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The paper presents results of a study on the response of species growing in experimental gaps in the patches dominated by Carex acutiformis, C. cespitosa and Salix cinerea. The study was performed in a meadow area subjected to the process of succession in the Reski Range in the Białowieski National Park. Four patterns of seedlings recruitment in the experimental gaps were distinguished: pattern I - great number of seedlings with high richness of species, pattern II - great number of seedlings with low richness of species, pattern III - low number of seedlings with great richness of species and pattern IV - low number of seedlings with low richness of species.

Aims The Gap Partitioning Hypothesis (GPH) posits that gaps create heterogeneity in resources crucial for tree regeneration in closed-canopy forests, allowing trees with contrasting strategies to coexist along resource gradients. Few studies have examined gap partitioning of temperate, ground-layer vascular plants. We used a ground-layer plant community of a temperate deciduous forest in northern Wisconsin, USA, as a model system to test whether the GPH extends to the relatively species-rich ground layer. Methods We used a well-replicated experimental approach that included a gap opening gradient (five gap sizes, 6, 10, 20, 30 and 46 m diameter, and undisturbed reference areas), a within-gap location gradient (gap edge to center), and a temporal gradient (0, 2, 6 and 13 years after gap creation). The data were observations of ground-layer plant abundance, published plant traits, and a modeled index of understory light environments. We ordinated the plant abundance data and evaluated the relationships of composition, traits and light environment by gap size, location along the forest-gap transect and time, with several approaches such as correlations, descriptivestatistics, non-parametric tests of group differences and indicator species importance values. Important Findings Ground-layer plant composition and traits differed across gap sizes, within-gap locations and over time. Gaps of all sizes differed in composition from undisturbed areas, and all pair-wise combinations of gap size also differed in composition, except the 6 m from the 10-m gaps. Large gaps (46 m) also displayed within-gap compositional gradients from gap edge to center locations. Compositional differences in gap size were evident 2 years after gap creation and, contrary to our hypotheses, remained different over the 13-year period, even in gaps with crown closure. In contrast to the neutral theory, species functional traits and microenvironmental conditions were related to variation in ground-layer composition. Species with smaller seeds, lower shade tolerance, later bloom times, shorter stature and longer leaves were associated with higher light, more central gap locations, larger gap sizes and greater time since gap creation. The correlation between gap size and ground-layer plant composition and traits provides evidence for gap partitioning by the diverse ground-layer community in this temperate deciduous forest community. [ABSTRACT FROM AUTHOR]

This study examines the ecological niche of American chestnut ( Castanea dentata (Marsh.) Borkh) and the latest blight resistant American chestnut × Chinese chestnut ( Castanea mollissima Blume) hybrids. Planted seedlings of chestnut, tulip poplar ( Liriodendron tulipifera L.) and chestnut oak ( Quercus prinus L.) were subjected to two levels of light and two soil types in parallel field and greenhouse studies. The field study took place in the Appalachian ridge and valley province of Virginia. Growth and survival were quantified after three growing seasons. The interaction between light levels and topographic position (soil type) was significant for growth rates in the field and greenhouse. Species were significantly different from each other although hybrid varieties were not significantly different from each other or from pure American chestnut. Tulip poplar showed the greatest growth rates under all treatments in the field. Both tulip poplar and chestnut had the greatest growth rates in large gaps within mesic, mid and lower slope (MML) sites in the field. In contrast to growth, optimal conditions for survival differed among species. Tulip poplar had the greatest survival (71%) within large gaps in MML sites while chestnuts and oaks had the greatest overall survival (64%) in small gaps within xeric, upper slope and ridge (XUR) sites. In the greenhouse, tulip poplar did not outperform chestnut. Discrepancies in field and greenhouse studies were accounted for by uncontrolled factors, such as rodent predation. We conclude that optimal sites for planting American chestnut hybrids are in small gaps located within XUR sites. [ABSTRACT FROM AUTHOR]

Restoration of giant sequoia populations is a high priority for managers, but few experimental studies have examined the efficacy of restoration treatments. To inform giant sequoia restoration treatment options, we assessed the response of giant sequoia regeneration (germination, mortality, and growth) to experimental gaps within a native giant sequoia grove. We created experimental gaps, ranging in size from 0.05 to 0.4 ha. Following gap creation, we sowed seeds and planted seedlings along north-south transects across gaps. Transects were planted on paired burned and unburned substrates. The seed-sowing treatment did not result in a cohort of established seedlings, although the amount of seeds sowed was far short of the potential amount released during intense fires. Mortality of planted seedlings did not vary with gap size (average 25% mortality). However, there was a distinct relationship between gap size and second year seedling growth. The relationship was best modeled with an asymptotic curve for both burned and unburned substrates. Relative seedling growth more than doubled as gap size increased from 0.05 to 0.2 ha, then increases in growth diminished. Growth rates of giant sequoia seedlings saturated above 70% light availability while increasing linearly with belowground resource availability. Long-lived pioneer species such as giant sequoia require restoration treatments that involve relatively severe disturbances to facilitate cohort establishment and recruitment. [ABSTRACT FROM AUTHOR]

In 1998–2001, I studied disturbance effects on the population structure and dynamics of a grassland strict biennial Pedicularis sylvatica, and on the species demography (monthly dynamics of seedling recruitment in 1998 and within- and between-year survival in 1998–2000). In two Czech populations, I established three experimental disturbance regimes: (1) a gap treatment, that simulated grazing by clipping vegetation and creating small gaps, (2) a mowing treatment, where I clipped the vegetation, and (3) a no management treatment, where I left the vegetation untreated. The number of recruiting seedlings varied greatly by year, and demographic structure of populations showed significant year-to-year oscillations in mean seedling numbers, from low (3 ± 0.7 s.e. per 0.25 m2 plot) to high (103 ± 20). Inversely in the same years and plots, mean adult numbers in populations oscillated from high (12 ± 2) to low (0.7 ± 0.3). Disturbance effects were only important for seedling recruitment in early census dates in all years. In 1998, most seedlings recruited in April–May in gaps in both sites, but most died before winter. Within- and between-year survival was not affected by disturbance regimes but fluctuated significantly among years. Between-year survival increased with increasing size of the overwintering bud and was higher in disturbance treatments. Since the oscillations in population structure did not significantly vary in response to experimental disturbances, population dynamics may be driven endogenously rather than by disturbance events. The weak disturbance effects on species demography may also indicate population resilience to changes in habitat quality. However, since disturbances promoted seedling recruitment, grazing or mowing regimes are strongly recommended, as they create regeneration opportunities and maintain habitat quality, meeting the species long-term conservation goals. [ABSTRACT FROM AUTHOR]