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Leaf optical properties and related leaf characteristics were compared for thirteen cloud forest tree species differing in successional status. Sun leaves were sampled for the eight pioneer species and sun and shade leaves were sampled for the five climax species. Sun leaves had a slightly higher absorptance than shade leaves, although differences were small. Sun leaves had a higher leaf mass per unit area (LMA) and a lower chlorophyll concentration per unit leaf mass, resulting in similar chlorophyll concentrations per unit leaf area and hence similar light harvesting capacities as shade leaves. However, shade leaves realized a higher efficiency of absorptance per unit leaf biomass than sun leaves. There were few differences in leaf characteristics of sun leaves between the climax and pioneer species. Absorptance values of cloud forest species were comparable with values reported for rain forest and more seasonal forest species. Intraspecific variation in leaf absorptance was largely the result of variation in LMA, whereas interspecific variation in leaf absorptance was largely a result of variation in chlorophyll concentration per unit leaf area.

The relationship between plant size and vegetative reproduction in clonal plants appears complex because vegetative expansion, growth, and reproduction are not clearly separable in such plants. In 'pseudo-annuals', which are clonal plants surviving the winter only as seeds and hibernacles produced by the rhizome apices, vegetative growth and reproduction are clearly separate processes so that the relationship between vegetative reproduction and plant size can be studied. We used the pseudo-annual Helianthus x laetiflorus Pers. to study the relationship between plant size and total rhizome biomass, rhizome (hibernacle) biomass, and number of hibernacles. We manipulated resource acquisition of the plants by reducing leaf area (leaf-clipping) and by fertilization, thus affecting plant size. Furthermore, we studied the success of thin and thick hibernacles in terms of future growth and reproduction in a separate experiment. The results showed that vegetative reproduction was positively related to plant size. The ratio between the number of hibernacles and mean hibernacle weight was affected by plant size in such a way that in small plants both number of hibernacles and mean hibernacle weight were reduced to the same extent as compared to those in large plants.However, the size distributions of plants of the next generation growing from thin and thick hibernacles did not differ. It remains unclear therefore why this pseudo-annual species produces thick hibernacles at all.

It has been shown in clonal perennial herbs that shoot natality decreases, and shoot mortality increases, in stands of increasing density. In a two-year garden experiment, we have tested Hutchings' (1979) hypothesis that these responses are the result of physiological integration, i.e. the exchange of resources and growth substances between shoots of a single clone. Dense monocultures of two rhizomatous graminoids, Brachypodium pinnatum and Carex flacca, were created that differed more than 10-fold in the density of clones (genets), but that had similar densities of shoots. A more effective shoot density control was expected in stands with the smaller clone densities (larger clones) due to more extensive clonal connections. Shoot turnover was evaluated by counting living and dead shoots at different times. In the summer of the second year, when shoot densities and stand structure were similar between treatments, shoot natality (the number of shoots born per plot) and shoot mortality (the number of shoots that died per plot) were usually unrelated to clone density in either species. If there was a significant treatment effect, it could be attributed to (small) differences in shoot density. Over the whole range of shoot densities, natality was negatively density-dependent. The number of shoots that died in a given growth period was proportional to the number of shoots present, suggesting that mortality rates were density independent. In Carex, however, there were some indications that mortality rate increased with increasing density. Our study confirms that clonal herbaceous species can effectively prevent an overproduction of shoots, but in contrast to Hutchings' (1979) propositions, we found no evidence that physiological integration may be the responsible mechanism. An alternative explanation for the observed patterns is proposed.

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