Flooding and grazing promote germination and seedling establishment in the perennial grass Paspalum dilatatum

Seed germination and seedling emergence are key processes for population recruitment. Flooding and grazing are disturbances forming gaps that may strongly influence recruitment patterns in space and time, but their combined effects and action mechanisms have rarely been addressed. In this study we analysed the effects of microhabitat conditions associated with winter flooding and spring‐summer defoliation on seed germination and seedling establishment of Paspalum dilatatum, a dominant perennial C₄ grass in native grasslands of the Flooding Pampa, Argentina. The dynamics of seedling emergence from natural seed banks and buried seeds was studied in a factorial experiment with flooding and defoliation treatments applied to soil monoliths (mesocosms) collected from natural grassland. Additional laboratory experiments were applied to investigate seed germination under different combinations of temperature, light quality and simulated flooding. Seed germination and seedling emergence of P. dilatatum were promoted by flooding and high intensity defoliation. Gaps generated by flooding were maintained by high intensity defoliation exercising a synergistic effect on survival seedlings. Flooding resulted in the breaking of seed dormancy and higher germination rates associated with alternating temperature and the activation of the phytochrome system. Our results indicate that microhabitat conditions associated with the disturbances forming gaps, such as flooding and heavy grazing, synergistically promote the recruitment process of this dominant grass species.     

Distribution and abundance of vines along the light gradient in a southern temperate rain forest

Question: Are vines light‐demanding species? Location: Temperate evergreen rain forest of southern Chile (40°39′S, 72°11′W). Methods: In 45 plots of 25 m² distributed in treefall canopy gaps, secondary forest stands and old‐growth forest (15 plots per light environment), all climbing and non‐supported vines were counted and identified to species level, and canopy openness was quantified using hemispherical photographs. Vine abundance and diversity (species richness and Simpson's index) were compared in the three light environments and similarity between vine communities was estimated using Jaccard's similarity coefficient. We also determined the relationship between light niche breadth and local dominance at the species level. Results: In total there were 2510 vine individuals of 14 species. Canopy openness was significantly different in the three light environments. Species richness, diversity, community composition and density of vines were similar in treefall gaps, secondary and old‐growth forest. Of the seven more common vine species, which accounted for 91% of all vines, three had even distribution, two were more abundant in the shaded understorey, and two had higher density in well‐lit sites. Local dominance of vine species and niche breadth were not significantly associated. Conclusions: Our study in a temperate rain forest questions the widespread notion of vines as pioneer‐like species, which may be a consequence of the abundance of some lianas in disturbed sites of tropical forests. Functional arguments are needed to justify a general hypothesis on light requirements of vines, which constitute a vast group of species.     

The Response of Ground Beetles (Coleoptera: Carabidae) to Selection Cutting in a South Carolina Bottomland Hardwood Forest

We compared the response of ground beetles (Coleoptera: Carabidae) to the creation of canopy gaps of different size (0.13, 0.26, and 0.50 ha) and age (1 and 7 years) in a bottomland hardwood forest (South Carolina, USA). Samples were collected four times in 2001 by malaise and pitfall traps placed at the center and edge of each gap, and 50 m into the surrounding forest. Species richness was higher at the center of young gaps than in old gaps or in the forest, but there was no statistical difference in species richness between old gaps and the forests surrounding them. Carabid abundance followed the same trend, but only with the exclusion of Semiardistomis viridis (Say), a very abundant species that differed in its response to gap age compared to most other species. The carabid assemblage at the gap edge was very similar to that of the forest, and there appeared to be no distinct edge community. Species known to occur in open or disturbed habitats were more abundant at the center of young gaps than at any other location. Generalist species were relatively unaffected by the disturbance, but one species (Dicaelus dilatatus Say) was significantly less abundant at the centers of young gaps. Forest inhabiting species were less abundant at the centers of old gaps than in the forest, but not in the centers of young gaps. Comparison of community similarity at various trapping locations showed that communities at the centers of old and young gaps had the lowest similarity (46.5%). The community similarity between young gap centers and nearby forest (49.1%) and old gap centers and nearby forest (50.0%) was similarly low. These results show that while the abundance and richness of carabids in old gaps was similar to that of the surrounding forest, the species composition between the two sites differed greatly.     

