Old-growth Tropical Rain Forest Research Articles

Effects of the forests-agriculture conversion on the availability and diversity of forest products in a neotropical rainforest region

Tropical rainforests offer a diverse array of real or potential forest products (FP). However, the ongoing conversion of these forests to agriculture raises concerns about the future availability and sustainability of FP. In this study, we examined the changes in availability (tree density and above-ground biomass) and species richness of native trees, recognized by local communities as sources of FP, with the forest-to-agriculture conversion in a Mesoamerican tropical rainforest region. Specifically, we tested hypotheses on whether species with FP had a higher, equal, or lower reduction in the availability, diversity, and probability of persistence than species without FP with the forest conversion. We interviewed landowners to identify tree species with FP and documented management practices and regulations for using these species. In fourteen 1 km2 landscapes, encompassing the entire range of forest-to-agriculture conversion (from 0 % to ∼100 % old-growth forest cover), we analyzed changes in the availability and richness of species with and without FP. In each landscape, we randomly established 30 plots (each 706.8 m2, totaling 420 plots and 29.7 ha sampling area) covered by old-growth forest, secondary forest, or agricultural fields (mostly cattle pastures). Over four years, we surveyed all trees with a diameter at breast height ≥ 10 cm in these plots. With the forest conversion, assemblages of tree species with FP exhibited a higher reduction in aboveground biomass than species without FP. However, assemblages of species with FP exhibited a significantly lower reduction in abundance, species richness, and a higher probability of persistence than assemblages of species without FP. Furthermore, we found evidence of implementing forest management practices favoring the preservation of species with FP in agricultural lands. Thus, we conclude that people intentionally foster the persistence of valuable species in their agricultural fields, which could have important implications for the structure and composition of future regenerating forests on abandoned agricultural lands. In the long term, this might lead to an overabundance of locally valuable species, as observed in old-growth tropical rainforests that native people ancestrally managed.

Spatial heterogeneity and influence mechanisms on soil respiration in an old-growth tropical montane rainforest with complex terrain

IntroductionAlthough numerous studies have investigated ecosystem-scale soil respiration (SR) at different ecosystem, our understanding of spatial heterogeneity of SR at plot scale is still incomplete, especially in tropical rainforests with complex topography. Further, the ecological factors that drive the variability of SR in tropical rainforests is also poorly understood.MethodsHere, we investigated the spatial variations and control mechanisms of SR in a 60-ha plot of old-growth tropical rainforest with complex topography. Specifically, we sampled a 60-ha plot in intervals of 20 m to measure SR with LI-8100, used semi-variogram of geostatistical tools to examine spatial heterogeneity of SR.ResultsThe mean SR rate in this plot was 4.312 ± 0.0410 (SE) μmol m−2 s−1. Geostatistical analysis indicated that the SR rate at this plot had a moderate spatial dependence, with a nugget-to-sill ratio of 68.1%. The coefficients variance of SR was 36.2% and the patch size was approximately 112 m. Stepwise linear regression analysis (involving a multiple regression tree) revealed that the independent factors regulated different types of SR’s. Liner mix-effect models showed that SR was significantly positively related to soil phosphorus and negatively to the slope in the 60-ha plot. Spatial disturbance of SR along multidimensional habitats that an increase in elevation of the multidimensional habitat, which was accompanied by enhanced SOC and soil phosphorous, also increased its SR in the 60-ha plot.DiscussionThis study would be helpful in designing future field experiments for a better understanding of SR at plot scale.

First fossil-leaf floras from Brunei Darussalam show dipterocarp dominance in Borneo by the Pliocene.

