Long-term exclusion of invasive ungulates alters tree recruitment and functional traits but not total forest carbon

Forests are major carbon (C) sinks, but their ability to sequester C and thus mitigate climate change, varies with the environment, disturbance regime, and biotic interactions. Herbivory by invasive, nonnative ungulates can have profound ecosystem effects, yet its consequences for forest C stocks remain poorly understood. We determined the impact of invasive ungulates on C pools, both above- and belowground (to 30 cm), and on forest structure and diversity using 26 paired long-term (>20 years) ungulate exclosures and adjacent unfenced control plots located in native temperate rainforests across New Zealand, spanning 36-41° S. Total ecosystem C was similar between ungulate exclosure (299.93 ± 25.94 Mg C ha^-1 ) and unfenced control (324.60 ± 38.39 Mg C ha^-1 ) plots. Most (60%) variation in total ecosystem C was explained by the biomass of the largest tree (mean diameter at breast height [dbh]: 88 cm) within each plot. Ungulate exclusion increased the abundance and diversity of saplings and small trees (dbh ≥2.5, <10 cm) compared with unfenced controls, but these accounted for ~5% of total ecosystem C, demonstrating that a few, large trees dominate the total forest ecosystem C but are unaffected by invasive ungulates at a timescale of 20-50 years. However, changes in understory C pools, species composition, and functional diversity did occur following long-term ungulate exclusion. Our findings suggest that, although the removal of invasive herbivores may not affect total forest C at the decadal scale, major shifts in the diversity and composition of regenerating species will have longer term consequences for ecosystem processes and forest C.

Hydrothermal conversion of toilet waste: effect of processing conditions on gas phase emissions

Globally, many populations suffer from a lack of access to basic sanitation facilities. This is partly caused by a combination of water resource shortages and the high cost of conventional centralised treatment systems. A novel decentralised treatment technology based on sub-critical hydrothermal processing of organic wastes at toilet-scale, contributes to addressing these economic and resource limitations. To be effective, this technology needs to satisfy a broad range of environmental and safety considerations, including the nature and quantity of formed gas products. We investigated the impact of four process parameters (temperature; O₂: COD ratio (λ); time; feed solids content) on off-gas composition by quantifying volatile organic compounds (VOCs), CO, H₂ and CO₂ in factorial experiments. Temperature and λ influenced VOCs generation greatly. The lowest VOC emissions occurred at 200% λ and 300 °C. Aldehydes and ketones were mostly generated at 200% λ and intermediate temperatures, sulphur compounds in the absence of oxygen, and aromatics, furans, and pyrroles at intermediate oxygen levels and elevated temperatures. Most CO was created at 300 °C but its concentration decreased at longer processing times. Processing conditions have complex impacts and require careful consideration when designing for real world deployment.

High-intensity deer culling increases growth of mountain beech seedlings in New Zealand

Browsing of mountain beech seedlings by introduced deer in the central North Island of New Zealand appears to have inhibited canopy regeneration over large areas. In 1998, a trial of high-, medium- and low-intensity deer-culling treatments was initiated in Kaimanawa and Kaweka Forest Parks to test whether mountain beech (Nothofagus solandri var. cliffortioides) forest regeneration could be restored by removing deer. Paired exclosure plots (one plot fenced to exclude deer and the other unfenced) were established within a high-intensity culling area, to monitor the benefits of recreational, commercial and aerial deer culling. Paired plots were also established within low- and medium-intensity culling areas. Medium-intensity culling was allowed through recreational and commercial deer culling. In two low-intensity culling treatment areas, deer management remained substantially unaltered. Annual relative growth rates of tagged seedlings from spring 1998 to spring 2001 from low-, medium- and high-intensity culling areas provide strong evidence that mountain beech seedling growth increases once browsing by deer is removed through fencing. Faecal pellet data indicated that high-intensity deer culling reduced deer abundance by 67% in comparison to medium- and low-intensity culling areas. This apparent reduction in deer abundance appears to have led to a doubling in mountain beech seedling growth in the high-intensity culling area outside fences, in comparison to low- and medium-intensity deer culling areas where there was little or no evidence of benefits for seedling growth.