The Management of Tree Root Systems in Urban and Suburban Settings II: A Review of Strategies to Mitigate Human Impacts

Abstract

Root systems of nearly all trees in the built environment are subject to impacts of human activities that can affect tree health and reduce longevity. These influences are present from early stages of nursery development and throughout the life of the tree. Reduced root systems from root loss or constriction can reduce stability and increase stress. Natural infection of urban tree roots after severing has not been shown to lead to extensive decay development. Roots often conflict with infrastructure in urban areas because of proximity. Strategies to provide root space under pavements and to reduce pavement heaving have been developed, but strategies for prevention of foundation and sewer pipe damage are limited to increasing separation or improved construction.

Evaluating the effects of trenching on growth, physiology and uprooting resistance of two urban tree species over 51-months

“…Nonetheless, previous experiments which used winching tests to investigate the reductions in rotational stiffness of trenched trees confirmed the little short-term effect of excavation damage on uprooting resistance, mostly due to the contribution of sinker roots to tree stability (Ghani et al, 2009). Few studies have evaluated so far the early impact of root severance on tree mechanical stability, but none, to our knowledge, has clarified the capacity of trees to re-establish their safety factor after a relief period that allowed trees to recover the severed roots (Forcaud et al, 2008;Watson et al, 2014). When the winching test was conducted again, four years after severance, differences in bending moment between control and severed trees were maintained or even increased.…”

“…Consistently, early research on root severance found that tree losses can increase up to 44% following severance (Morell, 1984) and that leaf wilting can occur within a few hours after roots are damaged (Hamilton, 1988). After reviewing a series of studies on root severance, however, Watson et al (2014) found that the impact of excavation on tree health was much lower than expected and that symptoms may not be visible for several years after the roots have been severed.…”

“…the ability to recover to the pre-damage condition) displayed by woody trees to excavation and hypothesized increased sensitivity of trees with severed roots to water stress (Wajja-Musukwe et al, 2008;North et al, 2017). A widespread conclusion of these studies was that root severance presumably caused stress, but neither the stress was measured directly, nor its effects on plant physiology characterized (Watson, 1998;Watson et al, 2014).…”

Interactive responses of root and shoot of camphor tree (Cinnamomum camphora L.) to asymmetric disturbance treatments

“…The connotation of root–shoot balance should not be limited to the mere root to shoot biomass partitioning, since the latter is a poor indicator of tree stability ( Nicoll et al., 1995 ). Reduced/restricted root systems, asymmetric root systems, and asymmetric crowns can reduce stability ( Watson et al., 2014 ; Tomao et al., 2015 ), indicating the importance of architectural elements. For example, wind-induced asymmetries can affect the below- and above-ground organs of trees, and a tree with an asymmetrical or restricted root system may be less stable.…”

Table_1.XLSX

“…For example, increasing canopy cover is a goal for many communities (Hauer and Peterson, 2016), so prioritizing a search for largestature underutilized trees could help address this secondary goal and help maximize ecosystem services provided by urban trees (McPherson et al, 2005). On the other hand, highly urbanized planting spaces under public management, such as sidewalk tree pits or planting sites under utility lines, can have restricted room for tree growth (Watson et al, 2014;Nguyen et al, 2017), and requiring small-stature species (Magarik et al, 2020). In this case, it may be more favorable to search for underutilized smallstature trees.…”