The Malay Archipelago is one of the most biodiverse regions on Earth, but it suffers high extinction risks due to severe anthropogenic pressures. Paleobotanical knowledge provides baselines for the conservation of living analogs and improved understanding of vegetation, biogeography, and paleoenvironments through time. The Malesian bioregion is well studied palynologically, but there have been very few investigations of Cenozoic paleobotany (plant macrofossils) in a century or more. We report the first paleobotanical survey of Brunei Darussalam, a sultanate on the north coast of Borneo that still preserves the majority of its extraordinarily diverse, old-growth tropical rainforests. We discovered abundant compression floras dominated by angiosperm leaves at two sites of probable Pliocene age: Berakas Beach, in the Liang Formation, and Kampong Lugu, in an undescribed stratigraphic unit. Both sites also yielded rich palynofloral assemblages from the macrofossil-bearing beds, indicating lowland fern-dominated swamp (Berakas Beach) and mangrove swamp (Kampong Lugu) depositional environments. Fern spores from at least nine families dominate both palynological assemblages, along with abundant fungal and freshwater algal remains, rare marine microplankton, at least four mangrove genera, and a diverse rainforest tree and liana contribution (at least 19 families) with scarce pollen of Dipterocarpaceae, today’s dominant regional life form. Compressed leaves and rare reproductive material represent influx to the depocenters from the adjacent coastal rainforests. Although only about 40% of specimens preserve informative details, we can distinguish 23 leaf and two reproductive morphotypes among the two sites. Dipterocarps are by far the most abundant group in both compression assemblages, providing rare, localized evidence for dipterocarp-dominated lowland rainforests in the Malay Archipelago before the Pleistocene. The dipterocarp fossils include winged Shorea fruits, at least two species of plicate Dipterocarpus leaves, and very common Dryobalanops leaves. We attribute additional leaf taxa to Rhamnaceae (Ziziphus), Melastomataceae, and Araceae (Rhaphidophora), all rare or new fossil records for the region. The dipterocarp leaf dominance contrasts sharply with the family’s <1% representation in the palynofloras from the same strata. This result directly demonstrates that dipterocarp pollen is prone to strong taphonomic filtering and underscores the importance of macrofossils for quantifying the timing of the dipterocarps’ rise to dominance in the region. Our work shows that complex coastal rainforests dominated by dipterocarps, adjacent to swamps and mangroves and otherwise similar to modern ecosystems, have existed in Borneo for at least 4–5 million years. Our findings add historical impetus for the conservation of these gravely imperiled and extremely biodiverse ecosystems.

Tropical Rainforest Successional Processes can Facilitate Successfully Recovery of Extremely Degraded Tropical Forest Ecosystems Following Intensive Mining Operations

Reforestation is an effective way to alleviate deforestation and its negative impacts on ecosystem services. In tropical rainforest ecosystem, however, frequent typhoons and heavy rainfall can result in landslides and uprooting of many seedlings, making reforestation efforts very difficult, especially within extremely degraded sites where soil conditions cannot support any plant life. Here, we described a reforestation protocol which is based on tropical rainforest successional processes to not only prevent landslides and tree uprooting due to frequent typhoon and heavy rain, but also accelerate tropical forest succession. This protocol first used the slope and soil layer of the undisturbed old-growth tropical rainforest as a reference to reconstruct slope and soil layers. Then multiple tropical tree species with high growth and survival rate were separately monocultured in the reconstructed soil layers. In the year of 2015 and 2016, we tested the effectiveness of this protocol to recover a 0.2 km2 extremely degraded tropical rainforest which consists of bare rock and thus does not support any plant life, in Sanya city, China. Our results showed that, both typhoons and heavy rains did not result in landslide or any tree damages in the area this reforestation protocol was used. Moreover, our separately monocultured eight fast-growing tree species have much higher fast-growing related functional traits than those for tree species in the adjacent undisturbed tropical seasonal forest, which in turn resulted in large soil water and nutrient loss within 3 years. This seemed to simulate a quick transition from primary succession (consist of bare rock and cannot support any plant life) to mid-stage of secondary tropical rainforest succession (many fast-growing pioneer tree species induced high soil water and nutrient loss). Thus, mixing the late-successional tropical tree species with each of the separately monocultured eight fast-growing tree species can accelerate recovery to the undisturbed tropical rainforest as soon as possible. Overall, based on tropical rainforest successional processes, our research provides an effective protocol for quickly and effectively restoring an extremely degraded tropical rainforest ecosystem. We expect that this work will be important for the future recovery of other extremely degraded tropical rainforest ecosystems.

