A 13C NMR study of Decomposing Logging Residues in an Australian Hoop Pine Plantation

Purpose Residue retention is important for nutrient and water economy in sub-tropical plantation forests. We examined decomposing hoop pine (Araucaria cunninghamii Ait. Ex D. Don) residues – foliage, branches and stem wood – to determine the changes in structural chemistry that occur during decomposition. Materials and methods Residues were incubated in situ using 0.05-m2 microplots. We used solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to determine the structural composition of harvest residues in the first 24 months of decomposition. Results and discussion The spectral data for branch and stem residues were generally similar to one another and showed few changes during decomposition. The lignin content of branch and foliage residues decreased during decomposition. When residues were mixed together during decomposition the O-alkyl fraction of foliage decreased initially then increased up to 24 months, while the alkyl carbon (C) fraction exhibited the opposite pattern. The decomposition of woody hoop pine residues (branch and stem wood) is surprisingly uniform across the major C forms elucidated with 13C NMR, with little evidence of preferential decomposition. When mixed with branch and stem materials, foliage residues showed significant short- and long-term compositional changes. This synergistic effect may be due to the C:N ratio of the treatments and the structure of the microbial decomposer community. Conclusions Twenty-four months of decomposition of hoop pine residues did not result in substantial accumulation of recalcitrant C forms, suggesting that they may not contribute to long-term C sequestration

A 13C NMR study of decomposing logging residues in an Australian hoop pine plantation

Purpose Residue retention is important for nutrient and water economy in subtropical plantation forests. We examined decomposing hoop pine (Araucaria cunninghamii Ait. Ex D. Don) residues-foliage, branches, and stem wood-to determine the changes in structural chemistry that occur during decomposition. Materials and methods Residues were incubated in situ using 0.05 m2 microplots. We used solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to determine the structural composition of harvest residues in the first 24 months of decomposition. Results and discussion The spectral data for branch and stem residues were generally similar to one another and showed few changes during decomposition. The lignin content of branch and foliage residues decreased during decomposition. When residues were mixed together during decomposition, the O-alkyl fraction of foliage decreased initially then increased up to 24 months, while the alkyl carbon (C) fraction exhibited the opposite pattern. The decomposition of woody hoop pine residues (branch and stem wood) is surprisingly uniform across the major C forms elucidated with 13C NMR, with little evidence of preferential decomposition. When mixed with branch and stem materials, foliage residues showed significant short- and long-term compositional changes. This synergistic effect may be due to the C/N ratio of the treatments and the structure of the microbial decomposer community. Conclusions Twenty-four months of decomposition of hoop pine residues did not result in substantial accumulation of recalcitrant C forms, suggesting that they may not contribute to long-term C sequestration.No Full Tex

Do young trees contribute to soil labile carbon and nitrogen recovery?

Hosseini Bai, S ORCiD: 0000-0001-8646-6423Purpose: This study aimed to evaluate the effects of tree cover (tree plots (Acacia disparrima and Eucalyptus crebra) vs. non-tree plots) on soil labile carbon (C) and nitrogen (N) recovery in revegetation trials, without and with topsoil removal, 3 years following tree planting. Materials and methods: Soil total C (TC) and total N (TN), hot-water-extractable organic C (HWEOC), hot-water-extractable total N (HWETN), microbial biomass (MB) and potentially mineralisable N (PMN) were measured. Results and discussion: Where topsoil had not been removed, soil TN, HWEOC, HWETN and PMN were significantly higher in the tree-covered plots compared to non-tree-covered plots. In contrast, tree cover did not significantly increase soil labile C and N when topsoil had been removed. Both leguminous and non-leguminous species (A. disparrima and E. crebra) had similar effects on soil labile C and N. Tree cover did not accelerate C and N recovery at their early stage of establishment when topsoil had been removed. Therefore, our finding suggests that topsoil-removed plots may need more than 3 years to replenish soil C and N to their initial levels. There was also a clear indication of C and N depletion in the topsoil in areas not covered by trees even though the topsoil had not been removed. Conclusions: Altogether, these results demonstrate the importance of longer-term monitoring of revegetation areas to be able to assess its success in improving soil quality. © 2014, Springer-Verlag Berlin Heidelberg

Ecophysiological status of different growth stage of understorey Acacia leiocalyx and Acacia disparrima in an Australian dry sclerophyll forest subjected to prescribed burning

