Tree Litterfall Research Articles

Quantification and Proxy Indicators of the Carbon Pool in Urban Tree Litterfall: A Case Study of Urban Green Spaces in Beijing

As major carbon (C) pools in cities, urban green spaces play a crucial role in reducing atmospheric carbon. To determine the importance of litterfall C storage in urban green spaces, we selected the leaf area index (LAI) as a proxy indicator for litterfall C density (LCD), and established a log-linear regression model between LCD and LAI to predict the annual litterfall C pool in large-scale urban green spaces using Sentinel-2 satellite remote sensing data. Forty-five sample units were randomly selected in typical urban green spaces in Beijing, China. A high-temperature combustion method was used to measure the LCD of the sampling units, and stepwise linear regression was used to filter the proxy indicator for LCD. The annual litterfall C pool in regions within the Fifth Ring Road was also estimated with inversion using remote sensing data. From 2015 to 2021, the estimated annual litterfall C pool was in the range of 4.5–5.8 × 1010 g, i.e., approximately 18.9% of the total C storage recorded for the urban green space, which was far greater than that observed in forest ecosystems. We concluded that the litterfall C pool in urban green spaces is seriously underestimated, and that urban tree litterfall has the potential to reduce greenhouse gas emissions if used as a carbon-neutral resource.

Sources of variation in nutrient loads collected through street sweeping in the Minneapolis-St. Paul Metropolitan Area, Minnesota, USA

Excess non-point nutrient loading continues to impair urban surface waters. Because of the potential contribution of tree litterfall to nutrient pollution in stormwater, street sweeping is a promising management tool for reducing eutrophication in urban and suburban regions. However, nutrient concentrations and loads of material removed through street sweeping have not been well characterized, impeding the development of pollution reduction credits and improvement of models for stormwater management. We evaluated the role of canopy cover over streets, street sweeper type, season, and sweeping frequency in contributing to variation in concentrations and loads of nitrogen (N), phosphorus (P), and solids recovered in street sweepings, using analyses of samples collected during regular street sweeping operations in five cities in the Minneapolis-St. Paul Metropolitan Area, Minnesota, USA. We expected that nutrient concentrations and loads would be highest in seasons and places of higher tree litterfall. We also expected that regenerative-air sweepers would recover higher loads compared to mechanical broom sweepers. Total N and P concentrations in sweepings increased most strongly with canopy cover in June, October, and November. Total N and P recovered in street sweepings similarly increased with canopy cover in June, October, and November, and peaked in early summer and autumn, times of high litterfall. In contrast, total dry mass in sweepings was greatest in early spring, following winter snowmelt. However, nutrient loads and concentrations did not differ between sweeper types. Our results add to growing evidence of the importance of street trees in contributing nutrient pollution to urban surface waters. Street sweeping focused on high-canopy streets during early summer and autumn is likely an effective management tool for stormwater nutrient pollution.

Seasonal dynamics of herbaceous layer biomass and its contribution to annual net primary production in an oak–hornbeam forest

The role of the herbaceous layer in carbon assimilation and nutrient cycling is still undiscovered and unappreciated. One reason is that simple methods of annual net primary production (ANPP) estimation often underestimate its value, while more accurate methods are too labor-demanding. Moreover, studies on herbaceous layer and litterfall biomass in the same study site are extremely rare and usually conducted during one vegetation season, providing temporally-specific estimates. We hypothesized that (1) the seasonal herb layer biomass dynamics show a two-peak shape and (2) contribution of herbaceous layer biomass production in annual litter production was not more than 5% of tree litterfall. We studied the herb layer and litterfall biomass dynamics in an oak-hornbeam forest in W Poland for three years (January 2013 – October 2015). Samples of the herb layer (ten samples for four sample plots) were collected weekly in March, April and May or every two weeks for the remainder of each year, and litterfall was collected every month. All herb plants were cut at the soil level from circular frames with an area of 0.16 m2. Litterfall was studied with thirty litter traps (height of 15 cm, and catching area of 0.36 m2). We performed Kruskal–Wallis tests with Dunn’s post hoc tests to assess differences in variables among all collection times and linear random effects models to assess variance sources. We observed the highest biomass in 2013 on May 3rd (47.05 g m−2), and the lowest on October 30th in 2015 (4.69 g m−2). The seasonal herb layer biomass dynamic showed a single-peak shape; a very distinct peak occurred in spring and continued in late spring, summer, and early autumn. The spring ephemeralAnemone nemorosahad the highest share of herbaceous layer ANPP with 27% and was responsible for the spring biomass peak every season. The mean contribution of the herb layer biomass in annual litterfall was 9.23%. Our results highlight the underestimation of the herb layer role in biomass production in forest ecosystems in previous studies.

