Neighbourhood-based spatial patterns of forest structure in Picea mexicana stands of northern Mexico

Quantitative assessment of forest structure provides insights into stand dynamics, as species mixing, size variability, and spatial arrangement influence regeneration, competition, and long-term population viability. We analysed three areas where Picea mexicana Martínez occurs on Cerro Mohinora in Chihuahua, Mexico, using data from 25 permanent plots to characterise stand structure and spatial patterns. The study integrates neighbourhood-based indices and spatial point-pattern analysis to describe stand heterogeneity and scale-related spatial structure in this endangered conifer. Horizontal structure was described using species mingling (Mi), dominance (Ui), and dimensional differentiation (Ti), while spatial structure was analysed using the Clark and Evans index (CE), the uniform angle index (Wi), the mean directional index (Ri), and the L(t) function. Species segregation was assessed using Pielou’s index (P′). The stands showed intermediate species mixing (Mi = 0.57-0.59), moderate dominance (Ui = 0.60-0.67), and moderate dimensional differentiation (Ti = 0.54-0.64), reflecting heterogeneous conditions typical of uneven stand development. Spatial analyses indicated aggregated patterns, particularly at short distances, and Pielou’s index revealed positive conspecific segregation of Picea mexicana. These results show that the spatial distribution of P. mexicana is mainly determined by micro-environmental conditions, shade tolerance and successional dynamics rather than by direct competitive exclusion. Structurally heterogeneous stands with preserved neighbourhood-scale organisation appear to provide favourable conditions for the persistence of this endangered species.