Tree Leaf Form in Brunei: A Heath Forest and a Mixed Dipterocarp Forest Compared1

Canopy‐top leaves of the dominant tree species from two 0.96‐ha plots in Brunei, northern Borneo, were sampled for structural and chemical analysis. Thirteen species from the mixed dipterocarp forest at Andulau and 14 from the lowland heath forest at Badas were studied. The heath‐forest species had significantly thicker leaves and were lower in nitrogen and ash concentration than those from the mixed dipterocarp forest. There were no significant differences between the two species groups in leaf mass per unit area (LMA), leaf fracture toughness, carbon concentration, 8¹³C, neutral detergent fiber concentration, sclerophylly index, and stomatal density. A significant negative correlation between %C and 8¹³C was found for the species from the mixed dipterocarp forest, but not those from the heath forest. The degree of sclerophylly measured in physical terms overlapped between the two sites to a considerable degree; however, all six species tested that were present in both plots had higher leaf fracture toughness in the heath forest. The possible reasons for the marked sclerophylly in the mixed dipterocarp forest are discussed.     

Nutrient fluxes via litterfall and leaf litter decomposition vary across a gradient of soil nutrient supply in a lowland tropical rain forest

The extent to which plant communities are determined by resource availability is a central theme in ecosystem science, but patterns of small-scale variation in resource availability are poorly known. Studies of carbon (C) and nutrient cycling provide insights into factors limiting tree growth and forest productivity. To investigate rates of tropical forest litter production and decomposition in relation to nutrient availability and topography in the absence of confounding large-scale variation in climate and altitude we quantified nutrient fluxes via litterfall and leaf litter decomposition within three distinct floristic associations of tropical rain forest growing along a soil fertility gradient at the Sepilok Forest Reserve (SFR), Sabah, Malaysia. The quantity and nutrient content of small litter decreased along a gradient of soil nutrient availability from alluvial forest (most fertile) through sandstone forest to heath forest (least fertile). Temporal variation in litterfall was greatest in the sandstone forest, where the amount of litter was correlated negatively with rainfall in the previous month. Mass loss and N and P release were fastest from alluvial forest litter, and slowest from heath forest litter. All litter types decomposed most rapidly in the alluvial forest. Stand-level N and P use efficiencies (ratios of litter dry mass to nutrient content) were greatest for the heath forest followed by the sandstone ridge, sandstone valley and alluvial forests, respectively. We conclude that nutrient supply limits productivity most in the heath forest and least in the alluvial forest. Nutrient supply limited productivity in sandstone forest, especially on ridge and hill top sites where nutrient limitation may be exacerbated by reduced rates of litter decomposition during dry periods. The fluxes of N and P varied significantly between the different floristic communities at SFR and these differences may contribute to small-scale variation in species composition.     

Hyper‐abundance of Native Wild Pigs (Sus scrofa) in a Lowland Dipterocarp Rain Forest of Peninsular Malaysia1

This study reports extraordinarily high density estimates for the wild pig (Sus scrofa) from an aseasonal tropical forest site within the species'native range. At Pasoh Forest Reserve, a 2500 ha area of lowland dipterocarp rain forest in Peninsular Malaysia, line transects were used to estimate pig density from May to October in 1996 and 1998. In 1996, 44 sightings of S. scrofa consisting of 166 individuals were recorded along 81 km of transects. In 1998, 39 sightings documented 129 individuals along 79.9 km of transects. Estimated population density was 47.0 pigs/km² in 1996 and 27.0 pigs/km²‐ in 1998. Sus scrofa biomass in this forest was estimated at 1837 kg/km² and 1346 kg/ km² in 1996 and 1998, respectively. Differences between years were attributed to changes in the density of young pigs, coincident with a mast‐seeding year of dipterocarp trees in 1996. Pig densities at Pasoh Forest Reserve were much higher than at other forest locations within the species' native range in Europe and Asia. Because Pasoh Forest Reserve is a forest fragment, two factors likely account for the extremely high pig densities: (1) local extinction of natural predators (mainly tigers and leopards) and (2) an abundant year‐round food supply of African oil palm fruits from extensive plantations bordering the reserve.     