Unique biogeochemical characteristics in coastal ghost forests – The transition from freshwater forested wetland to salt marsh under the influences of sea level rise

Seawater intrusion by rising sea levels has created large areas of ghost forests along low-lying coastal wetlands in the southeastern USA, but more information is needed to better understand its soil biogeochemistry. Here, we characterized several soil and environmental parameters, including tree litterfall, surface and soil porewater quality, emissions of greenhouse gases, and microbial communities along a forest-to-marsh transect, including a freshwater forested wetland, a salt-impacted degraded ghost forest, and a salt marsh in Winyah Bay, SC, USA. General water quality parameters such as electrical conductivity, dissolved oxygen, temperature and aboveground productivity showed distinct trends along the freshwater forested wetland → degraded ghost forest → salt marsh transect, whereas there were no obvious trends in soil biogeochemical parameters. Concentrations of dissolved organic carbon (DOC) in the degraded ghost forest were generally similar to the freshwater forested wetland, but on average were higher than those in the salt marsh. More labile molecular features observed through Fourier transform ion cyclotron resonance mass spectrometry indicated an increase in the DOC biodegradability along the forest-to-marsh transect. Greater DOC biodegradability in the degraded ghost forest was observed and confirmed through its generation of the highest average electrical currents from sediment microbial fuel cells. The lowest CH4 and CO2 fluxes, but the highest degradable DOC, were observed in the degraded ghost forest, suggesting that lateral C export is important in this wetland. Moreover, the degraded ghost forest was dominated by a unique microbial community, including high abundance of Woesearchaeia, which enables carbon metabolism via symbiotic and/or fermentation-based lifestyles. Our study illustrates a ghost forest with very different characteristics compared to its parental freshwater forested wetland and its transitioned salt marsh. Data obtained from the two endmember ecosystems along the salinity gradient transect were not useful in predicting the unique biogeochemical processes in the degraded ghost forest.

Soil carbon balance of afforested peatlands in the maritime temperate climatic zone

Drainage and conversion of natural peatlands into forestry increases soil CO2 emissions through decomposition of peat and modifies the quantity and quality of litter inputs and therefore the soil carbon balance. In organic soils, CO2 net emissions and removals, are reported using carbon emission factors (EF). The choice of specific default Tier 1 EF values from the IPCC 2013 Wetlands supplement depends on land use categories and climate zones. However, Tier 1 EF for afforested peatlands in the temperate maritime climate zone are based on data from eight sites, mainly located in the hemiboreal zone, and the uncertainty associated with these default values is a concern. In addition, moving from Tier 1 to higher-Tier carbon reporting values is highly desirable when large areas are affected by land use changes. In this study, we estimated site-specific soil carbon balance for the development of Tier 2 soil CO2 -C EFs for afforested peatlands. Soil heterotrophic respiration and aboveground litterfall were measured during two years at eight afforested peatland sites in Ireland. In addition, fine roots turnover rate and site-specific fine root biomass were used to quantify belowground litter inputs. Our findings found that draining of peatlands, and planting them with either Sitka spruce or lodgepole pine, resulted in soils being net carbon sources. The soil carbon balance at multi-year sites varied between 63 ± 92 and 309 ± 67 g C m-2 year-1 . Mean CO2 -C EF for afforested peatlands was 1.68 ± 0.33 tCO2 -Cha-1 year-1 . The improved CO2 -C EFs presented here for afforested peatlands are proposed as a basis to update national CO2 -C emissions from this land-use class in Ireland. Furthermore, new data from these sites will significantly contribute to the development of more reliable IPCC default Tier 1 CO2 -C EFs for afforested peatlands in the maritime temperate climate zone.