Atmospheric deposition of elements and its relevance for nutrient budgets of tropical forests

Atmospheric deposition is an important component of the nutrient cycles of terrestrial ecosystems, but field measurements are especially scarce in tropical regions. In this study we analysed 15 months of precipitation chemistry collected in an old growth tropical forest located in French Guiana. We measured nutrient inputs via bulk precipitation and throughfall and used the canopy budget model to estimate nutrient fluxes via canopy exchange and dry deposition. Based on this method we quantified net fluxes of macronutrients and compared their contribution to internal cycling rates via litterfall. Our results suggest that while atmospheric deposition of nitrogen was relatively high (13 kg ha−1 year−1), and mainly in organic forms, the N inputs via litterfall were an order of magnitude higher. In contrast to nitrogen, we found that atmospheric deposition of phosphorus (0.5 kg ha−1 year−1) supplied up to one third of the annual litterfall input to the forest floor. Most strikingly, combined annual inputs of potassium via atmospheric deposition (14 kg ha−1 year−1) and canopy leaching (22 kg ha−1 year−1) were three times larger than internal nutrient recycling via litterfall (11 kg ha−1 year−1). We conclude that atmospheric deposition of phosphorus and especially potassium may play an important role in sustaining the productivity of this old-growth tropical rainforest.

First checklist of the ants (Hymenoptera: Formicidae) of French Guiana.

We provide here a checklist of the ants of French Guiana, an overseas department of France situated in northern South America, with a very low human population density and predominantly covered by old-growth tropical rainforests. Based on 165 scientific papers, specimens deposited in collections, and unpublished surveys, a total of 659 valid species and subspecies from 84 genera and 12 subfamilies is presented. Although far from complete, these numbers represent approximately 10% of the ant diversity known to occur in the Neotropical realm. Additionally, three ant genera and 119 species are reported for the first time for French Guiana. Finally, five species are recognized as erroneous records for the the department in the literature. This checklist significantly expands the basic knowledge of the ants in the Guiana Shield, one of the world's most important biodiversity hotspots.

Plant Functional Traits Are the Mediators in Regulating Effects of Abiotic Site Conditions on Aboveground Carbon Stock-Evidence From a 30 ha Tropical Forest Plot.

Understanding the relative contribution of abiotic and biotic factors to the formation of ecosystem functioning across scales is vital to evaluate ecosystem services. Here, we elucidate the effects of abiotic site conditions (i.e., soil and topographic properties) and plant functional traits on variations of stand aboveground carbon (AGC) stock in an old-growth tropical montane rain forest. The response-effect framework in functional ecology is adopted in examining how plant functional traits respond to environmental changes and affect ecosystem functioning. We measured specific leaf area and wood density of 270 woody plant species and estimated stand AGC stocks in a 30-ha forest plot. The relationships among environmental factors (ENVIRONMENT), community-weighted means of functional traits (TRAITS) and stand AGC stocks across nested spatial scales were disentangled by structural equation modeling. The results showed that the stands composed of ‘acquisitive’ species (high specific leaf area and low wood density) had low AGC, whereas stands composed of ‘conservative’ species (low specific leaf area and high wood density) had high AGC. TRAITS responded to ENVIRONMENT and affected AGC directly. ENVIRONMENT had an indirect effect on AGC through its direct effect on TRAITS. TRAITS were more important than ENVIRONMENT in driving variations of AGC. The effects of TRAITS on AGC increased, while the effects of ENVIRONMENT on AGC decreased with the increase of spatial scales in the tropical montane rain forest. Our study suggests that plant functional traits are the mediators in regulating effects of abiotic site conditions on ecosystem functions.

Availability and species diversity of forest products in a Neotropical rainforest landscape

Abstract 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.

Successional status, seed dispersal mode and overstorey species influence tree regeneration in tropical rain-forest fragments in Western Ghats, India

Abstract:The effects of fragmentation and overstorey tree diversity on tree regeneration were assessed in tropical rain forests of the Western Ghats, India. Ninety plots were sampled for saplings (1–5 cm diameter at breast height (dbh); 5×5-m plots) and overstorey trees (&gt;9.55 cm dbh; 20×20-m plots) within two fragments (32 ha and 18 ha) and two continuous forests. We tested the hypotheses that fragmentation and expected seed-dispersal declines (1) reduce sapling densities and species richness of all species and old-growth species, and increase recruitment of early-successional species, (2) reduce the prevalence of dispersed recruits and (3) increase influence of local overstorey on sapling densities and richness. Continuous forests and fragments had similar sapling densities and species richness overall, but density and richness of old-growth species declined by 62% and 48%, respectively, in fragments. Fragments had 39% lower densities and 24% lower richness of immigrant saplings (presumed dispersed into sites as conspecific adults were absent nearby), and immigrant densities of old-growth bird-dispersed species declined by 79%. Sapling species richness (overall and old-growth) increased with overstorey species richness in fragments, but was unrelated to overstorey richness in continuous forests. Our results show that while forest fragments retain significant sapling diversity, losses of immigrant recruits and increased overstorey influence strengthen barriers to natural regeneration of old-growth tropical rain forests.

