Phosphorus cycling in primary and secondary seasonally dry tropical forests in Mexico

? Primary forests in the seasonally dry tropical regions of Mexico are disappearing under land-use pressure, creating a mosaic of secondary forests of different ages.

? In this study we measured the aboveground litterfall phosphorus (P) fluxes, litter-layer and soil P pools to compare the P cycles in primary and secondary seasonally dry tropical forests. Our hypothesis was that the previous agricultural land use of secondary forests would bring about a lower P flux in the litterfall, lower soil P pool, and higher nutrient resorption proficiency than in primary forests, as well as an increase of relative amounts of available P provided by the soil with forest aging.

? The expected litterfall P flux increase in the secondary forest following a previous agricultural land use did not occur. Phosphorus return to the soil by aboveground litterfall was unaffected by the succession stage of the forest. In addition, the total soil P pool did not change with forest age. However, available soil P (bicarbonate P-inorganic and P-organic pools) and hydroxide inorganic P pools were higher in primary than in secondary forest soils. Phosphorus concentration in litterfall increased significantly with forest age, suggesting that P is cycled more efficiently (by a higher nutrient resorption proficiency) when soil available P is less abundant. Despite these differences among forests, the results of our study gave evidence that P requirements by plants in primary and secondary forests are sufficiently met by the accumulation of dissolved (water extractable) P in the forest floor during the dry season and by soil bicarbonate-P pools.

? Our study on the effects of land cover change on P cycling, following the discontinuation of agricultural practices, leads to the conclusion that this ecosystem P dynamics will vary depending on the successional stage of the forests, and is strongly influenced by the seasonal rainfall pattern which determines plant-available P.

     

Winter soil CO2 efflux in two contrasting forest ecosystems on the eastern Tibetan Plateau,China

Significant CO2 fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO...     

Propagating framework trees to restore seasonally dry tropical forest in northern Thailand

In northern Thailand, a growing interest in restoring forests for wildlife conservation and environmental protection is increasing demand for high quality planting stock of a wide range of native forest tree species. Since most native tree species have never been grown in nurseries, their production is hindered by a lack of knowledge of basic propagation methods. Basic data on germination and performance of ten indigenous framework tree species, Castanopsis acuminatissima, Dalbergia rimosa, Diospyros glandulosa, Eugenia albiflora, Ficus glaberrima var. glaberrima, Lithocarpus craibianus, Melia toosendan, Prunus cerasoides, Quercus semiserrata and Spondias axillaris were collected during the production process. Different species produce seeds at different times of the year and they have different growth rates, yet saplings must attain a plantable size by the optimum planting time i.e. the start of the wet season. Germination percentages ranged from 38 to 89%, and the time in the nursery to reach a plantable size ranged from 119 days for Prunus cerasoides, when it had reached a mean height of 48.6 cm (SD 7.9), to 609 days for Lithocarpus craibianus, when it had reached mean height of 40.5 cm (SD 10.6). This paper discusses the scheduling of production for these candidate framework species.     

A comparative analysis of spatial, temporal, and ecological characteristics of forest fires in seasonally dry tropical ecosystems in the Western Ghats, India

The Western Ghats in India is one of the 25 global hotspots of biodiversity, and it is the hotspot with the highest human density. This study considers variations in the regional fire regime that are related to vegetation type and past human disturbances in a landscape. Using a combination of remote sensing data and GIS techniques, burnt areas were delineated in three different vegetation types and various metrics of fire size were estimated. Belt transects were enumerated to assess the vegetation characteristics and fire effects in the landscape. Temporal trends suggest increasingly short fire-return intervals in the landscape. In the tropical dry deciduous forest, the mean fire-return interval is 6 years, in the tropical dry thorn forest mean fire-return interval is 10 years, and in the tropical moist deciduous forest mean fire-return interval is 20 years. Tropical dry deciduous forests burned more frequently and had the largest number of fires in any given year as well as the single largest fire (9900 ha). Seventy percent, 56%, and 30% of the tropical moist deciduous forests, tropical dry thorn forests, and tropical dry deciduous forests, respectively have not burned during the 7-year period of study. The model of fire-return interval as a function of distance from park boundary explained 63% of the spatial variation of fire-return interval in the landscape. Forest fires had significant impacts on species diversity and regeneration in the tropical dry deciduous forests. Species diversity declined by 50% and 60% in the moderate and high frequency classes, respectively compared to the low fire frequency class. Sapling density declined by ca. 30% in both moderate and high frequency classes compared to low frequency class. In tropical moist deciduous ecosystems, there were substantial declines in species diversity, tree density, seedling and sapling densities in burned forests compared to the unburned forests. In contrast forest fires in tropical dry thorn forests had a marginal positive effect on ecosystem diversity, structure, and regeneration.     