Carbon dynamics, net primary productivity and human-appropriated net primary productivity across a forest-cocoa farm landscape in West Africa.

Terrestrial net primary productivity (NPP) is an important metric of ecosystem functioning; however, there are little empirical data on the NPP of human-modified ecosystems, particularly smallholder, perennial crops like cocoa (Theobroma cacao), which are extensive across the tropics. Human-appropriated NPP (HANPP) is a measure of the proportion of a natural system's NPP that has either been reduced through land-use change or harvested directly and, previously, has been calculated to estimate the scale of the human impact on the biosphere. Additionally, human modification can create shifts in NPP allocation and decomposition, with concomitant impacts on the carbon cycle. This study presents the results of 3years of intensive monitoring of forest and smallholder cocoa farms across disturbance, management intensity, distance from forest and farm age gradients. We measured among the highest reported NPP values in tropical forest, 17.57±2.1 and 17.7±1.6MgCha-1 year-1 for intact and logged forest, respectively; however, the average NPP of cocoa farms was still higher, 18.8±2.5MgCha-1 year-1 , which we found was driven by cocoa pod production. We found a dramatic shift in litterfall residence times, where cocoa leaves decomposed more slowly than forest leaves and shade tree litterfall decomposed considerably faster, indicating significant changes in rates of nutrient cycling. The average HANPP value for all cocoa farms was 2.1±1.1MgCha-1 year-1 ; however, depending on the density of shade trees, it ranged from -4.6 to 5.2MgCha-1 year-1 . Therefore, rather than being related to cocoa yield, HANPP was reduced by maintaining higher shade levels. Across our monitored farms, 18.9% of farm NPP was harvested (i.e., whole cocoa pods) and only 1.1% (i.e., cocoa beans) was removed from the system, suggesting that the scale of HANPP in smallholder cocoa agroforestry systems is relatively small.

Nitrogen and carbon cycling associated with litterfall production in monoculture teak and mixed species teak and flueggea stands

High demand for teak (Tectona grandis L.f.), a species of economic importance, was the reason Solomon Islands experienced a surge in community-wide planting of monoculture teak stands in the last two decades. Mixed species planting of teak and flueggea (Flueggea flexuosa Muell. Arg.) was introduced to overcome the reluctance of growers to thin their stands. However, there is lack of information on the effect of changing from monoculture to mixed species plantings on the cycling of nutrients especially carbon (C) and nitrogen (N). This study assessed litter quantity and quality, total C (TC), total N (TN), C:N ratio and C and N isotope compositions (δ13C and δ15N) over 18 months at two sites (Ringgi and Poitete). The treatments included teak planted at 833 stems per hectare (sph) (T1), teak planted in rows with two rows of flueggea at 833 sph (T2), 625 sph (T3) and 416 sph (T4), and teak planted in alternating rows with flueggea at 833 sph (T5). Treatment 1 (T1) produced significantly higher total litter than T4 at Ringgi. However, based on individual tree litterfall production, teak in T4 (lowest stocking rate) at both trials produced higher litter per tree than the teak in T3, T2, T5 and T1 while there was no significant difference with litter production of flueggea. An enrichment of litter δ15N was observed over time in either species, which suggested an increased N loss and transformations in both experimental sites. When comparing each treatment and using individual tree productivity, T4 significantly produced and returned higher litter TC and TN than T3, T2, T5 and T1. Overall, individual tree productivity demonstrated that mixed species stands had a significant potential for cycling higher rates of C and N than monoculture teak stands. Therefore, establishment of mixed species stands, especially T4 and T3, was recommended as a practical measure to address the widely experienced problem of reluctance by growers to thin high value trees while preserving the balance of C and N inputs into the ground.

