INFLUENCE OF IVORY PLANTS, GRASS COMPETITION AND FIRE ON THE EMERGENCE OF SEEDLINGS OF ACACIA KARROO, ACACIA NILOTICA ANDACACIA TORTILIS. The latter refers to the impact of pre-emergence burning on the growth of woody seedlings.
Introduction
Structure of savannas
Changes in secondary determinants, either through human intervention or natural processes, can result in an increase in the number of woody individuals if these changes promote successful dispersal. It is the relative increase in density of the woody component in savannas that is called 'bush encroachment'.
Reasons for bush encroachment
The direction of change in woody plant density can be determined by fire frequency (Roquesetat. 2001). While forest encroachment is associated with an absence of browsers (Roques et al., an absence of small-bodied herbivores may be important in woody plant establishment (Prins&.
Influence of fire and herbivory on woody seedlings .1 Fire
Fire increases grass palatability to grazers (Walker 1985) and maintains woody vegetation at an available height and condition acceptable to browsers (Trolope 1983; Walker 1985). A small drainage line crossed part of the study area, which was avoided in the experiment.
Weenen Nature Reserve
Specifically, mammalian herbivory was expected to influence seedling establishment in Abu Madi (high numbers of small-bodied herbivores), but not in Weenen Nature Reserve (no small-bodied herbivores). Specifically, whether pre-emergence burning, which reduces above-ground competition from grass grass, has a positive effect on rooting of Acacia seedlings.
Materials and Method
- Seed preparation
- Treatments
- Monitoring of seedlings
- Analysis
The survival and growth of seedlings from emergence (first recorded 13 days and 19 days after planting at Abu Madi and Weenen respectively) to the end of the growing season was checked at intervals. A logistic model (Genstat 5 Committee 1987) was used to describe the binomial data, which recorded the presence (1) or absence (0) of seedlings at each survey interval.
Results
Seed viability
- Seedling emergence
- Seedling survival
- Seedling growth
- Seedling survival
- Seedling growth
Furthermore, as shown by the trends in survival (Figure 4.2), although seedling survival decreased due to grass competition, A.tortilis seedlings and herbivory (Table 4.4), their effect was strongest at the beginning of the experimental period (Figure 4.2 ). Seedlings protected from herbivory had significantly more leaves and were larger in open areas throughout the experimental period (Table 4.6, Figure 4.4 a, b, f, g), but only after 82 days in grass areas (Figure 4.4 c, h). Seedlings exposed to herbivory had a higher leaf-to-height ratio than those protected from herbivory, but only in the open areas (Figure 4.4k) and not in the grass layer (Figure 4.4 1).
Seedling mortality was highest early in the growing season, within a few days of seedling emergence (Figure 4.5). Thereafter, seedling survival stabilized and seedling numbers continued to decline at a constant rate in all treatments. To examine differences in seedling growth, the average response of seedlings to treatment combinations was plotted (Figures 4.7 and 4.8).
General trends
Effect of herbivory on seedling establishment
In contrast, seedling survival was negatively affected by herbivory in Abu Madi (Figures 4.2 and 4.3), most during the first few weeks after emergence and to a lesser extent. In addition, both nyala and impala were observed on several occasions looking at seedlings at Abu Madi (personal observation). A striking difference between Abu Madi and Weenen is the complement of herbivores at both sites.
Populations of large-bodied herbivores at Weenen had no significant effect on the growth of woody seedlings (Figure 4.7), while a group of small-bodied herbivores at Abu Madi had a negative effect (Figure 4.4). At Abu Madi, seedlings that were not protected from herbivores showed a higher leaf-to-height ratio than protected seedlings.
Effect of grass competition on seedling establishment
Differences in seedling rooting due to grass fall were attributed to competition for light and moisture between herbaceous vegetation and shrub seedlings (Schultzet al. 1955). Seedlings planted in sedges at Abu Madi and Weenen were subject to aboveground competition with sedges and to a lesser extent tree canopy at Abu Madi. The effect of shade on the seedlings was evident in the greater etiolation shown by the seedlings grown in the turf grass of Abu Madi and Weenen seedlings, as they have a lower leaf-to-height ratio than the seedlings grown in the open.
60 greater in open areas, it was not in burned areas, suggesting that fire somehow counteracted the poorer emergence of seedlings in the grass. While fire appeared to improve conditions for seedlings emerging in the grass relative to seedlings in the open, overall emergence was nevertheless lower in burned than unburned areas (Table 4.7).