Species composition, similarity and diversity in three successional stages of a seasonally dry tropical forest

The objectives of this study were to describe the floristic composition, species diversity, similarity and richness among three stages of forest regeneration, and to investigate the influence of the previous land use on species composition in a seasonally dry tropical forest in northwestern Costa Rica. The species diversity and richness of woody stems with diameter greater or equal to 5 cm in 26 0.1 ha plots was found to be the greatest in the intermediate stage followed by the late and early stages. The structural changes of this chronosequence of successional stages were quantified with a modification of the Holdridge complexity index. Using satellite imagery for site selection and historical ground truth analysis the influence of past land use and the frequency of anthropogenic disturbances on species composition was illustrated.     

Boron in forest trees and forest ecosystems

This review critically examines the role of boron (B) in forests in view of recent findings on B nutrition and the continuing occurrence of B deficiency. Many perceptions about the role of B in plants and its uptake and mobility have been altered since the last review on B in forest trees in 1990. Now there is evidence for a fundamental role of B in the formation of the pectic structure in primary cell walls in plants, and further roles in membrane function are being explored. In plants, channel-mediated B uptake, active B uptake and B uptake by mycorrhizas have been shown, B transporters have been identified, and B retranslocation has been shown. We explore these findings and their consequences on forest trees and on ecosystems that they dominate. Particular emphasis is placed on B retranslocation and B in mycorrhizal symbiosis, given their importance in trees.     

Nutrient cycling and growth in forest ecosystems of south western Australia: Relevance to agricultural landscapes

Nutrient and hydrologic cycles in harvested native forests in southern Australia are largely balanced. For example, we have little or no evidence of any decline in nutrient capital or availability in harvested forests. Short-term and small-scale reductions in evapotranspiration due to loss of leaf area after harvesting are adequately balanced at the landscape scale by large areas of regenerating or older-age forest. In contrast, agricultural systems on similar soils are a) dependent on large inputs of fertilisers to maintain growth and b) frequently subject to increasing salinity and waterlogging or other forms of degradation. The large-scale replacement of long-lived communities of perennial and often deep- rooting native species with annual crops or other communities of shallow-rooting species might be better managed within the framework of knowledge developed from studies of native plant communities. However, application of such a mimic concept to systems of low natural productivity is limited when agricultural systems require continued high productivity. Nonetheless, the mimic concept may help in developing sustainable management of agriculture on marginal lands, and contribute to the nutritional resilience of agroecosystems. Relevant characteristics for mimic agroecosystems in south western Australia include: high species diversity, diversity of rooting attributes, utilisation of different forms of nutrients (especially of N and P) in space and time, and the promotion of practices which increase soil organic matter content. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nutrients in litterfall,forest floor and mineral soils in two adjacent forest ecosystems in Greece