Positive effects of tree species diversity on litterfall quantity and quality along a secondary successional chronosequence in a subtropical forest

Litterfall, as an important link between aboveground and belowground processes, plays a key role in forest ecosystems. Here, we test for effects of tree species richness on litter production and litter quality in subtropical forest. The study further encompasses a factorial gradient of secondary succession that resulted from human exploitation. Given that a large percentage of subtropical forests are in secondary successional stages, understanding the role of biodiversity on forest re-growth after disturbance appears critical. From January 2009 to December 2014, we monitored forest litterfall in 27 Comparative Study Plots that spanned a gradient of tree species richness (3–20 species) and secondary successional ages (~20 to 120 years) in Gutianshan Natural Nature Reserve, Zhejiang Province, China. The experiment is part of the biodiversity–ecosystem functioning research platform ‘BEF-China’. Tree litterfall was collected in monthly intervals using litter traps. Samples were separated into leaf and non-leaf components. Leaf litter was further sorted into dominant and other species. Community level monthly leaf litter C and N contents were analysed through a full year. General linear mixed-effects models were applied to test for effects of tree species richness and successional age on litter quantity and leaf litter C/N. Litterfall increased with species richness among and within successional age and this effect was consistent across years. Successionally older stands had higher litterfall and this effect was related to increased tree species richness. However, species richness did not change the intra- and inter-annual temporal stability of litterfall. Increasing tree species richness increased leaf litter quality (decreased C/N), while successional age had no effect. Our study indicates that more diverse forest stands produce more leaf litter and that this litter has higher N concentrations, which could promote forest growth through accelerated nutrient re-cycling.

Dead organic matter and the dynamics of carbon and greenhouse gas emissions in frequently burnt savannas

We developed a gain–loss approach to estimating the dynamics of the dead organic matter pool in northern Australian savannas consistent with the Intergovernmental Panel on Climate Change 2006 guidance. Previously, only emissions of methane and nitrous oxide were accounted in greenhouse gas budgets. The new approach is based on a modification of the Olson fuel accumulation equation. This modification includes the mean post-fire residue and accounts for losses from both fire and decomposition and for gains from grass production, tree litter fall and the death of trees. We apply the approach to a case study in western Arnhem Land, Northern Territory, Australia, in which the fire regime has been changed and the project has achieved recognised abatement of methane and nitrous oxide emissions. The carbon sequestration in the dead organic matter is ~85 times the annual emissions abatement in this project area and when expressed as an annual rate is ~3.5 times the abatement. We also show that the emissions abatement has previously been underestimated owing to an inability to fully account for dead organic matter dynamics. Future work could refine the models of dead organic matter to include seasonal dynamics in inputs.

Variable retention management influences biomass of Misodendrum and Usnea in Nothofagus pumilio southern Patagonian forests

Variable retention systems (retention of some existing trees in different densities along with significant elements of the original forest after logging) aim to mitigate the impact of harvesting in native temperate forests, improving biodiversity conservation in managed stands. This study evaluates the effect of variable retention harvesting on epiphytic lichens (Usnea barbata) and mistletoes (Misodendrum punctulatum) in Nothofagus pumilio forests. The abundance of these canopy-dwelling species can be estimated by measuring their litter fall. We quantified mistletoe, lichen and tree litter fall monthly for 3 years. Tree and lichen biomasses were influenced by canopy cover, being higher in primary forests than in harvested stands. However, aggregated retention showed the highest mistletoe biomass production. Furthermore, mistletoe biomass increased while lichen biomass decreased over the years after harvesting. Variable retention was useful in maintaining both lichen and mistletoe biomass after harvest, but aggregates were not enough to maintain the original level of lichen populations. Forest harvesting with variable retention generates positive (litter input) and negative (decline of host growth) effects of mistletoes and epiphytic lichens at community level, which should be evaluated during conservation and management planning.

