Size Variability and Spatial Pattern in Neighbourhoods of Small and Large Trees in Elephant Camp Natural Forest of Omo Forest Reserve, Nigeria

Competition represents the effect of distance and size of neighbouring trees. Relationship between distance and size differs due to spatial mixture of trees, and this may make no single tree size variable consistently related to distance. Hence, neighbourhood effect on trees due to competition is difficult to quantify. However, using relationship between size variable and optimum distance to detect competition provides understanding of mechanism structuring arrangement of trees in Elephant Camp Natural Forest. This study was designed to investigate size variability and spatial patterns of trees in the neighbourhoods of small and large trees in Elephant Camp Natural Forest, Nigeria. Four parallel line transects of 1 km long spaced at 50‐m interval were demarcated in the study area. Five (30 × 30 m) sample plots were established on each transect. Minimum diameter‐at‐breast height (DBH) and maximum DBH trees were selected in each plot, assigned small and large reference trees, respectively. Subplot of radius = 10 m (314.2 m 2 ) was demarcated around each reference tree. Trees (DBH ≥ 5 cm) within subplot were enumerated, identified to species level, and DBH, canopy diameters and their distance to the reference tree were measured. Data collected were analysed using nearest neighbour statistics (Clark and Evans, species mingling and DBH differentiation indices) and Pearson correlation analysis at α 0.05 . A total of 24 and 24 tree species representing 906.0 and 910.0 trees/ha were identified in subplots of small and large reference trees, respectively. Ten per cent (10%) equal of subplots of small and large reference trees expressed significant positive correlation ( r = 0.61–0.91) and negative correlation ( r = −0.78–0.88) between distance and sum of DBH. Fifteen per cent (15%) of subplots of small and large reference trees expressed significant negative ( r = −0.71 to −0.91) and positive correlation ( r = 0.76–0.93) between distance and sum of canopy area. The magnitude of positive linear variation of canopy area ( r = 0.76–0.93) was more than DBH ( r = 0.61–0.91). Significant positive correlation occurred mostly at ≤ 4.6 m. Regular distribution was the dominant pattern at the four distance scales and frequency of aggregate and regular patterns increased with increase in radius around small and large trees. Aggregate pattern was limited to 0–4.0 and 0–6.0 m around small and large reference trees, respectively. Large reference trees expressed relatvely higher mingling ( M i = 0.81) at 8.00 m compared to small reference trees ( M i = 0.73; 8.40 m). Stem diameter and canopy area were are responsive to neighbourhood effect in small and large trees, respectively. Nearest neighbourhood model based on canopy area detected most competitive interactions in most tree communities. Aggregately and regularly arranged heterospecific neighbours played roles in structured of the tree communities around large and small reference trees, respectively.