Productivity and modifications of ecosystem processes in gaps of a low Macchia in southern Italy

A De Marco,A Meola,F Esposito,A Virzo De Santo

doi:10.5194/we-8-55-2008

Abstract

Abstract. Disturbance in Mediterranean shrub lands creates gaps that break up the shrub cover and potentially restrict productivity and other ecosystem processes. Gaps make up to about 20% of the low Macchia area at the Castel Volturno nature reserve (southern Italy). The plant community consists mainly of small annual species (legumes, grasses and forbs) that germinate in November and die out before the onset of summer drought. The inter-annual variability in productivity and the relative abundance of legumes, grasses and forbs were assessed over 4 yr (2004–2007) to evaluate main potential modifications of ecosystem processes determined by the occurrence of gaps in the shrub cover. In the study years, at the peak production, plant mass varied from about 250 to 700 g m−2; biomass belowground allocation varied from 23% in the wettest to 44% in the driest year. Belowground/aboveground biomass ratios were negatively related to rainfall and positively related to the length of the dry period, showing that water availability controls biomass allocation patterns. Legumes were the most abundant fraction (about 60%) of the aboveground mass in the wettest year. In the drier years legumes exhibited a shorter life cycle and senesced by mid-spring. Among the three functional groups monitored, legumes were the most sensitive to water shortage and their biomass was positively related to the amount of rainfall and negatively related to the length of the dry period. The higher fraction of legume mass was associated with higher nitrogen content in plant tissues and in the soil. Senesced annual species decomposed more than senescent Phillyrea sp. leaves. The stability of organic carbon pool, evaluated through the endogenous mineralization coefficient (CEM), was lower in gaps than in understorey soils.

Highlights

Disturbance in Mediterranean shrub lands creates gaps that break up the shrub cover and potentially restrict productivity and other ecosystem processes
In heavily degraded woodlands and shrub lands, trees and shrubs are replaced by annual species w h i c h d o m in a t e o p e n c o m m u n i ti e s a n d c o n s ti tute approximately 15% of the regional flora
Mediterranean climate presents a marked seasonality with hot dry summer, moist winter and a great interannual variability in rainfall. In this climate annuals are most sensitive to drought, being strict drought avoiders with their life cycle tuned to the duration of soil water availability

Summary

Introduction

Disturbance in Mediterranean shrub lands creates gaps that break up the shrub cover and potentially restrict productivity and other ecosystem processes. The inter-annual variability in productivity and the relative abundance of legumes, grasses and forbs were assessed over 4 years (2004–2007) to evaluate main potential modifications of ecosystem processes determined by the occurrence of gaps in the shrub cover. Mediterranean climate presents a marked seasonality with hot dry summer, moist winter and a great interannual variability in rainfall In this climate annuals are most sensitive to drought, being strict drought avoiders with their life cycle tuned to the duration of soil water availability. Pereira et al (2007) comparing carbon fluxes in contrasting Mediterranean ecosystem in southern Portugal, found that during two years of severe droughts carbon sequestration was strongly restricted in an evergreen oak woodland whereas a grass land was a net source of carbon dioxide to the atmosphere. As drought spells in Mediterranean ecosystems are predicted to become longer and more frequent a s a c o n s e quence of climatic change (Christensen et al 2007), many studies have focused on how this could affect carbon sequestration in these ecosystems (Serrano-Ortiz et al 2007, Aires et al 2008, Allard et al 2008)

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