Canopy development of a determinate and an indeterminate cultivar of Vicia faba L. under contrasting plant distributions and densities

Field experiments were conducted in 1987 and 1988 to quantify differences in canopy formation between an indeterminate and a determinate genotype of Vicia faba L., grown at two plant densities and three spatial distributions. The number of stems per unit area produced by determinate plants was related to the growth rate before flowering. Leaf production per stem per unit of thermal time was similar in both plant types, but twice as many leaves per stem were produced by the indeterminate cultivar. The indeterminate cultivar produced fewer and smaller leaves in the warmer and drier weather of 1988 than in 1987. The determinate genotype produced similar sizes and numbers of leaves in both years, but fewer tillers developed in 1988 than in 1987. Accordingly, leaf mass per unit ground area was greater in 1987 than in 1988 in both genotypes. Except during early flowering, relationships between leaf mass and leaf area were constant, with higher specific leaf areas in the determinate than the indeterminate genotype. Shoot dry matter partitioning into leaves was identical in both years for indeterminate plants, but differed in determinate ones.
It is concluded that canopy development is regulated through individual leaf weight and leaf number per stem in non-tillering indeterminate, and by stem numbers per unit area in tillering determinate plants.     

Influence of Colophospermum mopane canopy cover on litter decomposition and nutrient dynamics in a semi‐arid African savannah

The objective of this study was to investigate the influence of mopane canopy cover on litter decomposition in a semi‐arid African savannah. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10‐ha pocket of open mopane woodland. Litterbags were placed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area. Decomposition was fastest in the intercanopy area exposed to solar radiation (k = 0.35 year^?1), intermediate beneath small trees (k = 0.28 year^?1) and slowest beneath large trees (k = 0.23 year^?1). Soil temperatures beneath small and large trees were 3–5 and 6–9°C lower than in the intercanopy area, respectively. Bacterial and fungal counts were significantly higher (P < 0.05) beneath large than small trees and in the intercanopy area. The amount of N and P released did not vary significantly among sampling sites. Soil moisture in the dry season was similar among sampling sites but rainy‐season soil moisture was significantly greater (P < 0.05) beneath large than small trees and in the intecanopy area. Mopane canopy cover retarded litter decomposition suggesting that photodegradation could be an important factor controlling carbon turnover in semi‐arid African savannahs.     

Post-pruning shoot growth increases fruit abscission and reduces stem carbohydrates and yield in macadamia

Background and Aims

There is good evidence for deciduous trees that competition for carbohydrates from shoot growth accentuates early fruit abscission and reduces yield but the effect for evergreen trees is not well defined. Here, whole-tree tip-pruning at anthesis is used to examine the effect of post-pruning shoot development on fruit abscission in the evergreen subtropical tree macadamia (Macadamia integrifolia, M. integrifolia × tetraphylla). Partial-tree tip-pruning is also used to test the localization of the effect.

Methods

In the first experiment (2005/2006), all branches on trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R treatment) and shoots were removed from others (NR treatment). Fruit set and stem total non-structural carbohydrates (TNSC) over time, and yield were measured. In the second experiment (2006/2007), upper branches of trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R) and shoots were removed from others (NR). Fruit set and yield were measured separately for upper (pruned) and lower (unpruned) branches.

Key Results

In the first experiment, R trees set far fewer fruit and had lower yield than NR trees. TNSC fell and rose in all treatments but the decline in R trees occurred earlier than in NR trees and coincided with early shoot growth and the increase in fruit abscission relative to the other treatments. In the second experiment, fruit abscission on upper branches of R trees increased relative to the other treatments but there was little difference in fruit abscission between treatments on lower branches.

Conclusions

This study is the first to demonstrate an increase in fruit abscission in an evergreen tree in response to pruning. The effect appeared to be related to competition for carbohydrates between post-pruning shoot growth and fruit development and was local, with shoot growth on pruned branches having no effect on fruit abscission on unpruned branches.     

Yellow‐chevroned Parakeet (Brotogeris chiriri) abundance and canopy foraging at a dry forest in western Brazil

I studied Brotogeris chiriri abundance and foraging activity at a dry forest of the Urucum mountains in western Mato Grosso do Sul, Brazil, to evaluate their relationships with food resource production. Brotogeris chiriri abundance sharply increased during the early wet season (mainly October 2001) when it mostly foraged for fleshy fruits. At that time Protium heptaphyllum, one of the most common tree species, bore a large crop of fruits, the arils of which were extensively consumed by B. chiriri. Conversely, only a few parakeets were recorded foraging from the late wet to the late dry season, when dry fruit production predominated. The monthly pattern of parakeet abundance paralleled both its monthly pattern of foraging activity and fleshy fruit availability. Moreover, the variations in foraging activity were highly correlated to fleshy fruit production. Thus, data presented here evidenced the effect of both fruiting pulses and a common tree species that produced a large and ephemeral fruit crop, on the dynamic of a small and mobile canopy forager at a primary dry forest.     

Identifying the interacting roles of stressors in driving the global loss of canopy‐forming to mat‐forming algae in marine ecosystems

Identifying the type and strength of interactions between local anthropogenic and other stressors can help to set achievable management targets for degraded marine ecosystems and support their resilience by identifying local actions. We undertook a meta‐analysis, using data from 118 studies to test the hypothesis that ongoing global declines in the dominant habitat along temperate rocky coastlines, forests of canopy‐forming algae and/or their replacement by mat‐forming algae are driven by the nonadditive interactions between local anthropogenic stressors that can be addressed through management actions (fishing, heavy metal pollution, nutrient enrichment and high sediment loads) and other stressors (presence of competitors or grazers, removal of canopy algae, limiting or excessive light, low or high salinity, increasing temperature, high wave exposure and high UV or CO₂), not as easily amenable to management actions. In general, the cumulative effects of local anthropogenic and other stressors had negative effects on the growth and survival of canopy‐forming algae. Conversely, the growth or survival of mat‐forming algae was either unaffected or significantly enhanced by the same pairs of stressors. Contrary to our predictions, the majority of interactions between stressors were additive. There were however synergistic interactions between nutrient enrichment and heavy metals, the presence of competitors, low light and increasing temperature, leading to amplified negative effects on canopy‐forming algae. There were also synergistic interactions between nutrient enrichment and increasing CO₂ and temperature leading to amplified positive effects on mat‐forming algae. Our review of the current literature shows that management of nutrient levels, rather than fishing, heavy metal pollution or high sediment loads, would provide the greatest opportunity for preventing the shift from canopy to mat‐forming algae, particularly in enclosed bays or estuaries because of the higher prevalence of synergistic interactions between nutrient enrichment with other local and global stressors, and as such it should be prioritized.