In Mediterranean regions, climate change increasingly affect tree species distributions. Conifer forests under continuing disturbance show a more rapid shift to dominance by beech and other temperate broadleaves. Thus, there is an urgent need to conserve coniferous vegetation to avoid local extinction. Gap opening has profound effects on the structure and dynamics of most forests and may represent a sustainable way to restore coniferous ecosystems in Mediterranean habitats. What kind of artificial canopy opening is the most sustainable and effective means for restoring coniferous ecosystem functions? We explored the efficacy of artificial gaps in regeneration and dynamics of coniferous in Mediterranean environment. We examined how regeneration of different tree species is associated with soil environmental conditions and how gaps of different sizes influence the ecology and management of Mediterranean forest. Specifically, we analyzed gap disturbance in silver fir and black pine stands, as they dominate central and southern Italian forests. We demonstrated a specificity between gap size and coniferous species regeneration, indicating that small gaps (about 200 m2) favor silver fir regeneration, while black pine, depending on its subspecies, regenerates both in small and medium gaps (about 500 m2). Further, we found that gap characteristics (age and shape) and suitable substrate availability are the primary factors affecting seedling establishment. Our results provide functional information to design a silvicultural system useful to manage the natural regeneration of Mediterranean forest minimizing the environmental and visual impact.
Mediterranean ecosystems are highly sensitive to climate change, as relatively minor decreases in rainfall and increases in temperature may lead to the expansion of adjacent semi-arid and arid ecosystems at the expense of Mediterranean ecosystems. Mediterranean ecosystems show changes in their community structure with competitive relationships between species leading to tree migration in the long term (
Gap cutting is a silvicultural tool that consists of removing all trees in very small areas,
group selection method (removing mature trees in small group or clusters -
patch-selection method (add some patch equal to the height of a mature tree within single-tree selection method -
group selection system (100-1000 m2,
irregular shelter wood (100-1000 m2 -
small patch cuts (1000-5000 m2 -
The successful regeneration of tree species in gaps depends not only on the gap size but also on many other variables such as: age of seed trees, proximity of seed source to gaps, mechanism of seed dispersal, substrate conditions, plant-herbivore relationship, number (density) of gaps, spatial and temporal gap distribution (
Generally, forest restoration management can be broken down into three approaches, each with different aims relating to different functions of the forests to be restored.
Forest restoration is used to rehabilitate a functional ecosystem without emphasizing production functions. The strategy is the restoration of the previously stable production potential. This case of restoration management is not limited to protected areas.
Conversion to a near-natural forest, leaving the forest to spontaneous development. This is always applicable to forests in protected areas. Nonetheless, this approach is the least applied among the three considered. A special variant of this approach is “zero management”,
Restoration of forests to a certain state (even if conditioned by man) requires long-term, active management to allow to the endangered species to survive. This approach is currently mostly applied to forests in protected areas and has the protection of biological diversity as priority (
The rehabilitation of conifer monocultures in stands with high diversity in composition and structure represents one of the main objectives of silviculture, to suggest management practices useful to meet the sustainable development. Therefore, a deeper knowledge on gap dynamics is fundamental to predict species composition and successional dynamic, and optimize silvicultural strategies for the sustainable management of coniferous forests (
The goal of this review is to summarize new and previously published data to provide a coherent picture of the role of treefall gaps in coniferous forest regeneration and dynamics. Our aim was to determine the degree to which there is empirical support for the gap hypothesis, defined as the variety of ideas on the role of gaps in the maintenance of diversity (
This review is based on the results of a literature survey which focused on papers published in the period 1958-2015 using as keywords (either alone or in combination): “gap size”, “gap age”, “gap shape” and “coniferous regeneration”. The majority of the articles included in this review were published in international peer review journals written in English and included at least one field experiment using gap creation for restoration or reforestation purpose. We found 110 papers that matched these criteria. We classified the selected papers according to the kind of gap, and the vegetation type. The experiments were divided according to the species and gap size. We summarized survival and mortality as well regeneration success of the silver fire, black pine and Calabrian pine in respect to the gap size and age.
It is well known that resources such as solar radiation, soil moisture, and soil nutrients, strongly vary from the edge to the interior of gaps, thus influencing species with different regeneration requirements. Based on this assumption, the first Italian experience with the use of gap cutting for the rehabilitation of conifer monoculture began in 1982, in a 80-100 years-old silver fir (
With an experiment started in a 90 year-old silver fir plantation in Serra S. Bruno, located in Southern Apennines (38° 33′ N, 16° 19′ E),
The results related to the mechanisms of vegetation dynamics in the Strict Natural Reserve of Sasso Fratino (Central Italy) may be used as basis for close-to-nature silvicultural choices in similar stands in order to increase forest functionality and stability.
