**2. Materials and methods**

Thirteen studies in central and southern Florida (27°–28°31′N, 80°–82°49′W) representing a range of *Eucalyptus* management options contributed to our analyses—(1) two *E. grandis* mulch wood studies, (2) two *E. grandis* cultivar planting density studies, (3) *E. grandis* x *E*. *urophylla* hybrid cultivar EH1 planting density demonstration, (4) EH1 fertilizer-planting density study at the Indian River Research and Education Center (IRREC), (5) five *E. grandis* WBs at Water Conserv II, Clermont, and the IRREC using BC, and (6) two *E. grandis* dendroremediation studies (**Table 1**).

#### **2.1** *E. grandis* **mulch wood plantations**

In central and south Florida, *E. grandis* mulch wood plantations are typically established at moderate planting densities (1495–1794 trees/ha) with 7–10 year rotations and re-established after two or three coppice stages. Mulch wood plantation management intensity is low," with all cultural treatments, such as chemical site preparation, single-pass bedding, and N + P fertilization implemented prior to planting. Post-establishment silvicultural treatments, such as herbaceous chemical release and mid-rotation fertilization, are uncommon in most mulch wood plantations throughout the entire management cycle, including the coppice stages.

The carbon sequestration and yield potential of improved *E. grandis* open-pollinated (OP) family seedlings and cultivar G2 clones under low operational culture were based on field demonstration Studies 1A and 1B, respectively, established on bedded cutover flatwoods sites on poorly drained, sandy Spodic soils. The planting density was 1495 trees/ha at a tree spacing of ≈ 1.8 m within row × 3.7 m between beds. Stem wood green weight estimates were based on felled tree samples and stand-level, whole-stem green weight estimates were fitted to the equation below using nonlinear regression [8]:

$$B(t) = e^{\left[b \circ c \times \ln(t) \circ d \times t\right]} \tag{1}$$

*Carbon Sequestration by Eucalypts in Florida, USA: Management Options Including Biochar… DOI: http://dx.doi.org/10.5772/intechopen.104923*


#### **Table 1.**

*Description of 13 Eucalyptus studies in Florida: location in FL, management option (mulch wood = MW, dendroremediation = DR). genotypes involved, soil type, culture (B = bedded, F = fertilized, H = herbicided, I = irrigated), planting density (trees/ha), and age (months) at final measurement.*

where *B(t)* = whole-stem green weight (metric tons/ha), *t* = stand age (years), and *b*, *c*, *d* are estimated parameters.

Stem wood carbon content was estimated as 25% of stem green weight. On sandy soils, 78% of total C sequestration for *E. grandis* was assumed to be in stem wood [16]. **Table 2** outlines the operational silvicultural treatments previously described, their associated costs, and stumpage and carbon price assumptions. Three coppice stages were assumed with coppice yields projected to be 80, 60, and 40% of the original stand for stages 2, 3, and 4, respectively.

#### **2.2** *E. grandis* **cultivar planting density studies**

Studies 2A and 2B on a phosphate mine clay settling area and former citrus beds, respectively, assessed the effect of planting densities (**Table 1**) on the biomass production of three *E. grandis* cultivars (G2, G3, and G5). Stand-level whole-stem green weight estimates (based on felled and standing trees in Florida) for each planting density were calculated by Eq. (1) using nonlinear regression [8]. The carbon content of stem wood was again assumed to be 25% of stem green weight.

The economic assumptions in **Table 2** were coupled with the assumptions that 78% of total C sequestration for *E. grandis* on sandy soils is in stem wood [16] and that response to BC followed that observed in Study 5E. Yields in two coppice rotations


#### **Table 2.**

*Management costs and timber stumpage and carbon credit assumptions for two management options for E. grandis grown on sandy soils in central and southern Florida.*

were projected to be 80 and 60% of the original stand for fertilization only and 90 and 80% of the original for fertilization + BC [18]. The application of BC priced at \$750 and \$1,000/ton assumed a 7% growth increase per ton of BC.
