Highlighting Complex Long-Term Succession Pathways in Mixed Forests of the Pacific Northwest: A Markov Chain Modelling Approach

Forest succession is an ecological phenomenon that can span centuries. Although the concept of succession was originally formulated as a deterministic sequence of different plant communities by F. Clements more than a century ago, nowadays it is recognized that stochastic events and disturbances play a pivotal role in forest succession. In spite of that, forest maps and management plans around the world are developed and focused on a unique “climax” community, likely due to the difficulty of quantifying alternative succession pathways. In this research, we explored the possibility of developing a Markov Chain model to study multiple pathway succession scenarios in mixed forests of western red cedar, hemlock and Pacific silver fir on northern Vancouver Island (western Canada). We created a transition matrix using the probabilities of change between alternative ecological stages as well as red cedar regeneration. Each ecological state was defined by the dominant tree species and ages. Our results indicate that, compared to the traditional Clementsian, deterministic one-pathway succession model, which is unable to replicate current stand distribution of these forests in the region, a three-pathway stochastic succession model, calibrated by a panel of experts, can mimic the observed landscape distribution among different stand types before commercial logging started in the region. We conclude that, while knowing the difficulty of parameterizing this type of models, their use is needed to recognize that for a given site, there may be multiple “climax” communities and hence forest management should account for them.

Delayed and altered post-fire recovery pathways of Mediterranean shrubland under 20-year drought manipulation

<p>Increasing anthropogenic and natural disturbances have disturbed 75% of global land area, indicating many plant communities are unstable or in recovery process. Increasing water deficits by rainfall reduction may decrease resilience (rate of recovery) and trigger different succession pathways (e.g. delayed, altered mature status and advanced degradation). Knowledge on the effects of future drought on community structure and demographic dynamics is key to project the fate of vegetation and yet it is limited. </p><p>Here we assessed the impacts of long-term (20 years) experimental drought (-30% rainfall) on the successional pathways of species diversity, community composition and demographic changes for an early-successional Mediterranean shrubland (4 years after a wildfire). The results indicated that experimental drought significantly decreased species richness and shifted community composition compared to control plots. Significant decreases in abundance and increases in death ratios at both community (all species) and shrub (shrub species) levels were found in experimental drought. However, the abundance of Globularia Alypum was significantly increased by drought while Erica multiflora was not affected; the death ratios for the two species were significantly lower in drought than control plots. Species richness, community composition and abundance followed pathway 2 (altered mature state) while shrubland abundance followed pathway 3 (advanced degradation). Principal Component Analysis (PCA) indicated that the variance in vegetation metrics was notably explained by the first two dimensions (49.4%), mainly related to the death ratio of G. alypum and E. multiflora (27.3% for PC1) and abundance of community and shrub levels (22.1% for PC2). The space variation in PC1 significantly increased over time, which was orthogonal with PC2. Within two dimensions of PC1 and PC2, the scores in control were significantly higher than drought. </p><p>Our findings suggest that drier condition simulated by long-term drought could delay and alter the succession pathways of species diversity, community composition and abundance of the plant communities in Mediterranean ecosystems. The results also imply the importance to analyse long-term drought and extreme events on ecosystem functions (the strength of carbon storage in vegetation and soil) for such recovering communities.</p>

Succession in the family business: drivers and pathways

Purpose – The succession process represents one of the most critical events in the family business lifecycle. The purpose of this paper is to explore this process while focussing first on the drivers behind the choice of successor and, second, on the impact of this choice on the entrepreneurial behavior of the siblings. Design/methodology/approach – The qualitative approach was used in which multiple case analyses were performed. A total of 12 cases were purposively selected from the Lebanese private sector, and semi-structured interviews were conducted with the successors and the founders when available. The interview data were transcribed and a coding scheme was created to generate relevant categories. Those categories were named and later re-assessed by an external researcher to ensure inter-rater reliability. Findings – The three dimensions of social capital were found to have a profound influence on the succession decision with much focus on familial stewardship as an emerging cognitive driving force. When “familial stewardship” is shared by incumbent and sibling, it strengthens the latter’s chances of being chosen as successor. Further, a succession pathways model was introduced that depicts the siblings’ behavior following the succession decision which seems to often trigger further entrepreneurship. Originality/value – This study is distinct as it introduces a new cognitive construct that helps rationalize the successor-selection decision in a Middle Eastern context. It also goes beyond the succession event to depict potential entrepreneurial behavior triggered by succession.

Vegetation Recovery in Response to the Exclusion of Grazing by Sika Deer (Cervus nippon) in Seminatural Grassland on Mt. Kushigata, Japan

We examined the recovery of vegetation in seminatural grassland in central Japan after eliminating grazing by sika deer (Cervus nippon) by fencing. By 2012, after 5 years of fencing for exclusion of sika deer, the species composition of quadrats within the enclosure reverted to the original species composition in 1981, not browsed by sika deer. Conversely, outside the fence was different from the baseline quadrats in 1981. Iris sanguinea, a prominent flower in the area, recovered within the enclosure, while it continued to decrease with grazing outside the fence. Nevertheless, the I. sanguinea cover had not recovered to the 1981 levels in the enclosure. Fencing can effectively restore vegetation as the species composition within the enclosure gradually reverts to the original vegetation. Preventing grazing in intensively grazed seminatural grassland might lead to different successional pathways. Since I. sanguinea did not recover fully within the enclosure and the species composition differed slightly from the original vegetation, this suggests that the vegetation within the enclosure will change to an alternative state. Therefore, different management is needed to promote the correct succession pathways for ecological restoration, perhaps by enhancing the colonization of target species, to prevent restored sites from giving rise to alternative states.

Structure and development patterns analysis of Fagus sylvatica s.l.- Quercus dalechampii Ten. stands in two areas in the Rhodope mountains of Xanthi region

This study was conducted in Fagus sylvatica-Quercus dalechampii stands in two areas in the Rhodope mountains of Xanthi. In order to analyse the structure and the development patterns of our stands, 23 plots were established, increment cores were taken, and stem analysis was conducted in 2 couples of dominant (competitive) beech and oak trees. The main results of this research indicate that a) In the mountainous part of the study area, natural and anthropogenic disturbances form the initiation, development and structure of beech-oak stands. However the fact that a number of oak trees survived after the disturbance in combination with landscape topography, which inhibited the dispersion of pine seeds, the species biology and the local climate, which is warmer than that of adjacent areas, influenced the succession pathways in the area and allowed oak to act as a pioneer species. b) Even though only one of the two structural types, tound in the submountainous part of the study area, was initiated by (anthropogenic) disturbances, the structure and composition of both structural types stands were and still are formed by illegal cuttings in which the oak wood is preferred. c) In both competing couples, the beech trees, after the first 80-85 years of their life, showed by far higher volume growth rates than the adjacent competitive oak trees which, in combination with the trees height growth patterns, implies, that in the future, a total domination of beech trees (in the two couples) will be observed. d) Forest practice must preserve the mixture of beech and oak in the mountainous part of the study area and enhance the presence of oak component in the submountainous part of the study area, in order to maintain· the diversity of these stands, to avoid the disadvantages of a homogenous forest and to mediate an orderly transition of community types, if the predicted increase in the average global temperatures comes true.