Comprehensive evaluation of windbreaks of fast-growing trees

View the project final report

Commodities

• Additional Plants: trees

Practices

• Crop Production: windbreaks

Single-row fast-growing cadaghi (Corymbia torelliana) windbreaks are as effective as multiple-row windbreaks in reducing wind. Although all studied windbreaks reduced wind and modified leeside microclimate, maximum reductions were obtained on the leeside of less porous windbreaks and when wind direction was perpendicular to the windbreak. Older windbreak trees had significantly more roots. Roots were confined to the top 50 cm of soil and had horizontal growth preference. Root number (N) was a significant variable for estimating root length density (LV). Oven-dry whole tree weight/100 m of windbreak length ranged from 802 to 20,145 kg for 2- to 20-year-old windbreaks.

Introduction

Windbreaks are used worldwide to mitigate wind-related agriculture problems. In the US Great Plains, windbreaks were planted from 1935 through 1942 in response to a decade long decrease in agricultural income, a series of dust storms and economic collapse in the wheat and corn belts. The primary objective was to stabilize microenvironment in the area. The National Windbreak Program in Australia started in 1993 to study the impact of windbreaks on microclimate and crop production (Cleugh et al., 2002). Both projects were successful and showed promising results (Munns and Stoecker, 1946; Cleugh et al., 2002). Windbreaks have also been used in South America (Peri and Bloomberg, 2002) and many developing countries (Nair, 1993). Apart from primarily reducing wind, windbreaks modifed microclimate (Cleugh, 1998, 2002; Peri and Bloomberg, 2002; Sudmeyer and Scott, 2002a; Brandle et al., 2004), reduced soil erosion and conserved nutrients (Sudmeyer and Scott, 2002a; Brandle et al., 2004; Kulshreshtha and Kort, 2009), and enhanced crop growth and increased crop yield (Cleugh, 1998; Nuberg et al., 2002; Sudmeyer and Scott, 2002b; Brandle et al., 2004). Windbreaks also provided many ecosystem services and environmental benefits including carbon sequestration and biodiversity conservation (Cleugh et al., 2002; Maize et al., 2008; Kulshreshtha and Kort, 2009). They also helped manage the spread of pathogens such as citrus canker (Xanthomonas campestris pv. citri) in South America and Australia (Leite and Mohan, 1990; Gottwald and Timmer, 1995; Muraro et al., 2001). Florida is one of the leading agricultural states in the nation. About 47,500 commercial farms produced a variety of crops, primarily vegetables and citrus, on approximately 3,743,348 ha in 2008. Florida was second in vegetable production and first in citrus production in the nation in 2007. Sales of vegetables alone exceeded $1.5 billion in 2008. The overall economic impact of Florida agriculture was estimated to be about $100 billion annually (FDACS, 2008). However, Florida agriculture still faces major challenges such as freezes, tropical storms and/or hurricanes, high winds, infertile soil, and diseases. Because of its geographical location, tropical storms and hurricanes from both Gulf of Mexico and Atlantic strike Florida frequently. Soil moisture is usually low because of the sandy soil and dry seasons. Also, Florida soils lack organic matter and cation exchange capacity (McAvoy, 2007), and nutrients easily leach during intense rain. Farms are also subjected to regular high winds. As wind eroded soils in Australia had large amounts of soil nutrients (Nuberg, 1998; Sudmeyer and Scott, 2002a), farms subjected to high winds are susceptible to soil erosion and nutrient loss. Florida’s citrus industry is severely impacted by citrus canker and greening (caused by Candidatus Liberibacter asiaticus). Wind scarring is another factor that reduces the quality of Florida agricultural products for fresh market (Albrigo, 1976; Miller et al., 1990; Miller and Burns, 1992; Núñez-Elisea and Crane, 1998; Morales and Davies, 2000; Núñez-Elisea and Crane, 2000; Stover et al., 2004). Wind scar occurs from sand abrasion and rubbing of plant parts primarily on young tender fruits. Therefore, windbreaks of ryegrass (Lolium perenne) (Workman et al., 2003) and sugarcane (Saccharum spp.) are used in vegetable farms to protect crops from wind damage. Wind speeds as low as 6.7 m s-1 have been reported to cause wind scarring in citrus (Metcalf, 1937). After extensive canker spread by 2004/05 hurricanes, windbreaks were promoted to manage canker in Florida and some citrus growers are planting windbreaks to protect citrus crop from canker and wind damages. Because of the urgency for windbreaks, fast-growing