A review of the roles of forest canopy gaps

Treefall gap, canopy opening caused by the death of one or more trees, is the dominant form of disturbance in many forest systems worldwide. Gaps play an important role in forest ecology helping to pre- serve bio- and pedo-diversity, influencing nutrient cycles, and maintain- ing the complex structure of the late-successional forests. Over the last 30 years, numerous reviews have been written describing gap dynamics. Here we synthesize current understanding on gap dynamics relating to tree regeneration with particular emphasis on gap characteristics consid- ered critical to develop ecologically sustainable forest management sys- tems and to conserve native biodiversity. Specifically, we addressed the question： how do gaps influence forest structure？ From the literature re- viewed, the size of gaps induces important changes in factors such as light intensity, soil humidity and soil biological properties that influence tree species regeneration and differ in gaps of different sizes. Shade- tolerant species can colonize small gaps; shade-intolerant species need large gaps for successful regeneration. Additionally, gap dynamics differ between temperate, boreal, and tropical forests, showing the importance of climate differences in driving forest regeneration. This review summa- rizes information of use to forest managers who design cutting regimes that mimic natural disturbances and who must consider forest structure, forest climate, and the role of natural disturbance in their designs.

Short-term effects of different fire severities on soil properties and Pinus halepensis regeneration

Considering that diverse fire severities can affect soil properties differently,the aim of this study was to examine to what extent changes in soil properties caused by fire could condition seedling establishment.This new approach is for identifying a new fire cause-effect chain to qualify the impacts of fire on soils with the purpose of using fire as a tool in forest management to favour Pinus halepensis Mill.regeneration.The study area was a reforested P.halepensis area which had been crossed by fire for78.8 ha,causing various degrees of damage.The forest was subdivided into three large areas according to the gravity of crown scorch,[low(LS),medium(MS)and high(HS)severity],on the basis of needle yellowing which usually occurs after exposure to direct flames.Results showed significant differences in soil properties with respect to fire severity.In the HS area,total nitrogen and carbon were considerably reduced while ash and phosphorus contents significantly increased.The changes in soil properties,in particular to nutrient levels,affected P.halepensis regeneration,mainly the first year after the fire.Greater regeneration occurred in areas affected by moderate fire severity in which the temperatures reached increased the mineralization of soil organic matter with the consequent release of nutrients available for seedling growth.Additionally,moderate fire severity suppressed the regeneration of grasses,reducing the interspecific competition.Heights of seedlings were inversely proportional to the density of grasses.Where the number was abundant(LS),the height was modest;conversely,where the number was low(HS),the greater hypsometric differentiation of pine seedlings was observed.These results suggest that moderate fire severity represents an environmental stress(hormesis)altering microscale conditions to increase pine germination and establishment.The exposure of P.halpensis to a moderate environmental factor that is damaging at higher intensities,induces an adaptive beneficial effect on seedling regeneration.This data can re-evaluate the assertion that coniferous burned areas,if left unmanaged,would remain unproductive for an indefinite period.

Short-term changes in soil properties after prescribed fire and mulching with fern in Mediterranean forests

Prescribed fire,although having low intensity and being able to reduce the risk of wildfire may modify soil properties in the short term,with possible increases in runoffand erosion risk.Soil mulching with vegetation residues is one of the most common post-fire management strategies.Residues of fern,which is abundant on the Mediterranean forest floor,may be used to replace straw for mulching fireaffected areas.However,the effects of prescribed fires are not completely understood,and there is no data regarding the use of fern to protect soil after fire in the literature.To fill this gap,selected soil chemical parameters were analyzed,on a comparative basis,in three Mediterranean forests(pine,oak and chestnut)in Calabria(Southern Italy).These parameters were measured immediately and one year after fire in unburned,burned and not treated,and burned and mulched soils.Changes in soil chemical properties among the different treatments were significant,and the effects of the prescribed fire and mulching were dependent on the time elapsed from their application and forest species.In general,mulching was not effective in limiting the changes in the monitored soil properties compared to the pre-fire values.Each forest species showed different temporal trends in changes of soil properties.

The relationships between selected soil properties and caesium-137 identify organic carbon,nitrogen and water soluble phenols as indicators of soil erosion processes in different forest stands

In the last few decades,the use of environmental radionuclides,particularly caesium-137(^(137)Cs),represented one of the most valid methods for estimating soil erosion.However,the cost associated with the use of the equipment needed for radiometric analyses is still high and,for this reason,finding more easily measurable indicators can be useful.There is a strong correlation between^(137)Cs,organic carbon(OC),nitrogen(N)and water soluble phenols(WSP)exists,indicating the latter parameters as possible early indicators of soil erosion.Based on the above assumptions,the main purpose of this work is to identify specific soil chemical parameters able to indicate early triggering of soil erosion.Specifically,several soil parameters such as pH,electric conductivity(EC),WSP,OC,N and C/N have been evaluated against^(137)Cs and on a comparative basis.In addition,since the rate of soil erosion depends on the degree of coverage and canopy structure,two different tree species(Pinus nigra laricio Poir.and Fagus sylvatica L.)have been considered in this contribution in which ten different scenarios of forest management have been analysed.The results show that the reduction in tree cover of managed sites triggers erosion and nutrient loss processes.It has been observed that the loss of^(137)Cs,compared to the control areas,is closely correlated with those of WSP,OC and N.These parameters(WSP,OC and N),more easily assessable,can be a valid tool to understand easily,triggering of erosive phenomena.