Habitat Associations and Community Structure of Dipterocarps in Response to Environment and Soil Conditions in Brunei Darussalam,Northwest Borneo

Plant habitat associations are well documented in Bornean lowland tropical forests, but few studies contrast the prevalence of associations across sites. We examined habitat associations and community composition of Dipterocarpaceae trees in two contrasting Bornean lowland mixed dipterocarp forests separated by approximately 100 km: Andulau (uniform topography, lower altitudinal range, sandy soils) and Belalong (highly dissected topography, higher altitudinal range, clay‐rich soils). Dipterocarpaceae trees ≥ 1 cm diameter at breast height (dbh) were censused in 20‐m wide belt transects established along topographic gradients at each site. Dipterocarp density, evenness, species richness, and diversity were significantly higher at Andulau than Belalong. Significant site associations (with either Andulau or Belalong) were detected for 19 (52%) of the 37 dipterocarp species tested. Dipterocarpaceae community composition at Belalong correlated with soil nutrient concentrations as well as measures of vegetation and topographic structure, but community composition at Andulau correlated with fewer habitat variables. Within each site, dipterocarp density, species richness, and diversity were consistently higher on ridges than in slopes and valleys. Significant within‐site associations to topographic habitats were less common at Andulau (10% of species tested) than at Belalong (15%). We conclude that edaphic and other environmental factors influence dipterocarp community composition at a local scale, and are more important drivers of community structure in the more variable environment at Belalong. Species richness and diversity of dipterocarps on small plots, however, were higher at Andulau, suggesting that factors other than environmental heterogeneity contribute to contrasts in dipterocarp tree species richness at small scales.     

Forest Structure and Primary Productivity in a Bornean Heath Forest

Aboveground forest structure, biomass, and primary productivity in a tropical heath forest in Central Kalimantan (Indonesian Borneo) were examined using data from 1-ha plots and stand-level allometric equations developed from harvested tree samples. The study site experienced a severe drought in 1997–1998 associated with the El Niño Southern Oscillation event. The drought effect on heath forest productivity was also assessed by evaluating changes in wood mass increment rates. Allometric relationships suggested that heath forest trees had leaves with smaller specific leaf area (SLA), and large heath forest trees allocate more to leaf mass compared to mixed dipterocarp forest trees. Aboveground biomass (for trees ≥ 4.8 cm DBH) in two 1-ha plots, P1 and P4, totaled 244.8 and 232.0 Mg/ha. Aboveground wood mass increment rate was –0.1 and 4.7 Mg/ha/yr in P1 and P4 during the drought period (from February to August 1998), while it quickly recovered to 8.1 and 8.5 Mg/ha/yr during the post-drought period (from August 1998 to August 1999 for P1 and from August 1998 to November 1999 for P4). This suggests a severe impact of the drought on heath forest productivity. Leaf characteristics of heath forest such as small SLA and long-lived leaves probably play a significant role in effective assimilation and maintenance of heath forest productivity under stressful conditions.     

Leaf litter decomposition rates in degraded and fragmented tropical rain forests of Borneo

Previously extensive tracts of primary rain forest have been degraded by human activities, and we examined how the effects of forest disturbance arising from habitat fragmentation and commercial selective logging affected ecosystem functioning in these habitats by studying leaf litter decomposition rates in litter bags placed on the forest floor. The rain forests of Borneo are dominated by trees from the family Dipterocarpaceae, and we compared leaf litter decomposition rates of three dipterocarp species at eight forest fragment sites (area 3–3529 ha) that had different histories of disturbance pre‐fragmentation: four fragments had been selectively logged prior to fragmentation and four had been formed from previously undisturbed forest. We compared these logged and unlogged forest fragments with sites in continuous forest that had been selectively logged (two sites) and fully protected and undisturbed (two sites). After 120 d, undisturbed continuous forest sites had the fastest rates of decomposition (52% mass loss). Forest fragments formed from unlogged forest (32% mass loss) had faster decomposition rates than logged forest fragments (28% mass loss), but slower rates than continuous logged forest (39% mass loss). Leaves of a light‐demanding species (Parashorea malaanonan) decomposed faster than those of a shade‐tolerant species (Hopea nervosa), but decomposition of all three dipterocarp species that we studied responded similarly to logging and fragmentation effects. Reduced decomposition rates in logged and fragmented forest sites may affect nutrient cycling and thus have detrimental consequences for forest regeneration. Conservation management to improve forest quality should be a priority, particularly in logged forest fragments.     