Characteristics of typhoon disturbed gaps in an old-growth tropical montane rainforest in Hainan Island, China

Disturbances that create gaps can shape the structure and function of forests. However, such disturbance regimes in Asian tropical montane rainforests remain largely unquantified. Least studied are typhoon disturbances that are attributable to climate change. We investigated gap characteristics in terms of size, age, and gap-maker to quantify the gap disturbance regimes in an intact old-growth tropical montane rainforest on Hainan Island, China. The intensity of typhoons has increased since 1949, and typhoon winds blow mostly (45.5%) from the northeast corner of Hainan Island, resulting in a higher frequency of gaps in the northeast. A total of 221 gap-makers (trees that fell to create canopy gaps) and 53 gaps were observed in a 3.16 ha old-growth rainforest. Most canopy gaps (85%) were <200 m2. The average size of canopy gaps was smaller in the rainforest than in other tropical forests, while the average size of expanded gaps was similar to those in other tropical forests. The maximum age of gaps was 23.5 years indicating that gaps had more rapid turnover than other parts of tropical forests. The frequency distribution of gap-makers followed a lognormal distribution with a distinctive peak at three gap-makers, which was different from the inverse J-shaped curve typical of other tropical forests. Gaps were recorded mainly on slopes between 20° and 35° and wood density of gap-makers was between 0.6 and 0.7 g cm−3. Our results suggest that small-scale disturbance was the dominant agent of gap formation in this old-growth rainforest that is subject to increasing typhoon disturbances.

Measurement and modeling of rainfall interception by two differently aged secondary forests in upland eastern Madagascar

Secondary forests occupy a larger area than old-growth rain forests in many tropical regions but their hydrological functioning is still poorly understood. In particular, little is known about the various components of evapotranspiration in these possibly vigorously regenerating forests. This paper reports on a comparison of measured and modeled canopy interception losses (I) from a semi-mature (ca. 20years) and a young (5–7years) secondary forest in the lower montane rain forest zone of eastern Madagascar. Measurements of gross rainfall (P), throughfall (Tf), and stemflow (Sf) were made in both forests for one year (October 2014–September 2015) and the revised analytical model of Gash et al. (1995) was tested for the first time in a tropical secondary forest setting. Overall measured Tf, Sf and derived I in the semi-mature forest were 71.0%, 1.7% and 27.3% of incident P, respectively. Corresponding values for the young forest were 75.8%, 6.2% and 18.0%. The high Sf for the young forest reflects the strongly upward thrusting habit of the branches of the dominant species (Psiadia altissima), which favours funneling of P. The value of I for the semi-mature forest is similar to values reported for old-growth tropical lower montane rain forests elsewhere but I for the younger forest is higher than reported for similarly aged tropical lowland forests. These findings can be explained largely by the prevailing low rainfall intensities and the frequent occurrence of small rainfall events. The revised analytical model was able to reproduce measured cumulative I at the two sites accurately and succeeded in capturing the variability in I associated with the seasonal variability in rainfall intensity, provided that Tf-based values for the average wet-canopy evaporation rates were used instead of values derived with the Penman-Monteith equation.

Response of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O fluxes in a mountainous tropical rainforest in equatorial Indonesia to El Niño events

Abstract. The possible impact of El Niño–Southern Oscillation (ENSO) events on the main components of CO2 and H2O fluxes between the tropical rainforest and the atmosphere is investigated. The fluxes were continuously measured in an old-growth mountainous tropical rainforest in Central Sulawesi in Indonesia using the eddy covariance method for the period from January 2004 to June 2008. During this period, two episodes of El Niño and one episode of La Niña were observed. All these ENSO episodes had moderate intensity and were of the central Pacific type. The temporal variability analysis of the main meteorological parameters and components of CO2 and H2O exchange showed a high sensitivity of evapotranspiration (ET) and gross primary production (GPP) of the tropical rainforest to meteorological variations caused by both El Niño and La Niña episodes. Incoming solar radiation is the main governing factor that is responsible for ET and GPP variability. Ecosystem respiration (RE) dynamics depend mainly on the air temperature changes and are almost insensitive to ENSO. Changes in precipitation due to moderate ENSO events did not have any notable effect on ET and GPP, mainly because of sufficient soil moisture conditions even in periods of an anomalous reduction in precipitation in the region.

