Epiphyte-phorophyte relationships: assessing the differences between Seasonal Semideciduous and Swamp Forests in Southeastern Brazil1

ABSTRACT Vascular epiphytes are responsible for a considerable portion of tropical biodiversity; however, the variation of epiphytes-phorophytes relationships in different vegetation types are still poorly understood. In this study, we aimed to assess the presence, abundance, vertical distribution, and life cycle (holoepiphyte and hemiepiphyte) of vascular epiphytes in two vegetation types [Seasonal Semideciduous Forest (- SSF), and Swamp Forest (- SF)] in order to determine any correlation with phorophyte size (diameter and height) and the specificity of phorophyte species to the epiphytic colonization. There was a higher number of phorophytes in SF; however, epiphytes density did not differ between the vegetation types. The recorded vertical distribution also showed different patterns: in the SSF, most epiphytes were found in the canopy, while in the SF they occurred mainly on the trunks of the trees. The abundance of epiphytes was positively correlated with the phorophyte size in the two vegetation types. In the SSF, colonization of phorophytes by epiphytes appeared to be less species-specific than in the SF, where trees density is likely to be a more significant factor to epiphytic colonization. The results showed the importance of the forest heterogeneity in the conservation and maintenance of vascular epiphytes assemblage, demonstrated by differences in the abundance and distribution of the epiphytes, even in contiguous forests.

Tree light capture and spatial variability of understory light increase with species mixing and tree size heterogeneity

Mixed and multi-layered forest ecosystems are sometimes more productive than monospecific and single-layered ones. It has been suggested that trees of different species and sizes occupy complementary positions in space, which would act as a mechanism to increase canopy light interception and wood production. However, greater canopy light interception reduces the average amount and variability of transmitted radiation, offering fewer opportunities for all species to regenerate and to maintain forest heterogeneity in the long run. We investigated whether increasing overstory heterogeneity indeed results in greater canopy light interception and lower variability in transmittance. We modeled the three-dimensional structure of forest stands with three typical forest structures, 10 mixtures of four tree species, and three different basal areas. We used the forest light interception model SamsaraLight and performed three-way analyses of covariance to analyze the effects of the three varied components of forest heterogeneity. We found no evidence that increasing structural heterogeneity increases canopy light interception. However, the light interception by mixed canopies was greater than the weighted average of light interception by the corresponding pure canopies. Variability in transmittance increased in some cases with compositional heterogeneity and, to a lesser extent, with tree size inequalities. The advantage of heterogeneous forests is in opportunities for natural regeneration, as well as in opportunities to enhance canopy light interception.

Short-term development of a multilayered forest stand after target diameter harvest in southern Sweden

Harvest strategies that emulate natural disturbances are being promoted to restore multilayered forest heterogeneity, notably the harvest of largest trees. However, their use also increases management complexity, and more information on their practical feasibility and effects on forests is needed. Therefore, in this study, target diameter cutting treatments were applied to a heterogeneously structured stand in southern Sweden (exemplifying a conifer-dominated forest of the hemiboreal forest region in northern Europe) to assess their effects on gap dynamics, natural regeneration, and stand growth. The target diameter cutting resulted in an exponentially decreasing gap size distribution, with the largest canopy gaps measuring 0.1–0.2 ha. The gap closure rate was higher than reported rates for gaps in natural forests. After 5 years, sufficient numbers of seedlings had regenerated, but proportions of intermediate- and late-successional tree species were low. The observed stand growth exceeded rates simulated using the growth model Standwise in the Heureka forest planning software package. The findings from this case study are useful for refining the general concept of close-to-nature forestry, but they need to be complemented with the information available from other regeneration studies after partial harvest.