Recovery of soil phosphorus on former bauxite mines through tropical forest restoration

Soil phosphorus (P) is a major driver of forest development and a critically limited nutrient in tropical soils, especially when topsoil is removed by mining. This nutrient can be present in soils in the form of different fractions, which have direct consequences for P availability to plants and, consequently, for restoration success. Therefore, understanding how the stocks of different soil P fractions change over the restoration process can be essential for guiding restoration interventions, monitoring, and adaptive management. Here, we investigated the recovery of soil P fractions by forest restoration interventions on bauxite mine sites in the Brazilian Atlantic Forest. We assessed the concentration of different fractions of soil organic and inorganic P at (1) a bauxite mine prepared for restoration; (2) two former bauxite mines undergoing forest restoration for 6 and 24 years; and (3) an old‐growth forest remnant. Overall, restored areas recovered levels of labile organic P (P_o‐NaHCO₃) at 5–40 cm and of moderately labile organic P (P_o‐NaOH) at different depths, exhibiting concentrations similar to those found in a conserved forest. The use of P‐rich fertilizers and forest topsoil may have greatly contributed to this outcome. Some other fractions, however, recovered only after 24 years of restoration. Other inorganic P fractions did not differ among mined, restored, and conserved sites: nonlabile P_i (residual P and P‐HCl), labile P_i (P_i‐NaHCO₃), and moderately labile P_i (P_i‐NaOH). Forest restoration was able to promote efficient recovery of important soil P fractions, highlighting the value of restoration efforts to mitigate soil degradation by mining.     

Leaf flushing during the dry season: the paradox of Asian monsoon forests

Aim Most deciduous species of dry monsoon forests in Thailand and India form new leaves 1–2 months before the first monsoon rains, during the hottest and driest part of the year around the spring equinox. Here we identify the proximate causes of this characteristic and counterintuitive ‘spring‐flushing’ of monsoon forest trees. Location Trees of 20 species were observed in semi‐deciduous dry monsoon forests of northern Thailand with a 5–6‐month‐long severe dry season and annual rainfall of 800–1500 mm. They were growing on dry ridges (dipterocarp–oak forest) or in moist gullies (mixed deciduous–evergreen forest) at 680–750 m altitude near Chiang Mai and in a dry lowland stand of Shorea siamensis in Uthai Thani province. Methods Two novel methods were developed to analyse temporal and spatial variation in vegetative dry‐season phenology indicative of differences in root access to subsoil water reserves. Results Evergreen and leaf exchanging species at cool, moist sites leafed soon after partial leaf shedding in January–February. Drought‐resistant dipterocarp species were evergreen at moist sites, deciduous at dry sites, and trees leafed soon after leaf shedding whenever subsoil water was available. Synchronous spring flushing of deciduous species around the spring equinox, as induced by increasing daylength, was common in Thailand's dipterocarp–oak forest and appears to be prevalent in Indian dry monsoon forests of the Deccan peninsula with its deep, water‐storing soils. Main conclusions In all observed species leafing during the dry season relied on subsoil water reserves, which buffer trees against prolonged climatic drought. Implicitly, rainfall periodicity, i.e. climate, is not the principal determinant of vegetative tree phenology. The establishment of new foliage before the summer rains is likely to optimize photosynthetic gain in dry monsoon forests with a relatively short, wet growing season.     