Hosseini Bai, S ORCiD: 0000-0001-8646-6423Purpose: Understorey Acacia spp. plays an important role in post-fire restoration because these understorey plants are tolerant to stress conditions. We investigated how the ecophysiological status of two species of understorey, Acacia leiocalyx and Acacia disparrima, varied depending on the plant growth stage after prescribed burning. Materials and methods: Plants were grouped in different size classes, namely seedlings, small and medium sizes, and physiological variables such as foliar gas exchange, water use efficiency and light dependency were measured at two experimental sites subjected to prescribed burning. Results and discussion: A. leiocalyx showed higher symbiotic N2 fixation and photosynthetic capacity compared to A. disparrima regardless of plant-size classes at both experimental sites. This could explain the greater relative growth rate of A. leiocalyx than that of A. disparrima. However, A. disparrima is more tolerant to shady conditions than A. leiocalyx. Conclusions: This finding may be an indication of how well these two species recover after fire, although A. leiocalyx may have faster regrowth, as it is fixing more N. © 2013 Springer-Verlag Berlin Heidelberg

Human footprints in urban forests: Implication of nitrogen deposition for nitrogen and carbon storage

Hosseini Bai, S ORCiD: 0000-0001-8646-6423Purpose: Rising levels of nitrogen (N) deposition are influencing urban forest carbon (C) and N dynamics due to greater human disturbance compared to those in rural areas. N deposition in combination with increased atmospheric carbon dioxide (CO2) and water limitation may alter C and N storage in urban forests. This review aimed to provide a better understanding of N and C storage under N deposition scenarios in urban forests. Results and discussion: Globally, fuel combustion and biomass burning contribute in approximately 70 and 16 % of the NOx emission respectively. It is also estimated that NHy and NOx are two to four times higher in urban forests compared to rural areas. However, higher N deposition may not always result in increased N and C storage in urban forests. In fact, urban forests may even show early symptoms of N and C losses under climate change. For example, urban forests in fire-prone areas require higher frequency of burning to reduce the threat of wildfires, leading to an acceleration of C and N loss. Additionally, chronic N deposition may result in an early N loss in urban forests due to faster N saturation and soil acidification in urban forests compared to rural forests. Studies of N deposition on urban forests using N isotope composition (δ15N) also showed that N loss from urban forests can occur through the direct leaching of the deposited NO3−-N. We also noted that using different 15N signal of soil and plant in combination of tree ring δ15N may provide a better understanding of N movement in urban forests. Conclusions: Although urban forests may become a source of C and N faster than rural forests, N-limited urban forests may benefit from N deposition to retain both N and C stocks longer than non-N-limited urban forests. Appropriate management practices may also help to delay such symptoms; however, the main source of emission still needs to be managed to reduce both N deposition and rising atmospheric CO2 in urban forests. Otherwise, the N and C stocks in urban forests may further decline when prolonged drought conditions under global climate change increase the frequency of fires and reduce plant photosynthesis. © 2015, Springer-Verlag Berlin Heidelberg

Do young trees contribute to soil labile carbon and nitrogen recovery?

Purpose: This study aimed to evaluate the effects of tree cover (tree plots (Acacia disparrima and Eucalyptus crebra) vs. non-tree plots) on soil labile carbon (C) and nitrogen (N) recovery in revegetation trials, without and with topsoil removal, 3 years following tree planting. Materials and methods: Soil total C (TC) and total N (TN), hot-water-extractable organic C (HWEOC), hot-water-extractable total N (HWETN), microbial biomass (MB) and potentially mineralisable N (PMN) were measured. Results and discussion: Where topsoil had not been removed, soil TN, HWEOC, HWETN and PMN were significantly higher in the tree-covered plots compared to non-tree-covered plots. In contrast, tree cover did not significantly increase soil labile C and N when topsoil had been removed. Both leguminous and non-leguminous species (A. disparrima and E. crebra) had similar effects on soil labile C and N. Tree cover did not accelerate C and N recovery at their early stage of establishment when topsoil had been removed. Therefore, our finding suggests that topsoil-removed plots may need more than 3 years to replenish soil C and N to their initial levels. There was also a clear indication of C and N depletion in the topsoil in areas not covered by trees even though the topsoil had not been removed. Conclusions: Altogether, these results demonstrate the importance of longer-term monitoring of revegetation areas to be able to assess its success in improving soil qualit

Growth and yield of 5 years old teak and flueggea in single and mixed species forestry systems in the Solomon Islands