The fluxes of masses and the nutrients Ca,Mg,K,N,P and S were determined in the litterfall of two adjacent forest ecosystems of Hungarian oak(Quercus frainetto L.)and European beech(Fagus sylvatica L.)in a mountainous area of northeastern Greece in 2010–2015.The foliar litterfall for both species reached about 70%of the total litterfall,and was significantly higher from the other two fractions(woody and rest litterfall).The fluxes of masses and nutrients were compared between ecosystems for each fraction separately.Only one significant statistical difference was found,that of K in the woody litterfall.In addition,the stocks of masses and nutrients were calculated in the forest floors and mineral soils of the two ecosystems.Likewise,the stocks of nutrients in the forest floors and mineral soils were compared between ecosystems.In the L horizon of the forest floors,statistical differences,as a result of species effect,were found for the stocks of Ca and N.In the FH horizons,the masses and all the nutrient stocks differed significantly,as the beech plot had much higher quantities of organic matter and nutrients.These higher quantities were probably due to low soil temperatures(microclimate)and high acidity in the beech plot(species effect)that slowed down decomposition.In the mineral soils,the propagation of random error derived from random errors of the individual soil layers was an important factor in the statistical comparisons.Because of the soil acidity in the beech plot,the stocks of exchangeable base cations were significantly higher in the oak plot,whereas the other nutrient stocks did not differ.     

Bird communities and seedling recruitment in restoring seasonally dry forest using the framework species method in Northern Thailand

This study examined the effects of framework trees, planted in 1998, and bird community on the natural recruitment of tree seedling species in a forest restoration experiment designed to test the framework species method of forest restoration established by Chiang Mai University’s Forest Restoration Research Unit (FORRU-CMU). Tree seedlings establishing beneath five framework tree species: Erythrina subumbrans (Hassk.) Merr., Hovenia dulcis Thunb., Melia toosendan Sieb. & Zucc., Prunus cerasoides D.Don and Spondias axillaries Roxb., were surveyed. Five trees of each species were selected in the 8-year-old trial plots. Birds visiting each tree were observed to determine possible seed dispersal activities. Thirty-six tree seedling species were found beneath the selected trees, of which 11 were wind-dispersed and 25 were animal-dispersed. The population density of animal-dispersed tree seedlings was higher than the wind-dispersed seedlings beneath all selected framework trees. The sample plots beneath P. cerasoides supported the highest population density of tree seedlings. Forty-nine bird species were recorded visiting the framework trees between July 2006 and June 2007. Non-frugivorous birds were recorded more frequently than the frugivorous birds. The effects of birds on seedling recruitment were different among each of the selected framework tree. Bigger trees, which attracted high number of birds by providing food resources, roosting and nesting sites may increase the seed deposition more than smaller trees with fewer attractants.     

New allometric equations for quantifying tree biomass and carbon sequestration in seasonally dry secondary forest in northern Thailand

New Forests - As tropical deforestation and forest degradation accelerate, carbon-credit trading could provide a financial incentive to preserve and regenerate forests. Since carbon trading relies...     

SIMULATION OF SOIL NITROGEN MINERALIZATION AND NITRIFICATION IN TWO NORTHERN HARDWOOD FOREST ECOSYSTEMS

INTRODUCTIoNMeasurementsofNmincralizationinun-fertilizedforestsoilsprovideanindexofavail-ableNfortreegrowth(AuchmoodyandFilipl973,Stonel973,AbereIal.l989,BinklcyandHartl989,MclilIoela/.l993).Histori-cally,tWoapproaches(IaboratoryandinsitlIincubations)havebcenuscdtoestimatetheratCofNmineralization,butneitheriswidelyaccepted(Keeney,l98o).Thegenerallackofagrementamongthemethodsisduetodiffer-encesintheirsensitivitytocnvironmentalfac-torswhichinfluencesoilNmineralization(Raisonetal.l987…     

Forest natural regeneration and biomass production after slash and burn in a seasonally dry forest in the Southern Brazilian Amazon

