Seasonal changes in litter fall and its quality from three sub-tropical fruit tree species at Nelspruit, South Africa

Litter fall from upper storey trees in agroforestry systems contributes to nutrient cycling for the benefit of all components of the system besides serving as mulch. This study examined the seasonal changes in the quantity and quality of leaf litter fall from three sub-tropical fruit trees viz: avocado (Persea americana L.), mango (Mangifera indica L.) and litchi (Litchi chinensis L.) which have potential for use in agroforestry. Leaf litter production was estimated using nylon mesh litter traps erected over five randomly selected trees of each species in a completely randomised design. Litter quality was determined by analysing ash content and polyphenol, carbon, cellulose, lignin and nutrient concentrations over a 2?year period (2007?C2008). Total annual leaf litter production during the study period (dry matter basis) was 8.3, 6.3 and 5.6?t?ha^?1?year^?1 for litchi, mango and avocado, respectively. In both years, leaf litter fall was greatest during autumn and lowest during winter in all species. There were no significant differences in S, Ca, Mg and Mn concentrations in the leaf litter, but polyphenol, N, P and K concentrations differed significantly (P?<?0.05) between species. It was concluded that litter quality from all three tree species was low and would require appropriate management to improve its quality.     

Nitrogen-fixing legume tree species for the reclamation of severely degraded lands in Brazil

The main challenges faced in the reclamation of severely degraded lands are in the management of the systems and finding plant species that will grow under the harsh conditions common in degraded soils. This is especially important in extremely adverse situations found in some substrates from mining activities or soils that have lost their upper horizons. Under these conditions, recolonization of the area by native vegetation through natural succession processes may be extremely limited. Once the main physical and chemical factors restrictive to plant growth are corrected or attenuated, the introduction of leguminous trees able to form symbioses with nodulating N?-fixing bacteria and arbuscular mycorrhizal fungi constitutes an efficient strategy to accelerate soil reclamation and initiate natural succession. These symbioses give the legume species a superior capacity to grow quickly in poor substrates and to withstand the harsh conditions presented in degraded soils. In this article we describe several successful results in Brazil using N?-fixing legume tree species for reclamation of areas degraded by soil erosion, construction and mining activities, emphasizing the potential of the technique to recover soil organic matter levels and restore ecosystem biodiversity and other environmental functions.     

Water-holding characteristics of litter in different forests at the Lianxiahe watershed

We surveyed the forest litter amount at the Lianxiahe watershed in the Three Gorges Reservoir Area and analyzed some hydrological characteristics such as the maximum water-holding capacity and water absorption rate of litter in six types of forests, i.e. the Cupressus funebris forest, the coniferous mixed forest, the coniferous and broad-leaved mixed forest, the broad-leaved forest, the Pinus massoniana forest, the bush forest. Results showed that the litter amount follows the order of the coniferous and broad-leaved mixed forest > the pure C. funebris forest, the P. massoniana forest > the coniferous mixed forest > the broad-leaved forest > the bush forest. The maximal water holding capacity of the undecomposed litter is in the order of the C. funebris forest > the coniferous mixed forest > the bush forest > the coniferous and broad-leaved mixed forest > the broad-leaved forest > the P. massoniana forest. The maximal water-holding capacity of the half-decomposed litter is the P. massoniana forest > the coniferous and broad-leaved mixed forest > the C. funebris forest > the coniferous mixed forest > the broad-leaved forest > the bush forest. In this watershed, the water holding capacity of the litter in the C. funebris forest is the highest, followed by the coniferous mixed forest, coniferous and broad-leaved mixed forest, P. massoniana forest, broad-leaved forest and bush forest. When the soil is covered only by litter, both the maximal rainfall amount and intensity in different forest stands are different if there is no water infiltration and runoff from the ground surface. __________ Translated from Journal of Huazhong Agricultural University, 2005, 27(2): 207–212 [译自: 华中农业大学学报, 2005, 24(2): 207–212]     

Decomposition of leaf litter of four native broad-leaved tree species in south China

