For seven species in a mature mesic forest in southeast Texas, we estimated species-specific parameters representing radial growth in high light and low light for tree saplings. Shade-intolerant species had higher asymptotic growth rates and lower low-light growth than tolerant species. Inspection of species positions on graphs of low-light growth versus high-light growth suggested that there was a trade-off between these two processes across species. By linking functions of growth versus light and mortality versus growth, we also found that shade-intolerant species had higher mortality risk at low light and stronger sensitivity of mortality to light than shade-tolerant species. Moreover, we found that low-light survival and high-light growth were negatively correlated across species. In contrast to northern hardwood forests, where sapling survival in low light may be achieved at the expense of growth, our results suggested that shade-tolerant species in this southern mixed forest can grow faster as well as survive better than shade-intolerant species in low light. We conclude that both sapling growth and survival are important components of shade tolerance and their relationships may be system-specific.

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Summary1 Using 18 years of permanent-plot data from a 4-ha stand, we investigated whether stand dynamics is predictable, i.e. driven by competition (inferred from species shade tolerances), or unpredictable (driven by frequent exogenous disturbance or other factors). We also considered whether small disturbance might accelerate or retard succession. The study involved dynamics of stems ≥ 4.5 cm diameter at breast height (d.b.h.) for 10 important species in a southern mixed hardwood forest 80 years after selective removal of Pinus taeda. 4 Over 18 years, ingrowth exceeded mortality loss slightly, resulting in an increase in number of stems of about 1%, from 995 to 1029 stems ha − 1 ; average live basal area (BA; 35.9 m 2 ha − 1 ) varied by less than 2% over eight surveys spanning 18 years. Basal area increased substantially for three species ( Ilex opaca , Pinus taeda , Acer rubrum ), and declined strongly for three others ( Quercus nigra , Q. hemisphaerica and Fagus grandifolia ). 5 The stand d.b.h. distribution had a rotated sigmoid form which became flatter over time. Species d.b.h. distributions were mostly bell-shaped for intolerant species, and irregular-to-monotonic declining for shade-tolerant species. Over time, bell-shaped distributions moved to the right and irregular distributions remained irregular. 6 A hurricane in 1986 caused loss of 4.5% of standing BA. Compositional change was most rapid during the hurricane interval and ingrowth was highest in the two intervals following the hurricane. Effects on species trends in density, basal area, mortality or recruitment were minor. 7 Temporal trends in species abundances mostly supported the hypothesis of predictable successional change related to competition for light. However, d.b.h. distributions of shade-tolerant species and rapid declines in BA of Quercus nigra and Fagus indicated that other processes are also important and will limit predictability of change.

Aim  Plant communities across the temperate zone are changing in response to successional processes and human‐induced disturbances. Here, we assess how upland forest under‐ and overstorey community composition has changed along an edaphic gradient. Location  Northern Wisconsin, USA. Methods  Forest sites initially sampled in the 1950s were resampled for overstorey composition and diversity, basal area, and understorey composition and diversity. We used clustering methods to identify groups of stands based on overstorey composition, and we used similarity indices, ordination and diversity indices to evaluate changes in species abundance and overall community structure. Results  Sites clustered into four overstorey groups along the edaphic gradient: ‘hemlock’ sites dominated by hemlock in 1950, ‘mesic’ sites dominated by northern hardwoods, ‘dry’ sites with a significant pine inclusion in the canopy and diverse ‘dry‐mesic’ sites in the middle. Collectively, forests gained maple, ash and cherry while losing pines, birches and red oaks. The hemlock forest sites gained hardwoods, while the dry‐mesic sites shifted towards a more mesic hardwood composition. Only the driest sites have remained relatively stable in species composition. Main conclusions  These trends reflect both ‘mesification’ and homogenization among northern forests. Highly diverse mid‐gradient and mesic hemlock‐dominated stands are transitioning to maple dominance. Fire suppression may be favouring invasions of more mesic plants into historically drier sites, while high deer abundance likely limits hemlock regeneration. If current trends continue, maples will dominate the majority of northern forests, with significant losses of local native species richness and substantial shifts in understorey composition.

We investigated the effects of light and flooding on growth and survivorship of saplings in a river floodplain forest of southeast Texas. Growth responses to light were consistent with the expectation that shade-intolerant species grow faster than shade-tolerant species in high light, and vice versa. Mortality risk was not associated with shade tolerance level unless high mortality risks associated with a period of high flooding were removed. These results support the hypothesis that shade-tolerant species in floodplains may be limited by flooding as previous studies suggested. Also, compared to their performance at a nearby mesic site, common species showed little intraspecific difference in shade tolerance, especially for shade-intolerant species. Finally, the positive correlation between low-light growth and survivorship suggests that carbon allocation to continued growth may be favored as a sapling strategy in floodplains.

We investigated the relationship between shade tolerance and sapling mortality using data collected over 15 years in a mesic forest in southeastern Texas. Seven species representing a range of shade-tolerance classes were included in the study. We used survival analysis to estimate species-specific sapling mortality risk (hazard) as a function of recent growth. We found that shade-intolerant species had higher mortality risk at zero growth than shade-tolerant species. The results strongly support the point that shade tolerance can be characterized by the relationship between sapling mortality and growth.

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