Nitrogen dynamics in land cleared of alien vegetation (<i>Acacia saligna</i>) and impacts on groundwater at Riverlands Nature Reserve (Western Cape, South Africa)

Woody invading alien plants, many of which are nitrogen-fixing legumes (Fabaceae family), are currently cleared in South African catchments to reduce water loss and preserve streamflow, and for the restoration of the ecosystem. This study tested the hypothesis that clearing invasive alien vegetation may disturb the vegetation-micro-organism-soil N cycling system by producing a large once-off input of fresh tree litterfall rich in N and by eliminating a large N sink. Three experimental plots were established at the Riverlands Nature Reserve (Western Cape, South Africa): a site invaded by Acacia saligna to be used as control; a site cleared of Acacia saligna; and a site with natural vegetation to be used as background. Nitrogen concentrations in soil and groundwater, volumetric soil water contents, root density and weather conditions were measured during 2007. Oxidised forms of nitrogen, in particular NO3-, were dominant in the system. Recharge and leachate were simulated with the HYDRUS-2D model and used as inputs into Visual MODFLOW to predict the spatial distribution of nitrate plus nitrite (NOx) in groundwater. NOx levels in soil and groundwater were higher in alien-invaded areas compared to fynbos-covered land. A quick release of NOx into groundwater was observed due to high residual N reserves in the rooting zone, decreased  evapotranspiration and increased recharge in the treatment cleared of alien vegetation. In the long run, high NOx concentrations in groundwater underlying cleared land will last only until all the excess nitrogen has been leached from the soil. A decrease in NOx concentration in groundwater can be expected thereafter. Clearing land of alien invasive legumes may therefore have a beneficial effect by reducing groundwater contamination from NOx and reducing water losses in catchments.

Influence of trees on soil nutrient pools in a silvopastoral system in the Brazilian Savannah

Silvopastoral systems (SPS) have been suggested as an approach to reduce pasture degradation and, consequently, reduce the deforestation of new areas in the Brazilian cerrado (savanna). This study assessed the contribution of trees to soil fertility in a silvopastoral system in Lagoa Santa, Minas Gerais State, Brazil, 19° 35′ 36″ S, 43° 51′ 56″ W; altitude 747 m. The SPS has developed since 1984, through the use of natural regeneration of the native species Zeyheria tuberculosa Vell. Bur., with a density of 160 trees ha−1. The forage component of the system was Brachiaria brizantha cv. Marandu. The control treatment was a pasture adjacent to SPS with the same forage but without the influence of trees. In 2005, the litterfall of trees (leaves, fruits, and stems) was collected monthly, and the dry matter yield and nutrient content were measured. Soil profile samples were collected in February 2006. The litterfall of trees represented considerable inputs of nitrogen (N), potassium (K), and calcium (Ca2+). In the soil, organic matter (OM) and K reduced with depth. At this planting density, this tree species contributed mainly to amelioration of soil acidity, in the 0–2 cm layer and/or in the profile as a whole. In contrast, there were no significant differences in N, P, and K content of the control and SPS soil. This can be related to the high C/N and lignin/N ratios of the litter inputs. Agroforestry systems are complex and the site specific interactions among the components (tree, forage, and animal) must be understood to develop locally adapted systems and optimize productive efficiency. Consequently simple prescriptions for the implementation of SPS by land managers are unlikely.

On linking multiyear biometric measurements of tree growth with eddy covariance‐based net ecosystem production

