Regional patterns of recruitment success and failure in two endemic California oaks

Global food demand is growing rapidly. Livestock grazing can provide a valuable source of protein, but conventional grazing is often unsustainable. We studied an 800,000-ha section of a threatened ecoregion in southeastern Australia. Conventional management in the region involves continuous livestock grazing with few rest periods and regular fertilizer application. By using remotely sensed data on tree cover and extensive field data on livestock grazing regimes, soil chemistry, tree diameters, and tree regeneration, we show that the region is facing a tree regeneration crisis. Under conventional management, across the region, millions of hectares of land currently supporting tens of millions of trees will be treeless within decades from now. This would have severe negative ramifications for biodiversity and key ecosystem services, including water infiltration and shade provision for livestock. However, we identified an unexpected win-win solution for tree regeneration and commercial grazing. A relatively new practice in the region is fast-rotational grazing, characterized by prolonged rest periods in between short, intensive grazing events. The probability of regeneration under fast-rotational grazing was up to 4-fold higher than under conventional grazing, and it did not differ significantly from the probability of regeneration in ungrazed areas. In addition, trees were more likely to regenerate where soil nutrient levels were low. These findings suggest that the tree regeneration crisis can be reversed by applying low-input, fastrotational grazing. New policy settings supporting these practices could signal a turning point for the region, from ecological decline to ecological recovery.countryside biogeography ͉ grassy box woodlands ͉ holistic management ͉ rotational grazing ͉ scattered trees

show abstract

“…The patterns reported here mirror those in other parts of the world (10,27). For example, in southern European oak systems (Quercus spp.…”

Section: Discussionsupporting

confidence: 83%

Reversing a tree regeneration crisis in an endangered ecoregion

Fischer¹,

Stott²,

Zerger

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

155

154

View full text Add to dashboard Cite

show abstract

“…For example, birds and bats control insect pests (4)(5)(6), and trees provide shade for livestock (7,8). Scattered trees occurring throughout the farmland matrix are prominent features of agricultural landscapes around the world, including in southern Europe (9,10), North America (11,12), Central America (13)(14)(15), and Australia (16). Farmland trees often represent relicts of largely cleared forest or woodland ecosystems (17,18) and are believed to play important roles in maintaining ecosystem function and farmland biodiversity (7,13,16).…”

mentioning

confidence: 99%

“…Scattered trees are declining not only in Australia, but declines also have been observed or predicted in Africa (26), Central America (27), North America (12), and Europe (10,(28)(29)(30), with grazing and agriculture typically playing important roles. Despite the global significance of tree decline in agricultural landscapes, spatially, and temporally explicit analyses of tree decline and its likely consequences remain rare (17,31).…”

