Spatial Patterns of Canopy Disturbance and Shortleaf Pine in a Mixedwood Forest

The spatial structure of forest ecosystems is dominated by the horizontal and vertical distribution of trees and their attributes across space. Canopy disturbance is a primary regulator of forest spatial structure. Although the importance of tree spatial pattern is widely acknowledged as it affects important ecosystem processes such as regeneration and recruitment into the overstory, quantitative reference spatial conditions to inform silvicultural systems are lacking. This is especially true for mixedwood forests, defined as those that contain hardwoods and softwoods in the canopy. We used data from a preexisting network of plots in a complex-stage mixedwood stand to investigate the influence of canopy disturbance on stand and neighborhood-scale spatial patterns. We reconstructed canopy disturbance history and linked detected stand-wide and gap-scale disturbance events to establishment and spatial patterns of shortleaf pine. The majority of shortleaf pine establishment coincided with stand-wide or gap-scale disturbance. Shortleaf pine was clustered at the stand scale but was randomly distributed at the neighborhood scale (i.e. five tree clusters), which was a legacy of the historical disturbance regime. These results may be used to improve natural disturbance-based silvicultural systems to restore and maintain mixedwood forests for enhanced resilience and provisioning of ecosystem goods and services. Study Implications: Shortleaf pine was clustered into compositionally distinct patches within the oak-pine stand. Based on our findings, we recommend managers of stands with patchy species composition consider silvicultural systems that focus on patches. This approach acknowledges the effects of intrastand spatial variability of biophysical conditions and interactions with stochastically occurring canopy disturbances on regeneration and recruitment. Patch clearcuts with reserves could be implemented with the openings correspondent to microsites that favor regeneration of shortleaf pine. Similar potential approaches could be seedtree, irregular shelterwood, and other regeneration methods suited to stand conditions and the silvics of the species of interest.

Tree recruitment, growth, and distribution at the circumpolar forest–tundra transition: introduction

Causes and consequences of changes in the circumpolar forest–tundra transition have received recent interest due to the increasing awareness of human-caused global climate change. The International Polar Year core project PPS Arctic focused these topics through exploring processes, changes, and spatiotemporal variability of biotic and abiotic drivers of change in the forest–tundra transition. The papers in this special feature present constraints and drivers of tree recruitment and tree encroachment of tundra areas, climate – tree growth relations in the ecotone, and changes in tree spatial pattern across the forest–tundra ecotone.

Tree spatial pattern within the forest–tundra ecotone: a comparison of sites across CanadaThis article is a contribution to the series Tree recruitment, growth, and distribution at the circumpolar forest–tundra transition.

Although many studies have focused on factors influencing treeline advance with climate change, less consideration has been given to potential changes in tree spatial pattern across the forest–tundra ecotone. We investigated trends in spatial pattern across the forest–tundra ecotone and geographical variation in the Yukon, Manitoba, and Labrador, Canada. Tree cover was measured in contiguous quadrats along transects up to 100 m long located in Forest, Ecotone, and Tundra sections across the forest–tundra transition. Spatial patterns were analyzed using new local variance to estimate patch size and wavelet analysis to determine the scale and amount of aggregation. Compared with the Forest, tree cover in the Ecotone was less aggregated at most sites, with fewer smaller patches of trees. We found evidence that shorter trees may be clumped at some sites, perhaps due to shelter from the wind, and we found little support for regular spacing that would indicate competition. With climate change, trees in the Ecotone will likely become more aggregated as patches enlarge and new patches establish. However, results were site-specific, varying with aspect and the presence of krummholz (stunted trees); therefore, strategies for adaptation of communities to climate change in Canada’s subarctic forest would need to reflect these differences.

Control of plot edge bias in forest stand growth simulation models

Techniques for reducing edge bias are discussed and a new approach, termed the linear expansion method, is presented. This method is applicable to a wide variety of plot shapes and sizes and is unbiased under very general assumptions about the forest tree spatial pattern. The accuracy and efficiency of the linear expansion method were compared with (i) no edge bias correction and (ii) corrections by plot image translation techniques for several forest stands and spatial patterns. Results indicated translation and the linear expansion method behaved equally well on square plots 0.08 ha in size. As the plot size diminished or its shape deviated from square, the linear expansion method provided greater accuracy and lower bias than translation techniques. The linear expansion method also provided useful accuracy on circular plots where translation was not feasible.