AbstractAnnual measurements of the diameter growth and litter fall of trees began in 1998 using a 1.0 ha permanent plot beneath a flux tower at the Takayama flux site, central Japan. This opened up an opportunity for studies that compare the interannual variability in tree growth with eddy covariance‐based net ecosystem production (NEP). A possible link between multiyear biometric‐based net primary production (NPP) and eddy covariance‐based NEP was investigated to determine the contribution of autotrophic production and heterotrophic respiration (HR) to the interannual variability of NEP in deciduous forest ecosystems. We also defined the NEP* as the measurable organic matter stored in an ecosystem during the interval in which soil respiration (SR) measurements were taken. The difference of biometric‐based NEP* from eddy covariance‐based NEP within a given year varied between 55% and 105%. Woody tissue NPP (stems and coarse roots) varied markedly from 0.88 to 1.96 Mg C ha−1 yr−1 during the 8‐year study period (1999–2006). Annual woody tissue NPP was positively correlated with eddy covariance‐based NEP (r2=0.52, P<0.05). However, neither foliage NPP (r2=0.03) nor HR (r2=0.06) were correlated with eddy covariance‐based NEP. Therefore, it was hypothesized that interannual variability in the ecosystem carbon exchange was directly responsible for much of the interannual variation in autotrophic production, especially carbon accumulation in the woody components of the ecosystem. Moreover, similar interannual variations of biometric‐based NEP* and eddy covariance‐based NEP with small variations in SR and foliage NPP suggest a constant net accumulation of carbon in nonliving pools at the Takayama site.

A non‐native invasive grass increases soil carbon flux in a Hawaiian tropical dry forest

AbstractNon‐native plants are invading terrestrial ecosystems across the globe, yet little is known about how invasions impact carbon (C) cycling or how these impacts will be influenced by climate change. We quantified the effect of a non‐native C4 grass invasion on soil C pools and fluxes in a Hawaiian tropical dry forest over 2 years in which annual precipitation was average (Year 1) and ∼60% higher than average (Year 2). Work was conducted in a series of forested plots where the grass understory was completely removed (removal plots) or left intact (grass plots) for 3 years before experiment initiation. We hypothesized that grass invasion would: (i) not change total soil C pools, (ii) increase the flux of C into and out of soils, and (iii) increase the sensitivity of soil C flux to variability in precipitation. In grass plots, grasses accounted for 25–34% of litter layer C and ∼70% of fine root C. However, no differences were observed between treatments in the size of any soil C pools. Moreover, grass‐derived C constituted a negligible fraction of the large mineral soil C pool (< 3%) despite being present in the system for ≥50 years. Tree litterfall was ∼45% lower in grass plots, but grass‐derived litterfall more than compensated for this reduction in both years. Annual cumulative soil‐surface CO2 efflux (Rsoil) was ∼40% higher in grass plots in both years, and increased in both treatments by ∼36% in the wetter Year 2. Despite minimal grass‐derived mineral soil C, > 75% of Rsoil in grass plots was of C4 (i.e. grass) origin. These results demonstrate that grass invasion in forest ecosystems can increase the flux of C into and out of soils without changing total C pools, at least over the short term and as long as the native tree canopy remains intact, and that invasion‐mediated changes in belowground C cycling are sensitive to precipitation.

Comparison of nitrogen content in tree litterfall in three dry dipterocarp forests under different fire regime in northeast Thailand

Tree litterfall was measured and nitrogen (N) return by tree litterfall was estimated in three plots, F0, F10, and F35, with different fire histories (protected from fire for 0, 10, and 35 years, respectively) in dry dipterocarp forests (DDF) in northeast Thailand. Annual litterfall was 3.92, 7.13, and 8.79 Mg ha-1, for F0, F10, and F35, respectively. Leaf litter was the main component in all the plots, ranging from 67.4 % to 77.9 %, peaking in the dry season. Other components of the litterfall had no clear seasonality. The N concentration of the tree litterfall increased in the rainy season and decreased in the dry season in all three plots. The N return due to the tree litterfall was estimated to be 33.4, 75.2, and 123.8 kg ha-1, for F0, F10, and F35, respectively. Fire protection increased the N return by tree litterfall, as well as tree litter production in DDF.