Patterns of Fine Root Mass and Distribution along a Disturbance Gradient in a Tropical Montane Forest, Central Sulawesi (Indonesia)

Large parts of the remaining tropical moist forests of South-east Asia are encroached at their margins by selective logging, rattan harvesting and the establishment of small agroforest plantations under the rainforest canopy. These slight to heavy disturbances affect aboveground forest structure by reducing wood biomass and canopy cover; however, they may also have a profound impact on the belowground compartment. In a lower montane moist forest of Central Sulawesi, we studied the profile totals of fine root biomass (FRB_tot, roots <2 mm until 50 cm of soil depth) and of fine root necromass (FRN_tot), the vertical distribution of fine root mass, and the fine root live/dead ratio by root coring in 12 forest stands that represented a gradient in forest use (or disturbance) intensity (forest use type A: undisturbed natural forest, B and C: slightly or moderately disturbed forests with selective timber extraction, D: heavily disturbed cacao agroforest systems under a remaining rainforest cover; each forest types being replicated three times). FRB_tot decreased significantly from forest A to the disturbed B, C and D forests, and reached less than 60% of the FRB_tot value of A in the agroforest systems D. A similar decrease with increasing disturbance intensity was found for FRN_tot. Forest disturbance intensity had no significant influence on the vertical distribution of fine root biomass in the profiles. According to correlation and principal components analyses, fractional canopy cover was the most important factor influencing FRB_tot and FRN_tot, whereas diameter at breast height, stand basal area, stem density, soil pH and base saturation had only a minor or no influence on root mass. A reduction in canopy cover from 90% (forest type A) to 75% (types C and D) was associated with a reduction in FRB_tot by about 45% which indicates that timber extraction leads not only to canopy gaps but to corresponding ‘root gaps’ in the soil as well. We conclude that forest encroachment that is widespread in large parts of South-east Asia’s remaining rainforests significantly reduces tree fine root biomass and associated carbon sequestration, even if it is conducted at moderate intensities only.     

Elimination of basic gaps at high pH values in 2‐DE

The appearance of gaps, vertical lanes lacking protein spots at the cathodic end of 2‐D maps generated with wide range IPG‐strips exceeding a pH value of 9, is shown to depend on the electro‐osmotic transport of water into the IPG‐strip. Substitution of urea solution with water is demonstrated to increase the hydrolysis rate of polyacrylamide in IPG‐strips explaining the gap formation. The use of 8 M urea or thiourea/urea solutions in the electrode wick enables overnight focusing without the appearance of gaps.     

Mind the gap: genetic distance increases with habitat gap size in Florida scrub jays

Habitat gap size has been negatively linked to movement probability in several species occupying fragmented landscapes. How these effects on movement behaviour in turn affect the genetic structure of fragmented populations at local scales is less well known. We tested, and confirmed, the hypothesis that genetic differentiation among adjacent populations of Florida scrub jays--an endangered bird species with poor dispersal abilities and a high degree of habitat specialization--increases with the width of habitat gaps separating them. This relationship was not an artefact of simple isolation-by-distance, as genetic distance was not correlated with the Euclidean distance between geographical centroids of the adjacent populations. Our results suggest that gap size affects movement behaviour even at remarkably local spatial scales, producing direct consequences on the genetic structure of fragmented populations. This finding shows that conserving genetic continuity for specialist species within fragmented habitat requires maintenance or restoration of preserve networks in which habitat gaps do not exceed a species-specific threshold distance.     

Stand dynamics of the shade-tolerant conifers Podocarpus nubigena and Saxegothaea conspicua in Chilean temperate rain forest

Abstract. Population structures were used to infer regeneration patterns of the conifers Podocarpus nubigena and Saxegothaea conspicua and associated angiosperm tree species in six stands in the temperate rainforests of the coastal ranges of southern Chile. On poorly-drained, nutrient-poor and high altitude sites, where most of the associated species were fairly shade-intolerant and light-crowned, dense all-aged populations and the presence of numerous saplings beneath the canopy suggested continuous regeneration of both P. nubigena and S. conspicua. On more favourable sites, where several of the associated angiosperms were highly shade-tolerant and densecrowned, both conifers, particularly P. nubigena, were less abundant, and their regeneration from seed appeared to be sporadic. S. conspicua's great longevity (≥ 750 yr) and frequent vegetative reproduction are probably crucial to its persistence in competition with shade-tolerant broadleaved species in undisturbed stands on favourable sites. Results of this study, and a review of related literature on southern temperate forests are not consistent with the hypothesis that heavily-shaded, infrequently-disturbed habitats are an evolutionary refuge for conifers. Sites likely to have high leaf area indices and infrequent disturbance are better exploited by shade-tolerant angiosperms.