The relationship of herbivory, grass competition and fire
This was recognized by outdoor seedlings in burned areas doing better than outdoor seedlings in unburned areas. Second, although seedlings in open patches were more visible and more accessible to herbivores than seedlings in the grass layer, survival was better in open patches, regardless of herbivore protection. However, the negative impact of fire on established seedlings is well documented in the literature, and therefore fire does not necessarily result in an increase in woody seedling density.
In light of consistently better seedling survival and growth in areas with reduced grass biomass, the direct impact of removing the grass layer by fire on seedling emergence deserves more attention. As herbivory was mainly concentrated on seedlings in bare patches, where seedlings showed better survival and growth than in the grass areas, it is expected that seedlings establishing within bare patches would show significantly improved growth in response to a release of herbivore pressure.
Analysis
Survival of the 14th day cohort of seedlings was examined in two ways; first, by testing seedling survival at each recording interval relative to the initial number of seedlings emerging in that cohort, and second, by examining survival and mortality between recording intervals. The survival of the total number of seedlings that emerged over the entire season was tested against survival at the end of the season. The standard errors of the predictions were used to illustrate differences in treatment combinations in terms of survival.
Since the elevation change in all basins was bimodally distributed, the values of the short and long components could be tested by analysis of variance. Disc grazing readings were performed on the grass component immediately adjacent to each seedling that survived at the end of the experimental period.
Results
- Laboratory work
- Seedling survival
- Veld condition assessment
- Species composition
The decrease in seedling survival was most pronounced at the beginning of the season between days 14 and 54. The addition of time, breed, and type of livestock to the model significantly reduced model variance, accounting for 53.8% of the variance. As shown by parameter estimates (Table 5.7), A.sieberiana time and sheep grazing negatively affected seedling survival (Table 5.8).
In this model, the negative influence of time was represented by one time interval, the comparison of seedling survival at the end of the season in relation to the total number of seedlings formed. The number of leaves and the leaf height ratio were also affected by the grazing system, especially towards the later stages of the growing season (Table 5.9 (a) and (c), Figure 5.5 (2)).
DERSC(4) BIN
Sward structure
The proportion of 'tall' and 'short' grass components, and the difference in the mean values of the modals, were investigated (Table. The tall grass category represented a very small proportion of the grass, and was highly variable. However, Fig. 5.8 showed that it ' high' component covers a very small part of the grass and the paddocks were very homogeneous.
Continuous grazing by sheep resulted in lower grass utilization than rotational grazing. Although the means of the 'tall' and 'short' components in these paddocks were very different, most of the grass heights were similar.
Discussion
- General trends
- The effect of veld condition on seedling establishment
- Management implications
While trampled plants have been found in cattle-grazed pastures, with trampling identified as fracture of the seedling stem, trampling to this extent has never been observed in sheep camps. The effect of such high livestock pressure resulted in heavy field utilization and extremely high grazing pressure. Due to the abnormally high stocking rate, livestock used all available grass in the pastures, including unpalatable species such as Cymbopogon excavatus and Aristidajunciformis, resulting in homogeneous grass fields.
Sheep did not use the pasture much, indicating that high stocking rates resulted in greater intensity of pasture use. If a dorsal turret moves against the direction of the wind, the passage of fire is slower than with a main posterior, which travels in the same direction as the wind.
Materials and methods
- Seed size
- Management implications
Furthermore, because Acacia species produce large quantities of seed each season and form very large seed banks in the soil (Sabiiti & Wein 1987), mortality from fire is likely to be offset by seed imports, and the seed bank is unlikely to be significantly will be depleted after a disaster. single fire. Furthermore, in the current study, seeds were placed on the soil surface and therefore received less protection from fire than seeds deeper in the soil. Although hot backburning resulted in significant seed mortality on the soil surface of Ukulinga, backburning is expected to have positive effects on seeds contained in the soil.
To reach temperatures sufficient for seed germination at deeper levels in the soil, the passage of a very hot fire near the soil surface is necessary. Therefore, the effect of a backfire and headfire on seeds should be investigated deeper in the soil to determine the overall effect of fire type on seedling recruitment.
CONCLUSION
Research note: Short-term effect of tires on the woody component of Sourish Mixed Bushveld. Tree community dynamics in a humid savanna of Côte d'Ivoire: Modeling the effects of fire and competition with grass and neighbors. In: Ecology of the World's Savannas (eds JC Tothill& JJ Mott), Australian Academy of Science, Canberra, pp.
Effect of fire on the Acacia longifolia seed bank and growth, mortality and reproduction of post-fire established seedlings in the South West Cape. Soil seed bank distribution and the effect of fire on seedling emergence in Acacia saligna growing on the central coast of New South Wales.