Impacts of an Extreme Precipitation Event on Dipterocarp Mortality and Habitat Filtering in a Bornean Tropical Rain Forest

The frequency of extreme precipitation events is predicted to increase in some tropical regions in response to global climate change, but the impacts of this form of disturbance on the structure and dynamics of tropical tree communities across heterogeneous landscapes remain understudied. We determined the effects of an extreme precipitation event (EPE) in July 2006 on mortality of dipterocarps on a 68 ha permanent inventory plot in Sepilok Forest Reserve, Sabah. For stems ≥30 cm dbh, 12 of the 15 species of Dipterocarpaceae on this plot have significant positive and/or negative associations to habitats defined by topography and soil type. Short‐term mortality induced by the EPE was much greater for individuals growing on the alluvial floodplain (13.7%) than in the mudstone (1.4%) or sandstone (0.0%) habitats, but mortality of dipterocarps did not differ among these habitats in the subsequent 5‐yr interval. The likelihood of mortality in response to the EPE was highest for a small group of fast growing dipterocarps that possess low wood density and a strong association to the alluvial forest habitat. This group of species represents a high percentage of dipterocarp individuals but a low proportion of dipterocarp diversity in this habitat. We conclude that disturbance induced by high rainfall events contributes to the episodic nature of tropical forest dynamics, and that increases in the frequency of these events would disproportionately impact low‐lying alluvial forest environments and some of the species growing in them.     

Liana habitat associations and community structure in a Bornean lowland tropical forest

Lianas (woody vines) contribute substantially to the diversity and structure of most tropical forests, yet little is known about the importance of habitat specialization in maintaining tropical liana diversity and the causes of variation among forests in liana abundance and species composition. We examined habitat associations, species diversity, species composition, and community structure of lianas at Sepilok Forest Reserve, Sabah, Malaysia in northeastern Borneo among three soil types that give rise to three distinct forest types of lowland tropical rain forest: alluvial, sandstone hill, and kerangas (heath) forest. Alluvial soils are more nutrient rich and have higher soil moisture than sandstone soils, whereas kerangas soils are the most nutrient poor and drought prone. Lianas ≥0.5-cm in diameter were measured, tagged, and identified to species in three square 0.25-ha plots in each forest type. The number of lianas ≥0.5 cm did not differ significantly among forest types and averaged 1348 lianas ha⁻¹, but mean liana stem diameter, basal area, estimated biomass, species richness, and Fisher’s diversity index were all greater for plots in alluvial than sandstone or kerangas forests. Liana species composition also differed greatly among the three habitats, with 71% of species showing significant positive or negative habitat associations. Sandstone forests were intermediate to alluvial and kerangas forests in most aspects of liana community structure and composition, and fewer species showed significant habitat associations with this forest type. Ranking of forest types with respect to liana density, biomass, and diversity matches the ranking in soil fertility and water availability (alluvial > sandstone hill > kerangas). These results suggest that edaphic factors play an important role in maintaining liana species diversity and structuring liana communities.     

A pre‐adaptive approach for tropical forest restoration during climate change using naturally occurring genetic variation in response to water limitation

Effective reforestation of degraded tropical forests depends on selecting planting material suited to the stressful environments typical at restoration sites that can be exacerbated by increased duration and intensity of dry spells expected with climate change. While reforestation efforts in nontropical systems are incorporating drought‐adapted genotypes into restoration programs to cope with drier conditions, such approaches have not been tested or implemented in tropical forests. As the first effort to examine genetic variation in plant response to drought in a tropical wet forest, we established a watering experiment using five replicated maternal lines (i.e. seedlings from different maternal trees) of five dipterocarp species native to Borneo. Apart from the expected species level variation in growth and herbivory (3‐fold variation in both cases), we also found intraspecific variation so that growth in some cases varied 2‐fold, and herbivory 3‐fold, among genetically different maternal lines. In two species we found that among‐maternal line variation in growth rate was negatively correlated with tolerance to water limitation, that is, the maternal lines that performed the best in the high water treatment lost proportionally more of their growth during water limitation. We argue that selection for tolerance to future drier conditions is not only likely to impact population genetics of entire forests, but likely extends from forest trees to the communities of canopy arthropods associated with these trees. In tropical reforestation efforts where increased drought is predicted from climate change, including plant material resilient to drier conditions may improve restoration effectiveness.     