Leaf litter decomposition of Castanopsis fissa, Cinnamomum camphora, Michelia macclurei and Mytilaria laosensis in mixed broad-leaved plantation and pine plantation was studied by the litterbag method for 1 year. Leaf litter decomposition rates of the four species were highest in Cinnamomum camphora, followed by Mytilaria laosensis, Michelia macclurei, and Castanopsis fissa. The decomposition rates of all four species were higher in the mixed than in pine plantation. The decomposition processes of all species followed Olson’s exponential model. The decomposition coefficients (k) of all species were also higher in the mixed plantation and had the same order as the decomposition rates. The nitrogen contents of leaf litter of the different species studied increased initially and then decreased with time. Net release of N only occurred in pine plantation. Potassium contents appeared to decrease first but later increase, and net release was only found in mixed plantation. Calcium, magnesium and boron all showed similar pattern of initial increase followed by later decrease. They all had net release in both mixed and pine plantations. The release of phosphorus varied greatly between species and showed no clear trend.     

Decreases by disturbance-dependent tree species in the eastern and central USA

Open pine and oak forest ecosystems and floodplain forests have declined because of fire and flooding suppression. I determined tree species that have contracted in area occupied (where area occupied was ≥0.5 % of total species composition) or decreased in percent composition (i.e., percentage of all stems) during recent surveys (2000–2013) to ≤85 % of area occupied or composition during older surveys (1968–1999). I then identified whether species were associated with frequent fire, flooding, wetlands, postfire conditions, or other disturbances. Of 35 species that decreased in area occupied or composition, 16 species were associated with fire or postfire disturbance and fire-dependent species decreased in composition from 20 to 14 % during tree surveys. Even though species of floodplain forests and wetlands comprise a small percent of overall tree composition, 12 decreasing species were associated with floodplain forests or wetlands. Fire maintains open oak and pine ecosystems and flooding maintains floodplain forests, generally suspending succession. Suppression of fire in upland forests and flooding in floodplain forests has allowed disturbance-sensitive species to remain established and advance successional forests throughout the USA.     

Soil macrofauna and litter nutrients in three tropical tree plantations on a disturbed site in Puerto Rico

Tree plantations are increasingly common in tropical landscapes due to their multiple uses. Plantations vary in structure and composition, and these variations may alter soil fauna communities. Recent studies have demonstrated the important role of soil fauna in the regulation of plant litter decomposition in the tropics. However, little is known about how plantation species affect soil fauna populations, which may in turn affect the biogeochemistry of the plantation system. We measured soil macroinvertebrate abundance and biomass in 9-year-old N₂-fixing Leucaena leucocephala, Casuarina equisetifolia, and non-N₂-fixing Eucalyptus robusta plantations on a degraded site in Puerto Rico. Nutrient concentrations and standing stocks of forest floor litter were also determined to examine the relationship between litter chemistry and soil macroinvertebrates. Leucaena plantations had significantly higher abundances and biomass of millipede species than Casuarina and Eucalyptus. Earthworm biomass did not differ among plantation treatments. Nitrogen, P, and K concentrations were generally higher in Leucaena litter, which resulted in higher standing stocks of these nutrients in fragmented, moderately decomposed litter (Oe horizon). Millipede biomass was highly correlated to N concentration and C/N ratio in the Oi litter horizon. These results suggest that plantation species differ in their influence on soil fauna, and the biomass and abundance of soil fauna can be regulated through careful selection of plantation species in degraded tropical lands.     

Effects of climatic conditions on tree-ring widths of three deciduous broad-leaved tree species at their northern distribution limit in Mont St. Hilaire,eastern Canada

This study examined the effects of climatic conditions on tree-ring widths of red oak (Quercus rubra), sugar maple (Acer saccharum) and American beech (Fagus grandifolia) at their northern distribution limit in Mont St. Hilaire, eastern Canada. A residual chronology of tree-ring width index was developed for each species. The tree-ring width of Q. rubra showed negative and positive correlations with May temperature and June precipitation in the current year, respectively. A. saccharum also showed similar patterns with Q. rubra, i.e., negative and positive correlations with June temperature and precipitation in the current year, respectively. F. grandifolia showed neither positive nor negative correlations with temperature and precipitation. The expressed population signals of tree-ring width chronologies of the three species indicated that climatic factors more greatly influenced the variations in tree-ring widths in the order Q. rubra > A. saccharum > F. grandifolia. Therefore, the radial growth of Q. rubra was most restricted by drought stress in early summer among the three species. Global warming is suggested to affect the radial growth of the three species differently by increasing drought stress at Mont St. Hilaire in eastern Canada.     

