Spatial contiguity and continuity of canopy gaps in mixed wood boreal forests: persistence, expansion, shrinkage and displacement

Abstract

Summary 1. Variation in forest gap size and duration are a result of spatial contiguity and continuity of gap infilling and tree mortality over time, which influences both species recruitment and successional pathways. 2. As many gaps in boreal forests are small, their size and duration will affect the conditions influencing species recruitment. We investigate the spatial dynamics of these gaps (i.e. those which are persistent, ephemeral, expanding, displaced or disappearing) and tested whether gap spatio‐temporal patterns are consistent over different temporal periods (1998–2003 and 2003–2007). 3. Forest canopy gaps were reconstructed for three plots (10, 10 and 6 ha in size) in southern boreal mixedwood forests around Lake Duparquet, north‐western Quebec (Canada), using a time series of high‐resolution canopy surface profiles from three light and ranging detection (lidar) system surveys during a 9‐year window. High‐resolution images were used to individually identify early and late successional gap makers. Dynamic changes in canopy gaps over a 9‐year period were investigated by implementing concepts of random set theory within a temporal GIS framework. Mortality was higher on the gap edges than in the forest interior, and shade tolerant species were more likely to be gap makers than shade intolerant species. Edge trees that died causing the expansion of gaps were much smaller than trees creating new gaps. Although the overall gap size distribution was consistent over the 9 years studied, the proportion of the total area opening and closing varied between periods. Independent analyses of time windows show an abundance of small gaps (below 40 m2) appearing and disappearing; however, analysis of spatial contiguity shows that the majority (over 80%) of gaps of all sizes were displaced and/or expanded. 4. Synthesis. Contrary to the previous perception that small gaps are ephemeral, which would favour the recruitment of late successional species, our findings indicate that gap displacement and expansion may be a mechanism explaining the maintenance of favourable conditions for the recruitment of shade intolerant individuals, which has been previously observed in high‐latitude old‐growth boreal forests.

Automated Detection of Forest Gaps in Spruce Dominated Stands Using Canopy Height Models Derived from Stereo Aerial Imagery

“…Gap size and distribution pattern were mapped from satellite imagery by Garbarino et al [23] and Hobi et al [24]. Vepakomma [25,26] used Light Detection and Ranging (LiDAR) to assess spatial contiguity and continuity of canopy gaps over time in mixed wood boreal forests. Rugani et al [27] based a similar research question using visual stereo interpretation of scanned color-infrared (CIR) aerial photographs.…”

Gap closure process by lateral extension growth of canopy trees and its effect on woody species regeneration in a temperate secondary forest, Northeast China

“…Gap dynamics in a landscape level have been detected widely recent years with the help of remote sensing technology (Andersen et al 2014). For example, Vepakomma et al (2012) characterized the gap dynamics over a 9-year period in a natural old-growth boreal forest based on Lidar monitoring, and found that gaps changed in various ways. However, these large-scale studies may not be suitable for acquiring detailed closure information which is closely related to species regeneration (Getzin et al 2014).…”

Gap formation following climatic events in spatially structured plant communities

“…Large gaps and gap centres are often colonized by light-demanding pioneer species1213, while small gaps are occupied more by shade-tolerant ones14. Small openings are also more frequently filled by clonal growth, whereas successful establishment via seed germination prevails in larger gaps15.…”