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Throughout eastern North America, chronic white-tailed deer overbrowsing and widespread exotic plant invasions degrade native plant diversity and abundance. However, because deer densities are high across entire regions, it is challenging to find large areas where deer have been at low density for long periods. We predicted native plant diversity and abundance would be significantly higher during gap-phase regeneration where deer have been maintained at low densities (~ 7 deer/km²) compared to where deer have been chronically overabundant. Simultaneously, we predicted that exotic plant diversity and abundance would be lower in gaps where deer have been maintained at low versus high densities. We also evaluated whether deer density interacts with gap age, gap size, and gaps in dry versus more mesic forest patches. We studied 41 gaps throughout an 88 km2 fenced military post where deer were maintained near pre-European-settlement densities for 67 years and in nearby forests where deer have been overabundant for decades. Native species richness, diversity, and cover were 37–65% higher, and exotic species cover was 80% lower in canopy gaps at low relative to high deer density. Stem height and density of multiple native canopy tree species (e.g., two Quercus spp.) were 5-20-fold higher within canopy gaps at low deer density. Moreover, 10 native woody species were indicators of low deer density, including three Quercus species, whereas no native woody species were indicators of high deer density. Deer were the primary filter underlying these different patterns in diversity, abundance, and plant height. Our findings demonstrate that gaps develop a vigorous and diverse native sapling layer, with far fewer exotics, in areas of low deer density without a history of chronic overbrowsing. We propose that military posts may be conservation and native plant regeneration hotspots wherever they regularly cull deer. [ABSTRACT FROM AUTHOR]

Retention forestry is replacing clear-cutting as the dominant silvicultural practice in many parts of the world. Higher retention levels are thought to promote faster, more complete ecological recovery after logging, but this hypothesis is insufficiently tested. We compared plant community dynamics in 0%, 40% and 70% retention stands to unharvested stands for 24 years after logging at the Date Creek Research Forest near Kispiox, BC, Canada. The study has a before-after control-impact experimental design with four replicates of each treatment. For terricolous understory plants, we used the similarity of cover, species richness and composition to pre-harvest and unharvested conditions as indicators of ecological integrity. Changes in cover, richness and composition were greatest at 0% retention. For nonvascular plants, changes were generally intermediate at 40% retention and smallest at 70% retention, and recovery increased with retention. The dominant moss Hylocomium splendens responded negatively to harvest in proportion to retention level, while most other species responded positively, shifting community composition. Most vascular plants responded positively to harvest, especially at 0% retention, with the exception of two late seral species, Platanthera orbiculata and Oplopanax horridus . Generally, understory communities in these largely unfragmented northern cedar-hemlock forests displayed less sensitivity to low retention levels than studies conducted elsewhere. For some vascular plant indicators, changes at 70% retention were equal to or greater than those at 40%. Thus, most -but not all- vegetation responses supported the hypothesis that higher retention enhances ecological recovery after logging. The non-linear results were apparently driven by suppression of understory conifer growth in small gaps at 70% retention and illustrate that evaluating ecological integrity strictly in terms of departure from an un-impacted benchmark system risks oversimplifying complex forest dynamics. [ABSTRACT FROM AUTHOR]

Aim: We studied the legacy effects of shrubs during the downgrade phase of high-cover patches. Specifically, are woody species able to modify environmental attributes at patch level to such an extent as to alter the colonization once they have vacated their original position? Methods: We monitored five environmental variables along an experimental four-stage downgrading gradient of high-cover patches during two years in cold- and warm-seasons, individual plant growth during three years, as well as the floristic composition of patches along the same gradient after 13 years. Results: The downgrade of high-cover patches reduces the aboveground protection due to the increase in wind speed (400-500%) and evaporation rate (43-160%) associated with shrub death and senescence. In addition, high-cover patches increase the total soil nitrogen (400-600%) and reduce the infiltration rate (44-73%) on the top layer. Leaf length and flower culms of grass tussocks were lower in bare soil patches (7.5 cm and 3) compared to whatever degradation stage of high-cover patches (9-10 cm and 18-32). Floristic composition after 13 years reveals that grass species occupied the patch stages differentially, with a disjunctive pattern among species within the Poa and Pappostipa genus. Conclusions: Legacy effects prompted by shrubs through changes in soil properties at the horizontal plane can conditioned the patch dynamics. The ability of different plant species to cope with the spatial heterogeneity at the horizontal plane should be included as a new criterion to define plant strategies from arid ecosystems according to the gap-phase dynamics and mosaic maintenance. [ABSTRACT FROM AUTHOR]

