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Schematic of plot layout pertaining to sapling growth assessments. Hypothetical sampling plot where growth of all saplings (i.e., occurring in the inner and outer circles) with height > 50 cm of Virgilia divaricata ('V' and 'v'), Acacia mearnsii ('R' and 'r') and A. melanoxylon ('X' and 'x') were measured. Additionally we assessed the effect of competition exerted by nearby saplings on the growth of focal saplings individually. For this assessment, each focal sapling (V, R, or X) occurred within the inner one meter radius circular plot (shaded), and each focal sapling's growth increment was related to the summed biomass (expressed as an index, see text) of all the remaining saplings (V, R, X, v, r, and x) within the remainder of the 1 meter radius (shaded) and 2 meter radius (unshaded) circular plots combined. Full-size DOI: 10.7717/peerj.5466/fig-1
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Background
Invasive alien plants with long-lived dormant seed banks and fast growth rates are difficult to manage. Acacia mearnsii and Acacia melanoxylon are two such invaders in the southern Cape of South Africa which occasionally co-occur with a native, ecologically analogous species, Virgilia divaricata . We compared the performance of these thr...
Contexts in source publication
Context 1
... study plots (2 m radius) were located where at least one individual of V. divaricata (considered as reference species) occurred interspersed within stands of co-occurring A. mearnsii and A. melanoxylon and little other vegetation (Fig. 1) within the Garden Route National Park where pine plantations were clear-felled three to five years prior to the study, and where saplings subsequently attained sizes of 0.2-8.0 cm groundline diameter (GLD; stem diameter at 8 cm above ground level). Saplings of such sizes are ideal for growth studies in displaying rapid (measurable) growth over a short period (Kozlowski, 1971). Acacia mearnsii considerably outnumbered the other two species in all the chosen study plots as we were unable to find sites containing more equitable numbers of saplings of the three species. Saplings of all three study species, with heights greater than 50 cm, were marked and numbered. The first measurements (T 1 ) were taken in August-September 2015, and the second (T 2 ) in June 2016. Measurements included GLD (cm), height (cm), and distance from plot centroid (cm), with a total of 1,252 saplings (34 of V. divaricata; 1,138 of A. mearnsii; 80 of A. melanoxylon) surveyed. For all marked saplings in the study plots, absolute growth increment (T 2 -T 1 ) was calculated for height, GLD, and biomass index 'BI' (calculated as GLD squared multiplied by height; Eccles, Kritzinger & Little, ...
Context 2
... assess competitive performance of individual saplings (of the three study species) in relation to the competition collectively exerted by nearby saplings, a subset of marked saplings was first identified as focal saplings. These focal saplings were all the saplings (21 for V. divaricata; 331 for A. mearnsii; 33 for A. melanoxylon) that occurred within the central 1 meter radius plot of the (2 meter radius) study plot (Fig. 1). The performance of each focal sapling was assessed in relation to the collective competition exerted by the remainder of saplings within the two meter radius plot. Plot competition was expressed as the total BI of all saplings (excluding the focal sapling), by summing the average BI of each sapling between T 1 and T 2 (a measure of saplings' average biomass during the study period). Relative growth rate in ...
Context 3
... DOI: 10.7717/peerj.5466/ fig-1 1947). We used mixed-model analysis of variance (ANOVA) (Littell, 2002) to assess the effects on seed bank density of species and depth class (as fixed effects), habitat type (as random effect), and second-order interactions among these (as fixed effects). The effects of species and depth class on seed viability were tested (representation across habitat types was too poor to enable inclusion of this factor). The viability expressed as proportions did not conform to assumptions of normality and homogeneity of variance and were subjected to a rank transformation. The ranked and unranked data were tested using a factorial ANOVA, yielding comparable results. Test results from the unranked data were regarded as valid, as the assumptions for ANOVA were reasonably satisfied (Montgomery, ...
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Riparian invasive alien plants are known to compete with native plant species for water, space, daylight, and different other resources by decreasing structural diversity of native vegetation and subsequently changing the functioning of the ecosystem. The aim of this study was to investigate the rate of native plant species recolonization after the...
Citations
... Propagule pressure refers to the rate and volume at which regenerative propagules, like seeds or ramets, are released into and persist in environments (Lockwood et al., 2005), which is directly related to the likelihood of an alien species becoming invasive (Colautti et al., 2006). The quantification of species' viable seed banks is thus vital for determining invasive potential and eradication feasibility (Eschtruth & Battles, 2009;Goets et al., 2018). ...
