Ancient stunted trees on cliffs

Abstract

diameter) per treatment. The tubes were then placed in a water bath with a temperature gradient from top to bottom of 20 to 10 °C. We used a spectrophometric assay procedure 10 to establish the TMA concentration in 10 litres of the medium that had previously contained four fish (ides, Leuciscus idus, 10 cm long), and recorded the resulting vertical migration behaviour of daphnids exposed to this medium. TMA concentration in this 'fish' water was between 10 and 25 ȖM.We found that even low concentrations of TMA induce Daphnia to migrate to deeper waters during the day in our test system. At night, they migrate back to the surface when exposed to small amounts of TMA, and stay near the bottom when TMA levels are high (more than 100 ȖM). When the lowest TMA concentration that induces vertical migration is compared with the activity in the fish water, it is clear that the reaction of Daphnia to fish water is stronger than just to TMA alone. This indicates that, although TMA is an active component of the 'fish factor', it is likely to be part of a cocktail of substances that deter Daphnia. The other substances probably help to reduce the chemical threshold that induces migration. It is not clear whether the TMA concentrations used in this study represent realistic values for aquatic systems, as we could find no published details of TMA concentrations in aquatic systems.It has been shown 9 that the fish kairomone is broken down by bacteria. We therefore compared the average day depth of daphnids exposed to 75 ȖM TMA in autoclaved water, and with the antibiotic ampicillin added and the TMA dissolved in non-autoclaved lake water. The migration activity of the Daphnia in non-sterile water slowly decreased over time (Fig. 2). After 72 hours, the average day depth of the animals in non-sterile conditions was no longer significantly different from the average day depth of animals in sterile control medium.To investigate whether simply adding any substance to the water induces vertical migration, we added the same amount of TMAO and triethylamine to sterile water (both at 75 ȖM). As with the control Daphnia, there was no significant increase in day depth. We therefore conclude that the reaction to TMA is a specific one, and not simply a response to a change in conductivity or ionic strength of the medium.

Effects of New Forestry Practices on Rare Epiphytic Macrolichens

“…Ek et al (1995) report that several threatened lichens confined to oak ( Quercus robur L.) often occur on trees growing on rock outcrops. Larson et al (1999) found that rock outcrops all around the world may support old, slow‐growing trees in areas where old trees are mainly lacking from other habitats. Thus, my findings that rock outcrops act as refugees for old‐growth forest species may be widely applicable to human‐influenced landscapes in various parts of the world (see also Ford et al 2002).…”

Persistence, multiple demographic strategies and conservation in long-lived Mediterranean plants

“…These traits could be especially significant in environments with low levels of disturbance, where complete losses of above-ground biomass are rare (Grime 2001), but also in nutrient-poor and/or abiotically harsh environments, where resprouting is prevented by resource limitation (Bellingham & Sparrow 2000). Thus, typical examples of persistence by longevity and/or vegetative reproduction should be more frequent among stress-tolerant species inhabiting arid, alpine and tundra habitats (Grime 1979(Grime , 2001, as well as other poor but stable habitats such as cliffs and ravines (Larson et al 1999(Larson et al , 2000.…”

Evidence for the widespread occurrence of ancient forests on cliffs

“…While these results confirm the prediction by Stahle & Chaney (1994) and Therrell & Stahle (1998) that unproductive rocky landscapes will support the best local examples of ancient forest, there have been few larger‐scale tests of the hypothesis as it applies to cliffs. Larson et al . (1999) have recently presented evidence that age and growth rate frequency distributions were the same for trees on North American to European cliffs, but few additional details were provided in that work.…”