This study estimates the aboveground biomass accumulation after forest clearing and slash burning and describes the structure and successional development of the secondary forest in the seasonally dry southern Amazon. The original burn study was conducted in four land clearings in 1997, 1998, and 1999. The size of the clearings varied from 1 to 9 ha. The native forest was felled, allowed to dry for approximately three months and then burned by the end of the dry season. A census was conducted in the central 1-ha forest on each site prior to the area's felling and burn. The aboveground biomass (AGB) and structure were similar to other primary tropical forests. However, the high density of Cecropia spp. before the forest felling and burn treatment indicates past low intensity disturbances. Seven and eight years after the fire, the fallow forests were still in an early successional stage dominated by Cecropia spp. The four areas had a high biomass accumulation during the studied period, varying from 7.5 to 15.0 Mg ha⁻¹ year⁻¹. The lower biomass accumulation in one plot was an effect of a higher fire severity, produced by the one-year difference in time between slash and burn of the forest, slowing the natural regeneration of Cecropia spp. The time needed for this forest to recover to the pre-fire AGB levels ranged from 20 to 30 years, assuming the current AGB accumulation rates are maintained. Considering these results, the maintenance of regenerating secondary forests in the Amazon would be a significant contribution to soil and watershed protection, minimizing biodiversity losses and perhaps mitigating climatic changes effects in the region.     

Environmental controls on the carbon isotope composition of ecosystem-respired CO2 in contrasting forest ecosystems in Canada and the USA

We compared the carbon isotope composition of ecosystem-respired CO2 (delta13C(R)) from 11 forest ecosystems in Canada and the USA and examined differences among forest delta13C(R) responses to seasonal variations in environmental conditions from May to October 2004. Our experimental approach was based on the assumption that variation in delta13C(R) is a good proxy for short-term changes in photosynthetic discrimination and associated shifts in the integrated ecosystem-level intercellular to ambient CO2 ratio (c(i)/c(a)). We compared delta13C(R) responses for three functional groups: deciduous, boreal and coastal forests. The delta13C(R) values were well predicted for each group and the highest R2 values determined for the coastal, deciduous and boreal groups were 0.81, 0.80 and 0.56, respectively. Consistent with previous studies, the highest correlations between delta13C(R) and changes in environmental conditions were achieved when the environmental variables were averaged for 2, 3 or 4 days before delta13C(R) sample collection. The relationships between delta13C(R) and environmental conditions were consistent with leaf-level responses, and were most apparent within functional groups, providing support for our approach. However, there were differences among groups in the strength or significance, or both, of the relationships between delta13C(R) and some environmental factors. For example, vapor pressure deficit (VPD) and soil temperature were significant determinants of variation in delta13C(R) in the boreal group, whereas photosynthetic photon flux (PPF) was not; however, in the coastal group, variation in delta13C(R) was strongly correlated with changes in PPF, and there was no significant relationship with VPD. At a single site, comparisons between our delta13C(R) measurements in 2004 and published values suggested the potential application of delta13C(R) measurements to assess year-to-year variation in ecosystem physiological responses to changing environmental conditions, but showed that, in such an analysis, all environmental factors influencing carbon isotope discrimination during photosynthetic gas exchange must be considered.     

Seasonal patterns of leaf gas exchange and water relations in dry rain forest trees of contrasting leaf phenology

Diurnal and seasonal patterns of leaf gas exchange and water relations were examined in tree species of contrasting leaf phenology growing in a seasonally dry tropical rain forest in north-eastern Australia. Two drought-deciduous species, Brachychiton australis (Schott and Endl.) A. Terracc. and Cochlospermum gillivraei Benth., and two evergreen species, Alphitonia excelsa (Fenzal) Benth. and Austromyrtus bidwillii (Benth.) Burret. were studied. The deciduous species had higher specific leaf areas and maximum photosynthetic rates per leaf dry mass in the wet season than the evergreens. During the transition from wet season to dry season, total canopy area was reduced by 70-90% in the deciduous species and stomatal conductance (g(s)) and assimilation rate (A) were markedly lower in the remaining leaves. Deciduous species maintained daytime leaf water potentials (Psi(L)) at close to or above wet season values by a combination of stomatal regulation and reduction in leaf area. Thus, the timing of leaf drop in deciduous species was not associated with large negative values of daytime Psi(L) (greater than -1.6 MPa) or predawn Psi(L) (greater than -1.0 MPa). The deciduous species appeared sensitive to small perturbations in soil and leaf water status that signalled the onset of drought. The evergreen species were less sensitive to the onset of drought and g(s) values were not significantly lower during the transitional period. In the dry season, the evergreen species maintained their canopies despite increasing water-stress; however, unlike Eucalyptus species from northern Australian savannas, A and g(s) were significantly lower than wet season values.     