... Disturbance generally predicts invasion at a localized scale (Hobbs & Huenneke, 1992;Richardson et al., 2020). Disturbance facilitates invasion by eliminating competition from native species, releasing resources and stimulating germination (Goets et al., 2018;Hierro et al., 2006). A globally common and important disturbance is fire, which may interact with alien plant invasion. ...
... The leaf litter layer was scraped away to avoid substantive sampling of seeds potentially released during the 2019 season (as sampling was aimed at the 2018 seed crop contained in the soil). For each sample, the soil was collected over a rectangular surface area of 30 × 15 cm and to a depth of 5 cm, as this zone contains most seeds (Bakker et al., 1996;Goets et al., 2018). ...
The New Zealand bottlebrush, Metrosideros excelsa (Myrtaceae), was introduced into South Africa in the 1940s as an ornamental plant and subsequently naturalized in coastal parts of the Cape Floristic Region. Knowledge of M. excelsa 's propagule pressure and response to fire in South Africa can inform evaluation of the species' invasion potential and management. We assessed M. excelsa 's canopy and soil seed banks in burnt and unburnt stands; and post‐fire regeneration via reseeding and resprouting in relation to fire severity and tree size. Soil seed banks were assessed using an emergence technique, but no seedlings emerged from soil collected under burnt or unburnt plants suggesting that the species does not maintain a viable soil‐stored seed bank or germination triggers were not met (though unlikely). The annual seed crop in the canopies of unburnt trees was approximately 0.5–23 million seeds per tree. Viability, assessed through tetrazolium stain testing, of canopy‐borne seeds on unburnt trees was 18%, whereas a canopy fire, ranging in severity from low to extreme, killed all canopy‐borne seeds. Fifteen months post‐fire, the seedling to pre‐fire (live) tree ratio was 0.01, whereas 43% of burnt trees survived via basal resprouting. Fire severity had a non‐linear effect on tree survival (survival was highest after medium and high fire severity and lowest after low and extreme fire severity), while larger trees were more likely to survive fire. These results suggest that even low‐severity (safe) burning may be a useful control measure as it kills canopy‐borne seeds and causes substantial mortality, particularly of smaller trees. An opportunistic evaluation of an uncontrolled (no comparison with untreated individuals) foliar herbicide application to post‐fire resprouting individuals also showed considerable (91%) mortality. However, rigorous herbicide trials (also with herbicide in conjunction with burning) are required to inform the management of M. excelsa .
... Wattles have several characteristics which make them desirable to introduce and simultaneously successful as invaders. The key reproductive traits include: short time to reproductive maturity, unspecialized pollination systems, copious seed production, effective seed dispersal systems, the accumulation of large, persistent seed banks and disturbance-cued germination (Milton and Hall, 1981;Holmes, 2002;Richardson and Kluge, 2008;Marchante et al., 2010;Castro-Díez et al., 2011;Gibson et al., 2011;Strydom et al., 2017;Goets et al., 2018;Chapters 5, 17 and 31, this volume). In addition, several species sprout or coppice from the roots , which increases their ability to persist (van Wilgen et al., 1992). ...
... The potential that A. mearnsii plantations have, to provide suitable microclimate conditions as well as a capacity to improve soil fertility, makes them ideal as a tree seedling nursery in the region. The current practice of removing the Acacia canopy followed by the planting of Shola tree seedlings will most likely trigger an outbreak of A. mearnsii regeneration (Dikshit 2015, Geldenhuys et al. 2017, Goets et al. 2018 which is likely to set back the plantation to an early development stage. It is also likely that this dense regeneration and the browsing by gaur and deer will hamper the establishment of the planted Shola tree saplings. ...
