Crown architecture, crown leaf area distribution, and individual tree growth efficiency vary across site, genetic entry, and planting density

Citrus yields have declined by almost 56% since Huanglongbing (HLB) was first found in Florida (2005). That reduction forced citrus growers to replant trees at much higher densities to counter-balance tree loss. The current project aims to determine how much water is required to grow citrus trees at higher planting densities without reducing their productivity. The study was initiated in November 2017 on eight-month-old sweet orange (Citrus sinensis) trees grafted on the ‘US-897′ (Cleopatra mandarin × Flying Dragon trifoliate orange) citrus rootstock planted in the University of Florida, Southwest Florida Research and Education Center (SWFREC) demonstration grove, in Immokalee, FL (lat. 26.42° N, long. 81.42° W). The soil in the grove is Immokalee fine sand (Sandy, siliceous, hyperthermic Arenic Alaquods). The demonstration grove included three densities on two rows of beds (447, 598, and 745 trees per ha) replicated four times each and three densities of three rows of beds (512, 717, 897 trees per ha) replicated six times. Each density treatment was irrigated at one of two irrigation rates (62% or 100%) during the first 15 months (2017–2019) then adjusted (2019–2020) to represent 26.5, 40.5, 53, and 81% based on recommended young citrus trees evapotranspiration (ETc). Tree growth measurements including trunk diameter, height, canopy volume, leaf area, and root development were evaluated. During the first year, reducing the irrigation rate from 100% to 62% ETc did not significantly reduce the young citrus tree growth. Conversely, the lower irrigation rate (62% ETc) had increased citrus tree’s leaf area, canopy volume and tree heights, root lifespan, and root length by 4, 9, 1, 2, and 24% compared with the higher irrigation rate (100%), respectively. Furthermore, the root lifespan was promoted by increasing planting density. For instance, the average root lifespan increased by 12% when planting density increased from 447 to 897 trees per ha, indicating that planting young trees much closer to each other enhanced the root’s longevity. However, when treatments were adjusted from April 2019 through June 2020, results changed. Increasing the irrigation rate from 26.5% to 81% ETc significantly enhanced the young citrus tree growth by increasing citrus tree’s canopy volume (four fold), tree heights (29%), root lifespan (86%), and root length (two fold), respectively. Thus, the application of 81% ETc irrigation rate in commercial citrus groves is more efficient for trees from two to four years of age.

Download Full-text

Increased Individual Tree Growth Maintains Stand Volume Growth after B-Level Thinning and Crop-Tree Management in Mature Oak Stands

Forest Science ◽

10.1093/forsci/fxz042 ◽

2019 ◽

Vol 65 (6) ◽

pp. 784-795

Author(s):

Jeffrey S Ward ◽

Jessica Wikle

Keyword(s):

Tree Growth ◽

Growth Response ◽

Volume Growth ◽

Diameter Growth ◽

Red Oak ◽

Individual Tree ◽

Stand Volume ◽

Tree Management ◽

Individual Tree Growth ◽

Partial Release

AbstractSix study areas were established in 80–125-year-old upland oak stands on average sites to compare stand and individual tree growth response following two active treatments (B-level thinning, crop tree) with an unmanaged control. Initial stocking of 104 percent was reduced to 62 percent and 60 percent on the B-level and crop-tree-management plots, respectively. Approximately 7,200 board feet per acre (International ¼) were harvested on the actively managed plots with upland oaks accounting for 81 percent of pre- and 86 percent of residual stand. Eleven-year diameter and volume growth of oak sawtimber trees was greater on actively managed plots. Growth response increased with degree of release and was maintained for the length of the study. Because of the increased individual tree growth of oaks in response to release, stand volume growth of oak sawtimber did not differ between treatments. In contrast to an 11-year decline of poletimber stocking on unmanaged plots, poletimber stocking increased on managed plots as diameter growth increased in response to partial release. This may increase difficulty of regenerating oak in the future. For those mature red oak stands where traditional regeneration prescriptions will not be implemented or will be delayed, commercial harvests can be conducted without compromising stand volume growth of oak.