Changes in the ratio of twig to foliage in litterfall with species composition, and consequences for decomposition across a long term chronosequence

In the past two centuries, anthropogenic fire suppression has affected many biomes, including boreal forests. Absence of fire in the boreal zone is often linked to declining soil fertility and increased carbon sequestration in the humus through changes in NPP and litter decomposition. We studied tree litterfall and litter decomposition for thirty lake islands in the boreal forested zone of Sweden, which differ naturally in fire regime: larger islands have burned far more frequently than smaller ones because they are intercepted more often by lightning. We used litter trays to show that the ratio of twig to foliar litterfall for Picea abies with prolonged absence of fire is largely responsible for the concomitant increased twig proportion in the total litterfall. We hypothesised that the increased twig proportion in the litterfall with time since fire would affect overall decomposition by reducing net litter quality and through impairing decomposition of associated foliar litters. We established a litter decomposition mesocosm experiment based on litter from the three main tree species found on the islands. From each of the thirty islands, we prepared a set of litterbags comprising three mixtures (all foliar litters combined, all twig litters combined, and all twig and foliar litters combined), plus monotypes (i.e. each of the separate foliage and twig litters for each species). Unlike most studies, we used the natural litterfall proportions in the mixtures. We found a (negative) effect of time since wildfire on decomposition rate for only the foliage‐twig mixtures, although twig litter did not inhibit the decomposition of foliar litter within these mixtures. The reduced decomposition rate in the foliage‐twig mixture from the small islands was therefore due to the increased proportion of twigs in the mixtures from these islands. Our results suggest that, with prolonged absence of fire, the increase of twig proportion in the foliage‐twig litterfall for P. abies combined with the shift to canopy dominance by P. abies may be important in contributing to reduced decomposition rates in boreal forest soils.

Biophysical and Ecological Interactions in a Temperate Tree-Based Intercropping System

SUMMARY Tree-based intercropping is considered an excellent farming system and can contribute much to our understanding of sustainable agriculture practices. Our current research goals are to address and quantify the numerous biophysical interactions that occur at the tree-crop interface in order to enhance our understanding of the ecology of tree-based intercropping (a form of agroforestry). In 1987, the University of Guelph established a large field experiment on 30 ha of prime agricultural land in Wellington county southern Ontario, Canada to investigate various aspects of intercropping trees with agricultural crops. A variety of spacing, crop compatibility and tree growth, and survival experiments were initiated at that time, utilizing 10 tree species within the genera Picea, Thuja, Pinus, Juglans, Quercus, Fraxinus, Acer, and Populus. Two between row-spacings (12.5 m or 15 m) and two within row-spacings (3 m, or 6 m) were utilized in conjunction with all possible combinations of three agricultural crops (soybean, corn, and either winter wheat or barley). Investigations over the last decade have documented several complementary biophysical interactions. Nitrogen (N) transfer from fall-shed leaves to adjacent crops with enhanced soil nitrification as the proposed mechanism was estimated to be 5 kg N ha−1. Soil organic carbon (C) adjacent to tree rows has increased by over 1%, largely as a result of tree litterfall inputs and fine root turnover. It is estimated that intercropping has reduced nitrate loading to adjacent waterways by 50%, a hypothesized function of deep percolate interception by tree roots. We have also noticed increased bird diversity and usage within the intercropped area as compared to mono-cropped adjacent agricultural areas, and have recorded increases in small mammal populations. Earthworm distribution and abundance was also found to be higher closer to the tree rows when compared to earthworm numbers in the crop alleys. We speculate that these are indicative of major changes in the flow of energy within the trophic structure identified with intercropping systems. In light of climate change mitigation processes, C sequestration and NO2 reduction potentials in tree-based intercropping systems were studied and compared to conventional agricultural systems. The results suggest that sequestration of C was 5 times more in the former system than in the latter. Competitive interactions between trees and crops for nutrients, moisture and light were also studied. The tangible benefits that are derived from properly designed and managed tree-based intercropping systems place this land management option above conventional agriculture in terms of long-term productivity and sustainability.