珠江三角洲3种典型森林类型乔木叶片生态化学计量学

以珠江三角洲3种典型森林类型(常绿阔叶林、针阔混交林和针叶林)为研究对象, 分析了各类型优势乔木叶片C、N、P化学计量特征。结果显示, 所有研究个体叶片C、N、P含量范围分别为434-537、6.8-23.0和0.56-2.10 mg·g^-1, C:N、C:P和N:P的分布区间分别为 21.22-70.74、227.14-844.64和5.26-20.91, 且N与P之间、C:N与C:P之间具有较好的协同性。3种森林类型中, 针叶林乔木叶片C含量最大, 加权平均值为(517.85 ± 35.96) mg·g^-1, 其次是针阔混交林((509.47 ± 19.38) mg·g^-1), 常绿阔叶林最小((481.59 ± 18.35) mg·g^-1); 针叶林乔木叶片N含量((12.20 ± 5.65) mg·g^-1)最大, 其次是常绿阔叶林((11.50 ± 4.24) mg·g^-1), 针阔混交林((10.51 ± 5.22) mg·g^-1)最小; 各森林类型乔木叶片P含量大小顺序与C含量完全相反, 为常绿阔叶林((1.31 ± 0.48) mg·g^-1)>针阔混交林((0.96 ± 0.61) mg·g^-1)>针叶林((0.77 ± 0.40) mg·g^-1)。针阔混交林乔木叶片C:N (51.35 ± 13.65)最大, 针叶林(47.40 ± 15.85)其次, 常绿阔叶林(45.59 ± 14.70)最小; 各森林类型乔木叶片C:P和N:P大小顺序相同, 均为针叶林(727.47 ± 231.52、15.71 ± 3.76)>针阔混交林(553.01 ± 152.32、10.93 ± 1.89)>常绿阔叶林(412.19 ± 200.91、9.46 ± 4.28)。同时根据乔木叶片N:P还发现, 少数阔叶树种和常绿阔叶林生产力受到N素限制。     

North—South Patterns within Arboreal Ant Assemblages from Rain Forests in Eastern Australia1

This paper describes the ant assemblages sampled from rain forest canopies ranging from southern Victoria through to Cape York Peninsula, Australia, and also in Brunei. Specifically, it examines the influence of decreasing latitude and variations in elevation on the character, richness, and abundance of the arboreal rain forest ant fauna, and also the relative contribution of ants to the total arthropod community. The sites that were examined included: cool temperate Nothofagus cunninghamii forest from a range of locations in Victoria; cool temperate N. moorei forest at both Werrikimbe and Styx River, New South Wales; notophyll vine forest in Lamington National Park, southeast Queensland; high elevation notophyll vine forest in Eungella National Park, central Queensland; complex notophyll vine forest at Robson Creek, Atherton Tablelands, north Queensland; complex mesophyll vine forest at Cape Tribulation, north Queensland; and mixed dipterocarp forest in Brunei. Although these sites represent a gradient increasingly tropical in character, botanically speaking, Eungella is less tropical than Lamington because of its high elevation. All samples were obtained by fogging the canopy with a rapid‐knockdown pyrethrin pesticide. In all cases, circular funnels were suspended beneath the foliage of individual trees or small plots of mixed canopy. Arthropods were collected four hours after fogging. Following ordinal sorting, ants were identified and counted to morphospecies level. The resulting catch were then standardized across sites as numbers caught per 0.5 m² sampling funnel. Generic and species richness were higher at the lowland tropical Cape Tribulation sites than at the sites to the south and was comparable with values in the Brunei site. Species richness was negatively correlated with latitude and elevation. Within the Australian rain forest, the lowland/highland break appears to be the strongest predictor of ant relative abundance, with a weaker latitudinal relationship superimposed.     