Download Full-text

Mechanism for the enhanced effect of mowing followed by glyphosate application to resprouts of perennial pepperweed (Lepidium latifolium)

Weed Science ◽

10.1614/ws-03-024r ◽

2004 ◽

Vol 52 (1) ◽

pp. 14-23 ◽

Cited By ~ 16

Author(s):

Mark J. Renz ◽

Joseph M. DiTomaso

Keyword(s):

Leaf Area ◽

Plant Architecture ◽

Canopy Structure ◽

Field Studies ◽

Herbicide Application ◽

Deposition Pattern ◽

Application Timing ◽

Spray Solution ◽

Area Distribution ◽

Leaf Area Distribution

Herbicides currently registered for use near water have been ineffective for control of perennial pepperweed. Previous research has demonstrated that mowing followed by an application of glyphosate at 3.33 kg ae ha−1to resprouting tissue can enhance the control of perennial pepperweed. The objectives of this study were to determine the mechanism(s) responsible for the enhanced effectiveness of glyphosate in combination with mowing. Mowing plants altered the leaf area distribution within the canopy. In mowed areas, the majority of leaf area was in the basal third of the canopy, whereas the bulk of the leaf area was in the top third of the canopy in unmowed plots. This change in plant architecture affected the deposition pattern of the spray solution. Unmowed plants retained 49 to 98% and 42 to 83% of a dye solution within the middle and top thirds of the canopy at the Colusa and Woodland sites, respectively, with only 1.9 to 6.0% dye deposited on the basal third of the canopy at both sites. In contrast, mowed plants had 18 to 34% and 26 to 70% of the dye retained in the basal third of the canopy at the Colusa and Woodland sites, respectively. Greenhouse studies showed that14C-glyphosate applied to basal leaves of mowed plants translocated significantly more to belowground tissue. Unmowed plants accumulated 0.37% of the applied14C-glyphosate in belowground tissue 48 h after labeling. In contrast, mowed plants accumulated 6.7%14C-glyphosate in the belowground tissue. In field studies, estimates of basipetal seasonal translocation rates using total nonstructural carbohydrate pools of roots indicate that mowing did not change the translocation rate. However, the delay in application timing to allow plants to resprout appeared to synchronize applications with maximal translocation of carbohydrates to belowground structures. We hypothesize that the change in the canopy structure of perennial pepperweed after mowing results in fewer aboveground sinks and greater deposition of herbicide to basal leaves where it can preferentially be translocated to the root system. Furthermore, the delay between mowing and resprouting synchronized maximal belowground translocation rates with herbicide application timing. These factors all appear to be involved in the observed enhanced control of perennial pepperweed when combining mowing and glyphosate.

Download Full-text

Growth response to thinning and its relation to site resources in Eucalyptusregnans

Canadian Journal of Forest Research ◽

10.1139/x95-009 ◽

1995 ◽

Vol 25 (1) ◽

pp. 69-80 ◽

Cited By ~ 27

Author(s):

P.W. West ◽

G.H.R. Osier

Keyword(s):

Biomass Production ◽

Tree Growth ◽

Aboveground Biomass ◽

Growth Response ◽

Radiation Absorption ◽

Light Use Efficiency ◽

Individual Tree ◽

Individual Tree Growth ◽

Use Efficiency ◽

Individual Trees

The factors determining individual tree growth response are examined during the 4 years following thinning in experiments in even-aged, 8- or 12-year-old regrowth Eucalyptusregnans F. Muell. forest at two sites in southern Australia. At one site, a vigorous understorey dominated by a sedge developed after the thinning. At that site, light-use efficiency by the trees was unaffected by thinning and the aboveground biomass production by the trees in the thinned stand was substantially less than that in the unthinned stand. At the other site, little understorey developed, light-use efficiency by trees in the thinned stand was greater than that in the unthinned stand, and aboveground biomass production was unaffected by thinning even though the leaf weight of the thinned stand was far below that of the unthinned stand. Where the understorey developed, it was concluded that it competed successfully with the trees for water, thereby reducing production in the thinned stand when compared with the unthinned stand. The individual tree growth response that occurred in the thinned stand at that site appeared to be due soley to the extra light available to individual trees following the canopy opening. Where the understorey did not develop, it was concluded that individual tree growth response was due not only to the extra light available to individual trees but also to the increased availability of belowground resources, most probably soil water. Application of a pre-existing stand growth model suggested that at that site the tendency for increased growth resulting from extra water availability in the thinned stand was just balanced by decreased growth due to lower radiation absorption by the reduced canopy, so that net production was unaffected by thinning.

Download Full-text