Mechanisms for changes in soil carbon storage with pasture to Pinus radiata land‐use change

AbstractIn this study, we simulated pasture to Pinus radiata land‐use change with the Generic Decomposition And Yield (G'DAY) ecosystem model to examine mechanisms responsible for the change in soil carbon (C) under pine. We parameterized the model for paired sites in New Zealand. Our simulations successfully reproduced empirical trends in ecosystem productivity and soil inorganic nitrogen (N), and modeled an increase in soil C and a small decline in soil N after 30 years under pine. We determined the mechanisms contributing to soil C change based on an established hypothesis that attributes increases in soil C storage to three main factors: increased ecosystem N inputs relative to outputs, increased C/N ratios in plant and soil, or a shift of N from plant to soil. The mechanisms we attributed to the simulated increase in soil C under pine were increased soil C inputs through tree litterfall, and an increase in the soil C/N ratio. In the first 7 years following pine establishment, a decline in soil C was simulated; this was matched by a decline in soil N. The simulated longer‐term increase in soil C with afforestation by pine contrasts with results from published field studies, which show either a decline or no change in soil C under pine. The discrepancy between measured and simulated changes in soil C was attributed to the G'DAY model overestimating the transfer of litter C into the mineral soil.

The role of ground vegetation in the uptake of mercury and methylmercury in a forest ecosystem

Litterfall from trees has been identified as an important pathway for deposition of mercury (Hg) and methylmercury (MeHg) in forested catchments, but very little is known about the role of ground vegetation in deposition and cycling of Hg compounds. This study was conducted to identify the origin of Hg compounds in the ground vegetation, and to estimate the role of its litterfall with respect to pools and fluxes of Hg in a coniferous forest in the German Fichtelgebirge mountains. Above and below ground biomass of the dominant ground vegetation (Vaccinium myrtillus, Deschampsia flexuosa and Calamagrostis villosa) were sampled at several plots successively during the growing season. The fluxes to the soil via litterfall of the ground vegetation were calculated using contents of Hg and MeHg in the annual fractions of aboveground biomass. With fluxes of 0.4 – 7.8 mg Hgtotal ha−1 a−1 and 0.01 – 0.04 mg MeHg ha−1 a−1 (depending on the plant species) this pathway contributes only a few percent to the total deposition of both compounds in the catchment. To identify the uptake pathways of Hg compounds, the same plant species were grown in a pot experiment with addition of isotope labelled Hg compounds (202Hg2+, Me198Hg) to a clean sand substrate. Only small proportions of 202Hg and Me198Hg in the substrate were taken up by the plants, but in all cases the proportion translocated into aboveground biomass after uptake was greater in case of Me198Hg. Thus, internal recycling in the plant-soil system is a source especially for MeHg in the ground vegetation. However, as compared to the input of Hg compounds by tree litterfall and storage in the forest floor, Hgtotal and MeHg in ground vegetation are of minor importance. High volatilization of added Hg isotopes raises the question of a re-emission of Hg compounds by the transpiration flux of the ground vegetation.

Biomass and net primary productivity of Bhabar Shisham forests in central Himalaya, India

This paper illustrates biomass (dry weight per unit area) and net primary productivity (NPP) in 5-, 10- and 15 years old Shisham ( Dalbergia sissoo Roxb.) forests planted after clear cutting of Sal ( Shorea robusta) mixed broad-leaved tree species in Bhabar (a nutrient poor and low water table site) adjacent to foothills in Kumaun of central Himalaya. The linear regression equations for all the aboveground and belowground components of trees and shrubs were developed for each forest. The forest floor biomass, litter input and understorey vegetation were also determined from each forest. The tree density was 625 trees ha −1 for each forest. The basal area, biomass, forest floor litter mass, tree litter fall and NPP of trees increased with increase in forest age, whereas the herb biomass and NPP significantly ( P<0.01) decreased with increasing forest age. The total vegetation biomass and NPP ranged from 52.5 (5 years) to 118.1 t ha −1 (15 years) and 11.4 (5 years) to 14.8 t ha −1 per year (15 years old), respectively. The biomass accumulation ratio (BAR) for different tree components increased with increase in forest age. The BAR ratio ranged from 5.2 in the 5 years old to 8.9 in 15 years old forest.