Effects of fire on understorey birds in Kimboza Forest Reserve in the eastern foothills of the Uluguru Mountains,Tanzania

Fire is one of the main threats facing the long‐term survival of the forests in the Eastern Arc Mountains. Yet, our understanding of how it affects fauna, particularly birds, is still poor. A fire that originated on surrounding farmland burned approximately half of Kimboza Forest Reserve between 13 and 15 October 2010. To better understand how birds respond to fire, a short‐term study of understorey bird diversity and abundance in this forest reserve was conducted by comparing burned and unburned sites twenty months post‐fire. Capture rates were significantly higher at the unburned site compared to the burned site. Bird species diversity was also higher at the unburned site than at the burned site. Despite the brevity of the study, the results suggest that fire has negative effects on forest avifauna and forest fires need to be prevented at Kimboza Forest Reserve as they affect the distribution and diversity of understorey birds.     

Incidence of Extrafloral Nectaries and Their Relationship with Growth and Survival of Lowland Tropical Rain Forest Trees

Mutualistic relationships between organisms have long captivated biologists, and extrafloral nectaries, or nectar‐producing glands, found on many plants are a good example. The nectar produced from these glands provides food for ants, which may defend the plant from potential herbivores in turn. However, relatively little is known about their impact on the long‐term growth and survival of plants that produce them. To better understand the ecological significance of extrafloral nectaries, we examined their incidence on lowland tropical rain forest trees in Yasuní National Park in Amazonian Ecuador, and collated data from two other tropical lowland forest sites (Barro Colorado Island, Panamá and Pasoh Forest Reserve, Malaysia). At Yasuní, extrafloral nectaries were found on 137 of 1123 species censused (12.2%), widely distributed among different angiosperm families. This rate of incidence is high but consistent with other tropical locations. Furthermore, this study adds 18 new genera and two new families (Urticaceae and Caricaceae) to the list of taxa exhibiting extrafloral nectaries. Using demographic data from long‐term forest dynamics plots at each site, we compared the growth and mortality rates of species with extrafloral nectaries to those without. After controlling for phylogeny, no general relationship between extrafloral nectary presence and demographic rates could be detected, suggesting little demographic signal from any community‐wide ecological effects.     

Disparity in Onset Timing and Frequency of Flowering and Fruiting Events in Two Bornean Peat‐Swamp Forests

The timing and frequency of flowering and fruiting events are key tropical forest characteristics that have substantial influence on fauna. Although our understanding of geographic variation in habitat‐wide timing and frequency of flowering and fruiting is advancing, corresponding information for individual tree species is limited. Thus, we compared climate and reproductive phenology of 16 tree species over 70 mo at two Bornean tropical peat‐swamp forest sites. We found significant inter‐site correlations in rainfall and temperature, and only small absolute temperature differences. In both sites, most species exhibited within‐site synchrony in flowering and fruiting onset. Broad‐scale flowering and fruiting onset frequency classifications showed high congruence between sites. Significant correlations in flowering and fruiting onset timing between sites were found for only 19 and 17 percent of the species, respectively. This remained the case when applying 1‐ and 2‐month lag periods for both sites, with neither site consistently lagging behind. Significant differences in the exact frequency of new flowering and fruiting events were detected for 44 and 58 percent of species, respectively, and no significant relationships between the onset timing synchrony and exact frequency of new reproductive events were found for either flowers or fruit. We conclude that inter‐site climatic and ecological similarities do not necessarily lead to high inter‐site synchrony in either onset timing or exact frequency of tree reproductive events. Potential reasons for this are discussed, as are the implications for understanding tropical forest ecology and improving forest restoration project seed collections.     

Soil nutrient dissimilarity and litter nutrient limitation as major drivers of home field advantage in riparian tropical forests

