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Drought‐induced woody plant mortality in an encroached semi‐arid savanna depends on topoedaphic factors and land management
Author(s) -
Twidwell Dirac,
Wonkka Carissa L.,
Taylor Charles A.,
Zou Chris B.,
Twidwell Jeremiah J.,
Rogers William E.
Publication year - 2014
Publication title -
applied vegetation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.096
H-Index - 64
eISSN - 1654-109X
pISSN - 1402-2001
DOI - 10.1111/avsc.12044
Subject(s) - woody plant , transect , arid , plant community , soil water , ecology , geography , agroforestry , biology , agronomy , ecological succession
Questions How do recent patterns of drought‐induced woody plant mortality in T exas semi‐arid savanna compare to the extended drought of the 1950s? Does the relative composition of the woody plant community shift ubiquitously across the landscape following woody plant mortality and dieback or are shifts dependent on differences among species, soils, land use and plant demography? Location T exas A grilife R esearch S tation, S onora, T exas, USA (30.1° N 100.3° W). Methods Following an exceptional drought from 1951 to 1957, a study was conducted to quantify rates of mortality for various woody plant species. In 2011, we repeated this study within three long‐term grazing treatments that were established in 1948. Ten transects were established in each treatment to quantify the frequency and cover of live and dead woody individuals for all woody species. Rates of woody plant dieback were determined for each species and tested for differences among height classes, soil categories, total woody densities and pastoral treatments. Results Flash droughts (defined as rapidly intensifying droughts characterized by moisture deficits and high temperatures) from 2000 to 2011 were the second most severe since 1919 (low PDSI = −4) and were only surpassed by the prolonged drought from 1951 to 1957 (low PDSI = −5.17). Drought‐induced shifts from one woody plant community to another did not occur uniformly across the landscape. Instead, high mortality rates of mature J uniperus ashei trees in deep soils (67.3%, 33 of 49 trees), combined with the recruitment of Q uercus species where grazing had been excluded for the last 60 yr, were the only patch types to shift from a J uniperus– Q uercus woodland to an alternate state. Conclusions Flash droughts since 2000 resulted in significant mortality and dieback, but dieback in cover was 28% higher following the more severe drought of the 1950s. Legacies from long‐term land management practices interacted with localized differences in topoedaphic factors to drive patch‐level shifts in woody vegetation following drought.