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Jones (1945) was a milestone paper exploring the natural forest concept with examples from the temperate and boreal ecosystems. It has become a classic because of its use of field observation of regeneration, succession and structure to assess theories about disturbance and the dynamic properties of natural forests. His main aim was to review some of the features of the structure and reproduction of the north temperate virgin forests, and this article presents, discusses and evaluates the main features of this legendary paper. Jones had international experience of both the ecological and silvicultural research communities and combined long-term field observations with theory to develop a realistic assessment of natural forest properties that formed the basis for current understanding. He demonstrated that natural disturbance regimes could generate a variety of structures and that a stable, 'climax' forest concept was often not supported by field data. He also showed that even-aged components are common in these forest ecosystems and that the recruitment of tree species proceeds irregularly even in undisturbed stands. His work has influenced subsequent development of related subjects such as disturbance theory, gap-phase dynamics and long-term vegetation changes and has left a legacy with practical relevance for nature conservation and silviculture. [ABSTRACT FROM AUTHOR]

1 Few studies have addressed the mechanisms of coexistence of shade-tolerant and intolerant tree species in the canopy of old-growth, lowland rain forests of southern South America. We explored the hypothesis that their forest dynamics result from frequent, single tree-fall gap episodes. 2 We analysed the disturbance regime and assessed the regeneration modes of shade-tolerant and intolerant canopy trees in a lowland, old growth North Patagonian rain forest in Chiloé Island (42° S) using dendroecological methods. 3 Dominant canopy trees were the shade-intolerant Nothofagus nitida (Fagaceae), Drimys winteri (Winteraceae) and the tolerant Podocarpus nubigena (Podocarpaceae). The oldest individuals, however, were represented by Saxegothaea conspicua, Podocarpaceae (shade tolerant > 498 years) and Weinmannia trichosperma, Cunoniaceae (intolerant > 382 years). Shade-tolerant species have regenerated continuously for the past 400 years, but recruitment of shade-intolerant species has increased only in the past 50 years. These regeneration patterns suggest a lack of catastrophic disturbance, at least since 1650. 4 Analysis of tree radial growth patterns revealed frequent moderate releases of both shade-tolerant and intolerant tree species, consistent with frequent small-scale disturbances, such as individual tree-fall gaps. Increased releases, peaking in 1940 and followed by enhanced recruitment, may be a consequence of individual tree-falls induced by low-intensity windstorms or limited selective logging. Such disturbances have occurred for at least 250 years, but have had little overall effect on stand structure and canopy composition. 5 The replacement and coexistence of shade-tolerant and intolerant tree species in the canopy of this North Patagonian forest can be explained by frequent small-scale disturbances (i.e. gap-phase dynamics) and by the absence of large-scale natural or anthropogenic disturbances over the past four centuries. Journal of Ecology (2004) 92, 598–608 [ABSTRACT FROM AUTHOR]

• the percentage of release signals typically ranged between 5 and 30% per decade; • release frequency per decade was over-dispersed compared to the random (Poisson) model; • cadences of increasing/decreasing tree growth lasted between 24 and 54 years (30 years on average); • stand-level fluctuations in tree growth were small compared to the total variation in tree increment; • a mixed-severity disturbance regime suggests unsteady gap-phase dynamics. Disturbances have been recognized as a key factor shaping the species composition, structure and dynamics of natural forest ecosystems. In Europe, where forests driven by spontaneous processes have survived in relic form, knowledge about natural disturbance regimes is still fragmentary. To expand this knowledge, we reconstructed stand-level growth and analyzed the spatio-temporal pattern of release signals in the increment chronologies of individual trees as indicators of disturbance events in the Western Carpathians (Central Europe). The study was carried out in five old-growth forests formed by Fagus sylvatica L., Abies alba Mill. and Picea abies (L.) H. Karst. Depending on the stand, the analyses included tree-ring series of 84–193 trees sampled over areas of 5.9–13.6 ha and aimed at determining (1) the spatio-temporal pattern of disturbance severity over the last two centuries, (2) whether disturbances have been synchronized in time across the study sites and (3) whether disturbances have induced pulsed dynamics of stand development manifested as fluctuations in radial tree increment at the level of entire stands. In the period 1850–2010, the percentage of decades with the proportion of released trees < 10, 10–20, 20–30 or more than 30% was 38, 41, 14 and 7%, respectively, and no instances of severe disturbances simultaneously impacting an extensive area and releasing the vast majority of trees were found. The release events were only weakly synchronized at the between-stand level. The spatial distribution of released trees varied over the decades, with a shift toward spatial independence for the most severe disturbances. At the stand level, the interchanging periods of increasing/decreasing tree growth lasted between 24 and 36 years, with the exception of one stand in which this period lasted 54 years. The revealed fluctuations in tree growth attributable to changes in stand density were relatively small and accounted on average for 7% of the total variation in annual tree increments. This suggests that local level disturbances introduce structural heterogeneity and strongly modify tree growth, but at the stand level, their effect is dispersed and causes only minor fluctuations. An over-dispersion of decadal release frequencies compared to the random model and spatial correlation of disturbing events on the one hand, and the lack of extensive disturbances, frequent occurrence of multiple releases in tree life histories, and small fluctuations in the reconstructed growth at the stand level on the other hand, suggest a disturbance regime which goes beyond random processes in a strict sense and is thus not entirely compatible with the classical model of gap-phase stand dynamics. [ABSTRACT FROM AUTHOR]