Decomposition is a key process driving carbon and nutrient cycling in ecosystems worldwide. The home field advantage effect (HFA) has been found to accelerate decomposition rates when litter originates from “home” when compared to other (“away”) sites. It is still poorly known how HFA plays out in tropical, riparian forests, particularly in forests under restoration. We carried out three independent reciprocal litter transplant experiments to test how litter quality, soil nutrient concentrations, and successional stage (age) influenced HFA in tropical riparian forests. These experimental areas formed a wide gradient of soil and litter nutrients, which we used to evaluate the more general hypothesis that HFA varies with dissimilarity in soil nutrients and litter quality. We found that HFA increased with soil nutrient dissimilarity, suggesting that litter translocation uncouples relationships between decomposers and litter characteristics; and with litter N:P, indicating P limitation in this system. We also found negative HFA effects at a site under restoration that presented low decomposer ability, suggesting that forest restoration does not necessarily recover decomposer communities and nutrient cycling. Within each of the independent experiments, the occurrence of HFA effects was limited and their magnitude was not related to forest age, nor soil and litter quality. Our results imply that HFA effects in tropical ecosystems are influenced by litter nutrient limitation and soil nutrient dissimilarity between home and away sites, but to further disentangle major HFA drivers in tropical areas, a gradient of dissimilarity between litter and soil properties must be implemented in future experimental designs.     

佛山地区存留自然林和存留人工林的土壤无机磷组分

为探讨热带亚热带森林,尤其城市及其周边地区残存森林土壤磷的有效性,对佛山地区14个残存林(7个自然林和7个人工林)的0~3 cm和3~23 cm矿质土壤的P有效性进行研究。结果表明,铁结合态无机P和还原剂可溶解无机P是土壤无机P的主要组分。在0~3 cm矿质层中,自然林土壤铝结合态无机P、Bray 1提取无机P和总无机P含量显著高于人工林;而在3~23 cm矿质土层中,自然林土壤钙结合态无机P含量显著高于人工林。其它土壤营养指标在自然林和人工林间差异不显著。相关分析结果表明,土壤有机质含量与钙结合态无机P除外的其它无机P组分含量均成显著正相关。聚类分析结果表明14个残存林土壤P有效性可分成3组,整体上人工林土壤P有效性比自然林低。这有助于认识城市化影响下城市及其周边地区残存森林土壤营养状况及加强养分管理。     

Relationships between soil hydrology and forest structure and composition in the southern Brazilian Amazon

Question: Is soil hydrology an important niche‐based driver of biodiversity in tropical forests? More specifically, we asked whether seasonal dynamics in soil water regime contributed to vegetation partitioning into distinct forest types. Location: Tropical rain forest in northwestern Mato Grosso, Brazil. Methods: We investigated the distribution of trees and lianas ≥ 1 cm DBH in ten transects that crossed distinct hydrological transitions. Soil water content and depth to water table were measured regularly over a 13‐month period. Results: A detrended correspondence analysis (DCA) of 20 dominant species and structural attributes in 10 × 10 m subplots segregated three major forest types: (1) high‐statured upland forest with intermediate stem density, (2) medium‐statured forest dominated by palms, and (3) low‐statured campinarana forest with high stem density. During the rainy season and transition into the dry season, distinct characteristics of the soil water regime (i.e. hydro‐indicators) were closely associated with each vegetation community. Stand structural attributes and hydro‐indicators were statistically different among forest types. Conclusions: Some upland species appeared intolerant of anaerobic conditions as they were not present in palm and campinarana sites, which experienced prolonged periods of saturation at the soil surface. A shallow impermeable layer restricted rooting depth in the campinarana community, which could heighten drought stress during the dry season. The only vegetation able to persist in campinarana sites were short‐statured trees that appear to be well‐adapted to the dual extremes of inundation and drought.     

Topography shapes the structure,composition and function of tropical forest landscapes

Topography is a key driver of tropical forest structure and composition, as it constrains local nutrient and hydraulic conditions within which trees grow. Yet, we do not fully understand how changes in forest physiognomy driven by topography impact other emergent properties of forests, such as their aboveground carbon density (ACD). Working in Borneo – at a site where 70‐m‐tall forests in alluvial valleys rapidly transition to stunted heath forests on nutrient‐depleted dip slopes – we combined field data with airborne laser scanning and hyperspectral imaging to characterise how topography shapes the vertical structure, wood density, diversity and ACD of nearly 15 km² of old‐growth forest. We found that subtle differences in elevation – which control soil chemistry and hydrology – profoundly influenced the structure, composition and diversity of the canopy. Capturing these processes was critical to explaining landscape‐scale heterogeneity in ACD, highlighting how emerging remote sensing technologies can provide new insights into long‐standing ecological questions.