Whether environmental conditions under exotic tree plantations abandoned in the Western Ghats of India can facilitate the natural regeneration of tropical montane forest (Shola forest) tree species is being debated. In many cases, the exotic tree plantations are being cleared to allow for the restoration of native ecosystems. In this paper, we examined whether exotic tree plantations have indeed a negative effect on the regeneration of Shola forest tree species. For this, we assessed the abundance, diversity, and composition of the regeneration of Shola forest tree species in plantations, each with different dominant tree species (Acacia mearnsii, Pinus sp., and Eucalyptus sp.). We tested the abundance of regenerating native tree species against the main plantation canopy species (plantation type) as well as other environmental factors (aspect, distance to nearest Shola forest, structural diversity, slope, elevation, presence of herbivores, and canopy closure). We found that the number of native tree species regenerating in all plantation types was at an acceptable level: 1960, 1773, and 462 individuals ha−1 for Acacia, Eucalyptus, and Pinus plantations, respectively. A rare fraction analysis showed that the highest number of Shola tree species were regenerating under Acacia mearnsii (25) followed by Eucalyptus (19) and Pinus (8) plantations. The density and diversity of regenerating Shola trees was greatest under Acacia plantations and northern aspects but declined with increasing elevation. The presence of herbivores also reduced the density and diversity of Shola tree regeneration. We concluded that the restoration of Shola forest in the Western Ghats is possible in existing stands of exotic tree species and this process can be accelerated with appropriate silvicultural methods. We additionally recommend that studies involving long-term exclosures can provide valuable insights into the effects of browsing on regeneration and species composition.
... Very few Acacia melanoxylon saplings were recorded in our study, and none underneath indigenous tree canopies. Although Acacia melanoxylon seeds may be dispersed by birds and water, resulting in low density seedbanks far away from the parent plants, mature trees have been shown to maintain large soil-stored seedbanks underneath their canopies (Milton and Hall 1981;Goets et al. 2018). Given that our plots were underneath large, mature Acacia melanoxylon trees, factors other than the availability of viable seedbanks are likely to have limited recruitment of this species, although Goets et al. (2018) found Acacia melanoxylon seedbanks to be particularly variable under mature parent plants in the study region. ...
... Although Acacia melanoxylon seeds may be dispersed by birds and water, resulting in low density seedbanks far away from the parent plants, mature trees have been shown to maintain large soil-stored seedbanks underneath their canopies (Milton and Hall 1981;Goets et al. 2018). Given that our plots were underneath large, mature Acacia melanoxylon trees, factors other than the availability of viable seedbanks are likely to have limited recruitment of this species, although Goets et al. (2018) found Acacia melanoxylon seedbanks to be particularly variable under mature parent plants in the study region. Evidence obtained from a germination trial suggested that germination of Acacia melanoxylon seeds is not impeded by allelopathic effects from parent plants or an indigenous Afrotemperate Forest species (Olea capensis macrocarpa) (Miles et al. 2022). ...
The alien tree Acacia melanoxylon (R.Br.) occurs extensively in the Southern Cape Afrotemperate Forest (South Africa). Concerns exist about its potential negative effects on indigenous tree sapling communities, ultimately with implications for forest composition and structure. We investigated whether Acacia melanoxylon affects Afrotemperate forest tree sapling composition in the Garden Route National Park. Using a paired plot design, we compared sapling species richness, diversity and density underneath 30 overstorey Acacia melanoxylon trees and 30 indigenous counterparts of the species Podocarpus latifolius (Thunb.) R.Br. ex Mirb, Afrocarpus falcatus (Thunb.) C.N.Page, or Olea capensis macrocarpa (C.H.Wright) I.Verd. We recorded 2 503 tree saplings from 27 indigenous species and only three Acacia melanoxylon saplings in the 60 plots. There were no significant differences in the richness, diversity or density of saplings underneath Acacia melanoxylon trees versus their indigenous counterparts. Non-metric multidimensional scaling and cluster analysis accordingly showed only minor differences in sapling species composition and abundance between Acacia melanoxylon and indigenous overstorey trees. We concluded that indigenous tree sapling composition is not significantly altered by the presence of Acacia melanoxylon trees at the densities (< 3 trees ha −1) at which this species commonly occurs in Afrotemperate forest in the Garden Route National Park. However, populations of Acacia melanoxylon in the forest interior act as a source of propagules for invasion in forest margins, riparian areas and neighbouring fynbos shrubland, while at high density the species may alter forest gap-forming dynamics. These invasive attributes need to be considered in the management of the species in the region.
... Regarding the frequency of river transport of A. dealbata´s seeds, and the fact that the density of seeds was low, we need to consider three aspects: First, we sampled towards the end of the seed fall period [1]; second, both rivers were under low-flow conditions, with close to minimum capacities for transporting seeds; third, seed bank densities at our study sites are very high compared to other species [88,89], only comparable to the seed banks for other Acacia species [90][91][92]. This suggests that A. dealbata's seeds may be transported both during low-flow conditions (Austral summer, corresponding to the seed fall period), when seeds directly fall into the river, as well as during high-flow months (Austral winter), entrained from the seed bank by overbank flows, during flooding events. ...
