Natural regeneration responses to thinning and burning treatments in ponderosa pine forests and implications for restoration

Understanding naturally occurring pine regeneration dynamics in response to thinning and burning treatments is necessary not only to measure the longevity of the restoration or fuels treatment, but also to assess how well regeneration meets forest sustainability guidelines and whether natural regeneration is sufficient for maintaining a sustainable forest structure and composition. A synthesis review was carried out on the effects of mechanical thinning and prescribed burn treatments on natural pine regeneration response in frequent-fire ponderosa pine forests across the western United States. The focus was on site-specific variability in pine regeneration dynamics, temporal trends in regeneration presence and abundance, and response to treatment as described in the current literature using 29 studies that met our evidence-based review protocols. Data showed that the effects of thinning and burning treatments on regeneration depended on time since treatment. Mechanical thinning, prescribed burning, and thinning plus burn treatments all increased seedling density, but there was high variability among sites and studies. There were mixed results in the short-term (< 10 years) with both increasing and decreasing regeneration, and a general increase in regeneration 11 − 20 years post-treatment. Some long-term studies (> 20 years) concluded that stands can return to pre-treatment densities in terms of total trees per hectare and forest floor duff levels when there are no maintenance treatments applied. Several studies showed the average ponderosa pine seedling presence, survival and growth found in today’s forests to be at a high density; this combined with missed fire cycles could contribute to future fire risk and reduce the efficacy of maintaining fuel reduction goals.

Regeneration dynamics in fragmented landscapes at the leading edge of distribution: Quercus suber woodlands as a study case

Aims We studied the regeneration dynamics of woodlands and abandoned old fields in a landscape dominated by Quercus suber in its lower limits of rainfall and temperature. Two hypotheses were established: (1) regeneration of Quercus species is strongly favored by the presence of tree cover; and (2) growth of Q. suber is driven by the climatic variables that represent the lower ecological limit of its leading distribution edge. Methods We selected woodlands and old fields with and without tree remnants (n = 3 per type), and analyzed stand structure, soil parameters and tree growth. Results Succession was arrested in old fields without tree remnants. By contrast, remnant trees were accelerators of forest recovery in old fields. Tree cover played a fundamental role in Quercus recruitment throughout seed dispersal and facilitation that mitigate the effects of summer drought on seedlings. Also, tree cover improved soil parameters (e.g., organic matter) that are important factors for understanding differences in regeneration. Winter/spring precipitation exerted a positive effect on tree growth, as well as temperatures during winter/spring and September. Conclusions Regeneration dynamics are modeled by the density of tree cover in the cold and dry edge of the distribution area of Q. suber where Q. ilex is increasing in abundance. Although temperature has a positive effect on the tree growth of Q. suber, when demographic processes are considered, decreases in water availability likely play a critical role in Q. ilex recruitment. This in turn changes dominance hierarchies, especially in abandoned areas with little or no tree cover.

Regeneration Dynamics in Fragmented Landscapes at the Leading Edge of Distribution: Quercus Suber L. as A Study Case

AimsWe studied the regeneration dynamics of woodlands and abandoned old fields in a landscape dominated by Quercus suber in its lower limits for rainfall and temperature. Two hypotheses were established: (1) recruitment of Q. suber is restricted more by abiotic variations than other species adapted to more extreme Mediterranean conditions; and (2) decreases in precipitation reduce growth, but temperature positively affects growth in the leading cold edge of this species distribution area.MethodsWe selected nine sites containing forest stands and old fields with and without tree remnants, and analyzed stand structure, soil parameters and tree growth.ResultsSuccession was arrested in plots without tree remnants after cultivation abandonment. By contrast, remnant trees were accelerators of forest recovery. Tree cover played a fundamental role in Quercus recruitment throughout seed dispersal and facilitation effects that ameliorate summer drought. However, soil variables also significantly explained much of the variance observed and are important for understanding differences in regeneration. Winter and spring precipitation exerted a positive effect on tree growth, as well as temperatures during winter/spring and September.ConclusionsRegeneration dynamics are modeled by the density of tree cover in the cold and dry edge of the distribution area of Q. suber where Q. ilex is increasing in abundance. Although temperature has a positive effect on the tree growth of Q. suber, when demographic processes are considered, decreases in water availability likely play a critical role in Q. ilex recruitment. This in turn changes dominance hierarchies, especially in abandoned areas with little or no tree cover.

Is deadwood helping regeneration? Natural regeneration dynamics in a stand replacing windthrow area.

&lt;p&gt;Forests provide many important ecosystem services. Natural disturbances, such as wildfires, pest outbreaks and windrows, are the main phenomena shaping forest ecosystems. Due to both climate and global changes, extreme events are increasing in frequency and forests are thus increasingly being affected by stand replacing disturbances. Mountain forest dynamics and ecosystems services are critically influenced by disturbances, in particular storm. In this framework, is crucial to understand these environmental modifications, finding the best management strategies to restore or maintain ecosystem services provided by forests. After large disturbance, there are two different issues to deal with: the large amount of deadwood on the ground, and the needs of&amp;#160; regeneration in order to re-establish the forest cover. To face these problems different management strategies can be adopted. Salvage logging (total or partial) and no-intervention are the two opposite approaches to handle the large amount of deadwood. Natural regeneration or reforestation, instead, are the main strategies to consider to re-establish forest cover. In this study we focused on post-windstorm conditions, in particular concerning large windthrows caused by the Vaia storm, occurred in October 2018 on Eastern Italian Alps. After such large-scale event, natural regeneration is the most convenient strategy to regenerate forest. This process should take place in an area with a high amount of coarse wood debris (CWD). For this reason is crucial to understand the interaction between windthrown timber and regeneration dynamics. In this study we analyzed how CWD is able to create a favorable regeneration microsite enhancing seedling establishment probability. In particular, we focused on two different facilitative mechanisms provided by CWD: microsite amelioration and seedling protection. The former has been analyzed measuring temperature and SWC in the proximity of seedling planted in the surrounding of deadwood elements, the latter by recording browsing evidence at the end of the season. &amp;#160;In order to infer the CWD contribution, control sites have been established in empty sites (no CWD presence in the surrounding). Our results showed that in southern slopes, microsite with significative lower temperature are found northern to the logs, decreasing water stress for saplings. The ameliorative function of logs and CWD in general contribute to decrease the transplanting shock, increasing the probability to establish for saplings. Moreover, the presence of lying deadwood decreased significantly the browsing on saplings. The result of our study highlighted the importance of favorable regeneration microsites provided by deadwood, both for natural regeneration dynamics and for increasing the survival probability for planted saplings. Favorable microsites and nurse biological legacies should be considered in defining post-disturbance management strategies, promoting only a partial salvage logging or non-intervention &amp;#160;approaches as much as possible.&lt;/p&gt;