Mechanisms promoting tree species co‐existence: Experimental evidence with saplings of subtropical forest ecosystems of China

Abstract

Questions: The maintenance of a diverse sapling pool is of particular importance for the regeneration and persistance of species-rich forest ecosystems. However, the mechanisms of co-existence of saplings have rarely been studied experimentally. Do species richness, species composition, species identity and stand density affect the co-existence, growth patterns and crown architecture of tree saplings?Location: Jiangxi Province, southeast China. Methods:In a field experiment, we manipulated the local neighbourhood of saplings of four early-successional subtropical species (Schima superba, Elaeocarpus decipiens, Quercus serrata and Castanea henryi) with regard to species richness (one, two and four species), species composition (monocultures, six-two-species combinations and one-four-species combination) and stand density (low, intermediate and high). We tested for treatment effects and impact of species identity on growth variables, biomass allocation, crown architectural traits and branch demography.Results: Species richness was a poor predictor of all response variables, but enhanced pruning and branch turnover. In contrast, species composition proved to be of great importance for growth, biomass allocation, crown architecture and branch demography. Local neighbourhood interactions of saplings were characterized by complementary or facilitative, as well as by competitive mechanisms. Intra-specific competition was higher than inter-specific competition for two species (C. henryi, Q. serrata) depending on the respective species combination. To a high degree, the competitive ability of species can be explained by species identity. Competition for light likely played a major role in our experiment, as evidenced by the strong response of crown architecture and branch demography to the manipulated predictor variables.Conclusions: Effects of species composition and species identity on growth rates and crown architecture variables of tree saplings point to niche separation as a mechanism of species co-existence, while effects of species richness were not yet prominent at the sapling life stage.

Crown responses to neighbor density and species identity in a young mixed deciduous stand

“…It is likely that the response of crowns to the local neighborhood will vary with stand development, although crowns of older Fagus trees have also demonstrated high plasticity in response to changes in the local canopy conditions (Schröter et al 2012;Dieler and Pretzsch 2013) suggesting that the response to competition could be sustained over tree life. Tree density significantly affected crown architecture as reported previously (Lang et al 2012), whereas neighbor species identity had a significant but less pronounced role despite the large range in species proportions examined. This lends support to the findings of Kaitaniemi and Lintunen (2010), who found that the effect of density (in a more limited range than in our study) and neighbor size (calculated as a competition index) alone were more important than the effect of neighbor identity when exploring the effect of Larix sibirica Ledeb.…”

“…Overall, several studies show that crown size and architecture respond to a variety of exogenous factors such as local competition (Thorpe et al 2010), site fertility (Dieler and Pretzsch 2013), topography (Lang et al 2012;Antin et al 2013) and climate (Lines et al 2012) and to endogenous factors such as tree size (Thorpe et al 2010, Antin et al 2013) and species identity (Purves et al 2007, Weiskittel et al 2010. In all studies, endogenous factors appeared to be far more important than exogenous factors, with tree species and tree size being the primary drivers of most crown variables.…”

Local neighborhood competition following an extraordinary snow break event: implications for tree-individual growth

“…These differences indicate that there is interspecific variation in functional traits between the four tree species. For three of the four species Lang et al (2012a) found species-specific differences in sapling growth in the same study region. Furthermore, Chen et al (1999) observed high growth rates for saplings of S. superba in forest gaps, and Q. serrata was recorded to be very slow growing (Xing et al 2012).…”

Throughfall kinetic energy in young subtropical forests: Investigation on tree species richness effects and spatial variability

“…Speciesspecific differences in growth and biomass allocation patterns as well as plant architecture are due to niche separation. As a result, stratified canopies with a high degree of crown overlap and, thus an increased mean vegetation cover and greater biomass density can be found in mixtures compared to monocultures (Lang et al, 2010(Lang et al, , 2012Menalled et al, 1998;Pretzsch, 2014). Concerning soil erosion, TKE in particular reacts strongly to these tree characteristics (Geißler et al, 2013;Nanko et al, 2006Nanko et al, , 2008.…”