Background
The silver wattle Acacia dealbata is a fast-growing tree from Australia that has become naturalised in different regions of the world, attaining invasive status in most of them. In Chile, A. dealbata reaches large abundances along banks and floodplains of invaded fluvial systems, suggesting that rivers may act as a vector for seed dispersal. As hydrochory has not been documented previously in this species, the aim of this study is to evaluate the potential for water dispersal of seeds of this invasive tree along rivers.
Methods
Seed samples from rivers were collected at three sites along two A. dealbata -invaded rivers within the Cachapoal basin, central Chile. Number of seeds collected was contrasted versus hydraulic and local conditions with RDA. Seed buoyancy and sedimentation velocity were determined and compared between sites with an ANCOVA. Finally, the probability of seed germination after long periods of immersion in water was assessed, simulating transport conditions in the flow. Germination results were tested with a GLM.
Results
Results indicate that increasing abundance of A. dealbata seeds in the flow is related to the level of turbulence of the flow. Seeds display high floatability but their sedimentation velocity is high when they do sink. Finally, silver wattle seeds can germinate after long periods (many weeks) of immersion in water; however, their probability of germination depends to a large extent on whether seeds are scarified or not.
Conclusions
Based on the evidence collected, we suggest that the seeds of A. dealbata have the necessary traits to be dispersed by rivers, this being the first research testing this hypothesis. The success of hydrochory of A. dealbata would depend on river flow turbulence, and whether there are natural mechanisms for scarifying the seeds either before or during transport. The proposed methodology can be used to assess river hydrochory for any tree species.
... Restoration projects are based on controlling ecosystem threats and then manipulating abiotic and biotic factors to facilitate their recovery (Palmer et al., 2016). Seed ecophysiology can provide important information for restoration plans (Baskin and Baskin, 2014;Khurana and Singh, 2001;, either to improve native seed efficient management (Baskin and Baskin, 2020;León-Lobos et al., 2020;Merritt and Dixon, 2011) or to control of invasive alien species present in the seed bank after the removal of the adult trees (Goets et al., 2018;Marushia et al., 2010;Reader and Bricker, 1994). Therefore, information on seed dormancy and germination for native and alien tree species is a cornerstone for restoration programs (Khurana and Singh, 2001;. ...
... In other words, if it is known when the alien species will germinate but the native species will not, chemical or mechanical control can be carried out at that time. This has been widely explored in the agriculture for crops and weeds Benech-Arnold et al., 2000;Malavert et al., 2020), but there are scarce works comparing alien and native woody species in natural systems (but see, Ferreras et al., 2015;Tecco et al., 2012) and even less have applied this knowledge to suggest management strategies (Goets et al., 2017(Goets et al., , 2018Moore and Lacey, 2009). ...
... Nevertheless, it is necessary to take into account not only the native species studied here, but also those naturally present in the seed bank of the site to be restored. In the case of G. triacanthos since the seeds need scarification, measures can be taken to mechanically intervene in the soil, using a disc harrow, trigger a germination pulse and control the emerged seedlings at that time (Colbach et al., 2014;Dessì et al., 2021;Goets et al., 2018). ...
Forest restoration plans can benefit from knowledge of seed ecophysiology. Naturally, seeds respond to environmental clues to trigger germination or persist in the seed bank. Controlling dormancy and germination moment in native species will allow more efficient seed management, both for direct seeding (in situ restoration) and for native plant cultivation in nurseries (ex situ restoration). In addition, the differences in germination conditions of native and alien invasive trees can be used as control windows of the alien species in the seed bank. The aim of this study was to identify the environmental factors regulating seed dormancy and germination of native and alien trees of the Talares, an endangered temperate forest of the Argentine Pampas region. Seeds of the native trees Schinus longifolius, Jodina rhombifolia, Celtis tala and the alien trees, Ligustrum lucidum, Ligustrum sinense and Gleditsia triacanthos were collected and the presence of dormancy was determined exposing the seeds to standard germination protocols. In case of dormancy presence, a post-maturation experiment was carried out in two conditions: i) cold and wet (stratification) and ii) dry and warm (after-ripening). The native species J. rhombifolia and C. tala showed seed dormancy but S. longifolius did not. For C. tala germination it was necessary a previous post-maturing process; however, environmental conditions for J. rhombifolia germination were not attained. Alien species showed a high germination, reaching up to 100% in at least one of the evaluated conditions, and displayed different emergence windows compare to natives. Since alien species germinated at lower temperatures than natives, a temporal window for chemical or mechanical control is proposed. Ecophysiology of seed dormancy and germination facilitates strategies for decision makers, as it can make native seeds use and aliens control more efficient to meet global restoration goals.
