Seedlings Of Pioneer Species Research Articles

Survival of the thickest? Impacts of extreme wave‐forcing on marsh seedlings are mediated by species morphology

AbstractAlthough tidal marshes are known for their coastal defense function during storm surges, the impact of extreme wave forcing on tidal marsh development is poorly understood. Seedling survival in the first season after germination, which may involve exposure to extreme wave events, is crucial for the natural establishment and human restoration of marshes. We hypothesize that species‐specific plant traits plays a significant role in seedlings survival and response to wave induced stress, i.e., through stem bending and uprooting. To test this hypothesis, seedlings of pioneer species (Bolboschoenus maritimus, Schoenoplectus tabernaemontani, Spartina anglica, and Puccinellia maritima) with contrasting biophysical traits were placed in the Large Wave Flume in Hannover (Germany) and exposed to storm wave conditions. Seedlings of P. maritima and S. anglica experienced a lower loss rate and bending angle after wave exposure compared to S. tabernaemontani and especially B. maritimus. The higher loss rates of B. maritimus and S. tabernaemontani result from deeper scouring around the stem base. Scouring depth was larger around stems of greater diameter and higher resistance to bending. Here, B. maritimus and S. tabernaemontani have both thicker and stiffer stems than S. anglica and P. maritima. Our results show that especially seedlings with thicker stems suffer from erosion and scouring, and have the highest risk of being lost during extreme wave events. This implies that for successful seedling establishment and eventually the establishment of a mature tidal marsh vegetation, the species composition and their capacity to cope with storm wave disturbances is crucial.

Potential allelopathic effect of Brachiaria decumbens root exudates on neotropical tree seedlings

The reforestation of degraded areas in the neotropics is hampered by the invasion of Brachiaria spp. The aggressiveness of these grasses may be related to the release of allelochemicals in the soil, and the sensitivity of tree seedlings of distinct successional classes to exudates of Brachiaria roots has not been addressed. Here, we evaluated the effects of exudates from Brachiaria decumbens roots on the growth, physiology and nitrogen metabolism of seedlings of six tree species native to Brazilian Atlantic Forest: Trema micrantha, Heliocarpus popayanensis and Cecropia pachystachya (pioneers), Cariniana estrellensis, Eugenia brasiliensis and Guarea kunthiana (non-pioneers). The seedlings were cultivated in fertile soil without (control) and with B. decumbens root exudates (AL treatment). Total leaf area and root and shoot dry weights of seedlings of pioneer species were drastically reduced by AL, whereas non-pioneers were less negatively affected. The gas exchange parameters and chlorophyll content of seedlings of both successional groups were altered by AL. AL decreased endogenous nitrate contents in the seedlings, in accordance with the inhibition of soil nitrification by this treatment. As consequence, AL reduced the endogenous protein contents of pioneer seedlings. Overall, these results demonstrate the negative allelopathic potential of exudates from B. decumbens roots on neotropical tree seedlings. Pioneer species, which are highly dependent on nitrate, were more negatively affected by the grass exudates, suggesting an indirect allelopathic effect mediated by the inhibition of soil nitrification, which may hamper the restoration of degraded areas. However, direct allelopathic mechanisms cannot be ruled out.

Effect of pre-logging stand type and harvesting roads on the densities of advanced-regenerated and postharvest-germinated tree seedlings after clear-cutting of hinoki cypress (Chamaecyparis obtusa) in Yoshinogari, Kyushu, Japan

