Chaparral bird community responses to prescribed fire and shrub removal in three management seasons

Chaparral, a type of shrubland common throughout the California Floristic Province, is subject to management and removal in regions where wildfire threatens human lives and property. Management practices include conducting prescribed burns outside of the historical fire season and employing mechanical fuel reduction (mastication). As the wildland–urban interface grows, particularly in coastal California, more of this ecosystem is subject to active management.
To understand the ecological implications of current California chaparral fire management practices, we studied bird species composition, abundance and foraging guilds in managed and unmanaged chaparral over 5 years. Study areas were located in Mendocino County in the coast ranges of northern California. We contrast six chaparral removal or “fuels manipulation” treatments: (1) fall fire, (2) winter fire, (3) spring fire, (4) fall mastication, (5) spring mastication and (6) untreated control. Treatments and controls were implemented in plots 2 ha or larger, and replicated four times each.
We find that species richness in prescribed fire treatments reaches comparable levels to controls in the first 3 years following treatment, whereas masticated units always have lower species richness. Generalized linear mixed models additionally confirm that mastication has highly negative effects on observed abundances of birds compared to controls and to prescribed fire.
The season in which fuels reduction occurred was less important to species richness, although fall fire was more beneficial to bird abundance than spring or winter fire. Fire treatments in all seasons maintain the same general bird community structure as controls, while mastication results in strongly differentiated assemblages, increasing granivores while nearly excluding foliage gleaners.
Synthesis and applications. We compare two California chaparral management techniques, prescribed fire and mastication, in three seasons (fall, winter and spring) in northern California, USA. We tracked chaparral bird community response in 23 experimental units for 2–5 years. We conclude that prescribed fire and mastication are not interchangeable management techniques, and that mastication negatively impacts bird communities, altering guild structure and reducing both diversity and abundance.

查帕拉尔灌丛（Chaparral）是加州植物区系省广泛分布的一类灌丛植被，在野火威胁人类生命与财产的区域，该类植被常被开展管理与清除作业。当前的管理措施包括在历史火季之外开展计划火烧（prescribed burns），以及采用机械碎枝减燃处理（mastication）。随着野地-城市交界带不断扩张，尤其在加州沿海地区，越来越多的这类生态系统被纳入主动管理范畴。

为明晰加州当前查帕拉尔灌丛火管理措施的生态影响，我们历时5年，对比了受管理与未受管理的查帕拉尔灌丛中的鸟类物种组成、丰度及觅食功能群。研究区域位于美国加州北部海岸山脉的门多西诺县。本研究设置了6种查帕拉尔灌丛清除或"燃料调控"处理方式：(1) 秋季火烧、(2) 冬季火烧、(3) 春季火烧、(4) 秋季碎枝减燃、(5) 春季碎枝减燃，以及(6) 未处理对照组。所有处理组与对照组均设置于面积不小于2公顷的样地中，且每组均重复4次。

研究结果显示，计划火烧处理样地的物种丰富度在处理后前3年即可达到与对照组相当的水平，而经碎枝减燃处理的样地物种丰富度始终低于对照组。广义线性混合模型进一步证实，相较于对照组与计划火烧处理组，碎枝减燃处理对鸟类观测丰度具有显著的负面影响。

燃料调控实施的季节对物种丰富度的影响相对较小，但秋季火烧对鸟类丰度的提升效果优于春季或冬季火烧。所有季节的火烧处理均维持了与对照组一致的鸟类群落整体结构，而碎枝减燃处理则导致群落组成出现显著分化：植食性种子取食者的占比上升，而叶面食虫者几乎被完全排除。

研究总结与应用启示：本研究在美国加州北部海岸山脉的3个季节（秋、冬、春）中，对比了两种查帕拉尔灌丛管理技术——计划火烧与碎枝减燃处理，并对23个实验样地内的鸟类群落响应进行了2至5年的跟踪监测。我们得出结论：计划火烧与碎枝减燃处理并非可互换的管理手段，碎枝减燃处理会对鸟类群落产生负面影响，改变其功能群结构，并降低物种多样性与种群丰度。