trees such as cadaghi (Corymbia torelliana), eucalypts (Eucalyptus grandis and E. amplifolia) and Australian pine (Casuarina spp.) are highly preferred due to their fast growth and evergreen nature. Cadaghi and eucalypts are not regulated in Florida, and are widely used in windbreaks (Rockwood et al., 2008). Though Australian pine is regulated because of its invasiveness, an amendment of the Florida Statute in 2009 allows commercial citrus growers only in Indian River, St. Lucie, and Martin Counties, where canker is widespread, to use Australian pine for windbreaks with a special permit. Among three species of Australian pine (C. glauca, C. equisetifolia and C. cunninghamiana) in Florida, C. cunninghamiana is considered the best for windbreaks because of its performance in other citrus growing countries and its least invasive potential (Castle et al., 2008). Trees are usually planted in multiple rows in windbreaks for optimum results, but windbreaks of only fast-growing species are rarely used. Because of limited space, current tree windbreaks in Florida are mostly of single rows. There are limited studies on the performance of fast-growing species windbreaks, planted either alone or in combination with other species (see Sun and Dickinson, 1997; Peri and Bloomberg, 2002). There is also little or no information available on the widely planted cadaghi. One of the major issues in windbreak planting is windbreak-crop competition. Competition for resources significantly impacted crop growth and reduced yield near windbreaks (Sudmeyer et al., 2002a, 2002b; Woodall and Ward, 2002; Unkovich et al., 2003). Therefore, above- and belowground competition must be minimized for optimal crop production. Compared to aboveground, belowground competition management is challenging because of the opaque soil. Underground competition near the windbreaks can be intense because fast-growing species produced relatively higher root length density (root length per unit volume of soil, LV) compared to slow-growing species (Coleman, 2007). Also, non-native species were generally competitive (Callaway and Aschehoug, 2000; Lopez-Zamora et al., 2004; Collins et al., 2007; Tamang et al., 2008). To manage underground competition effectively, information such as root architecture, distribution (both horizontal and vertical) and branching pattern is important. Carbon sequestration is an indirect benefit of windbreaks. When trees and shrubs are planted, carbon sequestration potential of farms significantly increases compared to monoculture crops. Incorporating multiple species in windbreaks increases nutrient use. Therefore, mixed species windbreaks can sequester carbon more efficiently. Along with the storage in aboveground parts, more than half of the carbon sequestered by trees is stored in the soil (Montagnini and Nair, 2004). Forests have received attention lately for their capacity to reduce carbon emissions, and extensive work has been done to estimate biomass in forests (Lambert et al., 2005; Cole and Ewel, 2006; Vallet et al., 2006; Alamgir and Al-Amin, 2008; Nogueira et al., 2008), but biomass production potential of windbreaks is little known and often neglected. For accurate biomass estimation of windbreaks, separate equations need to be developed for windbreak grown trees. In summary, windbreaks of different species and configurations have demonstrated potential for mitigating various wind-related agricultural problems across the globe (Gottwald and Timmer, 1995; Cleugh et al., 2002, Peri and Bloomberg, 2002; Brandle et al., 2004). Since wind-related agricultural issues in Florida are similar to those in other parts of the globe, windbreaks could potentially be used to mitigate such problems. However, single-row windbreaks and windbreaks of fast-growing trees such as that of cadaghi must be evaluated to see if they produce the same results and benefits of other multiple-row windbreak species. Root distribution of windbreak trees also need to be studied to effectively manage underground competition.

This study was conducted to evaluate single-row cadaghi windbreaks in southern Florida. The objectives were to study (a) single-row cadaghi windbreak function and its effect on microclimate, (b) root distribution of windbreak grown cadaghi trees, and (c) biomass in various aged cadaghi windbreaks. The hypotheses of this research were: Hypothesis 1: Single-row cadaghi windbreaks reduce wind and modify microclimate. Hypothesis 2: Older cadaghi trees produce comparatively more roots and number of roots (N) is a good predictor of root length density (root length per unit volume of soil, LV).