To clarify the effects of pre-logging forest type (hinoki plantation or lucidophyllous forest) and harvesting roads on tree regeneration, we examined the density of regenerated trees, physical properties of soil, and soil erosion 2 years after clear-cutting in northern Kyushu, Japan. The results showed that the density of regenerated individuals was affected by the forest type before logging and by road construction. In a clear-cut lucidophyllous forest, most of the recovering vegetation consisted of lucidophyllous species originating from advanced regeneration and seedlings of pioneer species. Conversely, since few individuals originated from advanced regeneration in the clear-cut hinoki plantation sites, recovery to climax stand conditions at these sites is likely to be delayed compared to areas of clear-cut lucidophyllous forest. Few regenerated individuals were observed on harvesting road surfaces. Similarly, vegetation recovery was limited on harvesting road surfaces and along the side-cast slopes adjacent to roads. The number of germinated seedlings of pioneer species was positively correlated with litter cover and thickness of the A horizon, and negatively correlated with the rate of apparent soil erosion. These findings indicated that the establishment of seedlings of pioneer species originating from buried seeds is affected by the thickness of the A horizon of the soil. Since the recovered vegetation and the leaf litter derived therefrom will inhibit soil erosion, we propose that advanced regeneration and soil physical properties immediately after clear-cutting are important for the rapid recovery of climax forest conditions and for the prevention of soil erosion after clear-cutting.

The Nature of Seedling Assemblages in a Fragmented Tropical Landscape: Implications for Forest Regeneration

AbstractWhether aging forest fragments are able to recover original assemblages or progressively move toward impoverished successional stages remains as an open question. This study tested the hypothesis that seedling assemblages in forest fragments differ from those across mature forest stands and examined to what extent the uncovered patterns supported the notion that edge‐affected habitats tend to support impoverished tree assemblages dominated by pioneer species. We contrasted a series of small forest remnants (3–91 ha) to old‐growth stands located in the largest (ca 3500 ha) and best preserved forest remnant in northeastern Brazil and found that tree seedling assemblages inhabiting forest fragments exhibited reduced species richness (up to 50%) at different spatial scales in comparison to seedling assemblages in mature forest and adult assemblages in both fragments and mature forest stands. Moreover, ordination analyses clearly segregated fragment seedling assemblages in taxonomic/functional terms and segregation correlated to the richness of pioneer species. Seedlings of pioneer species and those bearing medium‐sized seeds (0.6–1.5 cm) increased in fragments, whereas large‐seeded species (1.5–3.0 cm) were reduced by more than a half. Such a multiple‐scale replacement of the old‐growth flora by pioneers was also confirmed by an indicator species analysis and the resulting pioneer indicator species. Our results suggest that small forest fragments support impoverished and distorted seedling assemblages. This floristic/functional drift implies that forest remnants or edge‐affected habitats tend to be dominated by a small set of pioneer tree species rather than supporting a substantial portion of the old‐growth flora as do mature forest stands.

Frost as a limiting factor for recruitment and establishment of early development stages in an alpine glacier foreland?

AbstractQuestionsHow frost resistant are the early development stages (seeds, seedlings, plantlets and juveniles) of alpine plant species? Do summer frosts impair establishment of plant species typical of different successional stages on a central alpine glacier foreland?LocationRotmoos glacier foreland, Austrian Central Alps (Obergurgl, Tyrol, Austria).MethodsSeeds of 12 species typical of different successional stages were collected in the glacier foreland and either sown directly in the field or in a growth chamber (25/10 °C, 16/8 h) and grown to the investigated development stages. Frost resistance of the early development and adult stages was determined by exposing them to a set of freezing temperatures and assessing viability with the tetrazolium test (LT 50, i.e. 50% of samples being lethally frost damaged).ResultsDry seeds had the highest frost resistance (LT 50: −19 °C), followed by wet seeds after imbibition (LT 50: −8 °C). With the onset of germination, frost resistance decreased rapidly. While germinated seeds tolerated a mean of −3.2 °C, seedlings and juveniles were less frost resistant (LT 50: −2.5 °C). Along the primary succession, seedlings of pioneer species were significantly less frost resistant than early‐ and late‐successional species. However, field grown seedlings, mainly of pioneer species, showed higher frost resistance (mean: −5 °C) than the growth chamber seedlings (mean: −3 °C), indicating that frost hardening (transition from a lower to a higher level of frost resistance) is already possible during these early stages of development.ConclusionsThe low frost resistance during and after germination may not suffice to survive summer frosts and may at least in certain years explain the high seedling mortality rates recognized in the glacier foreland.