Large areas of semiarid grasslands in the southwestern United States have been virtually replaced by shrubs during the past century. Understanding the causes and consequences of such vegetation dynamics requires that we elucidate the interplay between external forces of change (e.g., climate, human impacts) and the internal forces within these ecosystems that foster resilience and/or stability. Several conceptual models of arid ecosystems address this interplay by including the potential role of autogenic shrub effects on ecosystem processes, which lead to the formation of “resource islands” and tend to promote shrub persistence. Specifically, during the process of shrub establishment and maturation, the cycling of nutrients is progressively confined to the zones of litter accumulation beneath shrubs, while bare intershrub spaces become increasingly nutrient poor. As shrub resource islands develop, there is increased interception and stemflow by shrub canopies, confining infiltration of nutrient-enriched ...

Impact of drought on desert shrubs : Effects of seasonality and degree of resource island development

We review the literature dealing with mediterranean climate, vegetation, phenology and ecophysiology relevant to the understanding of tree-ring formation in mediterranean regions. Tree rings have been used extensively in temperate regions to reconstruct responses of forests to past environmental changes. In mediterranean regions, studies of tree rings are scarce, despite their potential for understanding and predicting the effects of global change on important ecological processes such as desertification. In mediterranean regions, due to the great spatio-temporal variability of mediterranean environmental conditions, tree rings are sometimes not formed. Often, clear seasonality is lacking, and vegetation activity is not always associated with regular dormancy periods. We present examples of tree-ring morphology of five species (Arbutus unedo, Fraxinus ornus, Quercus cerris, Q. ilex, Q. pubescens) sampled in Tuscany, Italy, focusing on the difficulties we encountered during the dating. We present an interpretation of anomalies found in the wood structure and, more generally, of cambial activity in such environments. Furthermore, we propose a classification of tree-ring formation in mediterranean environments. Mediterranean tree rings can be dated and used for dendrochronological purposes, but great care should be taken in selecting sampling sites, species and sample trees.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/646D9FAA4C6EB3A6E30B9DF91D3D5157/S1464793102006000a.pdf/div-class-title-identification-measurement-and-interpretation-of-tree-rings-in-woody-species-from-mediterranean-climates-div.pdf

Identification, measurement and interpretation of tree rings in woody species from mediterranean climates

Mediterranean-type ecosystems have provided ecologists with some of the most scientifically-rewarding opportunities to formulate and evaluate hypotheses about large and small-scale ecological phenomena. Comparison of mediterranean-type climate ecosystems in different parts of the world has not only permitted a strong test for ecological convergence, but also critical understanding of key ecophysiological and population processes.

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Ecology and biogeography of mediterranean ecosystems in Chile, California, and Australia

Plant response to stress

Resource Use by Chaparral and Matorral

A B S T R A C T The annual rhythm of cambial activity is compared in Proustia cuneifolia and Acacia caven, two typical shrubs of the "matorral" in the semiarid region of central Chile. Proustia, a drought deciduous shrub, shows a typical desert cambial rhythm, highly sensitive to rainfall. The growth activity of this species is limited to the periods of adequate moisture. Acacia is an evergreen whose cambial activity is observed almost throughout the year; it is not synchronous with rainfall. Adaptation in this species seems to consist in developing long roots able to tap underground water. These results indicate that both shrubs, although growing together, have different adaptive strategies to the same xerophytic conditions. THE STUDY of the adaptations of plants to the

The annual rhythm of cambial activity in two woody species of the chilean “matorral”

A B S T R A C T The sclerophyllous evergreen shrub vegetation of southern California and central Chile is characterized by several examples of morphologically similar species. For each one out of a group of four Californian shrub species, four morphologically analogous sclerophyllous evergreens from Chile were chosen. In monthly intervals two-year branchlets from these eight species were collected and their cambium aetivity was evaluated by means of a histological analysis. Similar shrub species from Chile and California show a surprisingly strong coincidence in their seasonal fluctuations of cambium activity regardless of their systematic position. This observation is interpreted to mean that convergence has taken place.

The seasonal cambium activity of chilean and californian shrubs

Satureja gilliesii is a small shrub, representative of the Chilean mediterranean vegetation found on arid slopes and on partially degraded soils It has two types of branches: dolichoblasts with winter leaves and brachyblasts with smaller spring leaves The leaves are mesophytic and no stomatal control is detectable Dolichoblast leaves are shed at the beginning of drought but the brachyblast leaves that have become dry and brownish remain attached to the plant Even while the plant undergoes a severe water stress, these leaves survive throughout the drought period in a state of marked dehydration After the first winter rain, they become turgid and regain a green color Thus, S gilliesii shows a poikilohydric behavior such as that described for some angiosperms

Maria E. Aljaro

Papers

The annual rhythm of cambial activity in two woody species of the chilean “matorral”

The seasonal cambium activity of chilean and californian shrubs

Satureja gilliesii, a poikilohydric shrub from the Chilean mediterranean vegetation