mentioning

confidence: 99%

Tree decline and the future of Australian farmland biodiversity

Fischer

Zerger²,

Gibbons

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

118

View full text Add to dashboard Cite

Farmland biodiversity is greatly enhanced by the presence of trees. However, farmland trees are declining worldwide, including in North America, Central America, and parts of southern Europe. We show that tree decline and its likely consequences are particularly severe in Australia's temperate agricultural zone, which is a threatened ecoregion. Using field data on trees, remotely sensed imagery, and a demographic model for trees, we predict that by 2100, the number of trees on an average farm will contract to two-thirds of its present level. Statistical habitat models suggest that this tree decline will negatively affect many currently common animal species, with predicted declines in birds and bats of up to 50% by 2100. Declines were predicted for 24 of 32 bird species modeled and for all of six bat species modeled. Widespread declines in trees, birds, and bats may lead to a reduction in economically important ecosystem services such as shade provision for livestock and pest control. Moreover, many other species for which we have no empirical data also depend on trees, suggesting that fundamental changes in ecosystem functioning are likely. We conclude that Australia's temperate agricultural zone has crossed a threshold and no longer functions as a selfsustaining woodland ecosystem. A regime shift is occurring, with a woodland system deteriorating into a treeless pasture system. Management options exist to reverse tree decline, but new policy settings are required to encourage their widespread adoption.countryside biogeography | grassy box woodlands | ranchland | regime shift | scattered trees T he future of farmland biodiversity is a major concern around the world (1-3). Farmland biodiversity is valuable in its own right, but also because it provides ecosystem services that are of direct benefit to agricultural production. For example, birds and bats control insect pests (4-6), and trees provide shade for livestock (7,8). Scattered trees occurring throughout the farmland matrix are prominent features of agricultural landscapes around the world, including in southern Europe (9, 10), North America (11, 12), Central America (13-15), and Australia (16). Farmland trees often represent relicts of largely cleared forest or woodland ecosystems (17,18) and are believed to play important roles in maintaining ecosystem function and farmland biodiversity (7,13,16). Southeastern Australia's temperate agricultural zone is part of a threatened ecoregion (19) where farmland trees are declining rapidly. In cropping landscapes, trees are cleared to make way for agricultural machinery (20,21). In livestock grazing landscapes, trees are declining because of a combination of natural or accelerated tree mortality coupled with widespread recruitment failure (22). The decline of scattered trees is increasingly recognized as a threat to biodiversity and associated ecosystem services, both in the academic literature (7,17,20,(22)(23)(24) and increasingly in conservation policy (25).Scattered trees are declining not only in Australia, b...

show abstract

“…Seedlings and saplings are often rare in oak populations of Mediteranean-climate woodland and savanna ecosystems, despite the fact that mature oaks dominate the tree canopy layer (Plieninger et al 2003, Pons and Pausas 2006, Tyler et al 2006, Acacio et al 2007, Zavaleta et al 2007). This population size structure suggests recruitment-limited population decline, but connecting observed seedling and sapling densities to population trends is exceedingly difficult (Crawley andLong 1995, Clark et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Consumer control of oak demography in a Mediterranean-climate savanna

2011

View full text Add to dashboard Cite

Abstract. Tree recruitment is rare and oak populations are declining in many Mediterranean-climate oak savannas. Factors affecting acorn production, seedling establishment and initial seedling growth have been much studied in short-term experiments. However, fecundity and early survival rates have not been placed in a demographic framework that also considers sapling survival and growth and adult tree mortality. We use matrix models and life table response experiments to analyze long-term experimental and observation data on California valley oak (Quercus lobata Neé) near its southern range limit in Santa Barbara County to answer three questions: (1) How sensitive is oak population growth rate to variation in acorn production and initial seedling establishment vs. sapling survivorship and growth? (2) How do mammalian consumers-specifically, cattle, deer and rodents-impact valley oak seedling establishment and sapling survival and growth? (3) Can vertebrate consumers account for the observed population decline of valley oak in savannas in its southern range? We find that population growth is far more sensitive to consumermediated variation in sapling survivorship and growth than to variation in fecundity or seedling establishment and that consumers exert strong influence on the demography of the species. Deterministic, finite population growth rate (k) is ,1 for unprotected plants and for plants that are protected from cattle but still exposed to mule deer and rodents. Population growth rate increases to 1.03 with protection from both cattle and deer, mainly because plants are able to quickly reach the tree layer when they are protected from ungulate browsing. Population growth rate jumps to 1.15 for plants protected from both ungulates and rodents as a result of increased survivorship and height growth of established individuals and because of increased seedling establishment during the first year. Our experimental findings are consistent with observed patterns in natural populations in Santa Barbara County, where tree recruitment is rare in both grazed and non-grazed savannas but more common in areas such as roadsides that are refuges from cattle and deer.

show abstract

Regional patterns of recruitment success and failure in two endemic California oaks

Cited by 46 publications

References 20 publications

Reversing a tree regeneration crisis in an endangered ecoregion

Reversing a tree regeneration crisis in an endangered ecoregion

Tree decline and the future of Australian farmland biodiversity

Consumer control of oak demography in a Mediterranean-climate savanna

Contact Info

Product

Resources

About