Buttress root

Abstract: The formation of roots is in some respects one of the least fundamentally understood of all plant functions. Propagation by cuttings is the aspect that will occur first to most gardeners and horticulturists, and it is certainly the most useful application. But any observant traveller in the tropics can notice that some trees have the habit of forming roots in the air. Climbers like Cissus bear long fine strings of roots hanging down. Pandanus trees tend to have stout aerial roots issuing from the bases of the long branches, while the tangle of roots around the trunk of many of the Ficus species is characteristic. In Ficus bengalensis, in particular, stout cylindrical roots firmly embedded in the ground from a height of 3 to 5 meters give support to the long horizontal branches, enabling them to spread still further. In the big old specimen at Adyar near Madras, the spread of these branches all around the tree, each with a strong root growing out every few meters, makes a shaded area under which meetings of almost 5000 people are sometimes held. The history of how the formation of roots on stem cuttings was found to be under hormonal control is worth repeating here.

Abstract: Knowledge of the extent and distribution of tree root systems is essential for managing trees in the built environment. Despite recent ad- vances in root detection tools, published research on tree root architecture in urban settings has been limited and only partially synthesized. Root growth patterns of urban trees may differ considerably from similar species in forested or agricultural environments. This paper reviews literature documenting tree root growth in urban settings as well as literature addressing root architecture in nonurban settings that may contribute to present understanding of tree roots in built environments. Although tree species may have the genetic potential for generating deep root systems (>2 m), root- ing depth in urban situations is frequently restricted by impenetrable or inhospitable soil layers or by underground infrastructure. Lateral root extent is likewise subject to restriction by dense soils under hardscape or by absence of irrigation in dry areas. By combining results of numerous studies, the authors of this paper estimated the radius of an unrestricted root system initially increases at a rate of approximately 38 to 1, compared to trunk diameter; however, this ratio likely considerably declines as trees mature. Roots are often irregularly distributed around the tree and may be influ- enced by cardinal direction, terrain, tree lean, or obstacles in the built environment. Buttress roots, tap roots, and other root types are also discussed.

Abstract: Tree characteristics were recorded from 2829 standing trees in 24 0.25-ha terra firme forest plots in central Amazonia, 3 y after a surface fire had swept through the study area. Sixteen of the plots were within forest that burnt for the first time at the end of the 1997-98 El Nino (ENSO) event, and the remaining eight plots were within unburnt primary forest. In order to investigate the morphological correlates of tree mortality, we measured tree diameter at breast height (dbh) and bark thickness, and recorded burn height, bark roughness and the presence of latex, resin and buttress roots. Leaf litter depth was also recorded at the base of all trees in the unburnt forest. Using logistic regression models, tree mortality was best explained by the burn height, although dbh and the presence of buttresses were also important. Buttressed trees were associated with deeper leaf litter accumulation at their bases and higher char heights than trees without buttresses. Moreover, trees surviving the fire had significantly thicker bark than living trees in unburnt forest plots, indicating that thin-barked trees are more prone to selective mortality induced by heat stress. Latex did not appear to have had any significant effects on mortality, though resins were less abundant amongst the live trees in the burnt forest than in the unburnt controls. Levels of fire-mediated tree mortality in this study are compared with those in other Amazonian forest regions in light of historical factors affecting tree resistance to fires.

Abstract: Cyclones cause profound immediate impacts on tropical rainforest trees, including defoliation, limb loss, snapping of stems and uprooting. Some studies have shown that plant functional traits such as tree size, buttress roots and wood density are correlated with these forms of cyclone damage. On 20 March 2006, Severe Tropical Cyclone Larry crossed the north Queensland coast and proceeded inland across the Atherton Tablelands, impacting the critically endangered Mabi Type 5b rainforest. We investigated the effects of Cyclone Larry on common tree species by categorizing damage to trees as uprooted, snapped, limbs damaged (light, moderate, severe) or upright and estimating levels of defoliation. Damage was then related to functional traits including tree size, presence of buttress roots, wood density, and leaf size and strength. Levels of damage differed between species. Tree size (diameter at breast height) and the presence of buttress roots were not related to damage levels. Wood density was significantly negatively correlated to proportion of trees with snapped stems and significantly positively correlated with the proportion of trees upright with no or light limb damage. Levels of defoliation were significantly related to leaf strength (specific leaf area – SLA) and to leaf width, but not other components of leaf size (area or length) or petiole length. Species with high wood density and low SLA (e.g. Argyrodendron spp.) were found to have high cyclone resistance, the ability to resist damage, while species with low wood density and high SLA (e.g. Dendrocnide photinophylla) exhibited low resistance. However, traits related to low resistance are also those linked to rapid growth and high cyclone resilience, the ability to recover from damage, so it is unlikely that the Mabi forest will experience long-term changes in floristic composition following Cyclone Larry.