Competitive effect, but not competitive response, varies along a climatic gradient depending on tree species identity

Background: Understanding the role of species identity in interactions among individuals is crucial for assessing the productivity and stability of mixed forests over time. However, there is limited knowledge concerning the variation in competitive effect and response of different species along climatic gradients. In this study, we investigated the importance of climate, tree size, and competition on the growth of three tree species: spruce(Picea abies), fir(Abies alba), and beech(Fagus sylvatica), and examined their competitive response and effect along a climatic gradient.Methods: We selected 39 plots distributed across the European mountains with records of the position and growth of 5,759 individuals. For each target species, models relating tree growth to tree size, climate and competition were proposed. Competition was modelled using a neighbourhood competition index that considered the effects of inter-and intraspecific competition on target trees. Competitive responses and effects were related to climate.Likelihood methods and information theory were used to select the best model.Results: Our findings revealed that competition had a greater impact on target species growth than tree size or climate. Climate did influence the competitive effects of neighbouring species, but it did not affect the target species? response to competition. The strength of competitive effects varied along the gradient, contingent on the identity of the interacting species. When the target species exhibited an intermediate competitive effect relative to neighbouring species, both higher inter-than intraspecific competitive effects and competition reduction occurred along the gradient. Notably, species competitive effects were most pronounced when the target species' growth was at its peak and weakest when growing conditions were far from their maximum.Conclusions: Climate modulates the effects of competition from neighbouring trees on the target tree and not the susceptibility of the target tree to competition. The modelling approach should be useful in future research to expand our knowledge of how competition modulates forest communities across environmental gradients.

Fungal diversity and community composition responses to the reintroduction of fire in a non-managed Mediterranean shrubland ecosystem

Background:More than a decade of fire suppression has changed the structure of fire-adapted shrubland ecosystems in Spain’s National Parks,which are now at extreme risk of uncontrolled wildfires.Prescribed burning can mitigate the risk of wildfires by reducing the fuel load but prescribed burning may also alter the soil properties and reduce microbial and fungal activity,causing changes in the availability of nutrients deep in the soil layer.Although fungal communities are a vital part of post-fire restoration,some fire effects remain unclear.To examine the short-term effects of prescribed burning on soil fungal communities in Doñana Biological Reserve(SW Spain),we collected soil samples pre-burn and 1 day,6 and 12 months post-burn from burned plots to perform physicochemical and metabarcode DNA analyses.Results:Prescribed burning had no significant effect on the total fungal operational taxonomic unit richness and abundance.However,changes in soil pH,nitrogen and potassium content post-burn affected fungal community composition.Small non-significant changes in pH and phosphorous affected the composition of ectomycorrhizal fungi.Conclusions:The ectomycorrhizal fungal community appears to be resilient to the effects of low-to moderate-intensity fires and saprotrophic taxa may benefit from this kind of fire.This finding revealed that prescribed burning is a potentially valuable management tool for reducing fire hazards in shrublands that has little effect on the total richness and abundance of fungal communities.

Stand-level biomass models for predicting C stock for the main Spanish pine species

Background:National and international institutions periodically demand information on forest indicators that are used for global reporting.Among other aspects,the carbon accumulated in the biomass of forest species must be reported.For this purpose,one of the main sources of data is the National Forest Inventory(NFI),which together with statistical empirical approaches and updating procedures can even allow annual estimates of the requested indicators.Methods:Stand level biomass models,relating the dry weight of the biomass with the stand volume were developed for the five main pine species in the Iberian Peninsula(Pinus sylvestris,Pinus pinea,Pinus halepensis,Pinus nigra and Pinus pinaster).The dependence of the model on aridity and/or mean tree size was explored,as well as the importance of including the stand form factor to correct model bias.Furthermore,the capability of the models to estimate forest carbon stocks,updated for a given year,was also analysed.Results:The strong relationship between stand dry weight biomass and stand volume was modulated by the mean tree size,although the effect varied among the five pine species.Site humidity,measured using the Martonne aridity index,increased the biomass for a given volume in the cases of Pinus sylvestris,Pinus halepensis and Pinus nigra.Models that consider both mean tree size and stand form factor were more accurate and less biased than those that do not.The models developed allow carbon stocks in the main Iberian Peninsula pine forests to be estimated at stand level with biases of less than 0.2 Mg·ha^(-1).Conclusions:The results of this study reveal the importance of considering variables related with environmental conditions and stand structure when developing stand dry weight biomass models.The described methodology together with the models developed provide a precise tool that can be used for quantifying biomass and carbon stored in the Spanish pine forests in specific years when no field data are available.