Tropical rain forest structure, tree growth and dynamics along a 2700-m elevational transect in Costa Rica.

Rapid biological changes are expected to occur on tropical elevational gradients as species migrate upslope or go extinct in the face of global warming. We established a series of 9 1-ha plots in old-growth tropical rainforest in Costa Rica along a 2700 m relief elevational gradient to carry out long-term monitoring of tropical rain forest structure, dynamics and tree growth. Within each plot we mapped, identified, and annually measured diameter for all woody individuals with stem diameters >10 cm for periods of 3-10 years. Wood species diversity peaked at 400-600 m and decreased substantially at higher elevations. Basal area and stem number varied by less than two-fold, with the exception of the 2800 m cloud forest summit, where basal area and stem number were approximately double that of lower sites. Canopy gaps extending to the forest floor accounted for <3% of microsites at all elevations. Height of highest crowns and the coefficient of variation of crown height both decreased with increasing elevation. Rates of turnover of individuals and of stand basal area decreased with elevation, but rates of diameter growth and stand basal area showed no simple relation to elevation. We discuss issues encountered in the design and implementation of this network of plots, including biased sampling, missing key meteorological and biomass data, and strategies for improving species-level research. Taking full advantage of the major research potential of tropical forest elevational transects will require sustaining and extending ground based studies, incorporation of new remotely-sensed data and data-acquisition platforms, and new funding models to support decadal research on these rapidly-changing systems.

Annual tree growth, mortality, physical condition, and microsite in an old-growth tropical rain forest, 1983–2010

Tree species richness in a tropical rain forest typically exceeds several hundred species over mesoscale landscapes. There is no generally accepted ecological theory that accounts for the coexistence of so many species with the same general morphologies and the same basic requirements of light, nutrients, water, and physical space. In part this lack of theory rests on the lack of understanding of the post-establishment ecology for the vast majority of tropical tree species. Of even more immediate concern is the lack of data on tree performance in relation to climate; such data are critical to project effects of global climate change on tropical forests. Here we present data on the post-establishment ecology of 10 species of tropical wet forest trees selected to span a range of predicted life history patterns. The study site was terra firme old-growth tropical wet forest at the La Selva Biological Station in Costa Rica. Particular emphasis has been placed on evaluating the precision of measurements, metada...

Regional and seasonal patterns of litterfall in tropical South America

Abstract. The production of aboveground soft tissue represents an important share of total net primary production in tropical rain forests. Here we draw from a large number of published and unpublished datasets (n=81 sites) to assess the determinants of litterfall variation across South American tropical forests. We show that across old-growth tropical rainforests, litterfall averages 8.61±1.91 Mg ha−1 yr−1 (mean ± standard deviation, in dry mass units). Secondary forests have a lower annual litterfall than old-growth tropical forests with a mean of 8.01±3.41 Mg ha−1 yr−1. Annual litterfall shows no significant variation with total annual rainfall, either globally or within forest types. It does not vary consistently with soil type, except in the poorest soils (white sand soils), where litterfall is significantly lower than in other soil types (5.42±1.91 Mg ha−1 yr−1). We also study the determinants of litterfall seasonality, and find that it does not depend on annual rainfall or on soil type. However, litterfall seasonality is significantly positively correlated with rainfall seasonality. Finally, we assess how much carbon is stored in reproductive organs relative to photosynthetic organs. Mean leaf fall is 5.74±1.83 Mg ha−1 yr−1 (71% of total litterfall). Mean allocation into reproductive organs is 0.69±0.40 Mg ha−1 yr−1 (9% of total litterfall). The investment into reproductive organs divided by leaf litterfall increases with soil fertility, suggesting that on poor soils, the allocation to photosynthetic organs is prioritized over that to reproduction. Finally, we discuss the ecological and biogeochemical implications of these results.

