Summary Eastern Australia was subject to its hottest and driest year on record in 2019. This extreme drought resulted in massive canopy die‐back in eucalypt forests. The role of hydraulic failure and tree size on canopy die‐back in three eucalypt tree species during this drought was examined. We measured pre‐dawn and midday leaf water potential (Ψleaf), per cent loss of stem hydraulic conductivity and quantified hydraulic vulnerability to drought‐induced xylem embolism. Tree size and tree health was also surveyed. Trees with most, or all, of their foliage dead exhibited high rates of native embolism (78–100%). This is in contrast to trees with partial canopy die‐back (30–70% canopy die‐back: 72–78% native embolism), or relatively healthy trees (little evidence of canopy die‐back: 25–31% native embolism). Midday Ψleaf was significantly more negative in trees exhibiting partial canopy die‐back (−2.7 to −6.3 MPa), compared with relatively healthy trees (−2.1 to −4.5 MPa). In two of the species the majority of individuals showing complete canopy die‐back were in the small size classes. Our results indicate that hydraulic failure is strongly associated with canopy die‐back during drought in eucalypt forests. Our study provides valuable field data to help constrain models predicting mortality risk.

A survey of benthic invertebrate faunas in riparian-protected, riparian-grazed, and channelised reaches of five Southland streams with catchment sizes of 3-37 km 2 was carried out. It was part of a wider investigation to assess the effects of riparian grazing and channelisation on stream habitat and biota. In small streams (catchment areas 3-10 km 2 ; widths 1-4 m), channelisation or intensive grazing by cattle greatly reduced shading by riparian vegetation, resulting in substantial increases in daily maximum temperatures during summer. Channelisation also caused gross changes in channel morphology and intensive grazing of a reach with moist streamside soils was associated with increased bed sedimentation and bank damage. Marked changes in invertebrate communities were associated wilh these habitat modifications. In general, taxa favoured by cool water and low periphyton abundance (e.g., Plecoptera, Paraleptamphopus caeruleus, Deleatidium sp., and Helicopsyche albescens) decreased in density, whereas densities of taxa favoured by an abundance of periphyton (e.g., Chironomidae and Oxyethira albiceps) increased. In contrast, differences in physical habitat and invertebrate communities were minor between paired grazed and riparian-protected reaches of the larger streams (catchment areas 10-33 km 2 ; median widths 6-16 m) where grazing had little or no effect on Received 16 August 1991; accepted 3 December 1991 stream shading. These results indicate that in small streams, with median natural channel widths below c. 6 m, the effects on benthic invertebrates decrease in the following order, channelisation > intensive grazing by cattle > extensive grazing by cattle and/or sheep. Shade provided by riparian vegetation appears to play a vital role in maintaining cool, headwater, stream habitats for benthic invertebrate communities in these streams. M91053

Insectivorous bats are efficient predators of pest arthropods in agroecosystems. This pest control service has been estimated to be worth billions of dollars to agriculture globally. However, few studies have explicitly investigated the composition and abundance of dietary prey items consumed or assessed the ratio of pest and beneficial arthropods, making it difficult to evaluate the quality of the pest control service provided. In this study, we used metabarcoding to identify the prey items eaten by insectivorous bats over the cotton‐growing season in an intensive cropping region in northern New South Wales, Australia. We found that seven species of insectivorous bat (n = 58) consumed 728 prey species, 13 of which represented around 50% of total prey abundance consumed. Importantly, the identified prey items included major arthropod pests, comprising 65% of prey relative abundance and 13% of prey species recorded. Significant cotton pests such as Helicoverpa punctigera (Australian bollworm) and Achyra affinitalis (cotton webspinner) were detected in at least 76% of bat fecal samples, with Teleogryllus oceanicus (field crickets), Helicoverpa armigera (cotton bollworm), and Crocidosema plebejana (cotton tipworm) detected in 55% of bat fecal samples. Our results indicate that insectivorous bats are selective predators that exploit a narrow selection of preferred pest taxa and potentially play an important role in controlling lepidopteran pests on cotton farms. Our study provides crucial information for farmers to determine the service or disservice provided by insectivorous bats in relation to crops, for on‐farm decision making.

The effects of mixed sheep and cattle grazing of stream margins, channelisation, and the benefits of riparian retirement were assessed through a survey of five streams in Southland, New Zealand. Morphological and vegetation data affecting erosion processes and aquatic habitat were compared among grazed, channelised, and retired reaches. There is no evidence that grazing streambanks in floodplain streams of northern Southland will lead to rapid and severe deterioration of channel form, except in small streams (< 2 m wide) under intensive grazing of wet streamside soils. Generally, the dominant erosion mechanism-the undercutting of banks-is largely unaffected by grazing stream margins. In contrast, channelisation has led to severe streambank and streambed erosion in two of the three streams examined. The major factor in this degradation appears to be straightening and deepening the channel so that underlying uncohesive shingle is exposed to high flows. Riparian retirement had variable effects depending on the stability of the stream channel. On smaller, relatively inactive channels, it reduced localised bank erosion from livestock trampling, especially at cattle crossings. However, this damage (which sometimes can be quite visible) did not lead to significant change in average channel form or Received 16 August 1991; accepted 8 January 1992 width in the 7-15 years since the land has been converted to intensive agriculture from extensively grazed tussock. Retirement also increased vegetation overhang. On the larger channels that were more actively meandering, retirement had comparatively little benefit because any retirement or grazing effects were rapidly overtaken by channel migration. M91052