Diameter growth performance varies with species functional-group and habitat characteristics in subtropical rainforests

Abstract

We examined tree diameter growth in 20 plots subjected to various disturbance intensities (natural, low, moderate and intensive logging) in a bid to understand the general tree growth responses in relation to habitat characteristics in subtropical rainforests of north-eastern New South Wales, Australia. Species-specific regeneration strategy, maximum size and level of shade tolerance were used to classify species into 5 groups; emergent and shade tolerant main canopy (group 1), shade tolerant mid canopy (2), shade tolerant understoreys (3), moderate shade tolerant (4), and shade intolerant (5) tree species. Data series for trees ≥ 10 cm diameter at 1.3 m above the ground level (dbh) providing observations spanning over 36-years were used in multilevel regression analyses. The results showed that spatial and temporal effects in tree growth at the stand-level are a combination of the differences between species functional-group compositions and environmental gradients. High growth responses were observed in the shade intolerant species while increasing level of shade tolerance and decreasing maximum size decreased trees growth rates. Tree growth increased with altitude on a large scale across regions, and with disturbance intensity on a small scale at the plot (stand) level. Increase in northness (south through flat to north facing sites) increased growth in species group 1 for trees < 67 cm dbh, but beyond this dbh threshold the opposite was true. These showed that saplings of species group 1 may require increased illumination to reach the forest canopy, but once in the canopy, low soil water availability may be limiting to tree growth in the north facing sites. Decrease in northness was associated with increased growth in species group 2 indicating that reduced illumination and improved soil moisture in the south facing sites were conducive for maximum growth in this species group. Maximum growth potential in species group 4 and 5 increased with decrease in eastness, suggesting that the increased afternoon solar radiation and temperature were conducive for high growth rates in these species. Although topographic gradient may determine the spatial and temporal variations in tree growth where growth appeared to increase from the crest down the slope into the creek, its effects on soil fertility and water availability, and interactions between these and other factors may make it difficult to discern clear growth patterns.

Diameter growth performance of tree functional groups in Puerto Rican secondary tropical forests

“…Tree growth rates in our study decreased from shade intolerant and canopy emergent species through shade tolerant and middle and low story late successional species, as others results in literature (Francis and Lowe, 2000;Kariuki et al, 2006), supporting the notion that interspecif ic variation in maximum potential growth rate is one of the most important factors in the definition of functional groups (Baker et al, 2003). Variability in diameter increments between functional groups was considerable, with the mean value of the median 10-year diameter increment almost 4 times greater in fastest growing group (Large shade intolerant) relative to the slowest (Small shade intolerant).…”

“…Habitat characteristics influence soil water availability, solar radiation, and probably soil nutrient availability, factors that have been shown to influence stand-level growth responses (Kariuki et al, 2006). Surprisingly, the relationship between relative diameter growth and site characteristics was not statistically signif icant.…”

“…For our study, species were grouped on the basis of two criteria: regeneration strategy (shade intolerant/ shade tolerant dichotomy) and adult height, defined as average maximum tree height (Baker et al, 2003;Kariuki et al, 2006;Swaine and Whitmore, 1988). Shade intolerants (I) are species whose seeds can only germinate in open canopy gaps while shade tolerant species (T) are those that can germinate and grow in the shade.…”

Topoedaphic Variability and Patch Burning in Sand Sagebrush Shrubland

“…Aspect and slope values, originally expressed as degrees, were transformed using trigonometric functions (Guisan et al 1999) and the product of the transformed values resulted in values of "northness" and "eastness" (Kariuki et al 2006) that could be associated with each sampled plant:…”

Plant functional groups based on vegetative and reproductive traits in a subtropical forest community

“…There has been a great deal of work focused on defining and classifying PFTs (Chapin et al 1996;Skarpe 1996;Walker 1999;Kahmen and Poschlod 2004;Foster and Brooks 2005;Kariuki et al 2006). Some of them, for example, Vile et al (2006) who examined 34 herbaceous species, have proposed that plant ecological strategies can be quantified and modeled by principal components analysis, and some of them have tied PFTs with environmental factors such as linking tree growth of PFTs to habitats (Kariuki et al 2006), or to stress, grazing, and ploughing (Fernández-Alés et al 1993), and to strategies of soil water uptake (Golluscio and Sala 1993).…”