Geographic variation in nest-defence behaviour of the Red-tailed Hawk Buteo jamaicensis

A close fit was found between the number of years since European settlement and the call and dive-rates of Red-tailed Hawks. Call-rates were highest in the most recently settled sites.     

Effects of stream flooding on the distribution and diversity of groundwater‐dependent vegetation in riparian areas

1. Effects of the frequency and duration of flooding on the structural and functional characteristics of riparian vegetation were studied at four sites (n = 80, 50 × 50 cm, plots) along medium‐sized naturally meandering lowland streams. Special focus was on rich fens, which – due to their high species richness – are of high priority in nature conservation. 2. Reed beds, rich fens and meadows were all regularly flooded during the 20‐year study period, with a higher frequency in reed bed areas than in rich fen and meadow areas. In rich fens, species richness was higher in low frequency flooded areas (≤3 year^?1) than in areas with a high frequency of flooding (>3 year^?1) or no flooding, whereas species richness in reed beds and meadows was unaffected by flood frequency. 3. The percentage of stress‐tolerant species was higher in low intensity flooded rich fen areas than in high intensity and non‐flooded areas, indicating that the higher species richness in low frequency flooded rich fens was caused by competitive release. We found no indication that increased productivity was associated with high flooding frequencies. 4. We conclude that the restoration of morphological features in stream channels to increase the flooding regime can be beneficial for protected vegetation within riparian areas, but also that groundwater discharge thresholds and critical levels for protected vegetation should be identified and considered when introducing stream ecosystem restoration plans.     

Fire tolerance of perennial grass tussocks in a savanna woodland

Grass populations in tropical savannas are highly resilient in relation to different fire regimes, but the mechanisms conferring such resilience have been poorly studied. Here we examine one such mechanism, high adult survival during fire, for three perennial grass species in an Australian savanna: Eriachne triseta Nees ex Steud, Eriachne avenacea R.Br and Chrysopogon latifolius S.T.Blake. The study examined survivorship after 3 years, at plots subject to experimental fire regimes (experiencing 0, 1, 2 or 3 fires over the study period) at the Territory Wildlife Park near Darwin in the Northern Territory, Australia. Mean survivorship was 79.9%, 64.3% and 62.0% for E. avenacea, E. triseta and C. latifolius respectively. For the two species of Eriachne, mean survivorship was highest (E. avenacea, 94.6%; E. triseta, 77.1%) in unburnt plots, whereas survivorship of C. latifolius was highest (71.7%) under highest fire frequency. However, variation in survivorship among fire regime treatments was not statistically significant for any of the study species. This negligible difference in survivorship among regimes points to fire tolerance (sprouting ability) as an important mechanism contributing to the resilience and persistence of perennial grasses in these savannas.     

Regulation of Apical Dominance by Ethephon, Irradiance and CO2

Apical dominance of intact pea plants (Pisum sativum L. cv. Alaska) was found to be diminished by high irradiance and by increasing the CO₂ content of the air. Ethephon treatment of young plants resulted in an outgrowth of laterals, but this was significant only when the apical dominance already was weakened by high irradiance and/or CO₂.