Hydraulic patterns and safety margins, from stem to stomata, in three eastern U.S. tree species

Adequate water transport is necessary to prevent stomatal closure and allow for photosynthesis. Dysfunction in the water transport pathway can result in stomatal closure, and can be deleterious to overall plant health and survival. Although much is known about small branch hydraulics, little is known about the coordination of leaf and stem hydraulic function. Additionally, the daily variations in leaf hydraulic conductance (K(leaf)), stomatal conductance and water potential (Ψ(L)) have only been measured for a few species. The objective of the current study was to characterize stem and leaf vulnerability to hydraulic dysfunction for three eastern U.S. tree species (Acer rubrum, Liriodendron tulipifera and Pinus virginiana) and to measure in situ daily patterns of K(leaf), leaf and stem Ψ, and stomatal conductance in the field. Sap flow measurements were made on two of the three species to compare patterns of whole-plant water use with changes in K(leaf) and stomatal conductance. Overall, stems were more resistant to hydraulic dysfunction than leaves. Stem P50 (Ψ resulting in 50% loss in conductivity) ranged from -3.0 to -4.2 MPa, whereas leaf P50 ranged from -0.8 to -1.7 MPa. Field Ψ(L) declined over the course of the day, but only P. virginiana experienced reductions in K(leaf) (nearly 100% loss). Stomatal conductance was greatest overall in P. virginiana, but peaked midmorning and then declined in all three species. Midday stem Ψ in all three species remained well above the threshold for embolism formation. The daily course of sap flux in P. virginiana was bell-shaped, whereas in A. rubrum sap flux peaked early in the morning and then declined over the remainder of the day. An analysis of our data and data for 39 other species suggest that there may be at least three distinct trajectories of relationships between maximum K(leaf) and the % K(leaf) at Ψ(min). In one group of species, a trade-off between maximum K(leaf) and % K(leaf) at Ψ(min) appeared to exist, but no trade-off was evident in the other two trajectories.     

Competition and tree crowns: A neighborhood analysis of three boreal tree species

Competition for canopy space is a fundamental structuring feature of forest ecosystems and remains an enduring focus of research attention. We used a spatial neighborhood approach to quantify the influence of local competition on the size of individual tree crowns in north-central British Columbia, where forests are dominated by subalpine fir (Abies lasiocarpa), lodgepole pine (Pinus contorta) and interior spruce (Picea glauca × engelmanii). Using maximum likelihood methods, we quantified crown radius and length as functions of tree size and competition, estimated by the species identity and spatial arrangement of neighboring trees. Tree crown size depended on tree bole size in all species. Given low levels of competition, pine displayed the widest, shortest tree crowns compared to the relatively long and narrow crowns found in spruce and fir. Sensitivity to crowding by neighbors declined with increasing tree height in all but the pine crown radius model. Five of the six selected best models included separate competition coefficients for each neighboring tree species, evidence that species generally differ in their competitive effects on neighboring tree crowns. The selected crown radius model for lodgepole pine, a shade-intolerant species, treated all neighbors as equivalent competitors. In all species, competition from neighbors exerted an important influence on crown size. Per-capita effects of competition across different sizes and species of neighbors and target trees varied, but subalpine fir generally displayed the strongest competitive effects on neighbors. Results from this study provide evidence that species differ both in their response to competition and in their competitive influence on neighbors, factors that may contribute to maintaining coexistence.     

Effects of tree species diversity on leaf litter decomposition process in semi-arid Mediterranean oak forests

European Journal of Forest Research - Many studies have been conducted on the effects of changes in plant diversity and species composition on ecosystem functioning and plant productivity due to...     