Pre-fire aboveground biomass, estimated from LiDAR, spectral and field inventory data, as a major driver of burn severity in maritime pine (Pinus pinaster) ecosystems

Background:The characterization of surface and canopy fuel loadings in fire-prone pine ecosystems is critical for understanding fire behavior and anticipating the most harmful ecological effects of fire.Nevertheless,the joint consideration of both overstory and understory strata in burn severity assessments is often dismissed.The aim of this work was to assess the role of total,overstory and understory pre-fire aboveground biomass(AGB),estimated by means of airborne Light Detection and Ranging(LiDAR)and Landsat data,as drivers of burn severity in a megafire occurred in a pine ecosystem dominated by Pinus pinaster Ait.in the western Mediterranean Basin.Results:Total and overstory AGB were more accurately estimated(R^(2) equal to 0.72 and 0.68,respectively)from LiDAR and spectral data than understory AGB(R^(2)=0.26).Density and height percentile LiDAR metrics for several strata were found to be important predictors of AGB.Burn severity responded markedly and non-linearly to total(R^(2)=0.60)and overstory(R ^(2)=0.53)AGB,whereas the relationship with understory AGB was weaker(R ^(2)=0.21).Nevertheless,the overstory plus understory AGB contribution led to the highest ability to predict burn severity(RMSE=122.46 in dNBR scale),instead of the joint consideration as total AGB(RMSE=158.41).Conclusions:This study novelty evaluated the potential of pre-fire AGB,as a vegetation biophysical property derived from LiDAR,spectral and field plot inventory data,for predicting burn severity,separating the contri-bution of the fuel loads in the understory and overstory strata in Pinus pinaster stands.The evidenced relationships between burn severity and pre-fire AGB distribution in Pinus pinaster stands would allow the implementation of threshold criteria to support decision making in fuel treatments designed to minimize crown fire hazard.

Mapping forest vegetation patterns in an Atlantic-Mediterranean transitional area by integration of ordination and geostatistical techniques

Aims Forest vegetation variability may be explained by the complex inter-play among several spatial structuring factors,including climate and topography.We modelled the spatial variability of forest vegetation assemblages and significant environmental variables along a com-plex environmental gradient or coenocline to produce a detailed cartographic database portraying the distribution of forests along it.Methods We combined an analysis of ordination coenoclines with kriging over 772 field data plots from the third Spanish National Forest Inventory in an Atlantic-Mediterranean transitional area(northern Spain).Important Findings The best fitted empirical semivariogram revealed a strong spatial structure of forest species composition along the complex envi-ronmental gradient considered(the climatic-topographic gradient from north to south).The steady and gradual increase of semivari-ance with a marked lag distance indicates a gradual turnover of forest assemblages according to the climatic-topographic vari-ations(regional or local).Two changes in the slope of the semi-variogram suggest the existence of two different scales of spatial variation.The interpolation map by Kriging of forest vegetation assemblages along the main coenocline shows a clear spatial dis-tribution pattern of trees and shrubs in accordance with the spa-tial variation of significant environmental variables.We concluded that the multivariate geostatistical approach is a suitable technique for spatial analysis of forest systems employing data from national forest inventories based on a regular network of field plots.The development of an assortment of maps describing changes in veg-etation assemblages and variation in environmental variables is expected to be a suitable tool for an integrated forest management and planning.

BioClay^(TM)prolongs RNA interference-mediated crop protection against Botrytis cinerea

One of the most promising tools for the control of fungal plant diseases is spray-induced gene silencing(SIGS).In SIGS,small interfering RNA(siRNA)or double-stranded RNA(dsRNA)targeting essential or virulence-related pathogen genes are exogenously applied to plants and postharvest products to trigger RNA interference(RNAi)of the targeted genes,inhibiting fungal growth and disease.However,SIGS is limited by the unstable nature of RNA under environmental conditions.The use of layered double hydroxide or clay particles as carriers to deliver biologically active dsRNA,a formulation termed BioClay^(TM),can enhance RNA durability on plants,prolonging its activity against pathogens.Here,we demonstrate that dsRNA delivered as BioClay can prolong protection against Botrytis cinerea,a major plant fungal pathogen,on tomato leaves and fruit and on mature chickpea plants.BioClay increased the protection window from 1 to 3 weeks on tomato leaves and from 5 to 10 days on tomato fruits,when compared with naked dsRNA.In flowering chickpea plants,BioClay provided prolonged protection for up to 4 weeks,covering the critical period of poding,whereas naked dsRNA provided limited protection.This research represents a major step forward for the adoption of SIGS as an eco-friendly alternative to traditional fungicides.