Arboriculture & Urban Forestry 46(3): May 2020 Table 1. Main characteristics of the sampled areas in the study sites. Study site Altitude (m a.s.l.) Palermo 90 Sampled area (m²) 1,000 Slope Plain (< 5%) Citrus spp., Eriobotrya japonica, Celtis australis, Laurus nobilis Roccapalumba a.s.l.: above sea level through 20, and so forth) to standardize the number of sampling units. Then, we obtained the walnut density for both sites based on the specific sampled area of each sampling unit (100 m2 and 60 m2 for “Palermo” and “Roccapalumba,” respectively). Once density data fit a normal distribution (Shapiro-Wilk, W = 0.91, P = 0.07) and had equal variance (Levene’s index = 0.06, P = 0.8), we ran a t-test to check for dif- ferences in the density of naturalized walnuts between “Palermo” and “Roccapalumba.” Once climatic data did not follow a normal distribution, we compared the data (monthly values) between the two orchards using the nonparametric Kruskall-Wallis test. RESULTS The density of naturalized walnut individuals was higher in “Palermo” (200 ha-1 lumba” (75 ha-1 ) than in “Roccapa- ), with statistically significant differ- ences (t = -2.62, P = 0.02). In “Palermo,” the individuals were found scattered over the transects, whereas in “Roccapalumba,” all individuals were found beneath prickly pear plants. We found self- sown seedlings up to 50 cm high from the last fruiting season, thus being less than 1 year old (Figure 2). In “Palermo,” we also observed the tallest individuals, 3.8 m and 4.8 m high, aged 3 and 4 years, respec- tively, as assessed by the counting of the annual rings. In “Roccapalumba,” the tallest individual was 2.8 m high, with an estimated age of 2 to 3 years (Figure 3). There were significant differences in all climatic vari- ables between the two sites, with all values higher in “Palermo” (Table 2). Direct observations carried out on the mature walnut trees existing in “Palermo” allowed us to repeatedly notice, during the whole period of fruit ripening, hooded crow individuals (Corvus cornix L.) visiting the walnut canopies carry- ing nuts in their beaks (Figure 4). Interestingly, crows dropping the nuts on the ground in an attempt to crack out the shell were also observed. In “Roccapalumba,” we observed Corvus cornix and Pica pica L. (mag- pie) using prickly pear cladodes as perches, although no direct interaction with walnuts was recorded. In both areas, walnuts were found to be preyed upon by rats (personal observation). Figure 2. The natural regeneration of walnut in “Palermo” orchard, which includes: (A) two-year-old juveniles which resprouted after cutting; (B) one-year-old self-sown seedling, still bearing at the base the original nut (you can see the detail on the left); (C) a young individual 4.8 m high. ©2020 International Society of Arboriculture 455 600 Plain (< 10%) Opuntia ficus-indica 70% Typic (within rows) pelloxererts None Mowing and tillage only in the inter-rows 177 Dominant tree species Mean canopy cover (%) 90% Soil type Irrigation Understory input (mm) management Typic rhodoxeralfs 500 Mechanical weed control
May 2020
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