... Viability of the sample set of Acacia melanoxylon seeds subjected to stain testing was 90% which is comparable to the findings of Goets et al. (2018) in the same area. Germination of seeds planted in the nursery trial was 67% (range among germination trays, 60À90%) and there was a marginally significant difference between the three leachate treatments (H = 6.16; df = 2; P = 0.04; Fig. 1). ...
... The germination of Acacia melanoxylon seeds was not inhibited by its own leachates which can be expected as Acacia melanoxylon has long seed dispersal mechanisms (Goets et al., 2018). Other taxonomically related species that are known to inhibit their own germination are Acacia dealbata (Aguilera et al., 2017) and Vachellia tortilis raddiana (Savi.) ...
The invasive alien tree species Acacia melanoxylon R. Br has been known to invade some forest ecosystems in Europe through allelopathy (amongst other mechanisms) which allows a competitive advantage over indigenous species. Acacia melanoxylon is widespread in Southern Cape Afrotemperate Forest, South Africa, and may establish successfully in these forests in certain contexts. In a nursery trial we compared the allelopathic potential of phyllode or leaf leachates of Acacia melanoxylon and a common overstorey indigenous species, Olea capensis L. macrocarpa C.H. Wright on the germination of seeds of Acacia melanoxylon. We compared the germination of Acacia melanoxylon seeds among three treatments, namely Acacia melanoxylon leachate, Olea capensis macrocarpa leachate, and no leachate. Stain-testing of seeds showed high viability (90%). The average germination of Acacia melanoxylon was 67% and there was a marginally significant difference in the number of germinants between the three treatments (H= 6.16; df= 2; P= 0.04). Pairwise multiple comparisons of ranks revealed that germination was marginally higher under Acacia melanoxylon leachate treatment than the control (Z = 1.97; df = 2; P = 0.14), and marginally higher under Olea capensis macrocarpa leachate than the control (Z = 0.12; df = 2; P = 0.12). This suggests that germination of Acacia melanoxylon is improved, or at the least, unaffected, by allelopathic substances of itself or of a common Afrotemperate Forest overstorey species. We concluded that the lack of sensitivity of Acacia melanoxylon germination to allelopathic substances of itself or a common indigenous overstorey species likely contribute to its successful establishment in Southern Cape Afrotemperate Forest.
... The results of some studies suggest that the seeds of invasive plants tend to be better adjusted for survival in soil compared with native species [14]. Seed banks of invasive woody legumes (Acacia, Cytisus, Genista, etc.) have been studied extensively [1,[15][16][17], whereas seed banks of fleshy-fruited woody species received much less attention [18][19][20]. Recent studies have revealed that alien woody plant species form denser soil seed banks in the invaded range than in their native ranges [21] When seeds reach the soil and enter the seed bank, they gradually lose their germination potential, especially if they are short-lived [22]. ...
Soil seed banks of alien plant species are sources of propagules that play a crucial role in plant population dynamics. Studies on seed banks of woody alien species are crucial for understanding mechanisms of their encroachment on natural habitats. This study aimed to compare vertical distribution, density and composition of seed banks formed by native Cornus sanguinea subsp. sanguinea and alien C. alba, C. sericea and C. sanguinea subsp. australis in the Southern Hemiboreal zone of Europe. Five sites for each of four taxa were selected for the study, and seeds were sampled using the soil core method (400 samples in two soil layers: the upper, 0–5 cm, and the lower, 5–10 cm). Extracted seeds were tested with tetrazolium chloride stain to assess their viability. Differences in the seed banks among taxa were compared using generalised linear mixed models (GLMM). The GLMM analysis revealed significant differences in soil seed bank densities in the upper soil between the studied taxa (p < 0.001). We found that two of the alien taxa (C. alba and C. sanguinea subsp. australis) formed a much denser seed bank containing more viable seeds than the native Cornus sanguinea subsp. sanguinea. All three alien species contained more viable seeds (from 40.7% to 45.2% in the upper soil layer) than the native C. sanguinea subsp. sanguinea (19.4% in the upper and 18.2% in the lower soil layer). The cover of Cornus and habitat type had no significant effect on the density of the seed bank, according to GLMM. This study supports the hypothesis that seed banks of alien C. alba and C. sanguinea subsp. australis are denser than those of native C. sanguinea subsp. sanguinea. Furthermore, the seed bank of alien taxa contained more viable seeds than the seed bank of C. sanguinea subsp. sanguinea. Results of this study contribute to the understanding of the invasiveness of alien Cornus taxa.