Dynamics of some mineral nutrients and heavy metals in decomposing forest litter

The dynamics of three major mineral nutrients (K, Ca, Mg) and six heavy metals (Fe, Mn, Zn, Cu, Pb and Cd) were studied in decomposing natural, unpolluted litter in two forest types: Scots pine needle litter in a pure Scots pine forest and oak‐hornbeam leaf litter in a mixed oak‐hornbeam stand. Of the mineral nutrients, only K in the oak‐hornbeam system showed a significant decrease in concentration during the course of litter decomposition. For Ca and Mg in both systems and for K in the Scots pine system no clear relation between concentration and accumulated litter‐mass loss was observed. On the other hand, for Fe, Zn, Pb and Cd at both sites, as well as for Mn in the oak‐hornbeam stand and Cu in the Scots pine stand highly significant positive relations were found between heavy metal concentrations and accumulated mass loss. A decrease in concentration was noted only in the case of Mn in the Scots pine system. No clear pattern was found for Cu in the oak‐hornbeam stand. Concentrations of heavy metals in the decomposing litter reached levels at or above those reported to retard decomposition in other studies. At the oak‐hornbeam stand increased also the absolute amounts of Fe, Zn, Pb and Cd.     

Sap flow of the major tree species in the eastern mountainous region in northeast China

This study is based on Quercus mongolica, Fraxinus mandshurica, Phellodendron amurense, Juglans mandshurica, Tilia amurensis, and Pinus koraiensis trees of the same age (12 years) and seedling origin under the same site conditions. The sap flow density, water consumption, and related environmental factors were also measured using thermal dissipation method and ICT-2000TE (Transpiration-Environment) automatic measuring system for tree transpiration and environmental factors. On clear days during the growing season, the sap flow density exhibited mono-peak diurnal patterns, mostly between 10:00 and 14:00, except for Phellodendron amurense, whose sap flow showed two peaks during the daytime three times. The photosynthetically active radiation (PAR) and vapour pressure deficit (VPD) were the major factors influencing diurnal changes in sap flow, which explained 60%–74% variations in sap flow density for all species except Phellodendron amurense. Maximum sap flow densities for F. mandshurica, Phellodendron amurense, Q. mongolica, J. mandshurica, T. amurensis, and Pinus koraiensis were 516.36, 234.00, 625.93, 945.83, 507.93, and 286.21 cm³/(cm²·h), in July, June, September, August, August, and July, respectively. Water consumption during the whole growing season for J. mandshurica, T. amurensis, F. mandshurica, Pinus koraiensis, Phellodendron amurense, and Q. mongolica was 3,840, 2,820, 2,710, 2,120, 1,470, and 1,390 kg/sapling, respectively. __________ Translated from Scientia Silvae Sinicae, 2005, 41(3): 36–42 [译自: 林业科学, 2005, 41(3): 36–42]     

3树种抗旱性的灰色关联分析

运用灰色关联分析法,对3个树种的抗旱性与9项抗旱指标的相关性进行了分析。关联度分析结果表明:叶绿素含量、叶水势、叶片相对含水量以及电导率与3个树种的关联度分别为0.7674、0.7005、0.6793和0.6287,它们可作为3个树种重要的抗旱评价指标。     

Controls of litter quality on the carbon sink in soils through partitioning the products of decomposing litter in a forest succession series in South China

Through the long-term measurement and development of a method for partitioning the products of decomposing litter, the impact of chemical components of forest debris on soil organic carbon (SOC) accumulation was studied in a forest succession series in South China. We quantified how litter quality is strongly correlated with the partitioning of respiration, dissolved organic carbon (DOC) and fragments of decomposing litter. In the succession sequence of 60-year-old pine forest (PF), to 80-year-old mixed pine and evergreen broadleaved forest (MF) to more than 400-year-old monsoon evergreen broadleaved forest (MEBF), the litter C/N ratios and lignin contents were gradually decreasing, which in turn were correlated with increasing litter decomposition constants (k-values), gradually shortening residence times of standing litter pool. And, 53.5%, 65.6% and 76.2% of the gravimetric litter mass losses were going belowground through both DOC and fragmentation. Correspondingly, the SOC accumulation rates in the top 20 cm of mineral soils for the three forests from 1978 to 2008 were 26 ± 4, 33 ± 5 and 67 ± 5 g C m⁻² yr⁻¹, respectively. Results of the study support the idea that in order to increase carbon sequestration in soils and long-term functional ability of forest ecosystems to act as carbon sinks, “Kyoto Forests” should be designed and reconstructed with a high diversity of broadleaved species, especially containing nitrogen-fixing trees.     