Hosseini Bai, S ORCiD: 0000-0001-8646-6423Mixed species plantings of teak (Tectona grandis) and flueggea (Flueggea flexuosa) were introduced as a method for overcoming the reluctance of local growers to thin their teak. Flueggea is a well-used local species and removal of the flueggea for personal use would effectively thin the entire stand over time. Stocking rates and tree species composition are two important factors affecting tree growth and yield when a mixed species plantation is established. This study aimed to investigate the effects of stocking rates on early teak growth in a mixed species system in a humid tropical region of Western Province, Solomon Islands. The experimental design included: teak planted as a monoculture at standard stocking of 833 stems per hectare (sph) (Treatment 1); teak planted in rows alternating with 2 rows of flueggea at 833 sph; 625 sph; and 416 sph (Treatments 2,3 and 4 respectively); and teak planted in alternating rows with a single row of flueggea at 833 sph (Treatment 5). Teak basal area was optimum at the lowest stocking rates of 412 and 625 sph for both species. However, teak yield (volume per hectare) was greater in the higher stocking rate treatments. Teak basal area mean annual increment (BA MAI) decreased in higher stocking rates between the age of 4 and 5 years indicating the onset of suppression and the need for progressive thinning. Under correct silvicultural maintenance, the 833 sph planting density offers the benefits of higher stocking and lower maintenance. As the present investigation was confined to the establishment phase for teak, more studies are needed to understand the system development to maturity. © 2018, Springer Nature B.V

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

Hosseini Bai, S ORCiD: 0000-0001-8646-6423Purpose: 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). Materials and methods: 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). Results and discussion: 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. Conclusions: 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

Soil organic matter dynamics and nitrogen availability in response to site preparation and management during revegetation in tropical Central Queensland, Australia

Hosseini Bai, S ORCiD: 0000-0001-8646-6423Purpose: There is considerable interest in finding a cost-effective method of site preparation that effectively controls weeds during planting and further reduces the need for recurring herbicide applications. In this study, two weed control methods, herbicide and scalping, were examined. Both methods may have implications for soil organic matter (SOM) dynamics and nitrogen (N) which could consequently affect plant survival and vegetation establishment. This study aimed to investigate the dynamics of SOM, carbon (C) and N pools under site manipulation practices and the associated early plant survival and growth in tropical Australia. Materials and methods: A field trial was established in Central Queensland to examine the recovery of SOM, C and N pools following scalping and the alternative site preparation technique of sequential herbicide application. Both were contrasted with control plots which received neither treatment. Plant survival and growth were also monitored to improve our understanding of plant response to site preparation practices. Results and discussion: Scalped plots showed significantly lower values for labile C and N pools compared with the herbicide treatment and control. Generally, there was no significant difference between the herbicide and control for any of the parameters tested. Our observation indicated that herbicide application was significantly less effective than scalping to control weeds. A general decline in SOM parameters was observed in all the plots, including the control during the trial. Drought conditions were considered to be a major factor in the overall decline of SOM. Despite removal of the top soil, there was no significant difference in plant survival between herbicide and scalped areas (81% and 79% survival, respectively). Plant growth was not affected by the treatments in the first 6 months when weed competition in the herbicide areas and low nutrient availability in the scalped plots would have been significant factors in controlling growth rates. However, plants in the herbicide areas, irrespective of species, showed stronger growth than those in the scalped plots at week 61 when they had outgrown the weed competition. It is likely that differences in plant growth response to treatments will become negligible over time. Conclusions: Top soil removal was more effective than the use of herbicide in the long-term control of weeds. However, lower SOM and N availability in the scalped areas did not affect plant survival rates when compared with that of the herbicide areas. Whilst the preservation of soil organic matter is considered to be vital in short-term cropping systems, our results indicate that this is not the case for woody vegetation establishment and, in terms of cost and reduction of chemical use, removal of the organically rich top soil, with its accompanying seed burden may be both practical and desirable. © 2012 Springer-Verlag

Soil carbon and nitrogen dynamics in the first year following herbicide and scalping in a revegetation trial in south-east Queensland, Australia

Hosseini Bai, S ORCiD: 0000-0001-8646-6423During revegetation, the maintenance of soil carbon (C) pools and nitrogen (N) availability is considered essential for soil fertility and this study aimed to evaluate contrasting methods of site preparation (herbicide and scalping) with respect to the effects on soil organic matter (SOM) during the critical early establishment phase. Soil total C (TC), total N (TN), hot-water extractable organic C (HWEOC), hot-water extractable total N (HWETN), microbial biomass C and N (MBC and MBN), total inorganic N (TIN) and potentially mineralizable N (PMN) were measured over 53 weeks. MBC and MBN were the only variables affected by herbicide application. Scalping caused an immediate reduction in all variables, and the values remained low without any sign of recovery for the period of the study. The impact of scalping on HWETN and TIN lasted 22 weeks and stabilised afterwards. MBC and MBN were affected by both herbicide and scalping after initial treatment application and remained lower than control during the period of the study but did not decrease over time. While scalping had an inevitable impact on all soil properties that were measured, that impact did not worsen over time, and actually improved plant growth (unpublished data) while reducing site establishment costs. Therefore, it provides a useful alternative for weed control in revegetation projects where it is applied only once at site establishment and where SOM would be expected to recover as canopy closure is obtained and nutrient cycling through litterfall commences. © 2014 Springer-Verlag Berlin Heidelberg