Black pine
In 2000, a study was started on the effects of 108 and 207 m2 artificial gaps as a restoration method in two Black pine stands of 50 and 90 years old, respectively, in Monte Plaia, Central Apennines (42° 01′ N, 13° 54′ E). Three and nine years following gap creation,
Calabrian pine (
In summary, the irregular shelterwood system adopted in all these experimental sites showed a clear pattern of gap partitioning among tree species: shade-tolerant and intermediate shade-intolerant species achieved the highest probability of presence in the vicinity of gap edges. On the contrary, shade-intolerant wind-dispersed species achieved the highest probability of presence at the gap center. Small gaps are able to mimic the natural successional pattern that eventually can restore the late-successional condition of species. Trees in the border of gaps tend to have a higher rate of disturbance. While opening a gap in a dense forest may result in wind damage, such risk can be avoided or minimized by properly designed gap-cutting. Forest dynamics is also related to the temporal scale, that is an important factor in determining the modification of forest structure and plant species composition across forest succession.
Gaps created by irregular shelterwood system play an important role in forest ecology, helping to preserve bio- and pedo-diversity, influencing nutrient cycles, maintaining the complex structure of the late-successional forests, and minimizing the adverse impacts on complex ecological processes that shape together the forest landscape.
The size of gaps dramatically affects light intensity and consequently air and soil temperature, soil moisture and soil biological properties, which in turn influence tree species regeneration. Our results revealed that the availability of suitable substrates is the primary factor that limits seedling recruitment following gap logging. This review indicates a clear relationship between gap size and coniferous species regeneration in the Mediterranean environment, highlighting that small gaps (about 200 m2) favor silver fir and black pine regeneration, while large gaps (approximately 500 m2) promote Calabrian pine restoration. We reported the necessary information to design a management system that mimics the natural disturbance regime, favoring the restoration and conservation of coniferous species. Future research focused on below ground processes, including soil characteristics, microbial growth and composition, should be designed to increase the overall understanding of gap dynamics and their impact on the whole forest.
Structural dynamics and natural regeneration of different silver fir stands in Central and Southern Italy. (*): including one years old seedlings; (a) tree species are ordered by decreasing frequency.
Location | Foresttype | Gap size (m2) | d/h | Volumeremovedper gap (m2) | Mean dbh(cm) | No. stemsremovedper gap | Seedlingdensity(n/m2) | Meanheight(cm) | Years aftergap opening | Tree species a |
---|---|---|---|---|---|---|---|---|---|---|
Serra San Bruno(unpub. data) | Silver fir | 410 | 1:0.75 | 25.0 | 47.6(stem base) | 19 | 4.6 | 21.8 | 10 | silver fir, chestnut |
Silver fir | 185 | 1:0.5 | 9.9 | 40.1(stem base) | 8 | 8.4 | 17.1 | 10 | silver fir, chestnut | |
Silver fir | 872 | 1:1 | 62.9 | 35.6 | 46 | 0.4 | 51.9 | 18 | silver fir, maple, beech | |
Foreste Casentinesi | Silver fir | 540 | 1:1 | 27.8 | 32.4 | 35 | 1.3 | 22.6 | 18 | maple, silver fir, beech, rowan |
Silver fir | 379 | 1:0.75 | 13.9 | 39.4 | 6.2 | 5.4* | 10.1 | 11 | silver fir | |
Foreste Casentinesi(unpub. data) | Silver fir | 215 | 1:0.5 | 39.6 | 39.6 | 15 | 4.9* | 9.5 | 11 | silver fir |
Structural dynamics and natural regeneration of different Calabrian pine stands in Southern Italy. (*): including one years old seedlings; (a) tree species are ordered by decreasing frequency.
Location | Forest type | Gap size(m2) | d/h | Volumeremovedper gap (m2) | Mean dbh(cm) | No. stemsremovedper gap | Seedlingdensity(n/m2) | Meanheight(cm) | Years aftergap opening | Tree species a |
---|---|---|---|---|---|---|---|---|---|---|
Bufalaria | Calabrian pine | 1520 | 1:2 | 70.3 | 32.2 | 78 | 2.3* | 65.9 | 8 | pine, silver fir |
Calabrian pine | 855 | 1:1.5 | 40.3 | 34.6 | 43 | 2.1* | 46.6 | 8 | pine, silver fir | |
Calabrian pine | 380 | 1:1 | 15.1 | 32.1 | 20 | 0.3* | 40.2 | 8 | silver fir, pine |
Gap cutting applied in the rehabilitation of man-made conifer stands in Italy.
Forest types | Location | Stand Age(years) | Gap size(m2) | Stand surfaceremoved (%) | Interval(years) | Notes |
---|---|---|---|---|---|---|
Silver fir | SouthernApennines | 79-80 | 200-400 | 25 | 10 | Vegetation control, cleanings and thinning of regeneration |
Silver fir | CentralApennines | 70-80 | 500-600 | 25 | 10 | Cleanings and thinning of regeneration |
Black pine | CentralApennines | 60-70 | 150-250 | 25 | 10 | Larger gaps maintain an higher presence of pine |
Calabrian pine | SouthernApennines | 60-70 | 400-1500 | 25 | 10 | Larger gaps maintain an higher presence of pine |