Nighttime transpiration in woody plants from contrasting ecosystems

It is commonly assumed that transpiration does not occur at night because leaf stomata are closed in the dark. We tested this assumption across a diversity of ecosystems and woody plant species by various methods to explore the circumstances when this assumption is false. Our primary goals were: (1) to evaluate the nature and magnitude of nighttime transpiration, E(n), or stomatal conductance, g(n); and (2) to seek potential generalizations about where and when it occurs. Sap-flow, porometry and stable isotope tracer measurements were made on 18 tree and eight shrub species from seven ecosystem types. Coupled with environmental data, our findings revealed that most of these species transpired at night. For some species and circumstances, nighttime leaf water loss constituted a significant fraction of total daily water use. Our evidence shows that E(n) or g(n) can occur in all but one shrub species across the systems we investigated. However, under conditions of high nighttime evaporative demand or low soil water availability, stomata were closed and E(n) or g(n) approached zero in eleven tree and seven shrub species. When soil water was available, E(n) or g(n) was measurable in these same species demonstrating plasticity for E(n) or g(n). We detected E(n) or g(n) in both trees and shrubs, and values were highest in plants from sites with higher soil water contents and in plants from ecosystems that were less prone to atmospheric or soil water deficits. Irrespective of plant or ecosystem type, many species showed E(n) or g(n) when soil water deficits were slight or non-existent, or immediately after rainfall events that followed a period of soil water deficit. The strongest relationship was between E(n) or g(n) and warm, low humidity and (or) windy (> 0.8 m s(-1)) nights when the vapor pressure deficit remained high (> 0.2 kPa in wet sites, > 0.7 kPa in dry sites). Why E(n) or g(n) occurs likely varies with species and ecosystem type; however, our data support four plausible explanations: (1) it may facilitate carbon fixation earlier in the day because stomata are already open; (2) it may enhance nutrient supply to distal parts of the crown when these nutrients are most available (in wet soils) and transport is rapid; (3) it may allow for the delivery of dissolved O(2) via the parenchyma to woody tissue sinks; or (4) it may occur simply because of leaky cuticles in older leaves or when stomata cannot close fully because of obstructions from stomatal (waxy) plugs, leaf endophytes or asymmetrical guard cells (all non-adaptive reasons). We discuss the methodological, ecophysiological, and theoretical implications of the occurrence of E(n) or g(n) for investigations at a variety of scales.     

Differences in C and N release from Alliaria petiolata leaves and stems: consequences for nutrient cycling in forest ecosystems

European Journal of Forest Research - Garlic mustard (Alliaria petiolata (Bieb.) Cav. et Grande) is a widespread forest edge plant species in the European temperate zone and also one of the most...     

Comparative water relations of mature mahogany (Swietenia macrophylla) trees with and without lianas in a subhumid,seasonally dry forest in Bolivia

Many evergreen mahogany (Swietenia macrophylla King) trees in the seasonally dry Bajo Paragua forest in northeast Bolivia carry substantial liana loads. Evergreen lianas may impede the growth of their host trees in various ways, including competition for water. Hypotheses tested were that water relations status differs (a) between lianas and their host trees, and (b) between trees infested with lianas that were cut 3.5 months previously (treated trees) and control trees with intact lianas. Diurnal measurements of stomatal conductance (g(s)) and leaf water potential (Psi) were made on canopy leaves of treated and control trees and lianas at the start and end of the dry season. Lianas had higher (less negative) Psi values (mean and predawn) and higher diurnal g(s) (expressed as mean or sum of diurnal values) than mahogany trees, indicating that lianas had a higher demand for, and ability to obtain, water than their host trees. Control and treated trees had a similar water relations status, suggesting that removal of lianas had no effect on the water relations of the trees, even at the end of the dry season. We conclude that either both life forms have conservative water relations that were unaffected by water availability in our study, or that the trees and lianas have access to sufficient and different sources of water because of differences in their rooting depths. Our data are consistent with studies of temperate species, indicating that lianas do not interfere with water availability to their host trees.