Lowland Rain Forests of Sri Lanka

Ever-wet forests of SW Sri Lanka are biodiversity hot spots with a wealth of potentially useful and currently used species. Traditional peoples surrounding these forests depend on them for a variety of focds, medicinals and the like as well as for timber. Some of these forests are being preserved as storehouses of diversity that include rare endemics and wild relatives of useful plants. Other natural forests and plantations must be managed for multiple uses including timber and non-timber products used by the forest dependent villagers. Understanding the ecological, social and economic interdependence of forests and rural communities is vital for the future forestry sector development in Sri Lanka. As many of the plants used locally are characteristic of early stages of gap regeneration, timber and non-timber products are compatible uses, given sufficiently judicious management. Anthropological and biological research is now in progress to plan for multiple use management of Sri Lankan ever-wet forests.

Tree species richness of upper Amazonian forests

Upper Amazonian data for tree species richness in 1-hectare plots are reported. All plants >/=10 cm diameter were censused and identified in six plots in Amazonian Peru and one on the Venezuela-Brazil border. The two plots from the everwet forests near Iquitos, Peru, are the most species-rich in the world, with approximately 300 species >/=10 cm diameter in single hectares; all of the Peruvian plots are among the most species-rich ever reported. Contrary to accepted opinion, upper Amazonian forest, and perhaps Central African ones, have as many or more tree species as comparable Asian forests. Very high tree species richness seems to be a general property of mature lowland evergreen forests on fertile to moderately infertile soils on all three continents.

Palynological Light on Tropical Rainforest Dynamics

Although there are more than a hundred Quaternary pollen diagrams from the non-arid tropics, very few are from strictly lowland ever-wet rainforest. Nevertheless, those from more upland or seasonal sites imply major changes of size and location of all tropical forests which must have had repercussions on the composition of and niche realization in the lowland ever-wet forest. Among the ecologically most important implications are that these features of the forest have been constantly changing at varying rates for at least a million years and still are changing. While it is no longer possible necessarily to associate diversity with changelessness, the alternative extreme view that diversity is the outcome of Quaternary environmental change has yet to be demonstrated palynologically. The courses of expansions of some trees in the early stages of establishment of an Australian rainforest in the Holocene are fitted to standard population growth curves and the significance of fine resolution pollen analysis for the study of rainforest ecology is demonstrated.

Palynological light on tropical rainforest dynamics

Although there are more than a hundred Quaternary pollen diagrams from the non-arid tropics, very few are from strictly lowland ever-wet rainforest. Nevertheless, those from more upland or seasonal sites imply major changes of size and location of all tropical forests which must have had repercussions on the composition of and niche realization in the lowland ever-wet forest. Among the ecologically most important implications are that these features of the forest have been constantly changing at varying rates for at least a million years and still are changing. While it is no longer possible necessarily to associate diversity with changelessness, the alternative extreme view that diversity is the outcome of Quaternary environmental change has yet to be demonstrated palynologically. The courses of expansions of some trees in the early stages of establishment of an Australian rainforest in the Holocene are fitted to standard population growth curves and the significance of fine resolution pollen analysis for the study of rainforest ecology is demonstrated.