Improving methods in gap ecology: revisiting size and shape distributions using a model selection approach

Abstract

Questions We assess gap size and shape distributions, two important descriptors of the forest disturbance regime, by asking: which statistical model best describes gap size distribution; can simple geometric forms adequately describe gap shape; does gap size or shape vary with forest type, gap age or the method used for gap delimitation; and how similar are the studied forests and other tropical and temperate forests? Location Southeastern Atlantic Forest, Brazil. Methods Analysing over 150 gaps in two distinct forest types (seasonal and rain forests), a model selection framework was used to select appropriate probability distributions and functions to describe gap size and gap shape. The first was described using univariate probability distributions, whereas the latter was assessed based on the gap area–perimeter relationship. Comparisons of gap size and shape between sites, as well as size and age classes were then made based on the likelihood of models having different assumptions for the values of their parameters. Results The log‐normal distribution was the best descriptor of gap size distribution, independently of the forest type or gap delimitation method. Because gaps became more irregular as they increased in size, all geometric forms (triangle, rectangle and ellipse) were poor descriptors of gap shape. Only when small and large gaps (> 100 or 400 m2 depending on the delimitation method) were treated separately did the rectangle and isosceles triangle become accurate predictors of gap shape. Ellipsoidal shapes were poor descriptors. At both sites, gaps were at least 50% longer than they were wide, a finding with important implications for gap microclimate (e.g. light entrance regime) and, consequently, for gap regeneration. Conclusions In addition to more appropriate descriptions of gap size and shape, the model selection framework used here efficiently provided a means by which to compare the patterns of two different types of forest. With this framework we were able to recommend the log‐normal parameters μ and σ for future comparisons of gap size distribution, and to propose possible mechanisms related to random rates of gap expansion and closure. We also showed that gap shape varied highly and that no single geometric form was able to predict the shape of all gaps, the ellipse in particular should no longer be used as a standard gap shape.

Assessment of Natural Regeneration of Different Forms of Gaps in Atrush Forest

“…The spaces for the first category (X < 200) find that the triangular, oval, regular and irregular shape form the proportions (6, 30, 37 and 27%), respectively, and that the oval and regular forms are (67 %) of the first category spaces. This is consistent with what he indicated (De Lima et al, 2013). This is repeated with gaps with areas (400 < X < 200) m 2 where the triangular, oval, regular and irregular shapes form the proportions (9, 28, 39 and 24 %) respectively, and we find that the oval and regular shape forms a total of (67 %) of the second category areas.…”

“…While we find that the triangular shape formed a percentage (8 %) of the total shapes of gaps distributed in different proportions over the space categories for the gaps, where we find in the small area category (X < 200) m 2 the shape of the ratio (34 %), and in the second area category (200 < X < 400) m 2 ratio (25 %), while in regular forms of the fourth area category are (71 %), and this indicates that the oval and regular forms are the most common forms in the gaps, and there is no doubt that regular forms are prevalent in the study site (Guo et al, 2019;Pawlikowski et al, 2019;De Lima et al, 2013…”

“…The distribution of gaps in the study site was different in form, as they appeared in a triangular, oval, regular and irregular shape (De Lima et al, 2013). So the difference in the shapes between the gaps with different categories of areas and the same category of area, and this is what was estimated in Table (2 We find that Table (2) determines the numbers of gaps and their shapes for each area category, and from it we note the numbers of small gaps that come at the forefront for each category (X < 200) m 2 and (200 <X < 400) m 2 where the number of gaps in the first category (X < 200) ( 855) is a problem gap (48%) of the total gaps, followed by the second category (200 < X < 400) in which the number of gaps was (444) and formed a ratio of (25 %), while the third category (400 < X < 600), as the number of its gaps was (171) a problem formed by that (10 %) of the total gaps, while the number of gaps in the fourth and large category (X > 600) was ( 316) a gap and a percentage (17 %) of Total Gaps (Sapkota and Odén, 2009;Zeibig et al, 2005).…”

“…From the foregoing, we find that the regular and oval shape formed the largest percentage of shapes, where their proportions were (41 and 27 %) respectively, which means a total of (68 %) of the forms of total gaps. This means that the regular and oval shape of the gaps are the predominant forms in the forests, And that the determination of simple geometric shapes varies according to the type, age, and area of the forest (De Lima et al, 2013). Also, these shapes showed the random distribution of the shape of the gap over the gap areas (Dusan, et al, 2007).…”

O balanço de carbono em paisagens tropicais antropizadas

“…Most of the used a minimum diameter at breast height (DBH) as their inclusion criterion, but other surveys used diameter at ground height (DGH) or a minimum height (H). To simplify the analysis, we first grouped the original dbh cutoff criteria into some major dbh classes 3 (2.8-3.2), 5 (4.8-5.0) and 10 centimeters.Then, we obtained an equivalent value of dbh for those surveys using criteria such as diameter at ground height or a minimum height criterions, using the following equations:(A1.1) DGH= 0.7814 + 1.269*DBH, (A1.2) DBH = 1.656e-01 + 1.087e-02*H.This allometric relationships were obtained from data collected byLima (2013) which contained measurements of DBH, DGH and H. The conversion between DBH and DGH presented above is in line with the conversion obtained using the equation ofGehring et al (2008), but we decided to use ours equation because it was obtained from data collected in a stretch of Atlantic Forest of São Paulo state.…”