Resolving systematic errors in estimates of net ecosystem exchange of CO 2 and ecosystem respiration in a tropical forest biome

The controls on uptake and release of CO 2 by tropical rainforests, and the responses to a changing climate, are major uncertainties in global climate change models. Eddy-covariance measurements potentially provide detailed data on CO 2 exchange and responses to the environment in these forests, but accurate estimates of the net ecosystem exchange of CO 2 (NEE) and ecosystem respiration ( R eco) require careful analysis of data representativity, treatment of data gaps, and correction for systematic errors. This study uses the comprehensive data from our study site in an old-growth tropical rainforest near Santarem, Brazil, to examine the biases in NEE and R eco potentially associated with the two most important sources of systematic error in Eddy-covariance data: lost nighttime flux and missing canopy storage measurements. We present multiple estimates for the net carbon balance and R eco at our site, including the conventional “ u* filter”, a detailed bottom-up budget for respiration, estimates by similarity with 222Rn, and an independent estimate of respiration by extrapolation of daytime Eddy flux data to zero light. Eddy-covariance measurements between 2002 and 2006 showed a mean net ecosystem carbon loss of 0.25 ± 0.04 μmol m −2 s −1, with a mean respiration rate of 8.60 ± 0.11 μmol m −2 s −1 at our site. We found that lost nocturnal flux can potentially introduce significant bias into these results. We develop robust approaches to correct for these biases, showing that, where appropriate, a site-specific u* threshold can be used to avoid systematic bias in estimates of carbon exchange. Because of the presence of gaps in the data and the day–night asymmetry between storage and turbulence, inclusion of canopy storage is essential to accurate assessments of NEE. We found that short-term measurements of storage may be adequate to accurately model storage for use in obtaining ecosystem carbon balance, at sites where storage is not routinely measured. The analytical framework utilized in this study can be applied to other Eddy-covariance sites to help correct and validate measurements of the carbon cycle and its components.

CO 2 exchange of a tropical rainforest at Pasoh in Peninsular Malaysia

The eddy covariance method was used to observe carbon dioxide flux ( F c) for 3 years over an old-growth tropical rainforest at Pasoh in Peninsular Malaysia. The average nighttime F c and NEE were 3.6 and 4.7 μmol m −2 s −1, respectively, when friction velocity ( u * ) ≥ 0.2, while the average soil respiration rate measured occasionally with the chamber method was estimated to be 4.1 μmol m −2 s −1 if we used the relationship between volumetric soil water content, or 3.8 μmol m −2 s −1 if we used the pure average of nine observations. The comparison of F c, NEE and soil respiration strongly suggests that nighttime CO 2 efflux was underestimated even when the CO 2 storage term is considered. The correction of F c data for low u * did not correct this underestimate, and it was strongly suggested that this forest was not a strong carbon sink, as raw F c data, even with the u * filtering, implied. Monthly average daytime diurnal changes in CO 2 exchange over the canopy were fairly constant from 2003 to 2005 despite fluctuations in soil moisture, solar radiation, air temperature and vapor pressure deficit between dry and wet periods. An obvious inhibition of canopy CO 2 exchange in the afternoon coupling with increases in VPD and air temperature was observed year-round. In the case of nighttime NEE, a slight increase in wet period was observed. Diurnal pattern of CO 2 exchange revealed that obvious restriction of canopy photosynthesis in the afternoon was occurred in this forest irrespective of soil moisture. Seasonal and annual patterns of CO 2 exchange reveal that one of the main causes which induce the difference in NEE pattern between Amazonian and Southeast Asian rainforests was not the difference in daytime photosynthesis but the difference in ecosystem respiration related with dry and rainy seasons. The decrease of CO 2 uptake (increase of NEE) at wet period was also observed at this site, but did not form an obvious seasonality such as in Amazonian forests.