Mixed planted-fallows using coppicing and non-coppicing tree species for degraded Acrisols in eastern Zambia

The widespread planting of Sesbania sesban fallows for replenishing soil fertility in eastern Zambia has the potential of causing pest outbreaks in the future. The pure S. sesban fallows may not produce enough biomass needed for replenishing soil fertility in degraded soils. Therefore, an experiment was conducted at Kagoro in Katete district in the Eastern Province of Zambia from 1997 to 2002 to test whether multi-species fallows, combining non-coppicing with coppicing tree species, are better than mono-species fallows of either species for soil improvement and increasing subsequent maize yields. Mono-species fallows of S. sesban (non-coppicing), Gliricidia sepium, Leucaena leucocephala and Acacia angustissima (all three coppicing), and mixed fallows of G. sepium + S. sesban, L. leucocephala + S. sesban, A. angustissima + S. sesban and natural fallow were compared over a three-year period. Two maize (Zea mays) crops were grown subsequent to the fallows. The results established that S. sesban is poorly adapted and G. sepiumis superior to other species for degraded soils. At the end of three years, sole G. sepium fallow produced the greatest total biomass of 22.1 Mg ha⁻¹ and added 27 kg ha⁻¹ more N to soil than G. sepium + S. sesban mixture. During the first post-fallow year, the mixed fallow at 3.8 Mg ha⁻¹ produced 77% more coppice biomass than sole G. sepium, whereas in the second year both sole G. sepium and the mixture produced similar amounts of biomass (1.6 to 1.8 Mg ha⁻¹). The G. sepium + S. sesban mixture increased water infiltration rate more than sole G. sepium, but both these systems had similar effects in reducing soil resistance to penetration compared with continuous maize without fertilizer. Although sole G. sepium produced high biomass, it was G. sepium + S. sesban mixed fallow which resulted in 33% greater maize yield in the first post-fallow maize. However, both these G. sepium-based fallows had similar effects on the second post-fallow maize. Thus the results are not conclusive on the beneficial effects of G. sepium + S. sesban mixture over sole G. sepium. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nutrients leaching from green leaves of three potential agroforestry tree species

Nutrient (NH₄, PO₄ and K) leaching from oven dried green leaves of Emblica officinalis Gaerten, Sesbania grandiflora (L.) Pers. and Moringa oleifera Lam.were investigated in laboratory condition. Oven-dried green leaves were immersed in demineralized distilled water for 8 days. Electrical conductivity (EC), Total dissolved solids (TDS) and nutrients (NH₄, PO₄ and K) of leaching water samples were measured at 0.25, 0.5, 1, 2, 3, 4, 6, 8, 12, 24, 48, 72, 96, 144, and 192 h of intervals. All these species showed an increasing trend for EC and TDS in leachate and comparatively higher EC and TDS were observed in E. officinalis, which is followed, by S. grandiflora and M. oleifera. Significantly high amount (P < 0.05) of NH₄ was leached from S. grandiflora and PO₄ from M. oleifera. But, both S. grandiflora and M. oleifera leached significantly higher (P < 0.05) K than E. officinalis. Within the first 0.25 h, 100 % and 82 % of NH₄ and 68 % and 74 % of K were leached from leaves of S. grandiflora and M. oleifera respectively. S. grandiflora and M. oleifera leached 100 % of PO₄ within 6 h. The concentrtions of NH₄, PO₄ and K in the leachate from E. officinalis, S. grandiflora and M. oleifera were not significantly different (P > 0.05). The green leaves of S. grandiflora and M.oleifera can be a potential source of NH₄, PO₄ and K for a quick nutrient supplement to the agricultural crops in agroforestry practices.     