... If this was the case, we would expect the EICAT categories to be an underestimate of the real impacts. Given the difficulty managing acacias (Goets et al. 2018;Cheney et al. 2019), the extent of invasion in many regions (Richardson and Rejmánek 2011), and the often largescale impacts (Gaertner et al. 2009), the evidence based EICAT score might be an underestimate of the real impacts. Furthermore, restoration attempts clearly show the difficulties getting native communities back after acacia invasions (e.g., Le ) but this might not be well represented in the impact literature itself. ...
Species of the genus Acacia have been introduced worldwide and have negative environmental and socio-economic impacts in many introduced regions. This study makes use of environmental and socio-economic impact classification schemes for alien taxa (EICAT and SEICAT) to assess the impacts that 33 acacias introduced to South Africa have at a global scale. The aims of this study were: (1) to compare the EICAT impact categories which are based on literature with expert assessments; (2) to determine which environmental and socio-economic mechanisms underlie acacia impacts; and (3) to test if certain habitats experience higher impact magnitudes than others. Most acacias had a massive impact when evaluated by experts, while the impact was mostly major for EICAT. This could be due to the use of different definitions for the impact categories. It might also show that the data available is insufficient or inadequate in showing that such high impacts exist. Competition was found to be the most often recorded mechanism underlying acacia environmental impacts and was one of the mechanisms with the largest impact magnitude. Grassland, shrubland, marine-coastal and forest habitats were found to be impacted by acacias equally as much. Using impact scoring schemes as an evidence-based and transparent approach to determine the impact status of alien species provides a more robust method to aid management prioritisation and risk assessment than expert opinion alone. However, data quality and availability could limit their effectiveness, especially for less well studied species.
... Seed germination success can be affected by among other factors, the competitive interactions between species as well as their density in the microsite (Orrock and Christopher 2010); and thus influence the ultimate individual plant species' population fitness (Goets et al., 2018;Aschehoug et al. 2016;Johnson et al. 2008;Schupp 1993). It has been suggested that seeds of different species can sense each other prior to their emergence and shift their germination timing to ovoid competition (Ward 2016;Tielborger and Prasse 2009;Wang and Smith 2002). ...
Background
By transporting and scarifying the seeds during ingestion, avian frugivores reduce the competition with siblings, and may improve the germination which is critical for dispersal effectiveness and population recruitment. However, generally, there is limited knowledge on how deposited seeds interact/compete in the new microsite. We tested the hypothesis that the bird-dispersed seeds benefit from improved germination after their passage through the bird’s gut; and we investigated the potential impact of seed density on competition at the microsites by determining whether seed density and species diversity influence germination in the Free State Province, South Africa.
Results
Overall, the results partly supported the hypothesis. Germination trials with defecated seeds of five plant species compared with the manually depulped seeds showed that only Searsia lancea had significantly higher seed germination success and improved germination speed after passage through the bird gut while Ziziphus mucronata only benefited rapid germination. There was a significant correlation between seed size and the germination of bird-ingested seeds except in Olea subsp. africana possibly due to possession of extremely hard protective seed cover . Seed competition experiments pointed to Z. mucronata and O. subsp. africana having significant germination performance that was positively correlated to seed density and seed size while Ehretia rigida did not germinate at all. Seed species diversity in the germination trays did not have a significant impact since the seeds of two former plant species consistently displayed significantly higher germination across the competition levels.
Conclusions
We conclude that different plant species respond differently to seed ingestion by birds, and that further long-term tests for germination physiological responses of the seeds’ samples used in this study are required since poor germination observed in other tree/shrub species cannot be attributed to competition solely.