Foliar and ecosystem respiration in an old‐growth tropical rain forest

Foliar respiration is a major component of ecosystem respiration, yet extrapolations are often uncertain in tropical forests because of indirect estimates of leaf area index (LAI). A portable tower was used to directly measure LAI and night-time foliar respiration from 52 vertical transects throughout an old-growth tropical rain forest in Costa Rica. In this study, we (1) explored the effects of structural, functional and environmental variables on foliar respiration; (2) extrapolated foliar respiration to the ecosystem; and (3) estimated ecosystem respiration. Foliar respiration temperature response was constant within plant functional group, and foliar morphology drove much of the within-canopy variability in respiration and foliar nutrients. Foliar respiration per unit ground area was 3.5 +/- 0.2 micromol CO2 m(-2) s(-1), and ecosystem respiration was 9.4 +/- 0.5 micromol CO2 m(-2) s(-1)[soil = 41%; foliage = 37%; woody = 14%; coarse woody debris (CWD) = 7%]. When modelled with El Niño Southern Oscillation (ENSO) year temperatures, foliar respiration was 9% greater than when modelled with temperatures from a normal year, which is in the range of carbon sink versus source behaviour for this forest. Our ecosystem respiration estimate from component fluxes was 33% greater than night-time net ecosystem exchange for the same forest, suggesting that studies reporting a large carbon sink for tropical rain forests based solely on eddy flux measurements may be in error.

Comparison of satellite-derived estimates of gross primary production for Australian old-growth tropical rainforest

The moderate-resolution spectroradiometer (MODIS) sensor has provided estimates of near-real-time gross and annual net primary production (GPP and NPP) since March 2000. We compare 2 years (2000 and 2001) of satellite-based calculations of GPP in the seasonally wet tropical rainforests of north Queensland, Australia, with estimates derived from an ecosystem process model, physiological principles predicting growth using satellite data (3-PGS), that was previously calibrated with ground-based measurements at 21 sites. This comparison provides an independent evaluation of the MOD-17 GPP product because the 3-PGS simulations account for spatial variation in soil properties (available soil water and fertility) and rely on different sources of meteorological data and derived estimates of the fraction of photosynthetically active radiation (fPAR). Results of the comparison show that estimates of averaged annual and monthly GPP from MOD-17 are slightly higher in magnitude than those from 3-PGS, although the two models exhibit comparable seasonal dynamics over the 2-year analysis period. Some of the differences in estimates of productivity and temporal dynamics between 3-PGS and MODIS are a result of limitations in the types of input data used for each model. In addition, the particularly infertile soils of northern Australia account for a reduction in productivity that is not directly incorporated in the MOD-I7 algorithm. Further testing and continued improvement of the MOD-17 input datasets and algorithm construction will see improved estimates of satellite-derived productivity in tropical forest regions across the globe.

The response of epiphytes to anthropogenic disturbance of pine-oak forests in the highlands of Chiapas, Mexico

Epiphytes contribute up to over 30% of the vascular plant diversity of old-growth tropical rain forests, but little is known about their occurrence in exploited forests that are structurally altered. Here, I estimate epiphyte species richness and biomass on 35 oak host trees, equally divided over several trunk diameter classes, in each of 16 sites in anthropogenic disturbed montane pine-oak forests at similar elevations. The sites vary in their amount of disturbance from scarcely to heavily disturbed, related to the structure of the forest, and in their underlying distance in the landscape with a maximum of ca. 25 km. The explainable variation in the epiphyte vegetation is partitioned between environmental and spatial variables, using multivariate data analysis. In total, 74 species of epiphytes were encountered. Bromeliads dominate at all sites in terms of their biomass. Forest disturbance, measured as the proportion of sprouted oaks, has an expected negative effect on the epiphyte biomass and alpha diversity per ground surface area, but also on the epiphytes on the remaining and re-grown trees. This pattern was sustained after corrections for differences in host-tree size were made. Nevertheless, the epiphytes show resilience to disturbance if forests are selectively logged to spare big trees. Such remnant trees are essential for epiphytes that require the presence of accumulated suspended soil and they may also serve as nearby epiphyte seed sources for the re-growing trees. Anthropogenic disturbances also force a shift from mesic to more drought tolerant species. Hence, disturbance exerts an influence on the regional distribution of epiphytes, but a similar amount of variation (20–30%, depending on the used spatial descriptors) could entirely be attributed to the geographic position of the sites, independent from the influence of environmental variables. Nearby sites are more similar in epiphytes than distant sites (Mantel's r = 0.44, P = 0.002) and I postulate that this relates to differences in seed supply, viewing the development of the epiphyte community from a dispersal assembly perspective. For epiphyte conservation purposes, it is recommended to adopt a management of selective logging instead of cyclic clear-cutting and to spare large trees during logging. In addition, it is wise to try to attain a homogeneous distribution of epiphyte protective reserves within a uniform physiographic region.