Leaf-litter decomposition of 15 tree species in a lowland tropical rain forest in Sarawak: decomposition rates and initial litter chemistry

In a lowland tropical rain forest in Sarawak, leaf-litter decomposition and the initial litter chemistry of 15 tree species were studied. During 13 months of field experiment, weight loss of litter samples was between 44% and 91%, and calculated decomposition rate constants (k) ranged from 0.38 to 2.36 year⁻¹. The initial litter chemistry also varied widely (coefficients of variation: 19%–74%) and showed low N and P concentrations and high acid-insoluble residue (AIS) concentration. For nutrient-related litter chemistry, correlations with the decomposition rate were significant only for P concentration, C/P ratio, and AIS/P ratio (r _s = 0.59, −0.62, and −0.68, n = 15, P < 0.05, respectively). For organic constituents, correlations were significant for concentrations of AIS and total carbohydrates, and AIS/acid-soluble carbohydrate ratio (r _s = −0.81, 0.51, and −0.76, n = 15, P < 0.05, respectively). These results suggested that the relatively slow mean rate of decomposition (k = 1.10) was presumably due to the low litter quality (low P concentration and high AIS concentration), and that P might influence the decomposition rate; but organic constituents, especially the concentration of AIS, were more important components of initial litter chemistry than nutrient concentrations.     

Long-term ecological impacts of clear-fell logging on tree species diversity in a subtropical forest,southern Japan

Defining the spatial arrangement and length of the cutting cycle in a logged area is crucial for reconciling potential conflicts between timber yields and maintenance of ecosystem services in natural forests. In this study, we investigated long-term impacts of clear-fell logging on timber production and tree species diversity in a subtropical forest on the Ryukyu Islands, using an individual-based simulation model. We assumed six logging scenarios defined by combinations of forest type and regeneration processes, which acted as surrogates for spatial scales of clear-fell logging. These scenarios were simulated under cutting cycles ranging from 20 to 150 years. Short-cutting cycles resulted in dominance by the sprouting species Castanopsis sieboldii. The compositional shift was accelerated by the lack of seed dispersal from surrounding forest areas. The simulations demonstrated that a sustainable logging regime maintaining both yield and tree species diversity requires a cutting cycle longer than 50 years. The simulation results also suggest that the trade-off between the recovery of tree species diversity and timber production is favored more in stands surrounded by mature forest than in isolated stands or stands surrounded by immature forest. Ecological risk assessments based on model simulations provide an alternative to current forest management practices that rely on empirical knowledge.     

Soil denitrification rates in a subalpine watershed of the eastern Sierra Nevada

Denitrification rates in soils of six subalpine plant communities in an eastern Sierra Nevada watershed were determined by the acetylene inhibition method. Soil atmosphere samples were collected monthly from June 1986 through May 1987 in a riparian, wet meadow, dry meadow, north-facing forest, south-facing forest and barren site and analyzed for N₂O content using gas chromatography. Soil temperature, moisture, organic matter, C,N,C:N ratio, NO₃N and pH were examined to assess their effects on denitrification rates. Mean denitrification rates for the year varied from 103.3 μg m⁻²h⁻¹ in the north-facing forest to 120.2 μg m⁻²h⁻¹ at the barren site, but did not differ significantly among any of the six plant communities. However, comparisons among months within individual communities revealed that the denitrification rates in each community varied significantly over the year, and in three of the six sites significant correlations between denitrification rates and other soil parameters were detected. Soil acidity was positively correlated with denitrification rate in the riparian and wet meadow communities, and in the dry meadow, soil moisture was positively correlated while soil temperature and organic matter were negatively correlated with denitrification rate. Comparisons among sites within individual months revealed significant differences in denitrification rates in June, September, October and January, but no single site consistently exhibited the highest or lowest rate in all 4 months, and only in October, when denitrification rates were positively correlated with soil temperature and moisture, was variation in denitrification rates among sites explained by other soil parameters. For the six plant communities overall, soil denitrification rates were highly variable from June to October, increased sharply from October to December, and then declined from December to May.